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 2.21.90. 9 10 Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 11 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free 12 Software Foundation, Inc. 13 14 Permission is granted to copy, distribute and/or modify this document 15 under the terms of the GNU Free Documentation License, Version 1.3 or 16 any later version published by the Free Software Foundation; with no 17 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover 18 Texts. A copy of the license is included in the section entitled "GNU 19 Free Documentation License". 20 21 22 File: ld.info, Node: Top, Next: Overview, Up: (dir) 23 24 LD 25 ** 26 27 This file documents the GNU linker ld (GNU Binutils) version 2.21.90. 28 29 This document is distributed under the terms of the GNU Free 30 Documentation License version 1.3. A copy of the license is included 31 in the section entitled "GNU Free Documentation License". 32 33 * Menu: 34 35 * Overview:: Overview 36 * Invocation:: Invocation 37 * Scripts:: Linker Scripts 38 39 * Machine Dependent:: Machine Dependent Features 40 41 * BFD:: BFD 42 43 * Reporting Bugs:: Reporting Bugs 44 * MRI:: MRI Compatible Script Files 45 * GNU Free Documentation License:: GNU Free Documentation License 46 * LD Index:: LD Index 47 48 49 File: ld.info, Node: Overview, Next: Invocation, Prev: Top, Up: Top 50 51 1 Overview 52 ********** 53 54 `ld' combines a number of object and archive files, relocates their 55 data and ties up symbol references. Usually the last step in compiling 56 a program is to run `ld'. 57 58 `ld' accepts Linker Command Language files written in a superset of 59 AT&T's Link Editor Command Language syntax, to provide explicit and 60 total control over the linking process. 61 62 This version of `ld' uses the general purpose BFD libraries to 63 operate on object files. This allows `ld' to read, combine, and write 64 object files in many different formats--for example, COFF or `a.out'. 65 Different formats may be linked together to produce any available kind 66 of object file. *Note BFD::, for more information. 67 68 Aside from its flexibility, the GNU linker is more helpful than other 69 linkers in providing diagnostic information. Many linkers abandon 70 execution immediately upon encountering an error; whenever possible, 71 `ld' continues executing, allowing you to identify other errors (or, in 72 some cases, to get an output file in spite of the error). 73 74 75 File: ld.info, Node: Invocation, Next: Scripts, Prev: Overview, Up: Top 76 77 2 Invocation 78 ************ 79 80 The GNU linker `ld' is meant to cover a broad range of situations, and 81 to be as compatible as possible with other linkers. As a result, you 82 have many choices to control its behavior. 83 84 * Menu: 85 86 * Options:: Command Line Options 87 * Environment:: Environment Variables 88 89 90 File: ld.info, Node: Options, Next: Environment, Up: Invocation 91 92 2.1 Command Line Options 93 ======================== 94 95 The linker supports a plethora of command-line options, but in actual 96 practice few of them are used in any particular context. For instance, 97 a frequent use of `ld' is to link standard Unix object files on a 98 standard, supported Unix system. On such a system, to link a file 99 `hello.o': 100 101 ld -o OUTPUT /lib/crt0.o hello.o -lc 102 103 This tells `ld' to produce a file called OUTPUT as the result of 104 linking the file `/lib/crt0.o' with `hello.o' and the library `libc.a', 105 which will come from the standard search directories. (See the 106 discussion of the `-l' option below.) 107 108 Some of the command-line options to `ld' may be specified at any 109 point in the command line. However, options which refer to files, such 110 as `-l' or `-T', cause the file to be read at the point at which the 111 option appears in the command line, relative to the object files and 112 other file options. Repeating non-file options with a different 113 argument will either have no further effect, or override prior 114 occurrences (those further to the left on the command line) of that 115 option. Options which may be meaningfully specified more than once are 116 noted in the descriptions below. 117 118 Non-option arguments are object files or archives which are to be 119 linked together. They may follow, precede, or be mixed in with 120 command-line options, except that an object file argument may not be 121 placed between an option and its argument. 122 123 Usually the linker is invoked with at least one object file, but you 124 can specify other forms of binary input files using `-l', `-R', and the 125 script command language. If _no_ binary input files at all are 126 specified, the linker does not produce any output, and issues the 127 message `No input files'. 128 129 If the linker cannot recognize the format of an object file, it will 130 assume that it is a linker script. A script specified in this way 131 augments the main linker script used for the link (either the default 132 linker script or the one specified by using `-T'). This feature 133 permits the linker to link against a file which appears to be an object 134 or an archive, but actually merely defines some symbol values, or uses 135 `INPUT' or `GROUP' to load other objects. Specifying a script in this 136 way merely augments the main linker script, with the extra commands 137 placed after the main script; use the `-T' option to replace the 138 default linker script entirely, but note the effect of the `INSERT' 139 command. *Note Scripts::. 140 141 For options whose names are a single letter, option arguments must 142 either follow the option letter without intervening whitespace, or be 143 given as separate arguments immediately following the option that 144 requires them. 145 146 For options whose names are multiple letters, either one dash or two 147 can precede the option name; for example, `-trace-symbol' and 148 `--trace-symbol' are equivalent. Note--there is one exception to this 149 rule. Multiple letter options that start with a lower case 'o' can 150 only be preceded by two dashes. This is to reduce confusion with the 151 `-o' option. So for example `-omagic' sets the output file name to 152 `magic' whereas `--omagic' sets the NMAGIC flag on the output. 153 154 Arguments to multiple-letter options must either be separated from 155 the option name by an equals sign, or be given as separate arguments 156 immediately following the option that requires them. For example, 157 `--trace-symbol foo' and `--trace-symbol=foo' are equivalent. Unique 158 abbreviations of the names of multiple-letter options are accepted. 159 160 Note--if the linker is being invoked indirectly, via a compiler 161 driver (e.g. `gcc') then all the linker command line options should be 162 prefixed by `-Wl,' (or whatever is appropriate for the particular 163 compiler driver) like this: 164 165 gcc -Wl,--start-group foo.o bar.o -Wl,--end-group 166 167 This is important, because otherwise the compiler driver program may 168 silently drop the linker options, resulting in a bad link. Confusion 169 may also arise when passing options that require values through a 170 driver, as the use of a space between option and argument acts as a 171 separator, and causes the driver to pass only the option to the linker 172 and the argument to the compiler. In this case, it is simplest to use 173 the joined forms of both single- and multiple-letter options, such as: 174 175 gcc foo.o bar.o -Wl,-eENTRY -Wl,-Map=a.map 176 177 Here is a table of the generic command line switches accepted by the 178 GNU linker: 179 180 `@FILE' 181 Read command-line options from FILE. The options read are 182 inserted in place of the original @FILE option. If FILE does not 183 exist, or cannot be read, then the option will be treated 184 literally, and not removed. 185 186 Options in FILE are separated by whitespace. A whitespace 187 character may be included in an option by surrounding the entire 188 option in either single or double quotes. Any character 189 (including a backslash) may be included by prefixing the character 190 to be included with a backslash. The FILE may itself contain 191 additional @FILE options; any such options will be processed 192 recursively. 193 194 `-a KEYWORD' 195 This option is supported for HP/UX compatibility. The KEYWORD 196 argument must be one of the strings `archive', `shared', or 197 `default'. `-aarchive' is functionally equivalent to `-Bstatic', 198 and the other two keywords are functionally equivalent to 199 `-Bdynamic'. This option may be used any number of times. 200 201 `--audit AUDITLIB' 202 Adds AUDITLIB to the `DT_AUDIT' entry of the dynamic section. 203 AUDITLIB is not checked for existence, nor will it use the 204 DT_SONAME specified in the library. If specified multiple times 205 `DT_AUDIT' will contain a colon separated list of audit interfaces 206 to use. If the linker finds an object with an audit entry while 207 searching for shared libraries, it will add a corresponding 208 `DT_DEPAUDIT' entry in the output file. This option is only 209 meaningful on ELF platforms supporting the rtld-audit interface. 210 211 `-A ARCHITECTURE' 212 `--architecture=ARCHITECTURE' 213 In the current release of `ld', this option is useful only for the 214 Intel 960 family of architectures. In that `ld' configuration, the 215 ARCHITECTURE argument identifies the particular architecture in 216 the 960 family, enabling some safeguards and modifying the 217 archive-library search path. *Note `ld' and the Intel 960 family: 218 i960, for details. 219 220 Future releases of `ld' may support similar functionality for 221 other architecture families. 222 223 `-b INPUT-FORMAT' 224 `--format=INPUT-FORMAT' 225 `ld' may be configured to support more than one kind of object 226 file. If your `ld' is configured this way, you can use the `-b' 227 option to specify the binary format for input object files that 228 follow this option on the command line. Even when `ld' is 229 configured to support alternative object formats, you don't 230 usually need to specify this, as `ld' should be configured to 231 expect as a default input format the most usual format on each 232 machine. INPUT-FORMAT is a text string, the name of a particular 233 format supported by the BFD libraries. (You can list the 234 available binary formats with `objdump -i'.) *Note BFD::. 235 236 You may want to use this option if you are linking files with an 237 unusual binary format. You can also use `-b' to switch formats 238 explicitly (when linking object files of different formats), by 239 including `-b INPUT-FORMAT' before each group of object files in a 240 particular format. 241 242 The default format is taken from the environment variable 243 `GNUTARGET'. *Note Environment::. You can also define the input 244 format from a script, using the command `TARGET'; see *Note Format 245 Commands::. 246 247 `-c MRI-COMMANDFILE' 248 `--mri-script=MRI-COMMANDFILE' 249 For compatibility with linkers produced by MRI, `ld' accepts script 250 files written in an alternate, restricted command language, 251 described in *Note MRI Compatible Script Files: MRI. Introduce 252 MRI script files with the option `-c'; use the `-T' option to run 253 linker scripts written in the general-purpose `ld' scripting 254 language. If MRI-CMDFILE does not exist, `ld' looks for it in the 255 directories specified by any `-L' options. 256 257 `-d' 258 `-dc' 259 `-dp' 260 These three options are equivalent; multiple forms are supported 261 for compatibility with other linkers. They assign space to common 262 symbols even if a relocatable output file is specified (with 263 `-r'). The script command `FORCE_COMMON_ALLOCATION' has the same 264 effect. *Note Miscellaneous Commands::. 265 266 `--depaudit AUDITLIB' 267 `-P AUDITLIB' 268 Adds AUDITLIB to the `DT_DEPAUDIT' entry of the dynamic section. 269 AUDITLIB is not checked for existence, nor will it use the 270 DT_SONAME specified in the library. If specified multiple times 271 `DT_DEPAUDIT' will contain a colon separated list of audit 272 interfaces to use. This option is only meaningful on ELF 273 platforms supporting the rtld-audit interface. The -P option is 274 provided for Solaris compatibility. 275 276 `-e ENTRY' 277 `--entry=ENTRY' 278 Use ENTRY as the explicit symbol for beginning execution of your 279 program, rather than the default entry point. If there is no 280 symbol named ENTRY, the linker will try to parse ENTRY as a number, 281 and use that as the entry address (the number will be interpreted 282 in base 10; you may use a leading `0x' for base 16, or a leading 283 `0' for base 8). *Note Entry Point::, for a discussion of defaults 284 and other ways of specifying the entry point. 285 286 `--exclude-libs LIB,LIB,...' 287 Specifies a list of archive libraries from which symbols should 288 not be automatically exported. The library names may be delimited 289 by commas or colons. Specifying `--exclude-libs ALL' excludes 290 symbols in all archive libraries from automatic export. This 291 option is available only for the i386 PE targeted port of the 292 linker and for ELF targeted ports. For i386 PE, symbols 293 explicitly listed in a .def file are still exported, regardless of 294 this option. For ELF targeted ports, symbols affected by this 295 option will be treated as hidden. 296 297 `--exclude-modules-for-implib MODULE,MODULE,...' 298 Specifies a list of object files or archive members, from which 299 symbols should not be automatically exported, but which should be 300 copied wholesale into the import library being generated during 301 the link. The module names may be delimited by commas or colons, 302 and must match exactly the filenames used by `ld' to open the 303 files; for archive members, this is simply the member name, but 304 for object files the name listed must include and match precisely 305 any path used to specify the input file on the linker's 306 command-line. This option is available only for the i386 PE 307 targeted port of the linker. Symbols explicitly listed in a .def 308 file are still exported, regardless of this option. 309 310 `-E' 311 `--export-dynamic' 312 `--no-export-dynamic' 313 When creating a dynamically linked executable, using the `-E' 314 option or the `--export-dynamic' option causes the linker to add 315 all symbols to the dynamic symbol table. The dynamic symbol table 316 is the set of symbols which are visible from dynamic objects at 317 run time. 318 319 If you do not use either of these options (or use the 320 `--no-export-dynamic' option to restore the default behavior), the 321 dynamic symbol table will normally contain only those symbols 322 which are referenced by some dynamic object mentioned in the link. 323 324 If you use `dlopen' to load a dynamic object which needs to refer 325 back to the symbols defined by the program, rather than some other 326 dynamic object, then you will probably need to use this option when 327 linking the program itself. 328 329 You can also use the dynamic list to control what symbols should 330 be added to the dynamic symbol table if the output format supports 331 it. See the description of `--dynamic-list'. 332 333 Note that this option is specific to ELF targeted ports. PE 334 targets support a similar function to export all symbols from a 335 DLL or EXE; see the description of `--export-all-symbols' below. 336 337 `-EB' 338 Link big-endian objects. This affects the default output format. 339 340 `-EL' 341 Link little-endian objects. This affects the default output 342 format. 343 344 `-f NAME' 345 `--auxiliary=NAME' 346 When creating an ELF shared object, set the internal DT_AUXILIARY 347 field to the specified name. This tells the dynamic linker that 348 the symbol table of the shared object should be used as an 349 auxiliary filter on the symbol table of the shared object NAME. 350 351 If you later link a program against this filter object, then, when 352 you run the program, the dynamic linker will see the DT_AUXILIARY 353 field. If the dynamic linker resolves any symbols from the filter 354 object, it will first check whether there is a definition in the 355 shared object NAME. If there is one, it will be used instead of 356 the definition in the filter object. The shared object NAME need 357 not exist. Thus the shared object NAME may be used to provide an 358 alternative implementation of certain functions, perhaps for 359 debugging or for machine specific performance. 360 361 This option may be specified more than once. The DT_AUXILIARY 362 entries will be created in the order in which they appear on the 363 command line. 364 365 `-F NAME' 366 `--filter=NAME' 367 When creating an ELF shared object, set the internal DT_FILTER 368 field to the specified name. This tells the dynamic linker that 369 the symbol table of the shared object which is being created 370 should be used as a filter on the symbol table of the shared 371 object NAME. 372 373 If you later link a program against this filter object, then, when 374 you run the program, the dynamic linker will see the DT_FILTER 375 field. The dynamic linker will resolve symbols according to the 376 symbol table of the filter object as usual, but it will actually 377 link to the definitions found in the shared object NAME. Thus the 378 filter object can be used to select a subset of the symbols 379 provided by the object NAME. 380 381 Some older linkers used the `-F' option throughout a compilation 382 toolchain for specifying object-file format for both input and 383 output object files. The GNU linker uses other mechanisms for 384 this purpose: the `-b', `--format', `--oformat' options, the 385 `TARGET' command in linker scripts, and the `GNUTARGET' 386 environment variable. The GNU linker will ignore the `-F' option 387 when not creating an ELF shared object. 388 389 `-fini=NAME' 390 When creating an ELF executable or shared object, call NAME when 391 the executable or shared object is unloaded, by setting DT_FINI to 392 the address of the function. By default, the linker uses `_fini' 393 as the function to call. 394 395 `-g' 396 Ignored. Provided for compatibility with other tools. 397 398 `-G VALUE' 399 `--gpsize=VALUE' 400 Set the maximum size of objects to be optimized using the GP 401 register to SIZE. This is only meaningful for object file formats 402 such as MIPS ECOFF which supports putting large and small objects 403 into different sections. This is ignored for other object file 404 formats. 405 406 `-h NAME' 407 `-soname=NAME' 408 When creating an ELF shared object, set the internal DT_SONAME 409 field to the specified name. When an executable is linked with a 410 shared object which has a DT_SONAME field, then when the 411 executable is run the dynamic linker will attempt to load the 412 shared object specified by the DT_SONAME field rather than the 413 using the file name given to the linker. 414 415 `-i' 416 Perform an incremental link (same as option `-r'). 417 418 `-init=NAME' 419 When creating an ELF executable or shared object, call NAME when 420 the executable or shared object is loaded, by setting DT_INIT to 421 the address of the function. By default, the linker uses `_init' 422 as the function to call. 423 424 `-l NAMESPEC' 425 `--library=NAMESPEC' 426 Add the archive or object file specified by NAMESPEC to the list 427 of files to link. This option may be used any number of times. 428 If NAMESPEC is of the form `:FILENAME', `ld' will search the 429 library path for a file called FILENAME, otherwise it will search 430 the library path for a file called `libNAMESPEC.a'. 431 432 On systems which support shared libraries, `ld' may also search for 433 files other than `libNAMESPEC.a'. Specifically, on ELF and SunOS 434 systems, `ld' will search a directory for a library called 435 `libNAMESPEC.so' before searching for one called `libNAMESPEC.a'. 436 (By convention, a `.so' extension indicates a shared library.) 437 Note that this behavior does not apply to `:FILENAME', which 438 always specifies a file called FILENAME. 439 440 The linker will search an archive only once, at the location where 441 it is specified on the command line. If the archive defines a 442 symbol which was undefined in some object which appeared before 443 the archive on the command line, the linker will include the 444 appropriate file(s) from the archive. However, an undefined 445 symbol in an object appearing later on the command line will not 446 cause the linker to search the archive again. 447 448 See the `-(' option for a way to force the linker to search 449 archives multiple times. 450 451 You may list the same archive multiple times on the command line. 452 453 This type of archive searching is standard for Unix linkers. 454 However, if you are using `ld' on AIX, note that it is different 455 from the behaviour of the AIX linker. 456 457 `-L SEARCHDIR' 458 `--library-path=SEARCHDIR' 459 Add path SEARCHDIR to the list of paths that `ld' will search for 460 archive libraries and `ld' control scripts. You may use this 461 option any number of times. The directories are searched in the 462 order in which they are specified on the command line. 463 Directories specified on the command line are searched before the 464 default directories. All `-L' options apply to all `-l' options, 465 regardless of the order in which the options appear. `-L' options 466 do not affect how `ld' searches for a linker script unless `-T' 467 option is specified. 468 469 If SEARCHDIR begins with `=', then the `=' will be replaced by the 470 "sysroot prefix", a path specified when the linker is configured. 471 472 The default set of paths searched (without being specified with 473 `-L') depends on which emulation mode `ld' is using, and in some 474 cases also on how it was configured. *Note Environment::. 475 476 The paths can also be specified in a link script with the 477 `SEARCH_DIR' command. Directories specified this way are searched 478 at the point in which the linker script appears in the command 479 line. 480 481 `-m EMULATION' 482 Emulate the EMULATION linker. You can list the available 483 emulations with the `--verbose' or `-V' options. 484 485 If the `-m' option is not used, the emulation is taken from the 486 `LDEMULATION' environment variable, if that is defined. 487 488 Otherwise, the default emulation depends upon how the linker was 489 configured. 490 491 `-M' 492 `--print-map' 493 Print a link map to the standard output. A link map provides 494 information about the link, including the following: 495 496 * Where object files are mapped into memory. 497 498 * How common symbols are allocated. 499 500 * All archive members included in the link, with a mention of 501 the symbol which caused the archive member to be brought in. 502 503 * The values assigned to symbols. 504 505 Note - symbols whose values are computed by an expression 506 which involves a reference to a previous value of the same 507 symbol may not have correct result displayed in the link map. 508 This is because the linker discards intermediate results and 509 only retains the final value of an expression. Under such 510 circumstances the linker will display the final value 511 enclosed by square brackets. Thus for example a linker 512 script containing: 513 514 foo = 1 515 foo = foo * 4 516 foo = foo + 8 517 518 will produce the following output in the link map if the `-M' 519 option is used: 520 521 0x00000001 foo = 0x1 522 [0x0000000c] foo = (foo * 0x4) 523 [0x0000000c] foo = (foo + 0x8) 524 525 See *Note Expressions:: for more information about 526 expressions in linker scripts. 527 528 `-n' 529 `--nmagic' 530 Turn off page alignment of sections, and disable linking against 531 shared libraries. If the output format supports Unix style magic 532 numbers, mark the output as `NMAGIC'. 533 534 `-N' 535 `--omagic' 536 Set the text and data sections to be readable and writable. Also, 537 do not page-align the data segment, and disable linking against 538 shared libraries. If the output format supports Unix style magic 539 numbers, mark the output as `OMAGIC'. Note: Although a writable 540 text section is allowed for PE-COFF targets, it does not conform 541 to the format specification published by Microsoft. 542 543 `--no-omagic' 544 This option negates most of the effects of the `-N' option. It 545 sets the text section to be read-only, and forces the data segment 546 to be page-aligned. Note - this option does not enable linking 547 against shared libraries. Use `-Bdynamic' for this. 548 549 `-o OUTPUT' 550 `--output=OUTPUT' 551 Use OUTPUT as the name for the program produced by `ld'; if this 552 option is not specified, the name `a.out' is used by default. The 553 script command `OUTPUT' can also specify the output file name. 554 555 `-O LEVEL' 556 If LEVEL is a numeric values greater than zero `ld' optimizes the 557 output. This might take significantly longer and therefore 558 probably should only be enabled for the final binary. At the 559 moment this option only affects ELF shared library generation. 560 Future releases of the linker may make more use of this option. 561 Also currently there is no difference in the linker's behaviour 562 for different non-zero values of this option. Again this may 563 change with future releases. 564 565 `-q' 566 `--emit-relocs' 567 Leave relocation sections and contents in fully linked executables. 568 Post link analysis and optimization tools may need this 569 information in order to perform correct modifications of 570 executables. This results in larger executables. 571 572 This option is currently only supported on ELF platforms. 573 574 `--force-dynamic' 575 Force the output file to have dynamic sections. This option is 576 specific to VxWorks targets. 577 578 `-r' 579 `--relocatable' 580 Generate relocatable output--i.e., generate an output file that 581 can in turn serve as input to `ld'. This is often called "partial 582 linking". As a side effect, in environments that support standard 583 Unix magic numbers, this option also sets the output file's magic 584 number to `OMAGIC'. If this option is not specified, an absolute 585 file is produced. When linking C++ programs, this option _will 586 not_ resolve references to constructors; to do that, use `-Ur'. 587 588 When an input file does not have the same format as the output 589 file, partial linking is only supported if that input file does 590 not contain any relocations. Different output formats can have 591 further restrictions; for example some `a.out'-based formats do 592 not support partial linking with input files in other formats at 593 all. 594 595 This option does the same thing as `-i'. 596 597 `-R FILENAME' 598 `--just-symbols=FILENAME' 599 Read symbol names and their addresses from FILENAME, but do not 600 relocate it or include it in the output. This allows your output 601 file to refer symbolically to absolute locations of memory defined 602 in other programs. You may use this option more than once. 603 604 For compatibility with other ELF linkers, if the `-R' option is 605 followed by a directory name, rather than a file name, it is 606 treated as the `-rpath' option. 607 608 `-s' 609 `--strip-all' 610 Omit all symbol information from the output file. 611 612 `-S' 613 `--strip-debug' 614 Omit debugger symbol information (but not all symbols) from the 615 output file. 616 617 `-t' 618 `--trace' 619 Print the names of the input files as `ld' processes them. 620 621 `-T SCRIPTFILE' 622 `--script=SCRIPTFILE' 623 Use SCRIPTFILE as the linker script. This script replaces `ld''s 624 default linker script (rather than adding to it), so COMMANDFILE 625 must specify everything necessary to describe the output file. 626 *Note Scripts::. If SCRIPTFILE does not exist in the current 627 directory, `ld' looks for it in the directories specified by any 628 preceding `-L' options. Multiple `-T' options accumulate. 629 630 `-dT SCRIPTFILE' 631 `--default-script=SCRIPTFILE' 632 Use SCRIPTFILE as the default linker script. *Note Scripts::. 633 634 This option is similar to the `--script' option except that 635 processing of the script is delayed until after the rest of the 636 command line has been processed. This allows options placed after 637 the `--default-script' option on the command line to affect the 638 behaviour of the linker script, which can be important when the 639 linker command line cannot be directly controlled by the user. 640 (eg because the command line is being constructed by another tool, 641 such as `gcc'). 642 643 `-u SYMBOL' 644 `--undefined=SYMBOL' 645 Force SYMBOL to be entered in the output file as an undefined 646 symbol. Doing this may, for example, trigger linking of additional 647 modules from standard libraries. `-u' may be repeated with 648 different option arguments to enter additional undefined symbols. 649 This option is equivalent to the `EXTERN' linker script command. 650 651 `-Ur' 652 For anything other than C++ programs, this option is equivalent to 653 `-r': it generates relocatable output--i.e., an output file that 654 can in turn serve as input to `ld'. When linking C++ programs, 655 `-Ur' _does_ resolve references to constructors, unlike `-r'. It 656 does not work to use `-Ur' on files that were themselves linked 657 with `-Ur'; once the constructor table has been built, it cannot 658 be added to. Use `-Ur' only for the last partial link, and `-r' 659 for the others. 660 661 `--unique[=SECTION]' 662 Creates a separate output section for every input section matching 663 SECTION, or if the optional wildcard SECTION argument is missing, 664 for every orphan input section. An orphan section is one not 665 specifically mentioned in a linker script. You may use this option 666 multiple times on the command line; It prevents the normal 667 merging of input sections with the same name, overriding output 668 section assignments in a linker script. 669 670 `-v' 671 `--version' 672 `-V' 673 Display the version number for `ld'. The `-V' option also lists 674 the supported emulations. 675 676 `-x' 677 `--discard-all' 678 Delete all local symbols. 679 680 `-X' 681 `--discard-locals' 682 Delete all temporary local symbols. (These symbols start with 683 system-specific local label prefixes, typically `.L' for ELF 684 systems or `L' for traditional a.out systems.) 685 686 `-y SYMBOL' 687 `--trace-symbol=SYMBOL' 688 Print the name of each linked file in which SYMBOL appears. This 689 option may be given any number of times. On many systems it is 690 necessary to prepend an underscore. 691 692 This option is useful when you have an undefined symbol in your 693 link but don't know where the reference is coming from. 694 695 `-Y PATH' 696 Add PATH to the default library search path. This option exists 697 for Solaris compatibility. 698 699 `-z KEYWORD' 700 The recognized keywords are: 701 `combreloc' 702 Combines multiple reloc sections and sorts them to make 703 dynamic symbol lookup caching possible. 704 705 `defs' 706 Disallows undefined symbols in object files. Undefined 707 symbols in shared libraries are still allowed. 708 709 `execstack' 710 Marks the object as requiring executable stack. 711 712 `initfirst' 713 This option is only meaningful when building a shared object. 714 It marks the object so that its runtime initialization will 715 occur before the runtime initialization of any other objects 716 brought into the process at the same time. Similarly the 717 runtime finalization of the object will occur after the 718 runtime finalization of any other objects. 719 720 `interpose' 721 Marks the object that its symbol table interposes before all 722 symbols but the primary executable. 723 724 `lazy' 725 When generating an executable or shared library, mark it to 726 tell the dynamic linker to defer function call resolution to 727 the point when the function is called (lazy binding), rather 728 than at load time. Lazy binding is the default. 729 730 `loadfltr' 731 Marks the object that its filters be processed immediately at 732 runtime. 733 734 `muldefs' 735 Allows multiple definitions. 736 737 `nocombreloc' 738 Disables multiple reloc sections combining. 739 740 `nocopyreloc' 741 Disables production of copy relocs. 742 743 `nodefaultlib' 744 Marks the object that the search for dependencies of this 745 object will ignore any default library search paths. 746 747 `nodelete' 748 Marks the object shouldn't be unloaded at runtime. 749 750 `nodlopen' 751 Marks the object not available to `dlopen'. 752 753 `nodump' 754 Marks the object can not be dumped by `dldump'. 755 756 `noexecstack' 757 Marks the object as not requiring executable stack. 758 759 `norelro' 760 Don't create an ELF `PT_GNU_RELRO' segment header in the 761 object. 762 763 `now' 764 When generating an executable or shared library, mark it to 765 tell the dynamic linker to resolve all symbols when the 766 program is started, or when the shared library is linked to 767 using dlopen, instead of deferring function call resolution 768 to the point when the function is first called. 769 770 `origin' 771 Marks the object may contain $ORIGIN. 772 773 `relro' 774 Create an ELF `PT_GNU_RELRO' segment header in the object. 775 776 `max-page-size=VALUE' 777 Set the emulation maximum page size to VALUE. 778 779 `common-page-size=VALUE' 780 Set the emulation common page size to VALUE. 781 782 783 Other keywords are ignored for Solaris compatibility. 784 785 `-( ARCHIVES -)' 786 `--start-group ARCHIVES --end-group' 787 The ARCHIVES should be a list of archive files. They may be 788 either explicit file names, or `-l' options. 789 790 The specified archives are searched repeatedly until no new 791 undefined references are created. Normally, an archive is 792 searched only once in the order that it is specified on the 793 command line. If a symbol in that archive is needed to resolve an 794 undefined symbol referred to by an object in an archive that 795 appears later on the command line, the linker would not be able to 796 resolve that reference. By grouping the archives, they all be 797 searched repeatedly until all possible references are resolved. 798 799 Using this option has a significant performance cost. It is best 800 to use it only when there are unavoidable circular references 801 between two or more archives. 802 803 `--accept-unknown-input-arch' 804 `--no-accept-unknown-input-arch' 805 Tells the linker to accept input files whose architecture cannot be 806 recognised. The assumption is that the user knows what they are 807 doing and deliberately wants to link in these unknown input files. 808 This was the default behaviour of the linker, before release 809 2.14. The default behaviour from release 2.14 onwards is to 810 reject such input files, and so the `--accept-unknown-input-arch' 811 option has been added to restore the old behaviour. 812 813 `--as-needed' 814 `--no-as-needed' 815 This option affects ELF DT_NEEDED tags for dynamic libraries 816 mentioned on the command line after the `--as-needed' option. 817 Normally the linker will add a DT_NEEDED tag for each dynamic 818 library mentioned on the command line, regardless of whether the 819 library is actually needed or not. `--as-needed' causes a 820 DT_NEEDED tag to only be emitted for a library that satisfies an 821 undefined symbol reference from a regular object file or, if the 822 library is not found in the DT_NEEDED lists of other libraries 823 linked up to that point, an undefined symbol reference from 824 another dynamic library. `--no-as-needed' restores the default 825 behaviour. 826 827 `--add-needed' 828 `--no-add-needed' 829 These two options have been deprecated because of the similarity of 830 their names to the `--as-needed' and `--no-as-needed' options. 831 They have been replaced by `--copy-dt-needed-entries' and 832 `--no-copy-dt-needed-entries'. 833 834 `-assert KEYWORD' 835 This option is ignored for SunOS compatibility. 836 837 `-Bdynamic' 838 `-dy' 839 `-call_shared' 840 Link against dynamic libraries. This is only meaningful on 841 platforms for which shared libraries are supported. This option 842 is normally the default on such platforms. The different variants 843 of this option are for compatibility with various systems. You 844 may use this option multiple times on the command line: it affects 845 library searching for `-l' options which follow it. 846 847 `-Bgroup' 848 Set the `DF_1_GROUP' flag in the `DT_FLAGS_1' entry in the dynamic 849 section. This causes the runtime linker to handle lookups in this 850 object and its dependencies to be performed only inside the group. 851 `--unresolved-symbols=report-all' is implied. This option is only 852 meaningful on ELF platforms which support shared libraries. 853 854 `-Bstatic' 855 `-dn' 856 `-non_shared' 857 `-static' 858 Do not link against shared libraries. This is only meaningful on 859 platforms for which shared libraries are supported. The different 860 variants of this option are for compatibility with various 861 systems. You may use this option multiple times on the command 862 line: it affects library searching for `-l' options which follow 863 it. This option also implies `--unresolved-symbols=report-all'. 864 This option can be used with `-shared'. Doing so means that a 865 shared library is being created but that all of the library's 866 external references must be resolved by pulling in entries from 867 static libraries. 868 869 `-Bsymbolic' 870 When creating a shared library, bind references to global symbols 871 to the definition within the shared library, if any. Normally, it 872 is possible for a program linked against a shared library to 873 override the definition within the shared library. This option is 874 only meaningful on ELF platforms which support shared libraries. 875 876 `-Bsymbolic-functions' 877 When creating a shared library, bind references to global function 878 symbols to the definition within the shared library, if any. This 879 option is only meaningful on ELF platforms which support shared 880 libraries. 881 882 `--dynamic-list=DYNAMIC-LIST-FILE' 883 Specify the name of a dynamic list file to the linker. This is 884 typically used when creating shared libraries to specify a list of 885 global symbols whose references shouldn't be bound to the 886 definition within the shared library, or creating dynamically 887 linked executables to specify a list of symbols which should be 888 added to the symbol table in the executable. This option is only 889 meaningful on ELF platforms which support shared libraries. 890 891 The format of the dynamic list is the same as the version node 892 without scope and node name. See *Note VERSION:: for more 893 information. 894 895 `--dynamic-list-data' 896 Include all global data symbols to the dynamic list. 897 898 `--dynamic-list-cpp-new' 899 Provide the builtin dynamic list for C++ operator new and delete. 900 It is mainly useful for building shared libstdc++. 901 902 `--dynamic-list-cpp-typeinfo' 903 Provide the builtin dynamic list for C++ runtime type 904 identification. 905 906 `--check-sections' 907 `--no-check-sections' 908 Asks the linker _not_ to check section addresses after they have 909 been assigned to see if there are any overlaps. Normally the 910 linker will perform this check, and if it finds any overlaps it 911 will produce suitable error messages. The linker does know about, 912 and does make allowances for sections in overlays. The default 913 behaviour can be restored by using the command line switch 914 `--check-sections'. Section overlap is not usually checked for 915 relocatable links. You can force checking in that case by using 916 the `--check-sections' option. 917 918 `--copy-dt-needed-entries' 919 `--no-copy-dt-needed-entries' 920 This option affects the treatment of dynamic libraries referred to 921 by DT_NEEDED tags _inside_ ELF dynamic libraries mentioned on the 922 command line. Normally the linker won't add a DT_NEEDED tag to the 923 output binary for each library mentioned in a DT_NEEDED tag in an 924 input dynamic library. With `--copy-dt-needed-entries' specified 925 on the command line however any dynamic libraries that follow it 926 will have their DT_NEEDED entries added. The default behaviour 927 can be restored with `--no-copy-dt-needed-entries'. 928 929 This option also has an effect on the resolution of symbols in 930 dynamic libraries. With `--copy-dt-needed-entries' dynamic 931 libraries mentioned on the command line will be recursively 932 searched, following their DT_NEEDED tags to other libraries, in 933 order to resolve symbols required by the output binary. With the 934 default setting however the searching of dynamic libraries that 935 follow it will stop with the dynamic library itself. No DT_NEEDED 936 links will be traversed to resolve symbols. 937 938 `--cref' 939 Output a cross reference table. If a linker map file is being 940 generated, the cross reference table is printed to the map file. 941 Otherwise, it is printed on the standard output. 942 943 The format of the table is intentionally simple, so that it may be 944 easily processed by a script if necessary. The symbols are 945 printed out, sorted by name. For each symbol, a list of file 946 names is given. If the symbol is defined, the first file listed 947 is the location of the definition. The remaining files contain 948 references to the symbol. 949 950 `--no-define-common' 951 This option inhibits the assignment of addresses to common symbols. 952 The script command `INHIBIT_COMMON_ALLOCATION' has the same effect. 953 *Note Miscellaneous Commands::. 954 955 The `--no-define-common' option allows decoupling the decision to 956 assign addresses to Common symbols from the choice of the output 957 file type; otherwise a non-Relocatable output type forces 958 assigning addresses to Common symbols. Using `--no-define-common' 959 allows Common symbols that are referenced from a shared library to 960 be assigned addresses only in the main program. This eliminates 961 the unused duplicate space in the shared library, and also 962 prevents any possible confusion over resolving to the wrong 963 duplicate when there are many dynamic modules with specialized 964 search paths for runtime symbol resolution. 965 966 `--defsym=SYMBOL=EXPRESSION' 967 Create a global symbol in the output file, containing the absolute 968 address given by EXPRESSION. You may use this option as many 969 times as necessary to define multiple symbols in the command line. 970 A limited form of arithmetic is supported for the EXPRESSION in 971 this context: you may give a hexadecimal constant or the name of 972 an existing symbol, or use `+' and `-' to add or subtract 973 hexadecimal constants or symbols. If you need more elaborate 974 expressions, consider using the linker command language from a 975 script (*note Assignment: Symbol Definitions: Assignments.). 976 _Note:_ there should be no white space between SYMBOL, the equals 977 sign ("<=>"), and EXPRESSION. 978 979 `--demangle[=STYLE]' 980 `--no-demangle' 981 These options control whether to demangle symbol names in error 982 messages and other output. When the linker is told to demangle, 983 it tries to present symbol names in a readable fashion: it strips 984 leading underscores if they are used by the object file format, 985 and converts C++ mangled symbol names into user readable names. 986 Different compilers have different mangling styles. The optional 987 demangling style argument can be used to choose an appropriate 988 demangling style for your compiler. The linker will demangle by 989 default unless the environment variable `COLLECT_NO_DEMANGLE' is 990 set. These options may be used to override the default. 991 992 `-IFILE' 993 `--dynamic-linker=FILE' 994 Set the name of the dynamic linker. This is only meaningful when 995 generating dynamically linked ELF executables. The default dynamic 996 linker is normally correct; don't use this unless you know what 997 you are doing. 998 999 `--fatal-warnings' 1000 `--no-fatal-warnings' 1001 Treat all warnings as errors. The default behaviour can be 1002 restored with the option `--no-fatal-warnings'. 1003 1004 `--force-exe-suffix' 1005 Make sure that an output file has a .exe suffix. 