1// icf.cc -- Identical Code Folding. 2// 3// Copyright 2009, 2010 Free Software Foundation, Inc. 4// Written by Sriraman Tallam <tmsriram@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 151namespace 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 166static void 167preprocess_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 231static std::string 232get_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 section_size_type plen; 241 const unsigned char* contents = NULL; 242 243 if (first_iteration) 244 { 245 // Lock the object so we can read from it. This is only called 246 // single-threaded from queue_middle_tasks, so it is OK to lock. 247 // Unfortunately we have no way to pass in a Task token. 248 const Task* dummy_task = reinterpret_cast<const Task*>(-1); 249 Task_lock_obj<Object> tl(dummy_task, secn.first); 250 contents = secn.first->section_contents(secn.second, 251 &plen, 252 false); 253 } 254 255 // The buffer to hold all the contents including relocs. A checksum 256 // is then computed on this buffer. 257 std::string buffer; 258 std::string icf_reloc_buffer; 259 260 if (num_tracked_relocs) 261 *num_tracked_relocs = 0; 262 263 Icf::Reloc_info_list& reloc_info_list = 264 symtab->icf()->reloc_info_list(); 265 266 Icf::Reloc_info_list::iterator it_reloc_info_list = 267 reloc_info_list.find(secn); 268 269 buffer.clear(); 270 icf_reloc_buffer.clear(); 271 272 // Process relocs and put them into the buffer. 273 274 if (it_reloc_info_list != reloc_info_list.end()) 275 { 276 Icf::Sections_reachable_info v = 277 (it_reloc_info_list->second).section_info; 278 // Stores the information of the symbol pointed to by the reloc. 279 Icf::Symbol_info s = (it_reloc_info_list->second).symbol_info; 280 // Stores the addend and the symbol value. 281 Icf::Addend_info a = (it_reloc_info_list->second).addend_info; 282 // Stores the offset of the reloc. 283 Icf::Offset_info o = (it_reloc_info_list->second).offset_info; 284 Icf::Reloc_addend_size_info reloc_addend_size_info = 285 (it_reloc_info_list->second).reloc_addend_size_info; 286 Icf::Sections_reachable_info::iterator it_v = v.begin(); 287 Icf::Symbol_info::iterator it_s = s.begin(); 288 Icf::Addend_info::iterator it_a = a.begin(); 289 Icf::Offset_info::iterator it_o = o.begin(); 290 Icf::Reloc_addend_size_info::iterator it_addend_size = 291 reloc_addend_size_info.begin(); 292 293 for (; it_v != v.end(); ++it_v, ++it_s, ++it_a, ++it_o, ++it_addend_size) 294 { 295 // ADDEND_STR stores the symbol value and addend and offset, 296 // each atmost 16 hex digits long. it_a points to a pair 297 // where first is the symbol value and second is the 298 // addend. 299 char addend_str[50]; 300 301 // It would be nice if we could use format macros in inttypes.h 302 // here but there are not in ISO/IEC C++ 1998. 303 snprintf(addend_str, sizeof(addend_str), "%llx %llx %llux", 304 static_cast<long long>((*it_a).first), 305 static_cast<long long>((*it_a).second), 306 static_cast<unsigned long long>(*it_o)); 307 308 // If the symbol pointed to by the reloc is not in an ordinary 309 // section or if the symbol type is not FROM_OBJECT, then the 310 // object is NULL. 311 if (it_v->first == NULL) 312 { 313 if (first_iteration) 314 { 315 // If the symbol name is available, use it. 316 if ((*it_s) != NULL) 317 buffer.append((*it_s)->name()); 318 // Append the addend. 319 buffer.append(addend_str); 320 buffer.append("@"); 321 } 322 continue; 323 } 324 325 Section_id reloc_secn(it_v->first, it_v->second); 326 327 // If this reloc turns back and points to the same section, 328 // like a recursive call, use a special symbol to mark this. 329 if (reloc_secn.first == secn.first 330 && reloc_secn.second == secn.second) 331 { 332 if (first_iteration) 333 { 334 buffer.append("R"); 335 buffer.append(addend_str); 336 buffer.append("@"); 337 } 338 continue; 339 } 340 Icf::Uniq_secn_id_map& section_id_map = 341 symtab->icf()->section_to_int_map(); 342 Icf::Uniq_secn_id_map::iterator section_id_map_it = 343 section_id_map.find(reloc_secn); 344 bool is_sym_preemptible = (*it_s != NULL 345 && !