1 // icf.cc -- Identical Code Folding. 2 // 3 // Copyright (C) 2009-2014 Free Software Foundation, Inc. 4 // Written by Sriraman Tallam <tmsriram (at) google.com>. 5 6 // This file is part of gold. 7 8 // This program is free software; you can redistribute it and/or modify 9 // it under the terms of the GNU General Public License as published by 10 // the Free Software Foundation; either version 3 of the License, or 11 // (at your option) any later version. 12 13 // This program is distributed in the hope that it will be useful, 14 // but WITHOUT ANY WARRANTY; without even the implied warranty of 15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 16 // GNU General Public License for more details. 17 18 // You should have received a copy of the GNU General Public License 19 // along with this program; if not, write to the Free Software 20 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, 21 // MA 02110-1301, USA. 22 23 // Identical Code Folding Algorithm 24 // ---------------------------------- 25 // Detecting identical functions is done here and the basic algorithm 26 // is as follows. A checksum is computed on each foldable section using 27 // its contents and relocations. If the symbol name corresponding to 28 // a relocation is known it is used to compute the checksum. If the 29 // symbol name is not known the stringified name of the object and the 30 // section number pointed to by the relocation is used. The checksums 31 // are stored as keys in a hash map and a section is identical to some 32 // other section if its checksum is already present in the hash map. 33 // Checksum collisions are handled by using a multimap and explicitly 34 // checking the contents when two sections have the same checksum. 35 // 36 // However, two functions A and B with identical text but with 37 // relocations pointing to different foldable sections can be identical if 38 // the corresponding foldable sections to which their relocations point to 39 // turn out to be identical. Hence, this checksumming process must be 40 // done repeatedly until convergence is obtained. Here is an example for 41 // the following case : 42 // 43 // int funcA () int funcB () 44 // { { 45 // return foo(); return goo(); 46 // } } 47 // 48 // The functions funcA and funcB are identical if functions foo() and 49 // goo() are identical. 50 // 51 // Hence, as described above, we repeatedly do the checksumming, 52 // assigning identical functions to the same group, until convergence is 53 // obtained. Now, we have two different ways to do this depending on how 54 // we initialize. 55 // 56 // Algorithm I : 57 // ----------- 58 // We can start with marking all functions as different and repeatedly do 59 // the checksumming. This has the advantage that we do not need to wait 60 // for convergence. We can stop at any point and correctness will be 61 // guaranteed although not all cases would have been found. However, this 62 // has a problem that some cases can never be found even if it is run until 63 // convergence. Here is an example with mutually recursive functions : 64 // 65 // int funcA (int a) int funcB (int a) 66 // { { 67 // if (a == 1) if (a == 1) 68 // return 1; return 1; 69 // return 1 + funcB(a - 1); return 1 + funcA(a - 1); 70 // } } 71 // 72 // In this example funcA and funcB are identical and one of them could be 73 // folded into the other. However, if we start with assuming that funcA 74 // and funcB are not identical, the algorithm, even after it is run to 75 // convergence, cannot detect that they are identical. It should be noted 76 // that even if the functions were self-recursive, Algorithm I cannot catch 77 // that they are identical, at least as is. 78 // 79 // Algorithm II : 80 // ------------ 81 // Here we start with marking all functions as identical and then repeat 82 // the checksumming until convergence. This can detect the above case 83 // mentioned above. It can detect all cases that Algorithm I can and more. 84 // However, the caveat is that it has to be run to convergence. It cannot 85 // be stopped arbitrarily like Algorithm I as correctness cannot be 86 // guaranteed. Algorithm II is not implemented. 