1 This is ld.info, produced by makeinfo version 4.8 from ld.texinfo. 2 3 INFO-DIR-SECTION Software development 4 START-INFO-DIR-ENTRY 5 * Ld: (ld). The GNU linker. 6 END-INFO-DIR-ENTRY 7 8 This file documents the GNU linker LD (GNU Binutils) version 2.25. 9 10 Copyright (C) 1991-2014 Free Software Foundation, Inc. 11 12 Permission is granted to copy, distribute and/or modify this document 13 under the terms of the GNU Free Documentation License, Version 1.3 or 14 any later version published by the Free Software Foundation; with no 15 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover 16 Texts. A copy of the license is included in the section entitled "GNU 17 Free Documentation License". 18 19 20 File: ld.info, Node: Top, Next: Overview, Up: (dir) 21 22 LD 23 ** 24 25 This file documents the GNU linker ld (GNU Binutils) version 2.25. 26 27 This document is distributed under the terms of the GNU Free 28 Documentation License version 1.3. A copy of the license is included 29 in the section entitled "GNU Free Documentation License". 30 31 * Menu: 32 33 * Overview:: Overview 34 * Invocation:: Invocation 35 * Scripts:: Linker Scripts 36 37 * Machine Dependent:: Machine Dependent Features 38 39 * BFD:: BFD 40 41 * Reporting Bugs:: Reporting Bugs 42 * MRI:: MRI Compatible Script Files 43 * GNU Free Documentation License:: GNU Free Documentation License 44 * LD Index:: LD Index 45 46 47 File: ld.info, Node: Overview, Next: Invocation, Prev: Top, Up: Top 48 49 1 Overview 50 ********** 51 52 `ld' combines a number of object and archive files, relocates their 53 data and ties up symbol references. Usually the last step in compiling 54 a program is to run `ld'. 55 56 `ld' accepts Linker Command Language files written in a superset of 57 AT&T's Link Editor Command Language syntax, to provide explicit and 58 total control over the linking process. 59 60 This version of `ld' uses the general purpose BFD libraries to 61 operate on object files. This allows `ld' to read, combine, and write 62 object files in many different formats--for example, COFF or `a.out'. 63 Different formats may be linked together to produce any available kind 64 of object file. *Note BFD::, for more information. 65 66 Aside from its flexibility, the GNU linker is more helpful than other 67 linkers in providing diagnostic information. Many linkers abandon 68 execution immediately upon encountering an error; whenever possible, 69 `ld' continues executing, allowing you to identify other errors (or, in 70 some cases, to get an output file in spite of the error). 71 72 73 File: ld.info, Node: Invocation, Next: Scripts, Prev: Overview, Up: Top 74 75 2 Invocation 76 ************ 77 78 The GNU linker `ld' is meant to cover a broad range of situations, and 79 to be as compatible as possible with other linkers. As a result, you 80 have many choices to control its behavior. 81 82 * Menu: 83 84 * Options:: Command Line Options 85 * Environment:: Environment Variables 86 87 88 File: ld.info, Node: Options, Next: Environment, Up: Invocation 89 90 2.1 Command Line Options 91 ======================== 92 93 The linker supports a plethora of command-line options, but in actual 94 practice few of them are used in any particular context. For instance, 95 a frequent use of `ld' is to link standard Unix object files on a 96 standard, supported Unix system. On such a system, to link a file 97 `hello.o': 98 99 ld -o OUTPUT /lib/crt0.o hello.o -lc 100 101 This tells `ld' to produce a file called OUTPUT as the result of 102 linking the file `/lib/crt0.o' with `hello.o' and the library `libc.a', 103 which will come from the standard search directories. (See the 104 discussion of the `-l' option below.) 105 106 Some of the command-line options to `ld' may be specified at any 107 point in the command line. However, options which refer to files, such 108 as `-l' or `-T', cause the file to be read at the point at which the 109 option appears in the command line, relative to the object files and 110 other file options. Repeating non-file options with a different 111 argument will either have no further effect, or override prior 112 occurrences (those further to the left on the command line) of that 113 option. Options which may be meaningfully specified more than once are 114 noted in the descriptions below. 115 116 Non-option arguments are object files or archives which are to be 117 linked together. They may follow, precede, or be mixed in with 118 command-line options, except that an object file argument may not be 119 placed between an option and its argument. 120 121 Usually the linker is invoked with at least one object file, but you 122 can specify other forms of binary input files using `-l', `-R', and the 123 script command language. If _no_ binary input files at all are 124 specified, the linker does not produce any output, and issues the 125 message `No input files'. 126 127 If the linker cannot recognize the format of an object file, it will 128 assume that it is a linker script. A script specified in this way 129 augments the main linker script used for the link (either the default 130 linker script or the one specified by using `-T'). This feature 131 permits the linker to link against a file which appears to be an object 132 or an archive, but actually merely defines some symbol values, or uses 133 `INPUT' or `GROUP' to load other objects. Specifying a script in this 134 way merely augments the main linker script, with the extra commands 135 placed after the main script; use the `-T' option to replace the 136 default linker script entirely, but note the effect of the `INSERT' 137 command. *Note Scripts::. 138 139 For options whose names are a single letter, option arguments must 140 either follow the option letter without intervening whitespace, or be 141 given as separate arguments immediately following the option that 142 requires them. 143 144 For options whose names are multiple letters, either one dash or two 145 can precede the option name; for example, `-trace-symbol' and 146 `--trace-symbol' are equivalent. Note--there is one exception to this 147 rule. Multiple letter options that start with a lower case 'o' can 148 only be preceded by two dashes. This is to reduce confusion with the 149 `-o' option. So for example `-omagic' sets the output file name to 150 `magic' whereas `--omagic' sets the NMAGIC flag on the output. 151 152 Arguments to multiple-letter options must either be separated from 153 the option name by an equals sign, or be given as separate arguments 154 immediately following the option that requires them. For example, 155 `--trace-symbol foo' and `--trace-symbol=foo' are equivalent. Unique 156 abbreviations of the names of multiple-letter options are accepted. 157 158 Note--if the linker is being invoked indirectly, via a compiler 159 driver (e.g. `gcc') then all the linker command line options should be 160 prefixed by `-Wl,' (or whatever is appropriate for the particular 161 compiler driver) like this: 162 163 gcc -Wl,--start-group foo.o bar.o -Wl,--end-group 164 165 This is important, because otherwise the compiler driver program may 166 silently drop the linker options, resulting in a bad link. Confusion 167 may also arise when passing options that require values through a 168 driver, as the use of a space between option and argument acts as a 169 separator, and causes the driver to pass only the option to the linker 170 and the argument to the compiler. In this case, it is simplest to use 171 the joined forms of both single- and multiple-letter options, such as: 172 173 gcc foo.o bar.o -Wl,-eENTRY -Wl,-Map=a.map 174 175 Here is a table of the generic command line switches accepted by the 176 GNU linker: 177 178 `@FILE' 179 Read command-line options from FILE. The options read are 180 inserted in place of the original @FILE option. If FILE does not 181 exist, or cannot be read, then the option will be treated 182 literally, and not removed. 183 184 Options in FILE are separated by whitespace. A whitespace 185 character may be included in an option by surrounding the entire 186 option in either single or double quotes. Any character 187 (including a backslash) may be included by prefixing the character 188 to be included with a backslash. The FILE may itself contain 189 additional @FILE options; any such options will be processed 190 recursively. 191 192 `-a KEYWORD' 193 This option is supported for HP/UX compatibility. The KEYWORD 194 argument must be one of the strings `archive', `shared', or 195 `default'. `-aarchive' is functionally equivalent to `-Bstatic', 196 and the other two keywords are functionally equivalent to 197 `-Bdynamic'. This option may be used any number of times. 198 199 `--audit AUDITLIB' 200 Adds AUDITLIB to the `DT_AUDIT' entry of the dynamic section. 201 AUDITLIB is not checked for existence, nor will it use the 202 DT_SONAME specified in the library. If specified multiple times 203 `DT_AUDIT' will contain a colon separated list of audit interfaces 204 to use. If the linker finds an object with an audit entry while 205 searching for shared libraries, it will add a corresponding 206 `DT_DEPAUDIT' entry in the output file. This option is only 207 meaningful on ELF platforms supporting the rtld-audit interface. 208 209 `-A ARCHITECTURE' 210 `--architecture=ARCHITECTURE' 211 In the current release of `ld', this option is useful only for the 212 Intel 960 family of architectures. In that `ld' configuration, the 213 ARCHITECTURE argument identifies the particular architecture in 214 the 960 family, enabling some safeguards and modifying the 215 archive-library search path. *Note `ld' and the Intel 960 family: 216 i960, for details. 217 218 Future releases of `ld' may support similar functionality for 219 other architecture families. 220 221 `-b INPUT-FORMAT' 222 `--format=INPUT-FORMAT' 223 `ld' may be configured to support more than one kind of object 224 file. If your `ld' is configured this way, you can use the `-b' 225 option to specify the binary format for input object files that 226 follow this option on the command line. Even when `ld' is 227 configured to support alternative object formats, you don't 228 usually need to specify this, as `ld' should be configured to 229 expect as a default input format the most usual format on each 230 machine. INPUT-FORMAT is a text string, the name of a particular 231 format supported by the BFD libraries. (You can list the 232 available binary formats with `objdump -i'.) *Note BFD::. 233 234 You may want to use this option if you are linking files with an 235 unusual binary format. You can also use `-b' to switch formats 236 explicitly (when linking object files of different formats), by 237 including `-b INPUT-FORMAT' before each group of object files in a 238 particular format. 239 240 The default format is taken from the environment variable 241 `GNUTARGET'. *Note Environment::. You can also define the input 242 format from a script, using the command `TARGET'; see *Note Format 243 Commands::. 244 245 `-c MRI-COMMANDFILE' 246 `--mri-script=MRI-COMMANDFILE' 247 For compatibility with linkers produced by MRI, `ld' accepts script 248 files written in an alternate, restricted command language, 249 described in *Note MRI Compatible Script Files: MRI. Introduce 250 MRI script files with the option `-c'; use the `-T' option to run 251 linker scripts written in the general-purpose `ld' scripting 252 language. If MRI-CMDFILE does not exist, `ld' looks for it in the 253 directories specified by any `-L' options. 254 255 `-d' 256 `-dc' 257 `-dp' 258 These three options are equivalent; multiple forms are supported 259 for compatibility with other linkers. They assign space to common 260 symbols even if a relocatable output file is specified (with 261 `-r'). The script command `FORCE_COMMON_ALLOCATION' has the same 262 effect. *Note Miscellaneous Commands::. 263 264 `--depaudit AUDITLIB' 265 `-P AUDITLIB' 266 Adds AUDITLIB to the `DT_DEPAUDIT' entry of the dynamic section. 267 AUDITLIB is not checked for existence, nor will it use the 268 DT_SONAME specified in the library. If specified multiple times 269 `DT_DEPAUDIT' will contain a colon separated list of audit 270 interfaces to use. This option is only meaningful on ELF 271 platforms supporting the rtld-audit interface. The -P option is 272 provided for Solaris compatibility. 273 274 `-e ENTRY' 275 `--entry=ENTRY' 276 Use ENTRY as the explicit symbol for beginning execution of your 277 program, rather than the default entry point. If there is no 278 symbol named ENTRY, the linker will try to parse ENTRY as a number, 279 and use that as the entry address (the number will be interpreted 280 in base 10; you may use a leading `0x' for base 16, or a leading 281 `0' for base 8). *Note Entry Point::, for a discussion of defaults 282 and other ways of specifying the entry point. 283 284 `--exclude-libs LIB,LIB,...' 285 Specifies a list of archive libraries from which symbols should 286 not be automatically exported. The library names may be delimited 287 by commas or colons. Specifying `--exclude-libs ALL' excludes 288 symbols in all archive libraries from automatic export. This 289 option is available only for the i386 PE targeted port of the 290 linker and for ELF targeted ports. For i386 PE, symbols 291 explicitly listed in a .def file are still exported, regardless of 292 this option. For ELF targeted ports, symbols affected by this 293 option will be treated as hidden. 294 295 `--exclude-modules-for-implib MODULE,MODULE,...' 296 Specifies a list of object files or archive members, from which 297 symbols should not be automatically exported, but which should be 298 copied wholesale into the import library being generated during 299 the link. The module names may be delimited by commas or colons, 300 and must match exactly the filenames used by `ld' to open the 301 files; for archive members, this is simply the member name, but 302 for object files the name listed must include and match precisely 303 any path used to specify the input file on the linker's 304 command-line. This option is available only for the i386 PE 305 targeted port of the linker. Symbols explicitly listed in a .def 306 file are still exported, regardless of this option. 307 308 `-E' 309 `--export-dynamic' 310 `--no-export-dynamic' 311 When creating a dynamically linked executable, using the `-E' 312 option or the `--export-dynamic' option causes the linker to add 313 all symbols to the dynamic symbol table. The dynamic symbol table 314 is the set of symbols which are visible from dynamic objects at 315 run time. 316 317 If you do not use either of these options (or use the 318 `--no-export-dynamic' option to restore the default behavior), the 319 dynamic symbol table will normally contain only those symbols 320 which are referenced by some dynamic object mentioned in the link. 321 322 If you use `dlopen' to load a dynamic object which needs to refer 323 back to the symbols defined by the program, rather than some other 324 dynamic object, then you will probably need to use this option when 325 linking the program itself. 326 327 You can also use the dynamic list to control what symbols should 328 be added to the dynamic symbol table if the output format supports 329 it. See the description of `--dynamic-list'. 330 331 Note that this option is specific to ELF targeted ports. PE 332 targets support a similar function to export all symbols from a 333 DLL or EXE; see the description of `--export-all-symbols' below. 334 335 `-EB' 336 Link big-endian objects. This affects the default output format. 337 338 `-EL' 339 Link little-endian objects. This affects the default output 340 format. 341 342 `-f NAME' 343 `--auxiliary=NAME' 344 When creating an ELF shared object, set the internal DT_AUXILIARY 345 field to the specified name. This tells the dynamic linker that 346 the symbol table of the shared object should be used as an 347 auxiliary filter on the symbol table of the shared object NAME. 348 349 If you later link a program against this filter object, then, when 350 you run the program, the dynamic linker will see the DT_AUXILIARY 351 field. If the dynamic linker resolves any symbols from the filter 352 object, it will first check whether there is a definition in the 353 shared object NAME. If there is one, it will be used instead of 354 the definition in the filter object. The shared object NAME need 355 not exist. Thus the shared object NAME may be used to provide an 356 alternative implementation of certain functions, perhaps for 357 debugging or for machine specific performance. 358 359 This option may be specified more than once. The DT_AUXILIARY 360 entries will be created in the order in which they appear on the 361 command line. 362 363 `-F NAME' 364 `--filter=NAME' 365 When creating an ELF shared object, set the internal DT_FILTER 366 field to the specified name. This tells the dynamic linker that 367 the symbol table of the shared object which is being created 368 should be used as a filter on the symbol table of the shared 369 object NAME. 370 371 If you later link a program against this filter object, then, when 372 you run the program, the dynamic linker will see the DT_FILTER 373 field. The dynamic linker will resolve symbols according to the 374 symbol table of the filter object as usual, but it will actually 375 link to the definitions found in the shared object NAME. Thus the 376 filter object can be used to select a subset of the symbols 377 provided by the object NAME. 378 379 Some older linkers used the `-F' option throughout a compilation 380 toolchain for specifying object-file format for both input and 381 output object files. The GNU linker uses other mechanisms for 382 this purpose: the `-b', `--format', `--oformat' options, the 383 `TARGET' command in linker scripts, and the `GNUTARGET' 384 environment variable. The GNU linker will ignore the `-F' option 385 when not creating an ELF shared object. 386 387 `-fini=NAME' 388 When creating an ELF executable or shared object, call NAME when 389 the executable or shared object is unloaded, by setting DT_FINI to 390 the address of the function. By default, the linker uses `_fini' 391 as the function to call. 392 393 `-g' 394 Ignored. Provided for compatibility with other tools. 395 396 `-G VALUE' 397 `--gpsize=VALUE' 398 Set the maximum size of objects to be optimized using the GP 399 register to SIZE. This is only meaningful for object file formats 400 such as MIPS ELF that support putting large and small objects into 401 different sections. This is ignored for other object file formats. 402 403 `-h NAME' 404 `-soname=NAME' 405 When creating an ELF shared object, set the internal DT_SONAME 406 field to the specified name. When an executable is linked with a 407 shared object which has a DT_SONAME field, then when the 408 executable is run the dynamic linker will attempt to load the 409 shared object specified by the DT_SONAME field rather than the 410 using the file name given to the linker. 411 412 `-i' 413 Perform an incremental link (same as option `-r'). 414 415 `-init=NAME' 416 When creating an ELF executable or shared object, call NAME when 417 the executable or shared object is loaded, by setting DT_INIT to 418 the address of the function. By default, the linker uses `_init' 419 as the function to call. 420 421 `-l NAMESPEC' 422 `--library=NAMESPEC' 423 Add the archive or object file specified by NAMESPEC to the list 424 of files to link. This option may be used any number of times. 425 If NAMESPEC is of the form `:FILENAME', `ld' will search the 426 library path for a file called FILENAME, otherwise it will search 427 the library path for a file called `libNAMESPEC.a'. 428 429 On systems which support shared libraries, `ld' may also search for 430 files other than `libNAMESPEC.a'. Specifically, on ELF and SunOS 431 systems, `ld' will search a directory for a library called 432 `libNAMESPEC.so' before searching for one called `libNAMESPEC.a'. 433 (By convention, a `.so' extension indicates a shared library.) 434 Note that this behavior does not apply to `:FILENAME', which 435 always specifies a file called FILENAME. 436 437 The linker will search an archive only once, at the location where 438 it is specified on the command line. If the archive defines a 439 symbol which was undefined in some object which appeared before 440 the archive on the command line, the linker will include the 441 appropriate file(s) from the archive. However, an undefined 442 symbol in an object appearing later on the command line will not 443 cause the linker to search the archive again. 444 445 See the `-(' option for a way to force the linker to search 446 archives multiple times. 447 448 You may list the same archive multiple times on the command line. 449 450 This type of archive searching is standard for Unix linkers. 451 However, if you are using `ld' on AIX, note that it is different 452 from the behaviour of the AIX linker. 453 454 `-L SEARCHDIR' 455 `--library-path=SEARCHDIR' 456 Add path SEARCHDIR to the list of paths that `ld' will search for 457 archive libraries and `ld' control scripts. You may use this 458 option any number of times. The directories are searched in the 459 order in which they are specified on the command line. 460 Directories specified on the command line are searched before the 461 default directories. All `-L' options apply to all `-l' options, 462 regardless of the order in which the options appear. `-L' options 463 do not affect how `ld' searches for a linker script unless `-T' 464 option is specified. 465 466 If SEARCHDIR begins with `=', then the `=' will be replaced by the 467 "sysroot prefix", controlled by the `--sysroot' option, or 468 specified when the linker is configured. 469 470 The default set of paths searched (without being specified with 471 `-L') depends on which emulation mode `ld' is using, and in some 472 cases also on how it was configured. *Note Environment::. 473 474 The paths can also be specified in a link script with the 475 `SEARCH_DIR' command. Directories specified this way are searched 476 at the point in which the linker script appears in the command 477 line. 478 479 `-m EMULATION' 480 Emulate the EMULATION linker. You can list the available 481 emulations with the `--verbose' or `-V' options. 482 483 If the `-m' option is not used, the emulation is taken from the 484 `LDEMULATION' environment variable, if that is defined. 485 486 Otherwise, the default emulation depends upon how the linker was 487 configured. 488 489 `-M' 490 `--print-map' 491 Print a link map to the standard output. A link map provides 492 information about the link, including the following: 493 494 * Where object files are mapped into memory. 495 496 * How common symbols are allocated. 497 498 * All archive members included in the link, with a mention of 499 the symbol which caused the archive member to be brought in. 500 501 * The values assigned to symbols. 502 503 Note - symbols whose values are computed by an expression 504 which involves a reference to a previous value of the same 505 symbol may not have correct result displayed in the link map. 506 This is because the linker discards intermediate results and 507 only retains the final value of an expression. Under such 508 circumstances the linker will display the final value 509 enclosed by square brackets. Thus for example a linker 510 script containing: 511 512 foo = 1 513 foo = foo * 4 514 foo = foo + 8 515 516 will produce the following output in the link map if the `-M' 517 option is used: 518 519 0x00000001 foo = 0x1 520 [0x0000000c] foo = (foo * 0x4) 521 [0x0000000c] foo = (foo + 0x8) 522 523 See *Note Expressions:: for more information about 524 expressions in linker scripts. 525 526 `-n' 527 `--nmagic' 528 Turn off page alignment of sections, and disable linking against 529 shared libraries. If the output format supports Unix style magic 530 numbers, mark the output as `NMAGIC'. 531 532 `-N' 533 `--omagic' 534 Set the text and data sections to be readable and writable. Also, 535 do not page-align the data segment, and disable linking against 536 shared libraries. If the output format supports Unix style magic 537 numbers, mark the output as `OMAGIC'. Note: Although a writable 538 text section is allowed for PE-COFF targets, it does not conform 539 to the format specification published by Microsoft. 540 541 `--no-omagic' 542 This option negates most of the effects of the `-N' option. It 543 sets the text section to be read-only, and forces the data segment 544 to be page-aligned. Note - this option does not enable linking 545 against shared libraries. Use `-Bdynamic' for this. 546 547 `-o OUTPUT' 548 `--output=OUTPUT' 549 Use OUTPUT as the name for the program produced by `ld'; if this 550 option is not specified, the name `a.out' is used by default. The 551 script command `OUTPUT' can also specify the output file name. 552 553 `-O LEVEL' 554 If LEVEL is a numeric values greater than zero `ld' optimizes the 555 output. This might take significantly longer and therefore 556 probably should only be enabled for the final binary. At the 557 moment this option only affects ELF shared library generation. 558 Future releases of the linker may make more use of this option. 559 Also currently there is no difference in the linker's behaviour 560 for different non-zero values of this option. Again this may 561 change with future releases. 562 563 `--push-state' 564 The `--push-state' allows to preserve the current state of the 565 flags which govern the input file handling so that they can all be 566 restored with one corresponding `--pop-state' option. 567 568 The option which are covered are: `-Bdynamic', `-Bstatic', `-dn', 569 `-dy', `-call_shared', `-non_shared', `-static', `-N', `-n', 570 `--whole-archive', `--no-whole-archive', `-r', `-Ur', 571 `--copy-dt-needed-entries', `--no-copy-dt-needed-entries', 572 `--as-needed', `--no-as-needed', and `-a'. 573 574 One target for this option are specifications for `pkg-config'. 575 When used with the `--libs' option all possibly needed libraries 576 are listed and then possibly linked with all the time. It is 577 better to return something as follows: 578 579 -Wl,--push-state,--as-needed -libone -libtwo -Wl,--pop-state 580 581 Undoes the effect of -push-state, restores the previous values of 582 the flags governing input file handling. 583 584 `-q' 585 `--emit-relocs' 586 Leave relocation sections and contents in fully linked executables. 587 Post link analysis and optimization tools may need this 588 information in order to perform correct modifications of 589 executables. This results in larger executables. 590 591 This option is currently only supported on ELF platforms. 592 593 `--force-dynamic' 594 Force the output file to have dynamic sections. This option is 595 specific to VxWorks targets. 596 597 `-r' 598 `--relocatable' 599 Generate relocatable output--i.e., generate an output file that 600 can in turn serve as input to `ld'. This is often called "partial 601 linking". As a side effect, in environments that support standard 602 Unix magic numbers, this option also sets the output file's magic 603 number to `OMAGIC'. If this option is not specified, an absolute 604 file is produced. When linking C++ programs, this option _will 605 not_ resolve references to constructors; to do that, use `-Ur'. 606 607 When an input file does not have the same format as the output 608 file, partial linking is only supported if that input file does 609 not contain any relocations. Different output formats can have 610 further restrictions; for example some `a.out'-based formats do 611 not support partial linking with input files in other formats at 612 all. 613 614 This option does the same thing as `-i'. 615 616 `-R FILENAME' 617 `--just-symbols=FILENAME' 618 Read symbol names and their addresses from FILENAME, but do not 619 relocate it or include it in the output. This allows your output 620 file to refer symbolically to absolute locations of memory defined 621 in other programs. You may use this option more than once. 622 623 For compatibility with other ELF linkers, if the `-R' option is 624 followed by a directory name, rather than a file name, it is 625 treated as the `-rpath' option. 626 627 `-s' 628 `--strip-all' 629 Omit all symbol information from the output file. 630 631 `-S' 632 `--strip-debug' 633 Omit debugger symbol information (but not all symbols) from the 634 output file. 635 636 `-t' 637 `--trace' 638 Print the names of the input files as `ld' processes them. 639 640 `-T SCRIPTFILE' 641 `--script=SCRIPTFILE' 642 Use SCRIPTFILE as the linker script. This script replaces `ld''s 643 default linker script (rather than adding to it), so COMMANDFILE 644 must specify everything necessary to describe the output file. 645 *Note Scripts::. If SCRIPTFILE does not exist in the current 646 directory, `ld' looks for it in the directories specified by any 647 preceding `-L' options. Multiple `-T' options accumulate. 648 649 `-dT SCRIPTFILE' 650 `--default-script=SCRIPTFILE' 651 Use SCRIPTFILE as the default linker script. *Note Scripts::. 652 653 This option is similar to the `--script' option except that 654 processing of the script is delayed until after the rest of the 655 command line has been processed. This allows options placed after 656 the `--default-script' option on the command line to affect the 657 behaviour of the linker script, which can be important when the 658 linker command line cannot be directly controlled by the user. 659 (eg because the command line is being constructed by another tool, 660 such as `gcc'). 661 662 `-u SYMBOL' 663 `--undefined=SYMBOL' 664 Force SYMBOL to be entered in the output file as an undefined 665 symbol. Doing this may, for example, trigger linking of additional 666 modules from standard libraries. `-u' may be repeated with 667 different option arguments to enter additional undefined symbols. 668 This option is equivalent to the `EXTERN' linker script command. 669 670 `-Ur' 671 For anything other than C++ programs, this option is equivalent to 672 `-r': it generates relocatable output--i.e., an output file that 673 can in turn serve as input to `ld'. When linking C++ programs, 674 `-Ur' _does_ resolve references to constructors, unlike `-r'. It 675 does not work to use `-Ur' on files that were themselves linked 676 with `-Ur'; once the constructor table has been built, it cannot 677 be added to. Use `-Ur' only for the last partial link, and `-r' 678 for the others. 679 680 `--unique[=SECTION]' 681 Creates a separate output section for every input section matching 682 SECTION, or if the optional wildcard SECTION argument is missing, 683 for every orphan input section. An orphan section is one not 684 specifically mentioned in a linker script. You may use this option 685 multiple times on the command line; It prevents the normal 686 merging of input sections with the same name, overriding output 687 section assignments in a linker script. 688 689 `-v' 690 `--version' 691 `-V' 692 Display the version number for `ld'. The `-V' option also lists 693 the supported emulations. 694 695 `-x' 696 `--discard-all' 697 Delete all local symbols. 698 699 `-X' 700 `--discard-locals' 701 Delete all temporary local symbols. (These symbols start with 702 system-specific local label prefixes, typically `.L' for ELF 703 systems or `L' for traditional a.out systems.) 704 705 `-y SYMBOL' 706 `--trace-symbol=SYMBOL' 707 Print the name of each linked file in which SYMBOL appears. This 708 option may be given any number of times. On many systems it is 709 necessary to prepend an underscore. 710 711 This option is useful when you have an undefined symbol in your 712 link but don't know where the reference is coming from. 713 714 `-Y PATH' 715 Add PATH to the default library search path. This option exists 716 for Solaris compatibility. 717 718 `-z KEYWORD' 719 The recognized keywords are: 720 `combreloc' 721 Combines multiple reloc sections and sorts them to make 722 dynamic symbol lookup caching possible. 723 724 `defs' 725 Disallows undefined symbols in object files. Undefined 726 symbols in shared libraries are still allowed. 727 728 `execstack' 729 Marks the object as requiring executable stack. 730 731 `global' 732 This option is only meaningful when building a shared object. 733 It makes the symbols defined by this shared object available 734 for symbol resolution of subsequently loaded libraries. 735 736 `initfirst' 737 This option is only meaningful when building a shared object. 738 It marks the object so that its runtime initialization will 739 occur before the runtime initialization of any other objects 740 brought into the process at the same time. Similarly the 741 runtime finalization of the object will occur after the 742 runtime finalization of any other objects. 743 744 `interpose' 745 Marks the object that its symbol table interposes before all 746 symbols but the primary executable. 747 748 `lazy' 749 When generating an executable or shared library, mark it to 750 tell the dynamic linker to defer function call resolution to 751 the point when the function is called (lazy binding), rather 752 than at load time. Lazy binding is the default. 753 754 `loadfltr' 755 Marks the object that its filters be processed immediately at 756 runtime. 757 758 `muldefs' 759 Allows multiple definitions. 760 761 `nocombreloc' 762 Disables multiple reloc sections combining. 763 764 `nocopyreloc' 765 Disables production of copy relocs. 766 767 `nodefaultlib' 768 Marks the object that the search for dependencies of this 769 object will ignore any default library search paths. 770 771 `nodelete' 772 Marks the object shouldn't be unloaded at runtime. 773 774 `nodlopen' 775 Marks the object not available to `dlopen'. 776 777 `nodump' 778 Marks the object can not be dumped by `dldump'. 779 780 `noexecstack' 781 Marks the object as not requiring executable stack. 782 783 `norelro' 784 Don't create an ELF `PT_GNU_RELRO' segment header in the 785 object. 786 787 `now' 788 When generating an executable or shared library, mark it to 789 tell the dynamic linker to resolve all symbols when the 790 program is started, or when the shared library is linked to 791 using dlopen, instead of deferring function call resolution 792 to the point when the function is first called. 793 794 `origin' 795 Marks the object may contain $ORIGIN. 796 797 `relro' 798 Create an ELF `PT_GNU_RELRO' segment header in the object. 799 800 `max-page-size=VALUE' 801 Set the emulation maximum page size to VALUE. 802 803 `common-page-size=VALUE' 804 Set the emulation common page size to VALUE. 805 806 `stack-size=VALUE' 807 Specify a stack size for in an ELF `PT_GNU_STACK' segment. 808 Specifying zero will override any default non-zero sized 809 `PT_GNU_STACK' segment creation. 810 811 `bndplt' 812 Always generate BND prefix in PLT entries. Supported for 813 Linux/x86_64. 814 815 816 Other keywords are ignored for Solaris compatibility. 817 818 `-( ARCHIVES -)' 819 `--start-group ARCHIVES --end-group' 820 The ARCHIVES should be a list of archive files. They may be 821 either explicit file names, or `-l' options. 822 823 The specified archives are searched repeatedly until no new 824 undefined references are created. Normally, an archive is 825 searched only once in the order that it is specified on the 826 command line. If a symbol in that archive is needed to resolve an 827 undefined symbol referred to by an object in an archive that 828 appears later on the command line, the linker would not be able to 829 resolve that reference. By grouping the archives, they all be 830 searched repeatedly until all possible references are resolved. 831 832 Using this option has a significant performance cost. It is best 833 to use it only when there are unavoidable circular references 834 between two or more archives. 835 836 `--accept-unknown-input-arch' 837 `--no-accept-unknown-input-arch' 838 Tells the linker to accept input files whose architecture cannot be 839 recognised. The assumption is that the user knows what they are 840 doing and deliberately wants to link in these unknown input files. 841 This was the default behaviour of the linker, before release 842 2.14. The default behaviour from release 2.14 onwards is to 843 reject such input files, and so the `--accept-unknown-input-arch' 844 option has been added to restore the old behaviour. 845 846 `--as-needed' 847 `--no-as-needed' 848 This option affects ELF DT_NEEDED tags for dynamic libraries 849 mentioned on the command line after the `--as-needed' option. 850 Normally the linker will add a DT_NEEDED tag for each dynamic 851 library mentioned on the command line, regardless of whether the 852 library is actually needed or not. `--as-needed' causes a 853 DT_NEEDED tag to only be emitted for a library that _at that point 854 in the link_ satisfies a non-weak undefined symbol reference from 855 a regular object file or, if the library is not found in the 856 DT_NEEDED lists of other needed libraries, a non-weak undefined 857 symbol reference from another needed dynamic library. Object 858 files or libraries appearing on the command line _after_ the 859 library in question do not affect whether the library is seen as 860 needed. This is similar to the rules for extraction of object 861 files from archives. `--no-as-needed' restores the default 862 behaviour. 863 864 `--add-needed' 865 `--no-add-needed' 866 These two options have been deprecated because of the similarity of 867 their names to the `--as-needed' and `--no-as-needed' options. 868 They have been replaced by `--copy-dt-needed-entries' and 869 `--no-copy-dt-needed-entries'. 870 871 `-assert KEYWORD' 872 This option is ignored for SunOS compatibility. 873 874 `-Bdynamic' 875 `-dy' 876 `-call_shared' 877 Link against dynamic libraries. This is only meaningful on 878 platforms for which shared libraries are supported. This option 879 is normally the default on such platforms. The different variants 880 of this option are for compatibility with various systems. You 881 may use this option multiple times on the command line: it affects 882 library searching for `-l' options which follow it. 883 884 `-Bgroup' 885 Set the `DF_1_GROUP' flag in the `DT_FLAGS_1' entry in the dynamic 886 section. This causes the runtime linker to handle lookups in this 887 object and its dependencies to be performed only inside the group. 888 `--unresolved-symbols=report-all' is implied. This option is only 889 meaningful on ELF platforms which support shared libraries. 890 891 `-Bstatic' 892 `-dn' 893 `-non_shared' 894 `-static' 895 Do not link against shared libraries. This is only meaningful on 896 platforms for which shared libraries are supported. The different 897 variants of this option are for compatibility with various 898 systems. You may use this option multiple times on the command 899 line: it affects library searching for `-l' options which follow 900 it. This option also implies `--unresolved-symbols=report-all'. 901 This option can be used with `-shared'. Doing so means that a 902 shared library is being created but that all of the library's 903 external references must be resolved by pulling in entries from 904 static libraries. 905 906 `-Bsymbolic' 907 When creating a shared library, bind references to global symbols 908 to the definition within the shared library, if any. Normally, it 909 is possible for a program linked against a shared library to 910 override the definition within the shared library. This option is 911 only meaningful on ELF platforms which support shared libraries. 912 913 `-Bsymbolic-functions' 914 When creating a shared library, bind references to global function 915 symbols to the definition within the shared library, if any. This 916 option is only meaningful on ELF platforms which support shared 917 libraries. 918 919 `--dynamic-list=DYNAMIC-LIST-FILE' 920 Specify the name of a dynamic list file to the linker. This is 921 typically used when creating shared libraries to specify a list of 922 global symbols whose references shouldn't be bound to the 923 definition within the shared library, or creating dynamically 924 linked executables to specify a list of symbols which should be 925 added to the symbol table in the executable. This option is only 926 meaningful on ELF platforms which support shared libraries. 927 928 The format of the dynamic list is the same as the version node 929 without scope and node name. See *Note VERSION:: for more 930 information. 931 932 `--dynamic-list-data' 933 Include all global data symbols to the dynamic list. 934 935 `--dynamic-list-cpp-new' 936 Provide the builtin dynamic list for C++ operator new and delete. 937 It is mainly useful for building shared libstdc++. 938 939 `--dynamic-list-cpp-typeinfo' 940 Provide the builtin dynamic list for C++ runtime type 941 identification. 942 943 `--check-sections' 944 `--no-check-sections' 945 Asks the linker _not_ to check section addresses after they have 946 been assigned to see if there are any overlaps. Normally the 947 linker will perform this check, and if it finds any overlaps it 948 will produce suitable error messages. The linker does know about, 949 and does make allowances for sections in overlays. The default 950 behaviour can be restored by using the command line switch 951 `--check-sections'. Section overlap is not usually checked for 952 relocatable links. You can force checking in that case by using 953 the `--check-sections' option. 954 955 `--copy-dt-needed-entries' 956 `--no-copy-dt-needed-entries' 957 This option affects the treatment of dynamic libraries referred to 958 by DT_NEEDED tags _inside_ ELF dynamic libraries mentioned on the 959 command line. Normally the linker won't add a DT_NEEDED tag to the 960 output binary for each library mentioned in a DT_NEEDED tag in an 961 input dynamic library. With `--copy-dt-needed-entries' specified 962 on the command line however any dynamic libraries that follow it 963 will have their DT_NEEDED entries added. The default behaviour 964 can be restored with `--no-copy-dt-needed-entries'. 965 966 This option also has an effect on the resolution of symbols in 967 dynamic libraries. With `--copy-dt-needed-entries' dynamic 968 libraries mentioned on the command line will be recursively 969 searched, following their DT_NEEDED tags to other libraries, in 970 order to resolve symbols required by the output binary. With the 971 default setting however the searching of dynamic libraries that 972 follow it will stop with the dynamic library itself. No DT_NEEDED 973 links will be traversed to resolve symbols. 974 975 `--cref' 976 Output a cross reference table. If a linker map file is being 977 generated, the cross reference table is printed to the map file. 978 Otherwise, it is printed on the standard output. 979 980 The format of the table is intentionally simple, so that it may be 981 easily processed by a script if necessary. The symbols are 982 printed out, sorted by name. For each symbol, a list of file 983 names is given. If the symbol is defined, the first file listed 984 is the location of the definition. If the symbol is defined as a 985 common value then any files where this happens appear next. 986 Finally any files that reference the symbol are listed. 987 988 `--no-define-common' 989 This option inhibits the assignment of addresses to common symbols. 990 The script command `INHIBIT_COMMON_ALLOCATION' has the same effect. 991 *Note Miscellaneous Commands::. 992 993 The `--no-define-common' option allows decoupling the decision to 994 assign addresses to Common symbols from the choice of the output 995 file type; otherwise a non-Relocatable output type forces 996 assigning addresses to Common symbols. Using `--no-define-common' 997 allows Common symbols that are referenced from a shared library to 998 be assigned addresses only in the main program. This eliminates 999 the unused duplicate space in the shared library, and also 1000 prevents any possible confusion over resolving to the wrong 1001 duplicate when there are many dynamic modules with specialized 1002 search paths for runtime symbol resolution. 1003 1004 `--defsym=SYMBOL=EXPRESSION' 1005 Create a global symbol in the output file, containing the absolute 1006 address given by EXPRESSION. You may use this option as many 1007 times as necessary to define multiple symbols in the command line. 1008 A limited form of arithmetic is supported for the EXPRESSION in 1009 this context: you may give a hexadecimal constant or the name of 1010 an existing symbol, or use `+' and `-' to add or subtract 1011 hexadecimal constants or symbols. If you need more elaborate 1012 expressions, consider using the linker command language from a 1013 script (*note Assignment: Symbol Definitions: Assignments.). 1014 _Note:_ there should be no white space between SYMBOL, the equals 1015 sign ("<=>"), and EXPRESSION. 1016 1017 `--demangle[=STYLE]' 1018 `--no-demangle' 1019 These options control whether to demangle symbol names in error 1020 messages and other output. When the linker is told to demangle, 1021 it tries to present symbol names in a readable fashion: it strips 1022 leading underscores if they are used by the object file format, 1023 and converts C++ mangled symbol names into user readable names. 1024 Different compilers have different mangling styles. The optional 1025 demangling style argument can be used to choose an appropriate 1026 demangling style for your compiler. The linker will demangle by 1027 default unless the environment variable `COLLECT_NO_DEMANGLE' is 1028 set. These options may be used to override the default. 1029 1030 `-IFILE' 1031 `--dynamic-linker=FILE' 1032 Set the name of the dynamic linker. This is only meaningful when 1033 generating dynamically linked ELF executables. The default dynamic 1034 linker is normally correct; don't use this unless you know what 1035 you are doing. 1036 1037 `--fatal-warnings' 1038 `--no-fatal-warnings' 1039 Treat all warnings as errors. The default behaviour can be 1040 restored with the option `--no-fatal-warnings'. 