1006 1007 If a successfully built fully linked output file does not have a 1008 `.exe' or `.dll' suffix, this option forces the linker to copy the 1009 output file to one of the same name with a `.exe' suffix. This 1010 option is useful when using unmodified Unix makefiles on a 1011 Microsoft Windows host, since some versions of Windows won't run 1012 an image unless it ends in a `.exe' suffix. 1013 1014 `--gc-sections' 1015 `--no-gc-sections' 1016 Enable garbage collection of unused input sections. It is ignored 1017 on targets that do not support this option. The default behaviour 1018 (of not performing this garbage collection) can be restored by 1019 specifying `--no-gc-sections' on the command line. 1020 1021 `--gc-sections' decides which input sections are used by examining 1022 symbols and relocations. The section containing the entry symbol 1023 and all sections containing symbols undefined on the command-line 1024 will be kept, as will sections containing symbols referenced by 1025 dynamic objects. Note that when building shared libraries, the 1026 linker must assume that any visible symbol is referenced. Once 1027 this initial set of sections has been determined, the linker 1028 recursively marks as used any section referenced by their 1029 relocations. See `--entry' and `--undefined'. 1030 1031 This option can be set when doing a partial link (enabled with 1032 option `-r'). In this case the root of symbols kept must be 1033 explicitly specified either by an `--entry' or `--undefined' 1034 option or by a `ENTRY' command in the linker script. 1035 1036 `--print-gc-sections' 1037 `--no-print-gc-sections' 1038 List all sections removed by garbage collection. The listing is 1039 printed on stderr. This option is only effective if garbage 1040 collection has been enabled via the `--gc-sections') option. The 1041 default behaviour (of not listing the sections that are removed) 1042 can be restored by specifying `--no-print-gc-sections' on the 1043 command line. 1044 1045 `--print-output-format' 1046 Print the name of the default output format (perhaps influenced by 1047 other command-line options). This is the string that would appear 1048 in an `OUTPUT_FORMAT' linker script command (*note File 1049 Commands::). 1050 1051 `--help' 1052 Print a summary of the command-line options on the standard output 1053 and exit. 1054 1055 `--target-help' 1056 Print a summary of all target specific options on the standard 1057 output and exit. 1058 1059 `-Map=MAPFILE' 1060 Print a link map to the file MAPFILE. See the description of the 1061 `-M' option, above. 1062 1063 `--no-keep-memory' 1064 `ld' normally optimizes for speed over memory usage by caching the 1065 symbol tables of input files in memory. This option tells `ld' to 1066 instead optimize for memory usage, by rereading the symbol tables 1067 as necessary. This may be required if `ld' runs out of memory 1068 space while linking a large executable. 1069 1070 `--no-undefined' 1071 `-z defs' 1072 Report unresolved symbol references from regular object files. 1073 This is done even if the linker is creating a non-symbolic shared 1074 library. The switch `--[no-]allow-shlib-undefined' controls the 1075 behaviour for reporting unresolved references found in shared 1076 libraries being linked in. 1077 1078 `--allow-multiple-definition' 1079 `-z muldefs' 1080 Normally when a symbol is defined multiple times, the linker will 1081 report a fatal error. These options allow multiple definitions and 1082 the first definition will be used. 1083 1084 `--allow-shlib-undefined' 1085 `--no-allow-shlib-undefined' 1086 Allows or disallows undefined symbols in shared libraries. This 1087 switch is similar to `--no-undefined' except that it determines 1088 the behaviour when the undefined symbols are in a shared library 1089 rather than a regular object file. It does not affect how 1090 undefined symbols in regular object files are handled. 1091 1092 The default behaviour is to report errors for any undefined symbols 1093 referenced in shared libraries if the linker is being used to 1094 create an executable, but to allow them if the linker is being 1095 used to create a shared library. 1096 1097 The reasons for allowing undefined symbol references in shared 1098 libraries specified at link time are that: 1099 1100 * A shared library specified at link time may not be the same 1101 as the one that is available at load time, so the symbol 1102 might actually be resolvable at load time. 1103 1104 * There are some operating systems, eg BeOS and HPPA, where 1105 undefined symbols in shared libraries are normal. 1106 1107 The BeOS kernel for example patches shared libraries at load 1108 time to select whichever function is most appropriate for the 1109 current architecture. This is used, for example, to 1110 dynamically select an appropriate memset function. 1111 1112 `--no-undefined-version' 1113 Normally when a symbol has an undefined version, the linker will 1114 ignore it. This option disallows symbols with undefined version 1115 and a fatal error will be issued instead. 1116 1117 `--default-symver' 1118 Create and use a default symbol version (the soname) for 1119 unversioned exported symbols. 1120 1121 `--default-imported-symver' 1122 Create and use a default symbol version (the soname) for 1123 unversioned imported symbols. 1124 1125 `--no-warn-mismatch' 1126 Normally `ld' will give an error if you try to link together input 1127 files that are mismatched for some reason, perhaps because they 1128 have been compiled for different processors or for different 1129 endiannesses. This option tells `ld' that it should silently 1130 permit such possible errors. This option should only be used with 1131 care, in cases when you have taken some special action that 1132 ensures that the linker errors are inappropriate. 1133 1134 `--no-warn-search-mismatch' 1135 Normally `ld' will give a warning if it finds an incompatible 1136 library during a library search. This option silences the warning. 1137 1138 `--no-whole-archive' 1139 Turn off the effect of the `--whole-archive' option for subsequent 1140 archive files. 1141 1142 `--noinhibit-exec' 1143 Retain the executable output file whenever it is still usable. 1144 Normally, the linker will not produce an output file if it 1145 encounters errors during the link process; it exits without 1146 writing an output file when it issues any error whatsoever. 1147 1148 `-nostdlib' 1149 Only search library directories explicitly specified on the 1150 command line. Library directories specified in linker scripts 1151 (including linker scripts specified on the command line) are 1152 ignored. 1153 1154 `--oformat=OUTPUT-FORMAT' 1155 `ld' may be configured to support more than one kind of object 1156 file. If your `ld' is configured this way, you can use the 1157 `--oformat' option to specify the binary format for the output 1158 object file. Even when `ld' is configured to support alternative 1159 object formats, you don't usually need to specify this, as `ld' 1160 should be configured to produce as a default output format the most 1161 usual format on each machine. OUTPUT-FORMAT is a text string, the 1162 name of a particular format supported by the BFD libraries. (You 1163 can list the available binary formats with `objdump -i'.) The 1164 script command `OUTPUT_FORMAT' can also specify the output format, 1165 but this option overrides it. *Note BFD::. 1166 1167 `-pie' 1168 `--pic-executable' 1169 Create a position independent executable. This is currently only 1170 supported on ELF platforms. Position independent executables are 1171 similar to shared libraries in that they are relocated by the 1172 dynamic linker to the virtual address the OS chooses for them 1173 (which can vary between invocations). Like normal dynamically 1174 linked executables they can be executed and symbols defined in the 1175 executable cannot be overridden by shared libraries. 1176 1177 `-qmagic' 1178 This option is ignored for Linux compatibility. 1179 1180 `-Qy' 1181 This option is ignored for SVR4 compatibility. 1182 1183 `--relax' 1184 `--no-relax' 1185 An option with machine dependent effects. This option is only 1186 supported on a few targets. *Note `ld' and the H8/300: H8/300. 1187 *Note `ld' and the Intel 960 family: i960. *Note `ld' and Xtensa 1188 Processors: Xtensa. *Note `ld' and the 68HC11 and 68HC12: 1189 M68HC11/68HC12. *Note `ld' and PowerPC 32-bit ELF Support: 1190 PowerPC ELF32. 1191 1192 On some platforms the `--relax' option performs target specific, 1193 global optimizations that become possible when the linker resolves 1194 addressing in the program, such as relaxing address modes, 1195 synthesizing new instructions, selecting shorter version of current 1196 instructions, and combinig constant values. 1197 1198 On some platforms these link time global optimizations may make 1199 symbolic debugging of the resulting executable impossible. This 1200 is known to be the case for the Matsushita MN10200 and MN10300 1201 family of processors. 1202 1203 On platforms where this is not supported, `--relax' is accepted, 1204 but ignored. 1205 1206 On platforms where `--relax' is accepted the option `--no-relax' 1207 can be used to disable the feature. 1208 1209 `--retain-symbols-file=FILENAME' 1210 Retain _only_ the symbols listed in the file FILENAME, discarding 1211 all others. FILENAME is simply a flat file, with one symbol name 1212 per line. This option is especially useful in environments (such 1213 as VxWorks) where a large global symbol table is accumulated 1214 gradually, to conserve run-time memory. 1215 1216 `--retain-symbols-file' does _not_ discard undefined symbols, or 1217 symbols needed for relocations. 1218 1219 You may only specify `--retain-symbols-file' once in the command 1220 line. It overrides `-s' and `-S'. 1221 1222 `-rpath=DIR' 1223 Add a directory to the runtime library search path. This is used 1224 when linking an ELF executable with shared objects. All `-rpath' 1225 arguments are concatenated and passed to the runtime linker, which 1226 uses them to locate shared objects at runtime. The `-rpath' 1227 option is also used when locating shared objects which are needed 1228 by shared objects explicitly included in the link; see the 1229 description of the `-rpath-link' option. If `-rpath' is not used 1230 when linking an ELF executable, the contents of the environment 1231 variable `LD_RUN_PATH' will be used if it is defined. 1232 1233 The `-rpath' option may also be used on SunOS. By default, on 1234 SunOS, the linker will form a runtime search patch out of all the 1235 `-L' options it is given. If a `-rpath' option is used, the 1236 runtime search path will be formed exclusively using the `-rpath' 1237 options, ignoring the `-L' options. This can be useful when using 1238 gcc, which adds many `-L' options which may be on NFS mounted file 1239 systems. 1240 1241 For compatibility with other ELF linkers, if the `-R' option is 1242 followed by a directory name, rather than a file name, it is 1243 treated as the `-rpath' option. 1244 1245 `-rpath-link=DIR' 1246 When using ELF or SunOS, one shared library may require another. 1247 This happens when an `ld -shared' link includes a shared library 1248 as one of the input files. 1249 1250 When the linker encounters such a dependency when doing a 1251 non-shared, non-relocatable link, it will automatically try to 1252 locate the required shared library and include it in the link, if 1253 it is not included explicitly. In such a case, the `-rpath-link' 1254 option specifies the first set of directories to search. The 1255 `-rpath-link' option may specify a sequence of directory names 1256 either by specifying a list of names separated by colons, or by 1257 appearing multiple times. 1258 1259 This option should be used with caution as it overrides the search 1260 path that may have been hard compiled into a shared library. In 1261 such a case it is possible to use unintentionally a different 1262 search path than the runtime linker would do. 1263 1264 The linker uses the following search paths to locate required 1265 shared libraries: 1266 1. Any directories specified by `-rpath-link' options. 1267 1268 2. Any directories specified by `-rpath' options. The difference 1269 between `-rpath' and `-rpath-link' is that directories 1270 specified by `-rpath' options are included in the executable 1271 and used at runtime, whereas the `-rpath-link' option is only 1272 effective at link time. Searching `-rpath' in this way is 1273 only supported by native linkers and cross linkers which have 1274 been configured with the `--with-sysroot' option. 1275 1276 3. On an ELF system, for native linkers, if the `-rpath' and 1277 `-rpath-link' options were not used, search the contents of 1278 the environment variable `LD_RUN_PATH'. 1279 1280 4. On SunOS, if the `-rpath' option was not used, search any 1281 directories specified using `-L' options. 1282 1283 5. For a native linker, the search the contents of the 1284 environment variable `LD_LIBRARY_PATH'. 1285 1286 6. For a native ELF linker, the directories in `DT_RUNPATH' or 1287 `DT_RPATH' of a shared library are searched for shared 1288 libraries needed by it. The `DT_RPATH' entries are ignored if 1289 `DT_RUNPATH' entries exist. 1290 1291 7. The default directories, normally `/lib' and `/usr/lib'. 1292 1293 8. For a native linker on an ELF system, if the file 1294 `/etc/ld.so.conf' exists, the list of directories found in 1295 that file. 1296 1297 If the required shared library is not found, the linker will issue 1298 a warning and continue with the link. 1299 1300 `-shared' 1301 `-Bshareable' 1302 Create a shared library. This is currently only supported on ELF, 1303 XCOFF and SunOS platforms. On SunOS, the linker will 1304 automatically create a shared library if the `-e' option is not 1305 used and there are undefined symbols in the link. 1306 1307 `--sort-common' 1308 `--sort-common=ascending' 1309 `--sort-common=descending' 1310 This option tells `ld' to sort the common symbols by alignment in 1311 ascending or descending order when it places them in the 1312 appropriate output sections. The symbol alignments considered are 1313 sixteen-byte or larger, eight-byte, four-byte, two-byte, and 1314 one-byte. This is to prevent gaps between symbols due to alignment 1315 constraints. If no sorting order is specified, then descending 1316 order is assumed. 1317 1318 `--sort-section=name' 1319 This option will apply `SORT_BY_NAME' to all wildcard section 1320 patterns in the linker script. 1321 1322 `--sort-section=alignment' 1323 This option will apply `SORT_BY_ALIGNMENT' to all wildcard section 1324 patterns in the linker script. 1325 1326 `--split-by-file[=SIZE]' 1327 Similar to `--split-by-reloc' but creates a new output section for 1328 each input file when SIZE is reached. SIZE defaults to a size of 1329 1 if not given. 1330 1331 `--split-by-reloc[=COUNT]' 1332 Tries to creates extra sections in the output file so that no 1333 single output section in the file contains more than COUNT 1334 relocations. This is useful when generating huge relocatable 1335 files for downloading into certain real time kernels with the COFF 1336 object file format; since COFF cannot represent more than 65535 1337 relocations in a single section. Note that this will fail to work 1338 with object file formats which do not support arbitrary sections. 1339 The linker will not split up individual input sections for 1340 redistribution, so if a single input section contains more than 1341 COUNT relocations one output section will contain that many 1342 relocations. COUNT defaults to a value of 32768. 1343 1344 `--stats' 1345 Compute and display statistics about the operation of the linker, 1346 such as execution time and memory usage. 1347 1348 `--sysroot=DIRECTORY' 1349 Use DIRECTORY as the location of the sysroot, overriding the 1350 configure-time default. This option is only supported by linkers 1351 that were configured using `--with-sysroot'. 1352 1353 `--traditional-format' 1354 For some targets, the output of `ld' is different in some ways from 1355 the output of some existing linker. This switch requests `ld' to 1356 use the traditional format instead. 1357 1358 For example, on SunOS, `ld' combines duplicate entries in the 1359 symbol string table. This can reduce the size of an output file 1360 with full debugging information by over 30 percent. 1361 Unfortunately, the SunOS `dbx' program can not read the resulting 1362 program (`gdb' has no trouble). The `--traditional-format' switch 1363 tells `ld' to not combine duplicate entries. 1364 1365 `--section-start=SECTIONNAME=ORG' 1366 Locate a section in the output file at the absolute address given 1367 by ORG. You may use this option as many times as necessary to 1368 locate multiple sections in the command line. ORG must be a 1369 single hexadecimal integer; for compatibility with other linkers, 1370 you may omit the leading `0x' usually associated with hexadecimal 1371 values. _Note:_ there should be no white space between 1372 SECTIONNAME, the equals sign ("<=>"), and ORG. 1373 1374 `-Tbss=ORG' 1375 `-Tdata=ORG' 1376 `-Ttext=ORG' 1377 Same as `--section-start', with `.bss', `.data' or `.text' as the 1378 SECTIONNAME. 1379 1380 `-Ttext-segment=ORG' 1381 When creating an ELF executable or shared object, it will set the 1382 address of the first byte of the text segment. 1383 1384 `--unresolved-symbols=METHOD' 1385 Determine how to handle unresolved symbols. There are four 1386 possible values for `method': 1387 1388 `ignore-all' 1389 Do not report any unresolved symbols. 1390 1391 `report-all' 1392 Report all unresolved symbols. This is the default. 1393 1394 `ignore-in-object-files' 1395 Report unresolved symbols that are contained in shared 1396 libraries, but ignore them if they come from regular object 1397 files. 1398 1399 `ignore-in-shared-libs' 1400 Report unresolved symbols that come from regular object 1401 files, but ignore them if they come from shared libraries. 1402 This can be useful when creating a dynamic binary and it is 1403 known that all the shared libraries that it should be 1404 referencing are included on the linker's command line. 1405 1406 The behaviour for shared libraries on their own can also be 1407 controlled by the `--[no-]allow-shlib-undefined' option. 1408 1409 Normally the linker will generate an error message for each 1410 reported unresolved symbol but the option 1411 `--warn-unresolved-symbols' can change this to a warning. 1412 1413 `--dll-verbose' 1414 `--verbose[=NUMBER]' 1415 Display the version number for `ld' and list the linker emulations 1416 supported. Display which input files can and cannot be opened. 1417 Display the linker script being used by the linker. If the 1418 optional NUMBER argument > 1, plugin symbol status will also be 1419 displayed. 1420 1421 `--version-script=VERSION-SCRIPTFILE' 1422 Specify the name of a version script to the linker. This is 1423 typically used when creating shared libraries to specify 1424 additional information about the version hierarchy for the library 1425 being created. This option is only fully supported on ELF 1426 platforms which support shared libraries; see *Note VERSION::. It 1427 is partially supported on PE platforms, which can use version 1428 scripts to filter symbol visibility in auto-export mode: any 1429 symbols marked `local' in the version script will not be exported. 1430 *Note WIN32::. 1431 1432 `--warn-common' 1433 Warn when a common symbol is combined with another common symbol 1434 or with a symbol definition. Unix linkers allow this somewhat 1435 sloppy practise, but linkers on some other operating systems do 1436 not. This option allows you to find potential problems from 1437 combining global symbols. Unfortunately, some C libraries use 1438 this practise, so you may get some warnings about symbols in the 1439 libraries as well as in your programs. 1440 1441 There are three kinds of global symbols, illustrated here by C 1442 examples: 1443 1444 `int i = 1;' 1445 A definition, which goes in the initialized data section of 1446 the output file. 1447 1448 `extern int i;' 1449 An undefined reference, which does not allocate space. There 1450 must be either a definition or a common symbol for the 1451 variable somewhere. 1452 1453 `int i;' 1454 A common symbol. If there are only (one or more) common 1455 symbols for a variable, it goes in the uninitialized data 1456 area of the output file. The linker merges multiple common 1457 symbols for the same variable into a single symbol. If they 1458 are of different sizes, it picks the largest size. The 1459 linker turns a common symbol into a declaration, if there is 1460 a definition of the same variable. 1461 1462 The `--warn-common' option can produce five kinds of warnings. 1463 Each warning consists of a pair of lines: the first describes the 1464 symbol just encountered, and the second describes the previous 1465 symbol encountered with the same name. One or both of the two 1466 symbols will be a common symbol. 1467 1468 1. Turning a common symbol into a reference, because there is 1469 already a definition for the symbol. 1470 FILE(SECTION): warning: common of `SYMBOL' 1471 overridden by definition 1472 FILE(SECTION): warning: defined here 1473 1474 2. Turning a common symbol into a reference, because a later 1475 definition for the symbol is encountered. This is the same 1476 as the previous case, except that the symbols are encountered 1477 in a different order. 1478 FILE(SECTION): warning: definition of `SYMBOL' 1479 overriding common 1480 FILE(SECTION): warning: common is here 1481 1482 3. Merging a common symbol with a previous same-sized common 1483 symbol. 1484 FILE(SECTION): warning: multiple common 1485 of `SYMBOL' 1486 FILE(SECTION): warning: previous common is here 1487 1488 4. Merging a common symbol with a previous larger common symbol. 1489 FILE(SECTION): warning: common of `SYMBOL' 1490 overridden by larger common 1491 FILE(SECTION): warning: larger common is here 1492 1493 5. Merging a common symbol with a previous smaller common 1494 symbol. This is the same as the previous case, except that 1495 the symbols are encountered in a different order. 1496 FILE(SECTION): warning: common of `SYMBOL' 1497 overriding smaller common 1498 FILE(SECTION): warning: smaller common is here 1499 1500 `--warn-constructors' 1501 Warn if any global constructors are used. This is only useful for 1502 a few object file formats. For formats like COFF or ELF, the 1503 linker can not detect the use of global constructors. 1504 1505 `--warn-multiple-gp' 1506 Warn if multiple global pointer values are required in the output 1507 file. This is only meaningful for certain processors, such as the 1508 Alpha. Specifically, some processors put large-valued constants 1509 in a special section. A special register (the global pointer) 1510 points into the middle of this section, so that constants can be 1511 loaded efficiently via a base-register relative addressing mode. 1512 Since the offset in base-register relative mode is fixed and 1513 relatively small (e.g., 16 bits), this limits the maximum size of 1514 the constant pool. Thus, in large programs, it is often necessary 1515 to use multiple global pointer values in order to be able to 1516 address all possible constants. This option causes a warning to 1517 be issued whenever this case occurs. 1518 1519 `--warn-once' 1520 Only warn once for each undefined symbol, rather than once per 1521 module which refers to it. 1522 1523 `--warn-section-align' 1524 Warn if the address of an output section is changed because of 1525 alignment. Typically, the alignment will be set by an input 1526 section. The address will only be changed if it not explicitly 1527 specified; that is, if the `SECTIONS' command does not specify a 1528 start address for the section (*note SECTIONS::). 1529 1530 `--warn-shared-textrel' 1531 Warn if the linker adds a DT_TEXTREL to a shared object. 1532 1533 `--warn-alternate-em' 1534 Warn if an object has alternate ELF machine code. 1535 1536 `--warn-unresolved-symbols' 1537 If the linker is going to report an unresolved symbol (see the 1538 option `--unresolved-symbols') it will normally generate an error. 1539 This option makes it generate a warning instead. 1540 1541 `--error-unresolved-symbols' 1542 This restores the linker's default behaviour of generating errors 1543 when it is reporting unresolved symbols. 1544 1545 `--whole-archive' 1546 For each archive mentioned on the command line after the 1547 `--whole-archive' option, include every object file in the archive 1548 in the link, rather than searching the archive for the required 1549 object files. This is normally used to turn an archive file into 1550 a shared library, forcing every object to be included in the 1551 resulting shared library. This option may be used more than once. 1552 1553 Two notes when using this option from gcc: First, gcc doesn't know 1554 about this option, so you have to use `-Wl,-whole-archive'. 1555 Second, don't forget to use `-Wl,-no-whole-archive' after your 1556 list of archives, because gcc will add its own list of archives to 1557 your link and you may not want this flag to affect those as well. 1558 1559 `--wrap=SYMBOL' 1560 Use a wrapper function for SYMBOL. Any undefined reference to 1561 SYMBOL will be resolved to `__wrap_SYMBOL'. Any undefined 1562 reference to `__real_SYMBOL' will be resolved to SYMBOL. 1563 1564 This can be used to provide a wrapper for a system function. The 1565 wrapper function should be called `__wrap_SYMBOL'. If it wishes 1566 to call the system function, it should call `__real_SYMBOL'. 1567 1568 Here is a trivial example: 1569 1570 void * 1571 __wrap_malloc (size_t c) 1572 { 1573 printf ("malloc called with %zu\n", c); 1574 return __real_malloc (c); 1575 } 1576 1577 If you link other code with this file using `--wrap malloc', then 1578 all calls to `malloc' will call the function `__wrap_malloc' 1579 instead. The call to `__real_malloc' in `__wrap_malloc' will call 1580 the real `malloc' function. 1581 1582 You may wish to provide a `__real_malloc' function as well, so that 1583 links without the `--wrap' option will succeed. If you do this, 1584 you should not put the definition of `__real_malloc' in the same 1585 file as `__wrap_malloc'; if you do, the assembler may resolve the 1586 call before the linker has a chance to wrap it to `malloc'. 1587 1588 `--eh-frame-hdr' 1589 Request creation of `.eh_frame_hdr' section and ELF 1590 `PT_GNU_EH_FRAME' segment header. 1591 1592 `--no-ld-generated-unwind-info' 1593 Request creation of `.eh_frame' unwind info for linker generated 1594 code sections like PLT. This option is on by default if linker 1595 generated unwind info is supported. 1596 1597 `--enable-new-dtags' 1598 `--disable-new-dtags' 1599 This linker can create the new dynamic tags in ELF. But the older 1600 ELF systems may not understand them. If you specify 1601 `--enable-new-dtags', the dynamic tags will be created as needed. 1602 If you specify `--disable-new-dtags', no new dynamic tags will be 1603 created. By default, the new dynamic tags are not created. Note 1604 that those options are only available for ELF systems. 1605 1606 `--hash-size=NUMBER' 1607 Set the default size of the linker's hash tables to a prime number 1608 close to NUMBER. Increasing this value can reduce the length of 1609 time it takes the linker to perform its tasks, at the expense of 1610 increasing the linker's memory requirements. Similarly reducing 1611 this value can reduce the memory requirements at the expense of 1612 speed. 1613 1614 `--hash-style=STYLE' 1615 Set the type of linker's hash table(s). STYLE can be either 1616 `sysv' for classic ELF `.hash' section, `gnu' for new style GNU 1617 `.gnu.hash' section or `both' for both the classic ELF `.hash' and 1618 new style GNU `.gnu.hash' hash tables. The default is `sysv'. 1619 1620 `--reduce-memory-overheads' 1621 This option reduces memory requirements at ld runtime, at the 1622 expense of linking speed. This was introduced to select the old 1623 O(n^2) algorithm for link map file generation, rather than the new 1624 O(n) algorithm which uses about 40% more memory for symbol storage. 1625 1626 Another effect of the switch is to set the default hash table size 1627 to 1021, which again saves memory at the cost of lengthening the 1628 linker's run time. This is not done however if the `--hash-size' 1629 switch has been used. 1630 1631 The `--reduce-memory-overheads' switch may be also be used to 1632 enable other tradeoffs in future versions of the linker. 1633 1634 `--build-id' 1635 `--build-id=STYLE' 1636 Request creation of `.note.gnu.build-id' ELF note section. The 1637 contents of the note are unique bits identifying this linked file. 1638 STYLE can be `uuid' to use 128 random bits, `sha1' to use a 1639 160-bit SHA1 hash on the normative parts of the output contents, 1640 `md5' to use a 128-bit MD5 hash on the normative parts of the 1641 output contents, or `0xHEXSTRING' to use a chosen bit string 1642 specified as an even number of hexadecimal digits (`-' and `:' 1643 characters between digit pairs are ignored). If STYLE is omitted, 1644 `sha1' is used. 1645 1646 The `md5' and `sha1' styles produces an identifier that is always 1647 the same in an identical output file, but will be unique among all 1648 nonidentical output files. It is not intended to be compared as a 1649 checksum for the file's contents. A linked file may be changed 1650 later by other tools, but the build ID bit string identifying the 1651 original linked file does not change. 1652 1653 Passing `none' for STYLE disables the setting from any 1654 `--build-id' options earlier on the command line. 1655 1656 2.1.1 Options Specific to i386 PE Targets 1657 ----------------------------------------- 1658 1659 The i386 PE linker supports the `-shared' option, which causes the 1660 output to be a dynamically linked library (DLL) instead of a normal 1661 executable. You should name the output `*.dll' when you use this 1662 option. In addition, the linker fully supports the standard `*.def' 1663 files, which may be specified on the linker command line like an object 1664 file (in fact, it should precede archives it exports symbols from, to 1665 ensure that they get linked in, just like a normal object file). 1666 1667 In addition to the options common to all targets, the i386 PE linker 1668 support additional command line options that are specific to the i386 1669 PE target. Options that take values may be separated from their values 1670 by either a space or an equals sign. 1671 1672 `--add-stdcall-alias' 1673 If given, symbols with a stdcall suffix (@NN) will be exported 1674 as-is and also with the suffix stripped. [This option is specific 1675 to the i386 PE targeted port of the linker] 1676 1677 `--base-file FILE' 1678 Use FILE as the name of a file in which to save the base addresses 1679 of all the relocations needed for generating DLLs with `dlltool'. 1680 [This is an i386 PE specific option] 1681 1682 `--dll' 1683 Create a DLL instead of a regular executable. You may also use 1684 `-shared' or specify a `LIBRARY' in a given `.def' file. [This 1685 option is specific to the i386 PE targeted port of the linker] 1686 1687 `--enable-long-section-names' 1688 `--disable-long-section-names' 1689 The PE variants of the Coff object format add an extension that 1690 permits the use of section names longer than eight characters, the 1691 normal limit for Coff. By default, these names are only allowed 1692 in object files, as fully-linked executable images do not carry 1693 the Coff string table required to support the longer names. As a 1694 GNU extension, it is possible to allow their use in executable 1695 images as well, or to (probably pointlessly!) disallow it in 1696 object files, by using these two options. Executable images 1697 generated with these long section names are slightly non-standard, 1698 carrying as they do a string table, and may generate confusing 1699 output when examined with non-GNU PE-aware tools, such as file 1700 viewers and dumpers. However, GDB relies on the use of PE long 1701 section names to find Dwarf-2 debug information sections in an 1702 executable image at runtime, and so if neither option is specified 1703 on the command-line, `ld' will enable long section names, 1704 overriding the default and technically correct behaviour, when it 1705 finds the presence of debug information while linking an executable 1706 image and not stripping symbols. [This option is valid for all PE 1707 targeted ports of the linker] 1708 1709 `--enable-stdcall-fixup' 1710 `--disable-stdcall-fixup' 1711 If the link finds a symbol that it cannot resolve, it will attempt 1712 to do "fuzzy linking" by looking for another defined symbol that 1713 differs only in the format of the symbol name (cdecl vs stdcall) 1714 and will resolve that symbol by linking to the match. For 1715 example, the undefined symbol `_foo' might be linked to the 1716 function `_foo@12', or the undefined symbol `_bar@16' might be 1717 linked to the function `_bar'. When the linker does this, it 1718 prints a warning, since it normally should have failed to link, 1719 but sometimes import libraries generated from third-party dlls may 1720 need this feature to be usable. If you specify 1721 `--enable-stdcall-fixup', this feature is fully enabled and 1722 warnings are not printed. If you specify 1723 `--disable-stdcall-fixup', this feature is disabled and such 1724 mismatches are considered to be errors. [This option is specific 1725 to the i386 PE targeted port of the linker] 1726 1727 `--leading-underscore' 1728 `--no-leading-underscore' 1729 For most targets default symbol-prefix is an underscore and is 1730 defined in target's description. By this option it is possible to 1731 disable/enable the default underscore symbol-prefix. 1732 1733 `--export-all-symbols' 1734 If given, all global symbols in the objects used to build a DLL 1735 will be exported by the DLL. Note that this is the default if 1736 there otherwise wouldn't be any exported symbols. When symbols are 1737 explicitly exported via DEF files or implicitly exported via 1738 function attributes, the default is to not export anything else 1739 unless this option is given. Note that the symbols `DllMain@12', 1740 `DllEntryPoint@0', `DllMainCRTStartup@12', and `impure_ptr' will 1741 not be automatically exported. Also, symbols imported from other 1742 DLLs will not be re-exported, nor will symbols specifying the 1743 DLL's internal layout such as those beginning with `_head_' or 1744 ending with `_iname'. In addition, no symbols from `libgcc', 1745 `libstd++', `libmingw32', or `crtX.o' will be exported. Symbols 1746 whose names begin with `__rtti_' or `__builtin_' will not be 1747 exported, to help with C++ DLLs. Finally, there is an extensive 1748 list of cygwin-private symbols that are not exported (obviously, 1749 this applies on when building DLLs for cygwin targets). These 1750 cygwin-excludes are: `_cygwin_dll_entry@12', 1751 `_cygwin_crt0_common@8', `_cygwin_noncygwin_dll_entry@12', 1752 `_fmode', `_impure_ptr', `cygwin_attach_dll', `cygwin_premain0', 1753 `cygwin_premain1', `cygwin_premain2', `cygwin_premain3', and 1754 `environ'. [This option is specific to the i386 PE targeted port 1755 of the linker] 1756 1757 `--exclude-symbols SYMBOL,SYMBOL,...' 1758 Specifies a list of symbols which should not be automatically 1759 exported. The symbol names may be delimited by commas or colons. 1760 [This option is specific to the i386 PE targeted port of the 1761 linker] 1762 1763 `--exclude-all-symbols' 1764 Specifies no symbols should be automatically exported. [This 1765 option is specific to the i386 PE targeted port of the linker] 1766 1767 `--file-alignment' 1768 Specify the file alignment. Sections in the file will always 1769 begin at file offsets which are multiples of this number. This 1770 defaults to 512. [This option is specific to the i386 PE targeted 1771 port of the linker] 1772 1773 `--heap RESERVE' 1774 `--heap RESERVE,COMMIT' 1775 Specify the number of bytes of memory to reserve (and optionally 1776 commit) to be used as heap for this program. The default is 1Mb 1777 reserved, 4K committed. [This option is specific to the i386 PE 1778 targeted port of the linker] 1779 1780 `--image-base VALUE' 1781 Use VALUE as the base address of your program or dll. This is the 1782 lowest memory location that will be used when your program or dll 1783 is loaded. To reduce the need to relocate and improve performance 1784 of your dlls, each should have a unique base address and not 1785 overlap any other dlls. The default is 0x400000 for executables, 1786 and 0x10000000 for dlls. [This option is specific to the i386 PE 1787 targeted port of the linker] 1788 1789 `--kill-at' 1790 If given, the stdcall suffixes (@NN) will be stripped from symbols 1791 before they are exported. [This option is specific to the i386 PE 1792 targeted port of the linker] 1793 1794 `--large-address-aware' 1795 If given, the appropriate bit in the "Characteristics" field of 1796 the COFF header is set to indicate that this executable supports 1797 virtual addresses greater than 2 gigabytes. This should be used 1798 in conjunction with the /3GB or /USERVA=VALUE megabytes switch in 1799 the "[operating systems]" section of the BOOT.INI. Otherwise, 1800 this bit has no effect. [This option is specific to PE targeted 1801 ports of the linker] 1802 1803 `--major-image-version VALUE' 1804 Sets the major number of the "image version". Defaults to 1. 1805 [This option is specific to the i386 PE targeted port of the 1806 linker] 1807 1808 `--major-os-version VALUE' 1809 Sets the major number of the "os version". Defaults to 4. [This 1810 option is specific to the i386 PE targeted port of the linker] 1811 1812 `--major-subsystem-version VALUE' 1813 Sets the major number of the "subsystem version". Defaults to 4. 1814 [This option is specific to the i386 PE targeted port of the 1815 linker] 1816 1817 `--minor-image-version VALUE' 1818 Sets the minor number of the "image version". Defaults to 0. 1819 [This option is specific to the i386 PE targeted port of the 1820 linker] 1821 1822 `--minor-os-version VALUE' 1823 Sets the minor number of the "os version". Defaults to 0. [This 1824 option is specific to the i386 PE targeted port of the linker] 1825 1826 `--minor-subsystem-version VALUE' 1827 Sets the minor number of the "subsystem version". Defaults to 0. 1828 [This option is specific to the i386 PE targeted port of the 1829 linker] 1830 1831 `--output-def FILE' 1832 The linker will create the file FILE which will contain a DEF file 1833 corresponding to the DLL the linker is generating. This DEF file 1834 (which should be called `*.def') may be used to create an import 1835 library with `dlltool' or may be used as a reference to 1836 automatically or implicitly exported symbols. [This option is 1837 specific to the i386 PE targeted port of the linker] 1838 1839 `--out-implib FILE' 1840 The linker will create the file FILE which will contain an import 1841 lib corresponding to the DLL the linker is generating. This import 1842 lib (which should be called `*.dll.a' or `*.a' may be used to link 1843 clients against the generated DLL; this behaviour makes it 1844 possible to skip a separate `dlltool' import library creation step. 1845 [This option is specific to the i386 PE targeted port of the 1846 linker] 1847 1848 `--enable-auto-image-base' 1849 Automatically choose the image base for DLLs, unless one is 1850 specified using the `--image-base' argument. By using a hash 1851 generated from the dllname to create unique image bases for each 1852 DLL, in-memory collisions and relocations which can delay program 1853 execution are avoided. [This option is specific to the i386 PE 1854 targeted port of the linker] 1855 1856 `--disable-auto-image-base' 1857 Do not automatically generate a unique image base. If there is no 1858 user-specified image base (`--image-base') then use the platform 1859 default. [This option is specific to the i386 PE targeted port of 1860 the linker] 1861 1862 `--dll-search-prefix STRING' 1863 When linking dynamically to a dll without an import library, 1864 search for `<string><basename>.dll' in preference to 1865 `lib<basename>.dll'. This behaviour allows easy distinction 1866 between DLLs built for the various "subplatforms": native, cygwin, 1867 uwin, pw, etc. For instance, cygwin DLLs typically use 1868 `--dll-search-prefix=cyg'. [This option is specific to the i386 1869 PE targeted port of the linker] 1870 1871 `--enable-auto-import' 1872 Do sophisticated linking of `_symbol' to `__imp__symbol' for DATA 1873 imports from DLLs, and create the necessary thunking symbols when 1874 building the import libraries with those DATA exports. Note: Use 1875 of the 'auto-import' extension will cause the text section of the 1876 image file to be made writable. This does not conform to the 1877 PE-COFF format specification published by Microsoft. 1878 1879 Note - use of the 'auto-import' extension will also cause read only 1880 data which would normally be placed into the .rdata section to be 1881 placed into the .data section instead. This is in order to work 1882 around a problem with consts that is described here: 1883 http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html 1884 1885 Using 'auto-import' generally will 'just work' - but sometimes you 1886 may see this message: 1887 1888 "variable '<var>' can't be auto-imported. Please read the 1889 documentation for ld's `--enable-auto-import' for details." 1890 1891 This message occurs when some (sub)expression accesses an address 1892 ultimately given by the sum of two constants (Win32 import tables 1893 only allow one). Instances where this may occur include accesses 1894 to member fields of struct variables imported from a DLL, as well 1895 as using a constant index into an array variable imported from a 1896 DLL. Any multiword variable (arrays, structs, long long, etc) may 1897 trigger this error condition. However, regardless of the exact 1898 data type of the offending exported variable, ld will always 1899 detect it, issue the warning, and exit. 1900 1901 There are several ways to address this difficulty, regardless of 1902 the data type of the exported variable: 1903 1904 One way is to use -enable-runtime-pseudo-reloc switch. This leaves 1905 the task of adjusting references in your client code for runtime 1906 environment, so this method works only when runtime environment 1907 supports this feature. 1908 1909 A second solution is to force one of the 'constants' to be a 1910 variable - that is, unknown and un-optimizable at compile time. 1911 For arrays, there are two possibilities: a) make the indexee (the 1912 array's address) a variable, or b) make the 'constant' index a 1913 variable. Thus: 1914 1915 extern type extern_array[]; 1916 extern_array[1] --> 1917 { volatile type *t=extern_array; t[1] } 1918 1919 or 1920 1921 extern type extern_array[]; 1922 extern_array[1] --> 1923 { volatile int t=1; extern_array[t] } 1924 1925 For structs (and most other multiword data types) the only option 1926 is to make the struct itself (or the long long, or the ...) 1927 variable: 1928 1929 extern struct s extern_struct; 1930 extern_struct.field --> 1931 { volatile struct s *t=&extern_struct; t->field } 1932 1933 or 1934 1935 extern long long extern_ll; 1936 extern_ll --> 1937 { volatile long long * local_ll=&extern_ll; *local_ll } 1938 1939 A third method of dealing with this difficulty is to abandon 1940 'auto-import' for the offending symbol and mark it with 1941 `__declspec(dllimport)'. However, in practise that requires using 1942 compile-time #defines to indicate whether you are building a DLL, 1943 building client code that will link to the DLL, or merely 1944 building/linking to a static library. In making the choice 1945 between the various methods of resolving the 'direct address with 1946 constant offset' problem, you should consider typical real-world 1947 usage: 1948 1949 Original: 1950 --foo.h 1951 extern int arr[]; 1952 --foo.c 1953 #include "foo.h" 1954 void main(int argc, char **argv){ 1955 printf("%d\n",arr[1]); 1956 } 1957 1958 Solution 1: 1959 --foo.h 1960 extern int arr[]; 1961 --foo.c 1962 #include "foo.h" 1963 void main(int argc, char **argv){ 1964 /* This workaround is for win32 and cygwin; do not "optimize" */ 1965 volatile int *parr = arr; 1966 printf("%d\n",parr[1]); 1967 } 1968 1969 Solution 2: 1970 --foo.h 1971 /* Note: auto-export is assumed (no __declspec(dllexport)) */ 1972 #if (defined(_WIN32) || defined(__CYGWIN__)) && \ 1973 !