87 // 88 // Algorithm I is used because experiments show that about three 89 // iterations are more than enough to achieve convergence. Algorithm I can 90 // handle recursive calls if it is changed to use a special common symbol 91 // for recursive relocs. This seems to be the most common case that 92 // Algorithm I could not catch as is. Mutually recursive calls are not 93 // frequent and Algorithm I wins because of its ability to be stopped 94 // arbitrarily. 95 // 96 // Caveat with using function pointers : 97 // ------------------------------------ 98 // 99 // Programs using function pointer comparisons/checks should use function 100 // folding with caution as the result of such comparisons could be different 101 // when folding takes place. This could lead to unexpected run-time 102 // behaviour. 103 // 104 // Safe Folding : 105 // ------------ 106 // 107 // ICF in safe mode folds only ctors and dtors if their function pointers can 108 // never be taken. Also, for X86-64, safe folding uses the relocation 109 // type to determine if a function's pointer is taken or not and only folds 110 // functions whose pointers are definitely not taken. 111 // 112 // Caveat with safe folding : 113 // ------------------------ 114 // 115 // This applies only to x86_64. 116 // 117 // Position independent executables are created from PIC objects (compiled 118 // with -fPIC) and/or PIE objects (compiled with -fPIE). For PIE objects, the 119 // relocation types for function pointer taken and a call are the same. 120 // Now, it is not always possible to tell if an object used in the link of 121 // a pie executable is a PIC object or a PIE object. Hence, for pie 122 // executables, using relocation types to disambiguate function pointers is 123 // currently disabled. 124 // 125 // Further, it is not correct to use safe folding to build non-pie 126 // executables using PIC/PIE objects. PIC/PIE objects have different 127 // relocation types for function pointers than non-PIC objects, and the 128 // current implementation of safe folding does not handle those relocation 129 // types. Hence, if used, functions whose pointers are taken could still be 130 // folded causing unpredictable run-time behaviour if the pointers were used 131 // in comparisons. 132 // 133 // 134 // 135 // How to run : --icf=[safe|all|none] 136 // Optional parameters : --icf-iterations <num> --print-icf-sections 137 // 138 // Performance : Less than 20 % link-time overhead on industry strength 139 // applications. Up to 6 % text size reductions. 140 141 #include "gold.h" 142 #include "object.h" 143 #include "gc.h" 144 #include "icf.h" 145 #include "symtab.h" 146 #include "libiberty.h" 147 #include "demangle.h" 148 #include "elfcpp.h" 149 #include "int_encoding.h" 150 151 namespace gold 152 { 153 154 // This function determines if a section or a group of identical 155 // sections has unique contents. Such unique sections or groups can be 156 // declared final and need not be processed any further. 157 // Parameters : 158 // ID_SECTION : Vector mapping a section index to a Section_id pair. 159 // IS_SECN_OR_GROUP_UNIQUE : To check if a section or a group of identical 160 // sections is already known to be unique. 