1041 1042 `--force-exe-suffix' 1043 Make sure that an output file has a .exe suffix. 1044 1045 If a successfully built fully linked output file does not have a 1046 `.exe' or `.dll' suffix, this option forces the linker to copy the 1047 output file to one of the same name with a `.exe' suffix. This 1048 option is useful when using unmodified Unix makefiles on a 1049 Microsoft Windows host, since some versions of Windows won't run 1050 an image unless it ends in a `.exe' suffix. 1051 1052 `--gc-sections' 1053 `--no-gc-sections' 1054 Enable garbage collection of unused input sections. It is ignored 1055 on targets that do not support this option. The default behaviour 1056 (of not performing this garbage collection) can be restored by 1057 specifying `--no-gc-sections' on the command line. 1058 1059 `--gc-sections' decides which input sections are used by examining 1060 symbols and relocations. The section containing the entry symbol 1061 and all sections containing symbols undefined on the command-line 1062 will be kept, as will sections containing symbols referenced by 1063 dynamic objects. Note that when building shared libraries, the 1064 linker must assume that any visible symbol is referenced. Once 1065 this initial set of sections has been determined, the linker 1066 recursively marks as used any section referenced by their 1067 relocations. See `--entry' and `--undefined'. 1068 1069 This option can be set when doing a partial link (enabled with 1070 option `-r'). In this case the root of symbols kept must be 1071 explicitly specified either by an `--entry' or `--undefined' 1072 option or by a `ENTRY' command in the linker script. 1073 1074 `--print-gc-sections' 1075 `--no-print-gc-sections' 1076 List all sections removed by garbage collection. The listing is 1077 printed on stderr. This option is only effective if garbage 1078 collection has been enabled via the `--gc-sections') option. The 1079 default behaviour (of not listing the sections that are removed) 1080 can be restored by specifying `--no-print-gc-sections' on the 1081 command line. 1082 1083 `--print-output-format' 1084 Print the name of the default output format (perhaps influenced by 1085 other command-line options). This is the string that would appear 1086 in an `OUTPUT_FORMAT' linker script command (*note File 1087 Commands::). 1088 1089 `--help' 1090 Print a summary of the command-line options on the standard output 1091 and exit. 1092 1093 `--target-help' 1094 Print a summary of all target specific options on the standard 1095 output and exit. 1096 1097 `-Map=MAPFILE' 1098 Print a link map to the file MAPFILE. See the description of the 1099 `-M' option, above. 1100 1101 `--no-keep-memory' 1102 `ld' normally optimizes for speed over memory usage by caching the 1103 symbol tables of input files in memory. This option tells `ld' to 1104 instead optimize for memory usage, by rereading the symbol tables 1105 as necessary. This may be required if `ld' runs out of memory 1106 space while linking a large executable. 1107 1108 `--no-undefined' 1109 `-z defs' 1110 Report unresolved symbol references from regular object files. 1111 This is done even if the linker is creating a non-symbolic shared 1112 library. The switch `--[no-]allow-shlib-undefined' controls the 1113 behaviour for reporting unresolved references found in shared 1114 libraries being linked in. 1115 1116 `--allow-multiple-definition' 1117 `-z muldefs' 1118 Normally when a symbol is defined multiple times, the linker will 1119 report a fatal error. These options allow multiple definitions and 1120 the first definition will be used. 1121 1122 `--allow-shlib-undefined' 1123 `--no-allow-shlib-undefined' 1124 Allows or disallows undefined symbols in shared libraries. This 1125 switch is similar to `--no-undefined' except that it determines 1126 the behaviour when the undefined symbols are in a shared library 1127 rather than a regular object file. It does not affect how 1128 undefined symbols in regular object files are handled. 1129 1130 The default behaviour is to report errors for any undefined symbols 1131 referenced in shared libraries if the linker is being used to 1132 create an executable, but to allow them if the linker is being 1133 used to create a shared library. 1134 1135 The reasons for allowing undefined symbol references in shared 1136 libraries specified at link time are that: 1137 1138 * A shared library specified at link time may not be the same 1139 as the one that is available at load time, so the symbol 1140 might actually be resolvable at load time. 1141 1142 * There are some operating systems, eg BeOS and HPPA, where 1143 undefined symbols in shared libraries are normal. 1144 1145 The BeOS kernel for example patches shared libraries at load 1146 time to select whichever function is most appropriate for the 1147 current architecture. This is used, for example, to 1148 dynamically select an appropriate memset function. 1149 1150 `--no-undefined-version' 1151 Normally when a symbol has an undefined version, the linker will 1152 ignore it. This option disallows symbols with undefined version 1153 and a fatal error will be issued instead. 1154 1155 `--default-symver' 1156 Create and use a default symbol version (the soname) for 1157 unversioned exported symbols. 1158 1159 `--default-imported-symver' 1160 Create and use a default symbol version (the soname) for 1161 unversioned imported symbols. 1162 1163 `--no-warn-mismatch' 1164 Normally `ld' will give an error if you try to link together input 1165 files that are mismatched for some reason, perhaps because they 1166 have been compiled for different processors or for different 1167 endiannesses. This option tells `ld' that it should silently 1168 permit such possible errors. This option should only be used with 1169 care, in cases when you have taken some special action that 1170 ensures that the linker errors are inappropriate. 1171 1172 `--no-warn-search-mismatch' 1173 Normally `ld' will give a warning if it finds an incompatible 1174 library during a library search. This option silences the warning. 1175 1176 `--no-whole-archive' 1177 Turn off the effect of the `--whole-archive' option for subsequent 1178 archive files. 1179 1180 `--noinhibit-exec' 1181 Retain the executable output file whenever it is still usable. 1182 Normally, the linker will not produce an output file if it 1183 encounters errors during the link process; it exits without 1184 writing an output file when it issues any error whatsoever. 1185 1186 `-nostdlib' 1187 Only search library directories explicitly specified on the 1188 command line. Library directories specified in linker scripts 1189 (including linker scripts specified on the command line) are 1190 ignored. 1191 1192 `--oformat=OUTPUT-FORMAT' 1193 `ld' may be configured to support more than one kind of object 1194 file. If your `ld' is configured this way, you can use the 1195 `--oformat' option to specify the binary format for the output 1196 object file. Even when `ld' is configured to support alternative 1197 object formats, you don't usually need to specify this, as `ld' 1198 should be configured to produce as a default output format the most 1199 usual format on each machine. OUTPUT-FORMAT is a text string, the 1200 name of a particular format supported by the BFD libraries. (You 1201 can list the available binary formats with `objdump -i'.) The 1202 script command `OUTPUT_FORMAT' can also specify the output format, 1203 but this option overrides it. *Note BFD::. 1204 1205 `-pie' 1206 `--pic-executable' 1207 Create a position independent executable. This is currently only 1208 supported on ELF platforms. Position independent executables are 1209 similar to shared libraries in that they are relocated by the 1210 dynamic linker to the virtual address the OS chooses for them 1211 (which can vary between invocations). Like normal dynamically 1212 linked executables they can be executed and symbols defined in the 1213 executable cannot be overridden by shared libraries. 1214 1215 `-qmagic' 1216 This option is ignored for Linux compatibility. 1217 1218 `-Qy' 1219 This option is ignored for SVR4 compatibility. 1220 1221 `--relax' 1222 `--no-relax' 1223 An option with machine dependent effects. This option is only 1224 supported on a few targets. *Note `ld' and the H8/300: H8/300. 1225 *Note `ld' and the Intel 960 family: i960. *Note `ld' and Xtensa 1226 Processors: Xtensa. *Note `ld' and the 68HC11 and 68HC12: 1227 M68HC11/68HC12. *Note `ld' and the Altera Nios II: Nios II. 1228 *Note `ld' and PowerPC 32-bit ELF Support: PowerPC ELF32. 1229 1230 On some platforms the `--relax' option performs target specific, 1231 global optimizations that become possible when the linker resolves 1232 addressing in the program, such as relaxing address modes, 1233 synthesizing new instructions, selecting shorter version of current 1234 instructions, and combining constant values. 1235 1236 On some platforms these link time global optimizations may make 1237 symbolic debugging of the resulting executable impossible. This 1238 is known to be the case for the Matsushita MN10200 and MN10300 1239 family of processors. 1240 1241 On platforms where this is not supported, `--relax' is accepted, 1242 but ignored. 1243 1244 On platforms where `--relax' is accepted the option `--no-relax' 1245 can be used to disable the feature. 1246 1247 `--retain-symbols-file=FILENAME' 1248 Retain _only_ the symbols listed in the file FILENAME, discarding 1249 all others. FILENAME is simply a flat file, with one symbol name 1250 per line. This option is especially useful in environments (such 1251 as VxWorks) where a large global symbol table is accumulated 1252 gradually, to conserve run-time memory. 1253 1254 `--retain-symbols-file' does _not_ discard undefined symbols, or 1255 symbols needed for relocations. 1256 1257 You may only specify `--retain-symbols-file' once in the command 1258 line. It overrides `-s' and `-S'. 1259 1260 `-rpath=DIR' 1261 Add a directory to the runtime library search path. This is used 1262 when linking an ELF executable with shared objects. All `-rpath' 1263 arguments are concatenated and passed to the runtime linker, which 1264 uses them to locate shared objects at runtime. The `-rpath' 1265 option is also used when locating shared objects which are needed 1266 by shared objects explicitly included in the link; see the 1267 description of the `-rpath-link' option. If `-rpath' is not used 1268 when linking an ELF executable, the contents of the environment 1269 variable `LD_RUN_PATH' will be used if it is defined. 1270 1271 The `-rpath' option may also be used on SunOS. By default, on 1272 SunOS, the linker will form a runtime search patch out of all the 1273 `-L' options it is given. If a `-rpath' option is used, the 1274 runtime search path will be formed exclusively using the `-rpath' 1275 options, ignoring the `-L' options. This can be useful when using 1276 gcc, which adds many `-L' options which may be on NFS mounted file 1277 systems. 1278 1279 For compatibility with other ELF linkers, if the `-R' option is 1280 followed by a directory name, rather than a file name, it is 1281 treated as the `-rpath' option. 1282 1283 `-rpath-link=DIR' 1284 When using ELF or SunOS, one shared library may require another. 1285 This happens when an `ld -shared' link includes a shared library 1286 as one of the input files. 1287 1288 When the linker encounters such a dependency when doing a 1289 non-shared, non-relocatable link, it will automatically try to 1290 locate the required shared library and include it in the link, if 1291 it is not included explicitly. In such a case, the `-rpath-link' 1292 option specifies the first set of directories to search. The 1293 `-rpath-link' option may specify a sequence of directory names 1294 either by specifying a list of names separated by colons, or by 1295 appearing multiple times. 1296 1297 This option should be used with caution as it overrides the search 1298 path that may have been hard compiled into a shared library. In 1299 such a case it is possible to use unintentionally a different 1300 search path than the runtime linker would do. 1301 1302 The linker uses the following search paths to locate required 1303 shared libraries: 1304 1. Any directories specified by `-rpath-link' options. 1305 1306 2. Any directories specified by `-rpath' options. The difference 1307 between `-rpath' and `-rpath-link' is that directories 1308 specified by `-rpath' options are included in the executable 1309 and used at runtime, whereas the `-rpath-link' option is only 1310 effective at link time. Searching `-rpath' in this way is 1311 only supported by native linkers and cross linkers which have 1312 been configured with the `--with-sysroot' option. 1313 1314 3. On an ELF system, for native linkers, if the `-rpath' and 1315 `-rpath-link' options were not used, search the contents of 1316 the environment variable `LD_RUN_PATH'. 1317 1318 4. On SunOS, if the `-rpath' option was not used, search any 1319 directories specified using `-L' options. 1320 1321 5. For a native linker, search the contents of the environment 1322 variable `LD_LIBRARY_PATH'. 1323 1324 6. For a native ELF linker, the directories in `DT_RUNPATH' or 1325 `DT_RPATH' of a shared library are searched for shared 1326 libraries needed by it. The `DT_RPATH' entries are ignored if 1327 `DT_RUNPATH' entries exist. 1328 1329 7. The default directories, normally `/lib' and `/usr/lib'. 1330 1331 8. For a native linker on an ELF system, if the file 1332 `/etc/ld.so.conf' exists, the list of directories found in 1333 that file. 1334 1335 If the required shared library is not found, the linker will issue 1336 a warning and continue with the link. 1337 1338 `-shared' 1339 `-Bshareable' 1340 Create a shared library. This is currently only supported on ELF, 1341 XCOFF and SunOS platforms. On SunOS, the linker will 1342 automatically create a shared library if the `-e' option is not 1343 used and there are undefined symbols in the link. 1344 1345 `--sort-common' 1346 `--sort-common=ascending' 1347 `--sort-common=descending' 1348 This option tells `ld' to sort the common symbols by alignment in 1349 ascending or descending order when it places them in the 1350 appropriate output sections. The symbol alignments considered are 1351 sixteen-byte or larger, eight-byte, four-byte, two-byte, and 1352 one-byte. This is to prevent gaps between symbols due to alignment 1353 constraints. If no sorting order is specified, then descending 1354 order is assumed. 1355 1356 `--sort-section=name' 1357 This option will apply `SORT_BY_NAME' to all wildcard section 1358 patterns in the linker script. 1359 1360 `--sort-section=alignment' 1361 This option will apply `SORT_BY_ALIGNMENT' to all wildcard section 1362 patterns in the linker script. 1363 1364 `--split-by-file[=SIZE]' 1365 Similar to `--split-by-reloc' but creates a new output section for 1366 each input file when SIZE is reached. SIZE defaults to a size of 1367 1 if not given. 1368 1369 `--split-by-reloc[=COUNT]' 1370 Tries to creates extra sections in the output file so that no 1371 single output section in the file contains more than COUNT 1372 relocations. This is useful when generating huge relocatable 1373 files for downloading into certain real time kernels with the COFF 1374 object file format; since COFF cannot represent more than 65535 1375 relocations in a single section. Note that this will fail to work 1376 with object file formats which do not support arbitrary sections. 1377 The linker will not split up individual input sections for 1378 redistribution, so if a single input section contains more than 1379 COUNT relocations one output section will contain that many 1380 relocations. COUNT defaults to a value of 32768. 1381 1382 `--stats' 1383 Compute and display statistics about the operation of the linker, 1384 such as execution time and memory usage. 1385 1386 `--sysroot=DIRECTORY' 1387 Use DIRECTORY as the location of the sysroot, overriding the 1388 configure-time default. This option is only supported by linkers 1389 that were configured using `--with-sysroot'. 1390 1391 `--traditional-format' 1392 For some targets, the output of `ld' is different in some ways from 1393 the output of some existing linker. This switch requests `ld' to 1394 use the traditional format instead. 1395 1396 For example, on SunOS, `ld' combines duplicate entries in the 1397 symbol string table. This can reduce the size of an output file 1398 with full debugging information by over 30 percent. 1399 Unfortunately, the SunOS `dbx' program can not read the resulting 1400 program (`gdb' has no trouble). The `--traditional-format' switch 1401 tells `ld' to not combine duplicate entries. 1402 1403 `--section-start=SECTIONNAME=ORG' 1404 Locate a section in the output file at the absolute address given 1405 by ORG. You may use this option as many times as necessary to 1406 locate multiple sections in the command line. ORG must be a 1407 single hexadecimal integer; for compatibility with other linkers, 1408 you may omit the leading `0x' usually associated with hexadecimal 1409 values. _Note:_ there should be no white space between 1410 SECTIONNAME, the equals sign ("<=>"), and ORG. 1411 1412 `-Tbss=ORG' 1413 `-Tdata=ORG' 1414 `-Ttext=ORG' 1415 Same as `--section-start', with `.bss', `.data' or `.text' as the 1416 SECTIONNAME. 1417 1418 `-Ttext-segment=ORG' 1419 When creating an ELF executable, it will set the address of the 1420 first byte of the text segment. 1421 1422 `-Trodata-segment=ORG' 1423 When creating an ELF executable or shared object for a target where 1424 the read-only data is in its own segment separate from the 1425 executable text, it will set the address of the first byte of the 1426 read-only data segment. 1427 1428 `-Tldata-segment=ORG' 1429 When creating an ELF executable or shared object for x86-64 medium 1430 memory model, it will set the address of the first byte of the 1431 ldata segment. 1432 1433 `--unresolved-symbols=METHOD' 1434 Determine how to handle unresolved symbols. There are four 1435 possible values for `method': 1436 1437 `ignore-all' 1438 Do not report any unresolved symbols. 1439 1440 `report-all' 1441 Report all unresolved symbols. This is the default. 1442 1443 `ignore-in-object-files' 1444 Report unresolved symbols that are contained in shared 1445 libraries, but ignore them if they come from regular object 1446 files. 1447 1448 `ignore-in-shared-libs' 1449 Report unresolved symbols that come from regular object 1450 files, but ignore them if they come from shared libraries. 1451 This can be useful when creating a dynamic binary and it is 1452 known that all the shared libraries that it should be 1453 referencing are included on the linker's command line. 1454 1455 The behaviour for shared libraries on their own can also be 1456 controlled by the `--[no-]allow-shlib-undefined' option. 1457 1458 Normally the linker will generate an error message for each 1459 reported unresolved symbol but the option 1460 `--warn-unresolved-symbols' can change this to a warning. 1461 1462 `--dll-verbose' 1463 `--verbose[=NUMBER]' 1464 Display the version number for `ld' and list the linker emulations 1465 supported. Display which input files can and cannot be opened. 1466 Display the linker script being used by the linker. If the 1467 optional NUMBER argument > 1, plugin symbol status will also be 1468 displayed. 1469 1470 `--version-script=VERSION-SCRIPTFILE' 1471 Specify the name of a version script to the linker. This is 1472 typically used when creating shared libraries to specify 1473 additional information about the version hierarchy for the library 1474 being created. This option is only fully supported on ELF 1475 platforms which support shared libraries; see *Note VERSION::. It 1476 is partially supported on PE platforms, which can use version 1477 scripts to filter symbol visibility in auto-export mode: any 1478 symbols marked `local' in the version script will not be exported. 1479 *Note WIN32::. 1480 1481 `--warn-common' 1482 Warn when a common symbol is combined with another common symbol 1483 or with a symbol definition. Unix linkers allow this somewhat 1484 sloppy practice, but linkers on some other operating systems do 1485 not. This option allows you to find potential problems from 1486 combining global symbols. Unfortunately, some C libraries use 1487 this practice, so you may get some warnings about symbols in the 1488 libraries as well as in your programs. 1489 1490 There are three kinds of global symbols, illustrated here by C 1491 examples: 1492 1493 `int i = 1;' 1494 A definition, which goes in the initialized data section of 1495 the output file. 1496 1497 `extern int i;' 1498 An undefined reference, which does not allocate space. There 1499 must be either a definition or a common symbol for the 1500 variable somewhere. 1501 1502 `int i;' 1503 A common symbol. If there are only (one or more) common 1504 symbols for a variable, it goes in the uninitialized data 1505 area of the output file. The linker merges multiple common 1506 symbols for the same variable into a single symbol. If they 1507 are of different sizes, it picks the largest size. The 1508 linker turns a common symbol into a declaration, if there is 1509 a definition of the same variable. 1510 1511 The `--warn-common' option can produce five kinds of warnings. 1512 Each warning consists of a pair of lines: the first describes the 1513 symbol just encountered, and the second describes the previous 1514 symbol encountered with the same name. One or both of the two 1515 symbols will be a common symbol. 1516 1517 1. Turning a common symbol into a reference, because there is 1518 already a definition for the symbol. 1519 FILE(SECTION): warning: common of `SYMBOL' 1520 overridden by definition 1521 FILE(SECTION): warning: defined here 1522 1523 2. Turning a common symbol into a reference, because a later 1524 definition for the symbol is encountered. This is the same 1525 as the previous case, except that the symbols are encountered 1526 in a different order. 1527 FILE(SECTION): warning: definition of `SYMBOL' 1528 overriding common 1529 FILE(SECTION): warning: common is here 1530 1531 3. Merging a common symbol with a previous same-sized common 1532 symbol. 1533 FILE(SECTION): warning: multiple common 1534 of `SYMBOL' 1535 FILE(SECTION): warning: previous common is here 1536 1537 4. Merging a common symbol with a previous larger common symbol. 1538 FILE(SECTION): warning: common of `SYMBOL' 1539 overridden by larger common 1540 FILE(SECTION): warning: larger common is here 1541 1542 5. Merging a common symbol with a previous smaller common 1543 symbol. This is the same as the previous case, except that 1544 the symbols are encountered in a different order. 1545 FILE(SECTION): warning: common of `SYMBOL' 1546 overriding smaller common 1547 FILE(SECTION): warning: smaller common is here 1548 1549 `--warn-constructors' 1550 Warn if any global constructors are used. This is only useful for 1551 a few object file formats. For formats like COFF or ELF, the 1552 linker can not detect the use of global constructors. 1553 1554 `--warn-multiple-gp' 1555 Warn if multiple global pointer values are required in the output 1556 file. This is only meaningful for certain processors, such as the 1557 Alpha. Specifically, some processors put large-valued constants 1558 in a special section. A special register (the global pointer) 1559 points into the middle of this section, so that constants can be 1560 loaded efficiently via a base-register relative addressing mode. 1561 Since the offset in base-register relative mode is fixed and 1562 relatively small (e.g., 16 bits), this limits the maximum size of 1563 the constant pool. Thus, in large programs, it is often necessary 1564 to use multiple global pointer values in order to be able to 1565 address all possible constants. This option causes a warning to 1566 be issued whenever this case occurs. 1567 1568 `--warn-once' 1569 Only warn once for each undefined symbol, rather than once per 1570 module which refers to it. 1571 1572 `--warn-section-align' 1573 Warn if the address of an output section is changed because of 1574 alignment. Typically, the alignment will be set by an input 1575 section. The address will only be changed if it not explicitly 1576 specified; that is, if the `SECTIONS' command does not specify a 1577 start address for the section (*note SECTIONS::). 1578 1579 `--warn-shared-textrel' 1580 Warn if the linker adds a DT_TEXTREL to a shared object. 1581 1582 `--warn-alternate-em' 1583 Warn if an object has alternate ELF machine code. 1584 1585 `--warn-unresolved-symbols' 1586 If the linker is going to report an unresolved symbol (see the 1587 option `--unresolved-symbols') it will normally generate an error. 1588 This option makes it generate a warning instead. 1589 1590 `--error-unresolved-symbols' 1591 This restores the linker's default behaviour of generating errors 1592 when it is reporting unresolved symbols. 1593 1594 `--whole-archive' 1595 For each archive mentioned on the command line after the 1596 `--whole-archive' option, include every object file in the archive 1597 in the link, rather than searching the archive for the required 1598 object files. This is normally used to turn an archive file into 1599 a shared library, forcing every object to be included in the 1600 resulting shared library. This option may be used more than once. 1601 1602 Two notes when using this option from gcc: First, gcc doesn't know 1603 about this option, so you have to use `-Wl,-whole-archive'. 1604 Second, don't forget to use `-Wl,-no-whole-archive' after your 1605 list of archives, because gcc will add its own list of archives to 1606 your link and you may not want this flag to affect those as well. 1607 1608 `--wrap=SYMBOL' 1609 Use a wrapper function for SYMBOL. Any undefined reference to 1610 SYMBOL will be resolved to `__wrap_SYMBOL'. Any undefined 1611 reference to `__real_SYMBOL' will be resolved to SYMBOL. 1612 1613 This can be used to provide a wrapper for a system function. The 1614 wrapper function should be called `__wrap_SYMBOL'. If it wishes 1615 to call the system function, it should call `__real_SYMBOL'. 1616 1617 Here is a trivial example: 1618 1619 void * 1620 __wrap_malloc (size_t c) 1621 { 1622 printf ("malloc called with %zu\n", c); 1623 return __real_malloc (c); 1624 } 1625 1626 If you link other code with this file using `--wrap malloc', then 1627 all calls to `malloc' will call the function `__wrap_malloc' 1628 instead. The call to `__real_malloc' in `__wrap_malloc' will call 1629 the real `malloc' function. 1630 1631 You may wish to provide a `__real_malloc' function as well, so that 1632 links without the `--wrap' option will succeed. If you do this, 1633 you should not put the definition of `__real_malloc' in the same 1634 file as `__wrap_malloc'; if you do, the assembler may resolve the 1635 call before the linker has a chance to wrap it to `malloc'. 1636 1637 `--eh-frame-hdr' 1638 Request creation of `.eh_frame_hdr' section and ELF 1639 `PT_GNU_EH_FRAME' segment header. 1640 1641 `--no-ld-generated-unwind-info' 1642 Request creation of `.eh_frame' unwind info for linker generated 1643 code sections like PLT. This option is on by default if linker 1644 generated unwind info is supported. 1645 1646 `--enable-new-dtags' 1647 `--disable-new-dtags' 1648 This linker can create the new dynamic tags in ELF. But the older 1649 ELF systems may not understand them. If you specify 1650 `--enable-new-dtags', the new dynamic tags will be created as 1651 needed and older dynamic tags will be omitted. If you specify 1652 `--disable-new-dtags', no new dynamic tags will be created. By 1653 default, the new dynamic tags are not created. Note that those 1654 options are only available for ELF systems. 1655 1656 `--hash-size=NUMBER' 1657 Set the default size of the linker's hash tables to a prime number 1658 close to NUMBER. Increasing this value can reduce the length of 1659 time it takes the linker to perform its tasks, at the expense of 1660 increasing the linker's memory requirements. Similarly reducing 1661 this value can reduce the memory requirements at the expense of 1662 speed. 1663 1664 `--hash-style=STYLE' 1665 Set the type of linker's hash table(s). STYLE can be either 1666 `sysv' for classic ELF `.hash' section, `gnu' for new style GNU 1667 `.gnu.hash' section or `both' for both the classic ELF `.hash' and 1668 new style GNU `.gnu.hash' hash tables. The default is `sysv'. 1669 1670 `--reduce-memory-overheads' 1671 This option reduces memory requirements at ld runtime, at the 1672 expense of linking speed. This was introduced to select the old 1673 O(n^2) algorithm for link map file generation, rather than the new 1674 O(n) algorithm which uses about 40% more memory for symbol storage. 1675 1676 Another effect of the switch is to set the default hash table size 1677 to 1021, which again saves memory at the cost of lengthening the 1678 linker's run time. This is not done however if the `--hash-size' 1679 switch has been used. 1680 1681 The `--reduce-memory-overheads' switch may be also be used to 1682 enable other tradeoffs in future versions of the linker. 1683 1684 `--build-id' 1685 `--build-id=STYLE' 1686 Request the creation of a `.note.gnu.build-id' ELF note section or 1687 a `.build-id' COFF section. The contents of the note are unique 1688 bits identifying this linked file. STYLE can be `uuid' to use 128 1689 random bits, `sha1' to use a 160-bit SHA1 hash on the normative 1690 parts of the output contents, `md5' to use a 128-bit MD5 hash on 1691 the normative parts of the output contents, or `0xHEXSTRING' to 1692 use a chosen bit string specified as an even number of hexadecimal 1693 digits (`-' and `:' characters between digit pairs are ignored). 1694 If STYLE is omitted, `sha1' is used. 1695 1696 The `md5' and `sha1' styles produces an identifier that is always 1697 the same in an identical output file, but will be unique among all 1698 nonidentical output files. It is not intended to be compared as a 1699 checksum for the file's contents. A linked file may be changed 1700 later by other tools, but the build ID bit string identifying the 1701 original linked file does not change. 1702 1703 Passing `none' for STYLE disables the setting from any 1704 `--build-id' options earlier on the command line. 1705 1706 2.1.1 Options Specific to i386 PE Targets 1707 ----------------------------------------- 1708 1709 The i386 PE linker supports the `-shared' option, which causes the 1710 output to be a dynamically linked library (DLL) instead of a normal 1711 executable. You should name the output `*.dll' when you use this 1712 option. In addition, the linker fully supports the standard `*.def' 1713 files, which may be specified on the linker command line like an object 1714 file (in fact, it should precede archives it exports symbols from, to 1715 ensure that they get linked in, just like a normal object file). 1716 1717 In addition to the options common to all targets, the i386 PE linker 1718 support additional command line options that are specific to the i386 1719 PE target. Options that take values may be separated from their values 1720 by either a space or an equals sign. 1721 1722 `--add-stdcall-alias' 1723 If given, symbols with a stdcall suffix (@NN) will be exported 1724 as-is and also with the suffix stripped. [This option is specific 1725 to the i386 PE targeted port of the linker] 1726 1727 `--base-file FILE' 1728 Use FILE as the name of a file in which to save the base addresses 1729 of all the relocations needed for generating DLLs with `dlltool'. 1730 [This is an i386 PE specific option] 1731 1732 `--dll' 1733 Create a DLL instead of a regular executable. You may also use 1734 `-shared' or specify a `LIBRARY' in a given `.def' file. [This 1735 option is specific to the i386 PE targeted port of the linker] 1736 1737 `--enable-long-section-names' 1738 `--disable-long-section-names' 1739 The PE variants of the Coff object format add an extension that 1740 permits the use of section names longer than eight characters, the 1741 normal limit for Coff. By default, these names are only allowed 1742 in object files, as fully-linked executable images do not carry 1743 the Coff string table required to support the longer names. As a 1744 GNU extension, it is possible to allow their use in executable 1745 images as well, or to (probably pointlessly!) disallow it in 1746 object files, by using these two options. Executable images 1747 generated with these long section names are slightly non-standard, 1748 carrying as they do a string table, and may generate confusing 1749 output when examined with non-GNU PE-aware tools, such as file 1750 viewers and dumpers. However, GDB relies on the use of PE long 1751 section names to find Dwarf-2 debug information sections in an 1752 executable image at runtime, and so if neither option is specified 1753 on the command-line, `ld' will enable long section names, 1754 overriding the default and technically correct behaviour, when it 1755 finds the presence of debug information while linking an executable 1756 image and not stripping symbols. [This option is valid for all PE 1757 targeted ports of the linker] 1758 1759 `--enable-stdcall-fixup' 1760 `--disable-stdcall-fixup' 1761 If the link finds a symbol that it cannot resolve, it will attempt 1762 to do "fuzzy linking" by looking for another defined symbol that 1763 differs only in the format of the symbol name (cdecl vs stdcall) 1764 and will resolve that symbol by linking to the match. For 1765 example, the undefined symbol `_foo' might be linked to the 1766 function `_foo@12', or the undefined symbol `_bar@16' might be 1767 linked to the function `_bar'. When the linker does this, it 1768 prints a warning, since it normally should have failed to link, 1769 but sometimes import libraries generated from third-party dlls may 1770 need this feature to be usable. If you specify 1771 `--enable-stdcall-fixup', this feature is fully enabled and 1772 warnings are not printed. If you specify 1773 `--disable-stdcall-fixup', this feature is disabled and such 1774 mismatches are considered to be errors. [This option is specific 1775 to the i386 PE targeted port of the linker] 1776 1777 `--leading-underscore' 1778 `--no-leading-underscore' 1779 For most targets default symbol-prefix is an underscore and is 1780 defined in target's description. By this option it is possible to 1781 disable/enable the default underscore symbol-prefix. 1782 1783 `--export-all-symbols' 1784 If given, all global symbols in the objects used to build a DLL 1785 will be exported by the DLL. Note that this is the default if 1786 there otherwise wouldn't be any exported symbols. When symbols are 1787 explicitly exported via DEF files or implicitly exported via 1788 function attributes, the default is to not export anything else 1789 unless this option is given. Note that the symbols `DllMain@12', 1790 `DllEntryPoint@0', `DllMainCRTStartup@12', and `impure_ptr' will 1791 not be automatically exported. Also, symbols imported from other 1792 DLLs will not be re-exported, nor will symbols specifying the 1793 DLL's internal layout such as those beginning with `_head_' or 1794 ending with `_iname'. In addition, no symbols from `libgcc', 1795 `libstd++', `libmingw32', or `crtX.o' will be exported. Symbols 1796 whose names begin with `__rtti_' or `__builtin_' will not be 1797 exported, to help with C++ DLLs. Finally, there is an extensive 1798 list of cygwin-private symbols that are not exported (obviously, 1799 this applies on when building DLLs for cygwin targets). These 1800 cygwin-excludes are: `_cygwin_dll_entry@12', 1801 `_cygwin_crt0_common@8', `_cygwin_noncygwin_dll_entry@12', 1802 `_fmode', `_impure_ptr', `cygwin_attach_dll', `cygwin_premain0', 1803 `cygwin_premain1', `cygwin_premain2', `cygwin_premain3', and 1804 `environ'. [This option is specific to the i386 PE targeted port 1805 of the linker] 1806 1807 `--exclude-symbols SYMBOL,SYMBOL,...' 1808 Specifies a list of symbols which should not be automatically 1809 exported. The symbol names may be delimited by commas or colons. 1810 [This option is specific to the i386 PE targeted port of the 1811 linker] 1812 1813 `--exclude-all-symbols' 1814 Specifies no symbols should be automatically exported. [This 1815 option is specific to the i386 PE targeted port of the linker] 1816 1817 `--file-alignment' 1818 Specify the file alignment. Sections in the file will always 1819 begin at file offsets which are multiples of this number. This 1820 defaults to 512. [This option is specific to the i386 PE targeted 1821 port of the linker] 1822 1823 `--heap RESERVE' 1824 `--heap RESERVE,COMMIT' 1825 Specify the number of bytes of memory to reserve (and optionally 1826 commit) to be used as heap for this program. The default is 1MB 1827 reserved, 4K committed. [This option is specific to the i386 PE 1828 targeted port of the linker] 1829 1830 `--image-base VALUE' 1831 Use VALUE as the base address of your program or dll. This is the 1832 lowest memory location that will be used when your program or dll 1833 is loaded. To reduce the need to relocate and improve performance 1834 of your dlls, each should have a unique base address and not 1835 overlap any other dlls. The default is 0x400000 for executables, 1836 and 0x10000000 for dlls. [This option is specific to the i386 PE 1837 targeted port of the linker] 1838 1839 `--kill-at' 1840 If given, the stdcall suffixes (@NN) will be stripped from symbols 1841 before they are exported. [This option is specific to the i386 PE 1842 targeted port of the linker] 1843 1844 `--large-address-aware' 1845 If given, the appropriate bit in the "Characteristics" field of 1846 the COFF header is set to indicate that this executable supports 1847 virtual addresses greater than 2 gigabytes. This should be used 1848 in conjunction with the /3GB or /USERVA=VALUE megabytes switch in 1849 the "[operating systems]" section of the BOOT.INI. Otherwise, 1850 this bit has no effect. [This option is specific to PE targeted 1851 ports of the linker] 1852 1853 `--disable-large-address-aware' 1854 Reverts the effect of a previous `--large-address-aware' option. 1855 This is useful if `--large-address-aware' is always set by the 1856 compiler driver (e.g. Cygwin gcc) and the executable does not 1857 support virtual addresses greater than 2 gigabytes. [This option 1858 is specific to PE targeted ports of the linker] 1859 1860 `--major-image-version VALUE' 1861 Sets the major number of the "image version". Defaults to 1. 1862 [This option is specific to the i386 PE targeted port of the 1863 linker] 1864 1865 `--major-os-version VALUE' 1866 Sets the major number of the "os version". Defaults to 4. [This 1867 option is specific to the i386 PE targeted port of the linker] 1868 1869 `--major-subsystem-version VALUE' 1870 Sets the major number of the "subsystem version". Defaults to 4. 1871 [This option is specific to the i386 PE targeted port of the 1872 linker] 1873 1874 `--minor-image-version VALUE' 1875 Sets the minor number of the "image version". Defaults to 0. 1876 [This option is specific to the i386 PE targeted port of the 1877 linker] 1878 1879 `--minor-os-version VALUE' 1880 Sets the minor number of the "os version". Defaults to 0. [This 1881 option is specific to the i386 PE targeted port of the linker] 1882 1883 `--minor-subsystem-version VALUE' 1884 Sets the minor number of the "subsystem version". Defaults to 0. 1885 [This option is specific to the i386 PE targeted port of the 1886 linker] 1887 1888 `--output-def FILE' 1889 The linker will create the file FILE which will contain a DEF file 1890 corresponding to the DLL the linker is generating. This DEF file 1891 (which should be called `*.def') may be used to create an import 1892 library with `dlltool' or may be used as a reference to 1893 automatically or implicitly exported symbols. [This option is 1894 specific to the i386 PE targeted port of the linker] 1895 1896 `--out-implib FILE' 1897 The linker will create the file FILE which will contain an import 1898 lib corresponding to the DLL the linker is generating. This import 1899 lib (which should be called `*.dll.a' or `*.a' may be used to link 1900 clients against the generated DLL; this behaviour makes it 1901 possible to skip a separate `dlltool' import library creation step. 1902 [This option is specific to the i386 PE targeted port of the 1903 linker] 1904 1905 `--enable-auto-image-base' 1906 `--enable-auto-image-base=VALUE' 1907 Automatically choose the image base for DLLs, optionally starting 1908 with base VALUE, unless one is specified using the `--image-base' 1909 argument. By using a hash generated from the dllname to create 1910 unique image bases for each DLL, in-memory collisions and 1911 relocations which can delay program execution are avoided. [This 1912 option is specific to the i386 PE targeted port of the linker] 1913 1914 `--disable-auto-image-base' 1915 Do not automatically generate a unique image base. If there is no 1916 user-specified image base (`--image-base') then use the platform 1917 default. [This option is specific to the i386 PE targeted port of 1918 the linker] 1919 1920 `--dll-search-prefix STRING' 1921 When linking dynamically to a dll without an import library, 1922 search for `<string><basename>.dll' in preference to 1923 `lib<basename>.dll'. This behaviour allows easy distinction 1924 between DLLs built for the various "subplatforms": native, cygwin, 1925 uwin, pw, etc. For instance, cygwin DLLs typically use 1926 `--dll-search-prefix=cyg'. [This option is specific to the i386 1927 PE targeted port of the linker] 1928 1929 `--enable-auto-import' 1930 Do sophisticated linking of `_symbol' to `__imp__symbol' for DATA 1931 imports from DLLs, and create the necessary thunking symbols when 1932 building the import libraries with those DATA exports. Note: Use 1933 of the 'auto-import' extension will cause the text section of the 1934 image file to be made writable. This does not conform to the 1935 PE-COFF format specification published by Microsoft. 1936 1937 Note - use of the 'auto-import' extension will also cause read only 1938 data which would normally be placed into the .rdata section to be 1939 placed into the .data section instead. This is in order to work 1940 around a problem with consts that is described here: 1941 http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html 1942 1943 Using 'auto-import' generally will 'just work' - but sometimes you 1944 may see this message: 1945 1946 "variable '<var>' can't be auto-imported. Please read the 1947 documentation for ld's `--enable-auto-import' for details." 1948 1949 This message occurs when some (sub)expression accesses an address 1950 ultimately given by the sum of two constants (Win32 import tables 1951 only allow one). Instances where this may occur include accesses 1952 to member fields of struct variables imported from a DLL, as well 1953 as using a constant index into an array variable imported from a 1954 DLL. Any multiword variable (arrays, structs, long long, etc) may 1955 trigger this error condition. However, regardless of the exact 1956 data type of the offending exported variable, ld will always 1957 detect it, issue the warning, and exit. 1958 1959 There are several ways to address this difficulty, regardless of 1960 the data type of the exported variable: 1961 1962 One way is to use -enable-runtime-pseudo-reloc switch. This leaves 1963 the task of adjusting references in your client code for runtime 1964 environment, so this method works only when runtime environment 1965 supports this feature. 1966 1967 A second solution is to force one of the 'constants' to be a 1968 variable - that is, unknown and un-optimizable at compile time. 1969 For arrays, there are two possibilities: a) make the indexee (the 1970 array's address) a variable, or b) make the 'constant' index a 1971 variable. Thus: 1972 1973 extern type extern_array[]; 1974 extern_array[1] --> 1975 { volatile type *t=extern_array; t[1] } 1976 1977 or 1978 1979 extern type extern_array[]; 1980 extern_array[1] --> 1981 { volatile int t=1; extern_array[t] } 1982 1983 For structs (and most other multiword data types) the only option 1984 is to make the struct itself (or the long long, or the ...) 1985 variable: 1986 1987 extern struct s extern_struct; 1988 extern_struct.field --> 1989 { volatile struct s *t=&extern_struct; t->field } 1990 1991 or 1992 1993 extern long long extern_ll; 1994 extern_ll --> 1995 { volatile long long * local_ll=&extern_ll; *local_ll } 1996 1997 A third method of dealing with this difficulty is to abandon 1998 'auto-import' for the offending symbol and mark it with 1999 `__declspec(dllimport)'. However, in practice that requires using 2000 compile-time #defines to indicate whether you are building a DLL, 2001 building client code that will link to the DLL, or merely 2002 building/linking to a static library. In making the choice 2003 between the various methods of resolving the 'direct address with 2004 constant offset' problem, you should consider typical real-world 2005 usage: 2006 2007 Original: 2008 --foo.h 2009 extern int arr[]; 2010 --foo.c 2011 #include "foo.h" 2012 void main(int argc, char **argv){ 2013 printf("%d\n",arr[1]); 2014 } 2015 2016 Solution 1: 2017 --foo.h 2018 extern int arr[]; 2019 --foo.c 2020 #include "foo.h" 2021 void main(int argc, char **argv){ 2022 /* This workaround is for win32 and cygwin; do not "optimize" */ 2023 volatile int *parr = arr; 2024 printf("%d\n",parr[1]); 2025 } 2026 2027 Solution 2: 2028 --foo.h 2029 /* Note: auto-export is assumed (no __declspec(dllexport)) */ 2030 #if (defined(_WIN32) || defined(__CYGWIN__)) && \ 2031 !