(*it_s)->is_from_dynobj() 346 && !(*it_s)->is_undefined() 347 && (*it_s)->is_preemptible()); 348 if (!is_sym_preemptible 349 && section_id_map_it != section_id_map.end()) 350 { 351 // This is a reloc to a section that might be folded. 352 if (num_tracked_relocs) 353 (*num_tracked_relocs)++; 354 355 char kept_section_str[10]; 356 unsigned int secn_id = section_id_map_it->second; 357 snprintf(kept_section_str, sizeof(kept_section_str), "%u", 358 kept_section_id[secn_id]); 359 if (first_iteration) 360 { 361 buffer.append("ICF_R"); 362 buffer.append(addend_str); 363 } 364 icf_reloc_buffer.append(kept_section_str); 365 // Append the addend. 366 icf_reloc_buffer.append(addend_str); 367 icf_reloc_buffer.append("@"); 368 } 369 else 370 { 371 // This is a reloc to a section that cannot be folded. 372 // Process it only in the first iteration. 373 if (!first_iteration) 374 continue; 375 376 // Lock the object so we can read from it. This is only called 377 // single-threaded from queue_middle_tasks, so it is OK to lock. 378 // Unfortunately we have no way to pass in a Task token. 379 const Task* dummy_task = reinterpret_cast<const Task*>(-1); 380 Task_lock_obj<Object> tl(dummy_task, it_v->first); 381 382 uint64_t secn_flags = (it_v->first)->section_flags(it_v->second); 383 // This reloc points to a merge section. Hash the 384 // contents of this section. 385 if ((secn_flags & elfcpp::SHF_MERGE) != 0 386 && parameters->target().can_icf_inline_merge_sections ()) 387 { 388 uint64_t entsize = 389 (it_v->first)->section_entsize(it_v->second); 390 long long offset = it_a->first; 391 392 unsigned long long addend = it_a->second; 393 // Ignoring the addend when it is a negative value. See the 394 // comments in Merged_symbol_value::Value in object.h. 395 if (addend < 0xffffff00) 396 offset = offset + addend; 397 398 // For SHT_REL relocation sections, the addend is stored in the 399 // text section at the relocation offset. 400 uint64_t reloc_addend_value = 0; 401 const unsigned char* reloc_addend_ptr = 402 contents + static_cast<unsigned long long>(*it_o); 403 switch(*it_addend_size) 404 { 405 case 0: 406 { 407 break; 408 } 409 case 1: 410 { 411 reloc_addend_value = 412 read_from_pointer<8>(reloc_addend_ptr); 413 break; 414 } 415 case 2: 416 { 417 reloc_addend_value = 418 read_from_pointer<16>(reloc_addend_ptr); 419 break; 420 } 421 case 4: 422 { 423 reloc_addend_value = 424 read_from_pointer<32>(reloc_addend_ptr); 425 break; 426 } 427 case 8: 428 { 429 reloc_addend_value = 430 read_from_pointer<64>(reloc_addend_ptr); 431 break; 432 } 433 default: 434 gold_unreachable(); 435 } 436 offset = offset + reloc_addend_value; 437 438 section_size_type secn_len; 439 const unsigned char* str_contents = 440 (it_v->first)->section_contents(it_v->second, 441 &secn_len, 442 false) + offset; 443 if ((secn_flags & elfcpp::SHF_STRINGS) != 0) 444 { 445 // String merge section. 446 const char* str_char = 447 reinterpret_cast<const char*>(str_contents); 448 switch(entsize) 449 { 450 case 1: 451 { 452 buffer.append(str_char); 453 break; 454 } 455 case 2: 456 { 457 const uint16_t* ptr_16 = 458 reinterpret_cast<const uint16_t*>(str_char); 459 unsigned int strlen_16 = 0; 460 // Find the NULL character. 461 while(*(ptr_16 + strlen_16) != 0) 462 strlen_16++; 463 buffer.append(str_char, strlen_16 * 2); 464 } 465 break; 466 case 4: 467 { 468 const uint32_t* ptr_32 = 469 reinterpret_cast<const uint32_t*>(str_char); 470 unsigned int strlen_32 = 0; 471 // Find the NULL character. 472 while(*(ptr_32 + strlen_32) != 0) 473 strlen_32++; 474 buffer.append(str_char, strlen_32 * 4); 475 } 476 break; 477 default: 478 gold_unreachable(); 479 } 480 } 481 else 482 { 483 // Use the entsize to determine the length. 