(defined(FOO_BUILD_DLL) || defined(FOO_STATIC)) 1974 #define FOO_IMPORT __declspec(dllimport) 1975 #else 1976 #define FOO_IMPORT 1977 #endif 1978 extern FOO_IMPORT int arr[]; 1979 --foo.c 1980 #include "foo.h" 1981 void main(int argc, char **argv){ 1982 printf("%d\n",arr[1]); 1983 } 1984 1985 A fourth way to avoid this problem is to re-code your library to 1986 use a functional interface rather than a data interface for the 1987 offending variables (e.g. set_foo() and get_foo() accessor 1988 functions). [This option is specific to the i386 PE targeted port 1989 of the linker] 1990 1991 `--disable-auto-import' 1992 Do not attempt to do sophisticated linking of `_symbol' to 1993 `__imp__symbol' for DATA imports from DLLs. [This option is 1994 specific to the i386 PE targeted port of the linker] 1995 1996 `--enable-runtime-pseudo-reloc' 1997 If your code contains expressions described in -enable-auto-import 1998 section, that is, DATA imports from DLL with non-zero offset, this 1999 switch will create a vector of 'runtime pseudo relocations' which 2000 can be used by runtime environment to adjust references to such 2001 data in your client code. [This option is specific to the i386 PE 2002 targeted port of the linker] 2003 2004 `--disable-runtime-pseudo-reloc' 2005 Do not create pseudo relocations for non-zero offset DATA imports 2006 from DLLs. This is the default. [This option is specific to the 2007 i386 PE targeted port of the linker] 2008 2009 `--enable-extra-pe-debug' 2010 Show additional debug info related to auto-import symbol thunking. 2011 [This option is specific to the i386 PE targeted port of the 2012 linker] 2013 2014 `--section-alignment' 2015 Sets the section alignment. Sections in memory will always begin 2016 at addresses which are a multiple of this number. Defaults to 2017 0x1000. [This option is specific to the i386 PE targeted port of 2018 the linker] 2019 2020 `--stack RESERVE' 2021 `--stack RESERVE,COMMIT' 2022 Specify the number of bytes of memory to reserve (and optionally 2023 commit) to be used as stack for this program. The default is 2Mb 2024 reserved, 4K committed. [This option is specific to the i386 PE 2025 targeted port of the linker] 2026 2027 `--subsystem WHICH' 2028 `--subsystem WHICH:MAJOR' 2029 `--subsystem WHICH:MAJOR.MINOR' 2030 Specifies the subsystem under which your program will execute. The 2031 legal values for WHICH are `native', `windows', `console', 2032 `posix', and `xbox'. You may optionally set the subsystem version 2033 also. Numeric values are also accepted for WHICH. [This option 2034 is specific to the i386 PE targeted port of the linker] 2035 2036 The following options set flags in the `DllCharacteristics' field 2037 of the PE file header: [These options are specific to PE targeted 2038 ports of the linker] 2039 2040 `--dynamicbase' 2041 The image base address may be relocated using address space layout 2042 randomization (ASLR). This feature was introduced with MS Windows 2043 Vista for i386 PE targets. 2044 2045 `--forceinteg' 2046 Code integrity checks are enforced. 2047 2048 `--nxcompat' 2049 The image is compatible with the Data Execution Prevention. This 2050 feature was introduced with MS Windows XP SP2 for i386 PE targets. 2051 2052 `--no-isolation' 2053 Although the image understands isolation, do not isolate the image. 2054 2055 `--no-seh' 2056 The image does not use SEH. No SE handler may be called from this 2057 image. 2058 2059 `--no-bind' 2060 Do not bind this image. 2061 2062 `--wdmdriver' 2063 The driver uses the MS Windows Driver Model. 2064 2065 `--tsaware' 2066 The image is Terminal Server aware. 2067 2068 2069 2.1.2 Options specific to C6X uClinux targets 2070 --------------------------------------------- 2071 2072 The C6X uClinux target uses a binary format called DSBT to support 2073 shared libraries. Each shared library in the system needs to have a 2074 unique index; all executables use an index of 0. 2075 2076 `--dsbt-size SIZE' 2077 This option sets the number of entires in the DSBT of the current 2078 executable or shared library to SIZE. The default is to create a 2079 table with 64 entries. 2080 2081 `--dsbt-index INDEX' 2082 This option sets the DSBT index of the current executable or 2083 shared library to INDEX. The default is 0, which is appropriate 2084 for generating executables. If a shared library is generated with 2085 a DSBT index of 0, the `R_C6000_DSBT_INDEX' relocs are copied into 2086 the output file. 2087 2088 The `--no-merge-exidx-entries' switch disables the merging of 2089 adjacent exidx entries in frame unwind info. 2090 2091 2092 2.1.3 Options specific to Motorola 68HC11 and 68HC12 targets 2093 ------------------------------------------------------------ 2094 2095 The 68HC11 and 68HC12 linkers support specific options to control the 2096 memory bank switching mapping and trampoline code generation. 2097 2098 `--no-trampoline' 2099 This option disables the generation of trampoline. By default a 2100 trampoline is generated for each far function which is called 2101 using a `jsr' instruction (this happens when a pointer to a far 2102 function is taken). 2103 2104 `--bank-window NAME' 2105 This option indicates to the linker the name of the memory region 2106 in the `MEMORY' specification that describes the memory bank 2107 window. The definition of such region is then used by the linker 2108 to compute paging and addresses within the memory window. 2109 2110 2111 2.1.4 Options specific to Motorola 68K target 2112 --------------------------------------------- 2113 2114 The following options are supported to control handling of GOT 2115 generation when linking for 68K targets. 2116 2117 `--got=TYPE' 2118 This option tells the linker which GOT generation scheme to use. 2119 TYPE should be one of `single', `negative', `multigot' or 2120 `target'. For more information refer to the Info entry for `ld'. 2121 2122 2123 2124 File: ld.info, Node: Environment, Prev: Options, Up: Invocation 2125 2126 2.2 Environment Variables 2127 ========================= 2128 2129 You can change the behaviour of `ld' with the environment variables 2130 `GNUTARGET', `LDEMULATION' and `COLLECT_NO_DEMANGLE'. 2131 2132 `GNUTARGET' determines the input-file object format if you don't use 2133 `-b' (or its synonym `--format'). Its value should be one of the BFD 2134 names for an input format (*note BFD::). If there is no `GNUTARGET' in 2135 the environment, `ld' uses the natural format of the target. If 2136 `GNUTARGET' is set to `default' then BFD attempts to discover the input 2137 format by examining binary input files; this method often succeeds, but 2138 there are potential ambiguities, since there is no method of ensuring 2139 that the magic number used to specify object-file formats is unique. 2140 However, the configuration procedure for BFD on each system places the 2141 conventional format for that system first in the search-list, so 2142 ambiguities are resolved in favor of convention. 2143 2144 `LDEMULATION' determines the default emulation if you don't use the 2145 `-m' option. The emulation can affect various aspects of linker 2146 behaviour, particularly the default linker script. You can list the 2147 available emulations with the `--verbose' or `-V' options. If the `-m' 2148 option is not used, and the `LDEMULATION' environment variable is not 2149 defined, the default emulation depends upon how the linker was 2150 configured. 2151 2152 Normally, the linker will default to demangling symbols. However, if 2153 `COLLECT_NO_DEMANGLE' is set in the environment, then it will default 2154 to not demangling symbols. This environment variable is used in a 2155 similar fashion by the `gcc' linker wrapper program. The default may 2156 be overridden by the `--demangle' and `--no-demangle' options. 2157 2158 2159 File: ld.info, Node: Scripts, Next: Machine Dependent, Prev: Invocation, Up: Top 2160 2161 3 Linker Scripts 2162 **************** 2163 2164 Every link is controlled by a "linker script". This script is written 2165 in the linker command language. 2166 2167 The main purpose of the linker script is to describe how the 2168 sections in the input files should be mapped into the output file, and 2169 to control the memory layout of the output file. Most linker scripts 2170 do nothing more than this. However, when necessary, the linker script 2171 can also direct the linker to perform many other operations, using the 2172 commands described below. 2173 2174 The linker always uses a linker script. If you do not supply one 2175 yourself, the linker will use a default script that is compiled into the 2176 linker executable. You can use the `--verbose' command line option to 2177 display the default linker script. Certain command line options, such 2178 as `-r' or `-N', will affect the default linker script. 2179 2180 You may supply your own linker script by using the `-T' command line 2181 option. When you do this, your linker script will replace the default 2182 linker script. 2183 2184 You may also use linker scripts implicitly by naming them as input 2185 files to the linker, as though they were files to be linked. *Note 2186 Implicit Linker Scripts::. 2187 2188 * Menu: 2189 2190 * Basic Script Concepts:: Basic Linker Script Concepts 2191 * Script Format:: Linker Script Format 2192 * Simple Example:: Simple Linker Script Example 2193 * Simple Commands:: Simple Linker Script Commands 2194 * Assignments:: Assigning Values to Symbols 2195 * SECTIONS:: SECTIONS Command 2196 * MEMORY:: MEMORY Command 2197 * PHDRS:: PHDRS Command 2198 * VERSION:: VERSION Command 2199 * Expressions:: Expressions in Linker Scripts 2200 * Implicit Linker Scripts:: Implicit Linker Scripts 2201 2202 2203 File: ld.info, Node: Basic Script Concepts, Next: Script Format, Up: Scripts 2204 2205 3.1 Basic Linker Script Concepts 2206 ================================ 2207 2208 We need to define some basic concepts and vocabulary in order to 2209 describe the linker script language. 2210 2211 The linker combines input files into a single output file. The 2212 output file and each input file are in a special data format known as an 2213 "object file format". Each file is called an "object file". The 2214 output file is often called an "executable", but for our purposes we 2215 will also call it an object file. Each object file has, among other 2216 things, a list of "sections". We sometimes refer to a section in an 2217 input file as an "input section"; similarly, a section in the output 2218 file is an "output section". 2219 2220 Each section in an object file has a name and a size. Most sections 2221 also have an associated block of data, known as the "section contents". 2222 A section may be marked as "loadable", which mean that the contents 2223 should be loaded into memory when the output file is run. A section 2224 with no contents may be "allocatable", which means that an area in 2225 memory should be set aside, but nothing in particular should be loaded 2226 there (in some cases this memory must be zeroed out). A section which 2227 is neither loadable nor allocatable typically contains some sort of 2228 debugging information. 2229 2230 Every loadable or allocatable output section has two addresses. The 2231 first is the "VMA", or virtual memory address. This is the address the 2232 section will have when the output file is run. The second is the 2233 "LMA", or load memory address. This is the address at which the 2234 section will be loaded. In most cases the two addresses will be the 2235 same. An example of when they might be different is when a data section 2236 is loaded into ROM, and then copied into RAM when the program starts up 2237 (this technique is often used to initialize global variables in a ROM 2238 based system). In this case the ROM address would be the LMA, and the 2239 RAM address would be the VMA. 2240 2241 You can see the sections in an object file by using the `objdump' 2242 program with the `-h' option. 2243 2244 Every object file also has a list of "symbols", known as the "symbol 2245 table". A symbol may be defined or undefined. Each symbol has a name, 2246 and each defined symbol has an address, among other information. If 2247 you compile a C or C++ program into an object file, you will get a 2248 defined symbol for every defined function and global or static 2249 variable. Every undefined function or global variable which is 2250 referenced in the input file will become an undefined symbol. 2251 2252 You can see the symbols in an object file by using the `nm' program, 2253 or by using the `objdump' program with the `-t' option. 2254 2255 2256 File: ld.info, Node: Script Format, Next: Simple Example, Prev: Basic Script Concepts, Up: Scripts 2257 2258 3.2 Linker Script Format 2259 ======================== 2260 2261 Linker scripts are text files. 2262 2263 You write a linker script as a series of commands. Each command is 2264 either a keyword, possibly followed by arguments, or an assignment to a 2265 symbol. You may separate commands using semicolons. Whitespace is 2266 generally ignored. 2267 2268 Strings such as file or format names can normally be entered 2269 directly. If the file name contains a character such as a comma which 2270 would otherwise serve to separate file names, you may put the file name 2271 in double quotes. There is no way to use a double quote character in a 2272 file name. 2273 2274 You may include comments in linker scripts just as in C, delimited by 2275 `/*' and `*/'. As in C, comments are syntactically equivalent to 2276 whitespace. 2277 2278 2279 File: ld.info, Node: Simple Example, Next: Simple Commands, Prev: Script Format, Up: Scripts 2280 2281 3.3 Simple Linker Script Example 2282 ================================ 2283 2284 Many linker scripts are fairly simple. 2285 2286 The simplest possible linker script has just one command: 2287 `SECTIONS'. You use the `SECTIONS' command to describe the memory 2288 layout of the output file. 2289 2290 The `SECTIONS' command is a powerful command. Here we will describe 2291 a simple use of it. Let's assume your program consists only of code, 2292 initialized data, and uninitialized data. These will be in the 2293 `.text', `.data', and `.bss' sections, respectively. Let's assume 2294 further that these are the only sections which appear in your input 2295 files. 2296 2297 For this example, let's say that the code should be loaded at address 2298 0x10000, and that the data should start at address 0x8000000. Here is a 2299 linker script which will do that: 2300 SECTIONS 2301 { 2302 . = 0x10000; 2303 .text : { *(.text) } 2304 . = 0x8000000; 2305 .data : { *(.data) } 2306 .bss : { *(.bss) } 2307 } 2308 2309 You write the `SECTIONS' command as the keyword `SECTIONS', followed 2310 by a series of symbol assignments and output section descriptions 2311 enclosed in curly braces. 2312 2313 The first line inside the `SECTIONS' command of the above example 2314 sets the value of the special symbol `.', which is the location 2315 counter. If you do not specify the address of an output section in some 2316 other way (other ways are described later), the address is set from the 2317 current value of the location counter. The location counter is then 2318 incremented by the size of the output section. At the start of the 2319 `SECTIONS' command, the location counter has the value `0'. 2320 2321 The second line defines an output section, `.text'. The colon is 2322 required syntax which may be ignored for now. Within the curly braces 2323 after the output section name, you list the names of the input sections 2324 which should be placed into this output section. The `*' is a wildcard 2325 which matches any file name. The expression `*(.text)' means all 2326 `.text' input sections in all input files. 2327 2328 Since the location counter is `0x10000' when the output section 2329 `.text' is defined, the linker will set the address of the `.text' 2330 section in the output file to be `0x10000'. 2331 2332 The remaining lines define the `.data' and `.bss' sections in the 2333 output file. The linker will place the `.data' output section at 2334 address `0x8000000'. After the linker places the `.data' output 2335 section, the value of the location counter will be `0x8000000' plus the 2336 size of the `.data' output section. The effect is that the linker will 2337 place the `.bss' output section immediately after the `.data' output 2338 section in memory. 2339 2340 The linker will ensure that each output section has the required 2341 alignment, by increasing the location counter if necessary. In this 2342 example, the specified addresses for the `.text' and `.data' sections 2343 will probably satisfy any alignment constraints, but the linker may 2344 have to create a small gap between the `.data' and `.bss' sections. 2345 2346 That's it! That's a simple and complete linker script. 2347 2348 2349 File: ld.info, Node: Simple Commands, Next: Assignments, Prev: Simple Example, Up: Scripts 2350 2351 3.4 Simple Linker Script Commands 2352 ================================= 2353 2354 In this section we describe the simple linker script commands. 2355 2356 * Menu: 2357 2358 * Entry Point:: Setting the entry point 2359 * File Commands:: Commands dealing with files 2360 2361 * Format Commands:: Commands dealing with object file formats 2362 2363 * REGION_ALIAS:: Assign alias names to memory regions 2364 * Miscellaneous Commands:: Other linker script commands 2365 2366 2367 File: ld.info, Node: Entry Point, Next: File Commands, Up: Simple Commands 2368 2369 3.4.1 Setting the Entry Point 2370 ----------------------------- 2371 2372 The first instruction to execute in a program is called the "entry 2373 point". You can use the `ENTRY' linker script command to set the entry 2374 point. The argument is a symbol name: 2375 ENTRY(SYMBOL) 2376 2377 There are several ways to set the entry point. The linker will set 2378 the entry point by trying each of the following methods in order, and 2379 stopping when one of them succeeds: 2380 * the `-e' ENTRY command-line option; 2381 2382 * the `ENTRY(SYMBOL)' command in a linker script; 2383 2384 * the value of a target specific symbol, if it is defined; For many 2385 targets this is `start', but PE and BeOS based systems for example 2386 check a list of possible entry symbols, matching the first one 2387 found. 2388 2389 * the address of the first byte of the `.text' section, if present; 2390 2391 * The address `0'. 2392 2393 2394 File: ld.info, Node: File Commands, Next: Format Commands, Prev: Entry Point, Up: Simple Commands 2395 2396 3.4.2 Commands Dealing with Files 2397 --------------------------------- 2398 2399 Several linker script commands deal with files. 2400 2401 `INCLUDE FILENAME' 2402 Include the linker script FILENAME at this point. The file will 2403 be searched for in the current directory, and in any directory 2404 specified with the `-L' option. You can nest calls to `INCLUDE' 2405 up to 10 levels deep. 2406 2407 You can place `INCLUDE' directives at the top level, in `MEMORY' or 2408 `SECTIONS' commands, or in output section descriptions. 2409 2410 `INPUT(FILE, FILE, ...)' 2411 `INPUT(FILE FILE ...)' 2412 The `INPUT' command directs the linker to include the named files 2413 in the link, as though they were named on the command line. 2414 2415 For example, if you always want to include `subr.o' any time you do 2416 a link, but you can't be bothered to put it on every link command 2417 line, then you can put `INPUT (subr.o)' in your linker script. 2418 2419 In fact, if you like, you can list all of your input files in the 2420 linker script, and then invoke the linker with nothing but a `-T' 2421 option. 2422 2423 In case a "sysroot prefix" is configured, and the filename starts 2424 with the `/' character, and the script being processed was located 2425 inside the "sysroot prefix", the filename will be looked for in 2426 the "sysroot prefix". Otherwise, the linker will try to open the 2427 file in the current directory. If it is not found, the linker 2428 will search through the archive library search path. See the 2429 description of `-L' in *Note Command Line Options: Options. 2430 2431 If you use `INPUT (-lFILE)', `ld' will transform the name to 2432 `libFILE.a', as with the command line argument `-l'. 2433 2434 When you use the `INPUT' command in an implicit linker script, the 2435 files will be included in the link at the point at which the linker 2436 script file is included. This can affect archive searching. 2437 2438 `GROUP(FILE, FILE, ...)' 2439 `GROUP(FILE FILE ...)' 2440 The `GROUP' command is like `INPUT', except that the named files 2441 should all be archives, and they are searched repeatedly until no 2442 new undefined references are created. See the description of `-(' 2443 in *Note Command Line Options: Options. 2444 2445 `AS_NEEDED(FILE, FILE, ...)' 2446 `AS_NEEDED(FILE FILE ...)' 2447 This construct can appear only inside of the `INPUT' or `GROUP' 2448 commands, among other filenames. The files listed will be handled 2449 as if they appear directly in the `INPUT' or `GROUP' commands, 2450 with the exception of ELF shared libraries, that will be added only 2451 when they are actually needed. This construct essentially enables 2452 `--as-needed' option for all the files listed inside of it and 2453 restores previous `--as-needed' resp. `--no-as-needed' setting 2454 afterwards. 2455 2456 `OUTPUT(FILENAME)' 2457 The `OUTPUT' command names the output file. Using 2458 `OUTPUT(FILENAME)' in the linker script is exactly like using `-o 2459 FILENAME' on the command line (*note Command Line Options: 2460 Options.). If both are used, the command line option takes 2461 precedence. 2462 2463 You can use the `OUTPUT' command to define a default name for the 2464 output file other than the usual default of `a.out'. 2465 2466 `SEARCH_DIR(PATH)' 2467 The `SEARCH_DIR' command adds PATH to the list of paths where `ld' 2468 looks for archive libraries. Using `SEARCH_DIR(PATH)' is exactly 2469 like using `-L PATH' on the command line (*note Command Line 2470 Options: Options.). If both are used, then the linker will search 2471 both paths. Paths specified using the command line option are 2472 searched first. 2473 2474 `STARTUP(FILENAME)' 2475 The `STARTUP' command is just like the `INPUT' command, except 2476 that FILENAME will become the first input file to be linked, as 2477 though it were specified first on the command line. This may be 2478 useful when using a system in which the entry point is always the 2479 start of the first file. 2480 2481 2482 File: ld.info, Node: Format Commands, Next: REGION_ALIAS, Prev: File Commands, Up: Simple Commands 2483 2484 3.4.3 Commands Dealing with Object File Formats 2485 ----------------------------------------------- 2486 2487 A couple of linker script commands deal with object file formats. 2488 2489 `OUTPUT_FORMAT(BFDNAME)' 2490 `OUTPUT_FORMAT(DEFAULT, BIG, LITTLE)' 2491 The `OUTPUT_FORMAT' command names the BFD format to use for the 2492 output file (*note BFD::). Using `OUTPUT_FORMAT(BFDNAME)' is 2493 exactly like using `--oformat BFDNAME' on the command line (*note 2494 Command Line Options: Options.). If both are used, the command 2495 line option takes precedence. 2496 2497 You can use `OUTPUT_FORMAT' with three arguments to use different 2498 formats based on the `-EB' and `-EL' command line options. This 2499 permits the linker script to set the output format based on the 2500 desired endianness. 2501 2502 If neither `-EB' nor `-EL' are used, then the output format will 2503 be the first argument, DEFAULT. If `-EB' is used, the output 2504 format will be the second argument, BIG. If `-EL' is used, the 2505 output format will be the third argument, LITTLE. 2506 2507 For example, the default linker script for the MIPS ELF target 2508 uses this command: 2509 OUTPUT_FORMAT(elf32-bigmips, elf32-bigmips, elf32-littlemips) 2510 This says that the default format for the output file is 2511 `elf32-bigmips', but if the user uses the `-EL' command line 2512 option, the output file will be created in the `elf32-littlemips' 2513 format. 2514 2515 `TARGET(BFDNAME)' 2516 The `TARGET' command names the BFD format to use when reading input 2517 files. It affects subsequent `INPUT' and `GROUP' commands. This 2518 command is like using `-b BFDNAME' on the command line (*note 2519 Command Line Options: Options.). If the `TARGET' command is used 2520 but `OUTPUT_FORMAT' is not, then the last `TARGET' command is also 2521 used to set the format for the output file. *Note BFD::. 2522 2523 2524 File: ld.info, Node: REGION_ALIAS, Next: Miscellaneous Commands, Prev: Format Commands, Up: Simple Commands 2525 2526 3.4.4 Assign alias names to memory regions 2527 ------------------------------------------ 2528 2529 Alias names can be added to existing memory regions created with the 2530 *Note MEMORY:: command. Each name corresponds to at most one memory 2531 region. 2532 2533 REGION_ALIAS(ALIAS, REGION) 2534 2535 The `REGION_ALIAS' function creates an alias name ALIAS for the 2536 memory region REGION. This allows a flexible mapping of output sections 2537 to memory regions. An example follows. 2538 2539 Suppose we have an application for embedded systems which come with 2540 various memory storage devices. All have a general purpose, volatile 2541 memory `RAM' that allows code execution or data storage. Some may have 2542 a read-only, non-volatile memory `ROM' that allows code execution and 2543 read-only data access. The last variant is a read-only, non-volatile 2544 memory `ROM2' with read-only data access and no code execution 2545 capability. We have four output sections: 2546 2547 * `.text' program code; 2548 2549 * `.rodata' read-only data; 2550 2551 * `.data' read-write initialized data; 2552 2553 * `.bss' read-write zero initialized data. 2554 2555 The goal is to provide a linker command file that contains a system 2556 independent part defining the output sections and a system dependent 2557 part mapping the output sections to the memory regions available on the 2558 system. Our embedded systems come with three different memory setups 2559 `A', `B' and `C': 2560 Section Variant A Variant B Variant C 2561 .text RAM ROM ROM 2562 .rodata RAM ROM ROM2 2563 .data RAM RAM/ROM RAM/ROM2 2564 .bss RAM RAM RAM 2565 The notation `RAM/ROM' or `RAM/ROM2' means that this section is 2566 loaded into region `ROM' or `ROM2' respectively. Please note that the 2567 load address of the `.data' section starts in all three variants at the 2568 end of the `.rodata' section. 2569 2570 The base linker script that deals with the output sections follows. 2571 It includes the system dependent `linkcmds.memory' file that describes 2572 the memory layout: 2573 INCLUDE linkcmds.memory 2574 2575 SECTIONS 2576 { 2577 .text : 2578 { 2579 *(.text) 2580 } > REGION_TEXT 2581 .rodata : 2582 { 2583 *(.rodata) 2584 rodata_end = .; 2585 } > REGION_RODATA 2586 .data : AT (rodata_end) 2587 { 2588 data_start = .; 2589 *(.data) 2590 } > REGION_DATA 2591 data_size = SIZEOF(.data); 2592 data_load_start = LOADADDR(.data); 2593 .bss : 2594 { 2595 *(.bss) 2596 } > REGION_BSS 2597 } 2598 2599 Now we need three different `linkcmds.memory' files to define memory 2600 regions and alias names. The content of `linkcmds.memory' for the three 2601 variants `A', `B' and `C': 2602 `A' 2603 Here everything goes into the `RAM'. 2604 MEMORY 2605 { 2606 RAM : ORIGIN = 0, LENGTH = 4M 2607 } 2608 2609 REGION_ALIAS("REGION_TEXT", RAM); 2610 REGION_ALIAS("REGION_RODATA", RAM); 2611 REGION_ALIAS("REGION_DATA", RAM); 2612 REGION_ALIAS("REGION_BSS", RAM); 2613 2614 `B' 2615 Program code and read-only data go into the `ROM'. Read-write 2616 data goes into the `RAM'. An image of the initialized data is 2617 loaded into the `ROM' and will be copied during system start into 2618 the `RAM'. 2619 MEMORY 2620 { 2621 ROM : ORIGIN = 0, LENGTH = 3M 2622 RAM : ORIGIN = 0x10000000, LENGTH = 1M 2623 } 2624 2625 REGION_ALIAS("REGION_TEXT", ROM); 2626 REGION_ALIAS("REGION_RODATA", ROM); 2627 REGION_ALIAS("REGION_DATA", RAM); 2628 REGION_ALIAS("REGION_BSS", RAM); 2629 2630 `C' 2631 Program code goes into the `ROM'. Read-only data goes into the 2632 `ROM2'. Read-write data goes into the `RAM'. An image of the 2633 initialized data is loaded into the `ROM2' and will be copied 2634 during system start into the `RAM'. 2635 MEMORY 2636 { 2637 ROM : ORIGIN = 0, LENGTH = 2M 2638 ROM2 : ORIGIN = 0x10000000, LENGTH = 1M 2639 RAM : ORIGIN = 0x20000000, LENGTH = 1M 2640 } 2641 2642 REGION_ALIAS("REGION_TEXT", ROM); 2643 REGION_ALIAS("REGION_RODATA", ROM2); 2644 REGION_ALIAS("REGION_DATA", RAM); 2645 REGION_ALIAS("REGION_BSS", RAM); 2646 2647 It is possible to write a common system initialization routine to 2648 copy the `.data' section from `ROM' or `ROM2' into the `RAM' if 2649 necessary: 2650 #include <string.h> 2651 2652 extern char data_start []; 2653 extern char data_size []; 2654 extern char data_load_start []; 2655 2656 void copy_data(void) 2657 { 2658 if (data_start != data_load_start) 2659 { 2660 memcpy(data_start, data_load_start, (size_t) data_size); 2661 } 2662 } 2663 2664 2665 File: ld.info, Node: Miscellaneous Commands, Prev: REGION_ALIAS, Up: Simple Commands 2666 2667 3.4.5 Other Linker Script Commands 2668 ---------------------------------- 2669 2670 There are a few other linker scripts commands. 2671 2672 `ASSERT(EXP, MESSAGE)' 2673 Ensure that EXP is non-zero. If it is zero, then exit the linker 2674 with an error code, and print MESSAGE. 2675 2676 `EXTERN(SYMBOL SYMBOL ...)' 2677 Force SYMBOL to be entered in the output file as an undefined 2678 symbol. Doing this may, for example, trigger linking of additional 2679 modules from standard libraries. You may list several SYMBOLs for 2680 each `EXTERN', and you may use `EXTERN' multiple times. This 2681 command has the same effect as the `-u' command-line option. 2682 2683 `FORCE_COMMON_ALLOCATION' 2684 This command has the same effect as the `-d' command-line option: 2685 to make `ld' assign space to common symbols even if a relocatable 2686 output file is specified (`-r'). 2687 2688 `INHIBIT_COMMON_ALLOCATION' 2689 This command has the same effect as the `--no-define-common' 2690 command-line option: to make `ld' omit the assignment of addresses 2691 to common symbols even for a non-relocatable output file. 2692 2693 `INSERT [ AFTER | BEFORE ] OUTPUT_SECTION' 2694 This command is typically used in a script specified by `-T' to 2695 augment the default `SECTIONS' with, for example, overlays. It 2696 inserts all prior linker script statements after (or before) 2697 OUTPUT_SECTION, and also causes `-T' to not override the default 2698 linker script. The exact insertion point is as for orphan 2699 sections. *Note Location Counter::. The insertion happens after 2700 the linker has mapped input sections to output sections. Prior to 2701 the insertion, since `-T' scripts are parsed before the default 2702 linker script, statements in the `-T' script occur before the 2703 default linker script statements in the internal linker 2704 representation of the script. In particular, input section 2705 assignments will be made to `-T' output sections before those in 2706 the default script. Here is an example of how a `-T' script using 2707 `INSERT' might look: 2708 2709 SECTIONS 2710 { 2711 OVERLAY : 2712 { 2713 .ov1 { ov1*(.text) } 2714 .ov2 { ov2*(.text) } 2715 } 2716 } 2717 INSERT AFTER .text; 2718 2719 `NOCROSSREFS(SECTION SECTION ...)' 2720 This command may be used to tell `ld' to issue an error about any 2721 references among certain output sections. 2722 2723 In certain types of programs, particularly on embedded systems when 2724 using overlays, when one section is loaded into memory, another 2725 section will not be. Any direct references between the two 2726 sections would be errors. For example, it would be an error if 2727 code in one section called a function defined in the other section. 2728 2729 The `NOCROSSREFS' command takes a list of output section names. If 2730 `ld' detects any cross references between the sections, it reports 2731 an error and returns a non-zero exit status. Note that the 2732 `NOCROSSREFS' command uses output section names, not input section 2733 names. 2734 2735 `OUTPUT_ARCH(BFDARCH)' 2736 Specify a particular output machine architecture. The argument is 2737 one of the names used by the BFD library (*note BFD::). You can 2738 see the architecture of an object file by using the `objdump' 2739 program with the `-f' option. 2740 2741 `LD_FEATURE(STRING)' 2742 This command may be used to modify `ld' behavior. If STRING is 2743 `"SANE_EXPR"' then absolute symbols and numbers in a script are 2744 simply treated as numbers everywhere. *Note Expression Section::. 2745 2746 2747 File: ld.info, Node: Assignments, Next: SECTIONS, Prev: Simple Commands, Up: Scripts 2748 2749 3.5 Assigning Values to Symbols 2750 =============================== 2751 2752 You may assign a value to a symbol in a linker script. This will define 2753 the symbol and place it into the symbol table with a global scope. 2754 2755 * Menu: 2756 2757 * Simple Assignments:: Simple Assignments 2758 * PROVIDE:: PROVIDE 2759 * PROVIDE_HIDDEN:: PROVIDE_HIDDEN 2760 * Source Code Reference:: How to use a linker script defined symbol in source code 2761 2762 2763 File: ld.info, Node: Simple Assignments, Next: PROVIDE, Up: Assignments 2764 2765 3.5.1 Simple Assignments 2766 ------------------------ 2767 2768 You may assign to a symbol using any of the C assignment operators: 2769 2770 `SYMBOL = EXPRESSION ;' 2771 `SYMBOL += EXPRESSION ;' 2772 `SYMBOL -= EXPRESSION ;' 2773 `SYMBOL *= EXPRESSION ;' 2774 `SYMBOL /= EXPRESSION ;' 2775 `SYMBOL <<= EXPRESSION ;' 2776 `SYMBOL >>= EXPRESSION ;' 2777 `SYMBOL &= EXPRESSION ;' 2778 `SYMBOL |= EXPRESSION ;' 2779 2780 The first case will define SYMBOL to the value of EXPRESSION. In 2781 the other cases, SYMBOL must already be defined, and the value will be 2782 adjusted accordingly. 2783 2784 The special symbol name `.' indicates the location counter. You may 2785 only use this within a `SECTIONS' command. *Note Location Counter::. 2786 2787 The semicolon after EXPRESSION is required. 2788 2789 Expressions are defined below; see *Note Expressions::. 2790 2791 You may write symbol assignments as commands in their own right, or 2792 as statements within a `SECTIONS' command, or as part of an output 2793 section description in a `SECTIONS' command. 2794 2795 The section of the symbol will be set from the section of the 2796 expression; for more information, see *Note Expression Section::. 2797 2798 Here is an example showing the three different places that symbol 2799 assignments may be used: 2800 2801 floating_point = 0; 2802 SECTIONS 2803 { 2804 .text : 2805 { 2806 *(.text) 2807 _etext = .; 2808 } 2809 _bdata = (. + 3) & ~ 3; 2810 .data : { *(.data) } 2811 } 2812 In this example, the symbol `floating_point' will be defined as 2813 zero. The symbol `_etext' will be defined as the address following the 2814 last `.text' input section. The symbol `_bdata' will be defined as the 2815 address following the `.text' output section aligned upward to a 4 byte 2816 boundary. 2817 2818 2819 File: ld.info, Node: PROVIDE, Next: PROVIDE_HIDDEN, Prev: Simple Assignments, Up: Assignments 2820 2821 3.5.2 PROVIDE 2822 ------------- 2823 2824 In some cases, it is desirable for a linker script to define a symbol 2825 only if it is referenced and is not defined by any object included in 2826 the link. For example, traditional linkers defined the symbol `etext'. 2827 However, ANSI C requires that the user be able to use `etext' as a 2828 function name without encountering an error. The `PROVIDE' keyword may 2829 be used to define a symbol, such as `etext', only if it is referenced 2830 but not defined. The syntax is `PROVIDE(SYMBOL = EXPRESSION)'. 2831 2832 Here is an example of using `PROVIDE' to define `etext': 2833 SECTIONS 2834 { 2835 .text : 2836 { 2837 *(.text) 2838 _etext = .; 2839 PROVIDE(etext = .); 2840 } 2841 } 2842 2843 In this example, if the program defines `_etext' (with a leading 2844 underscore), the linker will give a multiple definition error. If, on 2845 the other hand, the program defines `etext' (with no leading 2846 underscore), the linker will silently use the definition in the program. 2847 If the program references `etext' but does not define it, the linker 2848 will use the definition in the linker script. 2849 2850 2851 File: ld.info, Node: PROVIDE_HIDDEN, Next: Source Code Reference, Prev: PROVIDE, Up: Assignments 2852 2853 3.5.3 PROVIDE_HIDDEN 2854 -------------------- 2855 2856 Similar to `PROVIDE'. For ELF targeted ports, the symbol will be 2857 hidden and won't be exported. 2858 2859 2860 File: ld.info, Node: Source Code Reference, Prev: PROVIDE_HIDDEN, Up: Assignments 2861 2862 3.5.4 Source Code Reference 2863 --------------------------- 2864 2865 Accessing a linker script defined variable from source code is not 2866 intuitive. In particular a linker script symbol is not equivalent to a 2867 variable declaration in a high level language, it is instead a symbol 2868 that does not have a value. 2869 2870 Before going further, it is important to note that compilers often 2871 transform names in the source code into different names when they are 2872 stored in the symbol table. For example, Fortran compilers commonly 2873 prepend or append an underscore, and C++ performs extensive `name 2874 mangling'. Therefore there might be a discrepancy between the name of 2875 a variable as it is used in source code and the name of the same 2876 variable as it is defined in a linker script. For example in C a 2877 linker script variable might be referred to as: 2878 2879 extern int foo; 2880 2881 But in the linker script it might be defined as: 2882 2883 _foo = 1000; 2884 2885 In the remaining examples however it is assumed that no name 2886 transformation has taken place. 2887 2888 When a symbol is declared in a high level language such as C, two 2889 things happen. The first is that the compiler reserves enough space in 2890 the program's memory to hold the _value_ of the symbol. The second is 2891 that the compiler creates an entry in the program's symbol table which 2892 holds the symbol's _address_. ie the symbol table contains the address 2893 of the block of memory holding the symbol's value. So for example the 2894 following C declaration, at file scope: 2895 2896 int foo = 1000; 2897 2898 creates a entry called `foo' in the symbol table. This entry holds 2899 the address of an `int' sized block of memory where the number 1000 is 2900 initially stored. 2901 2902 When a program references a symbol the compiler generates code that 2903 first accesses the symbol table to find the address of the symbol's 2904 memory block and then code to read the value from that memory block. 2905 So: 2906 2907 foo = 1; 2908 2909 looks up the symbol `foo' in the symbol table, gets the address 2910 associated with this symbol and then writes the value 1 into that 2911 address. Whereas: 2912 2913 int * a = & foo; 2914 2915 looks up the symbol `foo' in the symbol table, gets it address and 2916 then copies this address into the block of memory associated with the 2917 variable `a'. 2918 2919 Linker scripts symbol declarations, by contrast, create an entry in 2920 the symbol table but do not assign any memory to them. Thus they are 2921 an address without a value. So for example the linker script 2922 definition: 2923 2924 foo = 1000; 2925 2926 creates an entry in the symbol table called `foo' which holds the 2927 address of memory location 1000, but nothing special is stored at 2928 address 1000. This means that you cannot access the _value_ of a 2929 linker script defined symbol - it has no value - all you can do is 2930 access the _address_ of a linker script defined symbol. 2931 2932 Hence when you are using a linker script defined symbol in source 2933 code you should always take the address of the symbol, and never 2934 attempt to use its value. For example suppose you want to copy the 2935 contents of a section of memory called .ROM into a section called 2936 .FLASH and the linker script contains these declarations: 2937 2938 start_of_ROM = .ROM; 2939 end_of_ROM = .ROM + sizeof (.ROM) - 1; 2940 start_of_FLASH = .FLASH; 2941 2942 Then the C source code to perform the copy would be: 2943 2944 extern char start_of_ROM, end_of_ROM, start_of_FLASH; 2945 2946 memcpy (& start_of_FLASH, & start_of_ROM, & end_of_ROM - & start_of_ROM); 2947 2948 Note the use of the `&' operators. These are correct. 2949 2950 2951 File: ld.info, Node: SECTIONS, Next: MEMORY, Prev: Assignments, Up: Scripts 2952 2953 3.6 SECTIONS Command 2954 ==================== 2955 2956 The `SECTIONS' command tells the linker how to map input sections into 2957 output sections, and how to place the output sections in memory. 2958 2959 The format of the `SECTIONS' command is: 2960 SECTIONS 2961 { 2962 SECTIONS-COMMAND 2963 SECTIONS-COMMAND 2964 ... 2965 } 2966 2967 Each SECTIONS-COMMAND may of be one of the following: 2968 2969 * an `ENTRY' command (*note Entry command: Entry Point.) 2970 2971 * a symbol assignment (*note Assignments::) 2972 2973 * an output section description 2974 2975 * an overlay description 2976 2977 The `ENTRY' command and symbol assignments are permitted inside the 2978 `SECTIONS' command for convenience in using the location counter in 2979 those commands. This can also make the linker script easier to 2980 understand because you can use those commands at meaningful points in 2981 the layout of the output file. 2982 2983 Output section descriptions and overlay descriptions are described 2984 below. 2985 2986 If you do not use a `SECTIONS' command in your linker script, the 2987 linker will place each input section into an identically named output 2988 section in the order that the sections are first encountered in the 2989 input files. If all input sections are present in the first file, for 2990 example, the order of sections in the output file will match the order 2991 in the first input file. The first section will be at address zero. 2992 2993 * Menu: 2994 2995 * Output Section Description:: Output section description 2996 * Output Section Name:: Output section name 2997 * Output Section Address:: Output section address 2998 * Input Section:: Input section description 2999 * Output Section Data:: Output section data 3000 * Output Section Keywords:: Output section keywords 3001 * Output Section Discarding:: Output section discarding 3002 * Output Section Attributes:: Output section attributes 3003 * Overlay Description:: Overlay description 3004 3005 3006 File: ld.info, Node: Output Section Description, Next: Output Section Name, Up: SECTIONS 3007 3008 3.6.1 Output Section Description 3009 -------------------------------- 3010 3011 The full description of an output section looks like this: 3012 SECTION [ADDRESS] [(TYPE)] : 3013 [AT(LMA)] 3014 [ALIGN(SECTION_ALIGN)] 3015 [SUBALIGN(SUBSECTION_ALIGN)] 3016 [CONSTRAINT] 3017 { 3018 OUTPUT-SECTION-COMMAND 3019 OUTPUT-SECTION-COMMAND 3020 ... 3021 } [>REGION] [AT>LMA_REGION] [:PHDR :PHDR ...] [=FILLEXP] 3022 3023 Most output sections do not use most of the optional section 3024 attributes. 3025 3026 The whitespace around SECTION is required, so that the section name 3027 is unambiguous. The colon and the curly braces are also required. The 3028 line breaks and other white space are optional. 