(defined(FOO_BUILD_DLL) || defined(FOO_STATIC)) 2032 #define FOO_IMPORT __declspec(dllimport) 2033 #else 2034 #define FOO_IMPORT 2035 #endif 2036 extern FOO_IMPORT int arr[]; 2037 --foo.c 2038 #include "foo.h" 2039 void main(int argc, char **argv){ 2040 printf("%d\n",arr[1]); 2041 } 2042 2043 A fourth way to avoid this problem is to re-code your library to 2044 use a functional interface rather than a data interface for the 2045 offending variables (e.g. set_foo() and get_foo() accessor 2046 functions). [This option is specific to the i386 PE targeted port 2047 of the linker] 2048 2049 `--disable-auto-import' 2050 Do not attempt to do sophisticated linking of `_symbol' to 2051 `__imp__symbol' for DATA imports from DLLs. [This option is 2052 specific to the i386 PE targeted port of the linker] 2053 2054 `--enable-runtime-pseudo-reloc' 2055 If your code contains expressions described in -enable-auto-import 2056 section, that is, DATA imports from DLL with non-zero offset, this 2057 switch will create a vector of 'runtime pseudo relocations' which 2058 can be used by runtime environment to adjust references to such 2059 data in your client code. [This option is specific to the i386 PE 2060 targeted port of the linker] 2061 2062 `--disable-runtime-pseudo-reloc' 2063 Do not create pseudo relocations for non-zero offset DATA imports 2064 from DLLs. [This option is specific to the i386 PE targeted port 2065 of the linker] 2066 2067 `--enable-extra-pe-debug' 2068 Show additional debug info related to auto-import symbol thunking. 2069 [This option is specific to the i386 PE targeted port of the 2070 linker] 2071 2072 `--section-alignment' 2073 Sets the section alignment. Sections in memory will always begin 2074 at addresses which are a multiple of this number. Defaults to 2075 0x1000. [This option is specific to the i386 PE targeted port of 2076 the linker] 2077 2078 `--stack RESERVE' 2079 `--stack RESERVE,COMMIT' 2080 Specify the number of bytes of memory to reserve (and optionally 2081 commit) to be used as stack for this program. The default is 2MB 2082 reserved, 4K committed. [This option is specific to the i386 PE 2083 targeted port of the linker] 2084 2085 `--subsystem WHICH' 2086 `--subsystem WHICH:MAJOR' 2087 `--subsystem WHICH:MAJOR.MINOR' 2088 Specifies the subsystem under which your program will execute. The 2089 legal values for WHICH are `native', `windows', `console', 2090 `posix', and `xbox'. You may optionally set the subsystem version 2091 also. Numeric values are also accepted for WHICH. [This option 2092 is specific to the i386 PE targeted port of the linker] 2093 2094 The following options set flags in the `DllCharacteristics' field 2095 of the PE file header: [These options are specific to PE targeted 2096 ports of the linker] 2097 2098 `--high-entropy-va' 2099 Image is compatible with 64-bit address space layout randomization 2100 (ASLR). 2101 2102 `--dynamicbase' 2103 The image base address may be relocated using address space layout 2104 randomization (ASLR). This feature was introduced with MS Windows 2105 Vista for i386 PE targets. 2106 2107 `--forceinteg' 2108 Code integrity checks are enforced. 2109 2110 `--nxcompat' 2111 The image is compatible with the Data Execution Prevention. This 2112 feature was introduced with MS Windows XP SP2 for i386 PE targets. 2113 2114 `--no-isolation' 2115 Although the image understands isolation, do not isolate the image. 2116 2117 `--no-seh' 2118 The image does not use SEH. No SE handler may be called from this 2119 image. 2120 2121 `--no-bind' 2122 Do not bind this image. 2123 2124 `--wdmdriver' 2125 The driver uses the MS Windows Driver Model. 2126 2127 `--tsaware' 2128 The image is Terminal Server aware. 2129 2130 `--insert-timestamp' 2131 `--no-insert-timestamp' 2132 Insert a real timestamp into the image. This is the default 2133 behaviour as it matches legacy code and it means that the image 2134 will work with other, proprietary tools. The problem with this 2135 default is that it will result in slightly different images being 2136 produced each tiem the same sources are linked. The option 2137 `--no-insert-timestamp' can be used to insert a zero value for the 2138 timestamp, this ensuring that binaries produced from indentical 2139 sources will compare identically. 2140 2141 2.1.2 Options specific to C6X uClinux targets 2142 --------------------------------------------- 2143 2144 The C6X uClinux target uses a binary format called DSBT to support 2145 shared libraries. Each shared library in the system needs to have a 2146 unique index; all executables use an index of 0. 2147 2148 `--dsbt-size SIZE' 2149 This option sets the number of entires in the DSBT of the current 2150 executable or shared library to SIZE. The default is to create a 2151 table with 64 entries. 2152 2153 `--dsbt-index INDEX' 2154 This option sets the DSBT index of the current executable or 2155 shared library to INDEX. The default is 0, which is appropriate 2156 for generating executables. If a shared library is generated with 2157 a DSBT index of 0, the `R_C6000_DSBT_INDEX' relocs are copied into 2158 the output file. 2159 2160 The `--no-merge-exidx-entries' switch disables the merging of 2161 adjacent exidx entries in frame unwind info. 2162 2163 2164 2.1.3 Options specific to Motorola 68HC11 and 68HC12 targets 2165 ------------------------------------------------------------ 2166 2167 The 68HC11 and 68HC12 linkers support specific options to control the 2168 memory bank switching mapping and trampoline code generation. 2169 2170 `--no-trampoline' 2171 This option disables the generation of trampoline. By default a 2172 trampoline is generated for each far function which is called 2173 using a `jsr' instruction (this happens when a pointer to a far 2174 function is taken). 2175 2176 `--bank-window NAME' 2177 This option indicates to the linker the name of the memory region 2178 in the `MEMORY' specification that describes the memory bank 2179 window. The definition of such region is then used by the linker 2180 to compute paging and addresses within the memory window. 2181 2182 2183 2.1.4 Options specific to Motorola 68K target 2184 --------------------------------------------- 2185 2186 The following options are supported to control handling of GOT 2187 generation when linking for 68K targets. 2188 2189 `--got=TYPE' 2190 This option tells the linker which GOT generation scheme to use. 2191 TYPE should be one of `single', `negative', `multigot' or 2192 `target'. For more information refer to the Info entry for `ld'. 2193 2194 2195 2.1.5 Options specific to MIPS targets 2196 -------------------------------------- 2197 2198 The following options are supported to control microMIPS instruction 2199 generation when linking for MIPS targets. 2200 2201 `--insn32' 2202 `--no-insn32' 2203 These options control the choice of microMIPS instructions used in 2204 code generated by the linker, such as that in the PLT or lazy 2205 binding stubs, or in relaxation. If `--insn32' is used, then the 2206 linker only uses 32-bit instruction encodings. By default or if 2207 `--no-insn32' is used, all instruction encodings are used, 2208 including 16-bit ones where possible. 2209 2210 2211 2212 File: ld.info, Node: Environment, Prev: Options, Up: Invocation 2213 2214 2.2 Environment Variables 2215 ========================= 2216 2217 You can change the behaviour of `ld' with the environment variables 2218 `GNUTARGET', `LDEMULATION' and `COLLECT_NO_DEMANGLE'. 2219 2220 `GNUTARGET' determines the input-file object format if you don't use 2221 `-b' (or its synonym `--format'). Its value should be one of the BFD 2222 names for an input format (*note BFD::). If there is no `GNUTARGET' in 2223 the environment, `ld' uses the natural format of the target. If 2224 `GNUTARGET' is set to `default' then BFD attempts to discover the input 2225 format by examining binary input files; this method often succeeds, but 2226 there are potential ambiguities, since there is no method of ensuring 2227 that the magic number used to specify object-file formats is unique. 2228 However, the configuration procedure for BFD on each system places the 2229 conventional format for that system first in the search-list, so 2230 ambiguities are resolved in favor of convention. 2231 2232 `LDEMULATION' determines the default emulation if you don't use the 2233 `-m' option. The emulation can affect various aspects of linker 2234 behaviour, particularly the default linker script. You can list the 2235 available emulations with the `--verbose' or `-V' options. If the `-m' 2236 option is not used, and the `LDEMULATION' environment variable is not 2237 defined, the default emulation depends upon how the linker was 2238 configured. 2239 2240 Normally, the linker will default to demangling symbols. However, if 2241 `COLLECT_NO_DEMANGLE' is set in the environment, then it will default 2242 to not demangling symbols. This environment variable is used in a 2243 similar fashion by the `gcc' linker wrapper program. The default may 2244 be overridden by the `--demangle' and `--no-demangle' options. 2245 2246 2247 File: ld.info, Node: Scripts, Next: Machine Dependent, Prev: Invocation, Up: Top 2248 2249 3 Linker Scripts 2250 **************** 2251 2252 Every link is controlled by a "linker script". This script is written 2253 in the linker command language. 2254 2255 The main purpose of the linker script is to describe how the 2256 sections in the input files should be mapped into the output file, and 2257 to control the memory layout of the output file. Most linker scripts 2258 do nothing more than this. However, when necessary, the linker script 2259 can also direct the linker to perform many other operations, using the 2260 commands described below. 2261 2262 The linker always uses a linker script. If you do not supply one 2263 yourself, the linker will use a default script that is compiled into the 2264 linker executable. You can use the `--verbose' command line option to 2265 display the default linker script. Certain command line options, such 2266 as `-r' or `-N', will affect the default linker script. 2267 2268 You may supply your own linker script by using the `-T' command line 2269 option. When you do this, your linker script will replace the default 2270 linker script. 2271 2272 You may also use linker scripts implicitly by naming them as input 2273 files to the linker, as though they were files to be linked. *Note 2274 Implicit Linker Scripts::. 2275 2276 * Menu: 2277 2278 * Basic Script Concepts:: Basic Linker Script Concepts 2279 * Script Format:: Linker Script Format 2280 * Simple Example:: Simple Linker Script Example 2281 * Simple Commands:: Simple Linker Script Commands 2282 * Assignments:: Assigning Values to Symbols 2283 * SECTIONS:: SECTIONS Command 2284 * MEMORY:: MEMORY Command 2285 * PHDRS:: PHDRS Command 2286 * VERSION:: VERSION Command 2287 * Expressions:: Expressions in Linker Scripts 2288 * Implicit Linker Scripts:: Implicit Linker Scripts 2289 2290 2291 File: ld.info, Node: Basic Script Concepts, Next: Script Format, Up: Scripts 2292 2293 3.1 Basic Linker Script Concepts 2294 ================================ 2295 2296 We need to define some basic concepts and vocabulary in order to 2297 describe the linker script language. 2298 2299 The linker combines input files into a single output file. The 2300 output file and each input file are in a special data format known as an 2301 "object file format". Each file is called an "object file". The 2302 output file is often called an "executable", but for our purposes we 2303 will also call it an object file. Each object file has, among other 2304 things, a list of "sections". We sometimes refer to a section in an 2305 input file as an "input section"; similarly, a section in the output 2306 file is an "output section". 2307 2308 Each section in an object file has a name and a size. Most sections 2309 also have an associated block of data, known as the "section contents". 2310 A section may be marked as "loadable", which means that the contents 2311 should be loaded into memory when the output file is run. A section 2312 with no contents may be "allocatable", which means that an area in 2313 memory should be set aside, but nothing in particular should be loaded 2314 there (in some cases this memory must be zeroed out). A section which 2315 is neither loadable nor allocatable typically contains some sort of 2316 debugging information. 2317 2318 Every loadable or allocatable output section has two addresses. The 2319 first is the "VMA", or virtual memory address. This is the address the 2320 section will have when the output file is run. The second is the 2321 "LMA", or load memory address. This is the address at which the 2322 section will be loaded. In most cases the two addresses will be the 2323 same. An example of when they might be different is when a data section 2324 is loaded into ROM, and then copied into RAM when the program starts up 2325 (this technique is often used to initialize global variables in a ROM 2326 based system). In this case the ROM address would be the LMA, and the 2327 RAM address would be the VMA. 2328 2329 You can see the sections in an object file by using the `objdump' 2330 program with the `-h' option. 2331 2332 Every object file also has a list of "symbols", known as the "symbol 2333 table". A symbol may be defined or undefined. Each symbol has a name, 2334 and each defined symbol has an address, among other information. If 2335 you compile a C or C++ program into an object file, you will get a 2336 defined symbol for every defined function and global or static 2337 variable. Every undefined function or global variable which is 2338 referenced in the input file will become an undefined symbol. 2339 2340 You can see the symbols in an object file by using the `nm' program, 2341 or by using the `objdump' program with the `-t' option. 2342 2343 2344 File: ld.info, Node: Script Format, Next: Simple Example, Prev: Basic Script Concepts, Up: Scripts 2345 2346 3.2 Linker Script Format 2347 ======================== 2348 2349 Linker scripts are text files. 2350 2351 You write a linker script as a series of commands. Each command is 2352 either a keyword, possibly followed by arguments, or an assignment to a 2353 symbol. You may separate commands using semicolons. Whitespace is 2354 generally ignored. 2355 2356 Strings such as file or format names can normally be entered 2357 directly. If the file name contains a character such as a comma which 2358 would otherwise serve to separate file names, you may put the file name 2359 in double quotes. There is no way to use a double quote character in a 2360 file name. 2361 2362 You may include comments in linker scripts just as in C, delimited by 2363 `/*' and `*/'. As in C, comments are syntactically equivalent to 2364 whitespace. 2365 2366 2367 File: ld.info, Node: Simple Example, Next: Simple Commands, Prev: Script Format, Up: Scripts 2368 2369 3.3 Simple Linker Script Example 2370 ================================ 2371 2372 Many linker scripts are fairly simple. 2373 2374 The simplest possible linker script has just one command: 2375 `SECTIONS'. You use the `SECTIONS' command to describe the memory 2376 layout of the output file. 2377 2378 The `SECTIONS' command is a powerful command. Here we will describe 2379 a simple use of it. Let's assume your program consists only of code, 2380 initialized data, and uninitialized data. These will be in the 2381 `.text', `.data', and `.bss' sections, respectively. Let's assume 2382 further that these are the only sections which appear in your input 2383 files. 2384 2385 For this example, let's say that the code should be loaded at address 2386 0x10000, and that the data should start at address 0x8000000. Here is a 2387 linker script which will do that: 2388 SECTIONS 2389 { 2390 . = 0x10000; 2391 .text : { *(.text) } 2392 . = 0x8000000; 2393 .data : { *(.data) } 2394 .bss : { *(.bss) } 2395 } 2396 2397 You write the `SECTIONS' command as the keyword `SECTIONS', followed 2398 by a series of symbol assignments and output section descriptions 2399 enclosed in curly braces. 2400 2401 The first line inside the `SECTIONS' command of the above example 2402 sets the value of the special symbol `.', which is the location 2403 counter. If you do not specify the address of an output section in some 2404 other way (other ways are described later), the address is set from the 2405 current value of the location counter. The location counter is then 2406 incremented by the size of the output section. At the start of the 2407 `SECTIONS' command, the location counter has the value `0'. 2408 2409 The second line defines an output section, `.text'. The colon is 2410 required syntax which may be ignored for now. Within the curly braces 2411 after the output section name, you list the names of the input sections 2412 which should be placed into this output section. The `*' is a wildcard 2413 which matches any file name. The expression `*(.text)' means all 2414 `.text' input sections in all input files. 2415 2416 Since the location counter is `0x10000' when the output section 2417 `.text' is defined, the linker will set the address of the `.text' 2418 section in the output file to be `0x10000'. 2419 2420 The remaining lines define the `.data' and `.bss' sections in the 2421 output file. The linker will place the `.data' output section at 2422 address `0x8000000'. After the linker places the `.data' output 2423 section, the value of the location counter will be `0x8000000' plus the 2424 size of the `.data' output section. The effect is that the linker will 2425 place the `.bss' output section immediately after the `.data' output 2426 section in memory. 2427 2428 The linker will ensure that each output section has the required 2429 alignment, by increasing the location counter if necessary. In this 2430 example, the specified addresses for the `.text' and `.data' sections 2431 will probably satisfy any alignment constraints, but the linker may 2432 have to create a small gap between the `.data' and `.bss' sections. 2433 2434 That's it! That's a simple and complete linker script. 2435 2436 2437 File: ld.info, Node: Simple Commands, Next: Assignments, Prev: Simple Example, Up: Scripts 2438 2439 3.4 Simple Linker Script Commands 2440 ================================= 2441 2442 In this section we describe the simple linker script commands. 2443 2444 * Menu: 2445 2446 * Entry Point:: Setting the entry point 2447 * File Commands:: Commands dealing with files 2448 2449 * Format Commands:: Commands dealing with object file formats 2450 2451 * REGION_ALIAS:: Assign alias names to memory regions 2452 * Miscellaneous Commands:: Other linker script commands 2453 2454 2455 File: ld.info, Node: Entry Point, Next: File Commands, Up: Simple Commands 2456 2457 3.4.1 Setting the Entry Point 2458 ----------------------------- 2459 2460 The first instruction to execute in a program is called the "entry 2461 point". You can use the `ENTRY' linker script command to set the entry 2462 point. The argument is a symbol name: 2463 ENTRY(SYMBOL) 2464 2465 There are several ways to set the entry point. The linker will set 2466 the entry point by trying each of the following methods in order, and 2467 stopping when one of them succeeds: 2468 * the `-e' ENTRY command-line option; 2469 2470 * the `ENTRY(SYMBOL)' command in a linker script; 2471 2472 * the value of a target specific symbol, if it is defined; For many 2473 targets this is `start', but PE and BeOS based systems for example 2474 check a list of possible entry symbols, matching the first one 2475 found. 2476 2477 * the address of the first byte of the `.text' section, if present; 2478 2479 * The address `0'. 2480 2481 2482 File: ld.info, Node: File Commands, Next: Format Commands, Prev: Entry Point, Up: Simple Commands 2483 2484 3.4.2 Commands Dealing with Files 2485 --------------------------------- 2486 2487 Several linker script commands deal with files. 2488 2489 `INCLUDE FILENAME' 2490 Include the linker script FILENAME at this point. The file will 2491 be searched for in the current directory, and in any directory 2492 specified with the `-L' option. You can nest calls to `INCLUDE' 2493 up to 10 levels deep. 2494 2495 You can place `INCLUDE' directives at the top level, in `MEMORY' or 2496 `SECTIONS' commands, or in output section descriptions. 2497 2498 `INPUT(FILE, FILE, ...)' 2499 `INPUT(FILE FILE ...)' 2500 The `INPUT' command directs the linker to include the named files 2501 in the link, as though they were named on the command line. 2502 2503 For example, if you always want to include `subr.o' any time you do 2504 a link, but you can't be bothered to put it on every link command 2505 line, then you can put `INPUT (subr.o)' in your linker script. 2506 2507 In fact, if you like, you can list all of your input files in the 2508 linker script, and then invoke the linker with nothing but a `-T' 2509 option. 2510 2511 In case a "sysroot prefix" is configured, and the filename starts 2512 with the `/' character, and the script being processed was located 2513 inside the "sysroot prefix", the filename will be looked for in 2514 the "sysroot prefix". Otherwise, the linker will try to open the 2515 file in the current directory. If it is not found, the linker 2516 will search through the archive library search path. The "sysroot 2517 prefix" can also be forced by specifying `=' as the first 2518 character in the filename path. See also the description of `-L' 2519 in *Note Command Line Options: Options. 2520 2521 If you use `INPUT (-lFILE)', `ld' will transform the name to 2522 `libFILE.a', as with the command line argument `-l'. 2523 2524 When you use the `INPUT' command in an implicit linker script, the 2525 files will be included in the link at the point at which the linker 2526 script file is included. This can affect archive searching. 2527 2528 `GROUP(FILE, FILE, ...)' 2529 `GROUP(FILE FILE ...)' 2530 The `GROUP' command is like `INPUT', except that the named files 2531 should all be archives, and they are searched repeatedly until no 2532 new undefined references are created. See the description of `-(' 2533 in *Note Command Line Options: Options. 2534 2535 `AS_NEEDED(FILE, FILE, ...)' 2536 `AS_NEEDED(FILE FILE ...)' 2537 This construct can appear only inside of the `INPUT' or `GROUP' 2538 commands, among other filenames. The files listed will be handled 2539 as if they appear directly in the `INPUT' or `GROUP' commands, 2540 with the exception of ELF shared libraries, that will be added only 2541 when they are actually needed. This construct essentially enables 2542 `--as-needed' option for all the files listed inside of it and 2543 restores previous `--as-needed' resp. `--no-as-needed' setting 2544 afterwards. 2545 2546 `OUTPUT(FILENAME)' 2547 The `OUTPUT' command names the output file. Using 2548 `OUTPUT(FILENAME)' in the linker script is exactly like using `-o 2549 FILENAME' on the command line (*note Command Line Options: 2550 Options.). If both are used, the command line option takes 2551 precedence. 2552 2553 You can use the `OUTPUT' command to define a default name for the 2554 output file other than the usual default of `a.out'. 2555 2556 `SEARCH_DIR(PATH)' 2557 The `SEARCH_DIR' command adds PATH to the list of paths where `ld' 2558 looks for archive libraries. Using `SEARCH_DIR(PATH)' is exactly 2559 like using `-L PATH' on the command line (*note Command Line 2560 Options: Options.). If both are used, then the linker will search 2561 both paths. Paths specified using the command line option are 2562 searched first. 2563 2564 `STARTUP(FILENAME)' 2565 The `STARTUP' command is just like the `INPUT' command, except 2566 that FILENAME will become the first input file to be linked, as 2567 though it were specified first on the command line. This may be 2568 useful when using a system in which the entry point is always the 2569 start of the first file. 2570 2571 2572 File: ld.info, Node: Format Commands, Next: REGION_ALIAS, Prev: File Commands, Up: Simple Commands 2573 2574 3.4.3 Commands Dealing with Object File Formats 2575 ----------------------------------------------- 2576 2577 A couple of linker script commands deal with object file formats. 2578 2579 `OUTPUT_FORMAT(BFDNAME)' 2580 `OUTPUT_FORMAT(DEFAULT, BIG, LITTLE)' 2581 The `OUTPUT_FORMAT' command names the BFD format to use for the 2582 output file (*note BFD::). Using `OUTPUT_FORMAT(BFDNAME)' is 2583 exactly like using `--oformat BFDNAME' on the command line (*note 2584 Command Line Options: Options.). If both are used, the command 2585 line option takes precedence. 2586 2587 You can use `OUTPUT_FORMAT' with three arguments to use different 2588 formats based on the `-EB' and `-EL' command line options. This 2589 permits the linker script to set the output format based on the 2590 desired endianness. 2591 2592 If neither `-EB' nor `-EL' are used, then the output format will 2593 be the first argument, DEFAULT. If `-EB' is used, the output 2594 format will be the second argument, BIG. If `-EL' is used, the 2595 output format will be the third argument, LITTLE. 2596 2597 For example, the default linker script for the MIPS ELF target 2598 uses this command: 2599 OUTPUT_FORMAT(elf32-bigmips, elf32-bigmips, elf32-littlemips) 2600 This says that the default format for the output file is 2601 `elf32-bigmips', but if the user uses the `-EL' command line 2602 option, the output file will be created in the `elf32-littlemips' 2603 format. 2604 2605 `TARGET(BFDNAME)' 2606 The `TARGET' command names the BFD format to use when reading input 2607 files. It affects subsequent `INPUT' and `GROUP' commands. This 2608 command is like using `-b BFDNAME' on the command line (*note 2609 Command Line Options: Options.). If the `TARGET' command is used 2610 but `OUTPUT_FORMAT' is not, then the last `TARGET' command is also 2611 used to set the format for the output file. *Note BFD::. 2612 2613 2614 File: ld.info, Node: REGION_ALIAS, Next: Miscellaneous Commands, Prev: Format Commands, Up: Simple Commands 2615 2616 3.4.4 Assign alias names to memory regions 2617 ------------------------------------------ 2618 2619 Alias names can be added to existing memory regions created with the 2620 *Note MEMORY:: command. Each name corresponds to at most one memory 2621 region. 2622 2623 REGION_ALIAS(ALIAS, REGION) 2624 2625 The `REGION_ALIAS' function creates an alias name ALIAS for the 2626 memory region REGION. This allows a flexible mapping of output sections 2627 to memory regions. An example follows. 2628 2629 Suppose we have an application for embedded systems which come with 2630 various memory storage devices. All have a general purpose, volatile 2631 memory `RAM' that allows code execution or data storage. Some may have 2632 a read-only, non-volatile memory `ROM' that allows code execution and 2633 read-only data access. The last variant is a read-only, non-volatile 2634 memory `ROM2' with read-only data access and no code execution 2635 capability. We have four output sections: 2636 2637 * `.text' program code; 2638 2639 * `.rodata' read-only data; 2640 2641 * `.data' read-write initialized data; 2642 2643 * `.bss' read-write zero initialized data. 2644 2645 The goal is to provide a linker command file that contains a system 2646 independent part defining the output sections and a system dependent 2647 part mapping the output sections to the memory regions available on the 2648 system. Our embedded systems come with three different memory setups 2649 `A', `B' and `C': 2650 Section Variant A Variant B Variant C 2651 .text RAM ROM ROM 2652 .rodata RAM ROM ROM2 2653 .data RAM RAM/ROM RAM/ROM2 2654 .bss RAM RAM RAM 2655 The notation `RAM/ROM' or `RAM/ROM2' means that this section is 2656 loaded into region `ROM' or `ROM2' respectively. Please note that the 2657 load address of the `.data' section starts in all three variants at the 2658 end of the `.rodata' section. 2659 2660 The base linker script that deals with the output sections follows. 2661 It includes the system dependent `linkcmds.memory' file that describes 2662 the memory layout: 2663 INCLUDE linkcmds.memory 2664 2665 SECTIONS 2666 { 2667 .text : 2668 { 2669 *(.text) 2670 } > REGION_TEXT 2671 .rodata : 2672 { 2673 *(.rodata) 2674 rodata_end = .; 2675 } > REGION_RODATA 2676 .data : AT (rodata_end) 2677 { 2678 data_start = .; 2679 *(.data) 2680 } > REGION_DATA 2681 data_size = SIZEOF(.data); 2682 data_load_start = LOADADDR(.data); 2683 .bss : 2684 { 2685 *(.bss) 2686 } > REGION_BSS 2687 } 2688 2689 Now we need three different `linkcmds.memory' files to define memory 2690 regions and alias names. The content of `linkcmds.memory' for the three 2691 variants `A', `B' and `C': 2692 `A' 2693 Here everything goes into the `RAM'. 2694 MEMORY 2695 { 2696 RAM : ORIGIN = 0, LENGTH = 4M 2697 } 2698 2699 REGION_ALIAS("REGION_TEXT", RAM); 2700 REGION_ALIAS("REGION_RODATA", RAM); 2701 REGION_ALIAS("REGION_DATA", RAM); 2702 REGION_ALIAS("REGION_BSS", RAM); 2703 2704 `B' 2705 Program code and read-only data go into the `ROM'. Read-write 2706 data goes into the `RAM'. An image of the initialized data is 2707 loaded into the `ROM' and will be copied during system start into 2708 the `RAM'. 2709 MEMORY 2710 { 2711 ROM : ORIGIN = 0, LENGTH = 3M 2712 RAM : ORIGIN = 0x10000000, LENGTH = 1M 2713 } 2714 2715 REGION_ALIAS("REGION_TEXT", ROM); 2716 REGION_ALIAS("REGION_RODATA", ROM); 2717 REGION_ALIAS("REGION_DATA", RAM); 2718 REGION_ALIAS("REGION_BSS", RAM); 2719 2720 `C' 2721 Program code goes into the `ROM'. Read-only data goes into the 2722 `ROM2'. Read-write data goes into the `RAM'. An image of the 2723 initialized data is loaded into the `ROM2' and will be copied 2724 during system start into the `RAM'. 2725 MEMORY 2726 { 2727 ROM : ORIGIN = 0, LENGTH = 2M 2728 ROM2 : ORIGIN = 0x10000000, LENGTH = 1M 2729 RAM : ORIGIN = 0x20000000, LENGTH = 1M 2730 } 2731 2732 REGION_ALIAS("REGION_TEXT", ROM); 2733 REGION_ALIAS("REGION_RODATA", ROM2); 2734 REGION_ALIAS("REGION_DATA", RAM); 2735 REGION_ALIAS("REGION_BSS", RAM); 2736 2737 It is possible to write a common system initialization routine to 2738 copy the `.data' section from `ROM' or `ROM2' into the `RAM' if 2739 necessary: 2740 #include <string.h> 2741 2742 extern char data_start []; 2743 extern char data_size []; 2744 extern char data_load_start []; 2745 2746 void copy_data(void) 2747 { 2748 if (data_start != data_load_start) 2749 { 2750 memcpy(data_start, data_load_start, (size_t) data_size); 2751 } 2752 } 2753 2754 2755 File: ld.info, Node: Miscellaneous Commands, Prev: REGION_ALIAS, Up: Simple Commands 2756 2757 3.4.5 Other Linker Script Commands 2758 ---------------------------------- 2759 2760 There are a few other linker scripts commands. 2761 2762 `ASSERT(EXP, MESSAGE)' 2763 Ensure that EXP is non-zero. If it is zero, then exit the linker 2764 with an error code, and print MESSAGE. 2765 2766 `EXTERN(SYMBOL SYMBOL ...)' 2767 Force SYMBOL to be entered in the output file as an undefined 2768 symbol. Doing this may, for example, trigger linking of additional 2769 modules from standard libraries. You may list several SYMBOLs for 2770 each `EXTERN', and you may use `EXTERN' multiple times. This 2771 command has the same effect as the `-u' command-line option. 2772 2773 `FORCE_COMMON_ALLOCATION' 2774 This command has the same effect as the `-d' command-line option: 2775 to make `ld' assign space to common symbols even if a relocatable 2776 output file is specified (`-r'). 2777 2778 `INHIBIT_COMMON_ALLOCATION' 2779 This command has the same effect as the `--no-define-common' 2780 command-line option: to make `ld' omit the assignment of addresses 2781 to common symbols even for a non-relocatable output file. 2782 2783 `INSERT [ AFTER | BEFORE ] OUTPUT_SECTION' 2784 This command is typically used in a script specified by `-T' to 2785 augment the default `SECTIONS' with, for example, overlays. It 2786 inserts all prior linker script statements after (or before) 2787 OUTPUT_SECTION, and also causes `-T' to not override the default 2788 linker script. The exact insertion point is as for orphan 2789 sections. *Note Location Counter::. The insertion happens after 2790 the linker has mapped input sections to output sections. Prior to 2791 the insertion, since `-T' scripts are parsed before the default 2792 linker script, statements in the `-T' script occur before the 2793 default linker script statements in the internal linker 2794 representation of the script. In particular, input section 2795 assignments will be made to `-T' output sections before those in 2796 the default script. Here is an example of how a `-T' script using 2797 `INSERT' might look: 2798 2799 SECTIONS 2800 { 2801 OVERLAY : 2802 { 2803 .ov1 { ov1*(.text) } 2804 .ov2 { ov2*(.text) } 2805 } 2806 } 2807 INSERT AFTER .text; 2808 2809 `NOCROSSREFS(SECTION SECTION ...)' 2810 This command may be used to tell `ld' to issue an error about any 2811 references among certain output sections. 2812 2813 In certain types of programs, particularly on embedded systems when 2814 using overlays, when one section is loaded into memory, another 2815 section will not be. Any direct references between the two 2816 sections would be errors. For example, it would be an error if 2817 code in one section called a function defined in the other section. 2818 2819 The `NOCROSSREFS' command takes a list of output section names. If 2820 `ld' detects any cross references between the sections, it reports 2821 an error and returns a non-zero exit status. Note that the 2822 `NOCROSSREFS' command uses output section names, not input section 2823 names. 2824 2825 `OUTPUT_ARCH(BFDARCH)' 2826 Specify a particular output machine architecture. The argument is 2827 one of the names used by the BFD library (*note BFD::). You can 2828 see the architecture of an object file by using the `objdump' 2829 program with the `-f' option. 2830 2831 `LD_FEATURE(STRING)' 2832 This command may be used to modify `ld' behavior. If STRING is 2833 `"SANE_EXPR"' then absolute symbols and numbers in a script are 2834 simply treated as numbers everywhere. *Note Expression Section::. 2835 2836 2837 File: ld.info, Node: Assignments, Next: SECTIONS, Prev: Simple Commands, Up: Scripts 2838 2839 3.5 Assigning Values to Symbols 2840 =============================== 2841 2842 You may assign a value to a symbol in a linker script. This will define 2843 the symbol and place it into the symbol table with a global scope. 2844 2845 * Menu: 2846 2847 * Simple Assignments:: Simple Assignments 2848 * HIDDEN:: HIDDEN 2849 * PROVIDE:: PROVIDE 2850 * PROVIDE_HIDDEN:: PROVIDE_HIDDEN 2851 * Source Code Reference:: How to use a linker script defined symbol in source code 2852 2853 2854 File: ld.info, Node: Simple Assignments, Next: HIDDEN, Up: Assignments 2855 2856 3.5.1 Simple Assignments 2857 ------------------------ 2858 2859 You may assign to a symbol using any of the C assignment operators: 2860 2861 `SYMBOL = EXPRESSION ;' 2862 `SYMBOL += EXPRESSION ;' 2863 `SYMBOL -= EXPRESSION ;' 2864 `SYMBOL *= EXPRESSION ;' 2865 `SYMBOL /= EXPRESSION ;' 2866 `SYMBOL <<= EXPRESSION ;' 2867 `SYMBOL >>= EXPRESSION ;' 2868 `SYMBOL &= EXPRESSION ;' 2869 `SYMBOL |= EXPRESSION ;' 2870 2871 The first case will define SYMBOL to the value of EXPRESSION. In 2872 the other cases, SYMBOL must already be defined, and the value will be 2873 adjusted accordingly. 2874 2875 The special symbol name `.' indicates the location counter. You may 2876 only use this within a `SECTIONS' command. *Note Location Counter::. 2877 2878 The semicolon after EXPRESSION is required. 2879 2880 Expressions are defined below; see *Note Expressions::. 2881 2882 You may write symbol assignments as commands in their own right, or 2883 as statements within a `SECTIONS' command, or as part of an output 2884 section description in a `SECTIONS' command. 2885 2886 The section of the symbol will be set from the section of the 2887 expression; for more information, see *Note Expression Section::. 2888 2889 Here is an example showing the three different places that symbol 2890 assignments may be used: 2891 2892 floating_point = 0; 2893 SECTIONS 2894 { 2895 .text : 2896 { 2897 *(.text) 2898 _etext = .; 2899 } 2900 _bdata = (. + 3) & ~ 3; 2901 .data : { *(.data) } 2902 } 2903 In this example, the symbol `floating_point' will be defined as 2904 zero. The symbol `_etext' will be defined as the address following the 2905 last `.text' input section. The symbol `_bdata' will be defined as the 2906 address following the `.text' output section aligned upward to a 4 byte 2907 boundary. 2908 2909 2910 File: ld.info, Node: HIDDEN, Next: PROVIDE, Prev: Simple Assignments, Up: Assignments 2911 2912 3.5.2 HIDDEN 2913 ------------ 2914 2915 For ELF targeted ports, define a symbol that will be hidden and won't be 2916 exported. The syntax is `HIDDEN(SYMBOL = EXPRESSION)'. 2917 2918 Here is the example from *Note Simple Assignments::, rewritten to use 2919 `HIDDEN': 2920 2921 HIDDEN(floating_point = 0); 2922 SECTIONS 2923 { 2924 .text : 2925 { 2926 *(.text) 2927 HIDDEN(_etext = .); 2928 } 2929 HIDDEN(_bdata = (. + 3) & ~ 3); 2930 .data : { *(.data) } 2931 } 2932 In this case none of the three symbols will be visible outside this 2933 module. 2934 2935 2936 File: ld.info, Node: PROVIDE, Next: PROVIDE_HIDDEN, Prev: HIDDEN, Up: Assignments 2937 2938 3.5.3 PROVIDE 2939 ------------- 2940 2941 In some cases, it is desirable for a linker script to define a symbol 2942 only if it is referenced and is not defined by any object included in 2943 the link. For example, traditional linkers defined the symbol `etext'. 2944 However, ANSI C requires that the user be able to use `etext' as a 2945 function name without encountering an error. The `PROVIDE' keyword may 2946 be used to define a symbol, such as `etext', only if it is referenced 2947 but not defined. The syntax is `PROVIDE(SYMBOL = EXPRESSION)'. 2948 2949 Here is an example of using `PROVIDE' to define `etext': 2950 SECTIONS 2951 { 2952 .text : 2953 { 2954 *(.text) 2955 _etext = .; 2956 PROVIDE(etext = .); 2957 } 2958 } 2959 2960 In this example, if the program defines `_etext' (with a leading 2961 underscore), the linker will give a multiple definition error. If, on 2962 the other hand, the program defines `etext' (with no leading 2963 underscore), the linker will silently use the definition in the program. 2964 If the program references `etext' but does not define it, the linker 2965 will use the definition in the linker script. 2966 2967 2968 File: ld.info, Node: PROVIDE_HIDDEN, Next: Source Code Reference, Prev: PROVIDE, Up: Assignments 2969 2970 3.5.4 PROVIDE_HIDDEN 2971 -------------------- 2972 2973 Similar to `PROVIDE'. For ELF targeted ports, the symbol will be 2974 hidden and won't be exported. 2975 2976 2977 File: ld.info, Node: Source Code Reference, Prev: PROVIDE_HIDDEN, Up: Assignments 2978 2979 3.5.5 Source Code Reference 2980 --------------------------- 2981 2982 Accessing a linker script defined variable from source code is not 2983 intuitive. In particular a linker script symbol is not equivalent to a 2984 variable declaration in a high level language, it is instead a symbol 2985 that does not have a value. 2986 2987 Before going further, it is important to note that compilers often 2988 transform names in the source code into different names when they are 2989 stored in the symbol table. For example, Fortran compilers commonly 2990 prepend or append an underscore, and C++ performs extensive `name 2991 mangling'. Therefore there might be a discrepancy between the name of 2992 a variable as it is used in source code and the name of the same 2993 variable as it is defined in a linker script. For example in C a 2994 linker script variable might be referred to as: 2995 2996 extern int foo; 2997 2998 But in the linker script it might be defined as: 2999 3000 _foo = 1000; 3001 3002 In the remaining examples however it is assumed that no name 3003 transformation has taken place. 3004 3005 When a symbol is declared in a high level language such as C, two 3006 things happen. The first is that the compiler reserves enough space in 3007 the program's memory to hold the _value_ of the symbol. The second is 3008 that the compiler creates an entry in the program's symbol table which 3009 holds the symbol's _address_. ie the symbol table contains the address 3010 of the block of memory holding the symbol's value. So for example the 3011 following C declaration, at file scope: 3012 3013 int foo = 1000; 3014 3015 creates an entry called `foo' in the symbol table. This entry holds 3016 the address of an `int' sized block of memory where the number 1000 is 3017 initially stored. 3018 3019 When a program references a symbol the compiler generates code that 3020 first accesses the symbol table to find the address of the symbol's 3021 memory block and then code to read the value from that memory block. 3022 So: 3023 3024 foo = 1; 3025 3026 looks up the symbol `foo' in the symbol table, gets the address 3027 associated with this symbol and then writes the value 1 into that 3028 address. Whereas: 3029 3030 int * a = & foo; 3031 3032 looks up the symbol `foo' in the symbol table, gets its address and 3033 then copies this address into the block of memory associated with the 3034 variable `a'. 3035 3036 Linker scripts symbol declarations, by contrast, create an entry in 3037 the symbol table but do not assign any memory to them. Thus they are 3038 an address without a value. So for example the linker script 3039 definition: 3040 3041 foo = 1000; 3042 3043 creates an entry in the symbol table called `foo' which holds the 3044 address of memory location 1000, but nothing special is stored at 3045 address 1000. This means that you cannot access the _value_ of a 3046 linker script defined symbol - it has no value - all you can do is 3047 access the _address_ of a linker script defined symbol. 3048 3049 Hence when you are using a linker script defined symbol in source 3050 code you should always take the address of the symbol, and never 3051 attempt to use its value. For example suppose you want to copy the 3052 contents of a section of memory called .ROM into a section called 3053 .FLASH and the linker script contains these declarations: 3054 3055 start_of_ROM = .ROM; 3056 end_of_ROM = .ROM + sizeof (.ROM) - 1; 3057 start_of_FLASH = .FLASH; 3058 3059 Then the C source code to perform the copy would be: 3060 3061 extern char start_of_ROM, end_of_ROM, start_of_FLASH; 3062 3063 memcpy (& start_of_FLASH, & start_of_ROM, & end_of_ROM - & start_of_ROM); 3064 3065 Note the use of the `&' operators. These are correct. 3066 3067 3068 File: ld.info, Node: SECTIONS, Next: MEMORY, Prev: Assignments, Up: Scripts 3069 3070 3.6 SECTIONS Command 3071 ==================== 3072 3073 The `SECTIONS' command tells the linker how to map input sections into 3074 output sections, and how to place the output sections in memory. 3075 3076 The format of the `SECTIONS' command is: 3077 SECTIONS 3078 { 3079 SECTIONS-COMMAND 3080 SECTIONS-COMMAND 3081 ... 3082 } 3083 3084 Each SECTIONS-COMMAND may of be one of the following: 3085 3086 * an `ENTRY' command (*note Entry command: Entry Point.) 3087 3088 * a symbol assignment (*note Assignments::) 3089 3090 * an output section description 3091 3092 * an overlay description 3093 3094 The `ENTRY' command and symbol assignments are permitted inside the 3095 `SECTIONS' command for convenience in using the location counter in 3096 those commands. This can also make the linker script easier to 3097 understand because you can use those commands at meaningful points in 3098 the layout of the output file. 3099 3100 Output section descriptions and overlay descriptions are described 3101 below. 3102 3103 If you do not use a `SECTIONS' command in your linker script, the 3104 linker will place each input section into an identically named output 3105 section in the order that the sections are first encountered in the 3106 input files. If all input sections are present in the first file, for 3107 example, the order of sections in the output file will match the order 3108 in the first input file. The first section will be at address zero. 3109 3110 * Menu: 3111 3112 * Output Section Description:: Output section description 3113 * Output Section Name:: Output section name 3114 * Output Section Address:: Output section address 3115 * Input Section:: Input section description 3116 * Output Section Data:: Output section data 3117 * Output Section Keywords:: Output section keywords 3118 * Output Section Discarding:: Output section discarding 3119 * Output Section Attributes:: Output section attributes 3120 * Overlay Description:: Overlay description 3121 3122 3123 File: ld.info, Node: Output Section Description, Next: Output Section Name, Up: SECTIONS 3124 3125 3.6.1 Output Section Description 3126 -------------------------------- 3127 3128 The full description of an output section looks like this: 3129 SECTION [ADDRESS] [(TYPE)] : 3130 [AT(LMA)] 3131 [ALIGN(SECTION_ALIGN) | ALIGN_WITH_INPUT] 3132 [SUBALIGN(SUBSECTION_ALIGN)] 3133 [CONSTRAINT] 3134 { 3135 OUTPUT-SECTION-COMMAND 3136 OUTPUT-SECTION-COMMAND 3137 ... 3138 } [>REGION] [AT>LMA_REGION] [:PHDR :PHDR ...] [=FILLEXP] [,] 3139 3140 Most output sections do not use most of the optional section 3141 attributes. 3142 3143 The whitespace around SECTION is required, so that the section name 3144 is unambiguous. The colon and the curly braces are also required. The 3145 comma at the end may be required if a FILLEXP is used and the next 3146 SECTIONS-COMMAND looks like a continuation of the expression. The line 3147 breaks and other white space are optional. 