161 // SECTION_CONTENTS : Contains the section's text and relocs to sections 162 // that cannot be folded. SECTION_CONTENTS are NULL 163 // implies that this function is being called for the 164 // first time before the first iteration of icf. 165 166 static void 167 preprocess_for_unique_sections(const std::vector<Section_id>& id_section, 168 std::vector<bool>* is_secn_or_group_unique, 169 std::vector<std::string>* section_contents) 170 { 171 Unordered_map<uint32_t, unsigned int> uniq_map; 172 std::pair<Unordered_map<uint32_t, unsigned int>::iterator, bool> 173 uniq_map_insert; 174 175 for (unsigned int i = 0; i < id_section.size(); i++) 176 { 177 if ((*is_secn_or_group_unique)[i]) 178 continue; 179 180 uint32_t cksum; 181 Section_id secn = id_section[i]; 182 section_size_type plen; 183 if (section_contents == NULL) 184 { 185 // Lock the object so we can read from it. This is only called 186 // single-threaded from queue_middle_tasks, so it is OK to lock. 187 // Unfortunately we have no way to pass in a Task token. 188 const Task* dummy_task = reinterpret_cast<const Task*>(-1); 189 Task_lock_obj<Object> tl(dummy_task, secn.first); 190 const unsigned char* contents; 191 contents = secn.first->section_contents(secn.second, 192 &plen, 193 false); 194 cksum = xcrc32(contents, plen, 0xffffffff); 195 } 196 else 197 { 198 const unsigned char* contents_array = reinterpret_cast 199 <const unsigned char*>((*section_contents)[i].c_str()); 200 cksum = xcrc32(contents_array, (*section_contents)[i].length(), 201 0xffffffff); 202 } 203 uniq_map_insert = uniq_map.insert(std::make_pair(cksum, i)); 204 if (uniq_map_insert.second) 205 { 206 (*is_secn_or_group_unique)[i] = true; 207 } 208 else 209 { 210 (*is_secn_or_group_unique)[i] = false; 211 (*is_secn_or_group_unique)[uniq_map_insert.first->second] = false; 212 } 213 } 214 } 215 216 // This returns the buffer containing the section's contents, both 217 // text and relocs. Relocs are differentiated as those pointing to 218 // sections that could be folded and those that cannot. Only relocs 219 // pointing to sections that could be folded are recomputed on 220 // subsequent invocations of this function. 221 // Parameters : 222 // FIRST_ITERATION : true if it is the first invocation. 223 // SECN : Section for which contents are desired. 224 // SECTION_NUM : Unique section number of this section. 225 // NUM_TRACKED_RELOCS : Vector reference to store the number of relocs 226 // to ICF sections. 227 // KEPT_SECTION_ID : Vector which maps folded sections to kept sections. 228 // SECTION_CONTENTS : Store the section's text and relocs to non-ICF 229 // sections. 230 231 static std::string 232 get_section_contents(bool first_iteration, 233 const Section_id& secn, 234 unsigned int section_num, 235 unsigned int* num_tracked_relocs, 236 Symbol_table* symtab, 237 const std::vector<unsigned int>& kept_section_id, 238 std::vector<std::string>* section_contents) 239 { 240 // Lock the object so we can read from it. This is only called 241 // single-threaded from queue_middle_tasks, so it is OK to lock. 242 // Unfortunately we have no way to pass in a Task token. 243 const Task* dummy_task = reinterpret_cast<const Task*>(-1); 244 Task_lock_obj<Object> tl(dummy_task, secn.first); 245 246 section_size_type plen; 247 const unsigned char* contents = NULL; 248 if (first_iteration) 249 contents = secn.first->section_contents(secn.second, &plen, false); 250 251 // The buffer to hold all the contents including relocs. A checksum 252 // is then computed on this buffer. 253 std::string buffer; 254 std::string icf_reloc_buffer; 255 256 if (num_tracked_relocs) 257 *num_tracked_relocs = 0; 258 259 Icf::Reloc_info_list& reloc_info_list = 260 symtab->icf()->reloc_info_list(); 261 262 Icf::Reloc_info_list::iterator it_reloc_info_list = 263 reloc_info_list.find(secn); 264 265 buffer.clear(); 266 icf_reloc_buffer.clear(); 267 268 // Process relocs and put them into the buffer. 