3029 3030 Each OUTPUT-SECTION-COMMAND may be one of the following: 3031 3032 * a symbol assignment (*note Assignments::) 3033 3034 * an input section description (*note Input Section::) 3035 3036 * data values to include directly (*note Output Section Data::) 3037 3038 * a special output section keyword (*note Output Section Keywords::) 3039 3040 3041 File: ld.info, Node: Output Section Name, Next: Output Section Address, Prev: Output Section Description, Up: SECTIONS 3042 3043 3.6.2 Output Section Name 3044 ------------------------- 3045 3046 The name of the output section is SECTION. SECTION must meet the 3047 constraints of your output format. In formats which only support a 3048 limited number of sections, such as `a.out', the name must be one of 3049 the names supported by the format (`a.out', for example, allows only 3050 `.text', `.data' or `.bss'). If the output format supports any number 3051 of sections, but with numbers and not names (as is the case for Oasys), 3052 the name should be supplied as a quoted numeric string. A section name 3053 may consist of any sequence of characters, but a name which contains 3054 any unusual characters such as commas must be quoted. 3055 3056 The output section name `/DISCARD/' is special; *Note Output Section 3057 Discarding::. 3058 3059 3060 File: ld.info, Node: Output Section Address, Next: Input Section, Prev: Output Section Name, Up: SECTIONS 3061 3062 3.6.3 Output Section Address 3063 ---------------------------- 3064 3065 The ADDRESS is an expression for the VMA (the virtual memory address) 3066 of the output section. This address is optional, but if it is provided 3067 then the output address will be set exactly as specified. 3068 3069 If the output address is not specified then one will be chosen for 3070 the section, based on the heuristic below. This address will be 3071 adjusted to fit the alignment requirement of the output section. The 3072 alignment requirement is the strictest alignment of any input section 3073 contained within the output section. 3074 3075 The output section address heuristic is as follows: 3076 3077 * If an output memory REGION is set for the section then it is added 3078 to this region and its address will be the next free address in 3079 that region. 3080 3081 * If the MEMORY command has been used to create a list of memory 3082 regions then the first region which has attributes compatible with 3083 the section is selected to contain it. The section's output 3084 address will be the next free address in that region; *Note 3085 MEMORY::. 3086 3087 * If no memory regions were specified, or none match the section then 3088 the output address will be based on the current value of the 3089 location counter. 3090 3091 For example: 3092 3093 .text . : { *(.text) } 3094 3095 and 3096 3097 .text : { *(.text) } 3098 3099 are subtly different. The first will set the address of the `.text' 3100 output section to the current value of the location counter. The 3101 second will set it to the current value of the location counter aligned 3102 to the strictest alignment of any of the `.text' input sections. 3103 3104 The ADDRESS may be an arbitrary expression; *Note Expressions::. 3105 For example, if you want to align the section on a 0x10 byte boundary, 3106 so that the lowest four bits of the section address are zero, you could 3107 do something like this: 3108 .text ALIGN(0x10) : { *(.text) } 3109 This works because `ALIGN' returns the current location counter 3110 aligned upward to the specified value. 3111 3112 Specifying ADDRESS for a section will change the value of the 3113 location counter, provided that the section is non-empty. (Empty 3114 sections are ignored). 3115 3116 3117 File: ld.info, Node: Input Section, Next: Output Section Data, Prev: Output Section Address, Up: SECTIONS 3118 3119 3.6.4 Input Section Description 3120 ------------------------------- 3121 3122 The most common output section command is an input section description. 3123 3124 The input section description is the most basic linker script 3125 operation. You use output sections to tell the linker how to lay out 3126 your program in memory. You use input section descriptions to tell the 3127 linker how to map the input files into your memory layout. 3128 3129 * Menu: 3130 3131 * Input Section Basics:: Input section basics 3132 * Input Section Wildcards:: Input section wildcard patterns 3133 * Input Section Common:: Input section for common symbols 3134 * Input Section Keep:: Input section and garbage collection 3135 * Input Section Example:: Input section example 3136 3137 3138 File: ld.info, Node: Input Section Basics, Next: Input Section Wildcards, Up: Input Section 3139 3140 3.6.4.1 Input Section Basics 3141 ............................ 3142 3143 An input section description consists of a file name optionally followed 3144 by a list of section names in parentheses. 3145 3146 The file name and the section name may be wildcard patterns, which we 3147 describe further below (*note Input Section Wildcards::). 3148 3149 The most common input section description is to include all input 3150 sections with a particular name in the output section. For example, to 3151 include all input `.text' sections, you would write: 3152 *(.text) 3153 Here the `*' is a wildcard which matches any file name. To exclude 3154 a list of files from matching the file name wildcard, EXCLUDE_FILE may 3155 be used to match all files except the ones specified in the 3156 EXCLUDE_FILE list. For example: 3157 *(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors) 3158 will cause all .ctors sections from all files except `crtend.o' and 3159 `otherfile.o' to be included. 3160 3161 There are two ways to include more than one section: 3162 *(.text .rdata) 3163 *(.text) *(.rdata) 3164 The difference between these is the order in which the `.text' and 3165 `.rdata' input sections will appear in the output section. In the 3166 first example, they will be intermingled, appearing in the same order as 3167 they are found in the linker input. In the second example, all `.text' 3168 input sections will appear first, followed by all `.rdata' input 3169 sections. 3170 3171 You can specify a file name to include sections from a particular 3172 file. You would do this if one or more of your files contain special 3173 data that needs to be at a particular location in memory. For example: 3174 data.o(.data) 3175 3176 To refine the sections that are included based on the section flags 3177 of an input section, INPUT_SECTION_FLAGS may be used. 3178 3179 Here is a simple example for using Section header flags for ELF 3180 sections: 3181 3182 SECTIONS { 3183 .text : { INPUT_SECTION_FLAGS (SHF_MERGE & SHF_STRINGS) *(.text) } 3184 .text2 : { INPUT_SECTION_FLAGS (!SHF_WRITE) *(.text) } 3185 } 3186 3187 In this example, the output section `.text' will be comprised of any 3188 input section matching the name *(.text) whose section header flags 3189 `SHF_MERGE' and `SHF_STRINGS' are set. The output section `.text2' 3190 will be comprised of any input section matching the name *(.text) whose 3191 section header flag `SHF_WRITE' is clear. 3192 3193 You can also specify files within archives by writing a pattern 3194 matching the archive, a colon, then the pattern matching the file, with 3195 no whitespace around the colon. 3196 3197 `archive:file' 3198 matches file within archive 3199 3200 `archive:' 3201 matches the whole archive 3202 3203 `:file' 3204 matches file but not one in an archive 3205 3206 Either one or both of `archive' and `file' can contain shell 3207 wildcards. On DOS based file systems, the linker will assume that a 3208 single letter followed by a colon is a drive specifier, so `c:myfile.o' 3209 is a simple file specification, not `myfile.o' within an archive called 3210 `c'. `archive:file' filespecs may also be used within an 3211 `EXCLUDE_FILE' list, but may not appear in other linker script 3212 contexts. For instance, you cannot extract a file from an archive by 3213 using `archive:file' in an `INPUT' command. 3214 3215 If you use a file name without a list of sections, then all sections 3216 in the input file will be included in the output section. This is not 3217 commonly done, but it may by useful on occasion. For example: 3218 data.o 3219 3220 When you use a file name which is not an `archive:file' specifier 3221 and does not contain any wild card characters, the linker will first 3222 see if you also specified the file name on the linker command line or 3223 in an `INPUT' command. If you did not, the linker will attempt to open 3224 the file as an input file, as though it appeared on the command line. 3225 Note that this differs from an `INPUT' command, because the linker will 3226 not search for the file in the archive search path. 3227 3228 3229 File: ld.info, Node: Input Section Wildcards, Next: Input Section Common, Prev: Input Section Basics, Up: Input Section 3230 3231 3.6.4.2 Input Section Wildcard Patterns 3232 ....................................... 3233 3234 In an input section description, either the file name or the section 3235 name or both may be wildcard patterns. 3236 3237 The file name of `*' seen in many examples is a simple wildcard 3238 pattern for the file name. 3239 3240 The wildcard patterns are like those used by the Unix shell. 3241 3242 `*' 3243 matches any number of characters 3244 3245 `?' 3246 matches any single character 3247 3248 `[CHARS]' 3249 matches a single instance of any of the CHARS; the `-' character 3250 may be used to specify a range of characters, as in `[a-z]' to 3251 match any lower case letter 3252 3253 `\' 3254 quotes the following character 3255 3256 When a file name is matched with a wildcard, the wildcard characters 3257 will not match a `/' character (used to separate directory names on 3258 Unix). A pattern consisting of a single `*' character is an exception; 3259 it will always match any file name, whether it contains a `/' or not. 3260 In a section name, the wildcard characters will match a `/' character. 3261 3262 File name wildcard patterns only match files which are explicitly 3263 specified on the command line or in an `INPUT' command. The linker 3264 does not search directories to expand wildcards. 3265 3266 If a file name matches more than one wildcard pattern, or if a file 3267 name appears explicitly and is also matched by a wildcard pattern, the 3268 linker will use the first match in the linker script. For example, this 3269 sequence of input section descriptions is probably in error, because the 3270 `data.o' rule will not be used: 3271 .data : { *(.data) } 3272 .data1 : { data.o(.data) } 3273 3274 Normally, the linker will place files and sections matched by 3275 wildcards in the order in which they are seen during the link. You can 3276 change this by using the `SORT_BY_NAME' keyword, which appears before a 3277 wildcard pattern in parentheses (e.g., `SORT_BY_NAME(.text*)'). When 3278 the `SORT_BY_NAME' keyword is used, the linker will sort the files or 3279 sections into ascending order by name before placing them in the output 3280 file. 3281 3282 `SORT_BY_ALIGNMENT' is very similar to `SORT_BY_NAME'. The 3283 difference is `SORT_BY_ALIGNMENT' will sort sections into ascending 3284 order by alignment before placing them in the output file. 3285 3286 `SORT_BY_INIT_PRIORITY' is very similar to `SORT_BY_NAME'. The 3287 difference is `SORT_BY_INIT_PRIORITY' will sort sections into ascending 3288 order by numerical value of the GCC init_priority attribute encoded in 3289 the section name before placing them in the output file. 3290 3291 `SORT' is an alias for `SORT_BY_NAME'. 3292 3293 When there are nested section sorting commands in linker script, 3294 there can be at most 1 level of nesting for section sorting commands. 3295 3296 1. `SORT_BY_NAME' (`SORT_BY_ALIGNMENT' (wildcard section pattern)). 3297 It will sort the input sections by name first, then by alignment 3298 if 2 sections have the same name. 3299 3300 2. `SORT_BY_ALIGNMENT' (`SORT_BY_NAME' (wildcard section pattern)). 3301 It will sort the input sections by alignment first, then by name 3302 if 2 sections have the same alignment. 3303 3304 3. `SORT_BY_NAME' (`SORT_BY_NAME' (wildcard section pattern)) is 3305 treated the same as `SORT_BY_NAME' (wildcard section pattern). 3306 3307 4. `SORT_BY_ALIGNMENT' (`SORT_BY_ALIGNMENT' (wildcard section 3308 pattern)) is treated the same as `SORT_BY_ALIGNMENT' (wildcard 3309 section pattern). 3310 3311 5. All other nested section sorting commands are invalid. 3312 3313 When both command line section sorting option and linker script 3314 section sorting command are used, section sorting command always takes 3315 precedence over the command line option. 3316 3317 If the section sorting command in linker script isn't nested, the 3318 command line option will make the section sorting command to be treated 3319 as nested sorting command. 3320 3321 1. `SORT_BY_NAME' (wildcard section pattern ) with `--sort-sections 3322 alignment' is equivalent to `SORT_BY_NAME' (`SORT_BY_ALIGNMENT' 3323 (wildcard section pattern)). 3324 3325 2. `SORT_BY_ALIGNMENT' (wildcard section pattern) with 3326 `--sort-section name' is equivalent to `SORT_BY_ALIGNMENT' 3327 (`SORT_BY_NAME' (wildcard section pattern)). 3328 3329 If the section sorting command in linker script is nested, the 3330 command line option will be ignored. 3331 3332 If you ever get confused about where input sections are going, use 3333 the `-M' linker option to generate a map file. The map file shows 3334 precisely how input sections are mapped to output sections. 3335 3336 This example shows how wildcard patterns might be used to partition 3337 files. This linker script directs the linker to place all `.text' 3338 sections in `.text' and all `.bss' sections in `.bss'. The linker will 3339 place the `.data' section from all files beginning with an upper case 3340 character in `.DATA'; for all other files, the linker will place the 3341 `.data' section in `.data'. 3342 SECTIONS { 3343 .text : { *(.text) } 3344 .DATA : { [A-Z]*(.data) } 3345 .data : { *(.data) } 3346 .bss : { *(.bss) } 3347 } 3348 3349 3350 File: ld.info, Node: Input Section Common, Next: Input Section Keep, Prev: Input Section Wildcards, Up: Input Section 3351 3352 3.6.4.3 Input Section for Common Symbols 3353 ........................................ 3354 3355 A special notation is needed for common symbols, because in many object 3356 file formats common symbols do not have a particular input section. The 3357 linker treats common symbols as though they are in an input section 3358 named `COMMON'. 3359 3360 You may use file names with the `COMMON' section just as with any 3361 other input sections. You can use this to place common symbols from a 3362 particular input file in one section while common symbols from other 3363 input files are placed in another section. 3364 3365 In most cases, common symbols in input files will be placed in the 3366 `.bss' section in the output file. For example: 3367 .bss { *(.bss) *(COMMON) } 3368 3369 Some object file formats have more than one type of common symbol. 3370 For example, the MIPS ELF object file format distinguishes standard 3371 common symbols and small common symbols. In this case, the linker will 3372 use a different special section name for other types of common symbols. 3373 In the case of MIPS ELF, the linker uses `COMMON' for standard common 3374 symbols and `.scommon' for small common symbols. This permits you to 3375 map the different types of common symbols into memory at different 3376 locations. 3377 3378 You will sometimes see `[COMMON]' in old linker scripts. This 3379 notation is now considered obsolete. It is equivalent to `*(COMMON)'. 3380 3381 3382 File: ld.info, Node: Input Section Keep, Next: Input Section Example, Prev: Input Section Common, Up: Input Section 3383 3384 3.6.4.4 Input Section and Garbage Collection 3385 ............................................ 3386 3387 When link-time garbage collection is in use (`--gc-sections'), it is 3388 often useful to mark sections that should not be eliminated. This is 3389 accomplished by surrounding an input section's wildcard entry with 3390 `KEEP()', as in `KEEP(*(.init))' or `KEEP(SORT_BY_NAME(*)(.ctors))'. 3391 3392 3393 File: ld.info, Node: Input Section Example, Prev: Input Section Keep, Up: Input Section 3394 3395 3.6.4.5 Input Section Example 3396 ............................. 3397 3398 The following example is a complete linker script. It tells the linker 3399 to read all of the sections from file `all.o' and place them at the 3400 start of output section `outputa' which starts at location `0x10000'. 3401 All of section `.input1' from file `foo.o' follows immediately, in the 3402 same output section. All of section `.input2' from `foo.o' goes into 3403 output section `outputb', followed by section `.input1' from `foo1.o'. 3404 All of the remaining `.input1' and `.input2' sections from any files 3405 are written to output section `outputc'. 3406 3407 SECTIONS { 3408 outputa 0x10000 : 3409 { 3410 all.o 3411 foo.o (.input1) 3412 } 3413 outputb : 3414 { 3415 foo.o (.input2) 3416 foo1.o (.input1) 3417 } 3418 outputc : 3419 { 3420 *(.input1) 3421 *(.input2) 3422 } 3423 } 3424 3425 3426 File: ld.info, Node: Output Section Data, Next: Output Section Keywords, Prev: Input Section, Up: SECTIONS 3427 3428 3.6.5 Output Section Data 3429 ------------------------- 3430 3431 You can include explicit bytes of data in an output section by using 3432 `BYTE', `SHORT', `LONG', `QUAD', or `SQUAD' as an output section 3433 command. Each keyword is followed by an expression in parentheses 3434 providing the value to store (*note Expressions::). The value of the 3435 expression is stored at the current value of the location counter. 3436 3437 The `BYTE', `SHORT', `LONG', and `QUAD' commands store one, two, 3438 four, and eight bytes (respectively). After storing the bytes, the 3439 location counter is incremented by the number of bytes stored. 3440 3441 For example, this will store the byte 1 followed by the four byte 3442 value of the symbol `addr': 3443 BYTE(1) 3444 LONG(addr) 3445 3446 When using a 64 bit host or target, `QUAD' and `SQUAD' are the same; 3447 they both store an 8 byte, or 64 bit, value. When both host and target 3448 are 32 bits, an expression is computed as 32 bits. In this case `QUAD' 3449 stores a 32 bit value zero extended to 64 bits, and `SQUAD' stores a 32 3450 bit value sign extended to 64 bits. 3451 3452 If the object file format of the output file has an explicit 3453 endianness, which is the normal case, the value will be stored in that 3454 endianness. When the object file format does not have an explicit 3455 endianness, as is true of, for example, S-records, the value will be 3456 stored in the endianness of the first input object file. 3457 3458 Note--these commands only work inside a section description and not 3459 between them, so the following will produce an error from the linker: 3460 SECTIONS { .text : { *(.text) } LONG(1) .data : { *(.data) } } 3461 whereas this will work: 3462 SECTIONS { .text : { *(.text) ; LONG(1) } .data : { *(.data) } } 3463 3464 You may use the `FILL' command to set the fill pattern for the 3465 current section. It is followed by an expression in parentheses. Any 3466 otherwise unspecified regions of memory within the section (for example, 3467 gaps left due to the required alignment of input sections) are filled 3468 with the value of the expression, repeated as necessary. A `FILL' 3469 statement covers memory locations after the point at which it occurs in 3470 the section definition; by including more than one `FILL' statement, 3471 you can have different fill patterns in different parts of an output 3472 section. 3473 3474 This example shows how to fill unspecified regions of memory with the 3475 value `0x90': 3476 FILL(0x90909090) 3477 3478 The `FILL' command is similar to the `=FILLEXP' output section 3479 attribute, but it only affects the part of the section following the 3480 `FILL' command, rather than the entire section. If both are used, the 3481 `FILL' command takes precedence. *Note Output Section Fill::, for 3482 details on the fill expression. 3483 3484 3485 File: ld.info, Node: Output Section Keywords, Next: Output Section Discarding, Prev: Output Section Data, Up: SECTIONS 3486 3487 3.6.6 Output Section Keywords 3488 ----------------------------- 3489 3490 There are a couple of keywords which can appear as output section 3491 commands. 3492 3493 `CREATE_OBJECT_SYMBOLS' 3494 The command tells the linker to create a symbol for each input 3495 file. The name of each symbol will be the name of the 3496 corresponding input file. The section of each symbol will be the 3497 output section in which the `CREATE_OBJECT_SYMBOLS' command 3498 appears. 3499 3500 This is conventional for the a.out object file format. It is not 3501 normally used for any other object file format. 3502 3503 `CONSTRUCTORS' 3504 When linking using the a.out object file format, the linker uses an 3505 unusual set construct to support C++ global constructors and 3506 destructors. When linking object file formats which do not support 3507 arbitrary sections, such as ECOFF and XCOFF, the linker will 3508 automatically recognize C++ global constructors and destructors by 3509 name. For these object file formats, the `CONSTRUCTORS' command 3510 tells the linker to place constructor information in the output 3511 section where the `CONSTRUCTORS' command appears. The 3512 `CONSTRUCTORS' command is ignored for other object file formats. 3513 3514 The symbol `__CTOR_LIST__' marks the start of the global 3515 constructors, and the symbol `__CTOR_END__' marks the end. 3516 Similarly, `__DTOR_LIST__' and `__DTOR_END__' mark the start and 3517 end of the global destructors. The first word in the list is the 3518 number of entries, followed by the address of each constructor or 3519 destructor, followed by a zero word. The compiler must arrange to 3520 actually run the code. For these object file formats GNU C++ 3521 normally calls constructors from a subroutine `__main'; a call to 3522 `__main' is automatically inserted into the startup code for 3523 `main'. GNU C++ normally runs destructors either by using 3524 `atexit', or directly from the function `exit'. 3525 3526 For object file formats such as `COFF' or `ELF' which support 3527 arbitrary section names, GNU C++ will normally arrange to put the 3528 addresses of global constructors and destructors into the `.ctors' 3529 and `.dtors' sections. Placing the following sequence into your 3530 linker script will build the sort of table which the GNU C++ 3531 runtime code expects to see. 3532 3533 __CTOR_LIST__ = .; 3534 LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2) 3535 *(.ctors) 3536 LONG(0) 3537 __CTOR_END__ = .; 3538 __DTOR_LIST__ = .; 3539 LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2) 3540 *(.dtors) 3541 LONG(0) 3542 __DTOR_END__ = .; 3543 3544 If you are using the GNU C++ support for initialization priority, 3545 which provides some control over the order in which global 3546 constructors are run, you must sort the constructors at link time 3547 to ensure that they are executed in the correct order. When using 3548 the `CONSTRUCTORS' command, use `SORT_BY_NAME(CONSTRUCTORS)' 3549 instead. When using the `.ctors' and `.dtors' sections, use 3550 `*(SORT_BY_NAME(.ctors))' and `*(SORT_BY_NAME(.dtors))' instead of 3551 just `*(.ctors)' and `*(.dtors)'. 3552 3553 Normally the compiler and linker will handle these issues 3554 automatically, and you will not need to concern yourself with 3555 them. However, you may need to consider this if you are using C++ 3556 and writing your own linker scripts. 3557 3558 3559 3560 File: ld.info, Node: Output Section Discarding, Next: Output Section Attributes, Prev: Output Section Keywords, Up: SECTIONS 3561 3562 3.6.7 Output Section Discarding 3563 ------------------------------- 3564 3565 The linker will not create output sections with no contents. This is 3566 for convenience when referring to input sections that may or may not be 3567 present in any of the input files. For example: 3568 .foo : { *(.foo) } 3569 will only create a `.foo' section in the output file if there is a 3570 `.foo' section in at least one input file, and if the input sections 3571 are not all empty. Other link script directives that allocate space in 3572 an output section will also create the output section. 3573 3574 The linker will ignore address assignments (*note Output Section 3575 Address::) on discarded output sections, except when the linker script 3576 defines symbols in the output section. In that case the linker will 3577 obey the address assignments, possibly advancing dot even though the 3578 section is discarded. 3579 3580 The special output section name `/DISCARD/' may be used to discard 3581 input sections. Any input sections which are assigned to an output 3582 section named `/DISCARD/' are not included in the output file. 3583 3584 3585 File: ld.info, Node: Output Section Attributes, Next: Overlay Description, Prev: Output Section Discarding, Up: SECTIONS 3586 3587 3.6.8 Output Section Attributes 3588 ------------------------------- 3589 3590 We showed above that the full description of an output section looked 3591 like this: 3592 3593 SECTION [ADDRESS] [(TYPE)] : 3594 [AT(LMA)] 3595 [ALIGN(SECTION_ALIGN)] 3596 [SUBALIGN(SUBSECTION_ALIGN)] 3597 [CONSTRAINT] 3598 { 3599 OUTPUT-SECTION-COMMAND 3600 OUTPUT-SECTION-COMMAND 3601 ... 3602 } [>REGION] [AT>LMA_REGION] [:PHDR :PHDR ...] [=FILLEXP] 3603 3604 We've already described SECTION, ADDRESS, and 3605 OUTPUT-SECTION-COMMAND. In this section we will describe the remaining 3606 section attributes. 3607 3608 * Menu: 3609 3610 * Output Section Type:: Output section type 3611 * Output Section LMA:: Output section LMA 3612 * Forced Output Alignment:: Forced Output Alignment 3613 * Forced Input Alignment:: Forced Input Alignment 3614 * Output Section Constraint:: Output section constraint 3615 * Output Section Region:: Output section region 3616 * Output Section Phdr:: Output section phdr 3617 * Output Section Fill:: Output section fill 3618 3619 3620 File: ld.info, Node: Output Section Type, Next: Output Section LMA, Up: Output Section Attributes 3621 3622 3.6.8.1 Output Section Type 3623 ........................... 3624 3625 Each output section may have a type. The type is a keyword in 3626 parentheses. The following types are defined: 3627 3628 `NOLOAD' 3629 The section should be marked as not loadable, so that it will not 3630 be loaded into memory when the program is run. 3631 3632 `DSECT' 3633 `COPY' 3634 `INFO' 3635 `OVERLAY' 3636 These type names are supported for backward compatibility, and are 3637 rarely used. They all have the same effect: the section should be 3638 marked as not allocatable, so that no memory is allocated for the 3639 section when the program is run. 3640 3641 The linker normally sets the attributes of an output section based on 3642 the input sections which map into it. You can override this by using 3643 the section type. For example, in the script sample below, the `ROM' 3644 section is addressed at memory location `0' and does not need to be 3645 loaded when the program is run. 3646 SECTIONS { 3647 ROM 0 (NOLOAD) : { ... } 3648 ... 3649 } 3650 3651 3652 File: ld.info, Node: Output Section LMA, Next: Forced Output Alignment, Prev: Output Section Type, Up: Output Section Attributes 3653 3654 3.6.8.2 Output Section LMA 3655 .......................... 3656 3657 Every section has a virtual address (VMA) and a load address (LMA); see 3658 *Note Basic Script Concepts::. The virtual address is specified by the 3659 *note Output Section Address:: described earlier. The load address is 3660 specified by the `AT' or `AT>' keywords. Specifying a load address is 3661 optional. 3662 3663 The `AT' keyword takes an expression as an argument. This specifies 3664 the exact load address of the section. The `AT>' keyword takes the 3665 name of a memory region as an argument. *Note MEMORY::. The load 3666 address of the section is set to the next free address in the region, 3667 aligned to the section's alignment requirements. 3668 3669 If neither `AT' nor `AT>' is specified for an allocatable section, 3670 the linker will use the following heuristic to determine the load 3671 address: 3672 3673 * If the section has a specific VMA address, then this is used as 3674 the LMA address as well. 3675 3676 * If the section is not allocatable then its LMA is set to its VMA. 3677 3678 * Otherwise if a memory region can be found that is compatible with 3679 the current section, and this region contains at least one 3680 section, then the LMA is set so the difference between the VMA and 3681 LMA is the same as the difference between the VMA and LMA of the 3682 last section in the located region. 3683 3684 * If no memory regions have been declared then a default region that 3685 covers the entire address space is used in the previous step. 3686 3687 * If no suitable region could be found, or there was no previous 3688 section then the LMA is set equal to the VMA. 3689 3690 This feature is designed to make it easy to build a ROM image. For 3691 example, the following linker script creates three output sections: one 3692 called `.text', which starts at `0x1000', one called `.mdata', which is 3693 loaded at the end of the `.text' section even though its VMA is 3694 `0x2000', and one called `.bss' to hold uninitialized data at address 3695 `0x3000'. The symbol `_data' is defined with the value `0x2000', which 3696 shows that the location counter holds the VMA value, not the LMA value. 3697 3698 SECTIONS 3699 { 3700 .text 0x1000 : { *(.text) _etext = . ; } 3701 .mdata 0x2000 : 3702 AT ( ADDR (.text) + SIZEOF (.text) ) 3703 { _data = . ; *(.data); _edata = . ; } 3704 .bss 0x3000 : 3705 { _bstart = . ; *(.bss) *(COMMON) ; _bend = . ;} 3706 } 3707 3708 The run-time initialization code for use with a program generated 3709 with this linker script would include something like the following, to 3710 copy the initialized data from the ROM image to its runtime address. 3711 Notice how this code takes advantage of the symbols defined by the 3712 linker script. 3713 3714 extern char _etext, _data, _edata, _bstart, _bend; 3715 char *src = &_etext; 3716 char *dst = &_data; 3717 3718 /* ROM has data at end of text; copy it. */ 3719 while (dst < &_edata) 3720 *dst++ = *src++; 3721 3722 /* Zero bss. */ 3723 for (dst = &_bstart; dst< &_bend; dst++) 3724 *dst = 0; 3725 3726 3727 File: ld.info, Node: Forced Output Alignment, Next: Forced Input Alignment, Prev: Output Section LMA, Up: Output Section Attributes 3728 3729 3.6.8.3 Forced Output Alignment 3730 ............................... 3731 3732 You can increase an output section's alignment by using ALIGN. 3733 3734 3735 File: ld.info, Node: Forced Input Alignment, Next: Output Section Constraint, Prev: Forced Output Alignment, Up: Output Section Attributes 3736 3737 3.6.8.4 Forced Input Alignment 3738 .............................. 3739 3740 You can force input section alignment within an output section by using 3741 SUBALIGN. The value specified overrides any alignment given by input 3742 sections, whether larger or smaller. 3743 3744 3745 File: ld.info, Node: Output Section Constraint, Next: Output Section Region, Prev: Forced Input Alignment, Up: Output Section Attributes 3746 3747 3.6.8.5 Output Section Constraint 3748 ................................. 3749 3750 You can specify that an output section should only be created if all of 3751 its input sections are read-only or all of its input sections are 3752 read-write by using the keyword `ONLY_IF_RO' and `ONLY_IF_RW' 3753 respectively. 3754 3755 3756 File: ld.info, Node: Output Section Region, Next: Output Section Phdr, Prev: Output Section Constraint, Up: Output Section Attributes 3757 3758 3.6.8.6 Output Section Region 3759 ............................. 3760 3761 You can assign a section to a previously defined region of memory by 3762 using `>REGION'. *Note MEMORY::. 3763 3764 Here is a simple example: 3765 MEMORY { rom : ORIGIN = 0x1000, LENGTH = 0x1000 } 3766 SECTIONS { ROM : { *(.text) } >rom } 3767 3768 3769 File: ld.info, Node: Output Section Phdr, Next: Output Section Fill, Prev: Output Section Region, Up: Output Section Attributes 3770 3771 3.6.8.7 Output Section Phdr 3772 ........................... 3773 3774 You can assign a section to a previously defined program segment by 3775 using `:PHDR'. *Note PHDRS::. If a section is assigned to one or more 3776 segments, then all subsequent allocated sections will be assigned to 3777 those segments as well, unless they use an explicitly `:PHDR' modifier. 3778 You can use `:NONE' to tell the linker to not put the section in any 3779 segment at all. 3780 3781 Here is a simple example: 3782 PHDRS { text PT_LOAD ; } 3783 SECTIONS { .text : { *(.text) } :text } 3784 3785 3786 File: ld.info, Node: Output Section Fill, Prev: Output Section Phdr, Up: Output Section Attributes 3787 3788 3.6.8.8 Output Section Fill 3789 ........................... 3790 3791 You can set the fill pattern for an entire section by using `=FILLEXP'. 3792 FILLEXP is an expression (*note Expressions::). Any otherwise 3793 unspecified regions of memory within the output section (for example, 3794 gaps left due to the required alignment of input sections) will be 3795 filled with the value, repeated as necessary. If the fill expression 3796 is a simple hex number, ie. a string of hex digit starting with `0x' 3797 and without a trailing `k' or `M', then an arbitrarily long sequence of 3798 hex digits can be used to specify the fill pattern; Leading zeros 3799 become part of the pattern too. For all other cases, including extra 3800 parentheses or a unary `+', the fill pattern is the four least 3801 significant bytes of the value of the expression. In all cases, the 3802 number is big-endian. 3803 3804 You can also change the fill value with a `FILL' command in the 3805 output section commands; (*note Output Section Data::). 3806 3807 Here is a simple example: 3808 SECTIONS { .text : { *(.text) } =0x90909090 } 3809 3810 3811 File: ld.info, Node: Overlay Description, Prev: Output Section Attributes, Up: SECTIONS 3812 3813 3.6.9 Overlay Description 3814 ------------------------- 3815 3816 An overlay description provides an easy way to describe sections which 3817 are to be loaded as part of a single memory image but are to be run at 3818 the same memory address. At run time, some sort of overlay manager will 3819 copy the overlaid sections in and out of the runtime memory address as 3820 required, perhaps by simply manipulating addressing bits. This approach 3821 can be useful, for example, when a certain region of memory is faster 3822 than another. 3823 3824 Overlays are described using the `OVERLAY' command. The `OVERLAY' 3825 command is used within a `SECTIONS' command, like an output section 3826 description. The full syntax of the `OVERLAY' command is as follows: 3827 OVERLAY [START] : [NOCROSSREFS] [AT ( LDADDR )] 3828 { 3829 SECNAME1 3830 { 3831 OUTPUT-SECTION-COMMAND 3832 OUTPUT-SECTION-COMMAND 3833 ... 3834 } [:PHDR...] [=FILL] 3835 SECNAME2 3836 { 3837 OUTPUT-SECTION-COMMAND 3838 OUTPUT-SECTION-COMMAND 3839 ... 3840 } [:PHDR...] [=FILL] 3841 ... 3842 } [>REGION] [:PHDR...] [=FILL] 3843 3844 Everything is optional except `OVERLAY' (a keyword), and each 3845 section must have a name (SECNAME1 and SECNAME2 above). The section 3846 definitions within the `OVERLAY' construct are identical to those 3847 within the general `SECTIONS' contruct (*note SECTIONS::), except that 3848 no addresses and no memory regions may be defined for sections within 3849 an `OVERLAY'. 3850 3851 The sections are all defined with the same starting address. The 3852 load addresses of the sections are arranged such that they are 3853 consecutive in memory starting at the load address used for the 3854 `OVERLAY' as a whole (as with normal section definitions, the load 3855 address is optional, and defaults to the start address; the start 3856 address is also optional, and defaults to the current value of the 3857 location counter). 3858 3859 If the `NOCROSSREFS' keyword is used, and there any references among 3860 the sections, the linker will report an error. Since the sections all 3861 run at the same address, it normally does not make sense for one 3862 section to refer directly to another. *Note NOCROSSREFS: Miscellaneous 3863 Commands. 3864 3865 For each section within the `OVERLAY', the linker automatically 3866 provides two symbols. The symbol `__load_start_SECNAME' is defined as 3867 the starting load address of the section. The symbol 3868 `__load_stop_SECNAME' is defined as the final load address of the 3869 section. Any characters within SECNAME which are not legal within C 3870 identifiers are removed. C (or assembler) code may use these symbols 3871 to move the overlaid sections around as necessary. 3872 3873 At the end of the overlay, the value of the location counter is set 3874 to the start address of the overlay plus the size of the largest 3875 section. 3876 3877 Here is an example. Remember that this would appear inside a 3878 `SECTIONS' construct. 3879 OVERLAY 0x1000 : AT (0x4000) 3880 { 3881 .text0 { o1/*.o(.text) } 3882 .text1 { o2/*.o(.text) } 3883 } 3884 This will define both `.text0' and `.text1' to start at address 3885 0x1000. `.text0' will be loaded at address 0x4000, and `.text1' will 3886 be loaded immediately after `.text0'. The following symbols will be 3887 defined if referenced: `__load_start_text0', `__load_stop_text0', 3888 `__load_start_text1', `__load_stop_text1'. 3889 3890 C code to copy overlay `.text1' into the overlay area might look 3891 like the following. 3892 3893 extern char __load_start_text1, __load_stop_text1; 3894 memcpy ((char *) 0x1000, &__load_start_text1, 3895 &__load_stop_text1 - &__load_start_text1); 3896 3897 Note that the `OVERLAY' command is just syntactic sugar, since 3898 everything it does can be done using the more basic commands. The above 3899 example could have been written identically as follows. 3900 3901 .text0 0x1000 : AT (0x4000) { o1/*.o(.text) } 3902 PROVIDE (__load_start_text0 = LOADADDR (.text0)); 3903 PROVIDE (__load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0)); 3904 .text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) { o2/*.o(.text) } 3905 PROVIDE (__load_start_text1 = LOADADDR (.text1)); 3906 PROVIDE (__load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1)); 3907 . = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1)); 3908 3909 3910 File: ld.info, Node: MEMORY, Next: PHDRS, Prev: SECTIONS, Up: Scripts 3911 3912 3.7 MEMORY Command 3913 ================== 3914 3915 The linker's default configuration permits allocation of all available 3916 memory. You can override this by using the `MEMORY' command. 3917 3918 The `MEMORY' command describes the location and size of blocks of 3919 memory in the target. You can use it to describe which memory regions 3920 may be used by the linker, and which memory regions it must avoid. You 3921 can then assign sections to particular memory regions. The linker will 3922 set section addresses based on the memory regions, and will warn about 3923 regions that become too full. The linker will not shuffle sections 3924 around to fit into the available regions. 3925 3926 A linker script may contain at most one use of the `MEMORY' command. 3927 However, you can define as many blocks of memory within it as you 3928 wish. The syntax is: 3929 MEMORY 3930 { 3931 NAME [(ATTR)] : ORIGIN = ORIGIN, LENGTH = LEN 3932 ... 3933 } 3934 3935 The NAME is a name used in the linker script to refer to the region. 3936 The region name has no meaning outside of the linker script. Region 3937 names are stored in a separate name space, and will not conflict with 3938 symbol names, file names, or section names. Each memory region must 3939 have a distinct name within the `MEMORY' command. However you can add 3940 later alias names to existing memory regions with the *Note 3941 REGION_ALIAS:: command. 3942 3943 The ATTR string is an optional list of attributes that specify 3944 whether to use a particular memory region for an input section which is 3945 not explicitly mapped in the linker script. As described in *Note 3946 SECTIONS::, if you do not specify an output section for some input 3947 section, the linker will create an output section with the same name as 3948 the input section. If you define region attributes, the linker will use 3949 them to select the memory region for the output section that it creates. 3950 3951 The ATTR string must consist only of the following characters: 3952 `R' 3953 Read-only section 3954 3955 `W' 3956 Read/write section 3957 3958 `X' 3959 Executable section 3960 3961 `A' 3962 Allocatable section 3963 3964 `I' 3965 Initialized section 3966 3967 `L' 3968 Same as `I' 3969 3970 `!' 3971 Invert the sense of any of the attributes that follow 3972 3973 If a unmapped section matches any of the listed attributes other than 3974 `!', it will be placed in the memory region. The `!' attribute 3975 reverses this test, so that an unmapped section will be placed in the 3976 memory region only if it does not match any of the listed attributes. 3977 3978 The ORIGIN is an numerical expression for the start address of the 3979 memory region. The expression must evaluate to a constant and it 3980 cannot involve any symbols. The keyword `ORIGIN' may be abbreviated to 3981 `org' or `o' (but not, for example, `ORG'). 3982 3983 The LEN is an expression for the size in bytes of the memory region. 3984 As with the ORIGIN expression, the expression must be numerical only 3985 and must evaluate to a constant. The keyword `LENGTH' may be 3986 abbreviated to `len' or `l'. 3987 3988 In the following example, we specify that there are two memory 3989 regions available for allocation: one starting at `0' for 256 kilobytes, 3990 and the other starting at `0x40000000' for four megabytes. The linker 3991 will place into the `rom' memory region every section which is not 3992 explicitly mapped into a memory region, and is either read-only or 3993 executable. The linker will place other sections which are not 3994 explicitly mapped into a memory region into the `ram' memory region. 3995 3996 MEMORY 3997 { 3998 rom (rx) : ORIGIN = 0, LENGTH = 256K 3999 ram (!rx) : org = 0x40000000, l = 4M 4000 } 4001 4002 Once you define a memory region, you can direct the linker to place 4003 specific output sections into that memory region by using the `>REGION' 4004 output section attribute. For example, if you have a memory region 4005 named `mem', you would use `>mem' in the output section definition. 4006 *Note Output Section Region::. If no address was specified for the 4007 output section, the linker will set the address to the next available 4008 address within the memory region. If the combined output sections 4009 directed to a memory region are too large for the region, the linker 4010 will issue an error message. 4011 4012 It is possible to access the origin and length of a memory in an 4013 expression via the `ORIGIN(MEMORY)' and `LENGTH(MEMORY)' functions: 4014 4015 _fstack = ORIGIN(ram) + LENGTH(ram) - 4; 4016 4017 4018 File: ld.info, Node: PHDRS, Next: VERSION, Prev: MEMORY, Up: Scripts 4019 4020 3.8 PHDRS Command 4021 ================= 4022 4023 The ELF object file format uses "program headers", also knows as 4024 "segments". The program headers describe how the program should be 4025 loaded into memory. You can print them out by using the `objdump' 4026 program with the `-p' option. 4027 4028 When you run an ELF program on a native ELF system, the system loader 4029 reads the program headers in order to figure out how to load the 4030 program. This will only work if the program headers are set correctly. 4031 This manual does not describe the details of how the system loader 4032 interprets program headers; for more information, see the ELF ABI. 4033 4034 The linker will create reasonable program headers by default. 4035 However, in some cases, you may need to specify the program headers more 4036 precisely. You may use the `PHDRS' command for this purpose. When the 4037 linker sees the `PHDRS' command in the linker script, it will not 4038 create any program headers other than the ones specified. 