3148 3149 Each OUTPUT-SECTION-COMMAND may be one of the following: 3150 3151 * a symbol assignment (*note Assignments::) 3152 3153 * an input section description (*note Input Section::) 3154 3155 * data values to include directly (*note Output Section Data::) 3156 3157 * a special output section keyword (*note Output Section Keywords::) 3158 3159 3160 File: ld.info, Node: Output Section Name, Next: Output Section Address, Prev: Output Section Description, Up: SECTIONS 3161 3162 3.6.2 Output Section Name 3163 ------------------------- 3164 3165 The name of the output section is SECTION. SECTION must meet the 3166 constraints of your output format. In formats which only support a 3167 limited number of sections, such as `a.out', the name must be one of 3168 the names supported by the format (`a.out', for example, allows only 3169 `.text', `.data' or `.bss'). If the output format supports any number 3170 of sections, but with numbers and not names (as is the case for Oasys), 3171 the name should be supplied as a quoted numeric string. A section name 3172 may consist of any sequence of characters, but a name which contains 3173 any unusual characters such as commas must be quoted. 3174 3175 The output section name `/DISCARD/' is special; *Note Output Section 3176 Discarding::. 3177 3178 3179 File: ld.info, Node: Output Section Address, Next: Input Section, Prev: Output Section Name, Up: SECTIONS 3180 3181 3.6.3 Output Section Address 3182 ---------------------------- 3183 3184 The ADDRESS is an expression for the VMA (the virtual memory address) 3185 of the output section. This address is optional, but if it is provided 3186 then the output address will be set exactly as specified. 3187 3188 If the output address is not specified then one will be chosen for 3189 the section, based on the heuristic below. This address will be 3190 adjusted to fit the alignment requirement of the output section. The 3191 alignment requirement is the strictest alignment of any input section 3192 contained within the output section. 3193 3194 The output section address heuristic is as follows: 3195 3196 * If an output memory REGION is set for the section then it is added 3197 to this region and its address will be the next free address in 3198 that region. 3199 3200 * If the MEMORY command has been used to create a list of memory 3201 regions then the first region which has attributes compatible with 3202 the section is selected to contain it. The section's output 3203 address will be the next free address in that region; *Note 3204 MEMORY::. 3205 3206 * If no memory regions were specified, or none match the section then 3207 the output address will be based on the current value of the 3208 location counter. 3209 3210 For example: 3211 3212 .text . : { *(.text) } 3213 3214 and 3215 3216 .text : { *(.text) } 3217 3218 are subtly different. The first will set the address of the `.text' 3219 output section to the current value of the location counter. The 3220 second will set it to the current value of the location counter aligned 3221 to the strictest alignment of any of the `.text' input sections. 3222 3223 The ADDRESS may be an arbitrary expression; *Note Expressions::. 3224 For example, if you want to align the section on a 0x10 byte boundary, 3225 so that the lowest four bits of the section address are zero, you could 3226 do something like this: 3227 .text ALIGN(0x10) : { *(.text) } 3228 This works because `ALIGN' returns the current location counter 3229 aligned upward to the specified value. 3230 3231 Specifying ADDRESS for a section will change the value of the 3232 location counter, provided that the section is non-empty. (Empty 3233 sections are ignored). 3234 3235 3236 File: ld.info, Node: Input Section, Next: Output Section Data, Prev: Output Section Address, Up: SECTIONS 3237 3238 3.6.4 Input Section Description 3239 ------------------------------- 3240 3241 The most common output section command is an input section description. 3242 3243 The input section description is the most basic linker script 3244 operation. You use output sections to tell the linker how to lay out 3245 your program in memory. You use input section descriptions to tell the 3246 linker how to map the input files into your memory layout. 3247 3248 * Menu: 3249 3250 * Input Section Basics:: Input section basics 3251 * Input Section Wildcards:: Input section wildcard patterns 3252 * Input Section Common:: Input section for common symbols 3253 * Input Section Keep:: Input section and garbage collection 3254 * Input Section Example:: Input section example 3255 3256 3257 File: ld.info, Node: Input Section Basics, Next: Input Section Wildcards, Up: Input Section 3258 3259 3.6.4.1 Input Section Basics 3260 ............................ 3261 3262 An input section description consists of a file name optionally followed 3263 by a list of section names in parentheses. 3264 3265 The file name and the section name may be wildcard patterns, which we 3266 describe further below (*note Input Section Wildcards::). 3267 3268 The most common input section description is to include all input 3269 sections with a particular name in the output section. For example, to 3270 include all input `.text' sections, you would write: 3271 *(.text) 3272 Here the `*' is a wildcard which matches any file name. To exclude 3273 a list of files from matching the file name wildcard, EXCLUDE_FILE may 3274 be used to match all files except the ones specified in the 3275 EXCLUDE_FILE list. For example: 3276 *(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors) 3277 will cause all .ctors sections from all files except `crtend.o' and 3278 `otherfile.o' to be included. 3279 3280 There are two ways to include more than one section: 3281 *(.text .rdata) 3282 *(.text) *(.rdata) 3283 The difference between these is the order in which the `.text' and 3284 `.rdata' input sections will appear in the output section. In the 3285 first example, they will be intermingled, appearing in the same order as 3286 they are found in the linker input. In the second example, all `.text' 3287 input sections will appear first, followed by all `.rdata' input 3288 sections. 3289 3290 You can specify a file name to include sections from a particular 3291 file. You would do this if one or more of your files contain special 3292 data that needs to be at a particular location in memory. For example: 3293 data.o(.data) 3294 3295 To refine the sections that are included based on the section flags 3296 of an input section, INPUT_SECTION_FLAGS may be used. 3297 3298 Here is a simple example for using Section header flags for ELF 3299 sections: 3300 3301 SECTIONS { 3302 .text : { INPUT_SECTION_FLAGS (SHF_MERGE & SHF_STRINGS) *(.text) } 3303 .text2 : { INPUT_SECTION_FLAGS (!SHF_WRITE) *(.text) } 3304 } 3305 3306 In this example, the output section `.text' will be comprised of any 3307 input section matching the name *(.text) whose section header flags 3308 `SHF_MERGE' and `SHF_STRINGS' are set. The output section `.text2' 3309 will be comprised of any input section matching the name *(.text) whose 3310 section header flag `SHF_WRITE' is clear. 3311 3312 You can also specify files within archives by writing a pattern 3313 matching the archive, a colon, then the pattern matching the file, with 3314 no whitespace around the colon. 3315 3316 `archive:file' 3317 matches file within archive 3318 3319 `archive:' 3320 matches the whole archive 3321 3322 `:file' 3323 matches file but not one in an archive 3324 3325 Either one or both of `archive' and `file' can contain shell 3326 wildcards. On DOS based file systems, the linker will assume that a 3327 single letter followed by a colon is a drive specifier, so `c:myfile.o' 3328 is a simple file specification, not `myfile.o' within an archive called 3329 `c'. `archive:file' filespecs may also be used within an 3330 `EXCLUDE_FILE' list, but may not appear in other linker script 3331 contexts. For instance, you cannot extract a file from an archive by 3332 using `archive:file' in an `INPUT' command. 3333 3334 If you use a file name without a list of sections, then all sections 3335 in the input file will be included in the output section. This is not 3336 commonly done, but it may by useful on occasion. For example: 3337 data.o 3338 3339 When you use a file name which is not an `archive:file' specifier 3340 and does not contain any wild card characters, the linker will first 3341 see if you also specified the file name on the linker command line or 3342 in an `INPUT' command. If you did not, the linker will attempt to open 3343 the file as an input file, as though it appeared on the command line. 3344 Note that this differs from an `INPUT' command, because the linker will 3345 not search for the file in the archive search path. 3346 3347 3348 File: ld.info, Node: Input Section Wildcards, Next: Input Section Common, Prev: Input Section Basics, Up: Input Section 3349 3350 3.6.4.2 Input Section Wildcard Patterns 3351 ....................................... 3352 3353 In an input section description, either the file name or the section 3354 name or both may be wildcard patterns. 3355 3356 The file name of `*' seen in many examples is a simple wildcard 3357 pattern for the file name. 3358 3359 The wildcard patterns are like those used by the Unix shell. 3360 3361 `*' 3362 matches any number of characters 3363 3364 `?' 3365 matches any single character 3366 3367 `[CHARS]' 3368 matches a single instance of any of the CHARS; the `-' character 3369 may be used to specify a range of characters, as in `[a-z]' to 3370 match any lower case letter 3371 3372 `\' 3373 quotes the following character 3374 3375 When a file name is matched with a wildcard, the wildcard characters 3376 will not match a `/' character (used to separate directory names on 3377 Unix). A pattern consisting of a single `*' character is an exception; 3378 it will always match any file name, whether it contains a `/' or not. 3379 In a section name, the wildcard characters will match a `/' character. 3380 3381 File name wildcard patterns only match files which are explicitly 3382 specified on the command line or in an `INPUT' command. The linker 3383 does not search directories to expand wildcards. 3384 3385 If a file name matches more than one wildcard pattern, or if a file 3386 name appears explicitly and is also matched by a wildcard pattern, the 3387 linker will use the first match in the linker script. For example, this 3388 sequence of input section descriptions is probably in error, because the 3389 `data.o' rule will not be used: 3390 .data : { *(.data) } 3391 .data1 : { data.o(.data) } 3392 3393 Normally, the linker will place files and sections matched by 3394 wildcards in the order in which they are seen during the link. You can 3395 change this by using the `SORT_BY_NAME' keyword, which appears before a 3396 wildcard pattern in parentheses (e.g., `SORT_BY_NAME(.text*)'). When 3397 the `SORT_BY_NAME' keyword is used, the linker will sort the files or 3398 sections into ascending order by name before placing them in the output 3399 file. 3400 3401 `SORT_BY_ALIGNMENT' is very similar to `SORT_BY_NAME'. The 3402 difference is `SORT_BY_ALIGNMENT' will sort sections into descending 3403 order by alignment before placing them in the output file. Larger 3404 alignments are placed before smaller alignments in order to reduce the 3405 amount of padding necessary. 3406 3407 `SORT_BY_INIT_PRIORITY' is very similar to `SORT_BY_NAME'. The 3408 difference is `SORT_BY_INIT_PRIORITY' will sort sections into ascending 3409 order by numerical value of the GCC init_priority attribute encoded in 3410 the section name before placing them in the output file. 3411 3412 `SORT' is an alias for `SORT_BY_NAME'. 3413 3414 When there are nested section sorting commands in linker script, 3415 there can be at most 1 level of nesting for section sorting commands. 3416 3417 1. `SORT_BY_NAME' (`SORT_BY_ALIGNMENT' (wildcard section pattern)). 3418 It will sort the input sections by name first, then by alignment 3419 if two sections have the same name. 3420 3421 2. `SORT_BY_ALIGNMENT' (`SORT_BY_NAME' (wildcard section pattern)). 3422 It will sort the input sections by alignment first, then by name 3423 if two sections have the same alignment. 3424 3425 3. `SORT_BY_NAME' (`SORT_BY_NAME' (wildcard section pattern)) is 3426 treated the same as `SORT_BY_NAME' (wildcard section pattern). 3427 3428 4. `SORT_BY_ALIGNMENT' (`SORT_BY_ALIGNMENT' (wildcard section 3429 pattern)) is treated the same as `SORT_BY_ALIGNMENT' (wildcard 3430 section pattern). 3431 3432 5. All other nested section sorting commands are invalid. 3433 3434 When both command line section sorting option and linker script 3435 section sorting command are used, section sorting command always takes 3436 precedence over the command line option. 3437 3438 If the section sorting command in linker script isn't nested, the 3439 command line option will make the section sorting command to be treated 3440 as nested sorting command. 3441 3442 1. `SORT_BY_NAME' (wildcard section pattern ) with `--sort-sections 3443 alignment' is equivalent to `SORT_BY_NAME' (`SORT_BY_ALIGNMENT' 3444 (wildcard section pattern)). 3445 3446 2. `SORT_BY_ALIGNMENT' (wildcard section pattern) with 3447 `--sort-section name' is equivalent to `SORT_BY_ALIGNMENT' 3448 (`SORT_BY_NAME' (wildcard section pattern)). 3449 3450 If the section sorting command in linker script is nested, the 3451 command line option will be ignored. 3452 3453 `SORT_NONE' disables section sorting by ignoring the command line 3454 section sorting option. 3455 3456 If you ever get confused about where input sections are going, use 3457 the `-M' linker option to generate a map file. The map file shows 3458 precisely how input sections are mapped to output sections. 3459 3460 This example shows how wildcard patterns might be used to partition 3461 files. This linker script directs the linker to place all `.text' 3462 sections in `.text' and all `.bss' sections in `.bss'. The linker will 3463 place the `.data' section from all files beginning with an upper case 3464 character in `.DATA'; for all other files, the linker will place the 3465 `.data' section in `.data'. 3466 SECTIONS { 3467 .text : { *(.text) } 3468 .DATA : { [A-Z]*(.data) } 3469 .data : { *(.data) } 3470 .bss : { *(.bss) } 3471 } 3472 3473 3474 File: ld.info, Node: Input Section Common, Next: Input Section Keep, Prev: Input Section Wildcards, Up: Input Section 3475 3476 3.6.4.3 Input Section for Common Symbols 3477 ........................................ 3478 3479 A special notation is needed for common symbols, because in many object 3480 file formats common symbols do not have a particular input section. The 3481 linker treats common symbols as though they are in an input section 3482 named `COMMON'. 3483 3484 You may use file names with the `COMMON' section just as with any 3485 other input sections. You can use this to place common symbols from a 3486 particular input file in one section while common symbols from other 3487 input files are placed in another section. 3488 3489 In most cases, common symbols in input files will be placed in the 3490 `.bss' section in the output file. For example: 3491 .bss { *(.bss) *(COMMON) } 3492 3493 Some object file formats have more than one type of common symbol. 3494 For example, the MIPS ELF object file format distinguishes standard 3495 common symbols and small common symbols. In this case, the linker will 3496 use a different special section name for other types of common symbols. 3497 In the case of MIPS ELF, the linker uses `COMMON' for standard common 3498 symbols and `.scommon' for small common symbols. This permits you to 3499 map the different types of common symbols into memory at different 3500 locations. 3501 3502 You will sometimes see `[COMMON]' in old linker scripts. This 3503 notation is now considered obsolete. It is equivalent to `*(COMMON)'. 3504 3505 3506 File: ld.info, Node: Input Section Keep, Next: Input Section Example, Prev: Input Section Common, Up: Input Section 3507 3508 3.6.4.4 Input Section and Garbage Collection 3509 ............................................ 3510 3511 When link-time garbage collection is in use (`--gc-sections'), it is 3512 often useful to mark sections that should not be eliminated. This is 3513 accomplished by surrounding an input section's wildcard entry with 3514 `KEEP()', as in `KEEP(*(.init))' or `KEEP(SORT_BY_NAME(*)(.ctors))'. 3515 3516 3517 File: ld.info, Node: Input Section Example, Prev: Input Section Keep, Up: Input Section 3518 3519 3.6.4.5 Input Section Example 3520 ............................. 3521 3522 The following example is a complete linker script. It tells the linker 3523 to read all of the sections from file `all.o' and place them at the 3524 start of output section `outputa' which starts at location `0x10000'. 3525 All of section `.input1' from file `foo.o' follows immediately, in the 3526 same output section. All of section `.input2' from `foo.o' goes into 3527 output section `outputb', followed by section `.input1' from `foo1.o'. 3528 All of the remaining `.input1' and `.input2' sections from any files 3529 are written to output section `outputc'. 3530 3531 SECTIONS { 3532 outputa 0x10000 : 3533 { 3534 all.o 3535 foo.o (.input1) 3536 } 3537 outputb : 3538 { 3539 foo.o (.input2) 3540 foo1.o (.input1) 3541 } 3542 outputc : 3543 { 3544 *(.input1) 3545 *(.input2) 3546 } 3547 } 3548 3549 3550 File: ld.info, Node: Output Section Data, Next: Output Section Keywords, Prev: Input Section, Up: SECTIONS 3551 3552 3.6.5 Output Section Data 3553 ------------------------- 3554 3555 You can include explicit bytes of data in an output section by using 3556 `BYTE', `SHORT', `LONG', `QUAD', or `SQUAD' as an output section 3557 command. Each keyword is followed by an expression in parentheses 3558 providing the value to store (*note Expressions::). The value of the 3559 expression is stored at the current value of the location counter. 3560 3561 The `BYTE', `SHORT', `LONG', and `QUAD' commands store one, two, 3562 four, and eight bytes (respectively). After storing the bytes, the 3563 location counter is incremented by the number of bytes stored. 3564 3565 For example, this will store the byte 1 followed by the four byte 3566 value of the symbol `addr': 3567 BYTE(1) 3568 LONG(addr) 3569 3570 When using a 64 bit host or target, `QUAD' and `SQUAD' are the same; 3571 they both store an 8 byte, or 64 bit, value. When both host and target 3572 are 32 bits, an expression is computed as 32 bits. In this case `QUAD' 3573 stores a 32 bit value zero extended to 64 bits, and `SQUAD' stores a 32 3574 bit value sign extended to 64 bits. 3575 3576 If the object file format of the output file has an explicit 3577 endianness, which is the normal case, the value will be stored in that 3578 endianness. When the object file format does not have an explicit 3579 endianness, as is true of, for example, S-records, the value will be 3580 stored in the endianness of the first input object file. 3581 3582 Note--these commands only work inside a section description and not 3583 between them, so the following will produce an error from the linker: 3584 SECTIONS { .text : { *(.text) } LONG(1) .data : { *(.data) } } 3585 whereas this will work: 3586 SECTIONS { .text : { *(.text) ; LONG(1) } .data : { *(.data) } } 3587 3588 You may use the `FILL' command to set the fill pattern for the 3589 current section. It is followed by an expression in parentheses. Any 3590 otherwise unspecified regions of memory within the section (for example, 3591 gaps left due to the required alignment of input sections) are filled 3592 with the value of the expression, repeated as necessary. A `FILL' 3593 statement covers memory locations after the point at which it occurs in 3594 the section definition; by including more than one `FILL' statement, 3595 you can have different fill patterns in different parts of an output 3596 section. 3597 3598 This example shows how to fill unspecified regions of memory with the 3599 value `0x90': 3600 FILL(0x90909090) 3601 3602 The `FILL' command is similar to the `=FILLEXP' output section 3603 attribute, but it only affects the part of the section following the 3604 `FILL' command, rather than the entire section. If both are used, the 3605 `FILL' command takes precedence. *Note Output Section Fill::, for 3606 details on the fill expression. 3607 3608 3609 File: ld.info, Node: Output Section Keywords, Next: Output Section Discarding, Prev: Output Section Data, Up: SECTIONS 3610 3611 3.6.6 Output Section Keywords 3612 ----------------------------- 3613 3614 There are a couple of keywords which can appear as output section 3615 commands. 3616 3617 `CREATE_OBJECT_SYMBOLS' 3618 The command tells the linker to create a symbol for each input 3619 file. The name of each symbol will be the name of the 3620 corresponding input file. The section of each symbol will be the 3621 output section in which the `CREATE_OBJECT_SYMBOLS' command 3622 appears. 3623 3624 This is conventional for the a.out object file format. It is not 3625 normally used for any other object file format. 3626 3627 `CONSTRUCTORS' 3628 When linking using the a.out object file format, the linker uses an 3629 unusual set construct to support C++ global constructors and 3630 destructors. When linking object file formats which do not support 3631 arbitrary sections, such as ECOFF and XCOFF, the linker will 3632 automatically recognize C++ global constructors and destructors by 3633 name. For these object file formats, the `CONSTRUCTORS' command 3634 tells the linker to place constructor information in the output 3635 section where the `CONSTRUCTORS' command appears. The 3636 `CONSTRUCTORS' command is ignored for other object file formats. 3637 3638 The symbol `__CTOR_LIST__' marks the start of the global 3639 constructors, and the symbol `__CTOR_END__' marks the end. 3640 Similarly, `__DTOR_LIST__' and `__DTOR_END__' mark the start and 3641 end of the global destructors. The first word in the list is the 3642 number of entries, followed by the address of each constructor or 3643 destructor, followed by a zero word. The compiler must arrange to 3644 actually run the code. For these object file formats GNU C++ 3645 normally calls constructors from a subroutine `__main'; a call to 3646 `__main' is automatically inserted into the startup code for 3647 `main'. GNU C++ normally runs destructors either by using 3648 `atexit', or directly from the function `exit'. 3649 3650 For object file formats such as `COFF' or `ELF' which support 3651 arbitrary section names, GNU C++ will normally arrange to put the 3652 addresses of global constructors and destructors into the `.ctors' 3653 and `.dtors' sections. Placing the following sequence into your 3654 linker script will build the sort of table which the GNU C++ 3655 runtime code expects to see. 3656 3657 __CTOR_LIST__ = .; 3658 LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2) 3659 *(.ctors) 3660 LONG(0) 3661 __CTOR_END__ = .; 3662 __DTOR_LIST__ = .; 3663 LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2) 3664 *(.dtors) 3665 LONG(0) 3666 __DTOR_END__ = .; 3667 3668 If you are using the GNU C++ support for initialization priority, 3669 which provides some control over the order in which global 3670 constructors are run, you must sort the constructors at link time 3671 to ensure that they are executed in the correct order. When using 3672 the `CONSTRUCTORS' command, use `SORT_BY_NAME(CONSTRUCTORS)' 3673 instead. When using the `.ctors' and `.dtors' sections, use 3674 `*(SORT_BY_NAME(.ctors))' and `*(SORT_BY_NAME(.dtors))' instead of 3675 just `*(.ctors)' and `*(.dtors)'. 3676 3677 Normally the compiler and linker will handle these issues 3678 automatically, and you will not need to concern yourself with 3679 them. However, you may need to consider this if you are using C++ 3680 and writing your own linker scripts. 3681 3682 3683 3684 File: ld.info, Node: Output Section Discarding, Next: Output Section Attributes, Prev: Output Section Keywords, Up: SECTIONS 3685 3686 3.6.7 Output Section Discarding 3687 ------------------------------- 3688 3689 The linker will not normally create output sections with no contents. 3690 This is for convenience when referring to input sections that may or 3691 may not be present in any of the input files. For example: 3692 .foo : { *(.foo) } 3693 will only create a `.foo' section in the output file if there is a 3694 `.foo' section in at least one input file, and if the input sections 3695 are not all empty. Other link script directives that allocate space in 3696 an output section will also create the output section. So too will 3697 assignments to dot even if the assignment does not create space, except 3698 for `. = 0', `. = . + 0', `. = sym', `. = . + sym' and `. = ALIGN (. != 3699 0, expr, 1)' when `sym' is an absolute symbol of value 0 defined in the 3700 script. This allows you to force output of an empty section with `. = 3701 .'. 3702 3703 The linker will ignore address assignments (*note Output Section 3704 Address::) on discarded output sections, except when the linker script 3705 defines symbols in the output section. In that case the linker will 3706 obey the address assignments, possibly advancing dot even though the 3707 section is discarded. 3708 3709 The special output section name `/DISCARD/' may be used to discard 3710 input sections. Any input sections which are assigned to an output 3711 section named `/DISCARD/' are not included in the output file. 3712 3713 3714 File: ld.info, Node: Output Section Attributes, Next: Overlay Description, Prev: Output Section Discarding, Up: SECTIONS 3715 3716 3.6.8 Output Section Attributes 3717 ------------------------------- 3718 3719 We showed above that the full description of an output section looked 3720 like this: 3721 3722 SECTION [ADDRESS] [(TYPE)] : 3723 [AT(LMA)] 3724 [ALIGN(SECTION_ALIGN)] 3725 [SUBALIGN(SUBSECTION_ALIGN)] 3726 [CONSTRAINT] 3727 { 3728 OUTPUT-SECTION-COMMAND 3729 OUTPUT-SECTION-COMMAND 3730 ... 3731 } [>REGION] [AT>LMA_REGION] [:PHDR :PHDR ...] [=FILLEXP] 3732 3733 We've already described SECTION, ADDRESS, and 3734 OUTPUT-SECTION-COMMAND. In this section we will describe the remaining 3735 section attributes. 3736 3737 * Menu: 3738 3739 * Output Section Type:: Output section type 3740 * Output Section LMA:: Output section LMA 3741 * Forced Output Alignment:: Forced Output Alignment 3742 * Forced Input Alignment:: Forced Input Alignment 3743 * Output Section Constraint:: Output section constraint 3744 * Output Section Region:: Output section region 3745 * Output Section Phdr:: Output section phdr 3746 * Output Section Fill:: Output section fill 3747 3748 3749 File: ld.info, Node: Output Section Type, Next: Output Section LMA, Up: Output Section Attributes 3750 3751 3.6.8.1 Output Section Type 3752 ........................... 3753 3754 Each output section may have a type. The type is a keyword in 3755 parentheses. The following types are defined: 3756 3757 `NOLOAD' 3758 The section should be marked as not loadable, so that it will not 3759 be loaded into memory when the program is run. 3760 3761 `DSECT' 3762 `COPY' 3763 `INFO' 3764 `OVERLAY' 3765 These type names are supported for backward compatibility, and are 3766 rarely used. They all have the same effect: the section should be 3767 marked as not allocatable, so that no memory is allocated for the 3768 section when the program is run. 3769 3770 The linker normally sets the attributes of an output section based on 3771 the input sections which map into it. You can override this by using 3772 the section type. For example, in the script sample below, the `ROM' 3773 section is addressed at memory location `0' and does not need to be 3774 loaded when the program is run. 3775 SECTIONS { 3776 ROM 0 (NOLOAD) : { ... } 3777 ... 3778 } 3779 3780 3781 File: ld.info, Node: Output Section LMA, Next: Forced Output Alignment, Prev: Output Section Type, Up: Output Section Attributes 3782 3783 3.6.8.2 Output Section LMA 3784 .......................... 3785 3786 Every section has a virtual address (VMA) and a load address (LMA); see 3787 *Note Basic Script Concepts::. The virtual address is specified by the 3788 *note Output Section Address:: described earlier. The load address is 3789 specified by the `AT' or `AT>' keywords. Specifying a load address is 3790 optional. 3791 3792 The `AT' keyword takes an expression as an argument. This specifies 3793 the exact load address of the section. The `AT>' keyword takes the 3794 name of a memory region as an argument. *Note MEMORY::. The load 3795 address of the section is set to the next free address in the region, 3796 aligned to the section's alignment requirements. 3797 3798 If neither `AT' nor `AT>' is specified for an allocatable section, 3799 the linker will use the following heuristic to determine the load 3800 address: 3801 3802 * If the section has a specific VMA address, then this is used as 3803 the LMA address as well. 3804 3805 * If the section is not allocatable then its LMA is set to its VMA. 3806 3807 * Otherwise if a memory region can be found that is compatible with 3808 the current section, and this region contains at least one 3809 section, then the LMA is set so the difference between the VMA and 3810 LMA is the same as the difference between the VMA and LMA of the 3811 last section in the located region. 3812 3813 * If no memory regions have been declared then a default region that 3814 covers the entire address space is used in the previous step. 3815 3816 * If no suitable region could be found, or there was no previous 3817 section then the LMA is set equal to the VMA. 3818 3819 This feature is designed to make it easy to build a ROM image. For 3820 example, the following linker script creates three output sections: one 3821 called `.text', which starts at `0x1000', one called `.mdata', which is 3822 loaded at the end of the `.text' section even though its VMA is 3823 `0x2000', and one called `.bss' to hold uninitialized data at address 3824 `0x3000'. The symbol `_data' is defined with the value `0x2000', which 3825 shows that the location counter holds the VMA value, not the LMA value. 3826 3827 SECTIONS 3828 { 3829 .text 0x1000 : { *(.text) _etext = . ; } 3830 .mdata 0x2000 : 3831 AT ( ADDR (.text) + SIZEOF (.text) ) 3832 { _data = . ; *(.data); _edata = . ; } 3833 .bss 0x3000 : 3834 { _bstart = . ; *(.bss) *(COMMON) ; _bend = . ;} 3835 } 3836 3837 The run-time initialization code for use with a program generated 3838 with this linker script would include something like the following, to 3839 copy the initialized data from the ROM image to its runtime address. 3840 Notice how this code takes advantage of the symbols defined by the 3841 linker script. 3842 3843 extern char _etext, _data, _edata, _bstart, _bend; 3844 char *src = &_etext; 3845 char *dst = &_data; 3846 3847 /* ROM has data at end of text; copy it. */ 3848 while (dst < &_edata) 3849 *dst++ = *src++; 3850 3851 /* Zero bss. */ 3852 for (dst = &_bstart; dst< &_bend; dst++) 3853 *dst = 0; 3854 3855 3856 File: ld.info, Node: Forced Output Alignment, Next: Forced Input Alignment, Prev: Output Section LMA, Up: Output Section Attributes 3857 3858 3.6.8.3 Forced Output Alignment 3859 ............................... 3860 3861 You can increase an output section's alignment by using ALIGN. As an 3862 alternative you can enforce that the difference between the VMA and LMA 3863 remains intact throughout this output section with the ALIGN_WITH_INPUT 3864 attribute. 3865 3866 3867 File: ld.info, Node: Forced Input Alignment, Next: Output Section Constraint, Prev: Forced Output Alignment, Up: Output Section Attributes 3868 3869 3.6.8.4 Forced Input Alignment 3870 .............................. 3871 3872 You can force input section alignment within an output section by using 3873 SUBALIGN. The value specified overrides any alignment given by input 3874 sections, whether larger or smaller. 3875 3876 3877 File: ld.info, Node: Output Section Constraint, Next: Output Section Region, Prev: Forced Input Alignment, Up: Output Section Attributes 3878 3879 3.6.8.5 Output Section Constraint 3880 ................................. 3881 3882 You can specify that an output section should only be created if all of 3883 its input sections are read-only or all of its input sections are 3884 read-write by using the keyword `ONLY_IF_RO' and `ONLY_IF_RW' 3885 respectively. 3886 3887 3888 File: ld.info, Node: Output Section Region, Next: Output Section Phdr, Prev: Output Section Constraint, Up: Output Section Attributes 3889 3890 3.6.8.6 Output Section Region 3891 ............................. 3892 3893 You can assign a section to a previously defined region of memory by 3894 using `>REGION'. *Note MEMORY::. 3895 3896 Here is a simple example: 3897 MEMORY { rom : ORIGIN = 0x1000, LENGTH = 0x1000 } 3898 SECTIONS { ROM : { *(.text) } >rom } 3899 3900 3901 File: ld.info, Node: Output Section Phdr, Next: Output Section Fill, Prev: Output Section Region, Up: Output Section Attributes 3902 3903 3.6.8.7 Output Section Phdr 3904 ........................... 3905 3906 You can assign a section to a previously defined program segment by 3907 using `:PHDR'. *Note PHDRS::. If a section is assigned to one or more 3908 segments, then all subsequent allocated sections will be assigned to 3909 those segments as well, unless they use an explicitly `:PHDR' modifier. 3910 You can use `:NONE' to tell the linker to not put the section in any 3911 segment at all. 3912 3913 Here is a simple example: 3914 PHDRS { text PT_LOAD ; } 3915 SECTIONS { .text : { *(.text) } :text } 3916 3917 3918 File: ld.info, Node: Output Section Fill, Prev: Output Section Phdr, Up: Output Section Attributes 3919 3920 3.6.8.8 Output Section Fill 3921 ........................... 3922 3923 You can set the fill pattern for an entire section by using `=FILLEXP'. 3924 FILLEXP is an expression (*note Expressions::). Any otherwise 3925 unspecified regions of memory within the output section (for example, 3926 gaps left due to the required alignment of input sections) will be 3927 filled with the value, repeated as necessary. If the fill expression 3928 is a simple hex number, ie. a string of hex digit starting with `0x' 3929 and without a trailing `k' or `M', then an arbitrarily long sequence of 3930 hex digits can be used to specify the fill pattern; Leading zeros 3931 become part of the pattern too. For all other cases, including extra 3932 parentheses or a unary `+', the fill pattern is the four least 3933 significant bytes of the value of the expression. In all cases, the 3934 number is big-endian. 3935 3936 You can also change the fill value with a `FILL' command in the 3937 output section commands; (*note Output Section Data::). 3938 3939 Here is a simple example: 3940 SECTIONS { .text : { *(.text) } =0x90909090 } 3941 3942 3943 File: ld.info, Node: Overlay Description, Prev: Output Section Attributes, Up: SECTIONS 3944 3945 3.6.9 Overlay Description 3946 ------------------------- 3947 3948 An overlay description provides an easy way to describe sections which 3949 are to be loaded as part of a single memory image but are to be run at 3950 the same memory address. At run time, some sort of overlay manager will 3951 copy the overlaid sections in and out of the runtime memory address as 3952 required, perhaps by simply manipulating addressing bits. This approach 3953 can be useful, for example, when a certain region of memory is faster 3954 than another. 3955 3956 Overlays are described using the `OVERLAY' command. The `OVERLAY' 3957 command is used within a `SECTIONS' command, like an output section 3958 description. The full syntax of the `OVERLAY' command is as follows: 3959 OVERLAY [START] : [NOCROSSREFS] [AT ( LDADDR )] 3960 { 3961 SECNAME1 3962 { 3963 OUTPUT-SECTION-COMMAND 3964 OUTPUT-SECTION-COMMAND 3965 ... 3966 } [:PHDR...] [=FILL] 3967 SECNAME2 3968 { 3969 OUTPUT-SECTION-COMMAND 3970 OUTPUT-SECTION-COMMAND 3971 ... 3972 } [:PHDR...] [=FILL] 3973 ... 3974 } [>REGION] [:PHDR...] [=FILL] [,] 3975 3976 Everything is optional except `OVERLAY' (a keyword), and each 3977 section must have a name (SECNAME1 and SECNAME2 above). The section 3978 definitions within the `OVERLAY' construct are identical to those 3979 within the general `SECTIONS' construct (*note SECTIONS::), except that 3980 no addresses and no memory regions may be defined for sections within 3981 an `OVERLAY'. 3982 3983 The comma at the end may be required if a FILL is used and the next 3984 SECTIONS-COMMAND looks like a continuation of the expression. 3985 3986 The sections are all defined with the same starting address. The 3987 load addresses of the sections are arranged such that they are 3988 consecutive in memory starting at the load address used for the 3989 `OVERLAY' as a whole (as with normal section definitions, the load 3990 address is optional, and defaults to the start address; the start 3991 address is also optional, and defaults to the current value of the 3992 location counter). 3993 3994 If the `NOCROSSREFS' keyword is used, and there are any references 3995 among the sections, the linker will report an error. Since the 3996 sections all run at the same address, it normally does not make sense 3997 for one section to refer directly to another. *Note NOCROSSREFS: 3998 Miscellaneous Commands. 3999 4000 For each section within the `OVERLAY', the linker automatically 4001 provides two symbols. The symbol `__load_start_SECNAME' is defined as 4002 the starting load address of the section. The symbol 4003 `__load_stop_SECNAME' is defined as the final load address of the 4004 section. Any characters within SECNAME which are not legal within C 4005 identifiers are removed. C (or assembler) code may use these symbols 4006 to move the overlaid sections around as necessary. 4007 4008 At the end of the overlay, the value of the location counter is set 4009 to the start address of the overlay plus the size of the largest 4010 section. 4011 4012 Here is an example. Remember that this would appear inside a 4013 `SECTIONS' construct. 4014 OVERLAY 0x1000 : AT (0x4000) 4015 { 4016 .text0 { o1/*.o(.text) } 4017 .text1 { o2/*.o(.text) } 4018 } 4019 This will define both `.text0' and `.text1' to start at address 4020 0x1000. `.text0' will be loaded at address 0x4000, and `.text1' will 4021 be loaded immediately after `.text0'. The following symbols will be 4022 defined if referenced: `__load_start_text0', `__load_stop_text0', 4023 `__load_start_text1', `__load_stop_text1'. 4024 4025 C code to copy overlay `.text1' into the overlay area might look 4026 like the following. 4027 4028 extern char __load_start_text1, __load_stop_text1; 4029 memcpy ((char *) 0x1000, &__load_start_text1, 4030 &__load_stop_text1 - &__load_start_text1); 4031 4032 Note that the `OVERLAY' command is just syntactic sugar, since 4033 everything it does can be done using the more basic commands. The above 4034 example could have been written identically as follows. 4035 4036 .text0 0x1000 : AT (0x4000) { o1/*.o(.text) } 4037 PROVIDE (__load_start_text0 = LOADADDR (.text0)); 4038 PROVIDE (__load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0)); 4039 .text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) { o2/*.o(.text) } 4040 PROVIDE (__load_start_text1 = LOADADDR (.text1)); 4041 PROVIDE (__load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1)); 4042 . = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1)); 4043 4044 4045 File: ld.info, Node: MEMORY, Next: PHDRS, Prev: SECTIONS, Up: Scripts 4046 4047 3.7 MEMORY Command 4048 ================== 4049 4050 The linker's default configuration permits allocation of all available 4051 memory. You can override this by using the `MEMORY' command. 4052 4053 The `MEMORY' command describes the location and size of blocks of 4054 memory in the target. You can use it to describe which memory regions 4055 may be used by the linker, and which memory regions it must avoid. You 4056 can then assign sections to particular memory regions. The linker will 4057 set section addresses based on the memory regions, and will warn about 4058 regions that become too full. The linker will not shuffle sections 4059 around to fit into the available regions. 4060 4061 A linker script may contain at most one use of the `MEMORY' command. 4062 However, you can define as many blocks of memory within it as you 4063 wish. The syntax is: 4064 MEMORY 4065 { 4066 NAME [(ATTR)] : ORIGIN = ORIGIN, LENGTH = LEN 4067 ... 4068 } 4069 4070 The NAME is a name used in the linker script to refer to the region. 4071 The region name has no meaning outside of the linker script. Region 4072 names are stored in a separate name space, and will not conflict with 4073 symbol names, file names, or section names. Each memory region must 4074 have a distinct name within the `MEMORY' command. However you can add 4075 later alias names to existing memory regions with the *Note 4076 REGION_ALIAS:: command. 4077 4078 The ATTR string is an optional list of attributes that specify 4079 whether to use a particular memory region for an input section which is 4080 not explicitly mapped in the linker script. As described in *Note 4081 SECTIONS::, if you do not specify an output section for some input 4082 section, the linker will create an output section with the same name as 4083 the input section. If you define region attributes, the linker will use 4084 them to select the memory region for the output section that it creates. 4085 4086 The ATTR string must consist only of the following characters: 4087 `R' 4088 Read-only section 4089 4090 `W' 4091 Read/write section 4092 4093 `X' 4094 Executable section 4095 4096 `A' 4097 Allocatable section 4098 4099 `I' 4100 Initialized section 4101 4102 `L' 4103 Same as `I' 4104 4105 `!' 4106 Invert the sense of any of the attributes that follow 4107 4108 If a unmapped section matches any of the listed attributes other than 4109 `!', it will be placed in the memory region. The `!' attribute 4110 reverses this test, so that an unmapped section will be placed in the 4111 memory region only if it does not match any of the listed attributes. 4112 4113 The ORIGIN is an numerical expression for the start address of the 4114 memory region. The expression must evaluate to a constant and it 4115 cannot involve any symbols. The keyword `ORIGIN' may be abbreviated to 4116 `org' or `o' (but not, for example, `ORG'). 4117 4118 The LEN is an expression for the size in bytes of the memory region. 4119 As with the ORIGIN expression, the expression must be numerical only 4120 and must evaluate to a constant. The keyword `LENGTH' may be 4121 abbreviated to `len' or `l'. 4122 4123 In the following example, we specify that there are two memory 4124 regions available for allocation: one starting at `0' for 256 kilobytes, 4125 and the other starting at `0x40000000' for four megabytes. The linker 4126 will place into the `rom' memory region every section which is not 4127 explicitly mapped into a memory region, and is either read-only or 4128 executable. The linker will place other sections which are not 4129 explicitly mapped into a memory region into the `ram' memory region. 4130 4131 MEMORY 4132 { 4133 rom (rx) : ORIGIN = 0, LENGTH = 256K 4134 ram (!rx) : org = 0x40000000, l = 4M 4135 } 4136 4137 Once you define a memory region, you can direct the linker to place 4138 specific output sections into that memory region by using the `>REGION' 4139 output section attribute. For example, if you have a memory region 4140 named `mem', you would use `>mem' in the output section definition. 4141 *Note Output Section Region::. If no address was specified for the 4142 output section, the linker will set the address to the next available 4143 address within the memory region. If the combined output sections 4144 directed to a memory region are too large for the region, the linker 4145 will issue an error message. 4146 4147 It is possible to access the origin and length of a memory in an 4148 expression via the `ORIGIN(MEMORY)' and `LENGTH(MEMORY)' functions: 4149 4150 _fstack = ORIGIN(ram) + LENGTH(ram) - 4; 4151 4152 4153 File: ld.info, Node: PHDRS, Next: VERSION, Prev: MEMORY, Up: Scripts 4154 4155 3.8 PHDRS Command 4156 ================= 4157 4158 The ELF object file format uses "program headers", also knows as 4159 "segments". The program headers describe how the program should be 4160 loaded into memory. You can print them out by using the `objdump' 4161 program with the `-p' option. 4162 4163 When you run an ELF program on a native ELF system, the system loader 4164 reads the program headers in order to figure out how to load the 4165 program. This will only work if the program headers are set correctly. 4166 This manual does not describe the details of how the system loader 4167 interprets program headers; for more information, see the ELF ABI. 4168 4169 The linker will create reasonable program headers by default. 4170 However, in some cases, you may need to specify the program headers more 4171 precisely. You may use the `PHDRS' command for this purpose. When the 4172 linker sees the `PHDRS' command in the linker script, it will not 4173 create any program headers other than the ones specified. 4174 4175 The linker only pays attention to the `PHDRS' command when 4176 generating an ELF output file. In other cases, the linker will simply 4177 ignore `PHDRS'. 4178 4179 This is the syntax of the `PHDRS' command. The words `PHDRS', 4180 `FILEHDR', `AT', and `FLAGS' are keywords. 4181 4182 PHDRS 4183 { 4184 NAME TYPE [ FILEHDR ] [ PHDRS ] [ AT ( ADDRESS ) ] 4185 [ FLAGS ( FLAGS ) ] ; 4186 } 4187 4188 The NAME is used only for reference in the `SECTIONS' command of the 4189 linker script. It is not put into the output file. Program header 4190 names are stored in a separate name space, and will not conflict with 4191 symbol names, file names, or section names. Each program header must 4192 have a distinct name. The headers are processed in order and it is 4193 usual for them to map to sections in ascending load address order. 4194 4195 Certain program header types describe segments of memory which the 4196 system loader will load from the file. In the linker script, you 4197 specify the contents of these segments by placing allocatable output 4198 sections in the segments. You use the `:PHDR' output section attribute 4199 to place a section in a particular segment. *Note Output Section 4200 Phdr::. 