269 270 if (it_reloc_info_list != reloc_info_list.end()) 271 { 272 Icf::Sections_reachable_info &v = 273 (it_reloc_info_list->second).section_info; 274 // Stores the information of the symbol pointed to by the reloc. 275 const Icf::Symbol_info &s = (it_reloc_info_list->second).symbol_info; 276 // Stores the addend and the symbol value. 277 Icf::Addend_info &a = (it_reloc_info_list->second).addend_info; 278 // Stores the offset of the reloc. 279 const Icf::Offset_info &o = (it_reloc_info_list->second).offset_info; 280 const Icf::Reloc_addend_size_info &reloc_addend_size_info = 281 (it_reloc_info_list->second).reloc_addend_size_info; 282 Icf::Sections_reachable_info::iterator it_v = v.begin(); 283 Icf::Symbol_info::const_iterator it_s = s.begin(); 284 Icf::Addend_info::iterator it_a = a.begin(); 285 Icf::Offset_info::const_iterator it_o = o.begin(); 286 Icf::Reloc_addend_size_info::const_iterator it_addend_size = 287 reloc_addend_size_info.begin(); 288 289 for (; it_v != v.end(); ++it_v, ++it_s, ++it_a, ++it_o, ++it_addend_size) 290 { 291 if (first_iteration 292 && it_v->first != NULL) 293 { 294 Symbol_location loc; 295 loc.object = it_v->first; 296 loc.shndx = it_v->second; 297 loc.offset = convert_types<off_t, long long>(it_a->first 298 + it_a->second); 299 // Look through function descriptors 300 parameters->target().function_location(&loc); 301 if (loc.shndx != it_v->second) 302 { 303 it_v->second = loc.shndx; 304 // Modify symvalue/addend to the code entry. 305 it_a->first = loc.offset; 306 it_a->second = 0; 307 } 308 } 309 310 // ADDEND_STR stores the symbol value and addend and offset, 311 // each at most 16 hex digits long. it_a points to a pair 312 // where first is the symbol value and second is the 313 // addend. 314 char addend_str[50]; 315 316 // It would be nice if we could use format macros in inttypes.h 317 // here but there are not in ISO/IEC C++ 1998. 318 snprintf(addend_str, sizeof(addend_str), "%llx %llx %llux", 319 static_cast<long long>((*it_a).first), 320 static_cast<long long>((*it_a).second), 321 static_cast<unsigned long long>(*it_o)); 322 323 // If the symbol pointed to by the reloc is not in an ordinary 324 // section or if the symbol type is not FROM_OBJECT, then the 325 // object is NULL. 326 if (it_v->first == NULL) 327 { 328 if (first_iteration) 329 { 330 // If the symbol name is available, use it. 331 if ((*it_s) != NULL) 332 buffer.append((*it_s)->name()); 333 // Append the addend. 334 buffer.append(addend_str); 335 buffer.append("@"); 336 } 337 continue; 338 } 339 340 Section_id reloc_secn(it_v->first, it_v->second); 341 342 // If this reloc turns back and points to the same section, 343 // like a recursive call, use a special symbol to mark this. 344 if (reloc_secn.first == secn.first 345 && reloc_secn.second == secn.second) 346 { 347 if (first_iteration) 348 { 349 buffer.append("R"); 350 buffer.append(addend_str); 351 buffer.append("@"); 352 } 353 continue; 354 } 355 Icf::Uniq_secn_id_map& section_id_map = 356 symtab->icf()->section_to_int_map(); 357 Icf::Uniq_secn_id_map::iterator section_id_map_it = 358 section_id_map.find(reloc_secn); 359 bool is_sym_preemptible = (*it_s != NULL 360 && !(*it_s)->is_from_dynobj() 361 && !(*it_s)->is_undefined() 362 && (*it_s)->is_preemptible()); 363 if (!is_sym_preemptible 364 && section_id_map_it != section_id_map.end()) 365 { 366 // This is a reloc to a section that might be folded. 