4039 4040 The linker only pays attention to the `PHDRS' command when 4041 generating an ELF output file. In other cases, the linker will simply 4042 ignore `PHDRS'. 4043 4044 This is the syntax of the `PHDRS' command. The words `PHDRS', 4045 `FILEHDR', `AT', and `FLAGS' are keywords. 4046 4047 PHDRS 4048 { 4049 NAME TYPE [ FILEHDR ] [ PHDRS ] [ AT ( ADDRESS ) ] 4050 [ FLAGS ( FLAGS ) ] ; 4051 } 4052 4053 The NAME is used only for reference in the `SECTIONS' command of the 4054 linker script. It is not put into the output file. Program header 4055 names are stored in a separate name space, and will not conflict with 4056 symbol names, file names, or section names. Each program header must 4057 have a distinct name. The headers are processed in order and it is 4058 usual for them to map to sections in ascending load address order. 4059 4060 Certain program header types describe segments of memory which the 4061 system loader will load from the file. In the linker script, you 4062 specify the contents of these segments by placing allocatable output 4063 sections in the segments. You use the `:PHDR' output section attribute 4064 to place a section in a particular segment. *Note Output Section 4065 Phdr::. 4066 4067 It is normal to put certain sections in more than one segment. This 4068 merely implies that one segment of memory contains another. You may 4069 repeat `:PHDR', using it once for each segment which should contain the 4070 section. 4071 4072 If you place a section in one or more segments using `:PHDR', then 4073 the linker will place all subsequent allocatable sections which do not 4074 specify `:PHDR' in the same segments. This is for convenience, since 4075 generally a whole set of contiguous sections will be placed in a single 4076 segment. You can use `:NONE' to override the default segment and tell 4077 the linker to not put the section in any segment at all. 4078 4079 You may use the `FILEHDR' and `PHDRS' keywords after the program 4080 header type to further describe the contents of the segment. The 4081 `FILEHDR' keyword means that the segment should include the ELF file 4082 header. The `PHDRS' keyword means that the segment should include the 4083 ELF program headers themselves. If applied to a loadable segment 4084 (`PT_LOAD'), all prior loadable segments must have one of these 4085 keywords. 4086 4087 The TYPE may be one of the following. The numbers indicate the 4088 value of the keyword. 4089 4090 `PT_NULL' (0) 4091 Indicates an unused program header. 4092 4093 `PT_LOAD' (1) 4094 Indicates that this program header describes a segment to be 4095 loaded from the file. 4096 4097 `PT_DYNAMIC' (2) 4098 Indicates a segment where dynamic linking information can be found. 4099 4100 `PT_INTERP' (3) 4101 Indicates a segment where the name of the program interpreter may 4102 be found. 4103 4104 `PT_NOTE' (4) 4105 Indicates a segment holding note information. 4106 4107 `PT_SHLIB' (5) 4108 A reserved program header type, defined but not specified by the 4109 ELF ABI. 4110 4111 `PT_PHDR' (6) 4112 Indicates a segment where the program headers may be found. 4113 4114 EXPRESSION 4115 An expression giving the numeric type of the program header. This 4116 may be used for types not defined above. 4117 4118 You can specify that a segment should be loaded at a particular 4119 address in memory by using an `AT' expression. This is identical to the 4120 `AT' command used as an output section attribute (*note Output Section 4121 LMA::). The `AT' command for a program header overrides the output 4122 section attribute. 4123 4124 The linker will normally set the segment flags based on the sections 4125 which comprise the segment. You may use the `FLAGS' keyword to 4126 explicitly specify the segment flags. The value of FLAGS must be an 4127 integer. It is used to set the `p_flags' field of the program header. 4128 4129 Here is an example of `PHDRS'. This shows a typical set of program 4130 headers used on a native ELF system. 4131 4132 PHDRS 4133 { 4134 headers PT_PHDR PHDRS ; 4135 interp PT_INTERP ; 4136 text PT_LOAD FILEHDR PHDRS ; 4137 data PT_LOAD ; 4138 dynamic PT_DYNAMIC ; 4139 } 4140 4141 SECTIONS 4142 { 4143 . = SIZEOF_HEADERS; 4144 .interp : { *(.interp) } :text :interp 4145 .text : { *(.text) } :text 4146 .rodata : { *(.rodata) } /* defaults to :text */ 4147 ... 4148 . = . + 0x1000; /* move to a new page in memory */ 4149 .data : { *(.data) } :data 4150 .dynamic : { *(.dynamic) } :data :dynamic 4151 ... 4152 } 4153 4154 4155 File: ld.info, Node: VERSION, Next: Expressions, Prev: PHDRS, Up: Scripts 4156 4157 3.9 VERSION Command 4158 =================== 4159 4160 The linker supports symbol versions when using ELF. Symbol versions are 4161 only useful when using shared libraries. The dynamic linker can use 4162 symbol versions to select a specific version of a function when it runs 4163 a program that may have been linked against an earlier version of the 4164 shared library. 4165 4166 You can include a version script directly in the main linker script, 4167 or you can supply the version script as an implicit linker script. You 4168 can also use the `--version-script' linker option. 4169 4170 The syntax of the `VERSION' command is simply 4171 VERSION { version-script-commands } 4172 4173 The format of the version script commands is identical to that used 4174 by Sun's linker in Solaris 2.5. The version script defines a tree of 4175 version nodes. You specify the node names and interdependencies in the 4176 version script. You can specify which symbols are bound to which 4177 version nodes, and you can reduce a specified set of symbols to local 4178 scope so that they are not globally visible outside of the shared 4179 library. 4180 4181 The easiest way to demonstrate the version script language is with a 4182 few examples. 4183 4184 VERS_1.1 { 4185 global: 4186 foo1; 4187 local: 4188 old*; 4189 original*; 4190 new*; 4191 }; 4192 4193 VERS_1.2 { 4194 foo2; 4195 } VERS_1.1; 4196 4197 VERS_2.0 { 4198 bar1; bar2; 4199 extern "C++" { 4200 ns::*; 4201 "f(int, double)"; 4202 }; 4203 } VERS_1.2; 4204 4205 This example version script defines three version nodes. The first 4206 version node defined is `VERS_1.1'; it has no other dependencies. The 4207 script binds the symbol `foo1' to `VERS_1.1'. It reduces a number of 4208 symbols to local scope so that they are not visible outside of the 4209 shared library; this is done using wildcard patterns, so that any 4210 symbol whose name begins with `old', `original', or `new' is matched. 4211 The wildcard patterns available are the same as those used in the shell 4212 when matching filenames (also known as "globbing"). However, if you 4213 specify the symbol name inside double quotes, then the name is treated 4214 as literal, rather than as a glob pattern. 4215 4216 Next, the version script defines node `VERS_1.2'. This node depends 4217 upon `VERS_1.1'. The script binds the symbol `foo2' to the version 4218 node `VERS_1.2'. 4219 4220 Finally, the version script defines node `VERS_2.0'. This node 4221 depends upon `VERS_1.2'. The scripts binds the symbols `bar1' and 4222 `bar2' are bound to the version node `VERS_2.0'. 4223 4224 When the linker finds a symbol defined in a library which is not 4225 specifically bound to a version node, it will effectively bind it to an 4226 unspecified base version of the library. You can bind all otherwise 4227 unspecified symbols to a given version node by using `global: *;' 4228 somewhere in the version script. Note that it's slightly crazy to use 4229 wildcards in a global spec except on the last version node. Global 4230 wildcards elsewhere run the risk of accidentally adding symbols to the 4231 set exported for an old version. That's wrong since older versions 4232 ought to have a fixed set of symbols. 4233 4234 The names of the version nodes have no specific meaning other than 4235 what they might suggest to the person reading them. The `2.0' version 4236 could just as well have appeared in between `1.1' and `1.2'. However, 4237 this would be a confusing way to write a version script. 4238 4239 Node name can be omitted, provided it is the only version node in 4240 the version script. Such version script doesn't assign any versions to 4241 symbols, only selects which symbols will be globally visible out and 4242 which won't. 4243 4244 { global: foo; bar; local: *; }; 4245 4246 When you link an application against a shared library that has 4247 versioned symbols, the application itself knows which version of each 4248 symbol it requires, and it also knows which version nodes it needs from 4249 each shared library it is linked against. Thus at runtime, the dynamic 4250 loader can make a quick check to make sure that the libraries you have 4251 linked against do in fact supply all of the version nodes that the 4252 application will need to resolve all of the dynamic symbols. In this 4253 way it is possible for the dynamic linker to know with certainty that 4254 all external symbols that it needs will be resolvable without having to 4255 search for each symbol reference. 4256 4257 The symbol versioning is in effect a much more sophisticated way of 4258 doing minor version checking that SunOS does. The fundamental problem 4259 that is being addressed here is that typically references to external 4260 functions are bound on an as-needed basis, and are not all bound when 4261 the application starts up. If a shared library is out of date, a 4262 required interface may be missing; when the application tries to use 4263 that interface, it may suddenly and unexpectedly fail. With symbol 4264 versioning, the user will get a warning when they start their program if 4265 the libraries being used with the application are too old. 4266 4267 There are several GNU extensions to Sun's versioning approach. The 4268 first of these is the ability to bind a symbol to a version node in the 4269 source file where the symbol is defined instead of in the versioning 4270 script. This was done mainly to reduce the burden on the library 4271 maintainer. You can do this by putting something like: 4272 __asm__(".symver original_foo,foo (a] VERS_1.1"); 4273 in the C source file. This renames the function `original_foo' to 4274 be an alias for `foo' bound to the version node `VERS_1.1'. The 4275 `local:' directive can be used to prevent the symbol `original_foo' 4276 from being exported. A `.symver' directive takes precedence over a 4277 version script. 4278 4279 The second GNU extension is to allow multiple versions of the same 4280 function to appear in a given shared library. In this way you can make 4281 an incompatible change to an interface without increasing the major 4282 version number of the shared library, while still allowing applications 4283 linked against the old interface to continue to function. 4284 4285 To do this, you must use multiple `.symver' directives in the source 4286 file. Here is an example: 4287 4288 __asm__(".symver original_foo,foo@"); 4289 __asm__(".symver old_foo,foo (a] VERS_1.1"); 4290 __asm__(".symver old_foo1,foo (a] VERS_1.2"); 4291 __asm__(".symver new_foo,foo@@VERS_2.0"); 4292 4293 In this example, `foo@' represents the symbol `foo' bound to the 4294 unspecified base version of the symbol. The source file that contains 4295 this example would define 4 C functions: `original_foo', `old_foo', 4296 `old_foo1', and `new_foo'. 4297 4298 When you have multiple definitions of a given symbol, there needs to 4299 be some way to specify a default version to which external references to 4300 this symbol will be bound. You can do this with the `foo@@VERS_2.0' 4301 type of `.symver' directive. You can only declare one version of a 4302 symbol as the default in this manner; otherwise you would effectively 4303 have multiple definitions of the same symbol. 4304 4305 If you wish to bind a reference to a specific version of the symbol 4306 within the shared library, you can use the aliases of convenience 4307 (i.e., `old_foo'), or you can use the `.symver' directive to 4308 specifically bind to an external version of the function in question. 4309 4310 You can also specify the language in the version script: 4311 4312 VERSION extern "lang" { version-script-commands } 4313 4314 The supported `lang's are `C', `C++', and `Java'. The linker will 4315 iterate over the list of symbols at the link time and demangle them 4316 according to `lang' before matching them to the patterns specified in 4317 `version-script-commands'. The default `lang' is `C'. 4318 4319 Demangled names may contains spaces and other special characters. As 4320 described above, you can use a glob pattern to match demangled names, 4321 or you can use a double-quoted string to match the string exactly. In 4322 the latter case, be aware that minor differences (such as differing 4323 whitespace) between the version script and the demangler output will 4324 cause a mismatch. As the exact string generated by the demangler might 4325 change in the future, even if the mangled name does not, you should 4326 check that all of your version directives are behaving as you expect 4327 when you upgrade. 4328 4329 4330 File: ld.info, Node: Expressions, Next: Implicit Linker Scripts, Prev: VERSION, Up: Scripts 4331 4332 3.10 Expressions in Linker Scripts 4333 ================================== 4334 4335 The syntax for expressions in the linker script language is identical to 4336 that of C expressions. All expressions are evaluated as integers. All 4337 expressions are evaluated in the same size, which is 32 bits if both the 4338 host and target are 32 bits, and is otherwise 64 bits. 4339 4340 You can use and set symbol values in expressions. 4341 4342 The linker defines several special purpose builtin functions for use 4343 in expressions. 4344 4345 * Menu: 4346 4347 * Constants:: Constants 4348 * Symbolic Constants:: Symbolic constants 4349 * Symbols:: Symbol Names 4350 * Orphan Sections:: Orphan Sections 4351 * Location Counter:: The Location Counter 4352 * Operators:: Operators 4353 * Evaluation:: Evaluation 4354 * Expression Section:: The Section of an Expression 4355 * Builtin Functions:: Builtin Functions 4356 4357 4358 File: ld.info, Node: Constants, Next: Symbolic Constants, Up: Expressions 4359 4360 3.10.1 Constants 4361 ---------------- 4362 4363 All constants are integers. 4364 4365 As in C, the linker considers an integer beginning with `0' to be 4366 octal, and an integer beginning with `0x' or `0X' to be hexadecimal. 4367 Alternatively the linker accepts suffixes of `h' or `H' for 4368 hexadeciaml, `o' or `O' for octal, `b' or `B' for binary and `d' or `D' 4369 for decimal. Any integer value without a prefix or a suffix is 4370 considered to be decimal. 4371 4372 In addition, you can use the suffixes `K' and `M' to scale a 4373 constant by `1024' or `1024*1024' respectively. For example, the 4374 following all refer to the same quantity: 4375 4376 _fourk_1 = 4K; 4377 _fourk_2 = 4096; 4378 _fourk_3 = 0x1000; 4379 _fourk_4 = 10000o; 4380 4381 Note - the `K' and `M' suffixes cannot be used in conjunction with 4382 the base suffixes mentioned above. 4383 4384 4385 File: ld.info, Node: Symbolic Constants, Next: Symbols, Prev: Constants, Up: Expressions 4386 4387 3.10.2 Symbolic Constants 4388 ------------------------- 4389 4390 It is possible to refer to target specific constants via the use of the 4391 `CONSTANT(NAME)' operator, where NAME is one of: 4392 4393 `MAXPAGESIZE' 4394 The target's maximum page size. 4395 4396 `COMMONPAGESIZE' 4397 The target's default page size. 4398 4399 So for example: 4400 4401 .text ALIGN (CONSTANT (MAXPAGESIZE)) : { *(.text) } 4402 4403 will create a text section aligned to the largest page boundary 4404 supported by the target. 4405 4406 4407 File: ld.info, Node: Symbols, Next: Orphan Sections, Prev: Symbolic Constants, Up: Expressions 4408 4409 3.10.3 Symbol Names 4410 ------------------- 4411 4412 Unless quoted, symbol names start with a letter, underscore, or period 4413 and may include letters, digits, underscores, periods, and hyphens. 4414 Unquoted symbol names must not conflict with any keywords. You can 4415 specify a symbol which contains odd characters or has the same name as a 4416 keyword by surrounding the symbol name in double quotes: 4417 "SECTION" = 9; 4418 "with a space" = "also with a space" + 10; 4419 4420 Since symbols can contain many non-alphabetic characters, it is 4421 safest to delimit symbols with spaces. For example, `A-B' is one 4422 symbol, whereas `A - B' is an expression involving subtraction. 4423 4424 4425 File: ld.info, Node: Orphan Sections, Next: Location Counter, Prev: Symbols, Up: Expressions 4426 4427 3.10.4 Orphan Sections 4428 ---------------------- 4429 4430 Orphan sections are sections present in the input files which are not 4431 explicitly placed into the output file by the linker script. The 4432 linker will still copy these sections into the output file, but it has 4433 to guess as to where they should be placed. The linker uses a simple 4434 heuristic to do this. It attempts to place orphan sections after 4435 non-orphan sections of the same attribute, such as code vs data, 4436 loadable vs non-loadable, etc. If there is not enough room to do this 4437 then it places at the end of the file. 4438 4439 For ELF targets, the attribute of the section includes section type 4440 as well as section flag. 4441 4442 If an orphaned section's name is representable as a C identifier then 4443 the linker will automatically *note PROVIDE:: two symbols: 4444 __start_SECNAME and __end_SECNAME, where SECNAME is the name of the 4445 section. These indicate the start address and end address of the 4446 orphaned section respectively. Note: most section names are not 4447 representable as C identifiers because they contain a `.' character. 4448 4449 4450 File: ld.info, Node: Location Counter, Next: Operators, Prev: Orphan Sections, Up: Expressions 4451 4452 3.10.5 The Location Counter 4453 --------------------------- 4454 4455 The special linker variable "dot" `.' always contains the current 4456 output location counter. Since the `.' always refers to a location in 4457 an output section, it may only appear in an expression within a 4458 `SECTIONS' command. The `.' symbol may appear anywhere that an 4459 ordinary symbol is allowed in an expression. 4460 4461 Assigning a value to `.' will cause the location counter to be 4462 moved. This may be used to create holes in the output section. The 4463 location counter may not be moved backwards inside an output section, 4464 and may not be moved backwards outside of an output section if so doing 4465 creates areas with overlapping LMAs. 4466 4467 SECTIONS 4468 { 4469 output : 4470 { 4471 file1(.text) 4472 . = . + 1000; 4473 file2(.text) 4474 . += 1000; 4475 file3(.text) 4476 } = 0x12345678; 4477 } 4478 In the previous example, the `.text' section from `file1' is located 4479 at the beginning of the output section `output'. It is followed by a 4480 1000 byte gap. Then the `.text' section from `file2' appears, also 4481 with a 1000 byte gap following before the `.text' section from `file3'. 4482 The notation `= 0x12345678' specifies what data to write in the gaps 4483 (*note Output Section Fill::). 4484 4485 Note: `.' actually refers to the byte offset from the start of the 4486 current containing object. Normally this is the `SECTIONS' statement, 4487 whose start address is 0, hence `.' can be used as an absolute address. 4488 If `.' is used inside a section description however, it refers to the 4489 byte offset from the start of that section, not an absolute address. 4490 Thus in a script like this: 4491 4492 SECTIONS 4493 { 4494 . = 0x100 4495 .text: { 4496 *(.text) 4497 . = 0x200 4498 } 4499 . = 0x500 4500 .data: { 4501 *(.data) 4502 . += 0x600 4503 } 4504 } 4505 4506 The `.text' section will be assigned a starting address of 0x100 and 4507 a size of exactly 0x200 bytes, even if there is not enough data in the 4508 `.text' input sections to fill this area. (If there is too much data, 4509 an error will be produced because this would be an attempt to move `.' 4510 backwards). The `.data' section will start at 0x500 and it will have 4511 an extra 0x600 bytes worth of space after the end of the values from 4512 the `.data' input sections and before the end of the `.data' output 4513 section itself. 4514 4515 Setting symbols to the value of the location counter outside of an 4516 output section statement can result in unexpected values if the linker 4517 needs to place orphan sections. For example, given the following: 4518 4519 SECTIONS 4520 { 4521 start_of_text = . ; 4522 .text: { *(.text) } 4523 end_of_text = . ; 4524 4525 start_of_data = . ; 4526 .data: { *(.data) } 4527 end_of_data = . ; 4528 } 4529 4530 If the linker needs to place some input section, e.g. `.rodata', not 4531 mentioned in the script, it might choose to place that section between 4532 `.text' and `.data'. You might think the linker should place `.rodata' 4533 on the blank line in the above script, but blank lines are of no 4534 particular significance to the linker. As well, the linker doesn't 4535 associate the above symbol names with their sections. Instead, it 4536 assumes that all assignments or other statements belong to the previous 4537 output section, except for the special case of an assignment to `.'. 4538 I.e., the linker will place the orphan `.rodata' section as if the 4539 script was written as follows: 4540 4541 SECTIONS 4542 { 4543 start_of_text = . ; 4544 .text: { *(.text) } 4545 end_of_text = . ; 4546 4547 start_of_data = . ; 4548 .rodata: { *(.rodata) } 4549 .data: { *(.data) } 4550 end_of_data = . ; 4551 } 4552 4553 This may or may not be the script author's intention for the value of 4554 `start_of_data'. One way to influence the orphan section placement is 4555 to assign the location counter to itself, as the linker assumes that an 4556 assignment to `.' is setting the start address of a following output 4557 section and thus should be grouped with that section. So you could 4558 write: 4559 4560 SECTIONS 4561 { 4562 start_of_text = . ; 4563 .text: { *(.text) } 4564 end_of_text = . ; 4565 4566 . = . ; 4567 start_of_data = . ; 4568 .data: { *(.data) } 4569 end_of_data = . ; 4570 } 4571 4572 Now, the orphan `.rodata' section will be placed between 4573 `end_of_text' and `start_of_data'. 4574 4575 4576 File: ld.info, Node: Operators, Next: Evaluation, Prev: Location Counter, Up: Expressions 4577 4578 3.10.6 Operators 4579 ---------------- 4580 4581 The linker recognizes the standard C set of arithmetic operators, with 4582 the standard bindings and precedence levels: 4583 precedence associativity Operators Notes 4584 (highest) 4585 1 left ! - ~ (1) 4586 2 left * / % 4587 3 left + - 4588 4 left >> << 4589 5 left == != > < <= >= 4590 6 left & 4591 7 left | 4592 8 left && 4593 9 left || 4594 10 right ? : 4595 11 right &= += -= *= /= (2) 4596 (lowest) 4597 Notes: (1) Prefix operators (2) *Note Assignments::. 4598 4599 4600 File: ld.info, Node: Evaluation, Next: Expression Section, Prev: Operators, Up: Expressions 4601 4602 3.10.7 Evaluation 4603 ----------------- 4604 4605 The linker evaluates expressions lazily. It only computes the value of 4606 an expression when absolutely necessary. 4607 4608 The linker needs some information, such as the value of the start 4609 address of the first section, and the origins and lengths of memory 4610 regions, in order to do any linking at all. These values are computed 4611 as soon as possible when the linker reads in the linker script. 4612 4613 However, other values (such as symbol values) are not known or needed 4614 until after storage allocation. Such values are evaluated later, when 4615 other information (such as the sizes of output sections) is available 4616 for use in the symbol assignment expression. 4617 4618 The sizes of sections cannot be known until after allocation, so 4619 assignments dependent upon these are not performed until after 4620 allocation. 4621 4622 Some expressions, such as those depending upon the location counter 4623 `.', must be evaluated during section allocation. 4624 4625 If the result of an expression is required, but the value is not 4626 available, then an error results. For example, a script like the 4627 following 4628 SECTIONS 4629 { 4630 .text 9+this_isnt_constant : 4631 { *(.text) } 4632 } 4633 will cause the error message `non constant expression for initial 4634 address'. 4635 4636 4637 File: ld.info, Node: Expression Section, Next: Builtin Functions, Prev: Evaluation, Up: Expressions 4638 4639 3.10.8 The Section of an Expression 4640 ----------------------------------- 4641 4642 Addresses and symbols may be section relative, or absolute. A section 4643 relative symbol is relocatable. If you request relocatable output 4644 using the `-r' option, a further link operation may change the value of 4645 a section relative symbol. On the other hand, an absolute symbol will 4646 retain the same value throughout any further link operations. 4647 4648 Some terms in linker expressions are addresses. This is true of 4649 section relative symbols and for builtin functions that return an 4650 address, such as `ADDR', `LOADADDR', `ORIGIN' and `SEGMENT_START'. 4651 Other terms are simply numbers, or are builtin functions that return a 4652 non-address value, such as `LENGTH'. One complication is that unless 4653 you set `LD_FEATURE ("SANE_EXPR")' (*note Miscellaneous Commands::), 4654 numbers and absolute symbols are treated differently depending on their 4655 location, for compatibility with older versions of `ld'. Expressions 4656 appearing outside an output section definition treat all numbers as 4657 absolute addresses. Expressions appearing inside an output section 4658 definition treat absolute symbols as numbers. If `LD_FEATURE 4659 ("SANE_EXPR")' is given, then absolute symbols and numbers are simply 4660 treated as numbers everywhere. 4661 4662 In the following simple example, 4663 4664 SECTIONS 4665 { 4666 . = 0x100; 4667 __executable_start = 0x100; 4668 .data : 4669 { 4670 . = 0x10; 4671 __data_start = 0x10; 4672 *(.data) 4673 } 4674 ... 4675 } 4676 4677 both `.' and `__executable_start' are set to the absolute address 4678 0x100 in the first two assignments, then both `.' and `__data_start' 4679 are set to 0x10 relative to the `.data' section in the second two 4680 assignments. 4681 4682 For expressions involving numbers, relative addresses and absolute 4683 addresses, ld follows these rules to evaluate terms: 4684 4685 * Unary operations on a relative address, and binary operations on 4686 two relative addresses in the same section or between one relative 4687 address and a number, apply the operator to the offset part of the 4688 address(es). 4689 4690 * Unary operations on an absolute address, and binary operations on 4691 one or more absolute addresses or on two relative addresses not in 4692 the same section, first convert any non-absolute term to an 4693 absolute address before applying the operator. 4694 4695 The result section of each sub-expression is as follows: 4696 4697 * An operation involving only numbers results in a number. 4698 4699 * The result of comparisons, `&&' and `||' is also a number. 4700 4701 * The result of other binary arithmetic and logical operations on two 4702 relative addresses in the same section or two absolute addresess 4703 (after above conversions) is also a number. 4704 4705 * The result of other operations on relative addresses or one 4706 relative address and a number, is a relative address in the same 4707 section as the relative operand(s). 4708 4709 * The result of other operations on absolute addresses (after above 4710 conversions) is an absolute address. 4711 4712 You can use the builtin function `ABSOLUTE' to force an expression 4713 to be absolute when it would otherwise be relative. For example, to 4714 create an absolute symbol set to the address of the end of the output 4715 section `.data': 4716 SECTIONS 4717 { 4718 .data : { *(.data) _edata = ABSOLUTE(.); } 4719 } 4720 If `ABSOLUTE' were not used, `_edata' would be relative to the 4721 `.data' section. 4722 4723 Using `LOADADDR' also forces an expression absolute, since this 4724 particular builtin function returns an absolute address. 4725 4726 4727 File: ld.info, Node: Builtin Functions, Prev: Expression Section, Up: Expressions 4728 4729 3.10.9 Builtin Functions 4730 ------------------------ 4731 4732 The linker script language includes a number of builtin functions for 4733 use in linker script expressions. 4734 4735 `ABSOLUTE(EXP)' 4736 Return the absolute (non-relocatable, as opposed to non-negative) 4737 value of the expression EXP. Primarily useful to assign an 4738 absolute value to a symbol within a section definition, where 4739 symbol values are normally section relative. *Note Expression 4740 Section::. 4741 4742 `ADDR(SECTION)' 4743 Return the address (VMA) of the named SECTION. Your script must 4744 previously have defined the location of that section. In the 4745 following example, `start_of_output_1', `symbol_1' and `symbol_2' 4746 are assigned equivalent values, except that `symbol_1' will be 4747 relative to the `.output1' section while the other two will be 4748 absolute: 4749 SECTIONS { ... 4750 .output1 : 4751 { 4752 start_of_output_1 = ABSOLUTE(.); 4753 ... 4754 } 4755 .output : 4756 { 4757 symbol_1 = ADDR(.output1); 4758 symbol_2 = start_of_output_1; 4759 } 4760 ... } 4761 4762 `ALIGN(ALIGN)' 4763 `ALIGN(EXP,ALIGN)' 4764 Return the location counter (`.') or arbitrary expression aligned 4765 to the next ALIGN boundary. The single operand `ALIGN' doesn't 4766 change the value of the location counter--it just does arithmetic 4767 on it. The two operand `ALIGN' allows an arbitrary expression to 4768 be aligned upwards (`ALIGN(ALIGN)' is equivalent to `ALIGN(., 4769 ALIGN)'). 4770 4771 Here is an example which aligns the output `.data' section to the 4772 next `0x2000' byte boundary after the preceding section and sets a 4773 variable within the section to the next `0x8000' boundary after the 4774 input sections: 4775 SECTIONS { ... 4776 .data ALIGN(0x2000): { 4777 *(.data) 4778 variable = ALIGN(0x8000); 4779 } 4780 ... } 4781 The first use of `ALIGN' in this example specifies the 4782 location of a section because it is used as the optional ADDRESS 4783 attribute of a section definition (*note Output Section 4784 Address::). The second use of `ALIGN' is used to defines the 4785 value of a symbol. 4786 4787 The builtin function `NEXT' is closely related to `ALIGN'. 4788 4789 `ALIGNOF(SECTION)' 4790 Return the alignment in bytes of the named SECTION, if that 4791 section has been allocated. If the section has not been allocated 4792 when this is evaluated, the linker will report an error. In the 4793 following example, the alignment of the `.output' section is 4794 stored as the first value in that section. 4795 SECTIONS{ ... 4796 .output { 4797 LONG (ALIGNOF (.output)) 4798 ... 4799 } 4800 ... } 4801 4802 `BLOCK(EXP)' 4803 This is a synonym for `ALIGN', for compatibility with older linker 4804 scripts. It is most often seen when setting the address of an 4805 output section. 4806 4807 `DATA_SEGMENT_ALIGN(MAXPAGESIZE, COMMONPAGESIZE)' 4808 This is equivalent to either 4809 (ALIGN(MAXPAGESIZE) + (. & (MAXPAGESIZE - 1))) 4810 or 4811 (ALIGN(MAXPAGESIZE) + (. & (MAXPAGESIZE - COMMONPAGESIZE))) 4812 depending on whether the latter uses fewer COMMONPAGESIZE sized 4813 pages for the data segment (area between the result of this 4814 expression and `DATA_SEGMENT_END') than the former or not. If the 4815 latter form is used, it means COMMONPAGESIZE bytes of runtime 4816 memory will be saved at the expense of up to COMMONPAGESIZE wasted 4817 bytes in the on-disk file. 4818 4819 This expression can only be used directly in `SECTIONS' commands, 4820 not in any output section descriptions and only once in the linker 4821 script. COMMONPAGESIZE should be less or equal to MAXPAGESIZE and 4822 should be the system page size the object wants to be optimized 4823 for (while still working on system page sizes up to MAXPAGESIZE). 4824 4825 Example: 4826 . = DATA_SEGMENT_ALIGN(0x10000, 0x2000); 4827 4828 `DATA_SEGMENT_END(EXP)' 4829 This defines the end of data segment for `DATA_SEGMENT_ALIGN' 4830 evaluation purposes. 4831 4832 . = DATA_SEGMENT_END(.); 4833 4834 `DATA_SEGMENT_RELRO_END(OFFSET, EXP)' 4835 This defines the end of the `PT_GNU_RELRO' segment when `-z relro' 4836 option is used. Second argument is returned. When `-z relro' 4837 option is not present, `DATA_SEGMENT_RELRO_END' does nothing, 4838 otherwise `DATA_SEGMENT_ALIGN' is padded so that EXP + OFFSET is 4839 aligned to the most commonly used page boundary for particular 4840 target. If present in the linker script, it must always come in 4841 between `DATA_SEGMENT_ALIGN' and `DATA_SEGMENT_END'. 4842 4843 . = DATA_SEGMENT_RELRO_END(24, .); 4844 4845 `DEFINED(SYMBOL)' 4846 Return 1 if SYMBOL is in the linker global symbol table and is 4847 defined before the statement using DEFINED in the script, otherwise 4848 return 0. You can use this function to provide default values for 4849 symbols. For example, the following script fragment shows how to 4850 set a global symbol `begin' to the first location in the `.text' 4851 section--but if a symbol called `begin' already existed, its value 4852 is preserved: 4853 4854 SECTIONS { ... 4855 .text : { 4856 begin = DEFINED(begin) ? begin : . ; 4857 ... 4858 } 4859 ... 4860 } 4861 4862 `LENGTH(MEMORY)' 4863 Return the length of the memory region named MEMORY. 4864 4865 `LOADADDR(SECTION)' 4866 Return the absolute LMA of the named SECTION. (*note Output 4867 Section LMA::). 4868 4869 `MAX(EXP1, EXP2)' 4870 Returns the maximum of EXP1 and EXP2. 4871 4872 `MIN(EXP1, EXP2)' 4873 Returns the minimum of EXP1 and EXP2. 4874 4875 `NEXT(EXP)' 4876 Return the next unallocated address that is a multiple of EXP. 4877 This function is closely related to `ALIGN(EXP)'; unless you use 4878 the `MEMORY' command to define discontinuous memory for the output 4879 file, the two functions are equivalent. 4880 4881 `ORIGIN(MEMORY)' 4882 Return the origin of the memory region named MEMORY. 4883 4884 `SEGMENT_START(SEGMENT, DEFAULT)' 4885 Return the base address of the named SEGMENT. If an explicit 4886 value has been given for this segment (with a command-line `-T' 4887 option) that value will be returned; otherwise the value will be 4888 DEFAULT. At present, the `-T' command-line option can only be 4889 used to set the base address for the "text", "data", and "bss" 4890 sections, but you can use `SEGMENT_START' with any segment name. 4891 4892 `SIZEOF(SECTION)' 4893 Return the size in bytes of the named SECTION, if that section has 4894 been allocated. If the section has not been allocated when this is 4895 evaluated, the linker will report an error. In the following 4896 example, `symbol_1' and `symbol_2' are assigned identical values: 4897 SECTIONS{ ... 4898 .output { 4899 .start = . ; 4900 ... 4901 .end = . ; 4902 } 4903 symbol_1 = .end - .start ; 4904 symbol_2 = SIZEOF(.output); 4905 ... } 4906 4907 `SIZEOF_HEADERS' 4908 `sizeof_headers' 4909 Return the size in bytes of the output file's headers. This is 4910 information which appears at the start of the output file. You 4911 can use this number when setting the start address of the first 4912 section, if you choose, to facilitate paging. 4913 4914 When producing an ELF output file, if the linker script uses the 4915 `SIZEOF_HEADERS' builtin function, the linker must compute the 4916 number of program headers before it has determined all the section 4917 addresses and sizes. If the linker later discovers that it needs 4918 additional program headers, it will report an error `not enough 4919 room for program headers'. To avoid this error, you must avoid 4920 using the `SIZEOF_HEADERS' function, or you must rework your linker 4921 script to avoid forcing the linker to use additional program 4922 headers, or you must define the program headers yourself using the 4923 `PHDRS' command (*note PHDRS::). 4924 4925 4926 File: ld.info, Node: Implicit Linker Scripts, Prev: Expressions, Up: Scripts 4927 4928 3.11 Implicit Linker Scripts 4929 ============================ 4930 4931 If you specify a linker input file which the linker can not recognize as 4932 an object file or an archive file, it will try to read the file as a 4933 linker script. If the file can not be parsed as a linker script, the 4934 linker will report an error. 4935 4936 An implicit linker script will not replace the default linker script. 4937 4938 Typically an implicit linker script would contain only symbol 4939 assignments, or the `INPUT', `GROUP', or `VERSION' commands. 4940 4941 Any input files read because of an implicit linker script will be 4942 read at the position in the command line where the implicit linker 4943 script was read. This can affect archive searching. 4944 4945 4946 File: ld.info, Node: Machine Dependent, Next: BFD, Prev: Scripts, Up: Top 4947 4948 4 Machine Dependent Features 4949 **************************** 4950 4951 `ld' has additional features on some platforms; the following sections 4952 describe them. Machines where `ld' has no additional functionality are 4953 not listed. 4954 4955 * Menu: 4956 4957 4958 * H8/300:: `ld' and the H8/300 4959 4960 * i960:: `ld' and the Intel 960 family 4961 4962 * ARM:: `ld' and the ARM family 4963 4964 * HPPA ELF32:: `ld' and HPPA 32-bit ELF 4965 4966 * M68K:: `ld' and the Motorola 68K family 4967 4968 * MMIX:: `ld' and MMIX 4969 4970 * MSP430:: `ld' and MSP430 4971 4972 * M68HC11/68HC12:: `ld' and the Motorola 68HC11 and 68HC12 families 4973 4974 * PowerPC ELF32:: `ld' and PowerPC 32-bit ELF Support 4975 4976 * PowerPC64 ELF64:: `ld' and PowerPC64 64-bit ELF Support 4977 4978 * SPU ELF:: `ld' and SPU ELF Support 4979 4980 * TI COFF:: `ld' and TI COFF 4981 4982 * WIN32:: `ld' and WIN32 (cygwin/mingw) 4983 4984 * Xtensa:: `ld' and Xtensa Processors 4985 4986 4987 File: ld.info, Node: H8/300, Next: i960, Up: Machine Dependent 4988 4989 4.1 `ld' and the H8/300 4990 ======================= 4991 4992 For the H8/300, `ld' can perform these global optimizations when you 4993 specify the `--relax' command-line option. 4994 4995 _relaxing address modes_ 4996 `ld' finds all `jsr' and `jmp' instructions whose targets are 4997 within eight bits, and turns them into eight-bit program-counter 4998 relative `bsr' and `bra' instructions, respectively. 4999 5000 _synthesizing instructions_ 5001 `ld' finds all `mov.b' instructions which use the sixteen-bit 5002 absolute address form, but refer to the top page of memory, and 5003 changes them to use the eight-bit address form. (That is: the 5004 linker turns `mov.b `@'AA:16' into `mov.b `@'AA:8' whenever the 5005 address AA is in the top page of memory). 5006 5007 _bit manipulation instructions_ 5008 `ld' finds all bit manipulation instructions like `band, bclr, 5009 biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, 5010 bxor' which use 32 bit and 16 bit absolute address form, but refer 5011 to the top page of memory, and changes them to use the 8 bit 5012 address form. (That is: the linker turns `bset #xx:3,`@'AA:32' 5013 into `bset #xx:3,`@'AA:8' whenever the address AA is in the top 5014 page of memory). 5015 5016 _system control instructions_ 5017 `ld' finds all `ldc.w, stc.w' instructions which use the 32 bit 5018 absolute address form, but refer to the top page of memory, and 5019 changes them to use 16 bit address form. (That is: the linker 5020 turns `ldc.w `@'AA:32,ccr' into `ldc.w `@'AA:16,ccr' whenever the 5021 address AA is in the top page of memory). 5022 5023 5024 File: ld.info, Node: i960, Next: ARM, Prev: H8/300, Up: Machine Dependent 5025 5026 4.2 `ld' and the Intel 960 Family 5027 ================================= 5028 5029 You can use the `-AARCHITECTURE' command line option to specify one of 5030 the two-letter names identifying members of the 960 family; the option 5031 specifies the desired output target, and warns of any incompatible 5032 instructions in the input files. It also modifies the linker's search 5033 strategy for archive libraries, to support the use of libraries 5034 specific to each particular architecture, by including in the search 5035 loop names suffixed with the string identifying the architecture. 5036 5037 For example, if your `ld' command line included `-ACA' as well as 5038 `-ltry', the linker would look (in its built-in search paths, and in 5039 any paths you specify with `-L') for a library with the names 5040 5041 try 5042 libtry.a 5043 tryca 5044 libtryca.a 5045 5046 The first two possibilities would be considered in any event; the last 5047 two are due to the use of `-ACA'. 5048 5049 You can meaningfully use `-A' more than once on a command line, since 5050 the 960 architecture family allows combination of target architectures; 5051 each use will add another pair of name variants to search for when `-l' 5052 specifies a library. 5053 5054 `ld' supports the `--relax' option for the i960 family. If you 5055 specify `--relax', `ld' finds all `balx' and `calx' instructions whose 5056 targets are within 24 bits, and turns them into 24-bit program-counter 5057 relative `bal' and `cal' instructions, respectively. `ld' also turns 5058 `cal' instructions into `bal' instructions when it determines that the 5059 target subroutine is a leaf routine (that is, the target subroutine does 5060 not itself call any subroutines). 5061 5062 The `--fix-cortex-a8' switch enables a link-time workaround for an 5063 erratum in certain Cortex-A8 processors. The workaround is enabled by 5064 default if you are targeting the ARM v7-A architecture profile. It can 5065 be enabled otherwise by specifying `--fix-cortex-a8', or disabled 5066 unconditionally by specifying `--no-fix-cortex-a8'. 5067 5068 The erratum only affects Thumb-2 code. Please contact ARM for 5069 further details. 5070 5071 The `--no-merge-exidx-entries' switch disables the merging of 5072 adjacent exidx entries in debuginfo. 5073 5074 5075 File: ld.info, Node: M68HC11/68HC12, Next: PowerPC ELF32, Prev: MSP430, Up: Machine Dependent 5076 5077 4.3 `ld' and the Motorola 68HC11 and 68HC12 families 5078 ==================================================== 5079 5080 4.3.1 Linker Relaxation 5081 ----------------------- 5082 5083 For the Motorola 68HC11, `ld' can perform these global optimizations 5084 when you specify the `--relax' command-line option. 5085 5086 _relaxing address modes_ 5087 `ld' finds all `jsr' and `jmp' instructions whose targets are 5088 within eight bits, and turns them into eight-bit program-counter 5089 relative `bsr' and `bra' instructions, respectively. 5090 5091 `ld' also looks at all 16-bit extended addressing modes and 5092 transforms them in a direct addressing mode when the address is in 5093 page 0 (between 0 and 0x0ff). 5094 5095 _relaxing gcc instruction group_ 5096 When `gcc' is called with `-mrelax', it can emit group of 5097 instructions that the linker can optimize to use a 68HC11 direct 5098 addressing mode. These instructions consists of `bclr' or `bset' 5099 instructions. 5100 5101 5102 4.3.2 Trampoline Generation 5103 --------------------------- 5104 5105 For 68HC11 and 68HC12, `ld' can generate trampoline code to call a far 5106 function using a normal `jsr' instruction. The linker will also change 5107 the relocation to some far function to use the trampoline address 5108 instead of the function address. This is typically the case when a 5109 pointer to a function is taken. The pointer will in fact point to the 5110 function trampoline. 