4201 4202 It is normal to put certain sections in more than one segment. This 4203 merely implies that one segment of memory contains another. You may 4204 repeat `:PHDR', using it once for each segment which should contain the 4205 section. 4206 4207 If you place a section in one or more segments using `:PHDR', then 4208 the linker will place all subsequent allocatable sections which do not 4209 specify `:PHDR' in the same segments. This is for convenience, since 4210 generally a whole set of contiguous sections will be placed in a single 4211 segment. You can use `:NONE' to override the default segment and tell 4212 the linker to not put the section in any segment at all. 4213 4214 You may use the `FILEHDR' and `PHDRS' keywords after the program 4215 header type to further describe the contents of the segment. The 4216 `FILEHDR' keyword means that the segment should include the ELF file 4217 header. The `PHDRS' keyword means that the segment should include the 4218 ELF program headers themselves. If applied to a loadable segment 4219 (`PT_LOAD'), all prior loadable segments must have one of these 4220 keywords. 4221 4222 The TYPE may be one of the following. The numbers indicate the 4223 value of the keyword. 4224 4225 `PT_NULL' (0) 4226 Indicates an unused program header. 4227 4228 `PT_LOAD' (1) 4229 Indicates that this program header describes a segment to be 4230 loaded from the file. 4231 4232 `PT_DYNAMIC' (2) 4233 Indicates a segment where dynamic linking information can be found. 4234 4235 `PT_INTERP' (3) 4236 Indicates a segment where the name of the program interpreter may 4237 be found. 4238 4239 `PT_NOTE' (4) 4240 Indicates a segment holding note information. 4241 4242 `PT_SHLIB' (5) 4243 A reserved program header type, defined but not specified by the 4244 ELF ABI. 4245 4246 `PT_PHDR' (6) 4247 Indicates a segment where the program headers may be found. 4248 4249 EXPRESSION 4250 An expression giving the numeric type of the program header. This 4251 may be used for types not defined above. 4252 4253 You can specify that a segment should be loaded at a particular 4254 address in memory by using an `AT' expression. This is identical to the 4255 `AT' command used as an output section attribute (*note Output Section 4256 LMA::). The `AT' command for a program header overrides the output 4257 section attribute. 4258 4259 The linker will normally set the segment flags based on the sections 4260 which comprise the segment. You may use the `FLAGS' keyword to 4261 explicitly specify the segment flags. The value of FLAGS must be an 4262 integer. It is used to set the `p_flags' field of the program header. 4263 4264 Here is an example of `PHDRS'. This shows a typical set of program 4265 headers used on a native ELF system. 4266 4267 PHDRS 4268 { 4269 headers PT_PHDR PHDRS ; 4270 interp PT_INTERP ; 4271 text PT_LOAD FILEHDR PHDRS ; 4272 data PT_LOAD ; 4273 dynamic PT_DYNAMIC ; 4274 } 4275 4276 SECTIONS 4277 { 4278 . = SIZEOF_HEADERS; 4279 .interp : { *(.interp) } :text :interp 4280 .text : { *(.text) } :text 4281 .rodata : { *(.rodata) } /* defaults to :text */ 4282 ... 4283 . = . + 0x1000; /* move to a new page in memory */ 4284 .data : { *(.data) } :data 4285 .dynamic : { *(.dynamic) } :data :dynamic 4286 ... 4287 } 4288 4289 4290 File: ld.info, Node: VERSION, Next: Expressions, Prev: PHDRS, Up: Scripts 4291 4292 3.9 VERSION Command 4293 =================== 4294 4295 The linker supports symbol versions when using ELF. Symbol versions are 4296 only useful when using shared libraries. The dynamic linker can use 4297 symbol versions to select a specific version of a function when it runs 4298 a program that may have been linked against an earlier version of the 4299 shared library. 4300 4301 You can include a version script directly in the main linker script, 4302 or you can supply the version script as an implicit linker script. You 4303 can also use the `--version-script' linker option. 4304 4305 The syntax of the `VERSION' command is simply 4306 VERSION { version-script-commands } 4307 4308 The format of the version script commands is identical to that used 4309 by Sun's linker in Solaris 2.5. The version script defines a tree of 4310 version nodes. You specify the node names and interdependencies in the 4311 version script. You can specify which symbols are bound to which 4312 version nodes, and you can reduce a specified set of symbols to local 4313 scope so that they are not globally visible outside of the shared 4314 library. 4315 4316 The easiest way to demonstrate the version script language is with a 4317 few examples. 4318 4319 VERS_1.1 { 4320 global: 4321 foo1; 4322 local: 4323 old*; 4324 original*; 4325 new*; 4326 }; 4327 4328 VERS_1.2 { 4329 foo2; 4330 } VERS_1.1; 4331 4332 VERS_2.0 { 4333 bar1; bar2; 4334 extern "C++" { 4335 ns::*; 4336 "f(int, double)"; 4337 }; 4338 } VERS_1.2; 4339 4340 This example version script defines three version nodes. The first 4341 version node defined is `VERS_1.1'; it has no other dependencies. The 4342 script binds the symbol `foo1' to `VERS_1.1'. It reduces a number of 4343 symbols to local scope so that they are not visible outside of the 4344 shared library; this is done using wildcard patterns, so that any 4345 symbol whose name begins with `old', `original', or `new' is matched. 4346 The wildcard patterns available are the same as those used in the shell 4347 when matching filenames (also known as "globbing"). However, if you 4348 specify the symbol name inside double quotes, then the name is treated 4349 as literal, rather than as a glob pattern. 4350 4351 Next, the version script defines node `VERS_1.2'. This node depends 4352 upon `VERS_1.1'. The script binds the symbol `foo2' to the version 4353 node `VERS_1.2'. 4354 4355 Finally, the version script defines node `VERS_2.0'. This node 4356 depends upon `VERS_1.2'. The scripts binds the symbols `bar1' and 4357 `bar2' are bound to the version node `VERS_2.0'. 4358 4359 When the linker finds a symbol defined in a library which is not 4360 specifically bound to a version node, it will effectively bind it to an 4361 unspecified base version of the library. You can bind all otherwise 4362 unspecified symbols to a given version node by using `global: *;' 4363 somewhere in the version script. Note that it's slightly crazy to use 4364 wildcards in a global spec except on the last version node. Global 4365 wildcards elsewhere run the risk of accidentally adding symbols to the 4366 set exported for an old version. That's wrong since older versions 4367 ought to have a fixed set of symbols. 4368 4369 The names of the version nodes have no specific meaning other than 4370 what they might suggest to the person reading them. The `2.0' version 4371 could just as well have appeared in between `1.1' and `1.2'. However, 4372 this would be a confusing way to write a version script. 4373 4374 Node name can be omitted, provided it is the only version node in 4375 the version script. Such version script doesn't assign any versions to 4376 symbols, only selects which symbols will be globally visible out and 4377 which won't. 4378 4379 { global: foo; bar; local: *; }; 4380 4381 When you link an application against a shared library that has 4382 versioned symbols, the application itself knows which version of each 4383 symbol it requires, and it also knows which version nodes it needs from 4384 each shared library it is linked against. Thus at runtime, the dynamic 4385 loader can make a quick check to make sure that the libraries you have 4386 linked against do in fact supply all of the version nodes that the 4387 application will need to resolve all of the dynamic symbols. In this 4388 way it is possible for the dynamic linker to know with certainty that 4389 all external symbols that it needs will be resolvable without having to 4390 search for each symbol reference. 4391 4392 The symbol versioning is in effect a much more sophisticated way of 4393 doing minor version checking that SunOS does. The fundamental problem 4394 that is being addressed here is that typically references to external 4395 functions are bound on an as-needed basis, and are not all bound when 4396 the application starts up. If a shared library is out of date, a 4397 required interface may be missing; when the application tries to use 4398 that interface, it may suddenly and unexpectedly fail. With symbol 4399 versioning, the user will get a warning when they start their program if 4400 the libraries being used with the application are too old. 4401 4402 There are several GNU extensions to Sun's versioning approach. The 4403 first of these is the ability to bind a symbol to a version node in the 4404 source file where the symbol is defined instead of in the versioning 4405 script. This was done mainly to reduce the burden on the library 4406 maintainer. You can do this by putting something like: 4407 __asm__(".symver original_foo,foo (a] VERS_1.1"); 4408 in the C source file. This renames the function `original_foo' to 4409 be an alias for `foo' bound to the version node `VERS_1.1'. The 4410 `local:' directive can be used to prevent the symbol `original_foo' 4411 from being exported. A `.symver' directive takes precedence over a 4412 version script. 4413 4414 The second GNU extension is to allow multiple versions of the same 4415 function to appear in a given shared library. In this way you can make 4416 an incompatible change to an interface without increasing the major 4417 version number of the shared library, while still allowing applications 4418 linked against the old interface to continue to function. 4419 4420 To do this, you must use multiple `.symver' directives in the source 4421 file. Here is an example: 4422 4423 __asm__(".symver original_foo,foo@"); 4424 __asm__(".symver old_foo,foo (a] VERS_1.1"); 4425 __asm__(".symver old_foo1,foo (a] VERS_1.2"); 4426 __asm__(".symver new_foo,foo@@VERS_2.0"); 4427 4428 In this example, `foo@' represents the symbol `foo' bound to the 4429 unspecified base version of the symbol. The source file that contains 4430 this example would define 4 C functions: `original_foo', `old_foo', 4431 `old_foo1', and `new_foo'. 4432 4433 When you have multiple definitions of a given symbol, there needs to 4434 be some way to specify a default version to which external references to 4435 this symbol will be bound. You can do this with the `foo@@VERS_2.0' 4436 type of `.symver' directive. You can only declare one version of a 4437 symbol as the default in this manner; otherwise you would effectively 4438 have multiple definitions of the same symbol. 4439 4440 If you wish to bind a reference to a specific version of the symbol 4441 within the shared library, you can use the aliases of convenience 4442 (i.e., `old_foo'), or you can use the `.symver' directive to 4443 specifically bind to an external version of the function in question. 4444 4445 You can also specify the language in the version script: 4446 4447 VERSION extern "lang" { version-script-commands } 4448 4449 The supported `lang's are `C', `C++', and `Java'. The linker will 4450 iterate over the list of symbols at the link time and demangle them 4451 according to `lang' before matching them to the patterns specified in 4452 `version-script-commands'. The default `lang' is `C'. 4453 4454 Demangled names may contains spaces and other special characters. As 4455 described above, you can use a glob pattern to match demangled names, 4456 or you can use a double-quoted string to match the string exactly. In 4457 the latter case, be aware that minor differences (such as differing 4458 whitespace) between the version script and the demangler output will 4459 cause a mismatch. As the exact string generated by the demangler might 4460 change in the future, even if the mangled name does not, you should 4461 check that all of your version directives are behaving as you expect 4462 when you upgrade. 4463 4464 4465 File: ld.info, Node: Expressions, Next: Implicit Linker Scripts, Prev: VERSION, Up: Scripts 4466 4467 3.10 Expressions in Linker Scripts 4468 ================================== 4469 4470 The syntax for expressions in the linker script language is identical to 4471 that of C expressions. All expressions are evaluated as integers. All 4472 expressions are evaluated in the same size, which is 32 bits if both the 4473 host and target are 32 bits, and is otherwise 64 bits. 4474 4475 You can use and set symbol values in expressions. 4476 4477 The linker defines several special purpose builtin functions for use 4478 in expressions. 4479 4480 * Menu: 4481 4482 * Constants:: Constants 4483 * Symbolic Constants:: Symbolic constants 4484 * Symbols:: Symbol Names 4485 * Orphan Sections:: Orphan Sections 4486 * Location Counter:: The Location Counter 4487 * Operators:: Operators 4488 * Evaluation:: Evaluation 4489 * Expression Section:: The Section of an Expression 4490 * Builtin Functions:: Builtin Functions 4491 4492 4493 File: ld.info, Node: Constants, Next: Symbolic Constants, Up: Expressions 4494 4495 3.10.1 Constants 4496 ---------------- 4497 4498 All constants are integers. 4499 4500 As in C, the linker considers an integer beginning with `0' to be 4501 octal, and an integer beginning with `0x' or `0X' to be hexadecimal. 4502 Alternatively the linker accepts suffixes of `h' or `H' for 4503 hexadecimal, `o' or `O' for octal, `b' or `B' for binary and `d' or `D' 4504 for decimal. Any integer value without a prefix or a suffix is 4505 considered to be decimal. 4506 4507 In addition, you can use the suffixes `K' and `M' to scale a 4508 constant by `1024' or `1024*1024' respectively. For example, the 4509 following all refer to the same quantity: 4510 4511 _fourk_1 = 4K; 4512 _fourk_2 = 4096; 4513 _fourk_3 = 0x1000; 4514 _fourk_4 = 10000o; 4515 4516 Note - the `K' and `M' suffixes cannot be used in conjunction with 4517 the base suffixes mentioned above. 4518 4519 4520 File: ld.info, Node: Symbolic Constants, Next: Symbols, Prev: Constants, Up: Expressions 4521 4522 3.10.2 Symbolic Constants 4523 ------------------------- 4524 4525 It is possible to refer to target specific constants via the use of the 4526 `CONSTANT(NAME)' operator, where NAME is one of: 4527 4528 `MAXPAGESIZE' 4529 The target's maximum page size. 4530 4531 `COMMONPAGESIZE' 4532 The target's default page size. 4533 4534 So for example: 4535 4536 .text ALIGN (CONSTANT (MAXPAGESIZE)) : { *(.text) } 4537 4538 will create a text section aligned to the largest page boundary 4539 supported by the target. 4540 4541 4542 File: ld.info, Node: Symbols, Next: Orphan Sections, Prev: Symbolic Constants, Up: Expressions 4543 4544 3.10.3 Symbol Names 4545 ------------------- 4546 4547 Unless quoted, symbol names start with a letter, underscore, or period 4548 and may include letters, digits, underscores, periods, and hyphens. 4549 Unquoted symbol names must not conflict with any keywords. You can 4550 specify a symbol which contains odd characters or has the same name as a 4551 keyword by surrounding the symbol name in double quotes: 4552 "SECTION" = 9; 4553 "with a space" = "also with a space" + 10; 4554 4555 Since symbols can contain many non-alphabetic characters, it is 4556 safest to delimit symbols with spaces. For example, `A-B' is one 4557 symbol, whereas `A - B' is an expression involving subtraction. 4558 4559 4560 File: ld.info, Node: Orphan Sections, Next: Location Counter, Prev: Symbols, Up: Expressions 4561 4562 3.10.4 Orphan Sections 4563 ---------------------- 4564 4565 Orphan sections are sections present in the input files which are not 4566 explicitly placed into the output file by the linker script. The 4567 linker will still copy these sections into the output file, but it has 4568 to guess as to where they should be placed. The linker uses a simple 4569 heuristic to do this. It attempts to place orphan sections after 4570 non-orphan sections of the same attribute, such as code vs data, 4571 loadable vs non-loadable, etc. If there is not enough room to do this 4572 then it places at the end of the file. 4573 4574 For ELF targets, the attribute of the section includes section type 4575 as well as section flag. 4576 4577 If an orphaned section's name is representable as a C identifier then 4578 the linker will automatically *note PROVIDE:: two symbols: 4579 __start_SECNAME and __stop_SECNAME, where SECNAME is the name of the 4580 section. These indicate the start address and end address of the 4581 orphaned section respectively. Note: most section names are not 4582 representable as C identifiers because they contain a `.' character. 4583 4584 4585 File: ld.info, Node: Location Counter, Next: Operators, Prev: Orphan Sections, Up: Expressions 4586 4587 3.10.5 The Location Counter 4588 --------------------------- 4589 4590 The special linker variable "dot" `.' always contains the current 4591 output location counter. Since the `.' always refers to a location in 4592 an output section, it may only appear in an expression within a 4593 `SECTIONS' command. The `.' symbol may appear anywhere that an 4594 ordinary symbol is allowed in an expression. 4595 4596 Assigning a value to `.' will cause the location counter to be 4597 moved. This may be used to create holes in the output section. The 4598 location counter may not be moved backwards inside an output section, 4599 and may not be moved backwards outside of an output section if so doing 4600 creates areas with overlapping LMAs. 4601 4602 SECTIONS 4603 { 4604 output : 4605 { 4606 file1(.text) 4607 . = . + 1000; 4608 file2(.text) 4609 . += 1000; 4610 file3(.text) 4611 } = 0x12345678; 4612 } 4613 In the previous example, the `.text' section from `file1' is located 4614 at the beginning of the output section `output'. It is followed by a 4615 1000 byte gap. Then the `.text' section from `file2' appears, also 4616 with a 1000 byte gap following before the `.text' section from `file3'. 4617 The notation `= 0x12345678' specifies what data to write in the gaps 4618 (*note Output Section Fill::). 4619 4620 Note: `.' actually refers to the byte offset from the start of the 4621 current containing object. Normally this is the `SECTIONS' statement, 4622 whose start address is 0, hence `.' can be used as an absolute address. 4623 If `.' is used inside a section description however, it refers to the 4624 byte offset from the start of that section, not an absolute address. 4625 Thus in a script like this: 4626 4627 SECTIONS 4628 { 4629 . = 0x100 4630 .text: { 4631 *(.text) 4632 . = 0x200 4633 } 4634 . = 0x500 4635 .data: { 4636 *(.data) 4637 . += 0x600 4638 } 4639 } 4640 4641 The `.text' section will be assigned a starting address of 0x100 and 4642 a size of exactly 0x200 bytes, even if there is not enough data in the 4643 `.text' input sections to fill this area. (If there is too much data, 4644 an error will be produced because this would be an attempt to move `.' 4645 backwards). The `.data' section will start at 0x500 and it will have 4646 an extra 0x600 bytes worth of space after the end of the values from 4647 the `.data' input sections and before the end of the `.data' output 4648 section itself. 4649 4650 Setting symbols to the value of the location counter outside of an 4651 output section statement can result in unexpected values if the linker 4652 needs to place orphan sections. For example, given the following: 4653 4654 SECTIONS 4655 { 4656 start_of_text = . ; 4657 .text: { *(.text) } 4658 end_of_text = . ; 4659 4660 start_of_data = . ; 4661 .data: { *(.data) } 4662 end_of_data = . ; 4663 } 4664 4665 If the linker needs to place some input section, e.g. `.rodata', not 4666 mentioned in the script, it might choose to place that section between 4667 `.text' and `.data'. You might think the linker should place `.rodata' 4668 on the blank line in the above script, but blank lines are of no 4669 particular significance to the linker. As well, the linker doesn't 4670 associate the above symbol names with their sections. Instead, it 4671 assumes that all assignments or other statements belong to the previous 4672 output section, except for the special case of an assignment to `.'. 4673 I.e., the linker will place the orphan `.rodata' section as if the 4674 script was written as follows: 4675 4676 SECTIONS 4677 { 4678 start_of_text = . ; 4679 .text: { *(.text) } 4680 end_of_text = . ; 4681 4682 start_of_data = . ; 4683 .rodata: { *(.rodata) } 4684 .data: { *(.data) } 4685 end_of_data = . ; 4686 } 4687 4688 This may or may not be the script author's intention for the value of 4689 `start_of_data'. One way to influence the orphan section placement is 4690 to assign the location counter to itself, as the linker assumes that an 4691 assignment to `.' is setting the start address of a following output 4692 section and thus should be grouped with that section. So you could 4693 write: 4694 4695 SECTIONS 4696 { 4697 start_of_text = . ; 4698 .text: { *(.text) } 4699 end_of_text = . ; 4700 4701 . = . ; 4702 start_of_data = . ; 4703 .data: { *(.data) } 4704 end_of_data = . ; 4705 } 4706 4707 Now, the orphan `.rodata' section will be placed between 4708 `end_of_text' and `start_of_data'. 4709 4710 4711 File: ld.info, Node: Operators, Next: Evaluation, Prev: Location Counter, Up: Expressions 4712 4713 3.10.6 Operators 4714 ---------------- 4715 4716 The linker recognizes the standard C set of arithmetic operators, with 4717 the standard bindings and precedence levels: 4718 precedence associativity Operators Notes 4719 (highest) 4720 1 left ! - ~ (1) 4721 2 left * / % 4722 3 left + - 4723 4 left >> << 4724 5 left == != > < <= >= 4725 6 left & 4726 7 left | 4727 8 left && 4728 9 left || 4729 10 right ? : 4730 11 right &= += -= *= /= (2) 4731 (lowest) 4732 Notes: (1) Prefix operators (2) *Note Assignments::. 4733 4734 4735 File: ld.info, Node: Evaluation, Next: Expression Section, Prev: Operators, Up: Expressions 4736 4737 3.10.7 Evaluation 4738 ----------------- 4739 4740 The linker evaluates expressions lazily. It only computes the value of 4741 an expression when absolutely necessary. 4742 4743 The linker needs some information, such as the value of the start 4744 address of the first section, and the origins and lengths of memory 4745 regions, in order to do any linking at all. These values are computed 4746 as soon as possible when the linker reads in the linker script. 4747 4748 However, other values (such as symbol values) are not known or needed 4749 until after storage allocation. Such values are evaluated later, when 4750 other information (such as the sizes of output sections) is available 4751 for use in the symbol assignment expression. 4752 4753 The sizes of sections cannot be known until after allocation, so 4754 assignments dependent upon these are not performed until after 4755 allocation. 4756 4757 Some expressions, such as those depending upon the location counter 4758 `.', must be evaluated during section allocation. 4759 4760 If the result of an expression is required, but the value is not 4761 available, then an error results. For example, a script like the 4762 following 4763 SECTIONS 4764 { 4765 .text 9+this_isnt_constant : 4766 { *(.text) } 4767 } 4768 will cause the error message `non constant expression for initial 4769 address'. 4770 4771 4772 File: ld.info, Node: Expression Section, Next: Builtin Functions, Prev: Evaluation, Up: Expressions 4773 4774 3.10.8 The Section of an Expression 4775 ----------------------------------- 4776 4777 Addresses and symbols may be section relative, or absolute. A section 4778 relative symbol is relocatable. If you request relocatable output 4779 using the `-r' option, a further link operation may change the value of 4780 a section relative symbol. On the other hand, an absolute symbol will 4781 retain the same value throughout any further link operations. 4782 4783 Some terms in linker expressions are addresses. This is true of 4784 section relative symbols and for builtin functions that return an 4785 address, such as `ADDR', `LOADADDR', `ORIGIN' and `SEGMENT_START'. 4786 Other terms are simply numbers, or are builtin functions that return a 4787 non-address value, such as `LENGTH'. One complication is that unless 4788 you set `LD_FEATURE ("SANE_EXPR")' (*note Miscellaneous Commands::), 4789 numbers and absolute symbols are treated differently depending on their 4790 location, for compatibility with older versions of `ld'. Expressions 4791 appearing outside an output section definition treat all numbers as 4792 absolute addresses. Expressions appearing inside an output section 4793 definition treat absolute symbols as numbers. If `LD_FEATURE 4794 ("SANE_EXPR")' is given, then absolute symbols and numbers are simply 4795 treated as numbers everywhere. 4796 4797 In the following simple example, 4798 4799 SECTIONS 4800 { 4801 . = 0x100; 4802 __executable_start = 0x100; 4803 .data : 4804 { 4805 . = 0x10; 4806 __data_start = 0x10; 4807 *(.data) 4808 } 4809 ... 4810 } 4811 4812 both `.' and `__executable_start' are set to the absolute address 4813 0x100 in the first two assignments, then both `.' and `__data_start' 4814 are set to 0x10 relative to the `.data' section in the second two 4815 assignments. 4816 4817 For expressions involving numbers, relative addresses and absolute 4818 addresses, ld follows these rules to evaluate terms: 4819 4820 * Unary operations on an absolute address or number, and binary 4821 operations on two absolute addresses or two numbers, or between one 4822 absolute address and a number, apply the operator to the value(s). 4823 4824 * Unary operations on a relative address, and binary operations on 4825 two relative addresses in the same section or between one relative 4826 address and a number, apply the operator to the offset part of the 4827 address(es). 4828 4829 * Other binary operations, that is, between two relative addresses 4830 not in the same section, or between a relative address and an 4831 absolute address, first convert any non-absolute term to an 4832 absolute address before applying the operator. 4833 4834 The result section of each sub-expression is as follows: 4835 4836 * An operation involving only numbers results in a number. 4837 4838 * The result of comparisons, `&&' and `||' is also a number. 4839 4840 * The result of other binary arithmetic and logical operations on two 4841 relative addresses in the same section or two absolute addresses 4842 (after above conversions) is also a number. 4843 4844 * The result of other operations on relative addresses or one 4845 relative address and a number, is a relative address in the same 4846 section as the relative operand(s). 4847 4848 * The result of other operations on absolute addresses (after above 4849 conversions) is an absolute address. 4850 4851 You can use the builtin function `ABSOLUTE' to force an expression 4852 to be absolute when it would otherwise be relative. For example, to 4853 create an absolute symbol set to the address of the end of the output 4854 section `.data': 4855 SECTIONS 4856 { 4857 .data : { *(.data) _edata = ABSOLUTE(.); } 4858 } 4859 If `ABSOLUTE' were not used, `_edata' would be relative to the 4860 `.data' section. 4861 4862 Using `LOADADDR' also forces an expression absolute, since this 4863 particular builtin function returns an absolute address. 4864 4865 4866 File: ld.info, Node: Builtin Functions, Prev: Expression Section, Up: Expressions 4867 4868 3.10.9 Builtin Functions 4869 ------------------------ 4870 4871 The linker script language includes a number of builtin functions for 4872 use in linker script expressions. 4873 4874 `ABSOLUTE(EXP)' 4875 Return the absolute (non-relocatable, as opposed to non-negative) 4876 value of the expression EXP. Primarily useful to assign an 4877 absolute value to a symbol within a section definition, where 4878 symbol values are normally section relative. *Note Expression 4879 Section::. 4880 4881 `ADDR(SECTION)' 4882 Return the address (VMA) of the named SECTION. Your script must 4883 previously have defined the location of that section. In the 4884 following example, `start_of_output_1', `symbol_1' and `symbol_2' 4885 are assigned equivalent values, except that `symbol_1' will be 4886 relative to the `.output1' section while the other two will be 4887 absolute: 4888 SECTIONS { ... 4889 .output1 : 4890 { 4891 start_of_output_1 = ABSOLUTE(.); 4892 ... 4893 } 4894 .output : 4895 { 4896 symbol_1 = ADDR(.output1); 4897 symbol_2 = start_of_output_1; 4898 } 4899 ... } 4900 4901 `ALIGN(ALIGN)' 4902 `ALIGN(EXP,ALIGN)' 4903 Return the location counter (`.') or arbitrary expression aligned 4904 to the next ALIGN boundary. The single operand `ALIGN' doesn't 4905 change the value of the location counter--it just does arithmetic 4906 on it. The two operand `ALIGN' allows an arbitrary expression to 4907 be aligned upwards (`ALIGN(ALIGN)' is equivalent to `ALIGN(., 4908 ALIGN)'). 4909 4910 Here is an example which aligns the output `.data' section to the 4911 next `0x2000' byte boundary after the preceding section and sets a 4912 variable within the section to the next `0x8000' boundary after the 4913 input sections: 4914 SECTIONS { ... 4915 .data ALIGN(0x2000): { 4916 *(.data) 4917 variable = ALIGN(0x8000); 4918 } 4919 ... } 4920 The first use of `ALIGN' in this example specifies the 4921 location of a section because it is used as the optional ADDRESS 4922 attribute of a section definition (*note Output Section 4923 Address::). The second use of `ALIGN' is used to defines the 4924 value of a symbol. 4925 4926 The builtin function `NEXT' is closely related to `ALIGN'. 4927 4928 `ALIGNOF(SECTION)' 4929 Return the alignment in bytes of the named SECTION, if that 4930 section has been allocated. If the section has not been allocated 4931 when this is evaluated, the linker will report an error. In the 4932 following example, the alignment of the `.output' section is 4933 stored as the first value in that section. 4934 SECTIONS{ ... 4935 .output { 4936 LONG (ALIGNOF (.output)) 4937 ... 4938 } 4939 ... } 4940 4941 `BLOCK(EXP)' 4942 This is a synonym for `ALIGN', for compatibility with older linker 4943 scripts. It is most often seen when setting the address of an 4944 output section. 4945 4946 `DATA_SEGMENT_ALIGN(MAXPAGESIZE, COMMONPAGESIZE)' 4947 This is equivalent to either 4948 (ALIGN(MAXPAGESIZE) + (. & (MAXPAGESIZE - 1))) 4949 or 4950 (ALIGN(MAXPAGESIZE) + (. & (MAXPAGESIZE - COMMONPAGESIZE))) 4951 depending on whether the latter uses fewer COMMONPAGESIZE sized 4952 pages for the data segment (area between the result of this 4953 expression and `DATA_SEGMENT_END') than the former or not. If the 4954 latter form is used, it means COMMONPAGESIZE bytes of runtime 4955 memory will be saved at the expense of up to COMMONPAGESIZE wasted 4956 bytes in the on-disk file. 4957 4958 This expression can only be used directly in `SECTIONS' commands, 4959 not in any output section descriptions and only once in the linker 4960 script. COMMONPAGESIZE should be less or equal to MAXPAGESIZE and 4961 should be the system page size the object wants to be optimized 4962 for (while still working on system page sizes up to MAXPAGESIZE). 4963 4964 Example: 4965 . = DATA_SEGMENT_ALIGN(0x10000, 0x2000); 4966 4967 `DATA_SEGMENT_END(EXP)' 4968 This defines the end of data segment for `DATA_SEGMENT_ALIGN' 4969 evaluation purposes. 4970 4971 . = DATA_SEGMENT_END(.); 4972 4973 `DATA_SEGMENT_RELRO_END(OFFSET, EXP)' 4974 This defines the end of the `PT_GNU_RELRO' segment when `-z relro' 4975 option is used. When `-z relro' option is not present, 4976 `DATA_SEGMENT_RELRO_END' does nothing, otherwise 4977 `DATA_SEGMENT_ALIGN' is padded so that EXP + OFFSET is aligned to 4978 the most commonly used page boundary for particular target. If 4979 present in the linker script, it must always come in between 4980 `DATA_SEGMENT_ALIGN' and `DATA_SEGMENT_END'. Evaluates to the 4981 second argument plus any padding needed at the end of the 4982 `PT_GNU_RELRO' segment due to section alignment. 4983 4984 . = DATA_SEGMENT_RELRO_END(24, .); 4985 4986 `DEFINED(SYMBOL)' 4987 Return 1 if SYMBOL is in the linker global symbol table and is 4988 defined before the statement using DEFINED in the script, otherwise 4989 return 0. You can use this function to provide default values for 4990 symbols. For example, the following script fragment shows how to 4991 set a global symbol `begin' to the first location in the `.text' 4992 section--but if a symbol called `begin' already existed, its value 4993 is preserved: 4994 4995 SECTIONS { ... 4996 .text : { 4997 begin = DEFINED(begin) ? begin : . ; 4998 ... 4999 } 5000 ... 5001 } 5002 5003 `LENGTH(MEMORY)' 5004 Return the length of the memory region named MEMORY. 5005 5006 `LOADADDR(SECTION)' 5007 Return the absolute LMA of the named SECTION. (*note Output 5008 Section LMA::). 5009 5010 `LOG2CEIL(EXP)' 5011 Return the binary logarithm of EXP rounded towards infinity. 5012 `LOG2CEIL(0)' returns 0. 5013 5014 `MAX(EXP1, EXP2)' 5015 Returns the maximum of EXP1 and EXP2. 5016 5017 `MIN(EXP1, EXP2)' 5018 Returns the minimum of EXP1 and EXP2. 5019 5020 `NEXT(EXP)' 5021 Return the next unallocated address that is a multiple of EXP. 5022 This function is closely related to `ALIGN(EXP)'; unless you use 5023 the `MEMORY' command to define discontinuous memory for the output 5024 file, the two functions are equivalent. 5025 5026 `ORIGIN(MEMORY)' 5027 Return the origin of the memory region named MEMORY. 5028 5029 `SEGMENT_START(SEGMENT, DEFAULT)' 5030 Return the base address of the named SEGMENT. If an explicit 5031 value has already been given for this segment (with a command-line 5032 `-T' option) then that value will be returned otherwise the value 5033 will be DEFAULT. At present, the `-T' command-line option can 5034 only be used to set the base address for the "text", "data", and 5035 "bss" sections, but you can use `SEGMENT_START' with any segment 5036 name. 5037 5038 `SIZEOF(SECTION)' 5039 Return the size in bytes of the named SECTION, if that section has 5040 been allocated. If the section has not been allocated when this is 5041 evaluated, the linker will report an error. In the following 5042 example, `symbol_1' and `symbol_2' are assigned identical values: 5043 SECTIONS{ ... 5044 .output { 5045 .start = . ; 5046 ... 5047 .end = . ; 5048 } 5049 symbol_1 = .end - .start ; 5050 symbol_2 = SIZEOF(.output); 5051 ... } 5052 5053 `SIZEOF_HEADERS' 5054 `sizeof_headers' 5055 Return the size in bytes of the output file's headers. This is 5056 information which appears at the start of the output file. You 5057 can use this number when setting the start address of the first 5058 section, if you choose, to facilitate paging. 5059 5060 When producing an ELF output file, if the linker script uses the 5061 `SIZEOF_HEADERS' builtin function, the linker must compute the 5062 number of program headers before it has determined all the section 5063 addresses and sizes. If the linker later discovers that it needs 5064 additional program headers, it will report an error `not enough 5065 room for program headers'. To avoid this error, you must avoid 5066 using the `SIZEOF_HEADERS' function, or you must rework your linker 5067 script to avoid forcing the linker to use additional program 5068 headers, or you must define the program headers yourself using the 5069 `PHDRS' command (*note PHDRS::). 5070 5071 5072 File: ld.info, Node: Implicit Linker Scripts, Prev: Expressions, Up: Scripts 5073 5074 3.11 Implicit Linker Scripts 5075 ============================ 5076 5077 If you specify a linker input file which the linker can not recognize as 5078 an object file or an archive file, it will try to read the file as a 5079 linker script. If the file can not be parsed as a linker script, the 5080 linker will report an error. 5081 5082 An implicit linker script will not replace the default linker script. 5083 5084 Typically an implicit linker script would contain only symbol 5085 assignments, or the `INPUT', `GROUP', or `VERSION' commands. 5086 5087 Any input files read because of an implicit linker script will be 5088 read at the position in the command line where the implicit linker 5089 script was read. This can affect archive searching. 5090 5091 5092 File: ld.info, Node: Machine Dependent, Next: BFD, Prev: Scripts, Up: Top 5093 5094 4 Machine Dependent Features 5095 **************************** 5096 5097 `ld' has additional features on some platforms; the following sections 5098 describe them. Machines where `ld' has no additional functionality are 5099 not listed. 5100 5101 * Menu: 5102 5103 5104 * H8/300:: `ld' and the H8/300 5105 5106 * i960:: `ld' and the Intel 960 family 5107 5108 * M68HC11/68HC12:: `ld' and the Motorola 68HC11 and 68HC12 families 5109 5110 * ARM:: `ld' and the ARM family 5111 5112 * HPPA ELF32:: `ld' and HPPA 32-bit ELF 5113 5114 * M68K:: `ld' and the Motorola 68K family 5115 5116 * MIPS:: `ld' and the MIPS family 5117 5118 * MMIX:: `ld' and MMIX 5119 5120 * MSP430:: `ld' and MSP430 5121 5122 * NDS32:: `ld' and NDS32 5123 5124 * Nios II:: `ld' and the Altera Nios II 5125 5126 * PowerPC ELF32:: `ld' and PowerPC 32-bit ELF Support 5127 5128 * PowerPC64 ELF64:: `ld' and PowerPC64 64-bit ELF Support 5129 5130 * SPU ELF:: `ld' and SPU ELF Support 5131 5132 * TI COFF:: `ld' and TI COFF 5133 5134 * WIN32:: `ld' and WIN32 (cygwin/mingw) 5135 5136 * Xtensa:: `ld' and Xtensa Processors 5137 5138 5139 File: ld.info, Node: H8/300, Next: i960, Up: Machine Dependent 5140 5141 4.1 `ld' and the H8/300 5142 ======================= 5143 5144 For the H8/300, `ld' can perform these global optimizations when you 5145 specify the `--relax' command-line option. 5146 5147 _relaxing address modes_ 5148 `ld' finds all `jsr' and `jmp' instructions whose targets are 5149 within eight bits, and turns them into eight-bit program-counter 5150 relative `bsr' and `bra' instructions, respectively. 5151 5152 _synthesizing instructions_ 5153 `ld' finds all `mov.b' instructions which use the sixteen-bit 5154 absolute address form, but refer to the top page of memory, and 5155 changes them to use the eight-bit address form. (That is: the 5156 linker turns `mov.b `@'AA:16' into `mov.b `@'AA:8' whenever the 5157 address AA is in the top page of memory). 5158 5159 `ld' finds all `mov' instructions which use the register indirect 5160 with 32-bit displacement addressing mode, but use a small 5161 displacement inside 16-bit displacement range, and changes them to 5162 use the 16-bit displacement form. (That is: the linker turns 5163 `mov.b `@'D:32,ERx' into `mov.b `@'D:16,ERx' whenever the 5164 displacement D is in the 16 bit signed integer range. Only 5165 implemented in ELF-format ld). 5166 5167 _bit manipulation instructions_ 5168 `ld' finds all bit manipulation instructions like `band, bclr, 5169 biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, 5170 bxor' which use 32 bit and 16 bit absolute address form, but refer 5171 to the top page of memory, and changes them to use the 8 bit 5172 address form. (That is: the linker turns `bset #xx:3,`@'AA:32' 5173 into `bset #xx:3,`@'AA:8' whenever the address AA is in the top 5174 page of memory). 5175 5176 _system control instructions_ 5177 `ld' finds all `ldc.w, stc.w' instructions which use the 32 bit 5178 absolute address form, but refer to the top page of memory, and 5179 changes them to use 16 bit address form. (That is: the linker 5180 turns `ldc.w `@'AA:32,ccr' into `ldc.w `@'AA:16,ccr' whenever the 5181 address AA is in the top page of memory). 5182 5183 5184 File: ld.info, Node: i960, Next: M68HC11/68HC12, Prev: H8/300, Up: Machine Dependent 5185 5186 4.2 `ld' and the Intel 960 Family 5187 ================================= 5188 5189 You can use the `-AARCHITECTURE' command line option to specify one of 5190 the two-letter names identifying members of the 960 family; the option 5191 specifies the desired output target, and warns of any incompatible 5192 instructions in the input files. It also modifies the linker's search 5193 strategy for archive libraries, to support the use of libraries 5194 specific to each particular architecture, by including in the search 5195 loop names suffixed with the string identifying the architecture. 5196 5197 For example, if your `ld' command line included `-ACA' as well as 5198 `-ltry', the linker would look (in its built-in search paths, and in 5199 any paths you specify with `-L') for a library with the names 5200 5201 try 5202 libtry.a 5203 tryca 5204 libtryca.a 5205 5206 The first two possibilities would be considered in any event; the last 5207 two are due to the use of `-ACA'. 5208 5209 You can meaningfully use `-A' more than once on a command line, since 5210 the 960 architecture family allows combination of target architectures; 5211 each use will add another pair of name variants to search for when `-l' 5212 specifies a library. 5213 5214 `ld' supports the `--relax' option for the i960 family. If you 5215 specify `--relax', `ld' finds all `balx' and `calx' instructions whose 5216 targets are within 24 bits, and turns them into 24-bit program-counter 5217 relative `bal' and `cal' instructions, respectively. `ld' also turns 5218 `cal' instructions into `bal' instructions when it determines that the 5219 target subroutine is a leaf routine (that is, the target subroutine does 5220 not itself call any subroutines). 5221 5222 5223 File: ld.info, Node: M68HC11/68HC12, Next: ARM, Prev: i960, Up: Machine Dependent 5224 5225 4.3 `ld' and the Motorola 68HC11 and 68HC12 families 5226 ==================================================== 5227 5228 4.3.1 Linker Relaxation 5229 ----------------------- 5230 5231 For the Motorola 68HC11, `ld' can perform these global optimizations 5232 when you specify the `--relax' command-line option. 5233 5234 _relaxing address modes_ 5235 `ld' finds all `jsr' and `jmp' instructions whose targets are 5236 within eight bits, and turns them into eight-bit program-counter 5237 relative `bsr' and `bra' instructions, respectively. 5238 5239 `ld' also looks at all 16-bit extended addressing modes and 5240 transforms them in a direct addressing mode when the address is in 5241 page 0 (between 0 and 0x0ff). 5242 5243 _relaxing gcc instruction group_ 5244 When `gcc' is called with `-mrelax', it can emit group of 5245 instructions that the linker can optimize to use a 68HC11 direct 5246 addressing mode. These instructions consists of `bclr' or `bset' 5247 instructions. 5248 5249 5250 4.3.2 Trampoline Generation 5251 --------------------------- 5252 5253 For 68HC11 and 68HC12, `ld' can generate trampoline code to call a far 5254 function using a normal `jsr' instruction. The linker will also change 5255 the relocation to some far function to use the trampoline address 5256 instead of the function address. This is typically the case when a 5257 pointer to a function is taken. The pointer will in fact point to the 5258 function trampoline. 5259 5260 5261 File: ld.info, Node: ARM, Next: HPPA ELF32, Prev: M68HC11/68HC12, Up: Machine Dependent 5262 5263 4.4 `ld' and the ARM family 5264 =========================== 5265 5266 For the ARM, `ld' will generate code stubs to allow functions calls 5267 between ARM and Thumb code. These stubs only work with code that has 5268 been compiled and assembled with the `-mthumb-interwork' command line 5269 option. If it is necessary to link with old ARM object files or 5270 libraries, which have not been compiled with the -mthumb-interwork 5271 option then the `--support-old-code' command line switch should be 5272 given to the linker. This will make it generate larger stub functions 5273 which will work with non-interworking aware ARM code. Note, however, 5274 the linker does not support generating stubs for function calls to 5275 non-interworking aware Thumb code. 5276 5277 The `--thumb-entry' switch is a duplicate of the generic `--entry' 5278 switch, in that it sets the program's starting address. But it also 5279 sets the bottom bit of the address, so that it can be branched to using 5280 a BX instruction, and the program will start executing in Thumb mode 5281 straight away. 5282 5283 The `--use-nul-prefixed-import-tables' switch is specifying, that 5284 the import tables idata4 and idata5 have to be generated with a zero 5285 element prefix for import libraries. This is the old style to generate 5286 import tables. By default this option is turned off. 5287 5288 The `--be8' switch instructs `ld' to generate BE8 format 5289 executables. This option is only valid when linking big-endian objects. 5290 The resulting image will contain big-endian data and little-endian code. 5291 5292 The `R_ARM_TARGET1' relocation is typically used for entries in the 5293 `.init_array' section. It is interpreted as either `R_ARM_REL32' or 5294 `R_ARM_ABS32', depending on the target. The `--target1-rel' and 5295 `--target1-abs' switches override the default. 5296 5297 The `--target2=type' switch overrides the default definition of the 5298 `R_ARM_TARGET2' relocation. Valid values for `type', their meanings, 5299 and target defaults are as follows: 5300 `rel' 5301 `R_ARM_REL32' (arm*-*-elf, arm*-*-eabi) 5302 5303 `abs' 5304 `R_ARM_ABS32' (arm*-*-symbianelf) 5305 5306 `got-rel' 5307 `R_ARM_GOT_PREL' (arm*-*-linux, arm*-*-*bsd) 5308 5309 The `R_ARM_V4BX' relocation (defined by the ARM AAELF specification) 5310 enables objects compiled for the ARMv4 architecture to be 5311 interworking-safe when linked with other objects compiled for ARMv4t, 5312 but also allows pure ARMv4 binaries to be built from the same ARMv4 5313 objects. 5314 5315 In the latter case, the switch `--fix-v4bx' must be passed to the 5316 linker, which causes v4t `BX rM' instructions to be rewritten as `MOV 5317 PC,rM', since v4 processors do not have a `BX' instruction. 5318 5319 In the former case, the switch should not be used, and `R_ARM_V4BX' 5320 relocations are ignored. 