367 if (num_tracked_relocs) 368 (*num_tracked_relocs)++; 369 370 char kept_section_str[10]; 371 unsigned int secn_id = section_id_map_it->second; 372 snprintf(kept_section_str, sizeof(kept_section_str), "%u", 373 kept_section_id[secn_id]); 374 if (first_iteration) 375 { 376 buffer.append("ICF_R"); 377 buffer.append(addend_str); 378 } 379 icf_reloc_buffer.append(kept_section_str); 380 // Append the addend. 381 icf_reloc_buffer.append(addend_str); 382 icf_reloc_buffer.append("@"); 383 } 384 else 385 { 386 // This is a reloc to a section that cannot be folded. 387 // Process it only in the first iteration. 388 if (!first_iteration) 389 continue; 390 391 uint64_t secn_flags = (it_v->first)->section_flags(it_v->second); 392 // This reloc points to a merge section. Hash the 393 // contents of this section. 394 if ((secn_flags & elfcpp::SHF_MERGE) != 0 395 && parameters->target().can_icf_inline_merge_sections()) 396 { 397 uint64_t entsize = 398 (it_v->first)->section_entsize(it_v->second); 399 long long offset = it_a->first; 400 401 unsigned long long addend = it_a->second; 402 // Ignoring the addend when it is a negative value. See the 403 // comments in Merged_symbol_value::Value in object.h. 404 if (addend < 0xffffff00) 405 offset = offset + addend; 406 407 // For SHT_REL relocation sections, the addend is stored in the 408 // text section at the relocation offset. 409 uint64_t reloc_addend_value = 0; 410 const unsigned char* reloc_addend_ptr = 411 contents + static_cast<unsigned long long>(*it_o); 412 switch(*it_addend_size) 413 { 414 case 0: 415 { 416 break; 417 } 418 case 1: 419 { 420 reloc_addend_value = 421 read_from_pointer<8>(reloc_addend_ptr); 422 break; 423 } 424 case 2: 425 { 426 reloc_addend_value = 427 read_from_pointer<16>(reloc_addend_ptr); 428 break; 429 } 430 case 4: 431 { 432 reloc_addend_value = 433 read_from_pointer<32>(reloc_addend_ptr); 434 break; 435 } 436 case 8: 437 { 438 reloc_addend_value = 439 read_from_pointer<64>(reloc_addend_ptr); 440 break; 441 } 442 default: 443 gold_unreachable(); 444 } 445 offset = offset + reloc_addend_value; 446 447 section_size_type secn_len; 448 const unsigned char* str_contents = 449 (it_v->first)->section_contents(it_v->second, 450 &secn_len, 451 false) + offset; 452 if ((secn_flags & elfcpp::SHF_STRINGS) != 0) 453 { 454 // String merge section. 455 const char* str_char = 456 reinterpret_cast<const char*>(str_contents); 457 switch(entsize) 458 { 459 case 1: 460 { 461 buffer.append(str_char); 462 break; 463 } 464 case 2: 465 { 466 const uint16_t* ptr_16 = 467 reinterpret_cast<const uint16_t*>(str_char); 468 unsigned int strlen_16 = 0; 469 // Find the NULL character. 470 while(*(ptr_16 + strlen_16) != 0) 471 strlen_16++; 472 buffer.append(str_char, strlen_16 * 2); 473 } 474 break; 475 case 4: 476 { 477 const uint32_t* ptr_32 = 478 reinterpret_cast<const uint32_t*>(str_char); 479 unsigned int strlen_32 = 0; 480 // Find the NULL character. 481 while(*(ptr_32 + strlen_32) != 0) 482 strlen_32++; 483 buffer.append(str_char, strlen_32 * 4); 484 } 485 break; 486 default: 487 gold_unreachable(); 488 } 489 } 490 else 491 { 492 // Use the entsize to determine the length. 493 buffer.append(reinterpret_cast<const 494 char*>(str_contents), 495 entsize); 496 } 497 buffer.append("@"); 498 } 499 else if ((*it_s) != NULL) 500 { 501 // If symbol name is available use that. 502 buffer.append((*it_s)->name()); 503 // Append the addend. 504 buffer.append(addend_str); 505 buffer.append("@"); 506 } 507 else 508 { 509 // Symbol name is not available, like for a local symbol, 510 // use object and section id. 511 buffer.append(it_v->first->name()); 512 char secn_id[10]; 513 snprintf(secn_id, sizeof(secn_id), "%u",it_v->second); 514 buffer.append(secn_id); 515 // Append the addend. 