484 buffer.append(reinterpret_cast<const 485 char*>(str_contents), 486 entsize); 487 } 488 buffer.append("@"); 489 } 490 else if ((*it_s) != NULL) 491 { 492 // If symbol name is available use that. 493 buffer.append((*it_s)->name()); 494 // Append the addend. 495 buffer.append(addend_str); 496 buffer.append("@"); 497 } 498 else 499 { 500 // Symbol name is not available, like for a local symbol, 501 // use object and section id. 502 buffer.append(it_v->first->name()); 503 char secn_id[10]; 504 snprintf(secn_id, sizeof(secn_id), "%u",it_v->second); 505 buffer.append(secn_id); 506 // Append the addend. 507 buffer.append(addend_str); 508 buffer.append("@"); 509 } 510 } 511 } 512 } 513 514 if (first_iteration) 515 { 516 buffer.append("Contents = "); 517 buffer.append(reinterpret_cast<const char*>(contents), plen); 518 // Store the section contents that dont change to avoid recomputing 519 // during the next call to this function. 520 (*section_contents)[section_num] = buffer; 521 } 522 else 523 { 524 gold_assert(buffer.empty()); 525 // Reuse the contents computed in the previous iteration. 526 buffer.append((*section_contents)[section_num]); 527 } 528 529 buffer.append(icf_reloc_buffer); 530 return buffer; 531} 532 533// This function computes a checksum on each section to detect and form 534// groups of identical sections. The first iteration does this for all 535// sections. 536// Further iterations do this only for the kept sections from each group to 537// determine if larger groups of identical sections could be formed. The 538// first section in each group is the kept section for that group. 539// 540// CRC32 is the checksumming algorithm and can have collisions. That is, 541// two sections with different contents can have the same checksum. Hence, 542// a multimap is used to maintain more than one group of checksum 543// identical sections. A section is added to a group only after its 544// contents are explicitly compared with the kept section of the group. 545// 546// Parameters : 547// ITERATION_NUM : Invocation instance of this function. 548// NUM_TRACKED_RELOCS : Vector reference to store the number of relocs 549// to ICF sections. 550// KEPT_SECTION_ID : Vector which maps folded sections to kept sections. 551// ID_SECTION : Vector mapping a section to an unique integer. 552// IS_SECN_OR_GROUP_UNIQUE : To check if a section or a group of identical 553// sectionsis already known to be unique. 554// SECTION_CONTENTS : Store the section's text and relocs to non-ICF 555// sections. 556 557static bool 558match_sections(unsigned int iteration_num, 559 Symbol_table* symtab, 560 std::vector<unsigned int>* num_tracked_relocs, 561 std::vector<unsigned int>* kept_section_id, 562 const std::vector<Section_id>& id_section, 563 std::vector<bool>* is_secn_or_group_unique, 564 std::vector<std::string>* section_contents) 565{ 566 Unordered_multimap<uint32_t, unsigned int> section_cksum; 567 std::pair<Unordered_multimap<uint32_t, unsigned int>::iterator, 568 Unordered_multimap<uint32_t, unsigned int>::iterator> key_range; 569 bool converged = true; 570 571 if (iteration_num == 1) 572 preprocess_for_unique_sections(id_section, 573 is_secn_or_group_unique, 574 NULL); 575 else 576 preprocess_for_unique_sections(id_section, 577 is_secn_or_group_unique, 578 section_contents); 579 580 std::vector<std::string> full_section_contents; 581 582 for (unsigned int i = 0; i < id_section.size(); i++) 583 { 584 full_section_contents.push_back(""); 585 if ((*is_secn_or_group_unique)[i]) 586 continue; 587 588 Section_id secn = id_section[i]; 589 std::string this_secn_contents; 590 uint32_t cksum; 591 if (iteration_num == 1) 592 { 593 unsigned int num_relocs = 0; 594 this_secn_contents = get_section_contents(true, secn, i, &num_relocs, 595 symtab, (*kept_section_id), 596 section_contents); 597 (*num_tracked_relocs)[i] = num_relocs; 598 } 599 else 600 { 601 if ((*kept_section_id)[i] != i) 602 { 603 // This section is already folded into something. See 604 // if it should point to a different kept section. 