5321 5322 Replace `BX rM' instructions identified by `R_ARM_V4BX' relocations 5323 with a branch to the following veneer: 5324 5325 TST rM, #1 5326 MOVEQ PC, rM 5327 BX Rn 5328 5329 This allows generation of libraries/applications that work on ARMv4 5330 cores and are still interworking safe. Note that the above veneer 5331 clobbers the condition flags, so may cause incorrect program behavior 5332 in rare cases. 5333 5334 The `--use-blx' switch enables the linker to use ARM/Thumb BLX 5335 instructions (available on ARMv5t and above) in various situations. 5336 Currently it is used to perform calls via the PLT from Thumb code using 5337 BLX rather than using BX and a mode-switching stub before each PLT 5338 entry. This should lead to such calls executing slightly faster. 5339 5340 This option is enabled implicitly for SymbianOS, so there is no need 5341 to specify it if you are using that target. 5342 5343 The `--vfp11-denorm-fix' switch enables a link-time workaround for a 5344 bug in certain VFP11 coprocessor hardware, which sometimes allows 5345 instructions with denorm operands (which must be handled by support 5346 code) to have those operands overwritten by subsequent instructions 5347 before the support code can read the intended values. 5348 5349 The bug may be avoided in scalar mode if you allow at least one 5350 intervening instruction between a VFP11 instruction which uses a 5351 register and another instruction which writes to the same register, or 5352 at least two intervening instructions if vector mode is in use. The bug 5353 only affects full-compliance floating-point mode: you do not need this 5354 workaround if you are using "runfast" mode. Please contact ARM for 5355 further details. 5356 5357 If you know you are using buggy VFP11 hardware, you can enable this 5358 workaround by specifying the linker option `--vfp-denorm-fix=scalar' if 5359 you are using the VFP11 scalar mode only, or `--vfp-denorm-fix=vector' 5360 if you are using vector mode (the latter also works for scalar code). 5361 The default is `--vfp-denorm-fix=none'. 5362 5363 If the workaround is enabled, instructions are scanned for 5364 potentially-troublesome sequences, and a veneer is created for each 5365 such sequence which may trigger the erratum. The veneer consists of the 5366 first instruction of the sequence and a branch back to the subsequent 5367 instruction. The original instruction is then replaced with a branch to 5368 the veneer. The extra cycles required to call and return from the veneer 5369 are sufficient to avoid the erratum in both the scalar and vector cases. 5370 5371 The `--fix-arm1176' switch enables a link-time workaround for an 5372 erratum in certain ARM1176 processors. The workaround is enabled by 5373 default if you are targeting ARM v6 (excluding ARM v6T2) or earlier. 5374 It can be disabled unconditionally by specifying `--no-fix-arm1176'. 5375 5376 Further information is available in the "ARM1176JZ-S and ARM1176JZF-S 5377 Programmer Advice Notice" available on the ARM documentation website at: 5378 http://infocenter.arm.com/. 5379 5380 The `--no-enum-size-warning' switch prevents the linker from warning 5381 when linking object files that specify incompatible EABI enumeration 5382 size attributes. For example, with this switch enabled, linking of an 5383 object file using 32-bit enumeration values with another using 5384 enumeration values fitted into the smallest possible space will not be 5385 diagnosed. 5386 5387 The `--no-wchar-size-warning' switch prevents the linker from 5388 warning when linking object files that specify incompatible EABI 5389 `wchar_t' size attributes. For example, with this switch enabled, 5390 linking of an object file using 32-bit `wchar_t' values with another 5391 using 16-bit `wchar_t' values will not be diagnosed. 5392 5393 The `--pic-veneer' switch makes the linker use PIC sequences for 5394 ARM/Thumb interworking veneers, even if the rest of the binary is not 5395 PIC. This avoids problems on uClinux targets where `--emit-relocs' is 5396 used to generate relocatable binaries. 5397 5398 The linker will automatically generate and insert small sequences of 5399 code into a linked ARM ELF executable whenever an attempt is made to 5400 perform a function call to a symbol that is too far away. The 5401 placement of these sequences of instructions - called stubs - is 5402 controlled by the command line option `--stub-group-size=N'. The 5403 placement is important because a poor choice can create a need for 5404 duplicate stubs, increasing the code size. The linker will try to 5405 group stubs together in order to reduce interruptions to the flow of 5406 code, but it needs guidance as to how big these groups should be and 5407 where they should be placed. 5408 5409 The value of `N', the parameter to the `--stub-group-size=' option 5410 controls where the stub groups are placed. If it is negative then all 5411 stubs are placed after the first branch that needs them. If it is 5412 positive then the stubs can be placed either before or after the 5413 branches that need them. If the value of `N' is 1 (either +1 or -1) 5414 then the linker will choose exactly where to place groups of stubs, 5415 using its built in heuristics. A value of `N' greater than 1 (or 5416 smaller than -1) tells the linker that a single group of stubs can 5417 service at most `N' bytes from the input sections. 5418 5419 The default, if `--stub-group-size=' is not specified, is `N = +1'. 5420 5421 Farcalls stubs insertion is fully supported for the ARM-EABI target 5422 only, because it relies on object files properties not present 5423 otherwise. 5424 5425 The `--fix-cortex-a8' switch enables a link-time workaround for an 5426 erratum in certain Cortex-A8 processors. The workaround is enabled by 5427 default if you are targeting the ARM v7-A architecture profile. It can 5428 be enabled otherwise by specifying `--fix-cortex-a8', or disabled 5429 unconditionally by specifying `--no-fix-cortex-a8'. 5430 5431 The erratum only affects Thumb-2 code. Please contact ARM for 5432 further details. 5433 5434 The `--fix-cortex-a53-835769' switch enables a link-time workaround 5435 for erratum 835769 present on certain early revisions of Cortex-A53 5436 processors. The workaround is disabled by default. It can be enabled 5437 by specifying `--fix-cortex-a53-835769', or disabled unconditionally by 5438 specifying `--no-fix-cortex-a53-835769'. 5439 5440 Please contact ARM for further details. 5441 5442 The `--no-merge-exidx-entries' switch disables the merging of 5443 adjacent exidx entries in debuginfo. 5444 5445 The `--long-plt' option enables the use of 16 byte PLT entries which 5446 support up to 4Gb of code. The default is to use 12 byte PLT entries 5447 which only support 512Mb of code. 5448 5449 5450 File: ld.info, Node: HPPA ELF32, Next: M68K, Prev: ARM, Up: Machine Dependent 5451 5452 4.5 `ld' and HPPA 32-bit ELF Support 5453 ==================================== 5454 5455 When generating a shared library, `ld' will by default generate import 5456 stubs suitable for use with a single sub-space application. The 5457 `--multi-subspace' switch causes `ld' to generate export stubs, and 5458 different (larger) import stubs suitable for use with multiple 5459 sub-spaces. 5460 5461 Long branch stubs and import/export stubs are placed by `ld' in stub 5462 sections located between groups of input sections. `--stub-group-size' 5463 specifies the maximum size of a group of input sections handled by one 5464 stub section. Since branch offsets are signed, a stub section may 5465 serve two groups of input sections, one group before the stub section, 5466 and one group after it. However, when using conditional branches that 5467 require stubs, it may be better (for branch prediction) that stub 5468 sections only serve one group of input sections. A negative value for 5469 `N' chooses this scheme, ensuring that branches to stubs always use a 5470 negative offset. Two special values of `N' are recognized, `1' and 5471 `-1'. These both instruct `ld' to automatically size input section 5472 groups for the branch types detected, with the same behaviour regarding 5473 stub placement as other positive or negative values of `N' respectively. 5474 5475 Note that `--stub-group-size' does not split input sections. A 5476 single input section larger than the group size specified will of course 5477 create a larger group (of one section). If input sections are too 5478 large, it may not be possible for a branch to reach its stub. 5479 5480 5481 File: ld.info, Node: M68K, Next: MIPS, Prev: HPPA ELF32, Up: Machine Dependent 5482 5483 4.6 `ld' and the Motorola 68K family 5484 ==================================== 5485 5486 The `--got=TYPE' option lets you choose the GOT generation scheme. The 5487 choices are `single', `negative', `multigot' and `target'. When 5488 `target' is selected the linker chooses the default GOT generation 5489 scheme for the current target. `single' tells the linker to generate a 5490 single GOT with entries only at non-negative offsets. `negative' 5491 instructs the linker to generate a single GOT with entries at both 5492 negative and positive offsets. Not all environments support such GOTs. 5493 `multigot' allows the linker to generate several GOTs in the output 5494 file. All GOT references from a single input object file access the 5495 same GOT, but references from different input object files might access 5496 different GOTs. Not all environments support such GOTs. 5497 5498 5499 File: ld.info, Node: MIPS, Next: MMIX, Prev: M68K, Up: Machine Dependent 5500 5501 4.7 `ld' and the MIPS family 5502 ============================ 5503 5504 The `--insn32' and `--no-insn32' options control the choice of 5505 microMIPS instructions used in code generated by the linker, such as 5506 that in the PLT or lazy binding stubs, or in relaxation. If `--insn32' 5507 is used, then the linker only uses 32-bit instruction encodings. By 5508 default or if `--no-insn32' is used, all instruction encodings are used, 5509 including 16-bit ones where possible. 5510 5511 5512 File: ld.info, Node: MMIX, Next: MSP430, Prev: MIPS, Up: Machine Dependent 5513 5514 4.8 `ld' and MMIX 5515 ================= 5516 5517 For MMIX, there is a choice of generating `ELF' object files or `mmo' 5518 object files when linking. The simulator `mmix' understands the `mmo' 5519 format. The binutils `objcopy' utility can translate between the two 5520 formats. 5521 5522 There is one special section, the `.MMIX.reg_contents' section. 5523 Contents in this section is assumed to correspond to that of global 5524 registers, and symbols referring to it are translated to special 5525 symbols, equal to registers. In a final link, the start address of the 5526 `.MMIX.reg_contents' section corresponds to the first allocated global 5527 register multiplied by 8. Register `$255' is not included in this 5528 section; it is always set to the program entry, which is at the symbol 5529 `Main' for `mmo' files. 5530 5531 Global symbols with the prefix `__.MMIX.start.', for example 5532 `__.MMIX.start..text' and `__.MMIX.start..data' are special. The 5533 default linker script uses these to set the default start address of a 5534 section. 5535 5536 Initial and trailing multiples of zero-valued 32-bit words in a 5537 section, are left out from an mmo file. 5538 5539 5540 File: ld.info, Node: MSP430, Next: NDS32, Prev: MMIX, Up: Machine Dependent 5541 5542 4.9 `ld' and MSP430 5543 =================== 5544 5545 For the MSP430 it is possible to select the MPU architecture. The flag 5546 `-m [mpu type]' will select an appropriate linker script for selected 5547 MPU type. (To get a list of known MPUs just pass `-m help' option to 5548 the linker). 5549 5550 The linker will recognize some extra sections which are MSP430 5551 specific: 5552 5553 ``.vectors'' 5554 Defines a portion of ROM where interrupt vectors located. 5555 5556 ``.bootloader'' 5557 Defines the bootloader portion of the ROM (if applicable). Any 5558 code in this section will be uploaded to the MPU. 5559 5560 ``.infomem'' 5561 Defines an information memory section (if applicable). Any code in 5562 this section will be uploaded to the MPU. 5563 5564 ``.infomemnobits'' 5565 This is the same as the `.infomem' section except that any code in 5566 this section will not be uploaded to the MPU. 5567 5568 ``.noinit'' 5569 Denotes a portion of RAM located above `.bss' section. 5570 5571 The last two sections are used by gcc. 5572 5573 5574 File: ld.info, Node: NDS32, Next: Nios II, Prev: MSP430, Up: Machine Dependent 5575 5576 4.10 `ld' and NDS32 5577 =================== 5578 5579 For NDS32, there are some options to select relaxation behavior. The 5580 linker relaxes objects according to these options. 5581 5582 ``--m[no-]fp-as-gp'' 5583 Disable/enable fp-as-gp relaxation. 5584 5585 ``--mexport-symbols=FILE'' 5586 Exporting symbols and their address into FILE as linker script. 5587 5588 ``--m[no-]ex9'' 5589 Disable/enable link-time EX9 relaxation. 5590 5591 ``--mexport-ex9=FILE'' 5592 Export the EX9 table after linking. 5593 5594 ``--mimport-ex9=FILE'' 5595 Import the Ex9 table for EX9 relaxation. 5596 5597 ``--mupdate-ex9'' 5598 Update the existing EX9 table. 5599 5600 ``--mex9-limit=NUM'' 5601 Maximum number of entries in the ex9 table. 5602 5603 ``--mex9-loop-aware'' 5604 Avoid generating the EX9 instruction inside the loop. 5605 5606 ``--m[no-]ifc'' 5607 Disable/enable the link-time IFC optimization. 5608 5609 ``--mifc-loop-aware'' 5610 Avoid generating the IFC instruction inside the loop. 5611 5612 5613 File: ld.info, Node: Nios II, Next: PowerPC ELF32, Prev: NDS32, Up: Machine Dependent 5614 5615 4.11 `ld' and the Altera Nios II 5616 ================================ 5617 5618 Call and immediate jump instructions on Nios II processors are limited 5619 to transferring control to addresses in the same 256MB memory segment, 5620 which may result in `ld' giving `relocation truncated to fit' errors 5621 with very large programs. The command-line option `--relax' enables 5622 the generation of trampolines that can access the entire 32-bit address 5623 space for calls outside the normal `call' and `jmpi' address range. 5624 These trampolines are inserted at section boundaries, so may not 5625 themselves be reachable if an input section and its associated call 5626 trampolines are larger than 256MB. 5627 5628 The `--relax' option is enabled by default unless `-r' is also 5629 specified. You can disable trampoline generation by using the 5630 `--no-relax' linker option. You can also disable this optimization 5631 locally by using the `set .noat' directive in assembly-language source 5632 files, as the linker-inserted trampolines use the `at' register as a 5633 temporary. 5634 5635 Note that the linker `--relax' option is independent of assembler 5636 relaxation options, and that using the GNU assembler's `-relax-all' 5637 option interferes with the linker's more selective call instruction 5638 relaxation. 5639 5640 5641 File: ld.info, Node: PowerPC ELF32, Next: PowerPC64 ELF64, Prev: Nios II, Up: Machine Dependent 5642 5643 4.12 `ld' and PowerPC 32-bit ELF Support 5644 ======================================== 5645 5646 Branches on PowerPC processors are limited to a signed 26-bit 5647 displacement, which may result in `ld' giving `relocation truncated to 5648 fit' errors with very large programs. `--relax' enables the generation 5649 of trampolines that can access the entire 32-bit address space. These 5650 trampolines are inserted at section boundaries, so may not themselves 5651 be reachable if an input section exceeds 33M in size. You may combine 5652 `-r' and `--relax' to add trampolines in a partial link. In that case 5653 both branches to undefined symbols and inter-section branches are also 5654 considered potentially out of range, and trampolines inserted. 5655 5656 `--bss-plt' 5657 Current PowerPC GCC accepts a `-msecure-plt' option that generates 5658 code capable of using a newer PLT and GOT layout that has the 5659 security advantage of no executable section ever needing to be 5660 writable and no writable section ever being executable. PowerPC 5661 `ld' will generate this layout, including stubs to access the PLT, 5662 if all input files (including startup and static libraries) were 5663 compiled with `-msecure-plt'. `--bss-plt' forces the old BSS PLT 5664 (and GOT layout) which can give slightly better performance. 5665 5666 `--secure-plt' 5667 `ld' will use the new PLT and GOT layout if it is linking new 5668 `-fpic' or `-fPIC' code, but does not do so automatically when 5669 linking non-PIC code. This option requests the new PLT and GOT 5670 layout. A warning will be given if some object file requires the 5671 old style BSS PLT. 5672 5673 `--sdata-got' 5674 The new secure PLT and GOT are placed differently relative to other 5675 sections compared to older BSS PLT and GOT placement. The 5676 location of `.plt' must change because the new secure PLT is an 5677 initialized section while the old PLT is uninitialized. The 5678 reason for the `.got' change is more subtle: The new placement 5679 allows `.got' to be read-only in applications linked with `-z 5680 relro -z now'. However, this placement means that `.sdata' cannot 5681 always be used in shared libraries, because the PowerPC ABI 5682 accesses `.sdata' in shared libraries from the GOT pointer. 5683 `--sdata-got' forces the old GOT placement. PowerPC GCC doesn't 5684 use `.sdata' in shared libraries, so this option is really only 5685 useful for other compilers that may do so. 5686 5687 `--emit-stub-syms' 5688 This option causes `ld' to label linker stubs with a local symbol 5689 that encodes the stub type and destination. 5690 5691 `--no-tls-optimize' 5692 PowerPC `ld' normally performs some optimization of code sequences 5693 used to access Thread-Local Storage. Use this option to disable 5694 the optimization. 5695 5696 5697 File: ld.info, Node: PowerPC64 ELF64, Next: SPU ELF, Prev: PowerPC ELF32, Up: Machine Dependent 5698 5699 4.13 `ld' and PowerPC64 64-bit ELF Support 5700 ========================================== 5701 5702 `--stub-group-size' 5703 Long branch stubs, PLT call stubs and TOC adjusting stubs are 5704 placed by `ld' in stub sections located between groups of input 5705 sections. `--stub-group-size' specifies the maximum size of a 5706 group of input sections handled by one stub section. Since branch 5707 offsets are signed, a stub section may serve two groups of input 5708 sections, one group before the stub section, and one group after 5709 it. However, when using conditional branches that require stubs, 5710 it may be better (for branch prediction) that stub sections only 5711 serve one group of input sections. A negative value for `N' 5712 chooses this scheme, ensuring that branches to stubs always use a 5713 negative offset. Two special values of `N' are recognized, `1' 5714 and `-1'. These both instruct `ld' to automatically size input 5715 section groups for the branch types detected, with the same 5716 behaviour regarding stub placement as other positive or negative 5717 values of `N' respectively. 5718 5719 Note that `--stub-group-size' does not split input sections. A 5720 single input section larger than the group size specified will of 5721 course create a larger group (of one section). If input sections 5722 are too large, it may not be possible for a branch to reach its 5723 stub. 5724 5725 `--emit-stub-syms' 5726 This option causes `ld' to label linker stubs with a local symbol 5727 that encodes the stub type and destination. 5728 5729 `--dotsyms, --no-dotsyms' 5730 These two options control how `ld' interprets version patterns in 5731 a version script. Older PowerPC64 compilers emitted both a 5732 function descriptor symbol with the same name as the function, and 5733 a code entry symbol with the name prefixed by a dot (`.'). To 5734 properly version a function `foo', the version script thus needs 5735 to control both `foo' and `.foo'. The option `--dotsyms', on by 5736 default, automatically adds the required dot-prefixed patterns. 5737 Use `--no-dotsyms' to disable this feature. 5738 5739 `--no-tls-optimize' 5740 PowerPC64 `ld' normally performs some optimization of code 5741 sequences used to access Thread-Local Storage. Use this option to 5742 disable the optimization. 5743 5744 `--no-opd-optimize' 5745 PowerPC64 `ld' normally removes `.opd' section entries 5746 corresponding to deleted link-once functions, or functions removed 5747 by the action of `--gc-sections' or linker script `/DISCARD/'. 5748 Use this option to disable `.opd' optimization. 5749 5750 `--non-overlapping-opd' 5751 Some PowerPC64 compilers have an option to generate compressed 5752 `.opd' entries spaced 16 bytes apart, overlapping the third word, 5753 the static chain pointer (unused in C) with the first word of the 5754 next entry. This option expands such entries to the full 24 bytes. 5755 5756 `--no-toc-optimize' 5757 PowerPC64 `ld' normally removes unused `.toc' section entries. 5758 Such entries are detected by examining relocations that reference 5759 the TOC in code sections. A reloc in a deleted code section marks 5760 a TOC word as unneeded, while a reloc in a kept code section marks 5761 a TOC word as needed. Since the TOC may reference itself, TOC 5762 relocs are also examined. TOC words marked as both needed and 5763 unneeded will of course be kept. TOC words without any referencing 5764 reloc are assumed to be part of a multi-word entry, and are kept or 5765 discarded as per the nearest marked preceding word. This works 5766 reliably for compiler generated code, but may be incorrect if 5767 assembly code is used to insert TOC entries. Use this option to 5768 disable the optimization. 5769 5770 `--no-multi-toc' 5771 If given any toc option besides `-mcmodel=medium' or 5772 `-mcmodel=large', PowerPC64 GCC generates code for a TOC model 5773 where TOC entries are accessed with a 16-bit offset from r2. This 5774 limits the total TOC size to 64K. PowerPC64 `ld' extends this 5775 limit by grouping code sections such that each group uses less 5776 than 64K for its TOC entries, then inserts r2 adjusting stubs 5777 between inter-group calls. `ld' does not split apart input 5778 sections, so cannot help if a single input file has a `.toc' 5779 section that exceeds 64K, most likely from linking multiple files 5780 with `ld -r'. Use this option to turn off this feature. 5781 5782 `--no-toc-sort' 5783 By default, `ld' sorts TOC sections so that those whose file 5784 happens to have a section called `.init' or `.fini' are placed 5785 first, followed by TOC sections referenced by code generated with 5786 PowerPC64 gcc's `-mcmodel=small', and lastly TOC sections 5787 referenced only by code generated with PowerPC64 gcc's 5788 `-mcmodel=medium' or `-mcmodel=large' options. Doing this results 5789 in better TOC grouping for multi-TOC. Use this option to turn off 5790 this feature. 5791 5792 `--plt-align' 5793 `--no-plt-align' 5794 Use these options to control whether individual PLT call stubs are 5795 padded so that they don't cross a 32-byte boundary, or to the 5796 specified power of two boundary when using `--plt-align='. Note 5797 that this isn't alignment in the usual sense. By default PLT call 5798 stubs are packed tightly. 5799 5800 `--plt-static-chain' 5801 `--no-plt-static-chain' 5802 Use these options to control whether PLT call stubs load the static 5803 chain pointer (r11). `ld' defaults to not loading the static 5804 chain since there is never any need to do so on a PLT call. 5805 5806 `--plt-thread-safe' 5807 `--no-thread-safe' 5808 With power7's weakly ordered memory model, it is possible when 5809 using lazy binding for ld.so to update a plt entry in one thread 5810 and have another thread see the individual plt entry words update 5811 in the wrong order, despite ld.so carefully writing in the correct 5812 order and using memory write barriers. To avoid this we need some 5813 sort of read barrier in the call stub, or use LD_BIND_NOW=1. By 5814 default, `ld' looks for calls to commonly used functions that 5815 create threads, and if seen, adds the necessary barriers. Use 5816 these options to change the default behaviour. 5817 5818 5819 File: ld.info, Node: SPU ELF, Next: TI COFF, Prev: PowerPC64 ELF64, Up: Machine Dependent 5820 5821 4.14 `ld' and SPU ELF Support 5822 ============================= 5823 5824 `--plugin' 5825 This option marks an executable as a PIC plugin module. 5826 5827 `--no-overlays' 5828 Normally, `ld' recognizes calls to functions within overlay 5829 regions, and redirects such calls to an overlay manager via a stub. 5830 `ld' also provides a built-in overlay manager. This option turns 5831 off all this special overlay handling. 5832 5833 `--emit-stub-syms' 5834 This option causes `ld' to label overlay stubs with a local symbol 5835 that encodes the stub type and destination. 5836 5837 `--extra-overlay-stubs' 5838 This option causes `ld' to add overlay call stubs on all function 5839 calls out of overlay regions. Normally stubs are not added on 5840 calls to non-overlay regions. 5841 5842 `--local-store=lo:hi' 5843 `ld' usually checks that a final executable for SPU fits in the 5844 address range 0 to 256k. This option may be used to change the 5845 range. Disable the check entirely with `--local-store=0:0'. 5846 5847 `--stack-analysis' 5848 SPU local store space is limited. Over-allocation of stack space 5849 unnecessarily limits space available for code and data, while 5850 under-allocation results in runtime failures. If given this 5851 option, `ld' will provide an estimate of maximum stack usage. 5852 `ld' does this by examining symbols in code sections to determine 5853 the extents of functions, and looking at function prologues for 5854 stack adjusting instructions. A call-graph is created by looking 5855 for relocations on branch instructions. The graph is then searched 5856 for the maximum stack usage path. Note that this analysis does not 5857 find calls made via function pointers, and does not handle 5858 recursion and other cycles in the call graph. Stack usage may be 5859 under-estimated if your code makes such calls. Also, stack usage 5860 for dynamic allocation, e.g. alloca, will not be detected. If a 5861 link map is requested, detailed information about each function's 5862 stack usage and calls will be given. 5863 5864 `--emit-stack-syms' 5865 This option, if given along with `--stack-analysis' will result in 5866 `ld' emitting stack sizing symbols for each function. These take 5867 the form `__stack_<function_name>' for global functions, and 5868 `__stack_<number>_<function_name>' for static functions. 5869 `<number>' is the section id in hex. The value of such symbols is 5870 the stack requirement for the corresponding function. The symbol 5871 size will be zero, type `STT_NOTYPE', binding `STB_LOCAL', and 5872 section `SHN_ABS'. 5873 5874 5875 File: ld.info, Node: TI COFF, Next: WIN32, Prev: SPU ELF, Up: Machine Dependent 5876 5877 4.15 `ld''s Support for Various TI COFF Versions 5878 ================================================ 5879 5880 The `--format' switch allows selection of one of the various TI COFF 5881 versions. The latest of this writing is 2; versions 0 and 1 are also 5882 supported. The TI COFF versions also vary in header byte-order format; 5883 `ld' will read any version or byte order, but the output header format 5884 depends on the default specified by the specific target. 5885 5886 5887 File: ld.info, Node: WIN32, Next: Xtensa, Prev: TI COFF, Up: Machine Dependent 5888 5889 4.16 `ld' and WIN32 (cygwin/mingw) 5890 ================================== 5891 5892 This section describes some of the win32 specific `ld' issues. See 5893 *Note Command Line Options: Options. for detailed description of the 5894 command line options mentioned here. 5895 5896 _import libraries_ 5897 The standard Windows linker creates and uses so-called import 5898 libraries, which contains information for linking to dll's. They 5899 are regular static archives and are handled as any other static 5900 archive. The cygwin and mingw ports of `ld' have specific support 5901 for creating such libraries provided with the `--out-implib' 5902 command line option. 5903 5904 _exporting DLL symbols_ 5905 The cygwin/mingw `ld' has several ways to export symbols for dll's. 5906 5907 _using auto-export functionality_ 5908 By default `ld' exports symbols with the auto-export 5909 functionality, which is controlled by the following command 5910 line options: 5911 5912 * -export-all-symbols [This is the default] 5913 5914 * -exclude-symbols 5915 5916 * -exclude-libs 5917 5918 * -exclude-modules-for-implib 5919 5920 * -version-script 5921 5922 When auto-export is in operation, `ld' will export all the 5923 non-local (global and common) symbols it finds in a DLL, with 5924 the exception of a few symbols known to belong to the 5925 system's runtime and libraries. As it will often not be 5926 desirable to export all of a DLL's symbols, which may include 5927 private functions that are not part of any public interface, 5928 the command-line options listed above may be used to filter 5929 symbols out from the list for exporting. The `--output-def' 5930 option can be used in order to see the final list of exported 5931 symbols with all exclusions taken into effect. 5932 5933 If `--export-all-symbols' is not given explicitly on the 5934 command line, then the default auto-export behavior will be 5935 _disabled_ if either of the following are true: 5936 5937 * A DEF file is used. 5938 5939 * Any symbol in any object file was marked with the 5940 __declspec(dllexport) attribute. 5941 5942 _using a DEF file_ 5943 Another way of exporting symbols is using a DEF file. A DEF 5944 file is an ASCII file containing definitions of symbols which 5945 should be exported when a dll is created. Usually it is 5946 named `<dll name>.def' and is added as any other object file 5947 to the linker's command line. The file's name must end in 5948 `.def' or `.DEF'. 5949 5950 gcc -o <output> <objectfiles> <dll name>.def 5951 5952 Using a DEF file turns off the normal auto-export behavior, 5953 unless the `--export-all-symbols' option is also used. 5954 5955 Here is an example of a DEF file for a shared library called 5956 `xyz.dll': 5957 5958 LIBRARY "xyz.dll" BASE=0x20000000 5959 5960 EXPORTS 5961 foo 5962 bar 5963 _bar = bar 5964 another_foo = abc.dll.afoo 5965 var1 DATA 5966 doo = foo == foo2 5967 eoo DATA == var1 5968 5969 This example defines a DLL with a non-default base address 5970 and seven symbols in the export table. The third exported 5971 symbol `_bar' is an alias for the second. The fourth symbol, 5972 `another_foo' is resolved by "forwarding" to another module 5973 and treating it as an alias for `afoo' exported from the DLL 5974 `abc.dll'. The final symbol `var1' is declared to be a data 5975 object. The `doo' symbol in export library is an alias of 5976 `foo', which gets the string name in export table `foo2'. The 5977 `eoo' symbol is an data export symbol, which gets in export 5978 table the name `var1'. 5979 5980 The optional `LIBRARY <name>' command indicates the _internal_ 5981 name of the output DLL. If `<name>' does not include a suffix, 5982 the default library suffix, `.DLL' is appended. 5983 5984 When the .DEF file is used to build an application, rather 5985 than a library, the `NAME <name>' command should be used 5986 instead of `LIBRARY'. If `<name>' does not include a suffix, 5987 the default executable suffix, `.EXE' is appended. 5988 5989 With either `LIBRARY <name>' or `NAME <name>' the optional 5990 specification `BASE = <number>' may be used to specify a 5991 non-default base address for the image. 5992 5993 If neither `LIBRARY <name>' nor `NAME <name>' is specified, 5994 or they specify an empty string, the internal name is the 5995 same as the filename specified on the command line. 5996 5997 The complete specification of an export symbol is: 5998 5999 EXPORTS 6000 ( ( ( <name1> [ = <name2> ] ) 6001 | ( <name1> = <module-name> . <external-name>)) 6002 [ @ <integer> ] [NONAME] [DATA] [CONSTANT] [PRIVATE] [== <name3>] ) * 6003 6004 Declares `<name1>' as an exported symbol from the DLL, or 6005 declares `<name1>' as an exported alias for `<name2>'; or 6006 declares `<name1>' as a "forward" alias for the symbol 6007 `<external-name>' in the DLL `<module-name>'. Optionally, 6008 the symbol may be exported by the specified ordinal 6009 `<integer>' alias. The optional `<name3>' is the to be used 6010 string in import/export table for the symbol. 6011 6012 The optional keywords that follow the declaration indicate: 6013 6014 `NONAME': Do not put the symbol name in the DLL's export 6015 table. It will still be exported by its ordinal alias 6016 (either the value specified by the .def specification or, 6017 otherwise, the value assigned by the linker). The symbol 6018 name, however, does remain visible in the import library (if 6019 any), unless `PRIVATE' is also specified. 6020 6021 `DATA': The symbol is a variable or object, rather than a 6022 function. The import lib will export only an indirect 6023 reference to `foo' as the symbol `_imp__foo' (ie, `foo' must 6024 be resolved as `*_imp__foo'). 6025 6026 `CONSTANT': Like `DATA', but put the undecorated `foo' as 6027 well as `_imp__foo' into the import library. Both refer to the 6028 read-only import address table's pointer to the variable, not 6029 to the variable itself. This can be dangerous. If the user 6030 code fails to add the `dllimport' attribute and also fails to 6031 explicitly add the extra indirection that the use of the 6032 attribute enforces, the application will behave unexpectedly. 6033 6034 `PRIVATE': Put the symbol in the DLL's export table, but do 6035 not put it into the static import library used to resolve 6036 imports at link time. The symbol can still be imported using 6037 the `LoadLibrary/GetProcAddress' API at runtime or by by 6038 using the GNU ld extension of linking directly to the DLL 6039 without an import library. 6040 6041 See ld/deffilep.y in the binutils sources for the full 6042 specification of other DEF file statements 6043 6044 While linking a shared dll, `ld' is able to create a DEF file 6045 with the `--output-def <file>' command line option. 6046 6047 _Using decorations_ 6048 Another way of marking symbols for export is to modify the 6049 source code itself, so that when building the DLL each symbol 6050 to be exported is declared as: 6051 6052 __declspec(dllexport) int a_variable 6053 __declspec(dllexport) void a_function(int with_args) 6054 6055 All such symbols will be exported from the DLL. If, however, 6056 any of the object files in the DLL contain symbols decorated 6057 in this way, then the normal auto-export behavior is 6058 disabled, unless the `--export-all-symbols' option is also 6059 used. 6060 6061 Note that object files that wish to access these symbols must 6062 _not_ decorate them with dllexport. Instead, they should use 6063 dllimport, instead: 6064 6065 __declspec(dllimport) int a_variable 6066 __declspec(dllimport) void a_function(int with_args) 6067 6068 This complicates the structure of library header files, 6069 because when included by the library itself the header must 6070 declare the variables and functions as dllexport, but when 6071 included by client code the header must declare them as 6072 dllimport. There are a number of idioms that are typically 6073 used to do this; often client code can omit the __declspec() 6074 declaration completely. See `--enable-auto-import' and 6075 `automatic data imports' for more information. 6076 6077 _automatic data imports_ 6078 The standard Windows dll format supports data imports from dlls 6079 only by adding special decorations (dllimport/dllexport), which 6080 let the compiler produce specific assembler instructions to deal 6081 with this issue. This increases the effort necessary to port 6082 existing Un*x code to these platforms, especially for large c++ 6083 libraries and applications. The auto-import feature, which was 6084 initially provided by Paul Sokolovsky, allows one to omit the 6085 decorations to achieve a behavior that conforms to that on 6086 POSIX/Un*x platforms. This feature is enabled with the 6087 `--enable-auto-import' command-line option, although it is enabled 6088 by default on cygwin/mingw. The `--enable-auto-import' option 6089 itself now serves mainly to suppress any warnings that are 6090 ordinarily emitted when linked objects trigger the feature's use. 6091 6092 auto-import of variables does not always work flawlessly without 6093 additional assistance. Sometimes, you will see this message 6094 6095 "variable '<var>' can't be auto-imported. Please read the 6096 documentation for ld's `--enable-auto-import' for details." 6097 6098 The `--enable-auto-import' documentation explains why this error 6099 occurs, and several methods that can be used to overcome this 6100 difficulty. One of these methods is the _runtime pseudo-relocs_ 6101 feature, described below. 6102 6103 For complex variables imported from DLLs (such as structs or 6104 classes), object files typically contain a base address for the 6105 variable and an offset (_addend_) within the variable-to specify a 6106 particular field or public member, for instance. Unfortunately, 6107 the runtime loader used in win32 environments is incapable of 6108 fixing these references at runtime without the additional 6109 information supplied by dllimport/dllexport decorations. The 6110 standard auto-import feature described above is unable to resolve 6111 these references. 6112 6113 The `--enable-runtime-pseudo-relocs' switch allows these 6114 references to be resolved without error, while leaving the task of 6115 adjusting the references themselves (with their non-zero addends) 6116 to specialized code provided by the runtime environment. Recent 6117 versions of the cygwin and mingw environments and compilers 6118 provide this runtime support; older versions do not. However, the 6119 support is only necessary on the developer's platform; the 6120 compiled result will run without error on an older system. 6121 6122 `--enable-runtime-pseudo-relocs' is not the default; it must be 6123 explicitly enabled as needed. 6124 6125 _direct linking to a dll_ 6126 The cygwin/mingw ports of `ld' support the direct linking, 6127 including data symbols, to a dll without the usage of any import 6128 libraries. This is much faster and uses much less memory than 6129 does the traditional import library method, especially when 6130 linking large libraries or applications. When `ld' creates an 6131 import lib, each function or variable exported from the dll is 6132 stored in its own bfd, even though a single bfd could contain many 6133 exports. The overhead involved in storing, loading, and 6134 processing so many bfd's is quite large, and explains the 6135 tremendous time, memory, and storage needed to link against 6136 particularly large or complex libraries when using import libs. 6137 6138 Linking directly to a dll uses no extra command-line switches 6139 other than `-L' and `-l', because `ld' already searches for a 6140 number of names to match each library. All that is needed from 6141 the developer's perspective is an understanding of this search, in 6142 order to force ld to select the dll instead of an import library. 6143 6144 For instance, when ld is called with the argument `-lxxx' it will 6145 attempt to find, in the first directory of its search path, 6146 6147 libxxx.dll.a 6148 xxx.dll.a 6149 libxxx.a 6150 xxx.lib 6151 cygxxx.dll (*) 6152 libxxx.dll 6153 xxx.dll 6154 6155 before moving on to the next directory in the search path. 6156 6157 (*) Actually, this is not `cygxxx.dll' but in fact is 6158 `<prefix>xxx.dll', where `<prefix>' is set by the `ld' option 6159 `--dll-search-prefix=<prefix>'. In the case of cygwin, the 6160 standard gcc spec file includes `--dll-search-prefix=cyg', so in 6161 effect we actually search for `cygxxx.dll'. 6162 6163 Other win32-based unix environments, such as mingw or pw32, may 6164 use other `<prefix>'es, although at present only cygwin makes use 6165 of this feature. It was originally intended to help avoid name 6166 conflicts among dll's built for the various win32/un*x 6167 environments, so that (for example) two versions of a zlib dll 6168 could coexist on the same machine. 6169 6170 The generic cygwin/mingw path layout uses a `bin' directory for 6171 applications and dll's and a `lib' directory for the import 6172 libraries (using cygwin nomenclature): 6173 6174 bin/ 6175 cygxxx.dll 6176 lib/ 6177 libxxx.dll.a (in case of dll's) 6178 libxxx.a (in case of static archive) 6179 6180 Linking directly to a dll without using the import library can be 6181 done two ways: 6182 6183 1. Use the dll directly by adding the `bin' path to the link line 6184 gcc -Wl,-verbose -o a.exe -L../bin/ -lxxx 6185 6186 However, as the dll's often have version numbers appended to their 6187 names (`cygncurses-5.dll') this will often fail, unless one 6188 specifies `-L../bin -lncurses-5' to include the version. Import 6189 libs are generally not versioned, and do not have this difficulty. 6190 6191 2. Create a symbolic link from the dll to a file in the `lib' 6192 directory according to the above mentioned search pattern. This 6193 should be used to avoid unwanted changes in the tools needed for 6194 making the app/dll. 6195 6196 ln -s bin/cygxxx.dll lib/[cyg|lib|]xxx.dll[.a] 6197 6198 Then you can link without any make environment changes. 6199 6200 gcc -Wl,-verbose -o a.exe -L../lib/ -lxxx 6201 6202 This technique also avoids the version number problems, because 6203 the following is perfectly legal 6204 6205 bin/ 6206 cygxxx-5.dll 6207 lib/ 6208 libxxx.dll.a -> ../bin/cygxxx-5.dll 6209 6210 Linking directly to a dll without using an import lib will work 6211 even when auto-import features are exercised, and even when 6212 `--enable-runtime-pseudo-relocs' is used. 6213 6214 Given the improvements in speed and memory usage, one might 6215 justifiably wonder why import libraries are used at all. There 6216 are three reasons: 6217 6218 1. Until recently, the link-directly-to-dll functionality did _not_ 6219 work with auto-imported data. 6220 6221 2. Sometimes it is necessary to include pure static objects within 6222 the import library (which otherwise contains only bfd's for 6223 indirection symbols that point to the exports of a dll). Again, 6224 the import lib for the cygwin kernel makes use of this ability, 6225 and it is not possible to do this without an import lib. 6226 6227 3. Symbol aliases can only be resolved using an import lib. This 6228 is critical when linking against OS-supplied dll's (eg, the win32 6229 API) in which symbols are usually exported as undecorated aliases 6230 of their stdcall-decorated assembly names. 6231 6232 So, import libs are not going away. But the ability to replace 6233 true import libs with a simple symbolic link to (or a copy of) a 6234 dll, in many cases, is a useful addition to the suite of tools 6235 binutils makes available to the win32 developer. Given the 6236 massive improvements in memory requirements during linking, storage 6237 requirements, and linking speed, we expect that many developers 6238 will soon begin to use this feature whenever possible. 6239 6240 _symbol aliasing_ 6241 6242 _adding additional names_ 6243 Sometimes, it is useful to export symbols with additional 6244 names. A symbol `foo' will be exported as `foo', but it can 6245 also be exported as `_foo' by using special directives in the 6246 DEF file when creating the dll. This will affect also the 6247 optional created import library. Consider the following DEF 6248 file: 6249 6250 LIBRARY "xyz.dll" BASE=0x61000000 6251 6252 EXPORTS 6253 foo 6254 _foo = foo 6255 6256 The line `_foo = foo' maps the symbol `foo' to `_foo'. 6257 6258 Another method for creating a symbol alias is to create it in 6259 the source code using the "weak" attribute: 6260 6261 void foo () { /* Do something. */; } 6262 void _foo () __attribute__ ((weak, alias ("foo"))); 6263 6264 See the gcc manual for more information about attributes and 6265 weak symbols. 6266 6267 _renaming symbols_ 6268 Sometimes it is useful to rename exports. For instance, the 6269 cygwin kernel does this regularly. A symbol `_foo' can be 6270 exported as `foo' but not as `_foo' by using special 6271 directives in the DEF file. (This will also affect the import 6272 library, if it is created). In the following example: 6273 6274 LIBRARY "xyz.dll" BASE=0x61000000 6275 6276 EXPORTS 6277 _foo = foo 6278 6279 The line `_foo = foo' maps the exported symbol `foo' to 6280 `_foo'. 6281 6282 Note: using a DEF file disables the default auto-export behavior, 6283 unless the `--export-all-symbols' command line option is used. 6284 If, however, you are trying to rename symbols, then you should list 6285 _all_ desired exports in the DEF file, including the symbols that 6286 are not being renamed, and do _not_ use the `--export-all-symbols' 6287 option. If you list only the renamed symbols in the DEF file, and 6288 use `--export-all-symbols' to handle the other symbols, then the 6289 both the new names _and_ the original names for the renamed 6290 symbols will be exported. In effect, you'd be aliasing those 6291 symbols, not renaming them, which is probably not what you wanted. 6292 6293 _weak externals_ 6294 The Windows object format, PE, specifies a form of weak symbols 6295 called weak externals. When a weak symbol is linked and the 6296 symbol is not defined, the weak symbol becomes an alias for some 6297 other symbol. There are three variants of weak externals: 6298 * Definition is searched for in objects and libraries, 6299 historically called lazy externals. 6300 6301 * Definition is searched for only in other objects, not in 6302 libraries. This form is not presently implemented. 6303 6304 * No search; the symbol is an alias. This form is not presently 6305 implemented. 6306 As a GNU extension, weak symbols that do not specify an alternate 6307 symbol are supported. If the symbol is undefined when linking, 6308 the symbol uses a default value. 