516 buffer.append(addend_str); 517 buffer.append("@"); 518 } 519 } 520 } 521 } 522 523 if (first_iteration) 524 { 525 buffer.append("Contents = "); 526 buffer.append(reinterpret_cast<const char*>(contents), plen); 527 // Store the section contents that dont change to avoid recomputing 528 // during the next call to this function. 529 (*section_contents)[section_num] = buffer; 530 } 531 else 532 { 533 gold_assert(buffer.empty()); 534 // Reuse the contents computed in the previous iteration. 535 buffer.append((*section_contents)[section_num]); 536 } 537 538 buffer.append(icf_reloc_buffer); 539 return buffer; 540 } 541 542 // This function computes a checksum on each section to detect and form 543 // groups of identical sections. The first iteration does this for all 544 // sections. 545 // Further iterations do this only for the kept sections from each group to 546 // determine if larger groups of identical sections could be formed. The 547 // first section in each group is the kept section for that group. 548 // 549 // CRC32 is the checksumming algorithm and can have collisions. That is, 550 // two sections with different contents can have the same checksum. Hence, 551 // a multimap is used to maintain more than one group of checksum 552 // identical sections. A section is added to a group only after its 553 // contents are explicitly compared with the kept section of the group. 554 // 555 // Parameters : 556 // ITERATION_NUM : Invocation instance of this function. 557 // NUM_TRACKED_RELOCS : Vector reference to store the number of relocs 558 // to ICF sections. 559 // KEPT_SECTION_ID : Vector which maps folded sections to kept sections. 560 // ID_SECTION : Vector mapping a section to an unique integer. 561 // IS_SECN_OR_GROUP_UNIQUE : To check if a section or a group of identical 562 // sections is already known to be unique. 563 // SECTION_CONTENTS : Store the section's text and relocs to non-ICF 564 // sections. 565 566 static bool 567 match_sections(unsigned int iteration_num, 568 Symbol_table* symtab, 569 std::vector<unsigned int>* num_tracked_relocs, 570 std::vector<unsigned int>* kept_section_id, 571 const std::vector<Section_id>& id_section, 572 std::vector<bool>* is_secn_or_group_unique, 573 std::vector<std::string>* section_contents) 574 { 575 Unordered_multimap<uint32_t, unsigned int> section_cksum; 576 std::pair<Unordered_multimap<uint32_t, unsigned int>::iterator, 577 Unordered_multimap<uint32_t, unsigned int>::iterator> key_range; 578 bool converged = true; 579 580 if (iteration_num == 1) 581 preprocess_for_unique_sections(id_section, 582 is_secn_or_group_unique, 583 NULL); 584 else 585 preprocess_for_unique_sections(id_section, 586 is_secn_or_group_unique, 587 section_contents); 588 589 std::vector<std::string> full_section_contents; 590 591 for (unsigned int i = 0; i < id_section.size(); i++) 592 { 593 full_section_contents.push_back(""); 594 if ((*is_secn_or_group_unique)[i]) 595 continue; 596 597 Section_id secn = id_section[i]; 598 std::string this_secn_contents; 599 uint32_t cksum; 600 if (iteration_num == 1) 601 { 602 unsigned int num_relocs = 0; 603 this_secn_contents = get_section_contents(true, secn, i, &num_relocs, 604 symtab, (*kept_section_id), 605 section_contents); 606 (*num_tracked_relocs)[i] = num_relocs; 607 } 608 else 609 { 610 if ((*kept_section_id)[i] != i) 611 { 612 // This section is already folded into something. See 613 // if it should point to a different kept section. 614 unsigned int kept_section = (*kept_section_id)[i]; 615 if (kept_section != (*kept_section_id)[kept_section]) 616 { 617 (*kept_section_id)[i] = (*kept_section_id)[kept_section]; 618 } 619 continue; 620 } 621 this_secn_contents = get_section_contents(false, secn, i, NULL, 622 symtab, (*kept_section_id), 623 section_contents); 624 } 625 626 const unsigned char* this_secn_contents_array = 627 reinterpret_cast<const unsigned char*>(this_secn_contents.c_str()); 628 cksum = xcrc32(this_secn_contents_array, this_secn_contents.length(), 629 0xffffffff); 630 size_t count = section_cksum.count(cksum); 631 632 if (count == 0) 633 { 634 // Start a group with this cksum. 