5111 5112 5113 File: ld.info, Node: ARM, Next: HPPA ELF32, Prev: i960, Up: Machine Dependent 5114 5115 4.4 `ld' and the ARM family 5116 =========================== 5117 5118 For the ARM, `ld' will generate code stubs to allow functions calls 5119 between ARM and Thumb code. These stubs only work with code that has 5120 been compiled and assembled with the `-mthumb-interwork' command line 5121 option. If it is necessary to link with old ARM object files or 5122 libraries, which have not been compiled with the -mthumb-interwork 5123 option then the `--support-old-code' command line switch should be 5124 given to the linker. This will make it generate larger stub functions 5125 which will work with non-interworking aware ARM code. Note, however, 5126 the linker does not support generating stubs for function calls to 5127 non-interworking aware Thumb code. 5128 5129 The `--thumb-entry' switch is a duplicate of the generic `--entry' 5130 switch, in that it sets the program's starting address. But it also 5131 sets the bottom bit of the address, so that it can be branched to using 5132 a BX instruction, and the program will start executing in Thumb mode 5133 straight away. 5134 5135 The `--use-nul-prefixed-import-tables' switch is specifying, that 5136 the import tables idata4 and idata5 have to be generated with a zero 5137 elememt prefix for import libraries. This is the old style to generate 5138 import tables. By default this option is turned off. 5139 5140 The `--be8' switch instructs `ld' to generate BE8 format 5141 executables. This option is only valid when linking big-endian objects. 5142 The resulting image will contain big-endian data and little-endian code. 5143 5144 The `R_ARM_TARGET1' relocation is typically used for entries in the 5145 `.init_array' section. It is interpreted as either `R_ARM_REL32' or 5146 `R_ARM_ABS32', depending on the target. The `--target1-rel' and 5147 `--target1-abs' switches override the default. 5148 5149 The `--target2=type' switch overrides the default definition of the 5150 `R_ARM_TARGET2' relocation. Valid values for `type', their meanings, 5151 and target defaults are as follows: 5152 `rel' 5153 `R_ARM_REL32' (arm*-*-elf, arm*-*-eabi) 5154 5155 `abs' 5156 `R_ARM_ABS32' (arm*-*-symbianelf) 5157 5158 `got-rel' 5159 `R_ARM_GOT_PREL' (arm*-*-linux, arm*-*-*bsd) 5160 5161 The `R_ARM_V4BX' relocation (defined by the ARM AAELF specification) 5162 enables objects compiled for the ARMv4 architecture to be 5163 interworking-safe when linked with other objects compiled for ARMv4t, 5164 but also allows pure ARMv4 binaries to be built from the same ARMv4 5165 objects. 5166 5167 In the latter case, the switch `--fix-v4bx' must be passed to the 5168 linker, which causes v4t `BX rM' instructions to be rewritten as `MOV 5169 PC,rM', since v4 processors do not have a `BX' instruction. 5170 5171 In the former case, the switch should not be used, and `R_ARM_V4BX' 5172 relocations are ignored. 5173 5174 Replace `BX rM' instructions identified by `R_ARM_V4BX' relocations 5175 with a branch to the following veneer: 5176 5177 TST rM, #1 5178 MOVEQ PC, rM 5179 BX Rn 5180 5181 This allows generation of libraries/applications that work on ARMv4 5182 cores and are still interworking safe. Note that the above veneer 5183 clobbers the condition flags, so may cause incorrect progrm behavior in 5184 rare cases. 5185 5186 The `--use-blx' switch enables the linker to use ARM/Thumb BLX 5187 instructions (available on ARMv5t and above) in various situations. 5188 Currently it is used to perform calls via the PLT from Thumb code using 5189 BLX rather than using BX and a mode-switching stub before each PLT 5190 entry. This should lead to such calls executing slightly faster. 5191 5192 This option is enabled implicitly for SymbianOS, so there is no need 5193 to specify it if you are using that target. 5194 5195 The `--vfp11-denorm-fix' switch enables a link-time workaround for a 5196 bug in certain VFP11 coprocessor hardware, which sometimes allows 5197 instructions with denorm operands (which must be handled by support 5198 code) to have those operands overwritten by subsequent instructions 5199 before the support code can read the intended values. 5200 5201 The bug may be avoided in scalar mode if you allow at least one 5202 intervening instruction between a VFP11 instruction which uses a 5203 register and another instruction which writes to the same register, or 5204 at least two intervening instructions if vector mode is in use. The bug 5205 only affects full-compliance floating-point mode: you do not need this 5206 workaround if you are using "runfast" mode. Please contact ARM for 5207 further details. 5208 5209 If you know you are using buggy VFP11 hardware, you can enable this 5210 workaround by specifying the linker option `--vfp-denorm-fix=scalar' if 5211 you are using the VFP11 scalar mode only, or `--vfp-denorm-fix=vector' 5212 if you are using vector mode (the latter also works for scalar code). 5213 The default is `--vfp-denorm-fix=none'. 5214 5215 If the workaround is enabled, instructions are scanned for 5216 potentially-troublesome sequences, and a veneer is created for each 5217 such sequence which may trigger the erratum. The veneer consists of the 5218 first instruction of the sequence and a branch back to the subsequent 5219 instruction. The original instruction is then replaced with a branch to 5220 the veneer. The extra cycles required to call and return from the veneer 5221 are sufficient to avoid the erratum in both the scalar and vector cases. 5222 5223 The `--fix-arm1176' switch enables a link-time workaround for an 5224 erratum in certain ARM1176 processors. The workaround is enabled by 5225 default if you are targetting ARM v6 (excluding ARM v6T2) or earlier. 5226 It can be disabled unconditionally by specifying `--no-fix-arm1176'. 5227 5228 Further information is available in the "ARM1176JZ-S and ARM1176JZF-S 5229 Programmer Advice Notice" available on the ARM documentaion website at: 5230 http://infocenter.arm.com/. 5231 5232 The `--no-enum-size-warning' switch prevents the linker from warning 5233 when linking object files that specify incompatible EABI enumeration 5234 size attributes. For example, with this switch enabled, linking of an 5235 object file using 32-bit enumeration values with another using 5236 enumeration values fitted into the smallest possible space will not be 5237 diagnosed. 5238 5239 The `--no-wchar-size-warning' switch prevents the linker from 5240 warning when linking object files that specify incompatible EABI 5241 `wchar_t' size attributes. For example, with this switch enabled, 5242 linking of an object file using 32-bit `wchar_t' values with another 5243 using 16-bit `wchar_t' values will not be diagnosed. 5244 5245 The `--pic-veneer' switch makes the linker use PIC sequences for 5246 ARM/Thumb interworking veneers, even if the rest of the binary is not 5247 PIC. This avoids problems on uClinux targets where `--emit-relocs' is 5248 used to generate relocatable binaries. 5249 5250 The linker will automatically generate and insert small sequences of 5251 code into a linked ARM ELF executable whenever an attempt is made to 5252 perform a function call to a symbol that is too far away. The 5253 placement of these sequences of instructions - called stubs - is 5254 controlled by the command line option `--stub-group-size=N'. The 5255 placement is important because a poor choice can create a need for 5256 duplicate stubs, increasing the code sizw. The linker will try to 5257 group stubs together in order to reduce interruptions to the flow of 5258 code, but it needs guidance as to how big these groups should be and 5259 where they should be placed. 5260 5261 The value of `N', the parameter to the `--stub-group-size=' option 5262 controls where the stub groups are placed. If it is negative then all 5263 stubs are placed after the first branch that needs them. If it is 5264 positive then the stubs can be placed either before or after the 5265 branches that need them. If the value of `N' is 1 (either +1 or -1) 5266 then the linker will choose exactly where to place groups of stubs, 5267 using its built in heuristics. A value of `N' greater than 1 (or 5268 smaller than -1) tells the linker that a single group of stubs can 5269 service at most `N' bytes from the input sections. 5270 5271 The default, if `--stub-group-size=' is not specified, is `N = +1'. 5272 5273 Farcalls stubs insertion is fully supported for the ARM-EABI target 5274 only, because it relies on object files properties not present 5275 otherwise. 5276 5277 5278 File: ld.info, Node: HPPA ELF32, Next: M68K, Prev: ARM, Up: Machine Dependent 5279 5280 4.5 `ld' and HPPA 32-bit ELF Support 5281 ==================================== 5282 5283 When generating a shared library, `ld' will by default generate import 5284 stubs suitable for use with a single sub-space application. The 5285 `--multi-subspace' switch causes `ld' to generate export stubs, and 5286 different (larger) import stubs suitable for use with multiple 5287 sub-spaces. 5288 5289 Long branch stubs and import/export stubs are placed by `ld' in stub 5290 sections located between groups of input sections. `--stub-group-size' 5291 specifies the maximum size of a group of input sections handled by one 5292 stub section. Since branch offsets are signed, a stub section may 5293 serve two groups of input sections, one group before the stub section, 5294 and one group after it. However, when using conditional branches that 5295 require stubs, it may be better (for branch prediction) that stub 5296 sections only serve one group of input sections. A negative value for 5297 `N' chooses this scheme, ensuring that branches to stubs always use a 5298 negative offset. Two special values of `N' are recognized, `1' and 5299 `-1'. These both instruct `ld' to automatically size input section 5300 groups for the branch types detected, with the same behaviour regarding 5301 stub placement as other positive or negative values of `N' respectively. 5302 5303 Note that `--stub-group-size' does not split input sections. A 5304 single input section larger than the group size specified will of course 5305 create a larger group (of one section). If input sections are too 5306 large, it may not be possible for a branch to reach its stub. 5307 5308 5309 File: ld.info, Node: M68K, Next: MMIX, Prev: HPPA ELF32, Up: Machine Dependent 5310 5311 4.6 `ld' and the Motorola 68K family 5312 ==================================== 5313 5314 The `--got=TYPE' option lets you choose the GOT generation scheme. The 5315 choices are `single', `negative', `multigot' and `target'. When 5316 `target' is selected the linker chooses the default GOT generation 5317 scheme for the current target. `single' tells the linker to generate a 5318 single GOT with entries only at non-negative offsets. `negative' 5319 instructs the linker to generate a single GOT with entries at both 5320 negative and positive offsets. Not all environments support such GOTs. 5321 `multigot' allows the linker to generate several GOTs in the output 5322 file. All GOT references from a single input object file access the 5323 same GOT, but references from different input object files might access 5324 different GOTs. Not all environments support such GOTs. 5325 5326 5327 File: ld.info, Node: MMIX, Next: MSP430, Prev: M68K, Up: Machine Dependent 5328 5329 4.7 `ld' and MMIX 5330 ================= 5331 5332 For MMIX, there is a choice of generating `ELF' object files or `mmo' 5333 object files when linking. The simulator `mmix' understands the `mmo' 5334 format. The binutils `objcopy' utility can translate between the two 5335 formats. 5336 5337 There is one special section, the `.MMIX.reg_contents' section. 5338 Contents in this section is assumed to correspond to that of global 5339 registers, and symbols referring to it are translated to special 5340 symbols, equal to registers. In a final link, the start address of the 5341 `.MMIX.reg_contents' section corresponds to the first allocated global 5342 register multiplied by 8. Register `$255' is not included in this 5343 section; it is always set to the program entry, which is at the symbol 5344 `Main' for `mmo' files. 5345 5346 Global symbols with the prefix `__.MMIX.start.', for example 5347 `__.MMIX.start..text' and `__.MMIX.start..data' are special. The 5348 default linker script uses these to set the default start address of a 5349 section. 5350 5351 Initial and trailing multiples of zero-valued 32-bit words in a 5352 section, are left out from an mmo file. 5353 5354 5355 File: ld.info, Node: MSP430, Next: M68HC11/68HC12, Prev: MMIX, Up: Machine Dependent 5356 5357 4.8 `ld' and MSP430 5358 =================== 5359 5360 For the MSP430 it is possible to select the MPU architecture. The flag 5361 `-m [mpu type]' will select an appropriate linker script for selected 5362 MPU type. (To get a list of known MPUs just pass `-m help' option to 5363 the linker). 5364 5365 The linker will recognize some extra sections which are MSP430 5366 specific: 5367 5368 ``.vectors'' 5369 Defines a portion of ROM where interrupt vectors located. 5370 5371 ``.bootloader'' 5372 Defines the bootloader portion of the ROM (if applicable). Any 5373 code in this section will be uploaded to the MPU. 5374 5375 ``.infomem'' 5376 Defines an information memory section (if applicable). Any code in 5377 this section will be uploaded to the MPU. 5378 5379 ``.infomemnobits'' 5380 This is the same as the `.infomem' section except that any code in 5381 this section will not be uploaded to the MPU. 5382 5383 ``.noinit'' 5384 Denotes a portion of RAM located above `.bss' section. 5385 5386 The last two sections are used by gcc. 5387 5388 5389 File: ld.info, Node: PowerPC ELF32, Next: PowerPC64 ELF64, Prev: M68HC11/68HC12, Up: Machine Dependent 5390 5391 4.9 `ld' and PowerPC 32-bit ELF Support 5392 ======================================= 5393 5394 Branches on PowerPC processors are limited to a signed 26-bit 5395 displacement, which may result in `ld' giving `relocation truncated to 5396 fit' errors with very large programs. `--relax' enables the generation 5397 of trampolines that can access the entire 32-bit address space. These 5398 trampolines are inserted at section boundaries, so may not themselves 5399 be reachable if an input section exceeds 33M in size. You may combine 5400 `-r' and `--relax' to add trampolines in a partial link. In that case 5401 both branches to undefined symbols and inter-section branches are also 5402 considered potentially out of range, and trampolines inserted. 5403 5404 `--bss-plt' 5405 Current PowerPC GCC accepts a `-msecure-plt' option that generates 5406 code capable of using a newer PLT and GOT layout that has the 5407 security advantage of no executable section ever needing to be 5408 writable and no writable section ever being executable. PowerPC 5409 `ld' will generate this layout, including stubs to access the PLT, 5410 if all input files (including startup and static libraries) were 5411 compiled with `-msecure-plt'. `--bss-plt' forces the old BSS PLT 5412 (and GOT layout) which can give slightly better performance. 5413 5414 `--secure-plt' 5415 `ld' will use the new PLT and GOT layout if it is linking new 5416 `-fpic' or `-fPIC' code, but does not do so automatically when 5417 linking non-PIC code. This option requests the new PLT and GOT 5418 layout. A warning will be given if some object file requires the 5419 old style BSS PLT. 5420 5421 `--sdata-got' 5422 The new secure PLT and GOT are placed differently relative to other 5423 sections compared to older BSS PLT and GOT placement. The 5424 location of `.plt' must change because the new secure PLT is an 5425 initialized section while the old PLT is uninitialized. The 5426 reason for the `.got' change is more subtle: The new placement 5427 allows `.got' to be read-only in applications linked with `-z 5428 relro -z now'. However, this placement means that `.sdata' cannot 5429 always be used in shared libraries, because the PowerPC ABI 5430 accesses `.sdata' in shared libraries from the GOT pointer. 5431 `--sdata-got' forces the old GOT placement. PowerPC GCC doesn't 5432 use `.sdata' in shared libraries, so this option is really only 5433 useful for other compilers that may do so. 5434 5435 `--emit-stub-syms' 5436 This option causes `ld' to label linker stubs with a local symbol 5437 that encodes the stub type and destination. 5438 5439 `--no-tls-optimize' 5440 PowerPC `ld' normally performs some optimization of code sequences 5441 used to access Thread-Local Storage. Use this option to disable 5442 the optimization. 5443 5444 5445 File: ld.info, Node: PowerPC64 ELF64, Next: SPU ELF, Prev: PowerPC ELF32, Up: Machine Dependent 5446 5447 4.10 `ld' and PowerPC64 64-bit ELF Support 5448 ========================================== 5449 5450 `--stub-group-size' 5451 Long branch stubs, PLT call stubs and TOC adjusting stubs are 5452 placed by `ld' in stub sections located between groups of input 5453 sections. `--stub-group-size' specifies the maximum size of a 5454 group of input sections handled by one stub section. Since branch 5455 offsets are signed, a stub section may serve two groups of input 5456 sections, one group before the stub section, and one group after 5457 it. However, when using conditional branches that require stubs, 5458 it may be better (for branch prediction) that stub sections only 5459 serve one group of input sections. A negative value for `N' 5460 chooses this scheme, ensuring that branches to stubs always use a 5461 negative offset. Two special values of `N' are recognized, `1' 5462 and `-1'. These both instruct `ld' to automatically size input 5463 section groups for the branch types detected, with the same 5464 behaviour regarding stub placement as other positive or negative 5465 values of `N' respectively. 5466 5467 Note that `--stub-group-size' does not split input sections. A 5468 single input section larger than the group size specified will of 5469 course create a larger group (of one section). If input sections 5470 are too large, it may not be possible for a branch to reach its 5471 stub. 5472 5473 `--emit-stub-syms' 5474 This option causes `ld' to label linker stubs with a local symbol 5475 that encodes the stub type and destination. 5476 5477 `--dotsyms, --no-dotsyms' 5478 These two options control how `ld' interprets version patterns in 5479 a version script. Older PowerPC64 compilers emitted both a 5480 function descriptor symbol with the same name as the function, and 5481 a code entry symbol with the name prefixed by a dot (`.'). To 5482 properly version a function `foo', the version script thus needs 5483 to control both `foo' and `.foo'. The option `--dotsyms', on by 5484 default, automatically adds the required dot-prefixed patterns. 5485 Use `--no-dotsyms' to disable this feature. 5486 5487 `--no-tls-optimize' 5488 PowerPC64 `ld' normally performs some optimization of code 5489 sequences used to access Thread-Local Storage. Use this option to 5490 disable the optimization. 5491 5492 `--no-opd-optimize' 5493 PowerPC64 `ld' normally removes `.opd' section entries 5494 corresponding to deleted link-once functions, or functions removed 5495 by the action of `--gc-sections' or linker script `/DISCARD/'. 5496 Use this option to disable `.opd' optimization. 5497 5498 `--non-overlapping-opd' 5499 Some PowerPC64 compilers have an option to generate compressed 5500 `.opd' entries spaced 16 bytes apart, overlapping the third word, 5501 the static chain pointer (unused in C) with the first word of the 5502 next entry. This option expands such entries to the full 24 bytes. 5503 5504 `--no-toc-optimize' 5505 PowerPC64 `ld' normally removes unused `.toc' section entries. 5506 Such entries are detected by examining relocations that reference 5507 the TOC in code sections. A reloc in a deleted code section marks 5508 a TOC word as unneeded, while a reloc in a kept code section marks 5509 a TOC word as needed. Since the TOC may reference itself, TOC 5510 relocs are also examined. TOC words marked as both needed and 5511 unneeded will of course be kept. TOC words without any referencing 5512 reloc are assumed to be part of a multi-word entry, and are kept or 5513 discarded as per the nearest marked preceding word. This works 5514 reliably for compiler generated code, but may be incorrect if 5515 assembly code is used to insert TOC entries. Use this option to 5516 disable the optimization. 5517 5518 `--no-multi-toc' 5519 By default, PowerPC64 GCC generates code for a TOC model where TOC 5520 entries are accessed with a 16-bit offset from r2. This limits the 5521 total TOC size to 64K. PowerPC64 `ld' extends this limit by 5522 grouping code sections such that each group uses less than 64K for 5523 its TOC entries, then inserts r2 adjusting stubs between 5524 inter-group calls. `ld' does not split apart input sections, so 5525 cannot help if a single input file has a `.toc' section that 5526 exceeds 64K, most likely from linking multiple files with `ld -r'. 5527 Use this option to turn off this feature. 5528 5529 5530 File: ld.info, Node: SPU ELF, Next: TI COFF, Prev: PowerPC64 ELF64, Up: Machine Dependent 5531 5532 4.11 `ld' and SPU ELF Support 5533 ============================= 5534 5535 `--plugin' 5536 This option marks an executable as a PIC plugin module. 5537 5538 `--no-overlays' 5539 Normally, `ld' recognizes calls to functions within overlay 5540 regions, and redirects such calls to an overlay manager via a stub. 5541 `ld' also provides a built-in overlay manager. This option turns 5542 off all this special overlay handling. 5543 5544 `--emit-stub-syms' 5545 This option causes `ld' to label overlay stubs with a local symbol 5546 that encodes the stub type and destination. 5547 5548 `--extra-overlay-stubs' 5549 This option causes `ld' to add overlay call stubs on all function 5550 calls out of overlay regions. Normally stubs are not added on 5551 calls to non-overlay regions. 5552 5553 `--local-store=lo:hi' 5554 `ld' usually checks that a final executable for SPU fits in the 5555 address range 0 to 256k. This option may be used to change the 5556 range. Disable the check entirely with `--local-store=0:0'. 5557 5558 `--stack-analysis' 5559 SPU local store space is limited. Over-allocation of stack space 5560 unnecessarily limits space available for code and data, while 5561 under-allocation results in runtime failures. If given this 5562 option, `ld' will provide an estimate of maximum stack usage. 5563 `ld' does this by examining symbols in code sections to determine 5564 the extents of functions, and looking at function prologues for 5565 stack adjusting instructions. A call-graph is created by looking 5566 for relocations on branch instructions. The graph is then searched 5567 for the maximum stack usage path. Note that this analysis does not 5568 find calls made via function pointers, and does not handle 5569 recursion and other cycles in the call graph. Stack usage may be 5570 under-estimated if your code makes such calls. Also, stack usage 5571 for dynamic allocation, e.g. alloca, will not be detected. If a 5572 link map is requested, detailed information about each function's 5573 stack usage and calls will be given. 5574 5575 `--emit-stack-syms' 5576 This option, if given along with `--stack-analysis' will result in 5577 `ld' emitting stack sizing symbols for each function. These take 5578 the form `__stack_<function_name>' for global functions, and 5579 `__stack_<number>_<function_name>' for static functions. 5580 `<number>' is the section id in hex. The value of such symbols is 5581 the stack requirement for the corresponding function. The symbol 5582 size will be zero, type `STT_NOTYPE', binding `STB_LOCAL', and 5583 section `SHN_ABS'. 5584 5585 5586 File: ld.info, Node: TI COFF, Next: WIN32, Prev: SPU ELF, Up: Machine Dependent 5587 5588 4.12 `ld''s Support for Various TI COFF Versions 5589 ================================================ 5590 5591 The `--format' switch allows selection of one of the various TI COFF 5592 versions. The latest of this writing is 2; versions 0 and 1 are also 5593 supported. The TI COFF versions also vary in header byte-order format; 5594 `ld' will read any version or byte order, but the output header format 5595 depends on the default specified by the specific target. 5596 5597 5598 File: ld.info, Node: WIN32, Next: Xtensa, Prev: TI COFF, Up: Machine Dependent 5599 5600 4.13 `ld' and WIN32 (cygwin/mingw) 5601 ================================== 5602 5603 This section describes some of the win32 specific `ld' issues. See 5604 *Note Command Line Options: Options. for detailed description of the 5605 command line options mentioned here. 5606 5607 _import libraries_ 5608 The standard Windows linker creates and uses so-called import 5609 libraries, which contains information for linking to dll's. They 5610 are regular static archives and are handled as any other static 5611 archive. The cygwin and mingw ports of `ld' have specific support 5612 for creating such libraries provided with the `--out-implib' 5613 command line option. 5614 5615 _exporting DLL symbols_ 5616 The cygwin/mingw `ld' has several ways to export symbols for dll's. 5617 5618 _using auto-export functionality_ 5619 By default `ld' exports symbols with the auto-export 5620 functionality, which is controlled by the following command 5621 line options: 5622 5623 * -export-all-symbols [This is the default] 5624 5625 * -exclude-symbols 5626 5627 * -exclude-libs 5628 5629 * -exclude-modules-for-implib 5630 5631 * -version-script 5632 5633 When auto-export is in operation, `ld' will export all the 5634 non-local (global and common) symbols it finds in a DLL, with 5635 the exception of a few symbols known to belong to the 5636 system's runtime and libraries. As it will often not be 5637 desirable to export all of a DLL's symbols, which may include 5638 private functions that are not part of any public interface, 5639 the command-line options listed above may be used to filter 5640 symbols out from the list for exporting. The `--output-def' 5641 option can be used in order to see the final list of exported 5642 symbols with all exclusions taken into effect. 5643 5644 If `--export-all-symbols' is not given explicitly on the 5645 command line, then the default auto-export behavior will be 5646 _disabled_ if either of the following are true: 5647 5648 * A DEF file is used. 5649 5650 * Any symbol in any object file was marked with the 5651 __declspec(dllexport) attribute. 5652 5653 _using a DEF file_ 5654 Another way of exporting symbols is using a DEF file. A DEF 5655 file is an ASCII file containing definitions of symbols which 5656 should be exported when a dll is created. Usually it is 5657 named `<dll name>.def' and is added as any other object file 5658 to the linker's command line. The file's name must end in 5659 `.def' or `.DEF'. 5660 5661 gcc -o <output> <objectfiles> <dll name>.def 5662 5663 Using a DEF file turns off the normal auto-export behavior, 5664 unless the `--export-all-symbols' option is also used. 5665 5666 Here is an example of a DEF file for a shared library called 5667 `xyz.dll': 5668 5669 LIBRARY "xyz.dll" BASE=0x20000000 5670 5671 EXPORTS 5672 foo 5673 bar 5674 _bar = bar 5675 another_foo = abc.dll.afoo 5676 var1 DATA 5677 doo = foo == foo2 5678 eoo DATA == var1 5679 5680 This example defines a DLL with a non-default base address 5681 and seven symbols in the export table. The third exported 5682 symbol `_bar' is an alias for the second. The fourth symbol, 5683 `another_foo' is resolved by "forwarding" to another module 5684 and treating it as an alias for `afoo' exported from the DLL 5685 `abc.dll'. The final symbol `var1' is declared to be a data 5686 object. The `doo' symbol in export library is an alias of 5687 `foo', which gets the string name in export table `foo2'. The 5688 `eoo' symbol is an data export symbol, which gets in export 5689 table the name `var1'. 5690 5691 The optional `LIBRARY <name>' command indicates the _internal_ 5692 name of the output DLL. If `<name>' does not include a suffix, 5693 the default library suffix, `.DLL' is appended. 5694 5695 When the .DEF file is used to build an application, rather 5696 than a library, the `NAME <name>' command should be used 5697 instead of `LIBRARY'. If `<name>' does not include a suffix, 5698 the default executable suffix, `.EXE' is appended. 5699 5700 With either `LIBRARY <name>' or `NAME <name>' the optional 5701 specification `BASE = <number>' may be used to specify a 5702 non-default base address for the image. 5703 5704 If neither `LIBRARY <name>' nor `NAME <name>' is specified, 5705 or they specify an empty string, the internal name is the 5706 same as the filename specified on the command line. 5707 5708 The complete specification of an export symbol is: 5709 5710 EXPORTS 5711 ( ( ( <name1> [ = <name2> ] ) 5712 | ( <name1> = <module-name> . <external-name>)) 5713 [ @ <integer> ] [NONAME] [DATA] [CONSTANT] [PRIVATE] [== <name3>] ) * 5714 5715 Declares `<name1>' as an exported symbol from the DLL, or 5716 declares `<name1>' as an exported alias for `<name2>'; or 5717 declares `<name1>' as a "forward" alias for the symbol 5718 `<external-name>' in the DLL `<module-name>'. Optionally, 5719 the symbol may be exported by the specified ordinal 5720 `<integer>' alias. The optional `<name3>' is the to be used 5721 string in import/export table for the symbol. 5722 5723 The optional keywords that follow the declaration indicate: 5724 5725 `NONAME': Do not put the symbol name in the DLL's export 5726 table. It will still be exported by its ordinal alias 5727 (either the value specified by the .def specification or, 5728 otherwise, the value assigned by the linker). The symbol 5729 name, however, does remain visible in the import library (if 5730 any), unless `PRIVATE' is also specified. 5731 5732 `DATA': The symbol is a variable or object, rather than a 5733 function. The import lib will export only an indirect 5734 reference to `foo' as the symbol `_imp__foo' (ie, `foo' must 5735 be resolved as `*_imp__foo'). 5736 5737 `CONSTANT': Like `DATA', but put the undecorated `foo' as 5738 well as `_imp__foo' into the import library. Both refer to the 5739 read-only import address table's pointer to the variable, not 5740 to the variable itself. This can be dangerous. If the user 5741 code fails to add the `dllimport' attribute and also fails to 5742 explicitly add the extra indirection that the use of the 5743 attribute enforces, the application will behave unexpectedly. 5744 5745 `PRIVATE': Put the symbol in the DLL's export table, but do 5746 not put it into the static import library used to resolve 5747 imports at link time. The symbol can still be imported using 5748 the `LoadLibrary/GetProcAddress' API at runtime or by by 5749 using the GNU ld extension of linking directly to the DLL 5750 without an import library. 5751 5752 See ld/deffilep.y in the binutils sources for the full 5753 specification of other DEF file statements 5754 5755 While linking a shared dll, `ld' is able to create a DEF file 5756 with the `--output-def <file>' command line option. 5757 5758 _Using decorations_ 5759 Another way of marking symbols for export is to modify the 5760 source code itself, so that when building the DLL each symbol 5761 to be exported is declared as: 5762 5763 __declspec(dllexport) int a_variable 5764 __declspec(dllexport) void a_function(int with_args) 5765 5766 All such symbols will be exported from the DLL. If, however, 5767 any of the object files in the DLL contain symbols decorated 5768 in this way, then the normal auto-export behavior is 5769 disabled, unless the `--export-all-symbols' option is also 5770 used. 5771 5772 Note that object files that wish to access these symbols must 5773 _not_ decorate them with dllexport. Instead, they should use 5774 dllimport, instead: 5775 5776 __declspec(dllimport) int a_variable 5777 __declspec(dllimport) void a_function(int with_args) 5778 5779 This complicates the structure of library header files, 5780 because when included by the library itself the header must 5781 declare the variables and functions as dllexport, but when 5782 included by client code the header must declare them as 5783 dllimport. There are a number of idioms that are typically 5784 used to do this; often client code can omit the __declspec() 5785 declaration completely. See `--enable-auto-import' and 5786 `automatic data imports' for more information. 5787 5788 _automatic data imports_ 5789 The standard Windows dll format supports data imports from dlls 5790 only by adding special decorations (dllimport/dllexport), which 5791 let the compiler produce specific assembler instructions to deal 5792 with this issue. This increases the effort necessary to port 5793 existing Un*x code to these platforms, especially for large c++ 5794 libraries and applications. The auto-import feature, which was 5795 initially provided by Paul Sokolovsky, allows one to omit the 5796 decorations to achieve a behavior that conforms to that on 5797 POSIX/Un*x platforms. This feature is enabled with the 5798 `--enable-auto-import' command-line option, although it is enabled 5799 by default on cygwin/mingw. The `--enable-auto-import' option 5800 itself now serves mainly to suppress any warnings that are 5801 ordinarily emitted when linked objects trigger the feature's use. 5802 5803 auto-import of variables does not always work flawlessly without 5804 additional assistance. Sometimes, you will see this message 5805 5806 "variable '<var>' can't be auto-imported. Please read the 5807 documentation for ld's `--enable-auto-import' for details." 5808 5809 The `--enable-auto-import' documentation explains why this error 5810 occurs, and several methods that can be used to overcome this 5811 difficulty. One of these methods is the _runtime pseudo-relocs_ 5812 feature, described below. 5813 5814 For complex variables imported from DLLs (such as structs or 5815 classes), object files typically contain a base address for the 5816 variable and an offset (_addend_) within the variable-to specify a 5817 particular field or public member, for instance. Unfortunately, 5818 the runtime loader used in win32 environments is incapable of 5819 fixing these references at runtime without the additional 5820 information supplied by dllimport/dllexport decorations. The 5821 standard auto-import feature described above is unable to resolve 5822 these references. 5823 5824 The `--enable-runtime-pseudo-relocs' switch allows these 5825 references to be resolved without error, while leaving the task of 5826 adjusting the references themselves (with their non-zero addends) 5827 to specialized code provided by the runtime environment. Recent 5828 versions of the cygwin and mingw environments and compilers 5829 provide this runtime support; older versions do not. However, the 5830 support is only necessary on the developer's platform; the 5831 compiled result will run without error on an older system. 5832 5833 `--enable-runtime-pseudo-relocs' is not the default; it must be 5834 explicitly enabled as needed. 5835 5836 _direct linking to a dll_ 5837 The cygwin/mingw ports of `ld' support the direct linking, 5838 including data symbols, to a dll without the usage of any import 5839 libraries. This is much faster and uses much less memory than 5840 does the traditional import library method, especially when 5841 linking large libraries or applications. When `ld' creates an 5842 import lib, each function or variable exported from the dll is 5843 stored in its own bfd, even though a single bfd could contain many 5844 exports. The overhead involved in storing, loading, and 5845 processing so many bfd's is quite large, and explains the 5846 tremendous time, memory, and storage needed to link against 5847 particularly large or complex libraries when using import libs. 5848 5849 Linking directly to a dll uses no extra command-line switches 5850 other than `-L' and `-l', because `ld' already searches for a 5851 number of names to match each library. All that is needed from 5852 the developer's perspective is an understanding of this search, in 5853 order to force ld to select the dll instead of an import library. 5854 5855 For instance, when ld is called with the argument `-lxxx' it will 5856 attempt to find, in the first directory of its search path, 5857 5858 libxxx.dll.a 5859 xxx.dll.a 5860 libxxx.a 5861 xxx.lib 5862 cygxxx.dll (*) 5863 libxxx.dll 5864 xxx.dll 5865 5866 before moving on to the next directory in the search path. 5867 5868 (*) Actually, this is not `cygxxx.dll' but in fact is 5869 `<prefix>xxx.dll', where `<prefix>' is set by the `ld' option 5870 `--dll-search-prefix=<prefix>'. In the case of cygwin, the 5871 standard gcc spec file includes `--dll-search-prefix=cyg', so in 5872 effect we actually search for `cygxxx.dll'. 5873 5874 Other win32-based unix environments, such as mingw or pw32, may 5875 use other `<prefix>'es, although at present only cygwin makes use 5876 of this feature. It was originally intended to help avoid name 5877 conflicts among dll's built for the various win32/un*x 5878 environments, so that (for example) two versions of a zlib dll 5879 could coexist on the same machine. 5880 5881 The generic cygwin/mingw path layout uses a `bin' directory for 5882 applications and dll's and a `lib' directory for the import 5883 libraries (using cygwin nomenclature): 5884 5885 bin/ 5886 cygxxx.dll 5887 lib/ 5888 libxxx.dll.a (in case of dll's) 5889 libxxx.a (in case of static archive) 5890 5891 Linking directly to a dll without using the import library can be 5892 done two ways: 5893 5894 1. Use the dll directly by adding the `bin' path to the link line 5895 gcc -Wl,-verbose -o a.exe -L../bin/ -lxxx 5896 5897 However, as the dll's often have version numbers appended to their 5898 names (`cygncurses-5.dll') this will often fail, unless one 5899 specifies `-L../bin -lncurses-5' to include the version. Import 5900 libs are generally not versioned, and do not have this difficulty. 5901 5902 2. Create a symbolic link from the dll to a file in the `lib' 5903 directory according to the above mentioned search pattern. This 5904 should be used to avoid unwanted changes in the tools needed for 5905 making the app/dll. 5906 5907 ln -s bin/cygxxx.dll lib/[cyg|lib|]xxx.dll[.a] 5908 5909 Then you can link without any make environment changes. 5910 5911 gcc -Wl,-verbose -o a.exe -L../lib/ -lxxx 5912 5913 This technique also avoids the version number problems, because 5914 the following is perfectly legal 5915 5916 bin/ 5917 cygxxx-5.dll 5918 lib/ 5919 libxxx.dll.a -> ../bin/cygxxx-5.dll 5920 5921 Linking directly to a dll without using an import lib will work 5922 even when auto-import features are exercised, and even when 5923 `--enable-runtime-pseudo-relocs' is used. 5924 5925 Given the improvements in speed and memory usage, one might 5926 justifiably wonder why import libraries are used at all. There 5927 are three reasons: 5928 5929 1. Until recently, the link-directly-to-dll functionality did _not_ 5930 work with auto-imported data. 5931 5932 2. Sometimes it is necessary to include pure static objects within 5933 the import library (which otherwise contains only bfd's for 5934 indirection symbols that point to the exports of a dll). Again, 5935 the import lib for the cygwin kernel makes use of this ability, 5936 and it is not possible to do this without an import lib. 5937 5938 3. Symbol aliases can only be resolved using an import lib. This 5939 is critical when linking against OS-supplied dll's (eg, the win32 5940 API) in which symbols are usually exported as undecorated aliases 5941 of their stdcall-decorated assembly names. 5942 5943 So, import libs are not going away. But the ability to replace 5944 true import libs with a simple symbolic link to (or a copy of) a 5945 dll, in many cases, is a useful addition to the suite of tools 5946 binutils makes available to the win32 developer. Given the 5947 massive improvements in memory requirements during linking, storage 5948 requirements, and linking speed, we expect that many developers 5949 will soon begin to use this feature whenever possible. 5950 5951 _symbol aliasing_ 5952 5953 _adding additional names_ 5954 Sometimes, it is useful to export symbols with additional 5955 names. A symbol `foo' will be exported as `foo', but it can 5956 also be exported as `_foo' by using special directives in the 5957 DEF file when creating the dll. This will affect also the 5958 optional created import library. Consider the following DEF 5959 file: 5960 5961 LIBRARY "xyz.dll" BASE=0x61000000 5962 5963 EXPORTS 5964 foo 5965 _foo = foo 5966 5967 The line `_foo = foo' maps the symbol `foo' to `_foo'. 5968 5969 Another method for creating a symbol alias is to create it in 5970 the source code using the "weak" attribute: 5971 5972 void foo () { /* Do something. */; } 5973 void _foo () __attribute__ ((weak, alias ("foo"))); 5974 5975 See the gcc manual for more information about attributes and 5976 weak symbols. 5977 5978 _renaming symbols_ 5979 Sometimes it is useful to rename exports. For instance, the 5980 cygwin kernel does this regularly. A symbol `_foo' can be 5981 exported as `foo' but not as `_foo' by using special 5982 directives in the DEF file. (This will also affect the import 5983 library, if it is created). In the following example: 5984 5985 LIBRARY "xyz.dll" BASE=0x61000000 5986 5987 EXPORTS 5988 _foo = foo 5989 5990 The line `_foo = foo' maps the exported symbol `foo' to 5991 `_foo'. 5992 5993 Note: using a DEF file disables the default auto-export behavior, 5994 unless the `--export-all-symbols' command line option is used. 5995 If, however, you are trying to rename symbols, then you should list 5996 _all_ desired exports in the DEF file, including the symbols that 5997 are not being renamed, and do _not_ use the `--export-all-symbols' 5998 option. If you list only the renamed symbols in the DEF file, and 5999 use `--export-all-symbols' to handle the other symbols, then the 6000 both the new names _and_ the original names for the renamed 6001 symbols will be exported. In effect, you'd be aliasing those 6002 symbols, not renaming them, which is probably not what you wanted. 6003 6004 _weak externals_ 6005 The Windows object format, PE, specifies a form of weak symbols 6006 called weak externals. When a weak symbol is linked and the 6007 symbol is not defined, the weak symbol becomes an alias for some 6008 other symbol. There are three variants of weak externals: 6009 * Definition is searched for in objects and libraries, 6010 historically called lazy externals. 6011 6012 * Definition is searched for only in other objects, not in 6013 libraries. This form is not presently implemented. 6014 6015 * No search; the symbol is an alias. This form is not presently 6016 implemented. 6017 As a GNU extension, weak symbols that do not specify an alternate 6018 symbol are supported. If the symbol is undefined when linking, 6019 the symbol uses a default value. 6020 6021 _aligned common symbols_ 6022 As a GNU extension to the PE file format, it is possible to 6023 specify the desired alignment for a common symbol. This 6024 information is conveyed from the assembler or compiler to the 6025 linker by means of GNU-specific commands carried in the object 6026 file's `.drectve' section, which are recognized by `ld' and 6027 respected when laying out the common symbols. Native tools will 6028 be able to process object files employing this GNU extension, but 6029 will fail to respect the alignment instructions, and may issue 6030 noisy warnings about unknown linker directives. 6031 6032 6033 File: ld.info, Node: Xtensa, Prev: WIN32, Up: Machine Dependent 6034 6035 4.14 `ld' and Xtensa Processors 6036 =============================== 6037 6038 The default `ld' behavior for Xtensa processors is to interpret 6039 `SECTIONS' commands so that lists of explicitly named sections in a 6040 specification with a wildcard file will be interleaved when necessary to 6041 keep literal pools within the range of PC-relative load offsets. For 6042 example, with the command: 6043 6044 SECTIONS 6045 { 6046 .text : { 6047 *(.literal .text) 6048 } 6049 } 6050 6051 `ld' may interleave some of the `.literal' and `.text' sections from 6052 different object files to ensure that the literal pools are within the 6053 range of PC-relative load offsets. A valid interleaving might place 6054 the `.literal' sections from an initial group of files followed by the 6055 `.text' sections of that group of files. Then, the `.literal' sections 6056 from the rest of the files and the `.text' sections from the rest of 6057 the files would follow. 