605 unsigned int kept_section = (*kept_section_id)[i]; 606 if (kept_section != (*kept_section_id)[kept_section]) 607 { 608 (*kept_section_id)[i] = (*kept_section_id)[kept_section]; 609 } 610 continue; 611 } 612 this_secn_contents = get_section_contents(false, secn, i, NULL, 613 symtab, (*kept_section_id), 614 section_contents); 615 } 616 617 const unsigned char* this_secn_contents_array = 618 reinterpret_cast<const unsigned char*>(this_secn_contents.c_str()); 619 cksum = xcrc32(this_secn_contents_array, this_secn_contents.length(), 620 0xffffffff); 621 size_t count = section_cksum.count(cksum); 622 623 if (count == 0) 624 { 625 // Start a group with this cksum. 626 section_cksum.insert(std::make_pair(cksum, i)); 627 full_section_contents[i] = this_secn_contents; 628 } 629 else 630 { 631 key_range = section_cksum.equal_range(cksum); 632 Unordered_multimap<uint32_t, unsigned int>::iterator it; 633 // Search all the groups with this cksum for a match. 634 for (it = key_range.first; it != key_range.second; ++it) 635 { 636 unsigned int kept_section = it->second; 637 if (full_section_contents[kept_section].length() 638 != this_secn_contents.length()) 639 continue; 640 if (memcmp(full_section_contents[kept_section].c_str(), 641 this_secn_contents.c_str(), 642 this_secn_contents.length()) != 0) 643 continue; 644 (*kept_section_id)[i] = kept_section; 645 converged = false; 646 break; 647 } 648 if (it == key_range.second) 649 { 650 // Create a new group for this cksum. 651 section_cksum.insert(std::make_pair(cksum, i)); 652 full_section_contents[i] = this_secn_contents; 653 } 654 } 655 // If there are no relocs to foldable sections do not process 656 // this section any further. 657 if (iteration_num == 1 && (*num_tracked_relocs)[i] == 0) 658 (*is_secn_or_group_unique)[i] = true; 659 } 660 661 return converged; 662} 663 664// During safe icf (--icf=safe), only fold functions that are ctors or dtors. 665// This function returns true if the section name is that of a ctor or a dtor. 666 667static bool 668is_function_ctor_or_dtor(const std::string& section_name) 669{ 670 const char* mangled_func_name = strrchr(section_name.c_str(), '.'); 671 gold_assert(mangled_func_name != NULL); 672 if ((is_prefix_of("._ZN", mangled_func_name) 673 || is_prefix_of("._ZZ", mangled_func_name)) 674 && (is_gnu_v3_mangled_ctor(mangled_func_name + 1) 675 || is_gnu_v3_mangled_dtor(mangled_func_name + 1))) 676 { 677 return true; 678 } 679 return false; 680} 681 682// This is the main ICF function called in gold.cc. This does the 683// initialization and calls match_sections repeatedly (twice by default) 684// which computes the crc checksums and detects identical functions. 685 686void 687Icf::find_identical_sections(const Input_objects* input_objects, 688 Symbol_table* symtab) 689{ 690 unsigned int section_num = 0; 691 std::vector<unsigned int> num_tracked_relocs; 692 std::vector<bool> is_secn_or_group_unique; 693 std::vector<std::string> section_contents; 694 const Target& target = parameters->target(); 695 696 // Decide which sections are possible candidates first. 697 698 for (Input_objects::Relobj_iterator p = input_objects->relobj_begin(); 699 p != input_objects->relobj_end(); 700 ++p) 701 { 702 // Lock the object so we can read from it. This is only called 703 // single-threaded from queue_middle_tasks, so it is OK to lock. 704 // Unfortunately we have no way to pass in a Task token. 705 const Task* dummy_task = reinterpret_cast<const Task*>(-1); 706 Task_lock_obj<Object> tl(dummy_task, *p); 707 708 for (unsigned int i = 0;i < (*p)->shnum(); ++i) 709 { 710 const std::string section_name = (*p)->section_name(i); 711 if (!is_section_foldable_candidate(section_name)) 712 continue; 713 if (!