635 section_cksum.insert(std::make_pair(cksum, i)); 636 full_section_contents[i] = this_secn_contents; 637 } 638 else 639 { 640 key_range = section_cksum.equal_range(cksum); 641 Unordered_multimap<uint32_t, unsigned int>::iterator it; 642 // Search all the groups with this cksum for a match. 643 for (it = key_range.first; it != key_range.second; ++it) 644 { 645 unsigned int kept_section = it->second; 646 if (full_section_contents[kept_section].length() 647 != this_secn_contents.length()) 648 continue; 649 if (memcmp(full_section_contents[kept_section].c_str(), 650 this_secn_contents.c_str(), 651 this_secn_contents.length()) != 0) 652 continue; 653 (*kept_section_id)[i] = kept_section; 654 converged = false; 655 break; 656 } 657 if (it == key_range.second) 658 { 659 // Create a new group for this cksum. 660 section_cksum.insert(std::make_pair(cksum, i)); 661 full_section_contents[i] = this_secn_contents; 662 } 663 } 664 // If there are no relocs to foldable sections do not process 665 // this section any further. 666 if (iteration_num == 1 && (*num_tracked_relocs)[i] == 0) 667 (*is_secn_or_group_unique)[i] = true; 668 } 669 670 return converged; 671 } 672 673 // During safe icf (--icf=safe), only fold functions that are ctors or dtors. 674 // This function returns true if the section name is that of a ctor or a dtor. 675 676 static bool 677 is_function_ctor_or_dtor(const std::string& section_name) 678 { 679 const char* mangled_func_name = strrchr(section_name.c_str(), '.'); 680 gold_assert(mangled_func_name != NULL); 681 if ((is_prefix_of("._ZN", mangled_func_name) 682 || is_prefix_of("._ZZ", mangled_func_name)) 683 && (is_gnu_v3_mangled_ctor(mangled_func_name + 1) 684 || is_gnu_v3_mangled_dtor(mangled_func_name + 1))) 685 { 686 return true; 687 } 688 return false; 689 } 690 691 // This is the main ICF function called in gold.cc. This does the 692 // initialization and calls match_sections repeatedly (twice by default) 693 // which computes the crc checksums and detects identical functions. 694 695 void 696 Icf::find_identical_sections(const Input_objects* input_objects, 697 Symbol_table* symtab) 698 { 699 unsigned int section_num = 0; 700 std::vector<unsigned int> num_tracked_relocs; 701 std::vector<bool> is_secn_or_group_unique; 702 std::vector<std::string> section_contents; 703 const Target& target = parameters->target(); 704 705 // Decide which sections are possible candidates first. 706 707 for (Input_objects::Relobj_iterator p = input_objects->relobj_begin(); 708 p != input_objects->relobj_end(); 709 ++p) 710 { 711 // Lock the object so we can read from it. This is only called 712 // single-threaded from queue_middle_tasks, so it is OK to lock. 713 // Unfortunately we have no way to pass in a Task token. 714 const Task* dummy_task = reinterpret_cast<const Task*>(-1); 715 Task_lock_obj<Object> tl(dummy_task, *p); 716 717 for (unsigned int i = 0;i < (*p)->shnum(); ++i) 718 { 719 const std::string section_name = (*p)->section_name(i); 720 if (!is_section_foldable_candidate(section_name)) 721 continue; 722 if (!(*p)->is_section_included(i)) 723 continue; 724 if (parameters->options().gc_sections() 725 && symtab->gc()->is_section_garbage(*p, i)) 726 continue; 727 // With --icf=safe, check if the mangled function name is a ctor 728 // or a dtor. The mangled function name can be obtained from the 729 // section name by stripping the section prefix. 