6058 6059 Relaxation is enabled by default for the Xtensa version of `ld' and 6060 provides two important link-time optimizations. The first optimization 6061 is to combine identical literal values to reduce code size. A redundant 6062 literal will be removed and all the `L32R' instructions that use it 6063 will be changed to reference an identical literal, as long as the 6064 location of the replacement literal is within the offset range of all 6065 the `L32R' instructions. The second optimization is to remove 6066 unnecessary overhead from assembler-generated "longcall" sequences of 6067 `L32R'/`CALLXN' when the target functions are within range of direct 6068 `CALLN' instructions. 6069 6070 For each of these cases where an indirect call sequence can be 6071 optimized to a direct call, the linker will change the `CALLXN' 6072 instruction to a `CALLN' instruction, remove the `L32R' instruction, 6073 and remove the literal referenced by the `L32R' instruction if it is 6074 not used for anything else. Removing the `L32R' instruction always 6075 reduces code size but can potentially hurt performance by changing the 6076 alignment of subsequent branch targets. By default, the linker will 6077 always preserve alignments, either by switching some instructions 6078 between 24-bit encodings and the equivalent density instructions or by 6079 inserting a no-op in place of the `L32R' instruction that was removed. 6080 If code size is more important than performance, the `--size-opt' 6081 option can be used to prevent the linker from widening density 6082 instructions or inserting no-ops, except in a few cases where no-ops 6083 are required for correctness. 6084 6085 The following Xtensa-specific command-line options can be used to 6086 control the linker: 6087 6088 `--size-opt' 6089 When optimizing indirect calls to direct calls, optimize for code 6090 size more than performance. With this option, the linker will not 6091 insert no-ops or widen density instructions to preserve branch 6092 target alignment. There may still be some cases where no-ops are 6093 required to preserve the correctness of the code. 6094 6095 6096 File: ld.info, Node: BFD, Next: Reporting Bugs, Prev: Machine Dependent, Up: Top 6097 6098 5 BFD 6099 ***** 6100 6101 The linker accesses object and archive files using the BFD libraries. 6102 These libraries allow the linker to use the same routines to operate on 6103 object files whatever the object file format. A different object file 6104 format can be supported simply by creating a new BFD back end and adding 6105 it to the library. To conserve runtime memory, however, the linker and 6106 associated tools are usually configured to support only a subset of the 6107 object file formats available. You can use `objdump -i' (*note 6108 objdump: (binutils.info)objdump.) to list all the formats available for 6109 your configuration. 6110 6111 As with most implementations, BFD is a compromise between several 6112 conflicting requirements. The major factor influencing BFD design was 6113 efficiency: any time used converting between formats is time which 6114 would not have been spent had BFD not been involved. This is partly 6115 offset by abstraction payback; since BFD simplifies applications and 6116 back ends, more time and care may be spent optimizing algorithms for a 6117 greater speed. 6118 6119 One minor artifact of the BFD solution which you should bear in mind 6120 is the potential for information loss. There are two places where 6121 useful information can be lost using the BFD mechanism: during 6122 conversion and during output. *Note BFD information loss::. 6123 6124 * Menu: 6125 6126 * BFD outline:: How it works: an outline of BFD 6127 6128 6129 File: ld.info, Node: BFD outline, Up: BFD 6130 6131 5.1 How It Works: An Outline of BFD 6132 =================================== 6133 6134 When an object file is opened, BFD subroutines automatically determine 6135 the format of the input object file. They then build a descriptor in 6136 memory with pointers to routines that will be used to access elements of 6137 the object file's data structures. 6138 6139 As different information from the object files is required, BFD 6140 reads from different sections of the file and processes them. For 6141 example, a very common operation for the linker is processing symbol 6142 tables. Each BFD back end provides a routine for converting between 6143 the object file's representation of symbols and an internal canonical 6144 format. When the linker asks for the symbol table of an object file, it 6145 calls through a memory pointer to the routine from the relevant BFD 6146 back end which reads and converts the table into a canonical form. The 6147 linker then operates upon the canonical form. When the link is finished 6148 and the linker writes the output file's symbol table, another BFD back 6149 end routine is called to take the newly created symbol table and 6150 convert it into the chosen output format. 6151 6152 * Menu: 6153 6154 * BFD information loss:: Information Loss 6155 * Canonical format:: The BFD canonical object-file format 6156 6157 6158 File: ld.info, Node: BFD information loss, Next: Canonical format, Up: BFD outline 6159 6160 5.1.1 Information Loss 6161 ---------------------- 6162 6163 _Information can be lost during output._ The output formats supported 6164 by BFD do not provide identical facilities, and information which can 6165 be described in one form has nowhere to go in another format. One 6166 example of this is alignment information in `b.out'. There is nowhere 6167 in an `a.out' format file to store alignment information on the 6168 contained data, so when a file is linked from `b.out' and an `a.out' 6169 image is produced, alignment information will not propagate to the 6170 output file. (The linker will still use the alignment information 6171 internally, so the link is performed correctly). 6172 6173 Another example is COFF section names. COFF files may contain an 6174 unlimited number of sections, each one with a textual section name. If 6175 the target of the link is a format which does not have many sections 6176 (e.g., `a.out') or has sections without names (e.g., the Oasys format), 6177 the link cannot be done simply. You can circumvent this problem by 6178 describing the desired input-to-output section mapping with the linker 6179 command language. 6180 6181 _Information can be lost during canonicalization._ The BFD internal 6182 canonical form of the external formats is not exhaustive; there are 6183 structures in input formats for which there is no direct representation 6184 internally. This means that the BFD back ends cannot maintain all 6185 possible data richness through the transformation between external to 6186 internal and back to external formats. 6187 6188 This limitation is only a problem when an application reads one 6189 format and writes another. Each BFD back end is responsible for 6190 maintaining as much data as possible, and the internal BFD canonical 6191 form has structures which are opaque to the BFD core, and exported only 6192 to the back ends. When a file is read in one format, the canonical form 6193 is generated for BFD and the application. At the same time, the back 6194 end saves away any information which may otherwise be lost. If the data 6195 is then written back in the same format, the back end routine will be 6196 able to use the canonical form provided by the BFD core as well as the 6197 information it prepared earlier. Since there is a great deal of 6198 commonality between back ends, there is no information lost when 6199 linking or copying big endian COFF to little endian COFF, or `a.out' to 6200 `b.out'. When a mixture of formats is linked, the information is only 6201 lost from the files whose format differs from the destination. 6202 6203 6204 File: ld.info, Node: Canonical format, Prev: BFD information loss, Up: BFD outline 6205 6206 5.1.2 The BFD canonical object-file format 6207 ------------------------------------------ 6208 6209 The greatest potential for loss of information occurs when there is the 6210 least overlap between the information provided by the source format, 6211 that stored by the canonical format, and that needed by the destination 6212 format. A brief description of the canonical form may help you 6213 understand which kinds of data you can count on preserving across 6214 conversions. 6215 6216 _files_ 6217 Information stored on a per-file basis includes target machine 6218 architecture, particular implementation format type, a demand 6219 pageable bit, and a write protected bit. Information like Unix 6220 magic numbers is not stored here--only the magic numbers' meaning, 6221 so a `ZMAGIC' file would have both the demand pageable bit and the 6222 write protected text bit set. The byte order of the target is 6223 stored on a per-file basis, so that big- and little-endian object 6224 files may be used with one another. 6225 6226 _sections_ 6227 Each section in the input file contains the name of the section, 6228 the section's original address in the object file, size and 6229 alignment information, various flags, and pointers into other BFD 6230 data structures. 6231 6232 _symbols_ 6233 Each symbol contains a pointer to the information for the object 6234 file which originally defined it, its name, its value, and various 6235 flag bits. When a BFD back end reads in a symbol table, it 6236 relocates all symbols to make them relative to the base of the 6237 section where they were defined. Doing this ensures that each 6238 symbol points to its containing section. Each symbol also has a 6239 varying amount of hidden private data for the BFD back end. Since 6240 the symbol points to the original file, the private data format 6241 for that symbol is accessible. `ld' can operate on a collection 6242 of symbols of wildly different formats without problems. 6243 6244 Normal global and simple local symbols are maintained on output, 6245 so an output file (no matter its format) will retain symbols 6246 pointing to functions and to global, static, and common variables. 6247 Some symbol information is not worth retaining; in `a.out', type 6248 information is stored in the symbol table as long symbol names. 6249 This information would be useless to most COFF debuggers; the 6250 linker has command line switches to allow users to throw it away. 6251 6252 There is one word of type information within the symbol, so if the 6253 format supports symbol type information within symbols (for 6254 example, COFF, IEEE, Oasys) and the type is simple enough to fit 6255 within one word (nearly everything but aggregates), the 6256 information will be preserved. 6257 6258 _relocation level_ 6259 Each canonical BFD relocation record contains a pointer to the 6260 symbol to relocate to, the offset of the data to relocate, the 6261 section the data is in, and a pointer to a relocation type 6262 descriptor. Relocation is performed by passing messages through 6263 the relocation type descriptor and the symbol pointer. Therefore, 6264 relocations can be performed on output data using a relocation 6265 method that is only available in one of the input formats. For 6266 instance, Oasys provides a byte relocation format. A relocation 6267 record requesting this relocation type would point indirectly to a 6268 routine to perform this, so the relocation may be performed on a 6269 byte being written to a 68k COFF file, even though 68k COFF has no 6270 such relocation type. 6271 6272 _line numbers_ 6273 Object formats can contain, for debugging purposes, some form of 6274 mapping between symbols, source line numbers, and addresses in the 6275 output file. These addresses have to be relocated along with the 6276 symbol information. Each symbol with an associated list of line 6277 number records points to the first record of the list. The head 6278 of a line number list consists of a pointer to the symbol, which 6279 allows finding out the address of the function whose line number 6280 is being described. The rest of the list is made up of pairs: 6281 offsets into the section and line numbers. Any format which can 6282 simply derive this information can pass it successfully between 6283 formats (COFF, IEEE and Oasys). 6284 6285 6286 File: ld.info, Node: Reporting Bugs, Next: MRI, Prev: BFD, Up: Top 6287 6288 6 Reporting Bugs 6289 **************** 6290 6291 Your bug reports play an essential role in making `ld' reliable. 6292 6293 Reporting a bug may help you by bringing a solution to your problem, 6294 or it may not. But in any case the principal function of a bug report 6295 is to help the entire community by making the next version of `ld' work 6296 better. Bug reports are your contribution to the maintenance of `ld'. 6297 6298 In order for a bug report to serve its purpose, you must include the 6299 information that enables us to fix the bug. 6300 6301 * Menu: 6302 6303 * Bug Criteria:: Have you found a bug? 6304 * Bug Reporting:: How to report bugs 6305 6306 6307 File: ld.info, Node: Bug Criteria, Next: Bug Reporting, Up: Reporting Bugs 6308 6309 6.1 Have You Found a Bug? 6310 ========================= 6311 6312 If you are not sure whether you have found a bug, here are some 6313 guidelines: 6314 6315 * If the linker gets a fatal signal, for any input whatever, that is 6316 a `ld' bug. Reliable linkers never crash. 6317 6318 * If `ld' produces an error message for valid input, that is a bug. 6319 6320 * If `ld' does not produce an error message for invalid input, that 6321 may be a bug. In the general case, the linker can not verify that 6322 object files are correct. 6323 6324 * If you are an experienced user of linkers, your suggestions for 6325 improvement of `ld' are welcome in any case. 6326 6327 6328 File: ld.info, Node: Bug Reporting, Prev: Bug Criteria, Up: Reporting Bugs 6329 6330 6.2 How to Report Bugs 6331 ====================== 6332 6333 A number of companies and individuals offer support for GNU products. 6334 If you obtained `ld' from a support organization, we recommend you 6335 contact that organization first. 6336 6337 You can find contact information for many support companies and 6338 individuals in the file `etc/SERVICE' in the GNU Emacs distribution. 6339 6340 Otherwise, send bug reports for `ld' to 6341 `http://www.sourceware.org/bugzilla/'. 6342 6343 The fundamental principle of reporting bugs usefully is this: 6344 *report all the facts*. If you are not sure whether to state a fact or 6345 leave it out, state it! 6346 6347 Often people omit facts because they think they know what causes the 6348 problem and assume that some details do not matter. Thus, you might 6349 assume that the name of a symbol you use in an example does not matter. 6350 Well, probably it does not, but one cannot be sure. Perhaps the bug 6351 is a stray memory reference which happens to fetch from the location 6352 where that name is stored in memory; perhaps, if the name were 6353 different, the contents of that location would fool the linker into 6354 doing the right thing despite the bug. Play it safe and give a 6355 specific, complete example. That is the easiest thing for you to do, 6356 and the most helpful. 6357 6358 Keep in mind that the purpose of a bug report is to enable us to fix 6359 the bug if it is new to us. Therefore, always write your bug reports 6360 on the assumption that the bug has not been reported previously. 6361 6362 Sometimes people give a few sketchy facts and ask, "Does this ring a 6363 bell?" This cannot help us fix a bug, so it is basically useless. We 6364 respond by asking for enough details to enable us to investigate. You 6365 might as well expedite matters by sending them to begin with. 6366 6367 To enable us to fix the bug, you should include all these things: 6368 6369 * The version of `ld'. `ld' announces it if you start it with the 6370 `--version' argument. 6371 6372 Without this, we will not know whether there is any point in 6373 looking for the bug in the current version of `ld'. 6374 6375 * Any patches you may have applied to the `ld' source, including any 6376 patches made to the `BFD' library. 6377 6378 * The type of machine you are using, and the operating system name 6379 and version number. 6380 6381 * What compiler (and its version) was used to compile `ld'--e.g. 6382 "`gcc-2.7'". 6383 6384 * The command arguments you gave the linker to link your example and 6385 observe the bug. To guarantee you will not omit something 6386 important, list them all. A copy of the Makefile (or the output 6387 from make) is sufficient. 6388 6389 If we were to try to guess the arguments, we would probably guess 6390 wrong and then we might not encounter the bug. 6391 6392 * A complete input file, or set of input files, that will reproduce 6393 the bug. It is generally most helpful to send the actual object 6394 files provided that they are reasonably small. Say no more than 6395 10K. For bigger files you can either make them available by FTP 6396 or HTTP or else state that you are willing to send the object 6397 file(s) to whomever requests them. (Note - your email will be 6398 going to a mailing list, so we do not want to clog it up with 6399 large attachments). But small attachments are best. 6400 6401 If the source files were assembled using `gas' or compiled using 6402 `gcc', then it may be OK to send the source files rather than the 6403 object files. In this case, be sure to say exactly what version of 6404 `gas' or `gcc' was used to produce the object files. Also say how 6405 `gas' or `gcc' were configured. 6406 6407 * A description of what behavior you observe that you believe is 6408 incorrect. For example, "It gets a fatal signal." 6409 6410 Of course, if the bug is that `ld' gets a fatal signal, then we 6411 will certainly notice it. But if the bug is incorrect output, we 6412 might not notice unless it is glaringly wrong. You might as well 6413 not give us a chance to make a mistake. 6414 6415 Even if the problem you experience is a fatal signal, you should 6416 still say so explicitly. Suppose something strange is going on, 6417 such as, your copy of `ld' is out of sync, or you have encountered 6418 a bug in the C library on your system. (This has happened!) Your 6419 copy might crash and ours would not. If you told us to expect a 6420 crash, then when ours fails to crash, we would know that the bug 6421 was not happening for us. If you had not told us to expect a 6422 crash, then we would not be able to draw any conclusion from our 6423 observations. 6424 6425 * If you wish to suggest changes to the `ld' source, send us context 6426 diffs, as generated by `diff' with the `-u', `-c', or `-p' option. 6427 Always send diffs from the old file to the new file. If you even 6428 discuss something in the `ld' source, refer to it by context, not 6429 by line number. 6430 6431 The line numbers in our development sources will not match those 6432 in your sources. Your line numbers would convey no useful 6433 information to us. 6434 6435 Here are some things that are not necessary: 6436 6437 * A description of the envelope of the bug. 6438 6439 Often people who encounter a bug spend a lot of time investigating 6440 which changes to the input file will make the bug go away and which 6441 changes will not affect it. 6442 6443 This is often time consuming and not very useful, because the way 6444 we will find the bug is by running a single example under the 6445 debugger with breakpoints, not by pure deduction from a series of 6446 examples. We recommend that you save your time for something else. 6447 6448 Of course, if you can find a simpler example to report _instead_ 6449 of the original one, that is a convenience for us. Errors in the 6450 output will be easier to spot, running under the debugger will take 6451 less time, and so on. 6452 6453 However, simplification is not vital; if you do not want to do 6454 this, report the bug anyway and send us the entire test case you 6455 used. 6456 6457 * A patch for the bug. 6458 6459 A patch for the bug does help us if it is a good one. But do not 6460 omit the necessary information, such as the test case, on the 6461 assumption that a patch is all we need. We might see problems 6462 with your patch and decide to fix the problem another way, or we 6463 might not understand it at all. 6464 6465 Sometimes with a program as complicated as `ld' it is very hard to 6466 construct an example that will make the program follow a certain 6467 path through the code. If you do not send us the example, we will 6468 not be able to construct one, so we will not be able to verify 6469 that the bug is fixed. 6470 6471 And if we cannot understand what bug you are trying to fix, or why 6472 your patch should be an improvement, we will not install it. A 6473 test case will help us to understand. 6474 6475 * A guess about what the bug is or what it depends on. 6476 6477 Such guesses are usually wrong. Even we cannot guess right about 6478 such things without first using the debugger to find the facts. 6479 6480 6481 File: ld.info, Node: MRI, Next: GNU Free Documentation License, Prev: Reporting Bugs, Up: Top 6482 6483 Appendix A MRI Compatible Script Files 6484 ************************************** 6485 6486 To aid users making the transition to GNU `ld' from the MRI linker, 6487 `ld' can use MRI compatible linker scripts as an alternative to the 6488 more general-purpose linker scripting language described in *Note 6489 Scripts::. MRI compatible linker scripts have a much simpler command 6490 set than the scripting language otherwise used with `ld'. GNU `ld' 6491 supports the most commonly used MRI linker commands; these commands are 6492 described here. 6493 6494 In general, MRI scripts aren't of much use with the `a.out' object 6495 file format, since it only has three sections and MRI scripts lack some 6496 features to make use of them. 6497 6498 You can specify a file containing an MRI-compatible script using the 6499 `-c' command-line option. 6500 6501 Each command in an MRI-compatible script occupies its own line; each 6502 command line starts with the keyword that identifies the command (though 6503 blank lines are also allowed for punctuation). If a line of an 6504 MRI-compatible script begins with an unrecognized keyword, `ld' issues 6505 a warning message, but continues processing the script. 6506 6507 Lines beginning with `*' are comments. 6508 6509 You can write these commands using all upper-case letters, or all 6510 lower case; for example, `chip' is the same as `CHIP'. The following 6511 list shows only the upper-case form of each command. 6512 6513 `ABSOLUTE SECNAME' 6514 `ABSOLUTE SECNAME, SECNAME, ... SECNAME' 6515 Normally, `ld' includes in the output file all sections from all 6516 the input files. However, in an MRI-compatible script, you can 6517 use the `ABSOLUTE' command to restrict the sections that will be 6518 present in your output program. If the `ABSOLUTE' command is used 6519 at all in a script, then only the sections named explicitly in 6520 `ABSOLUTE' commands will appear in the linker output. You can 6521 still use other input sections (whatever you select on the command 6522 line, or using `LOAD') to resolve addresses in the output file. 6523 6524 `ALIAS OUT-SECNAME, IN-SECNAME' 6525 Use this command to place the data from input section IN-SECNAME 6526 in a section called OUT-SECNAME in the linker output file. 6527 6528 IN-SECNAME may be an integer. 6529 6530 `ALIGN SECNAME = EXPRESSION' 6531 Align the section called SECNAME to EXPRESSION. The EXPRESSION 6532 should be a power of two. 6533 6534 `BASE EXPRESSION' 6535 Use the value of EXPRESSION as the lowest address (other than 6536 absolute addresses) in the output file. 6537 6538 `CHIP EXPRESSION' 6539 `CHIP EXPRESSION, EXPRESSION' 6540 This command does nothing; it is accepted only for compatibility. 6541 6542 `END' 6543 This command does nothing whatever; it's only accepted for 6544 compatibility. 6545 6546 `FORMAT OUTPUT-FORMAT' 6547 Similar to the `OUTPUT_FORMAT' command in the more general linker 6548 language, but restricted to one of these output formats: 6549 6550 1. S-records, if OUTPUT-FORMAT is `S' 6551 6552 2. IEEE, if OUTPUT-FORMAT is `IEEE' 6553 6554 3. COFF (the `coff-m68k' variant in BFD), if OUTPUT-FORMAT is 6555 `COFF' 6556 6557 `LIST ANYTHING...' 6558 Print (to the standard output file) a link map, as produced by the 6559 `ld' command-line option `-M'. 6560 6561 The keyword `LIST' may be followed by anything on the same line, 6562 with no change in its effect. 6563 6564 `LOAD FILENAME' 6565 `LOAD FILENAME, FILENAME, ... FILENAME' 6566 Include one or more object file FILENAME in the link; this has the 6567 same effect as specifying FILENAME directly on the `ld' command 6568 line. 6569 6570 `NAME OUTPUT-NAME' 6571 OUTPUT-NAME is the name for the program produced by `ld'; the 6572 MRI-compatible command `NAME' is equivalent to the command-line 6573 option `-o' or the general script language command `OUTPUT'. 6574 6575 `ORDER SECNAME, SECNAME, ... SECNAME' 6576 `ORDER SECNAME SECNAME SECNAME' 6577 Normally, `ld' orders the sections in its output file in the order 6578 in which they first appear in the input files. In an 6579 MRI-compatible script, you can override this ordering with the 6580 `ORDER' command. The sections you list with `ORDER' will appear 6581 first in your output file, in the order specified. 6582 6583 `PUBLIC NAME=EXPRESSION' 6584 `PUBLIC NAME,EXPRESSION' 6585 `PUBLIC NAME EXPRESSION' 6586 Supply a value (EXPRESSION) for external symbol NAME used in the 6587 linker input files. 6588 6589 `SECT SECNAME, EXPRESSION' 6590 `SECT SECNAME=EXPRESSION' 6591 `SECT SECNAME EXPRESSION' 6592 You can use any of these three forms of the `SECT' command to 6593 specify the start address (EXPRESSION) for section SECNAME. If 6594 you have more than one `SECT' statement for the same SECNAME, only 6595 the _first_ sets the start address. 6596 6597 6598 File: ld.info, Node: GNU Free Documentation License, Next: LD Index, Prev: MRI, Up: Top 6599 6600 Appendix B GNU Free Documentation License 6601 ***************************************** 6602 6603 Version 1.3, 3 November 2008 6604 6605 Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. 6606 `http://fsf.org/' 6607 6608 Everyone is permitted to copy and distribute verbatim copies 6609 of this license document, but changing it is not allowed. 6610 6611 0. PREAMBLE 6612 6613 The purpose of this License is to make a manual, textbook, or other 6614 functional and useful document "free" in the sense of freedom: to 6615 assure everyone the effective freedom to copy and redistribute it, 6616 with or without modifying it, either commercially or 6617 noncommercially. Secondarily, this License preserves for the 6618 author and publisher a way to get credit for their work, while not 6619 being considered responsible for modifications made by others. 6620 6621 This License is a kind of "copyleft", which means that derivative 6622 works of the document must themselves be free in the same sense. 6623 It complements the GNU General Public License, which is a copyleft 6624 license designed for free software. 6625 6626 We have designed this License in order to use it for manuals for 6627 free software, because free software needs free documentation: a 6628 free program should come with manuals providing the same freedoms 6629 that the software does. But this License is not limited to 6630 software manuals; it can be used for any textual work, regardless 6631 of subject matter or whether it is published as a printed book. 6632 We recommend this License principally for works whose purpose is 6633 instruction or reference. 6634 6635 1. APPLICABILITY AND DEFINITIONS 6636 6637 This License applies to any manual or other work, in any medium, 6638 that contains a notice placed by the copyright holder saying it 6639 can be distributed under the terms of this License. Such a notice 6640 grants a world-wide, royalty-free license, unlimited in duration, 6641 to use that work under the conditions stated herein. The 6642 "Document", below, refers to any such manual or work. Any member 6643 of the public is a licensee, and is addressed as "you". You 6644 accept the license if you copy, modify or distribute the work in a 6645 way requiring permission under copyright law. 6646 6647 A "Modified Version" of the Document means any work containing the 6648 Document or a portion of it, either copied verbatim, or with 6649 modifications and/or translated into another language. 6650 6651 A "Secondary Section" is a named appendix or a front-matter section 6652 of the Document that deals exclusively with the relationship of the 6653 publishers or authors of the Document to the Document's overall 6654 subject (or to related matters) and contains nothing that could 6655 fall directly within that overall subject. (Thus, if the Document 6656 is in part a textbook of mathematics, a Secondary Section may not 6657 explain any mathematics.) The relationship could be a matter of 6658 historical connection with the subject or with related matters, or 6659 of legal, commercial, philosophical, ethical or political position 6660 regarding them. 6661 6662 The "Invariant Sections" are certain Secondary Sections whose 6663 titles are designated, as being those of Invariant Sections, in 6664 the notice that says that the Document is released under this 6665 License. If a section does not fit the above definition of 6666 Secondary then it is not allowed to be designated as Invariant. 6667 The Document may contain zero Invariant Sections. If the Document 6668 does not identify any Invariant Sections then there are none. 6669 6670 The "Cover Texts" are certain short passages of text that are 6671 listed, as Front-Cover Texts or Back-Cover Texts, in the notice 6672 that says that the Document is released under this License. A 6673 Front-Cover Text may be at most 5 words, and a Back-Cover Text may 6674 be at most 25 words. 6675 6676 A "Transparent" copy of the Document means a machine-readable copy, 6677 represented in a format whose specification is available to the 6678 general public, that is suitable for revising the document 6679 straightforwardly with generic text editors or (for images 6680 composed of pixels) generic paint programs or (for drawings) some 6681 widely available drawing editor, and that is suitable for input to 6682 text formatters or for automatic translation to a variety of 6683 formats suitable for input to text formatters. A copy made in an 6684 otherwise Transparent file format whose markup, or absence of 6685 markup, has been arranged to thwart or discourage subsequent 6686 modification by readers is not Transparent. An image format is 6687 not Transparent if used for any substantial amount of text. A 6688 copy that is not "Transparent" is called "Opaque". 6689 6690 Examples of suitable formats for Transparent copies include plain 6691 ASCII without markup, Texinfo input format, LaTeX input format, 6692 SGML or XML using a publicly available DTD, and 6693 standard-conforming simple HTML, PostScript or PDF designed for 6694 human modification. Examples of transparent image formats include 6695 PNG, XCF and JPG. Opaque formats include proprietary formats that 6696 can be read and edited only by proprietary word processors, SGML or 6697 XML for which the DTD and/or processing tools are not generally 6698 available, and the machine-generated HTML, PostScript or PDF 6699 produced by some word processors for output purposes only. 6700 6701 The "Title Page" means, for a printed book, the title page itself, 6702 plus such following pages as are needed to hold, legibly, the 6703 material this License requires to appear in the title page. For 6704 works in formats which do not have any title page as such, "Title 6705 Page" means the text near the most prominent appearance of the 6706 work's title, preceding the beginning of the body of the text. 6707 6708 The "publisher" means any person or entity that distributes copies 6709 of the Document to the public. 6710 6711 A section "Entitled XYZ" means a named subunit of the Document 6712 whose title either is precisely XYZ or contains XYZ in parentheses 6713 following text that translates XYZ in another language. (Here XYZ 6714 stands for a specific section name mentioned below, such as 6715 "Acknowledgements", "Dedications", "Endorsements", or "History".) 6716 To "Preserve the Title" of such a section when you modify the 6717 Document means that it remains a section "Entitled XYZ" according 6718 to this definition. 6719 6720 The Document may include Warranty Disclaimers next to the notice 6721 which states that this License applies to the Document. These 6722 Warranty Disclaimers are considered to be included by reference in 6723 this License, but only as regards disclaiming warranties: any other 6724 implication that these Warranty Disclaimers may have is void and 6725 has no effect on the meaning of this License. 6726 6727 2. VERBATIM COPYING 6728 6729 You may copy and distribute the Document in any medium, either 6730 commercially or noncommercially, provided that this License, the 6731 copyright notices, and the license notice saying this License 6732 applies to the Document are reproduced in all copies, and that you 6733 add no other conditions whatsoever to those of this License. You 6734 may not use technical measures to obstruct or control the reading 6735 or further copying of the copies you make or distribute. However, 6736 you may accept compensation in exchange for copies. If you 6737 distribute a large enough number of copies you must also follow 6738 the conditions in section 3. 6739 6740 You may also lend copies, under the same conditions stated above, 6741 and you may publicly display copies. 6742 6743 3. COPYING IN QUANTITY 6744 6745 If you publish printed copies (or copies in media that commonly 6746 have printed covers) of the Document, numbering more than 100, and 6747 the Document's license notice requires Cover Texts, you must 6748 enclose the copies in covers that carry, clearly and legibly, all 6749 these Cover Texts: Front-Cover Texts on the front cover, and 6750 Back-Cover Texts on the back cover. Both covers must also clearly 6751 and legibly identify you as the publisher of these copies. The 6752 front cover must present the full title with all words of the 6753 title equally prominent and visible. You may add other material 6754 on the covers in addition. Copying with changes limited to the 6755 covers, as long as they preserve the title of the Document and 6756 satisfy these conditions, can be treated as verbatim copying in 6757 other respects. 6758 6759 If the required texts for either cover are too voluminous to fit 6760 legibly, you should put the first ones listed (as many as fit 6761 reasonably) on the actual cover, and continue the rest onto 6762 adjacent pages. 6763 6764 If you publish or distribute Opaque copies of the Document 6765 numbering more than 100, you must either include a 6766 machine-readable Transparent copy along with each Opaque copy, or 6767 state in or with each Opaque copy a computer-network location from 6768 which the general network-using public has access to download 6769 using public-standard network protocols a complete Transparent 6770 copy of the Document, free of added material. If you use the 6771 latter option, you must take reasonably prudent steps, when you 6772 begin distribution of Opaque copies in quantity, to ensure that 6773 this Transparent copy will remain thus accessible at the stated 6774 location until at least one year after the last time you 6775 distribute an Opaque copy (directly or through your agents or 6776 retailers) of that edition to the public. 6777 6778 It is requested, but not required, that you contact the authors of 6779 the Document well before redistributing any large number of 6780 copies, to give them a chance to provide you with an updated 6781 version of the Document. 6782 6783 4. MODIFICATIONS 6784 6785 You may copy and distribute a Modified Version of the Document 6786 under the conditions of sections 2 and 3 above, provided that you 6787 release the Modified Version under precisely this License, with 6788 the Modified Version filling the role of the Document, thus 6789 licensing distribution and modification of the Modified Version to 6790 whoever possesses a copy of it. In addition, you must do these 6791 things in the Modified Version: 6792 6793 A. Use in the Title Page (and on the covers, if any) a title 6794 distinct from that of the Document, and from those of 6795 previous versions (which should, if there were any, be listed 6796 in the History section of the Document). You may use the 6797 same title as a previous version if the original publisher of 6798 that version gives permission. 6799 6800 B. List on the Title Page, as authors, one or more persons or 6801 entities responsible for authorship of the modifications in 6802 the Modified Version, together with at least five of the 6803 principal authors of the Document (all of its principal 6804 authors, if it has fewer than five), unless they release you 6805 from this requirement. 6806 6807 C. State on the Title page the name of the publisher of the 6808 Modified Version, as the publisher. 6809 6810 D. Preserve all the copyright notices of the Document. 6811 6812 E. Add an appropriate copyright notice for your modifications 6813 adjacent to the other copyright notices. 6814 6815 F. Include, immediately after the copyright notices, a license 6816 notice giving the public permission to use the Modified 6817 Version under the terms of this License, in the form shown in 6818 the Addendum below. 6819 6820 G. Preserve in that license notice the full lists of Invariant 6821 Sections and required Cover Texts given in the Document's 6822 license notice. 6823 6824 H. Include an unaltered copy of this License. 6825 6826 I. Preserve the section Entitled "History", Preserve its Title, 6827 and add to it an item stating at least the title, year, new 6828 authors, and publisher of the Modified Version as given on 6829 the Title Page. If there is no section Entitled "History" in 6830 the Document, create one stating the title, year, authors, 6831 and publisher of the Document as given on its Title Page, 6832 then add an item describing the Modified Version as stated in 6833 the previous sentence. 6834 6835 J. Preserve the network location, if any, given in the Document 6836 for public access to a Transparent copy of the Document, and 6837 likewise the network locations given in the Document for 6838 previous versions it was based on. These may be placed in 6839 the "History" section. You may omit a network location for a 6840 work that was published at least four years before the 6841 Document itself, or if the original publisher of the version 6842 it refers to gives permission. 6843 6844 K. For any section Entitled "Acknowledgements" or "Dedications", 6845 Preserve the Title of the section, and preserve in the 6846 section all the substance and tone of each of the contributor 6847 acknowledgements and/or dedications given therein. 6848 6849 L. Preserve all the Invariant Sections of the Document, 6850 unaltered in their text and in their titles. Section numbers 6851 or the equivalent are not considered part of the section 6852 titles. 6853 6854 M. Delete any section Entitled "Endorsements". Such a section 6855 may not be included in the Modified Version. 6856 6857 N. Do not retitle any existing section to be Entitled 6858 "Endorsements" or to conflict in title with any Invariant 6859 Section. 6860 6861 O. Preserve any Warranty Disclaimers. 6862 6863 If the Modified Version includes new front-matter sections or 6864 appendices that qualify as Secondary Sections and contain no 6865 material copied from the Document, you may at your option 6866 designate some or all of these sections as invariant. To do this, 6867 add their titles to the list of Invariant Sections in the Modified 6868 Version's license notice. These titles must be distinct from any 6869 other section titles. 6870 6871 You may add a section Entitled "Endorsements", provided it contains 6872 nothing but endorsements of your Modified Version by various 6873 parties--for example, statements of peer review or that the text 6874 has been approved by an organization as the authoritative 6875 definition of a standard. 6876 6877 You may add a passage of up to five words as a Front-Cover Text, 6878 and a passage of up to 25 words as a Back-Cover Text, to the end 6879 of the list of Cover Texts in the Modified Version. Only one 6880 passage of Front-Cover Text and one of Back-Cover Text may be 6881 added by (or through arrangements made by) any one entity. If the 6882 Document already includes a cover text for the same cover, 6883 previously added by you or by arrangement made by the same entity 6884 you are acting on behalf of, you may not add another; but you may 6885 replace the old one, on explicit permission from the previous 6886 publisher that added the old one. 6887 6888 The author(s) and publisher(s) of the Document do not by this 6889 License give permission to use their names for publicity for or to 6890 assert or imply endorsement of any Modified Version. 6891 6892 5. COMBINING DOCUMENTS 6893 6894 You may combine the Document with other documents released under 6895 this License, under the terms defined in section 4 above for 6896 modified versions, provided that you include in the combination 6897 all of the Invariant Sections of all of the original documents, 6898 unmodified, and list them all as Invariant Sections of your 6899 combined work in its license notice, and that you preserve all 6900 their Warranty Disclaimers. 6901 6902 The combined work need only contain one copy of this License, and 6903 multiple identical Invariant Sections may be replaced with a single 6904 copy. If there are multiple Invariant Sections with the same name 6905 but different contents, make the title of each such section unique 6906 by adding at the end of it, in parentheses, the name of the 6907 original author or publisher of that section if known, or else a 6908 unique number. Make the same adjustment to the section titles in 6909 the list of Invariant Sections in the license notice of the 6910 combined work. 6911 6912 In the combination, you must combine any sections Entitled 6913 "History" in the various original documents, forming one section 6914 Entitled "History"; likewise combine any sections Entitled 6915 "Acknowledgements", and any sections Entitled "Dedications". You 6916 must delete all sections Entitled "Endorsements." 6917 6918 6. COLLECTIONS OF DOCUMENTS 6919 6920 You may make a collection consisting of the Document and other 6921 documents released under this License, and replace the individual 6922 copies of this License in the various documents with a single copy 6923 that is included in the collection, provided that you follow the 6924 rules of this License for verbatim copying of each of the 6925 documents in all other respects. 6926 6927 You may extract a single document from such a collection, and 6928 distribute it individually under this License, provided you insert 6929 a copy of this License into the extracted document, and follow 6930 this License in all other respects regarding verbatim copying of 6931 that document. 6932 6933 7. AGGREGATION WITH INDEPENDENT WORKS 6934 6935 A compilation of the Document or its derivatives with other 6936 separate and independent documents or works, in or on a volume of 6937 a storage or distribution medium, is called an "aggregate" if the 6938 copyright resulting from the compilation is not used to limit the 6939 legal rights of the compilation's users beyond what the individual 6940 works permit. When the Document is included in an aggregate, this 6941 License does not apply to the other works in the aggregate which 6942 are not themselves derivative works of the Document. 