6309 6310 _aligned common symbols_ 6311 As a GNU extension to the PE file format, it is possible to 6312 specify the desired alignment for a common symbol. This 6313 information is conveyed from the assembler or compiler to the 6314 linker by means of GNU-specific commands carried in the object 6315 file's `.drectve' section, which are recognized by `ld' and 6316 respected when laying out the common symbols. Native tools will 6317 be able to process object files employing this GNU extension, but 6318 will fail to respect the alignment instructions, and may issue 6319 noisy warnings about unknown linker directives. 6320 6321 6322 6323 File: ld.info, Node: Xtensa, Prev: WIN32, Up: Machine Dependent 6324 6325 4.17 `ld' and Xtensa Processors 6326 =============================== 6327 6328 The default `ld' behavior for Xtensa processors is to interpret 6329 `SECTIONS' commands so that lists of explicitly named sections in a 6330 specification with a wildcard file will be interleaved when necessary to 6331 keep literal pools within the range of PC-relative load offsets. For 6332 example, with the command: 6333 6334 SECTIONS 6335 { 6336 .text : { 6337 *(.literal .text) 6338 } 6339 } 6340 6341 `ld' may interleave some of the `.literal' and `.text' sections from 6342 different object files to ensure that the literal pools are within the 6343 range of PC-relative load offsets. A valid interleaving might place 6344 the `.literal' sections from an initial group of files followed by the 6345 `.text' sections of that group of files. Then, the `.literal' sections 6346 from the rest of the files and the `.text' sections from the rest of 6347 the files would follow. 6348 6349 Relaxation is enabled by default for the Xtensa version of `ld' and 6350 provides two important link-time optimizations. The first optimization 6351 is to combine identical literal values to reduce code size. A redundant 6352 literal will be removed and all the `L32R' instructions that use it 6353 will be changed to reference an identical literal, as long as the 6354 location of the replacement literal is within the offset range of all 6355 the `L32R' instructions. The second optimization is to remove 6356 unnecessary overhead from assembler-generated "longcall" sequences of 6357 `L32R'/`CALLXN' when the target functions are within range of direct 6358 `CALLN' instructions. 6359 6360 For each of these cases where an indirect call sequence can be 6361 optimized to a direct call, the linker will change the `CALLXN' 6362 instruction to a `CALLN' instruction, remove the `L32R' instruction, 6363 and remove the literal referenced by the `L32R' instruction if it is 6364 not used for anything else. Removing the `L32R' instruction always 6365 reduces code size but can potentially hurt performance by changing the 6366 alignment of subsequent branch targets. By default, the linker will 6367 always preserve alignments, either by switching some instructions 6368 between 24-bit encodings and the equivalent density instructions or by 6369 inserting a no-op in place of the `L32R' instruction that was removed. 6370 If code size is more important than performance, the `--size-opt' 6371 option can be used to prevent the linker from widening density 6372 instructions or inserting no-ops, except in a few cases where no-ops 6373 are required for correctness. 6374 6375 The following Xtensa-specific command-line options can be used to 6376 control the linker: 6377 6378 `--size-opt' 6379 When optimizing indirect calls to direct calls, optimize for code 6380 size more than performance. With this option, the linker will not 6381 insert no-ops or widen density instructions to preserve branch 6382 target alignment. There may still be some cases where no-ops are 6383 required to preserve the correctness of the code. 6384 6385 6386 File: ld.info, Node: BFD, Next: Reporting Bugs, Prev: Machine Dependent, Up: Top 6387 6388 5 BFD 6389 ***** 6390 6391 The linker accesses object and archive files using the BFD libraries. 6392 These libraries allow the linker to use the same routines to operate on 6393 object files whatever the object file format. A different object file 6394 format can be supported simply by creating a new BFD back end and adding 6395 it to the library. To conserve runtime memory, however, the linker and 6396 associated tools are usually configured to support only a subset of the 6397 object file formats available. You can use `objdump -i' (*note 6398 objdump: (binutils.info)objdump.) to list all the formats available for 6399 your configuration. 6400 6401 As with most implementations, BFD is a compromise between several 6402 conflicting requirements. The major factor influencing BFD design was 6403 efficiency: any time used converting between formats is time which 6404 would not have been spent had BFD not been involved. This is partly 6405 offset by abstraction payback; since BFD simplifies applications and 6406 back ends, more time and care may be spent optimizing algorithms for a 6407 greater speed. 6408 6409 One minor artifact of the BFD solution which you should bear in mind 6410 is the potential for information loss. There are two places where 6411 useful information can be lost using the BFD mechanism: during 6412 conversion and during output. *Note BFD information loss::. 6413 6414 * Menu: 6415 6416 * BFD outline:: How it works: an outline of BFD 6417 6418 6419 File: ld.info, Node: BFD outline, Up: BFD 6420 6421 5.1 How It Works: An Outline of BFD 6422 =================================== 6423 6424 When an object file is opened, BFD subroutines automatically determine 6425 the format of the input object file. They then build a descriptor in 6426 memory with pointers to routines that will be used to access elements of 6427 the object file's data structures. 6428 6429 As different information from the object files is required, BFD 6430 reads from different sections of the file and processes them. For 6431 example, a very common operation for the linker is processing symbol 6432 tables. Each BFD back end provides a routine for converting between 6433 the object file's representation of symbols and an internal canonical 6434 format. When the linker asks for the symbol table of an object file, it 6435 calls through a memory pointer to the routine from the relevant BFD 6436 back end which reads and converts the table into a canonical form. The 6437 linker then operates upon the canonical form. When the link is finished 6438 and the linker writes the output file's symbol table, another BFD back 6439 end routine is called to take the newly created symbol table and 6440 convert it into the chosen output format. 6441 6442 * Menu: 6443 6444 * BFD information loss:: Information Loss 6445 * Canonical format:: The BFD canonical object-file format 6446 6447 6448 File: ld.info, Node: BFD information loss, Next: Canonical format, Up: BFD outline 6449 6450 5.1.1 Information Loss 6451 ---------------------- 6452 6453 _Information can be lost during output._ The output formats supported 6454 by BFD do not provide identical facilities, and information which can 6455 be described in one form has nowhere to go in another format. One 6456 example of this is alignment information in `b.out'. There is nowhere 6457 in an `a.out' format file to store alignment information on the 6458 contained data, so when a file is linked from `b.out' and an `a.out' 6459 image is produced, alignment information will not propagate to the 6460 output file. (The linker will still use the alignment information 6461 internally, so the link is performed correctly). 6462 6463 Another example is COFF section names. COFF files may contain an 6464 unlimited number of sections, each one with a textual section name. If 6465 the target of the link is a format which does not have many sections 6466 (e.g., `a.out') or has sections without names (e.g., the Oasys format), 6467 the link cannot be done simply. You can circumvent this problem by 6468 describing the desired input-to-output section mapping with the linker 6469 command language. 6470 6471 _Information can be lost during canonicalization._ The BFD internal 6472 canonical form of the external formats is not exhaustive; there are 6473 structures in input formats for which there is no direct representation 6474 internally. This means that the BFD back ends cannot maintain all 6475 possible data richness through the transformation between external to 6476 internal and back to external formats. 6477 6478 This limitation is only a problem when an application reads one 6479 format and writes another. Each BFD back end is responsible for 6480 maintaining as much data as possible, and the internal BFD canonical 6481 form has structures which are opaque to the BFD core, and exported only 6482 to the back ends. When a file is read in one format, the canonical form 6483 is generated for BFD and the application. At the same time, the back 6484 end saves away any information which may otherwise be lost. If the data 6485 is then written back in the same format, the back end routine will be 6486 able to use the canonical form provided by the BFD core as well as the 6487 information it prepared earlier. Since there is a great deal of 6488 commonality between back ends, there is no information lost when 6489 linking or copying big endian COFF to little endian COFF, or `a.out' to 6490 `b.out'. When a mixture of formats is linked, the information is only 6491 lost from the files whose format differs from the destination. 6492 6493 6494 File: ld.info, Node: Canonical format, Prev: BFD information loss, Up: BFD outline 6495 6496 5.1.2 The BFD canonical object-file format 6497 ------------------------------------------ 6498 6499 The greatest potential for loss of information occurs when there is the 6500 least overlap between the information provided by the source format, 6501 that stored by the canonical format, and that needed by the destination 6502 format. A brief description of the canonical form may help you 6503 understand which kinds of data you can count on preserving across 6504 conversions. 6505 6506 _files_ 6507 Information stored on a per-file basis includes target machine 6508 architecture, particular implementation format type, a demand 6509 pageable bit, and a write protected bit. Information like Unix 6510 magic numbers is not stored here--only the magic numbers' meaning, 6511 so a `ZMAGIC' file would have both the demand pageable bit and the 6512 write protected text bit set. The byte order of the target is 6513 stored on a per-file basis, so that big- and little-endian object 6514 files may be used with one another. 6515 6516 _sections_ 6517 Each section in the input file contains the name of the section, 6518 the section's original address in the object file, size and 6519 alignment information, various flags, and pointers into other BFD 6520 data structures. 6521 6522 _symbols_ 6523 Each symbol contains a pointer to the information for the object 6524 file which originally defined it, its name, its value, and various 6525 flag bits. When a BFD back end reads in a symbol table, it 6526 relocates all symbols to make them relative to the base of the 6527 section where they were defined. Doing this ensures that each 6528 symbol points to its containing section. Each symbol also has a 6529 varying amount of hidden private data for the BFD back end. Since 6530 the symbol points to the original file, the private data format 6531 for that symbol is accessible. `ld' can operate on a collection 6532 of symbols of wildly different formats without problems. 6533 6534 Normal global and simple local symbols are maintained on output, 6535 so an output file (no matter its format) will retain symbols 6536 pointing to functions and to global, static, and common variables. 6537 Some symbol information is not worth retaining; in `a.out', type 6538 information is stored in the symbol table as long symbol names. 6539 This information would be useless to most COFF debuggers; the 6540 linker has command line switches to allow users to throw it away. 6541 6542 There is one word of type information within the symbol, so if the 6543 format supports symbol type information within symbols (for 6544 example, COFF, IEEE, Oasys) and the type is simple enough to fit 6545 within one word (nearly everything but aggregates), the 6546 information will be preserved. 6547 6548 _relocation level_ 6549 Each canonical BFD relocation record contains a pointer to the 6550 symbol to relocate to, the offset of the data to relocate, the 6551 section the data is in, and a pointer to a relocation type 6552 descriptor. Relocation is performed by passing messages through 6553 the relocation type descriptor and the symbol pointer. Therefore, 6554 relocations can be performed on output data using a relocation 6555 method that is only available in one of the input formats. For 6556 instance, Oasys provides a byte relocation format. A relocation 6557 record requesting this relocation type would point indirectly to a 6558 routine to perform this, so the relocation may be performed on a 6559 byte being written to a 68k COFF file, even though 68k COFF has no 6560 such relocation type. 6561 6562 _line numbers_ 6563 Object formats can contain, for debugging purposes, some form of 6564 mapping between symbols, source line numbers, and addresses in the 6565 output file. These addresses have to be relocated along with the 6566 symbol information. Each symbol with an associated list of line 6567 number records points to the first record of the list. The head 6568 of a line number list consists of a pointer to the symbol, which 6569 allows finding out the address of the function whose line number 6570 is being described. The rest of the list is made up of pairs: 6571 offsets into the section and line numbers. Any format which can 6572 simply derive this information can pass it successfully between 6573 formats (COFF, IEEE and Oasys). 6574 6575 6576 File: ld.info, Node: Reporting Bugs, Next: MRI, Prev: BFD, Up: Top 6577 6578 6 Reporting Bugs 6579 **************** 6580 6581 Your bug reports play an essential role in making `ld' reliable. 6582 6583 Reporting a bug may help you by bringing a solution to your problem, 6584 or it may not. But in any case the principal function of a bug report 6585 is to help the entire community by making the next version of `ld' work 6586 better. Bug reports are your contribution to the maintenance of `ld'. 6587 6588 In order for a bug report to serve its purpose, you must include the 6589 information that enables us to fix the bug. 6590 6591 * Menu: 6592 6593 * Bug Criteria:: Have you found a bug? 6594 * Bug Reporting:: How to report bugs 6595 6596 6597 File: ld.info, Node: Bug Criteria, Next: Bug Reporting, Up: Reporting Bugs 6598 6599 6.1 Have You Found a Bug? 6600 ========================= 6601 6602 If you are not sure whether you have found a bug, here are some 6603 guidelines: 6604 6605 * If the linker gets a fatal signal, for any input whatever, that is 6606 a `ld' bug. Reliable linkers never crash. 6607 6608 * If `ld' produces an error message for valid input, that is a bug. 6609 6610 * If `ld' does not produce an error message for invalid input, that 6611 may be a bug. In the general case, the linker can not verify that 6612 object files are correct. 6613 6614 * If you are an experienced user of linkers, your suggestions for 6615 improvement of `ld' are welcome in any case. 6616 6617 6618 File: ld.info, Node: Bug Reporting, Prev: Bug Criteria, Up: Reporting Bugs 6619 6620 6.2 How to Report Bugs 6621 ====================== 6622 6623 A number of companies and individuals offer support for GNU products. 6624 If you obtained `ld' from a support organization, we recommend you 6625 contact that organization first. 6626 6627 You can find contact information for many support companies and 6628 individuals in the file `etc/SERVICE' in the GNU Emacs distribution. 6629 6630 Otherwise, send bug reports for `ld' to 6631 `http://www.sourceware.org/bugzilla/'. 6632 6633 The fundamental principle of reporting bugs usefully is this: 6634 *report all the facts*. If you are not sure whether to state a fact or 6635 leave it out, state it! 6636 6637 Often people omit facts because they think they know what causes the 6638 problem and assume that some details do not matter. Thus, you might 6639 assume that the name of a symbol you use in an example does not matter. 6640 Well, probably it does not, but one cannot be sure. Perhaps the bug 6641 is a stray memory reference which happens to fetch from the location 6642 where that name is stored in memory; perhaps, if the name were 6643 different, the contents of that location would fool the linker into 6644 doing the right thing despite the bug. Play it safe and give a 6645 specific, complete example. That is the easiest thing for you to do, 6646 and the most helpful. 6647 6648 Keep in mind that the purpose of a bug report is to enable us to fix 6649 the bug if it is new to us. Therefore, always write your bug reports 6650 on the assumption that the bug has not been reported previously. 6651 6652 Sometimes people give a few sketchy facts and ask, "Does this ring a 6653 bell?" This cannot help us fix a bug, so it is basically useless. We 6654 respond by asking for enough details to enable us to investigate. You 6655 might as well expedite matters by sending them to begin with. 6656 6657 To enable us to fix the bug, you should include all these things: 6658 6659 * The version of `ld'. `ld' announces it if you start it with the 6660 `--version' argument. 6661 6662 Without this, we will not know whether there is any point in 6663 looking for the bug in the current version of `ld'. 6664 6665 * Any patches you may have applied to the `ld' source, including any 6666 patches made to the `BFD' library. 6667 6668 * The type of machine you are using, and the operating system name 6669 and version number. 6670 6671 * What compiler (and its version) was used to compile `ld'--e.g. 6672 "`gcc-2.7'". 6673 6674 * The command arguments you gave the linker to link your example and 6675 observe the bug. To guarantee you will not omit something 6676 important, list them all. A copy of the Makefile (or the output 6677 from make) is sufficient. 6678 6679 If we were to try to guess the arguments, we would probably guess 6680 wrong and then we might not encounter the bug. 6681 6682 * A complete input file, or set of input files, that will reproduce 6683 the bug. It is generally most helpful to send the actual object 6684 files provided that they are reasonably small. Say no more than 6685 10K. For bigger files you can either make them available by FTP 6686 or HTTP or else state that you are willing to send the object 6687 file(s) to whomever requests them. (Note - your email will be 6688 going to a mailing list, so we do not want to clog it up with 6689 large attachments). But small attachments are best. 6690 6691 If the source files were assembled using `gas' or compiled using 6692 `gcc', then it may be OK to send the source files rather than the 6693 object files. In this case, be sure to say exactly what version of 6694 `gas' or `gcc' was used to produce the object files. Also say how 6695 `gas' or `gcc' were configured. 6696 6697 * A description of what behavior you observe that you believe is 6698 incorrect. For example, "It gets a fatal signal." 6699 6700 Of course, if the bug is that `ld' gets a fatal signal, then we 6701 will certainly notice it. But if the bug is incorrect output, we 6702 might not notice unless it is glaringly wrong. You might as well 6703 not give us a chance to make a mistake. 6704 6705 Even if the problem you experience is a fatal signal, you should 6706 still say so explicitly. Suppose something strange is going on, 6707 such as, your copy of `ld' is out of sync, or you have encountered 6708 a bug in the C library on your system. (This has happened!) Your 6709 copy might crash and ours would not. If you told us to expect a 6710 crash, then when ours fails to crash, we would know that the bug 6711 was not happening for us. If you had not told us to expect a 6712 crash, then we would not be able to draw any conclusion from our 6713 observations. 6714 6715 * If you wish to suggest changes to the `ld' source, send us context 6716 diffs, as generated by `diff' with the `-u', `-c', or `-p' option. 6717 Always send diffs from the old file to the new file. If you even 6718 discuss something in the `ld' source, refer to it by context, not 6719 by line number. 6720 6721 The line numbers in our development sources will not match those 6722 in your sources. Your line numbers would convey no useful 6723 information to us. 6724 6725 Here are some things that are not necessary: 6726 6727 * A description of the envelope of the bug. 6728 6729 Often people who encounter a bug spend a lot of time investigating 6730 which changes to the input file will make the bug go away and which 6731 changes will not affect it. 6732 6733 This is often time consuming and not very useful, because the way 6734 we will find the bug is by running a single example under the 6735 debugger with breakpoints, not by pure deduction from a series of 6736 examples. We recommend that you save your time for something else. 6737 6738 Of course, if you can find a simpler example to report _instead_ 6739 of the original one, that is a convenience for us. Errors in the 6740 output will be easier to spot, running under the debugger will take 6741 less time, and so on. 6742 6743 However, simplification is not vital; if you do not want to do 6744 this, report the bug anyway and send us the entire test case you 6745 used. 6746 6747 * A patch for the bug. 6748 6749 A patch for the bug does help us if it is a good one. But do not 6750 omit the necessary information, such as the test case, on the 6751 assumption that a patch is all we need. We might see problems 6752 with your patch and decide to fix the problem another way, or we 6753 might not understand it at all. 6754 6755 Sometimes with a program as complicated as `ld' it is very hard to 6756 construct an example that will make the program follow a certain 6757 path through the code. If you do not send us the example, we will 6758 not be able to construct one, so we will not be able to verify 6759 that the bug is fixed. 6760 6761 And if we cannot understand what bug you are trying to fix, or why 6762 your patch should be an improvement, we will not install it. A 6763 test case will help us to understand. 6764 6765 * A guess about what the bug is or what it depends on. 6766 6767 Such guesses are usually wrong. Even we cannot guess right about 6768 such things without first using the debugger to find the facts. 6769 6770 6771 File: ld.info, Node: MRI, Next: GNU Free Documentation License, Prev: Reporting Bugs, Up: Top 6772 6773 Appendix A MRI Compatible Script Files 6774 ************************************** 6775 6776 To aid users making the transition to GNU `ld' from the MRI linker, 6777 `ld' can use MRI compatible linker scripts as an alternative to the 6778 more general-purpose linker scripting language described in *Note 6779 Scripts::. MRI compatible linker scripts have a much simpler command 6780 set than the scripting language otherwise used with `ld'. GNU `ld' 6781 supports the most commonly used MRI linker commands; these commands are 6782 described here. 6783 6784 In general, MRI scripts aren't of much use with the `a.out' object 6785 file format, since it only has three sections and MRI scripts lack some 6786 features to make use of them. 6787 6788 You can specify a file containing an MRI-compatible script using the 6789 `-c' command-line option. 6790 6791 Each command in an MRI-compatible script occupies its own line; each 6792 command line starts with the keyword that identifies the command (though 6793 blank lines are also allowed for punctuation). If a line of an 6794 MRI-compatible script begins with an unrecognized keyword, `ld' issues 6795 a warning message, but continues processing the script. 6796 6797 Lines beginning with `*' are comments. 6798 6799 You can write these commands using all upper-case letters, or all 6800 lower case; for example, `chip' is the same as `CHIP'. The following 6801 list shows only the upper-case form of each command. 6802 6803 `ABSOLUTE SECNAME' 6804 `ABSOLUTE SECNAME, SECNAME, ... SECNAME' 6805 Normally, `ld' includes in the output file all sections from all 6806 the input files. However, in an MRI-compatible script, you can 6807 use the `ABSOLUTE' command to restrict the sections that will be 6808 present in your output program. If the `ABSOLUTE' command is used 6809 at all in a script, then only the sections named explicitly in 6810 `ABSOLUTE' commands will appear in the linker output. You can 6811 still use other input sections (whatever you select on the command 6812 line, or using `LOAD') to resolve addresses in the output file. 6813 6814 `ALIAS OUT-SECNAME, IN-SECNAME' 6815 Use this command to place the data from input section IN-SECNAME 6816 in a section called OUT-SECNAME in the linker output file. 6817 6818 IN-SECNAME may be an integer. 6819 6820 `ALIGN SECNAME = EXPRESSION' 6821 Align the section called SECNAME to EXPRESSION. The EXPRESSION 6822 should be a power of two. 6823 6824 `BASE EXPRESSION' 6825 Use the value of EXPRESSION as the lowest address (other than 6826 absolute addresses) in the output file. 6827 6828 `CHIP EXPRESSION' 6829 `CHIP EXPRESSION, EXPRESSION' 6830 This command does nothing; it is accepted only for compatibility. 6831 6832 `END' 6833 This command does nothing whatever; it's only accepted for 6834 compatibility. 6835 6836 `FORMAT OUTPUT-FORMAT' 6837 Similar to the `OUTPUT_FORMAT' command in the more general linker 6838 language, but restricted to one of these output formats: 6839 6840 1. S-records, if OUTPUT-FORMAT is `S' 6841 6842 2. IEEE, if OUTPUT-FORMAT is `IEEE' 6843 6844 3. COFF (the `coff-m68k' variant in BFD), if OUTPUT-FORMAT is 6845 `COFF' 6846 6847 `LIST ANYTHING...' 6848 Print (to the standard output file) a link map, as produced by the 6849 `ld' command-line option `-M'. 6850 6851 The keyword `LIST' may be followed by anything on the same line, 6852 with no change in its effect. 6853 6854 `LOAD FILENAME' 6855 `LOAD FILENAME, FILENAME, ... FILENAME' 6856 Include one or more object file FILENAME in the link; this has the 6857 same effect as specifying FILENAME directly on the `ld' command 6858 line. 6859 6860 `NAME OUTPUT-NAME' 6861 OUTPUT-NAME is the name for the program produced by `ld'; the 6862 MRI-compatible command `NAME' is equivalent to the command-line 6863 option `-o' or the general script language command `OUTPUT'. 6864 6865 `ORDER SECNAME, SECNAME, ... SECNAME' 6866 `ORDER SECNAME SECNAME SECNAME' 6867 Normally, `ld' orders the sections in its output file in the order 6868 in which they first appear in the input files. In an 6869 MRI-compatible script, you can override this ordering with the 6870 `ORDER' command. The sections you list with `ORDER' will appear 6871 first in your output file, in the order specified. 6872 6873 `PUBLIC NAME=EXPRESSION' 6874 `PUBLIC NAME,EXPRESSION' 6875 `PUBLIC NAME EXPRESSION' 6876 Supply a value (EXPRESSION) for external symbol NAME used in the 6877 linker input files. 6878 6879 `SECT SECNAME, EXPRESSION' 6880 `SECT SECNAME=EXPRESSION' 6881 `SECT SECNAME EXPRESSION' 6882 You can use any of these three forms of the `SECT' command to 6883 specify the start address (EXPRESSION) for section SECNAME. If 6884 you have more than one `SECT' statement for the same SECNAME, only 6885 the _first_ sets the start address. 6886 6887 6888 File: ld.info, Node: GNU Free Documentation License, Next: LD Index, Prev: MRI, Up: Top 6889 6890 Appendix B GNU Free Documentation License 6891 ***************************************** 6892 6893 Version 1.3, 3 November 2008 6894 6895 Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. 6896 `http://fsf.org/' 6897 6898 Everyone is permitted to copy and distribute verbatim copies 6899 of this license document, but changing it is not allowed. 6900 6901 0. PREAMBLE 6902 6903 The purpose of this License is to make a manual, textbook, or other 6904 functional and useful document "free" in the sense of freedom: to 6905 assure everyone the effective freedom to copy and redistribute it, 6906 with or without modifying it, either commercially or 6907 noncommercially. Secondarily, this License preserves for the 6908 author and publisher a way to get credit for their work, while not 6909 being considered responsible for modifications made by others. 6910 6911 This License is a kind of "copyleft", which means that derivative 6912 works of the document must themselves be free in the same sense. 6913 It complements the GNU General Public License, which is a copyleft 6914 license designed for free software. 6915 6916 We have designed this License in order to use it for manuals for 6917 free software, because free software needs free documentation: a 6918 free program should come with manuals providing the same freedoms 6919 that the software does. But this License is not limited to 6920 software manuals; it can be used for any textual work, regardless 6921 of subject matter or whether it is published as a printed book. 6922 We recommend this License principally for works whose purpose is 6923 instruction or reference. 6924 6925 1. APPLICABILITY AND DEFINITIONS 6926 6927 This License applies to any manual or other work, in any medium, 6928 that contains a notice placed by the copyright holder saying it 6929 can be distributed under the terms of this License. Such a notice 6930 grants a world-wide, royalty-free license, unlimited in duration, 6931 to use that work under the conditions stated herein. The 6932 "Document", below, refers to any such manual or work. Any member 6933 of the public is a licensee, and is addressed as "you". You 6934 accept the license if you copy, modify or distribute the work in a 6935 way requiring permission under copyright law. 6936 6937 A "Modified Version" of the Document means any work containing the 6938 Document or a portion of it, either copied verbatim, or with 6939 modifications and/or translated into another language. 6940 6941 A "Secondary Section" is a named appendix or a front-matter section 6942 of the Document that deals exclusively with the relationship of the 6943 publishers or authors of the Document to the Document's overall 6944 subject (or to related matters) and contains nothing that could 6945 fall directly within that overall subject. (Thus, if the Document 6946 is in part a textbook of mathematics, a Secondary Section may not 6947 explain any mathematics.) The relationship could be a matter of 6948 historical connection with the subject or with related matters, or 6949 of legal, commercial, philosophical, ethical or political position 6950 regarding them. 6951 6952 The "Invariant Sections" are certain Secondary Sections whose 6953 titles are designated, as being those of Invariant Sections, in 6954 the notice that says that the Document is released under this 6955 License. If a section does not fit the above definition of 6956 Secondary then it is not allowed to be designated as Invariant. 6957 The Document may contain zero Invariant Sections. If the Document 6958 does not identify any Invariant Sections then there are none. 6959 6960 The "Cover Texts" are certain short passages of text that are 6961 listed, as Front-Cover Texts or Back-Cover Texts, in the notice 6962 that says that the Document is released under this License. A 6963 Front-Cover Text may be at most 5 words, and a Back-Cover Text may 6964 be at most 25 words. 6965 6966 A "Transparent" copy of the Document means a machine-readable copy, 6967 represented in a format whose specification is available to the 6968 general public, that is suitable for revising the document 6969 straightforwardly with generic text editors or (for images 6970 composed of pixels) generic paint programs or (for drawings) some 6971 widely available drawing editor, and that is suitable for input to 6972 text formatters or for automatic translation to a variety of 6973 formats suitable for input to text formatters. A copy made in an 6974 otherwise Transparent file format whose markup, or absence of 6975 markup, has been arranged to thwart or discourage subsequent 6976 modification by readers is not Transparent. An image format is 6977 not Transparent if used for any substantial amount of text. A 6978 copy that is not "Transparent" is called "Opaque". 6979 6980 Examples of suitable formats for Transparent copies include plain 6981 ASCII without markup, Texinfo input format, LaTeX input format, 6982 SGML or XML using a publicly available DTD, and 6983 standard-conforming simple HTML, PostScript or PDF designed for 6984 human modification. Examples of transparent image formats include 6985 PNG, XCF and JPG. Opaque formats include proprietary formats that 6986 can be read and edited only by proprietary word processors, SGML or 6987 XML for which the DTD and/or processing tools are not generally 6988 available, and the machine-generated HTML, PostScript or PDF 6989 produced by some word processors for output purposes only. 6990 6991 The "Title Page" means, for a printed book, the title page itself, 6992 plus such following pages as are needed to hold, legibly, the 6993 material this License requires to appear in the title page. For 6994 works in formats which do not have any title page as such, "Title 6995 Page" means the text near the most prominent appearance of the 6996 work's title, preceding the beginning of the body of the text. 6997 6998 The "publisher" means any person or entity that distributes copies 6999 of the Document to the public. 7000 7001 A section "Entitled XYZ" means a named subunit of the Document 7002 whose title either is precisely XYZ or contains XYZ in parentheses 7003 following text that translates XYZ in another language. (Here XYZ 7004 stands for a specific section name mentioned below, such as 7005 "Acknowledgements", "Dedications", "Endorsements", or "History".) 7006 To "Preserve the Title" of such a section when you modify the 7007 Document means that it remains a section "Entitled XYZ" according 7008 to this definition. 7009 7010 The Document may include Warranty Disclaimers next to the notice 7011 which states that this License applies to the Document. These 7012 Warranty Disclaimers are considered to be included by reference in 7013 this License, but only as regards disclaiming warranties: any other 7014 implication that these Warranty Disclaimers may have is void and 7015 has no effect on the meaning of this License. 7016 7017 2. VERBATIM COPYING 7018 7019 You may copy and distribute the Document in any medium, either 7020 commercially or noncommercially, provided that this License, the 7021 copyright notices, and the license notice saying this License 7022 applies to the Document are reproduced in all copies, and that you 7023 add no other conditions whatsoever to those of this License. You 7024 may not use technical measures to obstruct or control the reading 7025 or further copying of the copies you make or distribute. However, 7026 you may accept compensation in exchange for copies. If you 7027 distribute a large enough number of copies you must also follow 7028 the conditions in section 3. 7029 7030 You may also lend copies, under the same conditions stated above, 7031 and you may publicly display copies. 7032 7033 3. COPYING IN QUANTITY 7034 7035 If you publish printed copies (or copies in media that commonly 7036 have printed covers) of the Document, numbering more than 100, and 7037 the Document's license notice requires Cover Texts, you must 7038 enclose the copies in covers that carry, clearly and legibly, all 7039 these Cover Texts: Front-Cover Texts on the front cover, and 7040 Back-Cover Texts on the back cover. Both covers must also clearly 7041 and legibly identify you as the publisher of these copies. The 7042 front cover must present the full title with all words of the 7043 title equally prominent and visible. You may add other material 7044 on the covers in addition. Copying with changes limited to the 7045 covers, as long as they preserve the title of the Document and 7046 satisfy these conditions, can be treated as verbatim copying in 7047 other respects. 7048 7049 If the required texts for either cover are too voluminous to fit 7050 legibly, you should put the first ones listed (as many as fit 7051 reasonably) on the actual cover, and continue the rest onto 7052 adjacent pages. 7053 7054 If you publish or distribute Opaque copies of the Document 7055 numbering more than 100, you must either include a 7056 machine-readable Transparent copy along with each Opaque copy, or 7057 state in or with each Opaque copy a computer-network location from 7058 which the general network-using public has access to download 7059 using public-standard network protocols a complete Transparent 7060 copy of the Document, free of added material. If you use the 7061 latter option, you must take reasonably prudent steps, when you 7062 begin distribution of Opaque copies in quantity, to ensure that 7063 this Transparent copy will remain thus accessible at the stated 7064 location until at least one year after the last time you 7065 distribute an Opaque copy (directly or through your agents or 7066 retailers) of that edition to the public. 7067 7068 It is requested, but not required, that you contact the authors of 7069 the Document well before redistributing any large number of 7070 copies, to give them a chance to provide you with an updated 7071 version of the Document. 7072 7073 4. MODIFICATIONS 7074 7075 You may copy and distribute a Modified Version of the Document 7076 under the conditions of sections 2 and 3 above, provided that you 7077 release the Modified Version under precisely this License, with 7078 the Modified Version filling the role of the Document, thus 7079 licensing distribution and modification of the Modified Version to 7080 whoever possesses a copy of it. In addition, you must do these 7081 things in the Modified Version: 7082 7083 A. Use in the Title Page (and on the covers, if any) a title 7084 distinct from that of the Document, and from those of 7085 previous versions (which should, if there were any, be listed 7086 in the History section of the Document). You may use the 7087 same title as a previous version if the original publisher of 7088 that version gives permission. 7089 7090 B. List on the Title Page, as authors, one or more persons or 7091 entities responsible for authorship of the modifications in 7092 the Modified Version, together with at least five of the 7093 principal authors of the Document (all of its principal 7094 authors, if it has fewer than five), unless they release you 7095 from this requirement. 7096 7097 C. State on the Title page the name of the publisher of the 7098 Modified Version, as the publisher. 7099 7100 D. Preserve all the copyright notices of the Document. 7101 7102 E. Add an appropriate copyright notice for your modifications 7103 adjacent to the other copyright notices. 7104 7105 F. Include, immediately after the copyright notices, a license 7106 notice giving the public permission to use the Modified 7107 Version under the terms of this License, in the form shown in 7108 the Addendum below. 7109 7110 G. Preserve in that license notice the full lists of Invariant 7111 Sections and required Cover Texts given in the Document's 7112 license notice. 7113 7114 H. Include an unaltered copy of this License. 7115 7116 I. Preserve the section Entitled "History", Preserve its Title, 7117 and add to it an item stating at least the title, year, new 7118 authors, and publisher of the Modified Version as given on 7119 the Title Page. If there is no section Entitled "History" in 7120 the Document, create one stating the title, year, authors, 7121 and publisher of the Document as given on its Title Page, 7122 then add an item describing the Modified Version as stated in 7123 the previous sentence. 7124 7125 J. Preserve the network location, if any, given in the Document 7126 for public access to a Transparent copy of the Document, and 7127 likewise the network locations given in the Document for 7128 previous versions it was based on. These may be placed in 7129 the "History" section. You may omit a network location for a 7130 work that was published at least four years before the 7131 Document itself, or if the original publisher of the version 7132 it refers to gives permission. 7133 7134 K. For any section Entitled "Acknowledgements" or "Dedications", 7135 Preserve the Title of the section, and preserve in the 7136 section all the substance and tone of each of the contributor 7137 acknowledgements and/or dedications given therein. 7138 7139 L. Preserve all the Invariant Sections of the Document, 7140 unaltered in their text and in their titles. Section numbers 7141 or the equivalent are not considered part of the section 7142 titles. 7143 7144 M. Delete any section Entitled "Endorsements". Such a section 7145 may not be included in the Modified Version. 7146 7147 N. Do not retitle any existing section to be Entitled 7148 "Endorsements" or to conflict in title with any Invariant 7149 Section. 7150 7151 O. Preserve any Warranty Disclaimers. 7152 7153 If the Modified Version includes new front-matter sections or 7154 appendices that qualify as Secondary Sections and contain no 7155 material copied from the Document, you may at your option 7156 designate some or all of these sections as invariant. To do this, 7157 add their titles to the list of Invariant Sections in the Modified 7158 Version's license notice. These titles must be distinct from any 7159 other section titles. 7160 7161 You may add a section Entitled "Endorsements", provided it contains 7162 nothing but endorsements of your Modified Version by various 7163 parties--for example, statements of peer review or that the text 7164 has been approved by an organization as the authoritative 7165 definition of a standard. 7166 7167 You may add a passage of up to five words as a Front-Cover Text, 7168 and a passage of up to 25 words as a Back-Cover Text, to the end 7169 of the list of Cover Texts in the Modified Version. Only one 7170 passage of Front-Cover Text and one of Back-Cover Text may be 7171 added by (or through arrangements made by) any one entity. If the 7172 Document already includes a cover text for the same cover, 7173 previously added by you or by arrangement made by the same entity 7174 you are acting on behalf of, you may not add another; but you may 7175 replace the old one, on explicit permission from the previous 7176 publisher that added the old one. 7177 7178 The author(s) and publisher(s) of the Document do not by this 7179 License give permission to use their names for publicity for or to 7180 assert or imply endorsement of any Modified Version. 7181 7182 5. COMBINING DOCUMENTS 7183 7184 You may combine the Document with other documents released under 7185 this License, under the terms defined in section 4 above for 7186 modified versions, provided that you include in the combination 7187 all of the Invariant Sections of all of the original documents, 7188 unmodified, and list them all as Invariant Sections of your 7189 combined work in its license notice, and that you preserve all 7190 their Warranty Disclaimers. 7191 7192 The combined work need only contain one copy of this License, and 7193 multiple identical Invariant Sections may be replaced with a single 7194 copy. If there are multiple Invariant Sections with the same name 7195 but different contents, make the title of each such section unique 7196 by adding at the end of it, in parentheses, the name of the 7197 original author or publisher of that section if known, or else a 7198 unique number. Make the same adjustment to the section titles in 7199 the list of Invariant Sections in the license notice of the 7200 combined work. 7201 7202 In the combination, you must combine any sections Entitled 7203 "History" in the various original documents, forming one section 7204 Entitled "History"; likewise combine any sections Entitled 7205 "Acknowledgements", and any sections Entitled "Dedications". You 7206 must delete all sections Entitled "Endorsements." 7207 7208 6. COLLECTIONS OF DOCUMENTS 7209 7210 You may make a collection consisting of the Document and other 7211 documents released under this License, and replace the individual 7212 copies of this License in the various documents with a single copy 7213 that is included in the collection, provided that you follow the 7214 rules of this License for verbatim copying of each of the 7215 documents in all other respects. 7216 7217 You may extract a single document from such a collection, and 7218 distribute it individually under this License, provided you insert 7219 a copy of this License into the extracted document, and follow 7220 this License in all other respects regarding verbatim copying of 7221 that document. 7222 7223 7. AGGREGATION WITH INDEPENDENT WORKS 7224 7225 A compilation of the Document or its derivatives with other 7226 separate and independent documents or works, in or on a volume of 7227 a storage or distribution medium, is called an "aggregate" if the 7228 copyright resulting from the compilation is not used to limit the 7229 legal rights of the compilation's users beyond what the individual 7230 works permit. When the Document is included in an aggregate, this 7231 License does not apply to the other works in the aggregate which 7232 are not themselves derivative works of the Document. 7233 7234 If the Cover Text requirement of section 3 is applicable to these 7235 copies of the Document, then if the Document is less than one half 7236 of the entire aggregate, the Document's Cover Texts may be placed 7237 on covers that bracket the Document within the aggregate, or the 7238 electronic equivalent of covers if the Document is in electronic 7239 form. Otherwise they must appear on printed covers that bracket 7240 the whole aggregate. 