730 if (parameters->options().icf_safe_folding() 731 && !is_function_ctor_or_dtor(section_name) 732 && (!target.can_check_for_function_pointers() 733 || section_has_function_pointers(*p, i))) 734 { 735 continue; 736 } 737 this->id_section_.push_back(Section_id(*p, i)); 738 this->section_id_[Section_id(*p, i)] = section_num; 739 this->kept_section_id_.push_back(section_num); 740 num_tracked_relocs.push_back(0); 741 is_secn_or_group_unique.push_back(false); 742 section_contents.push_back(""); 743 section_num++; 744 } 745 } 746 747 unsigned int num_iterations = 0; 748 749 // Default number of iterations to run ICF is 2. 750 unsigned int max_iterations = (parameters->options().icf_iterations() > 0) 751 ? parameters->options().icf_iterations() 752 : 2; 753 754 bool converged = false; 755 756 while (!converged && (num_iterations < max_iterations)) 757 { 758 num_iterations++; 759 converged = match_sections(num_iterations, symtab, 760 &num_tracked_relocs, &this->kept_section_id_, 761 this->id_section_, &is_secn_or_group_unique, 762 §ion_contents); 763 } 764 765 if (parameters->options().print_icf_sections()) 766 { 767 if (converged) 768 gold_info(_("%s: ICF Converged after %u iteration(s)"), 769 program_name, num_iterations); 770 else 771 gold_info(_("%s: ICF stopped after %u iteration(s)"), 772 program_name, num_iterations); 773 } 774 775 // Unfold --keep-unique symbols. 776 for (options::String_set::const_iterator p = 777 parameters->options().keep_unique_begin(); 778 p != parameters->options().keep_unique_end(); 779 ++p) 780 { 781 const char* name = p->c_str(); 782 Symbol* sym = symtab->lookup(name); 783 if (sym == NULL) 784 { 785 gold_warning(_("Could not find symbol %s to unfold\n"), name); 786 } 787 else if (sym->source() == Symbol::FROM_OBJECT 788 && !sym->object()->is_dynamic()) 789 { 790 Object* obj = sym->object(); 791 bool is_ordinary; 792 unsigned int shndx = sym->shndx(&is_ordinary); 793 if (is_ordinary) 794 { 795 this->unfold_section(obj, shndx); 796 } 797 } 798 799 } 800 801 this->icf_ready(); 802 } 803 804 // Unfolds the section denoted by OBJ and SHNDX if folded. 805 806 void 807 Icf::unfold_section(Object* obj, unsigned int shndx) 808 { 809 Section_id secn(obj, shndx); 810 Uniq_secn_id_map::iterator it = this->section_id_.find(secn); 811 if (it == this->section_id_.end()) 812 return; 813 unsigned int section_num = it->second; 814 unsigned int kept_section_id = this->kept_section_id_[section_num]; 815 if (kept_section_id != section_num) 816 this->kept_section_id_[section_num] = section_num; 817 } 818 819 // This function determines if the section corresponding to the 820 // given object and index is folded based on if the kept section 821 // is different from this section. 822 823 bool 824 Icf::is_section_folded(Object* obj, unsigned int shndx) 825 { 826 Section_id secn(obj, shndx); 827 Uniq_secn_id_map::iterator it = this->section_id_.find(secn); 828 if (it == this->section_id_.end()) 829 return false; 830 unsigned int section_num = it->second; 831 unsigned int kept_section_id = this->kept_section_id_[section_num]; 832 return kept_section_id != section_num; 833 } 834 835 // This function returns the folded section for the given section. 836 837 Section_id 838 Icf::get_folded_section(Object* dup_obj, unsigned int dup_shndx) 839 { 840 Section_id dup_secn(dup_obj, dup_shndx); 841 Uniq_secn_id_map::iterator it = this->section_id_.find(dup_secn); 842 gold_assert(it != this->section_id_.end()); 843 unsigned int section_num = it->second; 844 unsigned int kept_section_id = this->kept_section_id_[section_num]; 845 Section_id folded_section = this->id_section_[kept_section_id]; 846 return folded_section; 847 } 848 849 } // End of namespace gold. 850