(*p)->is_section_included(i)) 714 continue; 715 if (parameters->options().gc_sections() 716 && symtab->gc()->is_section_garbage(*p, i)) 717 continue; 718 // With --icf=safe, check if the mangled function name is a ctor 719 // or a dtor. The mangled function name can be obtained from the 720 // section name by stripping the section prefix. 721 if (parameters->options().icf_safe_folding() 722 && !is_function_ctor_or_dtor(section_name) 723 && (!target.can_check_for_function_pointers() 724 || section_has_function_pointers(*p, i))) 725 { 726 continue; 727 } 728 this->id_section_.push_back(Section_id(*p, i)); 729 this->section_id_[Section_id(*p, i)] = section_num; 730 this->kept_section_id_.push_back(section_num); 731 num_tracked_relocs.push_back(0); 732 is_secn_or_group_unique.push_back(false); 733 section_contents.push_back(""); 734 section_num++; 735 } 736 } 737 738 unsigned int num_iterations = 0; 739 740 // Default number of iterations to run ICF is 2. 741 unsigned int max_iterations = (parameters->options().icf_iterations() > 0) 742 ? parameters->options().icf_iterations() 743 : 2; 744 745 bool converged = false; 746 747 while (!converged && (num_iterations < max_iterations)) 748 { 749 num_iterations++; 750 converged = match_sections(num_iterations, symtab, 751 &num_tracked_relocs, &this->kept_section_id_, 752 this->id_section_, &is_secn_or_group_unique, 753 §ion_contents); 754 } 755 756 if (parameters->options().print_icf_sections()) 757 { 758 if (converged) 759 gold_info(_("%s: ICF Converged after %u iteration(s)"), 760 program_name, num_iterations); 761 else 762 gold_info(_("%s: ICF stopped after %u iteration(s)"), 763 program_name, num_iterations); 764 } 765 766 // Unfold --keep-unique symbols. 767 for (options::String_set::const_iterator p = 768 parameters->options().keep_unique_begin(); 769 p != parameters->options().keep_unique_end(); 770 ++p) 771 { 772 const char* name = p->c_str(); 773 Symbol* sym = symtab->lookup(name); 774 if (sym == NULL) 775 { 776 gold_warning(_("Could not find symbol %s to unfold\n"), name); 777 } 778 else if (sym->source() == Symbol::FROM_OBJECT 779 && !sym->object()->is_dynamic()) 780 { 781 Object* obj = sym->object(); 782 bool is_ordinary; 783 unsigned int shndx = sym->shndx(&is_ordinary); 784 if (is_ordinary) 785 { 786 this->unfold_section(obj, shndx); 787 } 788 } 789 790 } 791 792 this->icf_ready(); 793} 794 795// Unfolds the section denoted by OBJ and SHNDX if folded. 796 797void 798Icf::unfold_section(Object* obj, unsigned int shndx) 799{ 800 Section_id secn(obj, shndx); 801 Uniq_secn_id_map::iterator it = this->section_id_.find(secn); 802 if (it == this->section_id_.end()) 803 return; 804 unsigned int section_num = it->second; 805 unsigned int kept_section_id = this->kept_section_id_[section_num]; 806 if (kept_section_id != section_num) 807 this->kept_section_id_[section_num] = section_num; 808} 809 810// This function determines if the section corresponding to the 811// given object and index is folded based on if the kept section 812// is different from this section. 813 814bool 815Icf::is_section_folded(Object* obj, unsigned int shndx) 816{ 817 Section_id secn(obj, shndx); 818 Uniq_secn_id_map::iterator it = this->section_id_.find(secn); 819 if (it == this->section_id_.end()) 820 return false; 821 unsigned int section_num = it->second; 822 unsigned int kept_section_id = this->kept_section_id_[section_num]; 823 return kept_section_id != section_num; 824} 825 826// This function returns the folded section for the given section. 827 828Section_id 829Icf::get_folded_section(Object* dup_obj, unsigned int dup_shndx) 830{ 831 Section_id dup_secn(dup_obj, dup_shndx); 832 Uniq_secn_id_map::iterator it = this->section_id_.find(dup_secn); 833 gold_assert(it != this->section_id_.end()); 834 unsigned int section_num = it->second; 835 unsigned int kept_section_id = this->kept_section_id_[section_num]; 836 Section_id folded_section = this->id_section_[kept_section_id]; 837 return folded_section; 838} 839 840} // End of namespace gold. 841