7241 7242 8. TRANSLATION 7243 7244 Translation is considered a kind of modification, so you may 7245 distribute translations of the Document under the terms of section 7246 4. Replacing Invariant Sections with translations requires special 7247 permission from their copyright holders, but you may include 7248 translations of some or all Invariant Sections in addition to the 7249 original versions of these Invariant Sections. You may include a 7250 translation of this License, and all the license notices in the 7251 Document, and any Warranty Disclaimers, provided that you also 7252 include the original English version of this License and the 7253 original versions of those notices and disclaimers. In case of a 7254 disagreement between the translation and the original version of 7255 this License or a notice or disclaimer, the original version will 7256 prevail. 7257 7258 If a section in the Document is Entitled "Acknowledgements", 7259 "Dedications", or "History", the requirement (section 4) to 7260 Preserve its Title (section 1) will typically require changing the 7261 actual title. 7262 7263 9. TERMINATION 7264 7265 You may not copy, modify, sublicense, or distribute the Document 7266 except as expressly provided under this License. Any attempt 7267 otherwise to copy, modify, sublicense, or distribute it is void, 7268 and will automatically terminate your rights under this License. 7269 7270 However, if you cease all violation of this License, then your 7271 license from a particular copyright holder is reinstated (a) 7272 provisionally, unless and until the copyright holder explicitly 7273 and finally terminates your license, and (b) permanently, if the 7274 copyright holder fails to notify you of the violation by some 7275 reasonable means prior to 60 days after the cessation. 7276 7277 Moreover, your license from a particular copyright holder is 7278 reinstated permanently if the copyright holder notifies you of the 7279 violation by some reasonable means, this is the first time you have 7280 received notice of violation of this License (for any work) from 7281 that copyright holder, and you cure the violation prior to 30 days 7282 after your receipt of the notice. 7283 7284 Termination of your rights under this section does not terminate 7285 the licenses of parties who have received copies or rights from 7286 you under this License. If your rights have been terminated and 7287 not permanently reinstated, receipt of a copy of some or all of 7288 the same material does not give you any rights to use it. 7289 7290 10. FUTURE REVISIONS OF THIS LICENSE 7291 7292 The Free Software Foundation may publish new, revised versions of 7293 the GNU Free Documentation License from time to time. Such new 7294 versions will be similar in spirit to the present version, but may 7295 differ in detail to address new problems or concerns. See 7296 `http://www.gnu.org/copyleft/'. 7297 7298 Each version of the License is given a distinguishing version 7299 number. If the Document specifies that a particular numbered 7300 version of this License "or any later version" applies to it, you 7301 have the option of following the terms and conditions either of 7302 that specified version or of any later version that has been 7303 published (not as a draft) by the Free Software Foundation. If 7304 the Document does not specify a version number of this License, 7305 you may choose any version ever published (not as a draft) by the 7306 Free Software Foundation. If the Document specifies that a proxy 7307 can decide which future versions of this License can be used, that 7308 proxy's public statement of acceptance of a version permanently 7309 authorizes you to choose that version for the Document. 7310 7311 11. RELICENSING 7312 7313 "Massive Multiauthor Collaboration Site" (or "MMC Site") means any 7314 World Wide Web server that publishes copyrightable works and also 7315 provides prominent facilities for anybody to edit those works. A 7316 public wiki that anybody can edit is an example of such a server. 7317 A "Massive Multiauthor Collaboration" (or "MMC") contained in the 7318 site means any set of copyrightable works thus published on the MMC 7319 site. 7320 7321 "CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0 7322 license published by Creative Commons Corporation, a not-for-profit 7323 corporation with a principal place of business in San Francisco, 7324 California, as well as future copyleft versions of that license 7325 published by that same organization. 7326 7327 "Incorporate" means to publish or republish a Document, in whole or 7328 in part, as part of another Document. 7329 7330 An MMC is "eligible for relicensing" if it is licensed under this 7331 License, and if all works that were first published under this 7332 License somewhere other than this MMC, and subsequently 7333 incorporated in whole or in part into the MMC, (1) had no cover 7334 texts or invariant sections, and (2) were thus incorporated prior 7335 to November 1, 2008. 7336 7337 The operator of an MMC Site may republish an MMC contained in the 7338 site under CC-BY-SA on the same site at any time before August 1, 7339 2009, provided the MMC is eligible for relicensing. 7340 7341 7342 ADDENDUM: How to use this License for your documents 7343 ==================================================== 7344 7345 To use this License in a document you have written, include a copy of 7346 the License in the document and put the following copyright and license 7347 notices just after the title page: 7348 7349 Copyright (C) YEAR YOUR NAME. 7350 Permission is granted to copy, distribute and/or modify this document 7351 under the terms of the GNU Free Documentation License, Version 1.3 7352 or any later version published by the Free Software Foundation; 7353 with no Invariant Sections, no Front-Cover Texts, and no Back-Cover 7354 Texts. A copy of the license is included in the section entitled ``GNU 7355 Free Documentation License''. 7356 7357 If you have Invariant Sections, Front-Cover Texts and Back-Cover 7358 Texts, replace the "with...Texts." line with this: 7359 7360 with the Invariant Sections being LIST THEIR TITLES, with 7361 the Front-Cover Texts being LIST, and with the Back-Cover Texts 7362 being LIST. 7363 7364 If you have Invariant Sections without Cover Texts, or some other 7365 combination of the three, merge those two alternatives to suit the 7366 situation. 7367 7368 If your document contains nontrivial examples of program code, we 7369 recommend releasing these examples in parallel under your choice of 7370 free software license, such as the GNU General Public License, to 7371 permit their use in free software. 7372 7373 7374 File: ld.info, Node: LD Index, Prev: GNU Free Documentation License, Up: Top 7375 7376 LD Index 7377 ******** 7378 7379 [index] 7380 * Menu: 7381 7382 * ": Symbols. (line 6) 7383 * -(: Options. (line 731) 7384 * --accept-unknown-input-arch: Options. (line 749) 7385 * --add-needed: Options. (line 777) 7386 * --add-stdcall-alias: Options. (line 1635) 7387 * --allow-multiple-definition: Options. (line 1029) 7388 * --allow-shlib-undefined: Options. (line 1035) 7389 * --architecture=ARCH: Options. (line 123) 7390 * --as-needed: Options. (line 759) 7391 * --audit AUDITLIB: Options. (line 112) 7392 * --auxiliary=NAME: Options. (line 255) 7393 * --bank-window: Options. (line 2089) 7394 * --base-file: Options. (line 1640) 7395 * --be8: ARM. (line 28) 7396 * --bss-plt: PowerPC ELF32. (line 16) 7397 * --build-id: Options. (line 1597) 7398 * --build-id=STYLE: Options. (line 1597) 7399 * --check-sections: Options. (line 856) 7400 * --copy-dt-needed-entries: Options. (line 868) 7401 * --cref: Options. (line 888) 7402 * --default-imported-symver: Options. (line 1072) 7403 * --default-script=SCRIPT: Options. (line 562) 7404 * --default-symver: Options. (line 1068) 7405 * --defsym=SYMBOL=EXP: Options. (line 917) 7406 * --demangle[=STYLE]: Options. (line 930) 7407 * --depaudit AUDITLIB: Options. (line 177) 7408 * --disable-auto-image-base: Options. (line 1827) 7409 * --disable-auto-import: Options. (line 1962) 7410 * --disable-large-address-aware: Options. (line 1766) 7411 * --disable-long-section-names: Options. (line 1650) 7412 * --disable-new-dtags: Options. (line 1559) 7413 * --disable-runtime-pseudo-reloc: Options. (line 1975) 7414 * --disable-stdcall-fixup: Options. (line 1672) 7415 * --discard-all: Options. (line 608) 7416 * --discard-locals: Options. (line 612) 7417 * --dll: Options. (line 1645) 7418 * --dll-search-prefix: Options. (line 1833) 7419 * --dotsyms: PowerPC64 ELF64. (line 33) 7420 * --dsbt-index: Options. (line 2066) 7421 * --dsbt-size: Options. (line 2061) 7422 * --dynamic-linker=FILE: Options. (line 943) 7423 * --dynamic-list-cpp-new: Options. (line 848) 7424 * --dynamic-list-cpp-typeinfo: Options. (line 852) 7425 * --dynamic-list-data: Options. (line 845) 7426 * --dynamic-list=DYNAMIC-LIST-FILE: Options. (line 832) 7427 * --dynamicbase: Options. (line 2015) 7428 * --eh-frame-hdr: Options. (line 1550) 7429 * --emit-relocs: Options. (line 497) 7430 * --emit-stack-syms: SPU ELF. (line 46) 7431 * --emit-stub-syms <1>: SPU ELF. (line 15) 7432 * --emit-stub-syms <2>: PowerPC ELF32. (line 47) 7433 * --emit-stub-syms: PowerPC64 ELF64. (line 29) 7434 * --enable-auto-image-base: Options. (line 1818) 7435 * --enable-auto-import: Options. (line 1842) 7436 * --enable-extra-pe-debug: Options. (line 1980) 7437 * --enable-long-section-names: Options. (line 1650) 7438 * --enable-new-dtags: Options. (line 1559) 7439 * --enable-runtime-pseudo-reloc: Options. (line 1967) 7440 * --enable-stdcall-fixup: Options. (line 1672) 7441 * --entry=ENTRY: Options. (line 187) 7442 * --error-unresolved-symbols: Options. (line 1503) 7443 * --exclude-all-symbols: Options. (line 1726) 7444 * --exclude-libs: Options. (line 197) 7445 * --exclude-modules-for-implib: Options. (line 208) 7446 * --exclude-symbols: Options. (line 1720) 7447 * --export-all-symbols: Options. (line 1696) 7448 * --export-dynamic: Options. (line 221) 7449 * --extra-overlay-stubs: SPU ELF. (line 19) 7450 * --fatal-warnings: Options. (line 950) 7451 * --file-alignment: Options. (line 1730) 7452 * --filter=NAME: Options. (line 276) 7453 * --fix-arm1176: ARM. (line 111) 7454 * --fix-cortex-a53-835769: ARM. (line 174) 7455 * --fix-cortex-a8: ARM. (line 165) 7456 * --fix-v4bx: ARM. (line 49) 7457 * --fix-v4bx-interworking: ARM. (line 62) 7458 * --force-dynamic: Options. (line 506) 7459 * --force-exe-suffix: Options. (line 955) 7460 * --forceinteg: Options. (line 2020) 7461 * --format=FORMAT: Options. (line 134) 7462 * --format=VERSION: TI COFF. (line 6) 7463 * --gc-sections: Options. (line 965) 7464 * --got: Options. (line 2102) 7465 * --got=TYPE: M68K. (line 6) 7466 * --gpsize=VALUE: Options. (line 309) 7467 * --hash-size=NUMBER: Options. (line 1569) 7468 * --hash-style=STYLE: Options. (line 1577) 7469 * --heap: Options. (line 1736) 7470 * --help: Options. (line 1002) 7471 * --high-entropy-va: Options. (line 2011) 7472 * --image-base: Options. (line 1743) 7473 * --insert-timestamp: Options. (line 2043) 7474 * --insn32 <1>: MIPS. (line 6) 7475 * --insn32: Options. (line 2114) 7476 * --just-symbols=FILE: Options. (line 529) 7477 * --kill-at: Options. (line 1752) 7478 * --large-address-aware: Options. (line 1757) 7479 * --ld-generated-unwind-info: Options. (line 1554) 7480 * --leading-underscore: Options. (line 1690) 7481 * --library-path=DIR: Options. (line 367) 7482 * --library=NAMESPEC: Options. (line 334) 7483 * --local-store=lo:hi: SPU ELF. (line 24) 7484 * --long-plt: ARM. (line 185) 7485 * --major-image-version: Options. (line 1773) 7486 * --major-os-version: Options. (line 1778) 7487 * --major-subsystem-version: Options. (line 1782) 7488 * --merge-exidx-entries: ARM. (line 182) 7489 * --minor-image-version: Options. (line 1787) 7490 * --minor-os-version: Options. (line 1792) 7491 * --minor-subsystem-version: Options. (line 1796) 7492 * --mri-script=MRI-CMDFILE: Options. (line 158) 7493 * --multi-subspace: HPPA ELF32. (line 6) 7494 * --nmagic: Options. (line 439) 7495 * --no-accept-unknown-input-arch: Options. (line 749) 7496 * --no-add-needed: Options. (line 777) 7497 * --no-allow-shlib-undefined: Options. (line 1035) 7498 * --no-as-needed: Options. (line 759) 7499 * --no-bind: Options. (line 2034) 7500 * --no-check-sections: Options. (line 856) 7501 * --no-copy-dt-needed-entries: Options. (line 868) 7502 * --no-define-common: Options. (line 901) 7503 * --no-demangle: Options. (line 930) 7504 * --no-dotsyms: PowerPC64 ELF64. (line 33) 7505 * --no-enum-size-warning: ARM. (line 120) 7506 * --no-export-dynamic: Options. (line 221) 7507 * --no-fatal-warnings: Options. (line 950) 7508 * --no-fix-arm1176: ARM. (line 111) 7509 * --no-fix-cortex-a53-835769: ARM. (line 174) 7510 * --no-fix-cortex-a8: ARM. (line 165) 7511 * --no-gc-sections: Options. (line 965) 7512 * --no-insn32 <1>: MIPS. (line 6) 7513 * --no-insn32: Options. (line 2115) 7514 * --no-isolation: Options. (line 2027) 7515 * --no-keep-memory: Options. (line 1014) 7516 * --no-leading-underscore: Options. (line 1690) 7517 * --no-merge-exidx-entries <1>: ARM. (line 182) 7518 * --no-merge-exidx-entries: Options. (line 2073) 7519 * --no-multi-toc: PowerPC64 ELF64. (line 74) 7520 * --no-omagic: Options. (line 454) 7521 * --no-opd-optimize: PowerPC64 ELF64. (line 48) 7522 * --no-overlays: SPU ELF. (line 9) 7523 * --no-plt-align: PowerPC64 ELF64. (line 96) 7524 * --no-plt-static-chain: PowerPC64 ELF64. (line 104) 7525 * --no-plt-thread-safe: PowerPC64 ELF64. (line 110) 7526 * --no-print-gc-sections: Options. (line 987) 7527 * --no-seh: Options. (line 2030) 7528 * --no-tls-optimize <1>: PowerPC64 ELF64. (line 43) 7529 * --no-tls-optimize: PowerPC ELF32. (line 51) 7530 * --no-toc-optimize: PowerPC64 ELF64. (line 60) 7531 * --no-toc-sort: PowerPC64 ELF64. (line 86) 7532 * --no-trampoline: Options. (line 2083) 7533 * --no-undefined: Options. (line 1021) 7534 * --no-undefined-version: Options. (line 1063) 7535 * --no-warn-mismatch: Options. (line 1076) 7536 * --no-warn-search-mismatch: Options. (line 1085) 7537 * --no-wchar-size-warning: ARM. (line 127) 7538 * --no-whole-archive: Options. (line 1089) 7539 * --noinhibit-exec: Options. (line 1093) 7540 * --non-overlapping-opd: PowerPC64 ELF64. (line 54) 7541 * --nxcompat: Options. (line 2023) 7542 * --oformat=OUTPUT-FORMAT: Options. (line 1105) 7543 * --omagic: Options. (line 445) 7544 * --out-implib: Options. (line 1809) 7545 * --output-def: Options. (line 1801) 7546 * --output=OUTPUT: Options. (line 460) 7547 * --pic-executable: Options. (line 1118) 7548 * --pic-veneer: ARM. (line 133) 7549 * --plt-align: PowerPC64 ELF64. (line 96) 7550 * --plt-static-chain: PowerPC64 ELF64. (line 104) 7551 * --plt-thread-safe: PowerPC64 ELF64. (line 110) 7552 * --plugin: SPU ELF. (line 6) 7553 * --pop-state: Options. (line 494) 7554 * --print-gc-sections: Options. (line 987) 7555 * --print-map: Options. (line 402) 7556 * --print-output-format: Options. (line 996) 7557 * --push-state: Options. (line 476) 7558 * --reduce-memory-overheads: Options. (line 1583) 7559 * --relax: Options. (line 1134) 7560 * --relax on i960: i960. (line 31) 7561 * --relax on Nios II: Nios II. (line 6) 7562 * --relax on PowerPC: PowerPC ELF32. (line 6) 7563 * --relax on Xtensa: Xtensa. (line 27) 7564 * --relocatable: Options. (line 510) 7565 * --retain-symbols-file=FILENAME: Options. (line 1160) 7566 * --script=SCRIPT: Options. (line 553) 7567 * --sdata-got: PowerPC ELF32. (line 33) 7568 * --section-alignment: Options. (line 1985) 7569 * --section-start=SECTIONNAME=ORG: Options. (line 1316) 7570 * --secure-plt: PowerPC ELF32. (line 26) 7571 * --sort-common: Options. (line 1258) 7572 * --sort-section=alignment: Options. (line 1273) 7573 * --sort-section=name: Options. (line 1269) 7574 * --split-by-file: Options. (line 1277) 7575 * --split-by-reloc: Options. (line 1282) 7576 * --stack: Options. (line 1991) 7577 * --stack-analysis: SPU ELF. (line 29) 7578 * --stats: Options. (line 1295) 7579 * --strip-all: Options. (line 540) 7580 * --strip-debug: Options. (line 544) 7581 * --stub-group-size: PowerPC64 ELF64. (line 6) 7582 * --stub-group-size=N <1>: ARM. (line 138) 7583 * --stub-group-size=N: HPPA ELF32. (line 12) 7584 * --subsystem: Options. (line 1998) 7585 * --support-old-code: ARM. (line 6) 7586 * --sysroot=DIRECTORY: Options. (line 1299) 7587 * --target-help: Options. (line 1006) 7588 * --target1-abs: ARM. (line 32) 7589 * --target1-rel: ARM. (line 32) 7590 * --target2=TYPE: ARM. (line 37) 7591 * --thumb-entry=ENTRY: ARM. (line 17) 7592 * --trace: Options. (line 549) 7593 * --trace-symbol=SYMBOL: Options. (line 618) 7594 * --traditional-format: Options. (line 1304) 7595 * --tsaware: Options. (line 2040) 7596 * --undefined=SYMBOL: Options. (line 575) 7597 * --unique[=SECTION]: Options. (line 593) 7598 * --unresolved-symbols: Options. (line 1346) 7599 * --use-blx: ARM. (line 74) 7600 * --use-nul-prefixed-import-tables: ARM. (line 23) 7601 * --verbose[=NUMBER]: Options. (line 1375) 7602 * --version: Options. (line 602) 7603 * --version-script=VERSION-SCRIPTFILE: Options. (line 1383) 7604 * --vfp11-denorm-fix: ARM. (line 83) 7605 * --warn-alternate-em: Options. (line 1495) 7606 * --warn-common: Options. (line 1394) 7607 * --warn-constructors: Options. (line 1462) 7608 * --warn-multiple-gp: Options. (line 1467) 7609 * --warn-once: Options. (line 1481) 7610 * --warn-section-align: Options. (line 1485) 7611 * --warn-shared-textrel: Options. (line 1492) 7612 * --warn-unresolved-symbols: Options. (line 1498) 7613 * --wdmdriver: Options. (line 2037) 7614 * --whole-archive: Options. (line 1507) 7615 * --wrap=SYMBOL: Options. (line 1521) 7616 * -A ARCH: Options. (line 122) 7617 * -a KEYWORD: Options. (line 105) 7618 * -assert KEYWORD: Options. (line 784) 7619 * -b FORMAT: Options. (line 134) 7620 * -Bdynamic: Options. (line 787) 7621 * -Bgroup: Options. (line 797) 7622 * -Bshareable: Options. (line 1251) 7623 * -Bstatic: Options. (line 804) 7624 * -Bsymbolic: Options. (line 819) 7625 * -Bsymbolic-functions: Options. (line 826) 7626 * -c MRI-CMDFILE: Options. (line 158) 7627 * -call_shared: Options. (line 787) 7628 * -d: Options. (line 168) 7629 * -dc: Options. (line 168) 7630 * -dn: Options. (line 804) 7631 * -dp: Options. (line 168) 7632 * -dT SCRIPT: Options. (line 562) 7633 * -dy: Options. (line 787) 7634 * -E: Options. (line 221) 7635 * -e ENTRY: Options. (line 187) 7636 * -EB: Options. (line 248) 7637 * -EL: Options. (line 251) 7638 * -F NAME: Options. (line 276) 7639 * -f NAME: Options. (line 255) 7640 * -fini=NAME: Options. (line 300) 7641 * -g: Options. (line 306) 7642 * -G VALUE: Options. (line 309) 7643 * -h NAME: Options. (line 316) 7644 * -i: Options. (line 325) 7645 * -IFILE: Options. (line 943) 7646 * -init=NAME: Options. (line 328) 7647 * -L DIR: Options. (line 367) 7648 * -l NAMESPEC: Options. (line 334) 7649 * -M: Options. (line 402) 7650 * -m EMULATION: Options. (line 392) 7651 * -Map=MAPFILE: Options. (line 1010) 7652 * -N: Options. (line 445) 7653 * -n: Options. (line 439) 7654 * -no-relax: Options. (line 1134) 7655 * -non_shared: Options. (line 804) 7656 * -nostdlib: Options. (line 1099) 7657 * -O LEVEL: Options. (line 466) 7658 * -o OUTPUT: Options. (line 460) 7659 * -P AUDITLIB: Options. (line 177) 7660 * -pie: Options. (line 1118) 7661 * -q: Options. (line 497) 7662 * -qmagic: Options. (line 1128) 7663 * -Qy: Options. (line 1131) 7664 * -r: Options. (line 510) 7665 * -R FILE: Options. (line 529) 7666 * -rpath-link=DIR: Options. (line 1196) 7667 * -rpath=DIR: Options. (line 1174) 7668 * -S: Options. (line 544) 7669 * -s: Options. (line 540) 7670 * -shared: Options. (line 1251) 7671 * -soname=NAME: Options. (line 316) 7672 * -static: Options. (line 804) 7673 * -t: Options. (line 549) 7674 * -T SCRIPT: Options. (line 553) 7675 * -Tbss=ORG: Options. (line 1325) 7676 * -Tdata=ORG: Options. (line 1325) 7677 * -Tldata-segment=ORG: Options. (line 1341) 7678 * -Trodata-segment=ORG: Options. (line 1335) 7679 * -Ttext-segment=ORG: Options. (line 1331) 7680 * -Ttext=ORG: Options. (line 1325) 7681 * -u SYMBOL: Options. (line 575) 7682 * -Ur: Options. (line 583) 7683 * -v: Options. (line 602) 7684 * -V: Options. (line 602) 7685 * -x: Options. (line 608) 7686 * -X: Options. (line 612) 7687 * -Y PATH: Options. (line 627) 7688 * -y SYMBOL: Options. (line 618) 7689 * -z defs: Options. (line 1021) 7690 * -z KEYWORD: Options. (line 631) 7691 * -z muldefs: Options. (line 1029) 7692 * .: Location Counter. (line 6) 7693 * /DISCARD/: Output Section Discarding. 7694 (line 26) 7695 * 32-bit PLT entries: ARM. (line 185) 7696 * :PHDR: Output Section Phdr. 7697 (line 6) 7698 * =FILLEXP: Output Section Fill. 7699 (line 6) 7700 * >REGION: Output Section Region. 7701 (line 6) 7702 * [COMMON]: Input Section Common. 7703 (line 29) 7704 * ABSOLUTE (MRI): MRI. (line 33) 7705 * absolute and relocatable symbols: Expression Section. (line 6) 7706 * absolute expressions: Expression Section. (line 6) 7707 * ABSOLUTE(EXP): Builtin Functions. (line 10) 7708 * ADDR(SECTION): Builtin Functions. (line 17) 7709 * address, section: Output Section Address. 7710 (line 6) 7711 * ALIAS (MRI): MRI. (line 44) 7712 * ALIGN (MRI): MRI. (line 50) 7713 * align expression: Builtin Functions. (line 38) 7714 * align location counter: Builtin Functions. (line 38) 7715 * ALIGN(ALIGN): Builtin Functions. (line 38) 7716 * ALIGN(EXP,ALIGN): Builtin Functions. (line 38) 7717 * ALIGN(SECTION_ALIGN): Forced Output Alignment. 7718 (line 6) 7719 * aligned common symbols: WIN32. (line 424) 7720 * ALIGNOF(SECTION): Builtin Functions. (line 64) 7721 * allocating memory: MEMORY. (line 6) 7722 * architecture: Miscellaneous Commands. 7723 (line 72) 7724 * architectures: Options. (line 122) 7725 * archive files, from cmd line: Options. (line 334) 7726 * archive search path in linker script: File Commands. (line 76) 7727 * arithmetic: Expressions. (line 6) 7728 * arithmetic operators: Operators. (line 6) 7729 * ARM interworking support: ARM. (line 6) 7730 * ARM1176 erratum workaround: ARM. (line 111) 7731 * AS_NEEDED(FILES): File Commands. (line 56) 7732 * ASSERT: Miscellaneous Commands. 7733 (line 9) 7734 * assertion in linker script: Miscellaneous Commands. 7735 (line 9) 7736 * assignment in scripts: Assignments. (line 6) 7737 * AT(LMA): Output Section LMA. (line 6) 7738 * AT>LMA_REGION: Output Section LMA. (line 6) 7739 * automatic data imports: WIN32. (line 191) 7740 * back end: BFD. (line 6) 7741 * BASE (MRI): MRI. (line 54) 7742 * BE8: ARM. (line 28) 7743 * BFD canonical format: Canonical format. (line 11) 7744 * BFD requirements: BFD. (line 16) 7745 * big-endian objects: Options. (line 248) 7746 * binary input format: Options. (line 134) 7747 * BLOCK(EXP): Builtin Functions. (line 77) 7748 * bug criteria: Bug Criteria. (line 6) 7749 * bug reports: Bug Reporting. (line 6) 7750 * bugs in ld: Reporting Bugs. (line 6) 7751 * BYTE(EXPRESSION): Output Section Data. 7752 (line 6) 7753 * C++ constructors, arranging in link: Output Section Keywords. 7754 (line 19) 7755 * CHIP (MRI): MRI. (line 58) 7756 * COLLECT_NO_DEMANGLE: Environment. (line 29) 7757 * combining symbols, warnings on: Options. (line 1394) 7758 * command files: Scripts. (line 6) 7759 * command line: Options. (line 6) 7760 * common allocation: Options. (line 168) 7761 * common allocation in linker script: Miscellaneous Commands. 7762 (line 20) 7763 * common symbol placement: Input Section Common. 7764 (line 6) 7765 * COMMONPAGESIZE: Symbolic Constants. (line 13) 7766 * compatibility, MRI: Options. (line 158) 7767 * CONSTANT: Symbolic Constants. (line 6) 7768 * constants in linker scripts: Constants. (line 6) 7769 * constraints on output sections: Output Section Constraint. 7770 (line 6) 7771 * constructors: Options. (line 583) 7772 * CONSTRUCTORS: Output Section Keywords. 7773 (line 19) 7774 * constructors, arranging in link: Output Section Keywords. 7775 (line 19) 7776 * Cortex-A53 erratum 835769 workaround: ARM. (line 174) 7777 * Cortex-A8 erratum workaround: ARM. (line 165) 7778 * crash of linker: Bug Criteria. (line 9) 7779 * CREATE_OBJECT_SYMBOLS: Output Section Keywords. 7780 (line 9) 7781 * creating a DEF file: WIN32. (line 158) 7782 * cross reference table: Options. (line 888) 7783 * cross references: Miscellaneous Commands. 7784 (line 56) 7785 * current output location: Location Counter. (line 6) 7786 * data: Output Section Data. 7787 (line 6) 7788 * DATA_SEGMENT_ALIGN(MAXPAGESIZE, COMMONPAGESIZE): Builtin Functions. 7789 (line 82) 7790 * DATA_SEGMENT_END(EXP): Builtin Functions. (line 103) 7791 * DATA_SEGMENT_RELRO_END(OFFSET, EXP): Builtin Functions. (line 109) 7792 * dbx: Options. (line 1309) 7793 * DEF files, creating: Options. (line 1801) 7794 * default emulation: Environment. (line 21) 7795 * default input format: Environment. (line 9) 7796 * DEFINED(SYMBOL): Builtin Functions. (line 122) 7797 * deleting local symbols: Options. (line 608) 7798 * demangling, default: Environment. (line 29) 7799 * demangling, from command line: Options. (line 930) 7800 * direct linking to a dll: WIN32. (line 239) 7801 * discarding sections: Output Section Discarding. 7802 (line 6) 7803 * discontinuous memory: MEMORY. (line 6) 7804 * DLLs, creating: Options. (line 1809) 7805 * DLLs, linking to: Options. (line 1833) 7806 * dot: Location Counter. (line 6) 7807 * dot inside sections: Location Counter. (line 36) 7808 * dot outside sections: Location Counter. (line 66) 7809 * dynamic linker, from command line: Options. (line 943) 7810 * dynamic symbol table: Options. (line 221) 7811 * ELF program headers: PHDRS. (line 6) 7812 * emulation: Options. (line 392) 7813 * emulation, default: Environment. (line 21) 7814 * END (MRI): MRI. (line 62) 7815 * endianness: Options. (line 248) 7816 * entry point: Entry Point. (line 6) 7817 * entry point, from command line: Options. (line 187) 7818 * entry point, thumb: ARM. (line 17) 7819 * ENTRY(SYMBOL): Entry Point. (line 6) 7820 * error on valid input: Bug Criteria. (line 12) 7821 * example of linker script: Simple Example. (line 6) 7822 * exporting DLL symbols: WIN32. (line 19) 7823 * expression evaluation order: Evaluation. (line 6) 7824 * expression sections: Expression Section. (line 6) 7825 * expression, absolute: Builtin Functions. (line 10) 7826 * expressions: Expressions. (line 6) 7827 * EXTERN: Miscellaneous Commands. 7828 (line 13) 7829 * fatal signal: Bug Criteria. (line 9) 7830 * file name wildcard patterns: Input Section Wildcards. 7831 (line 6) 7832 * FILEHDR: PHDRS. (line 62) 7833 * filename symbols: Output Section Keywords. 7834 (line 9) 7835 * fill pattern, entire section: Output Section Fill. 7836 (line 6) 7837 * FILL(EXPRESSION): Output Section Data. 7838 (line 39) 7839 * finalization function: Options. (line 300) 7840 * first input file: File Commands. (line 84) 7841 * first instruction: Entry Point. (line 6) 7842 * FIX_V4BX: ARM. (line 49) 7843 * FIX_V4BX_INTERWORKING: ARM. (line 62) 7844 * FORCE_COMMON_ALLOCATION: Miscellaneous Commands. 7845 (line 20) 7846 * forcing input section alignment: Forced Input Alignment. 7847 (line 6) 7848 * forcing output section alignment: Forced Output Alignment. 7849 (line 6) 7850 * forcing the creation of dynamic sections: Options. (line 506) 7851 * FORMAT (MRI): MRI. (line 66) 7852 * functions in expressions: Builtin Functions. (line 6) 7853 * garbage collection <1>: Options. (line 965) 7854 * garbage collection <2>: Input Section Keep. (line 6) 7855 * garbage collection: Options. (line 987) 7856 * generating optimized output: Options. (line 466) 7857 * GNU linker: Overview. (line 6) 7858 * GNUTARGET: Environment. (line 9) 7859 * GROUP(FILES): File Commands. (line 49) 7860 * grouping input files: File Commands. (line 49) 7861 * groups of archives: Options. (line 731) 7862 * H8/300 support: H8/300. (line 6) 7863 * header size: Builtin Functions. (line 190) 7864 * heap size: Options. (line 1736) 7865 * help: Options. (line 1002) 7866 * HIDDEN: HIDDEN. (line 6) 7867 * holes: Location Counter. (line 12) 7868 * holes, filling: Output Section Data. 7869 (line 39) 7870 * HPPA multiple sub-space stubs: HPPA ELF32. (line 6) 7871 * HPPA stub grouping: HPPA ELF32. (line 12) 7872 * i960 support: i960. (line 6) 7873 * image base: Options. (line 1743) 7874 * implicit linker scripts: Implicit Linker Scripts. 7875 (line 6) 7876 * import libraries: WIN32. (line 10) 7877 * INCLUDE FILENAME: File Commands. (line 9) 7878 * including a linker script: File Commands. (line 9) 7879 * including an entire archive: Options. (line 1507) 7880 * incremental link: Options. (line 325) 7881 * INHIBIT_COMMON_ALLOCATION: Miscellaneous Commands. 7882 (line 25) 7883 * initialization function: Options. (line 328) 7884 * initialized data in ROM: Output Section LMA. (line 39) 7885 * input file format in linker script: Format Commands. (line 35) 7886 * input filename symbols: Output Section Keywords. 7887 (line 9) 7888 * input files in linker scripts: File Commands. (line 19) 7889 * input files, displaying: Options. (line 549) 7890 * input format: Options. (line 134) 7891 * input object files in linker scripts: File Commands. (line 19) 7892 * input section alignment: Forced Input Alignment. 7893 (line 6) 7894 * input section basics: Input Section Basics. 7895 (line 6) 7896 * input section wildcards: Input Section Wildcards. 7897 (line 6) 7898 * input sections: Input Section. (line 6) 7899 * INPUT(FILES): File Commands. (line 19) 7900 * INSERT: Miscellaneous Commands. 7901 (line 30) 7902 * insert user script into default script: Miscellaneous Commands. 7903 (line 30) 7904 * integer notation: Constants. (line 6) 7905 * integer suffixes: Constants. (line 15) 7906 * internal object-file format: Canonical format. (line 11) 7907 * invalid input: Bug Criteria. (line 14) 7908 * K and M integer suffixes: Constants. (line 15) 7909 * KEEP: Input Section Keep. (line 6) 7910 * l =: MEMORY. (line 74) 7911 * lazy evaluation: Evaluation. (line 6) 7912 * ld bugs, reporting: Bug Reporting. (line 6) 7913 * LD_FEATURE(STRING): Miscellaneous Commands. 7914 (line 78) 7915 * ldata segment origin, cmd line: Options. (line 1342) 7916 * LDEMULATION: Environment. (line 21) 7917 * len =: MEMORY. (line 74) 7918 * LENGTH =: MEMORY. (line 74) 7919 * LENGTH(MEMORY): Builtin Functions. (line 139) 7920 * library search path in linker script: File Commands. (line 76) 7921 * link map: Options. (line 402) 7922 * link-time runtime library search path: Options. (line 1196) 7923 * linker crash: Bug Criteria. (line 9) 7924 * linker script concepts: Basic Script Concepts. 7925 (line 6) 7926 * linker script example: Simple Example. (line 6) 7927 * linker script file commands: File Commands. (line 6) 7928 * linker script format: Script Format. (line 6) 7929 * linker script input object files: File Commands. (line 19) 7930 * linker script simple commands: Simple Commands. (line 6) 7931 * linker scripts: Scripts. (line 6) 7932 * LIST (MRI): MRI. (line 77) 7933 * little-endian objects: Options. (line 251) 7934 * LOAD (MRI): MRI. (line 84) 7935 * load address: Output Section LMA. (line 6) 7936 * LOADADDR(SECTION): Builtin Functions. (line 142) 7937 * loading, preventing: Output Section Type. 7938 (line 22) 7939 * local symbols, deleting: Options. (line 612) 7940 * location counter: Location Counter. (line 6) 7941 * LOG2CEIL(EXP): Builtin Functions. (line 146) 7942 * LONG(EXPRESSION): Output Section Data. 7943 (line 6) 7944 * M and K integer suffixes: Constants. (line 15) 7945 * M68HC11 and 68HC12 support: M68HC11/68HC12. (line 6) 7946 * machine architecture: Miscellaneous Commands. 7947 (line 72) 7948 * machine dependencies: Machine Dependent. (line 6) 7949 * mapping input sections to output sections: Input Section. (line 6) 7950 * MAX: Builtin Functions. (line 149) 7951 * MAXPAGESIZE: Symbolic Constants. (line 10) 7952 * MEMORY: MEMORY. (line 6) 7953 * memory region attributes: MEMORY. (line 34) 7954 * memory regions: MEMORY. (line 6) 7955 * memory regions and sections: Output Section Region. 7956 (line 6) 7957 * memory usage: Options. (line 1014) 7958 * Merging exidx entries: ARM. (line 182) 7959 * MIN: Builtin Functions. (line 152) 7960 * MIPS microMIPS instruction choice selection: MIPS. (line 6) 7961 * Motorola 68K GOT generation: M68K. (line 6) 7962 * MRI compatibility: MRI. (line 6) 7963 * MSP430 extra sections: MSP430. (line 11) 7964 * NAME (MRI): MRI. (line 90) 7965 * name, section: Output Section Name. 7966 (line 6) 7967 * names: Symbols. (line 6) 7968 * naming the output file: Options. (line 460) 7969 * NEXT(EXP): Builtin Functions. (line 156) 7970 * Nios II call relaxation: Nios II. (line 6) 7971 * NMAGIC: Options. (line 439) 7972 * NO_ENUM_SIZE_WARNING: ARM. (line 120) 7973 * NO_WCHAR_SIZE_WARNING: ARM. (line 127) 7974 * NOCROSSREFS(SECTIONS): Miscellaneous Commands. 7975 (line 56) 7976 * NOLOAD: Output Section Type. 7977 (line 22) 7978 * not enough room for program headers: Builtin Functions. (line 195) 7979 * o =: MEMORY. (line 69) 7980 * objdump -i: BFD. (line 6) 7981 * object file management: BFD. (line 6) 7982 * object files: Options. (line 29) 7983 * object formats available: BFD. (line 6) 7984 * object size: Options. (line 309) 7985 * OMAGIC: Options. (line 445) 7986 * ONLY_IF_RO: Output Section Constraint. 7987 (line 6) 7988 * ONLY_IF_RW: Output Section Constraint. 7989 (line 6) 7990 * opening object files: BFD outline. (line 6) 7991 * operators for arithmetic: Operators. (line 6) 7992 * options: Options. (line 6) 7993 * ORDER (MRI): MRI. (line 95) 7994 * org =: MEMORY. (line 69) 7995 * ORIGIN =: MEMORY. (line 69) 7996 * ORIGIN(MEMORY): Builtin Functions. (line 162) 7997 * orphan: Orphan Sections. (line 6) 7998 * output file after errors: Options. (line 1093) 7999 * output file format in linker script: Format Commands. (line 10) 8000 * output file name in linker script: File Commands. (line 66) 8001 * output format: Options. (line 996) 8002 * output section alignment: Forced Output Alignment. 8003 (line 6) 8004 * output section attributes: Output Section Attributes. 8005 (line 6) 8006 * output section data: Output Section Data. 8007 (line 6) 8008 * OUTPUT(FILENAME): File Commands. (line 66) 8009 * OUTPUT_ARCH(BFDARCH): Miscellaneous Commands. 8010 (line 72) 8011 * OUTPUT_FORMAT(BFDNAME): Format Commands. (line 10) 8012 * OVERLAY: Overlay Description. 8013 (line 6) 8014 * overlays: Overlay Description. 8015 (line 6) 8016 * partial link: Options. (line 510) 8017 * PE import table prefixing: ARM. (line 23) 8018 * PHDRS: PHDRS. (line 62) 8019 * PIC_VENEER: ARM. (line 133) 8020 * pop state governing input file handling: Options. (line 494) 8021 * position independent executables: Options. (line 1120) 8022 * PowerPC ELF32 options: PowerPC ELF32. (line 16) 8023 * PowerPC GOT: PowerPC ELF32. (line 33) 8024 * PowerPC long branches: PowerPC ELF32. (line 6) 8025 * PowerPC PLT: PowerPC ELF32. (line 16) 8026 * PowerPC stub symbols: PowerPC ELF32. (line 47) 8027 * PowerPC TLS optimization: PowerPC ELF32. (line 51) 8028 * PowerPC64 dot symbols: PowerPC64 ELF64. (line 33) 8029 * PowerPC64 ELF64 options: PowerPC64 ELF64. (line 6) 8030 * PowerPC64 multi-TOC: PowerPC64 ELF64. (line 74) 8031 * PowerPC64 OPD optimization: PowerPC64 ELF64. (line 48) 8032 * PowerPC64 OPD spacing: PowerPC64 ELF64. (line 54) 8033 * PowerPC64 PLT call stub static chain: PowerPC64 ELF64. (line 104) 8034 * PowerPC64 PLT call stub thread safety: PowerPC64 ELF64. (line 110) 8035 * PowerPC64 PLT stub alignment: PowerPC64 ELF64. (line 96) 8036 * PowerPC64 stub grouping: PowerPC64 ELF64. (line 6) 8037 * PowerPC64 stub symbols: PowerPC64 ELF64. (line 29) 8038 * PowerPC64 TLS optimization: PowerPC64 ELF64. (line 43) 8039 * PowerPC64 TOC optimization: PowerPC64 ELF64. (line 60) 8040 * PowerPC64 TOC sorting: PowerPC64 ELF64. (line 86) 8041 * precedence in expressions: Operators. (line 6) 8042 * prevent unnecessary loading: Output Section Type. 8043 (line 22) 8044 * program headers: PHDRS. (line 6) 8045 * program headers and sections: Output Section Phdr. 8046 (line 6) 8047 * program headers, not enough room: Builtin Functions. (line 195) 8048 * program segments: PHDRS. (line 6) 8049 * PROVIDE: PROVIDE. (line 6) 8050 * PROVIDE_HIDDEN: PROVIDE_HIDDEN. (line 6) 8051 * PUBLIC (MRI): MRI. (line 103) 8052 * push state governing input file handling: Options. (line 476) 8053 * QUAD(EXPRESSION): Output Section Data. 8054 (line 6) 8055 * quoted symbol names: Symbols. (line 6) 8056 * read-only text: Options. (line 439) 8057 * read/write from cmd line: Options. (line 445) 8058 * region alias: REGION_ALIAS. (line 6) 8059 * region names: REGION_ALIAS. (line 6) 8060 * REGION_ALIAS(ALIAS, REGION): REGION_ALIAS. (line 6) 8061 * regions of memory: MEMORY. (line 6) 8062 * relative expressions: Expression Section. (line 6) 8063 * relaxing addressing modes: Options. (line 1134) 8064 * relaxing on H8/300: H8/300. (line 9) 8065 * relaxing on i960: i960. (line 31) 8066 * relaxing on M68HC11: M68HC11/68HC12. (line 12) 8067 * relaxing on NDS32: NDS32. (line 6) 8068 * relaxing on Xtensa: Xtensa. (line 27) 8069 * relocatable and absolute symbols: Expression Section. (line 6) 8070 * relocatable output: Options. (line 510) 8071 * removing sections: Output Section Discarding. 8072 (line 6) 8073 * reporting bugs in ld: Reporting Bugs. (line 6) 8074 * requirements for BFD: BFD. (line 16) 8075 * retain relocations in final executable: Options. (line 497) 8076 * retaining specified symbols: Options. (line 1160) 8077 * rodata segment origin, cmd line: Options. (line 1336) 8078 * ROM initialized data: Output Section LMA. (line 39) 8079 * round up expression: Builtin Functions. (line 38) 8080 * round up location counter: Builtin Functions. (line 38) 8081 * runtime library name: Options. (line 316) 8082 * runtime library search path: Options. (line 1174) 8083 * runtime pseudo-relocation: WIN32. (line 217) 8084 * scaled integers: Constants. (line 15) 8085 * scommon section: Input Section Common. 8086 (line 20) 8087 * script files: Options. (line 553) 8088 * scripts: Scripts. (line 6) 8089 * search directory, from cmd line: Options. (line 367) 8090 * search path in linker script: File Commands. (line 76) 8091 * SEARCH_DIR(PATH): File Commands. (line 76) 8092 * SECT (MRI): MRI. (line 109) 8093 * section address: Output Section Address. 8094 (line 6) 8095 * section address in expression: Builtin Functions. (line 17) 8096 * section alignment: Builtin Functions. (line 64) 8097 * section alignment, warnings on: Options. (line 1485) 8098 * section data: Output Section Data. 8099 (line 6) 8100 * section fill pattern: Output Section Fill. 8101 (line 6) 8102 * section load address: Output Section LMA. (line 6) 8103 * section load address in expression: Builtin Functions. (line 142) 8104 * section name: Output Section Name. 8105 (line 6) 8106 * section name wildcard patterns: Input Section Wildcards. 8107 (line 6) 8108 * section size: Builtin Functions. (line 174) 8109 * section, assigning to memory region: Output Section Region. 8110 (line 6) 8111 * section, assigning to program header: Output Section Phdr. 8112 (line 6) 8113 * SECTIONS: SECTIONS. (line 6) 8114 * sections, discarding: Output Section Discarding. 8115 (line 6) 8116 * segment origins, cmd line: Options. (line 1325) 8117 * SEGMENT_START(SEGMENT, DEFAULT): Builtin Functions. (line 165) 8118 * segments, ELF: PHDRS. (line 6) 8119 * shared libraries: Options. (line 1253) 8120 * SHORT(EXPRESSION): Output Section Data. 8121 (line 6) 8122 * SIZEOF(SECTION): Builtin Functions. (line 174) 8123 * SIZEOF_HEADERS: Builtin Functions. (line 190) 8124 * small common symbols: Input Section Common. 8125 (line 20) 8126 * SORT: Input Section Wildcards. 8127 (line 65) 8128 * SORT_BY_ALIGNMENT: Input Section Wildcards. 8129 (line 54) 8130 * SORT_BY_INIT_PRIORITY: Input Section Wildcards. 8131 (line 60) 8132 * SORT_BY_NAME: Input Section Wildcards. 8133 (line 46) 8134 * SORT_NONE: Input Section Wildcards. 8135 (line 106) 8136 * SPU: SPU ELF. (line 29) 8137 * SPU ELF options: SPU ELF. (line 6) 8138 * SPU extra overlay stubs: SPU ELF. (line 19) 8139 * SPU local store size: SPU ELF. (line 24) 8140 * SPU overlay stub symbols: SPU ELF. (line 15) 8141 * SPU overlays: SPU ELF. (line 9) 8142 * SPU plugins: SPU ELF. (line 6) 8143 * SQUAD(EXPRESSION): Output Section Data. 8144 (line 6) 8145 * stack size: Options. (line 1991) 8146 * standard Unix system: Options. (line 7) 8147 * start of execution: Entry Point. (line 6) 8148 * STARTUP(FILENAME): File Commands. (line 84) 8149 * strip all symbols: Options. (line 540) 8150 * strip debugger symbols: Options. (line 544) 8151 * stripping all but some symbols: Options. (line 1160) 8152 * STUB_GROUP_SIZE: ARM. (line 138) 8153 * SUBALIGN(SUBSECTION_ALIGN): Forced Input Alignment. 8154 (line 6) 8155 * suffixes for integers: Constants. (line 15) 8156 * symbol defaults: Builtin Functions. (line 122) 8157 * symbol definition, scripts: Assignments. (line 6) 8158 * symbol names: Symbols. (line 6) 8159 * symbol tracing: Options. (line 618) 8160 * symbol versions: VERSION. (line 6) 8161 * symbol-only input: Options. (line 529) 8162 * symbolic constants: Symbolic Constants. (line 6) 8163 * symbols, from command line: Options. (line 917) 8164 * symbols, relocatable and absolute: Expression Section. (line 6) 8165 * symbols, retaining selectively: Options. (line 1160) 8166 * synthesizing linker: Options. (line 1134) 8167 * synthesizing on H8/300: H8/300. (line 14) 8168 * TARGET(BFDNAME): Format Commands. (line 35) 8169 * TARGET1: ARM. (line 32) 8170 * TARGET2: ARM. (line 37) 8171 * text segment origin, cmd line: Options. (line 1332) 8172 * thumb entry point: ARM. (line 17) 8173 * TI COFF versions: TI COFF. (line 6) 8174 * traditional format: Options. (line 1304) 8175 * trampoline generation on M68HC11: M68HC11/68HC12. (line 31) 8176 * trampoline generation on M68HC12: M68HC11/68HC12. (line 31) 8177 * unallocated address, next: Builtin Functions. (line 156) 8178 * undefined symbol: Options. (line 575) 8179 * undefined symbol in linker script: Miscellaneous Commands. 8180 (line 13) 8181 * undefined symbols, warnings on: Options. (line 1481) 8182 * uninitialized data placement: Input Section Common. 8183 (line 6) 8184 * unspecified memory: Output Section Data. 8185 (line 39) 8186 * usage: Options. (line 1002) 8187 * USE_BLX: ARM. (line 74) 8188 * using a DEF file: WIN32. (line 57) 8189 * using auto-export functionality: WIN32. (line 22) 8190 * Using decorations: WIN32. (line 162) 8191 * variables, defining: Assignments. (line 6) 8192 * verbose[=NUMBER]: Options. (line 1375) 8193 * version: Options. (line 602) 8194 * version script: VERSION. (line 6) 8195 * version script, symbol versions: Options. (line 1383) 8196 * VERSION {script text}: VERSION. (line 6) 8197 * versions of symbols: VERSION. (line 6) 8198 * VFP11_DENORM_FIX: ARM. (line 83) 8199 * warnings, on combining symbols: Options. (line 1394) 8200 * warnings, on section alignment: Options. (line 1485) 8201 * warnings, on undefined symbols: Options. (line 1481) 8202 * weak externals: WIN32. (line 407) 8203 * what is this?: Overview. (line 6) 8204 * wildcard file name patterns: Input Section Wildcards. 8205 (line 6) 8206 * Xtensa options: Xtensa. (line 56) 8207 * Xtensa processors: Xtensa. (line 6) 8208 8209 8210 8211 Tag Table: 8212 Node: Top710 8213 Node: Overview1493 8214 Node: Invocation2607 8215 Node: Options3015 8216 Node: Environment98821 8217 Node: Scripts100581 8218 Node: Basic Script Concepts102315 8219 Node: Script Format105023 8220 Node: Simple Example105886 8221 Node: Simple Commands108982 8222 Node: Entry Point109488 8223 Node: File Commands110421 8224 Node: Format Commands114541 8225 Node: REGION_ALIAS116497 8226 Node: Miscellaneous Commands121329 8227 Node: Assignments124937 8228 Node: Simple Assignments125448 8229 Node: HIDDEN127183 8230 Node: PROVIDE127813 8231 Node: PROVIDE_HIDDEN129006 8232 Node: Source Code Reference129250 8233 Node: SECTIONS132832 8234 Node: Output Section Description134723 8235 Node: Output Section Name135967 8236 Node: Output Section Address136843 8237 Node: Input Section139078 8238 Node: Input Section Basics139879 8239 Node: Input Section Wildcards143785 8240 Node: Input Section Common148992 8241 Node: Input Section Keep150474 8242 Node: Input Section Example150964 8243 Node: Output Section Data151932 8244 Node: Output Section Keywords154709 8245 Node: Output Section Discarding158278 8246 Node: Output Section Attributes159771 8247 Node: Output Section Type160872 8248 Node: Output Section LMA161943 8249 Node: Forced Output Alignment165014 8250 Node: Forced Input Alignment165444 8251 Node: Output Section Constraint165833 8252 Node: Output Section Region166261 8253 Node: Output Section Phdr166694 8254 Node: Output Section Fill167358 8255 Node: Overlay Description168500 8256 Node: MEMORY172946 8257 Node: PHDRS177281 8258 Node: VERSION182535 8259 Node: Expressions190628 8260 Node: Constants191557 8261 Node: Symbolic Constants192432 8262 Node: Symbols192983 8263 Node: Orphan Sections193730 8264 Node: Location Counter194895 8265 Node: Operators199331 8266 Node: Evaluation200253 8267 Node: Expression Section201617 8268 Node: Builtin Functions205481 8269 Node: Implicit Linker Scripts213677 8270 Node: Machine Dependent214452 8271 Node: H8/300215576 8272 Node: i960217638 8273 Node: M68HC11/68HC12219334 8274 Node: ARM220776 8275 Node: HPPA ELF32229814 8276 Node: M68K231437 8277 Node: MIPS232346 8278 Node: MMIX232870 8279 Node: MSP430234035 8280 Node: NDS32235075 8281 Node: Nios II236041 8282 Node: PowerPC ELF32237357 8283 Node: PowerPC64 ELF64240188 8284 Node: SPU ELF246422 8285 Node: TI COFF249054 8286 Node: WIN32249580 8287 Node: Xtensa269706 8288 Node: BFD272671 8289 Node: BFD outline274126 8290 Node: BFD information loss275412 8291 Node: Canonical format277929 8292 Node: Reporting Bugs282286 8293 Node: Bug Criteria282980 8294 Node: Bug Reporting283679 8295 Node: MRI290718 8296 Node: GNU Free Documentation License295361 8297 Node: LD Index320517 8298 8299 End Tag Table 8300