6943 6944 If the Cover Text requirement of section 3 is applicable to these 6945 copies of the Document, then if the Document is less than one half 6946 of the entire aggregate, the Document's Cover Texts may be placed 6947 on covers that bracket the Document within the aggregate, or the 6948 electronic equivalent of covers if the Document is in electronic 6949 form. Otherwise they must appear on printed covers that bracket 6950 the whole aggregate. 6951 6952 8. TRANSLATION 6953 6954 Translation is considered a kind of modification, so you may 6955 distribute translations of the Document under the terms of section 6956 4. Replacing Invariant Sections with translations requires special 6957 permission from their copyright holders, but you may include 6958 translations of some or all Invariant Sections in addition to the 6959 original versions of these Invariant Sections. You may include a 6960 translation of this License, and all the license notices in the 6961 Document, and any Warranty Disclaimers, provided that you also 6962 include the original English version of this License and the 6963 original versions of those notices and disclaimers. In case of a 6964 disagreement between the translation and the original version of 6965 this License or a notice or disclaimer, the original version will 6966 prevail. 6967 6968 If a section in the Document is Entitled "Acknowledgements", 6969 "Dedications", or "History", the requirement (section 4) to 6970 Preserve its Title (section 1) will typically require changing the 6971 actual title. 6972 6973 9. TERMINATION 6974 6975 You may not copy, modify, sublicense, or distribute the Document 6976 except as expressly provided under this License. Any attempt 6977 otherwise to copy, modify, sublicense, or distribute it is void, 6978 and will automatically terminate your rights under this License. 6979 6980 However, if you cease all violation of this License, then your 6981 license from a particular copyright holder is reinstated (a) 6982 provisionally, unless and until the copyright holder explicitly 6983 and finally terminates your license, and (b) permanently, if the 6984 copyright holder fails to notify you of the violation by some 6985 reasonable means prior to 60 days after the cessation. 6986 6987 Moreover, your license from a particular copyright holder is 6988 reinstated permanently if the copyright holder notifies you of the 6989 violation by some reasonable means, this is the first time you have 6990 received notice of violation of this License (for any work) from 6991 that copyright holder, and you cure the violation prior to 30 days 6992 after your receipt of the notice. 6993 6994 Termination of your rights under this section does not terminate 6995 the licenses of parties who have received copies or rights from 6996 you under this License. If your rights have been terminated and 6997 not permanently reinstated, receipt of a copy of some or all of 6998 the same material does not give you any rights to use it. 6999 7000 10. FUTURE REVISIONS OF THIS LICENSE 7001 7002 The Free Software Foundation may publish new, revised versions of 7003 the GNU Free Documentation License from time to time. Such new 7004 versions will be similar in spirit to the present version, but may 7005 differ in detail to address new problems or concerns. See 7006 `http://www.gnu.org/copyleft/'. 7007 7008 Each version of the License is given a distinguishing version 7009 number. If the Document specifies that a particular numbered 7010 version of this License "or any later version" applies to it, you 7011 have the option of following the terms and conditions either of 7012 that specified version or of any later version that has been 7013 published (not as a draft) by the Free Software Foundation. If 7014 the Document does not specify a version number of this License, 7015 you may choose any version ever published (not as a draft) by the 7016 Free Software Foundation. If the Document specifies that a proxy 7017 can decide which future versions of this License can be used, that 7018 proxy's public statement of acceptance of a version permanently 7019 authorizes you to choose that version for the Document. 7020 7021 11. RELICENSING 7022 7023 "Massive Multiauthor Collaboration Site" (or "MMC Site") means any 7024 World Wide Web server that publishes copyrightable works and also 7025 provides prominent facilities for anybody to edit those works. A 7026 public wiki that anybody can edit is an example of such a server. 7027 A "Massive Multiauthor Collaboration" (or "MMC") contained in the 7028 site means any set of copyrightable works thus published on the MMC 7029 site. 7030 7031 "CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0 7032 license published by Creative Commons Corporation, a not-for-profit 7033 corporation with a principal place of business in San Francisco, 7034 California, as well as future copyleft versions of that license 7035 published by that same organization. 7036 7037 "Incorporate" means to publish or republish a Document, in whole or 7038 in part, as part of another Document. 7039 7040 An MMC is "eligible for relicensing" if it is licensed under this 7041 License, and if all works that were first published under this 7042 License somewhere other than this MMC, and subsequently 7043 incorporated in whole or in part into the MMC, (1) had no cover 7044 texts or invariant sections, and (2) were thus incorporated prior 7045 to November 1, 2008. 7046 7047 The operator of an MMC Site may republish an MMC contained in the 7048 site under CC-BY-SA on the same site at any time before August 1, 7049 2009, provided the MMC is eligible for relicensing. 7050 7051 7052 ADDENDUM: How to use this License for your documents 7053 ==================================================== 7054 7055 To use this License in a document you have written, include a copy of 7056 the License in the document and put the following copyright and license 7057 notices just after the title page: 7058 7059 Copyright (C) YEAR YOUR NAME. 7060 Permission is granted to copy, distribute and/or modify this document 7061 under the terms of the GNU Free Documentation License, Version 1.3 7062 or any later version published by the Free Software Foundation; 7063 with no Invariant Sections, no Front-Cover Texts, and no Back-Cover 7064 Texts. A copy of the license is included in the section entitled ``GNU 7065 Free Documentation License''. 7066 7067 If you have Invariant Sections, Front-Cover Texts and Back-Cover 7068 Texts, replace the "with...Texts." line with this: 7069 7070 with the Invariant Sections being LIST THEIR TITLES, with 7071 the Front-Cover Texts being LIST, and with the Back-Cover Texts 7072 being LIST. 7073 7074 If you have Invariant Sections without Cover Texts, or some other 7075 combination of the three, merge those two alternatives to suit the 7076 situation. 7077 7078 If your document contains nontrivial examples of program code, we 7079 recommend releasing these examples in parallel under your choice of 7080 free software license, such as the GNU General Public License, to 7081 permit their use in free software. 7082 7083 7084 File: ld.info, Node: LD Index, Prev: GNU Free Documentation License, Up: Top 7085 7086 LD Index 7087 ******** 7088 7089 [index] 7090 * Menu: 7091 7092 * ": Symbols. (line 6) 7093 * -(: Options. (line 696) 7094 * --accept-unknown-input-arch: Options. (line 714) 7095 * --add-needed: Options. (line 738) 7096 * --add-stdcall-alias: Options. (line 1583) 7097 * --allow-multiple-definition: Options. (line 989) 7098 * --allow-shlib-undefined: Options. (line 995) 7099 * --architecture=ARCH: Options. (line 123) 7100 * --as-needed: Options. (line 724) 7101 * --audit AUDITLIB: Options. (line 112) 7102 * --auxiliary=NAME: Options. (line 255) 7103 * --bank-window: Options. (line 2015) 7104 * --base-file: Options. (line 1588) 7105 * --be8: ARM. (line 28) 7106 * --bss-plt: PowerPC ELF32. (line 16) 7107 * --build-id: Options. (line 1545) 7108 * --build-id=STYLE: Options. (line 1545) 7109 * --check-sections: Options. (line 817) 7110 * --copy-dt-needed-entries: Options. (line 829) 7111 * --cref: Options. (line 849) 7112 * --default-imported-symver: Options. (line 1032) 7113 * --default-script=SCRIPT: Options. (line 541) 7114 * --default-symver: Options. (line 1028) 7115 * --defsym=SYMBOL=EXP: Options. (line 877) 7116 * --demangle[=STYLE]: Options. (line 890) 7117 * --depaudit AUDITLIB: Options. (line 177) 7118 * --disable-auto-image-base: Options. (line 1767) 7119 * --disable-auto-import: Options. (line 1902) 7120 * --disable-long-section-names: Options. (line 1598) 7121 * --disable-new-dtags: Options. (line 1508) 7122 * --disable-runtime-pseudo-reloc: Options. (line 1915) 7123 * --disable-stdcall-fixup: Options. (line 1620) 7124 * --discard-all: Options. (line 587) 7125 * --discard-locals: Options. (line 591) 7126 * --dll: Options. (line 1593) 7127 * --dll-search-prefix: Options. (line 1773) 7128 * --dotsyms: PowerPC64 ELF64. (line 33) 7129 * --dsbt-index: Options. (line 1992) 7130 * --dsbt-size: Options. (line 1987) 7131 * --dynamic-linker=FILE: Options. (line 903) 7132 * --dynamic-list-cpp-new: Options. (line 809) 7133 * --dynamic-list-cpp-typeinfo: Options. (line 813) 7134 * --dynamic-list-data: Options. (line 806) 7135 * --dynamic-list=DYNAMIC-LIST-FILE: Options. (line 793) 7136 * --dynamicbase: Options. (line 1951) 7137 * --eh-frame-hdr: Options. (line 1499) 7138 * --emit-relocs: Options. (line 476) 7139 * --emit-stack-syms: SPU ELF. (line 46) 7140 * --emit-stub-syms <1>: SPU ELF. (line 15) 7141 * --emit-stub-syms <2>: PowerPC ELF32. (line 47) 7142 * --emit-stub-syms: PowerPC64 ELF64. (line 29) 7143 * --enable-auto-image-base: Options. (line 1759) 7144 * --enable-auto-import: Options. (line 1782) 7145 * --enable-extra-pe-debug: Options. (line 1920) 7146 * --enable-long-section-names: Options. (line 1598) 7147 * --enable-new-dtags: Options. (line 1508) 7148 * --enable-runtime-pseudo-reloc: Options. (line 1907) 7149 * --enable-stdcall-fixup: Options. (line 1620) 7150 * --entry=ENTRY: Options. (line 187) 7151 * --error-unresolved-symbols: Options. (line 1452) 7152 * --exclude-all-symbols: Options. (line 1674) 7153 * --exclude-libs: Options. (line 197) 7154 * --exclude-modules-for-implib: Options. (line 208) 7155 * --exclude-symbols: Options. (line 1668) 7156 * --export-all-symbols: Options. (line 1644) 7157 * --export-dynamic: Options. (line 221) 7158 * --extra-overlay-stubs: SPU ELF. (line 19) 7159 * --fatal-warnings: Options. (line 910) 7160 * --file-alignment: Options. (line 1678) 7161 * --filter=NAME: Options. (line 276) 7162 * --fix-arm1176: ARM. (line 111) 7163 * --fix-cortex-a8: i960. (line 39) 7164 * --fix-v4bx: ARM. (line 49) 7165 * --fix-v4bx-interworking: ARM. (line 62) 7166 * --force-dynamic: Options. (line 485) 7167 * --force-exe-suffix: Options. (line 915) 7168 * --forceinteg: Options. (line 1956) 7169 * --format=FORMAT: Options. (line 134) 7170 * --format=VERSION: TI COFF. (line 6) 7171 * --gc-sections: Options. (line 925) 7172 * --got: Options. (line 2028) 7173 * --got=TYPE: M68K. (line 6) 7174 * --gpsize=VALUE: Options. (line 309) 7175 * --hash-size=NUMBER: Options. (line 1517) 7176 * --hash-style=STYLE: Options. (line 1525) 7177 * --heap: Options. (line 1684) 7178 * --help: Options. (line 962) 7179 * --image-base: Options. (line 1691) 7180 * --just-symbols=FILE: Options. (line 508) 7181 * --kill-at: Options. (line 1700) 7182 * --large-address-aware: Options. (line 1705) 7183 * --ld-generated-unwind-info: Options. (line 1503) 7184 * --leading-underscore: Options. (line 1638) 7185 * --library-path=DIR: Options. (line 368) 7186 * --library=NAMESPEC: Options. (line 335) 7187 * --local-store=lo:hi: SPU ELF. (line 24) 7188 * --major-image-version: Options. (line 1714) 7189 * --major-os-version: Options. (line 1719) 7190 * --major-subsystem-version: Options. (line 1723) 7191 * --merge-exidx-entries: i960. (line 48) 7192 * --minor-image-version: Options. (line 1728) 7193 * --minor-os-version: Options. (line 1733) 7194 * --minor-subsystem-version: Options. (line 1737) 7195 * --mri-script=MRI-CMDFILE: Options. (line 158) 7196 * --multi-subspace: HPPA ELF32. (line 6) 7197 * --nmagic: Options. (line 439) 7198 * --no-accept-unknown-input-arch: Options. (line 714) 7199 * --no-add-needed: Options. (line 738) 7200 * --no-allow-shlib-undefined: Options. (line 995) 7201 * --no-as-needed: Options. (line 724) 7202 * --no-bind: Options. (line 1970) 7203 * --no-check-sections: Options. (line 817) 7204 * --no-copy-dt-needed-entries: Options. (line 829) 7205 * --no-define-common: Options. (line 861) 7206 * --no-demangle: Options. (line 890) 7207 * --no-dotsyms: PowerPC64 ELF64. (line 33) 7208 * --no-enum-size-warning: ARM. (line 120) 7209 * --no-export-dynamic: Options. (line 221) 7210 * --no-fatal-warnings: Options. (line 910) 7211 * --no-fix-arm1176: ARM. (line 111) 7212 * --no-fix-cortex-a8: i960. (line 39) 7213 * --no-gc-sections: Options. (line 925) 7214 * --no-isolation: Options. (line 1963) 7215 * --no-keep-memory: Options. (line 974) 7216 * --no-leading-underscore: Options. (line 1638) 7217 * --no-merge-exidx-entries <1>: Options. (line 1999) 7218 * --no-merge-exidx-entries: i960. (line 48) 7219 * --no-multi-toc: PowerPC64 ELF64. (line 74) 7220 * --no-omagic: Options. (line 454) 7221 * --no-opd-optimize: PowerPC64 ELF64. (line 48) 7222 * --no-overlays: SPU ELF. (line 9) 7223 * --no-print-gc-sections: Options. (line 947) 7224 * --no-seh: Options. (line 1966) 7225 * --no-tls-optimize <1>: PowerPC ELF32. (line 51) 7226 * --no-tls-optimize: PowerPC64 ELF64. (line 43) 7227 * --no-toc-optimize: PowerPC64 ELF64. (line 60) 7228 * --no-trampoline: Options. (line 2009) 7229 * --no-undefined: Options. (line 981) 7230 * --no-undefined-version: Options. (line 1023) 7231 * --no-warn-mismatch: Options. (line 1036) 7232 * --no-warn-search-mismatch: Options. (line 1045) 7233 * --no-wchar-size-warning: ARM. (line 127) 7234 * --no-whole-archive: Options. (line 1049) 7235 * --noinhibit-exec: Options. (line 1053) 7236 * --non-overlapping-opd: PowerPC64 ELF64. (line 54) 7237 * --nxcompat: Options. (line 1959) 7238 * --oformat=OUTPUT-FORMAT: Options. (line 1065) 7239 * --omagic: Options. (line 445) 7240 * --out-implib: Options. (line 1750) 7241 * --output-def: Options. (line 1742) 7242 * --output=OUTPUT: Options. (line 460) 7243 * --pic-executable: Options. (line 1078) 7244 * --pic-veneer: ARM. (line 133) 7245 * --plugin: SPU ELF. (line 6) 7246 * --print-gc-sections: Options. (line 947) 7247 * --print-map: Options. (line 402) 7248 * --print-output-format: Options. (line 956) 7249 * --reduce-memory-overheads: Options. (line 1531) 7250 * --relax: Options. (line 1094) 7251 * --relax on i960: i960. (line 31) 7252 * --relax on PowerPC: PowerPC ELF32. (line 6) 7253 * --relax on Xtensa: Xtensa. (line 27) 7254 * --relocatable: Options. (line 489) 7255 * --retain-symbols-file=FILENAME: Options. (line 1120) 7256 * --script=SCRIPT: Options. (line 532) 7257 * --sdata-got: PowerPC ELF32. (line 33) 7258 * --section-alignment: Options. (line 1925) 7259 * --section-start=SECTIONNAME=ORG: Options. (line 1276) 7260 * --secure-plt: PowerPC ELF32. (line 26) 7261 * --sort-common: Options. (line 1218) 7262 * --sort-section=alignment: Options. (line 1233) 7263 * --sort-section=name: Options. (line 1229) 7264 * --split-by-file: Options. (line 1237) 7265 * --split-by-reloc: Options. (line 1242) 7266 * --stack: Options. (line 1931) 7267 * --stack-analysis: SPU ELF. (line 29) 7268 * --stats: Options. (line 1255) 7269 * --strip-all: Options. (line 519) 7270 * --strip-debug: Options. (line 523) 7271 * --stub-group-size: PowerPC64 ELF64. (line 6) 7272 * --stub-group-size=N <1>: HPPA ELF32. (line 12) 7273 * --stub-group-size=N: ARM. (line 138) 7274 * --subsystem: Options. (line 1938) 7275 * --support-old-code: ARM. (line 6) 7276 * --sysroot=DIRECTORY: Options. (line 1259) 7277 * --target-help: Options. (line 966) 7278 * --target1-abs: ARM. (line 32) 7279 * --target1-rel: ARM. (line 32) 7280 * --target2=TYPE: ARM. (line 37) 7281 * --thumb-entry=ENTRY: ARM. (line 17) 7282 * --trace: Options. (line 528) 7283 * --trace-symbol=SYMBOL: Options. (line 597) 7284 * --traditional-format: Options. (line 1264) 7285 * --tsaware: Options. (line 1976) 7286 * --undefined=SYMBOL: Options. (line 554) 7287 * --unique[=SECTION]: Options. (line 572) 7288 * --unresolved-symbols: Options. (line 1295) 7289 * --use-blx: ARM. (line 74) 7290 * --use-nul-prefixed-import-tables: ARM. (line 23) 7291 * --verbose[=NUMBER]: Options. (line 1324) 7292 * --version: Options. (line 581) 7293 * --version-script=VERSION-SCRIPTFILE: Options. (line 1332) 7294 * --vfp11-denorm-fix: ARM. (line 83) 7295 * --warn-alternate-em: Options. (line 1444) 7296 * --warn-common: Options. (line 1343) 7297 * --warn-constructors: Options. (line 1411) 7298 * --warn-multiple-gp: Options. (line 1416) 7299 * --warn-once: Options. (line 1430) 7300 * --warn-section-align: Options. (line 1434) 7301 * --warn-shared-textrel: Options. (line 1441) 7302 * --warn-unresolved-symbols: Options. (line 1447) 7303 * --wdmdriver: Options. (line 1973) 7304 * --whole-archive: Options. (line 1456) 7305 * --wrap=SYMBOL: Options. (line 1470) 7306 * -A ARCH: Options. (line 122) 7307 * -a KEYWORD: Options. (line 105) 7308 * -assert KEYWORD: Options. (line 745) 7309 * -b FORMAT: Options. (line 134) 7310 * -Bdynamic: Options. (line 748) 7311 * -Bgroup: Options. (line 758) 7312 * -Bshareable: Options. (line 1211) 7313 * -Bstatic: Options. (line 765) 7314 * -Bsymbolic: Options. (line 780) 7315 * -Bsymbolic-functions: Options. (line 787) 7316 * -c MRI-CMDFILE: Options. (line 158) 7317 * -call_shared: Options. (line 748) 7318 * -d: Options. (line 168) 7319 * -dc: Options. (line 168) 7320 * -dn: Options. (line 765) 7321 * -dp: Options. (line 168) 7322 * -dT SCRIPT: Options. (line 541) 7323 * -dy: Options. (line 748) 7324 * -E: Options. (line 221) 7325 * -e ENTRY: Options. (line 187) 7326 * -EB: Options. (line 248) 7327 * -EL: Options. (line 251) 7328 * -F NAME: Options. (line 276) 7329 * -f NAME: Options. (line 255) 7330 * -fini=NAME: Options. (line 300) 7331 * -g: Options. (line 306) 7332 * -G VALUE: Options. (line 309) 7333 * -h NAME: Options. (line 317) 7334 * -i: Options. (line 326) 7335 * -IFILE: Options. (line 903) 7336 * -init=NAME: Options. (line 329) 7337 * -L DIR: Options. (line 368) 7338 * -l NAMESPEC: Options. (line 335) 7339 * -M: Options. (line 402) 7340 * -m EMULATION: Options. (line 392) 7341 * -Map=MAPFILE: Options. (line 970) 7342 * -n: Options. (line 439) 7343 * -N: Options. (line 445) 7344 * -no-relax: Options. (line 1094) 7345 * -non_shared: Options. (line 765) 7346 * -nostdlib: Options. (line 1059) 7347 * -O LEVEL: Options. (line 466) 7348 * -o OUTPUT: Options. (line 460) 7349 * -P AUDITLIB: Options. (line 177) 7350 * -pie: Options. (line 1078) 7351 * -q: Options. (line 476) 7352 * -qmagic: Options. (line 1088) 7353 * -Qy: Options. (line 1091) 7354 * -r: Options. (line 489) 7355 * -R FILE: Options. (line 508) 7356 * -rpath-link=DIR: Options. (line 1156) 7357 * -rpath=DIR: Options. (line 1134) 7358 * -s: Options. (line 519) 7359 * -S: Options. (line 523) 7360 * -shared: Options. (line 1211) 7361 * -soname=NAME: Options. (line 317) 7362 * -static: Options. (line 765) 7363 * -t: Options. (line 528) 7364 * -T SCRIPT: Options. (line 532) 7365 * -Tbss=ORG: Options. (line 1285) 7366 * -Tdata=ORG: Options. (line 1285) 7367 * -Ttext-segment=ORG: Options. (line 1291) 7368 * -Ttext=ORG: Options. (line 1285) 7369 * -u SYMBOL: Options. (line 554) 7370 * -Ur: Options. (line 562) 7371 * -v: Options. (line 581) 7372 * -V: Options. (line 581) 7373 * -x: Options. (line 587) 7374 * -X: Options. (line 591) 7375 * -Y PATH: Options. (line 606) 7376 * -y SYMBOL: Options. (line 597) 7377 * -z defs: Options. (line 981) 7378 * -z KEYWORD: Options. (line 610) 7379 * -z muldefs: Options. (line 989) 7380 * .: Location Counter. (line 6) 7381 * /DISCARD/: Output Section Discarding. 7382 (line 21) 7383 * :PHDR: Output Section Phdr. 7384 (line 6) 7385 * =FILLEXP: Output Section Fill. 7386 (line 6) 7387 * >REGION: Output Section Region. 7388 (line 6) 7389 * [COMMON]: Input Section Common. 7390 (line 29) 7391 * ABSOLUTE (MRI): MRI. (line 33) 7392 * absolute and relocatable symbols: Expression Section. (line 6) 7393 * absolute expressions: Expression Section. (line 6) 7394 * ABSOLUTE(EXP): Builtin Functions. (line 10) 7395 * ADDR(SECTION): Builtin Functions. (line 17) 7396 * address, section: Output Section Address. 7397 (line 6) 7398 * ALIAS (MRI): MRI. (line 44) 7399 * ALIGN (MRI): MRI. (line 50) 7400 * align expression: Builtin Functions. (line 38) 7401 * align location counter: Builtin Functions. (line 38) 7402 * ALIGN(ALIGN): Builtin Functions. (line 38) 7403 * ALIGN(EXP,ALIGN): Builtin Functions. (line 38) 7404 * ALIGN(SECTION_ALIGN): Forced Output Alignment. 7405 (line 6) 7406 * aligned common symbols: WIN32. (line 424) 7407 * ALIGNOF(SECTION): Builtin Functions. (line 64) 7408 * allocating memory: MEMORY. (line 6) 7409 * architecture: Miscellaneous Commands. 7410 (line 72) 7411 * architectures: Options. (line 122) 7412 * archive files, from cmd line: Options. (line 335) 7413 * archive search path in linker script: File Commands. (line 74) 7414 * arithmetic: Expressions. (line 6) 7415 * arithmetic operators: Operators. (line 6) 7416 * ARM interworking support: ARM. (line 6) 7417 * ARM1176 erratum workaround: ARM. (line 111) 7418 * AS_NEEDED(FILES): File Commands. (line 54) 7419 * ASSERT: Miscellaneous Commands. 7420 (line 9) 7421 * assertion in linker script: Miscellaneous Commands. 7422 (line 9) 7423 * assignment in scripts: Assignments. (line 6) 7424 * AT(LMA): Output Section LMA. (line 6) 7425 * AT>LMA_REGION: Output Section LMA. (line 6) 7426 * automatic data imports: WIN32. (line 191) 7427 * back end: BFD. (line 6) 7428 * BASE (MRI): MRI. (line 54) 7429 * BE8: ARM. (line 28) 7430 * BFD canonical format: Canonical format. (line 11) 7431 * BFD requirements: BFD. (line 16) 7432 * big-endian objects: Options. (line 248) 7433 * binary input format: Options. (line 134) 7434 * BLOCK(EXP): Builtin Functions. (line 77) 7435 * bug criteria: Bug Criteria. (line 6) 7436 * bug reports: Bug Reporting. (line 6) 7437 * bugs in ld: Reporting Bugs. (line 6) 7438 * BYTE(EXPRESSION): Output Section Data. 7439 (line 6) 7440 * C++ constructors, arranging in link: Output Section Keywords. 7441 (line 19) 7442 * CHIP (MRI): MRI. (line 58) 7443 * COLLECT_NO_DEMANGLE: Environment. (line 29) 7444 * combining symbols, warnings on: Options. (line 1343) 7445 * command files: Scripts. (line 6) 7446 * command line: Options. (line 6) 7447 * common allocation: Options. (line 861) 7448 * common allocation in linker script: Miscellaneous Commands. 7449 (line 20) 7450 * common symbol placement: Input Section Common. 7451 (line 6) 7452 * COMMONPAGESIZE: Symbolic Constants. (line 13) 7453 * compatibility, MRI: Options. (line 158) 7454 * CONSTANT: Symbolic Constants. (line 6) 7455 * constants in linker scripts: Constants. (line 6) 7456 * constraints on output sections: Output Section Constraint. 7457 (line 6) 7458 * CONSTRUCTORS: Output Section Keywords. 7459 (line 19) 7460 * constructors: Options. (line 562) 7461 * constructors, arranging in link: Output Section Keywords. 7462 (line 19) 7463 * Cortex-A8 erratum workaround: i960. (line 39) 7464 * crash of linker: Bug Criteria. (line 9) 7465 * CREATE_OBJECT_SYMBOLS: Output Section Keywords. 7466 (line 9) 7467 * creating a DEF file: WIN32. (line 158) 7468 * cross reference table: Options. (line 849) 7469 * cross references: Miscellaneous Commands. 7470 (line 56) 7471 * current output location: Location Counter. (line 6) 7472 * data: Output Section Data. 7473 (line 6) 7474 * DATA_SEGMENT_ALIGN(MAXPAGESIZE, COMMONPAGESIZE): Builtin Functions. 7475 (line 82) 7476 * DATA_SEGMENT_END(EXP): Builtin Functions. (line 103) 7477 * DATA_SEGMENT_RELRO_END(OFFSET, EXP): Builtin Functions. (line 109) 7478 * dbx: Options. (line 1269) 7479 * DEF files, creating: Options. (line 1742) 7480 * default emulation: Environment. (line 21) 7481 * default input format: Environment. (line 9) 7482 * DEFINED(SYMBOL): Builtin Functions. (line 120) 7483 * deleting local symbols: Options. (line 587) 7484 * demangling, default: Environment. (line 29) 7485 * demangling, from command line: Options. (line 890) 7486 * direct linking to a dll: WIN32. (line 239) 7487 * discarding sections: Output Section Discarding. 7488 (line 6) 7489 * discontinuous memory: MEMORY. (line 6) 7490 * DLLs, creating: Options. (line 1742) 7491 * DLLs, linking to: Options. (line 1773) 7492 * dot: Location Counter. (line 6) 7493 * dot inside sections: Location Counter. (line 36) 7494 * dot outside sections: Location Counter. (line 66) 7495 * dynamic linker, from command line: Options. (line 903) 7496 * dynamic symbol table: Options. (line 221) 7497 * ELF program headers: PHDRS. (line 6) 7498 * emulation: Options. (line 392) 7499 * emulation, default: Environment. (line 21) 7500 * END (MRI): MRI. (line 62) 7501 * endianness: Options. (line 248) 7502 * entry point: Entry Point. (line 6) 7503 * entry point, from command line: Options. (line 187) 7504 * entry point, thumb: ARM. (line 17) 7505 * ENTRY(SYMBOL): Entry Point. (line 6) 7506 * error on valid input: Bug Criteria. (line 12) 7507 * example of linker script: Simple Example. (line 6) 7508 * exporting DLL symbols: WIN32. (line 19) 7509 * expression evaluation order: Evaluation. (line 6) 7510 * expression sections: Expression Section. (line 6) 7511 * expression, absolute: Builtin Functions. (line 10) 7512 * expressions: Expressions. (line 6) 7513 * EXTERN: Miscellaneous Commands. 7514 (line 13) 7515 * fatal signal: Bug Criteria. (line 9) 7516 * file name wildcard patterns: Input Section Wildcards. 7517 (line 6) 7518 * FILEHDR: PHDRS. (line 62) 7519 * filename symbols: Output Section Keywords. 7520 (line 9) 7521 * fill pattern, entire section: Output Section Fill. 7522 (line 6) 7523 * FILL(EXPRESSION): Output Section Data. 7524 (line 39) 7525 * finalization function: Options. (line 300) 7526 * first input file: File Commands. (line 82) 7527 * first instruction: Entry Point. (line 6) 7528 * FIX_V4BX: ARM. (line 49) 7529 * FIX_V4BX_INTERWORKING: ARM. (line 62) 7530 * FORCE_COMMON_ALLOCATION: Miscellaneous Commands. 7531 (line 20) 7532 * forcing input section alignment: Forced Input Alignment. 7533 (line 6) 7534 * forcing output section alignment: Forced Output Alignment. 7535 (line 6) 7536 * forcing the creation of dynamic sections: Options. (line 485) 7537 * FORMAT (MRI): MRI. (line 66) 7538 * functions in expressions: Builtin Functions. (line 6) 7539 * garbage collection <1>: Input Section Keep. (line 6) 7540 * garbage collection: Options. (line 925) 7541 * generating optimized output: Options. (line 466) 7542 * GNU linker: Overview. (line 6) 7543 * GNUTARGET: Environment. (line 9) 7544 * GROUP(FILES): File Commands. (line 47) 7545 * grouping input files: File Commands. (line 47) 7546 * groups of archives: Options. (line 696) 7547 * H8/300 support: H8/300. (line 6) 7548 * header size: Builtin Functions. (line 183) 7549 * heap size: Options. (line 1684) 7550 * help: Options. (line 962) 7551 * holes: Location Counter. (line 12) 7552 * holes, filling: Output Section Data. 7553 (line 39) 7554 * HPPA multiple sub-space stubs: HPPA ELF32. (line 6) 7555 * HPPA stub grouping: HPPA ELF32. (line 12) 7556 * i960 support: i960. (line 6) 7557 * image base: Options. (line 1691) 7558 * implicit linker scripts: Implicit Linker Scripts. 7559 (line 6) 7560 * import libraries: WIN32. (line 10) 7561 * INCLUDE FILENAME: File Commands. (line 9) 7562 * including a linker script: File Commands. (line 9) 7563 * including an entire archive: Options. (line 1456) 7564 * incremental link: Options. (line 326) 7565 * INHIBIT_COMMON_ALLOCATION: Miscellaneous Commands. 7566 (line 25) 7567 * initialization function: Options. (line 329) 7568 * initialized data in ROM: Output Section LMA. (line 39) 7569 * input file format in linker script: Format Commands. (line 35) 7570 * input filename symbols: Output Section Keywords. 7571 (line 9) 7572 * input files in linker scripts: File Commands. (line 19) 7573 * input files, displaying: Options. (line 528) 7574 * input format: Options. (line 134) 7575 * input object files in linker scripts: File Commands. (line 19) 7576 * input section alignment: Forced Input Alignment. 7577 (line 6) 7578 * input section basics: Input Section Basics. 7579 (line 6) 7580 * input section wildcards: Input Section Wildcards. 7581 (line 6) 7582 * input sections: Input Section. (line 6) 7583 * INPUT(FILES): File Commands. (line 19) 7584 * INSERT: Miscellaneous Commands. 7585 (line 30) 7586 * insert user script into default script: Miscellaneous Commands. 7587 (line 30) 7588 * integer notation: Constants. (line 6) 7589 * integer suffixes: Constants. (line 15) 7590 * internal object-file format: Canonical format. (line 11) 7591 * invalid input: Bug Criteria. (line 14) 7592 * K and M integer suffixes: Constants. (line 15) 7593 * KEEP: Input Section Keep. (line 6) 7594 * l =: MEMORY. (line 74) 7595 * lazy evaluation: Evaluation. (line 6) 7596 * ld bugs, reporting: Bug Reporting. (line 6) 7597 * LD_FEATURE(STRING): Miscellaneous Commands. 7598 (line 78) 7599 * LDEMULATION: Environment. (line 21) 7600 * len =: MEMORY. (line 74) 7601 * LENGTH =: MEMORY. (line 74) 7602 * LENGTH(MEMORY): Builtin Functions. (line 137) 7603 * library search path in linker script: File Commands. (line 74) 7604 * link map: Options. (line 402) 7605 * link-time runtime library search path: Options. (line 1156) 7606 * linker crash: Bug Criteria. (line 9) 7607 * linker script concepts: Basic Script Concepts. 7608 (line 6) 7609 * linker script example: Simple Example. (line 6) 7610 * linker script file commands: File Commands. (line 6) 7611 * linker script format: Script Format. (line 6) 7612 * linker script input object files: File Commands. (line 19) 7613 * linker script simple commands: Simple Commands. (line 6) 7614 * linker scripts: Scripts. (line 6) 7615 * LIST (MRI): MRI. (line 77) 7616 * little-endian objects: Options. (line 251) 7617 * LOAD (MRI): MRI. (line 84) 7618 * load address: Output Section LMA. (line 6) 7619 * LOADADDR(SECTION): Builtin Functions. (line 140) 7620 * loading, preventing: Output Section Type. 7621 (line 22) 7622 * local symbols, deleting: Options. (line 591) 7623 * location counter: Location Counter. (line 6) 7624 * LONG(EXPRESSION): Output Section Data. 7625 (line 6) 7626 * M and K integer suffixes: Constants. (line 15) 7627 * M68HC11 and 68HC12 support: M68HC11/68HC12. (line 6) 7628 * machine architecture: Miscellaneous Commands. 7629 (line 72) 7630 * machine dependencies: Machine Dependent. (line 6) 7631 * mapping input sections to output sections: Input Section. (line 6) 7632 * MAX: Builtin Functions. (line 143) 7633 * MAXPAGESIZE: Symbolic Constants. (line 10) 7634 * MEMORY: MEMORY. (line 6) 7635 * memory region attributes: MEMORY. (line 34) 7636 * memory regions: MEMORY. (line 6) 7637 * memory regions and sections: Output Section Region. 7638 (line 6) 7639 * memory usage: Options. (line 974) 7640 * MIN: Builtin Functions. (line 146) 7641 * Motorola 68K GOT generation: M68K. (line 6) 7642 * MRI compatibility: MRI. (line 6) 7643 * MSP430 extra sections: MSP430. (line 11) 7644 * NAME (MRI): MRI. (line 90) 7645 * name, section: Output Section Name. 7646 (line 6) 7647 * names: Symbols. (line 6) 7648 * naming the output file: Options. (line 460) 7649 * NEXT(EXP): Builtin Functions. (line 150) 7650 * NMAGIC: Options. (line 439) 7651 * NO_ENUM_SIZE_WARNING: ARM. (line 120) 7652 * NO_WCHAR_SIZE_WARNING: ARM. (line 127) 7653 * NOCROSSREFS(SECTIONS): Miscellaneous Commands. 7654 (line 56) 7655 * NOLOAD: Output Section Type. 7656 (line 22) 7657 * not enough room for program headers: Builtin Functions. (line 188) 7658 * o =: MEMORY. (line 69) 7659 * objdump -i: BFD. (line 6) 7660 * object file management: BFD. (line 6) 7661 * object files: Options. (line 29) 7662 * object formats available: BFD. (line 6) 7663 * object size: Options. (line 309) 7664 * OMAGIC: Options. (line 445) 7665 * ONLY_IF_RO: Output Section Constraint. 7666 (line 6) 7667 * ONLY_IF_RW: Output Section Constraint. 7668 (line 6) 7669 * opening object files: BFD outline. (line 6) 7670 * operators for arithmetic: Operators. (line 6) 7671 * options: Options. (line 6) 7672 * ORDER (MRI): MRI. (line 95) 7673 * org =: MEMORY. (line 69) 7674 * ORIGIN =: MEMORY. (line 69) 7675 * ORIGIN(MEMORY): Builtin Functions. (line 156) 7676 * orphan: Orphan Sections. (line 6) 7677 * output file after errors: Options. (line 1053) 7678 * output file format in linker script: Format Commands. (line 10) 7679 * output file name in linker script: File Commands. (line 64) 7680 * output format: Options. (line 956) 7681 * output section alignment: Forced Output Alignment. 7682 (line 6) 7683 * output section attributes: Output Section Attributes. 7684 (line 6) 7685 * output section data: Output Section Data. 7686 (line 6) 7687 * OUTPUT(FILENAME): File Commands. (line 64) 7688 * OUTPUT_ARCH(BFDARCH): Miscellaneous Commands. 7689 (line 72) 7690 * OUTPUT_FORMAT(BFDNAME): Format Commands. (line 10) 7691 * OVERLAY: Overlay Description. 7692 (line 6) 7693 * overlays: Overlay Description. 7694 (line 6) 7695 * partial link: Options. (line 489) 7696 * PE import table prefixing: ARM. (line 23) 7697 * PHDRS: PHDRS. (line 6) 7698 * PIC_VENEER: ARM. (line 133) 7699 * position independent executables: Options. (line 1080) 7700 * PowerPC ELF32 options: PowerPC ELF32. (line 16) 7701 * PowerPC GOT: PowerPC ELF32. (line 33) 7702 * PowerPC long branches: PowerPC ELF32. (line 6) 7703 * PowerPC PLT: PowerPC ELF32. (line 16) 7704 * PowerPC stub symbols: PowerPC ELF32. (line 47) 7705 * PowerPC TLS optimization: PowerPC ELF32. (line 51) 7706 * PowerPC64 dot symbols: PowerPC64 ELF64. (line 33) 7707 * PowerPC64 ELF64 options: PowerPC64 ELF64. (line 6) 7708 * PowerPC64 multi-TOC: PowerPC64 ELF64. (line 74) 7709 * PowerPC64 OPD optimization: PowerPC64 ELF64. (line 48) 7710 * PowerPC64 OPD spacing: PowerPC64 ELF64. (line 54) 7711 * PowerPC64 stub grouping: PowerPC64 ELF64. (line 6) 7712 * PowerPC64 stub symbols: PowerPC64 ELF64. (line 29) 7713 * PowerPC64 TLS optimization: PowerPC64 ELF64. (line 43) 7714 * PowerPC64 TOC optimization: PowerPC64 ELF64. (line 60) 7715 * precedence in expressions: Operators. (line 6) 7716 * prevent unnecessary loading: Output Section Type. 7717 (line 22) 7718 * program headers: PHDRS. (line 6) 7719 * program headers and sections: Output Section Phdr. 7720 (line 6) 7721 * program headers, not enough room: Builtin Functions. (line 188) 7722 * program segments: PHDRS. (line 6) 7723 * PROVIDE: PROVIDE. (line 6) 7724 * PROVIDE_HIDDEN: PROVIDE_HIDDEN. (line 6) 7725 * PUBLIC (MRI): MRI. (line 103) 7726 * QUAD(EXPRESSION): Output Section Data. 7727 (line 6) 7728 * quoted symbol names: Symbols. (line 6) 7729 * read-only text: Options. (line 439) 7730 * read/write from cmd line: Options. (line 445) 7731 * region alias: REGION_ALIAS. (line 6) 7732 * region names: REGION_ALIAS. (line 6) 7733 * REGION_ALIAS(ALIAS, REGION): REGION_ALIAS. (line 6) 7734 * regions of memory: MEMORY. (line 6) 7735 * relative expressions: Expression Section. (line 6) 7736 * relaxing addressing modes: Options. (line 1094) 7737 * relaxing on H8/300: H8/300. (line 9) 7738 * relaxing on i960: i960. (line 31) 7739 * relaxing on M68HC11: M68HC11/68HC12. (line 12) 7740 * relaxing on Xtensa: Xtensa. (line 27) 7741 * relocatable and absolute symbols: Expression Section. (line 6) 7742 * relocatable output: Options. (line 489) 7743 * removing sections: Output Section Discarding. 7744 (line 6) 7745 * reporting bugs in ld: Reporting Bugs. (line 6) 7746 * requirements for BFD: BFD. (line 16) 7747 * retain relocations in final executable: Options. (line 476) 7748 * retaining specified symbols: Options. (line 1120) 7749 * ROM initialized data: Output Section LMA. (line 39) 7750 * round up expression: Builtin Functions. (line 38) 7751 * round up location counter: Builtin Functions. (line 38) 7752 * runtime library name: Options. (line 317) 7753 * runtime library search path: Options. (line 1134) 7754 * runtime pseudo-relocation: WIN32. (line 217) 7755 * scaled integers: Constants. (line 15) 7756 * scommon section: Input Section Common. 7757 (line 20) 7758 * script files: Options. (line 532) 7759 * scripts: Scripts. (line 6) 7760 * search directory, from cmd line: Options. (line 368) 7761 * search path in linker script: File Commands. (line 74) 7762 * SEARCH_DIR(PATH): File Commands. (line 74) 7763 * SECT (MRI): MRI. (line 109) 7764 * section address: Output Section Address. 7765 (line 6) 7766 * section address in expression: Builtin Functions. (line 17) 7767 * section alignment: Builtin Functions. (line 64) 7768 * section alignment, warnings on: Options. (line 1434) 7769 * section data: Output Section Data. 7770 (line 6) 7771 * section fill pattern: Output Section Fill. 7772 (line 6) 7773 * section load address: Output Section LMA. (line 6) 7774 * section load address in expression: Builtin Functions. (line 140) 7775 * section name: Output Section Name. 7776 (line 6) 7777 * section name wildcard patterns: Input Section Wildcards. 7778 (line 6) 7779 * section size: Builtin Functions. (line 167) 7780 * section, assigning to memory region: Output Section Region. 7781 (line 6) 7782 * section, assigning to program header: Output Section Phdr. 7783 (line 6) 7784 * SECTIONS: SECTIONS. (line 6) 7785 * sections, discarding: Output Section Discarding. 7786 (line 6) 7787 * segment origins, cmd line: Options. (line 1285) 7788 * SEGMENT_START(SEGMENT, DEFAULT): Builtin Functions. (line 159) 7789 * segments, ELF: PHDRS. (line 6) 7790 * shared libraries: Options. (line 1213) 7791 * SHORT(EXPRESSION): Output Section Data. 7792 (line 6) 7793 * SIZEOF(SECTION): Builtin Functions. (line 167) 7794 * SIZEOF_HEADERS: Builtin Functions. (line 183) 7795 * small common symbols: Input Section Common. 7796 (line 20) 7797 * SORT: Input Section Wildcards. 7798 (line 63) 7799 * SORT_BY_ALIGNMENT: Input Section Wildcards. 7800 (line 54) 7801 * SORT_BY_INIT_PRIORITY: Input Section Wildcards. 7802 (line 58) 7803 * SORT_BY_NAME: Input Section Wildcards. 7804 (line 46) 7805 * SPU: SPU ELF. (line 29) 7806 * SPU ELF options: SPU ELF. (line 6) 7807 * SPU extra overlay stubs: SPU ELF. (line 19) 7808 * SPU local store size: SPU ELF. (line 24) 7809 * SPU overlay stub symbols: SPU ELF. (line 15) 7810 * SPU overlays: SPU ELF. (line 9) 7811 * SPU plugins: SPU ELF. (line 6) 7812 * SQUAD(EXPRESSION): Output Section Data. 7813 (line 6) 7814 * stack size: Options. (line 1931) 7815 * standard Unix system: Options. (line 7) 7816 * start of execution: Entry Point. (line 6) 7817 * STARTUP(FILENAME): File Commands. (line 82) 7818 * strip all symbols: Options. (line 519) 7819 * strip debugger symbols: Options. (line 523) 7820 * stripping all but some symbols: Options. (line 1120) 7821 * STUB_GROUP_SIZE: ARM. (line 138) 7822 * SUBALIGN(SUBSECTION_ALIGN): Forced Input Alignment. 7823 (line 6) 7824 * suffixes for integers: Constants. (line 15) 7825 * symbol defaults: Builtin Functions. (line 120) 7826 * symbol definition, scripts: Assignments. (line 6) 7827 * symbol names: Symbols. (line 6) 7828 * symbol tracing: Options. (line 597) 7829 * symbol versions: VERSION. (line 6) 7830 * symbol-only input: Options. (line 508) 7831 * symbolic constants: Symbolic Constants. (line 6) 7832 * symbols, from command line: Options. (line 877) 7833 * symbols, relocatable and absolute: Expression Section. (line 6) 7834 * symbols, retaining selectively: Options. (line 1120) 7835 * synthesizing linker: Options. (line 1094) 7836 * synthesizing on H8/300: H8/300. (line 14) 7837 * TARGET(BFDNAME): Format Commands. (line 35) 7838 * TARGET1: ARM. (line 32) 7839 * TARGET2: ARM. (line 37) 7840 * text segment origin, cmd line: Options. (line 1292) 7841 * thumb entry point: ARM. (line 17) 7842 * TI COFF versions: TI COFF. (line 6) 7843 * traditional format: Options. (line 1264) 7844 * trampoline generation on M68HC11: M68HC11/68HC12. (line 31) 7845 * trampoline generation on M68HC12: M68HC11/68HC12. (line 31) 7846 * unallocated address, next: Builtin Functions. (line 150) 7847 * undefined symbol: Options. (line 554) 7848 * undefined symbol in linker script: Miscellaneous Commands. 7849 (line 13) 7850 * undefined symbols, warnings on: Options. (line 1430) 7851 * uninitialized data placement: Input Section Common. 7852 (line 6) 7853 * unspecified memory: Output Section Data. 7854 (line 39) 7855 * usage: Options. (line 962) 7856 * USE_BLX: ARM. (line 74) 7857 * using a DEF file: WIN32. (line 57) 7858 * using auto-export functionality: WIN32. (line 22) 7859 * Using decorations: WIN32. (line 162) 7860 * variables, defining: Assignments. (line 6) 7861 * verbose[=NUMBER]: Options. (line 1324) 7862 * version: Options. (line 581) 7863 * version script: VERSION. (line 6) 7864 * version script, symbol versions: Options. (line 1332) 7865 * VERSION {script text}: VERSION. (line 6) 7866 * versions of symbols: VERSION. (line 6) 7867 * VFP11_DENORM_FIX: ARM. (line 83) 7868 * warnings, on combining symbols: Options. (line 1343) 7869 * warnings, on section alignment: Options. (line 1434) 7870 * warnings, on undefined symbols: Options. (line 1430) 7871 * weak externals: WIN32. (line 407) 7872 * what is this?: Overview. (line 6) 7873 * wildcard file name patterns: Input Section Wildcards. 7874 (line 6) 7875 * Xtensa options: Xtensa. (line 56) 7876 * Xtensa processors: Xtensa. (line 6) 7877 7878 7879 7880 Tag Table: 7881 Node: Top816 7882 Node: Overview1602 7883 Node: Invocation2716 7884 Node: Options3124 7885 Node: Environment94796 7886 Node: Scripts96556 7887 Node: Basic Script Concepts98290 7888 Node: Script Format100997 7889 Node: Simple Example101860 7890 Node: Simple Commands104956 7891 Node: Entry Point105462 7892 Node: File Commands106395 7893 Node: Format Commands110396 7894 Node: REGION_ALIAS112352 7895 Node: Miscellaneous Commands117184 7896 Node: Assignments120792 7897 Node: Simple Assignments121283 7898 Node: PROVIDE123019 7899 Node: PROVIDE_HIDDEN124224 7900 Node: Source Code Reference124468 7901 Node: SECTIONS128048 7902 Node: Output Section Description129939 7903 Node: Output Section Name131026 7904 Node: Output Section Address131902 7905 Node: Input Section134137 7906 Node: Input Section Basics134938 7907 Node: Input Section Wildcards138844 7908 Node: Input Section Common143844 7909 Node: Input Section Keep145326 7910 Node: Input Section Example145816 7911 Node: Output Section Data146784 7912 Node: Output Section Keywords149561 7913 Node: Output Section Discarding153130 7914 Node: Output Section Attributes154311 7915 Node: Output Section Type155412 7916 Node: Output Section LMA156483 7917 Node: Forced Output Alignment159554 7918 Node: Forced Input Alignment159822 7919 Node: Output Section Constraint160211 7920 Node: Output Section Region160639 7921 Node: Output Section Phdr161072 7922 Node: Output Section Fill161736 7923 Node: Overlay Description162878 7924 Node: MEMORY167181 7925 Node: PHDRS171516 7926 Node: VERSION176770 7927 Node: Expressions184863 7928 Node: Constants185792 7929 Node: Symbolic Constants186667 7930 Node: Symbols187218 7931 Node: Orphan Sections187965 7932 Node: Location Counter189129 7933 Node: Operators193565 7934 Node: Evaluation194487 7935 Node: Expression Section195851 7936 Node: Builtin Functions199508 7937 Node: Implicit Linker Scripts207469 7938 Node: Machine Dependent208244 7939 Node: H8/300209260 7940 Node: i960210885 7941 Node: M68HC11/68HC12213089 7942 Node: ARM214543 7943 Node: HPPA ELF32222506 7944 Node: M68K224129 7945 Node: MMIX225038 7946 Node: MSP430226203 7947 Node: PowerPC ELF32227252 7948 Node: PowerPC64 ELF64230088 7949 Node: SPU ELF234504 7950 Node: TI COFF237136 7951 Node: WIN32237662 7952 Node: Xtensa257787 7953 Node: BFD260752 7954 Node: BFD outline262207 7955 Node: BFD information loss263493 7956 Node: Canonical format266010 7957 Node: Reporting Bugs270367 7958 Node: Bug Criteria271061 7959 Node: Bug Reporting271760 7960 Node: MRI278799 7961 Node: GNU Free Documentation License283442 7962 Node: LD Index308598 7963 7964 End Tag Table 7965