1 //===- Writer.cpp ---------------------------------------------------------===//
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
12 #include "LinkerScript.h"
13 #include "OutputSections.h"
14 #include "Relocations.h"
16 #include "SymbolTable.h"
19 #include "llvm/ADT/StringMap.h"
20 #include "llvm/ADT/StringSwitch.h"
21 #include "llvm/Support/FileOutputBuffer.h"
22 #include "llvm/Support/StringSaver.h"
23 #include "llvm/Support/raw_ostream.h"
26 using namespace llvm::ELF;
27 using namespace llvm::object;
30 using namespace lld::elf;
33 // The writer writes a SymbolTable result to a file.
34 template <class ELFT> class Writer {
36 typedef typename ELFT::uint uintX_t;
37 typedef typename ELFT::Shdr Elf_Shdr;
38 typedef typename ELFT::Ehdr Elf_Ehdr;
39 typedef typename ELFT::Phdr Elf_Phdr;
40 typedef typename ELFT::Sym Elf_Sym;
41 typedef typename ELFT::SymRange Elf_Sym_Range;
42 typedef typename ELFT::Rela Elf_Rela;
43 Writer(SymbolTable<ELFT> &S) : Symtab(S) {}
47 // This describes a program header entry.
48 // Each contains type, access flags and range of output sections that will be
51 Phdr(unsigned Type, unsigned Flags) {
56 OutputSectionBase<ELFT> *First = nullptr;
57 OutputSectionBase<ELFT> *Last = nullptr;
60 void copyLocalSymbols();
61 void addReservedSymbols();
62 void createSections();
63 void addPredefinedSections();
67 void assignAddresses();
68 void assignFileOffsets();
71 void fixSectionAlignments();
72 void fixAbsoluteSymbols();
77 bool needsInterpSection() const {
78 return !Symtab.getSharedFiles().empty() && !Config->DynamicLinker.empty();
80 bool isOutputDynamic() const {
81 return !Symtab.getSharedFiles().empty() || Config->Pic;
84 void addCommonSymbols(std::vector<DefinedCommon *> &Syms);
86 std::unique_ptr<FileOutputBuffer> Buffer;
88 BumpPtrAllocator Alloc;
89 std::vector<OutputSectionBase<ELFT> *> OutputSections;
90 std::vector<std::unique_ptr<OutputSectionBase<ELFT>>> OwningSections;
92 void addRelIpltSymbols();
93 void addStartEndSymbols();
94 void addStartStopSymbols(OutputSectionBase<ELFT> *Sec);
96 SymbolTable<ELFT> &Symtab;
97 std::vector<Phdr> Phdrs;
100 uintX_t SectionHeaderOff;
102 } // anonymous namespace
104 template <class ELFT>
105 StringRef elf::getOutputSectionName(InputSectionBase<ELFT> *S) {
106 StringRef Dest = Script<ELFT>::X->getOutputSection(S);
110 StringRef Name = S->getSectionName();
111 for (StringRef V : {".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.",
112 ".init_array.", ".fini_array.", ".ctors.", ".dtors.",
113 ".tbss.", ".gcc_except_table.", ".tdata."})
114 if (Name.startswith(V))
115 return V.drop_back();
119 template <class ELFT>
120 void elf::reportDiscarded(InputSectionBase<ELFT> *IS,
121 const std::unique_ptr<elf::ObjectFile<ELFT>> &File) {
122 if (!Config->PrintGcSections || !IS || IS->Live)
124 errs() << "removing unused section from '" << IS->getSectionName()
125 << "' in file '" << File->getName() << "'\n";
128 template <class ELFT> void elf::writeResult(SymbolTable<ELFT> *Symtab) {
129 typedef typename ELFT::uint uintX_t;
130 typedef typename ELFT::Ehdr Elf_Ehdr;
132 // Create singleton output sections.
133 OutputSection<ELFT> Bss(".bss", SHT_NOBITS, SHF_ALLOC | SHF_WRITE);
134 DynamicSection<ELFT> Dynamic;
135 EhOutputSection<ELFT> EhFrame;
136 GotSection<ELFT> Got;
137 InterpSection<ELFT> Interp;
138 PltSection<ELFT> Plt;
139 RelocationSection<ELFT> RelaDyn(Config->Rela ? ".rela.dyn" : ".rel.dyn",
141 StringTableSection<ELFT> DynStrTab(".dynstr", true);
142 StringTableSection<ELFT> ShStrTab(".shstrtab", false);
143 SymbolTableSection<ELFT> DynSymTab(DynStrTab);
144 VersionTableSection<ELFT> VerSym;
145 VersionNeedSection<ELFT> VerNeed;
147 OutputSectionBase<ELFT> ElfHeader("", 0, SHF_ALLOC);
148 ElfHeader.setSize(sizeof(Elf_Ehdr));
149 OutputSectionBase<ELFT> ProgramHeaders("", 0, SHF_ALLOC);
150 ProgramHeaders.updateAlignment(sizeof(uintX_t));
152 // Instantiate optional output sections if they are needed.
153 std::unique_ptr<BuildIdSection<ELFT>> BuildId;
154 std::unique_ptr<EhFrameHeader<ELFT>> EhFrameHdr;
155 std::unique_ptr<GnuHashTableSection<ELFT>> GnuHashTab;
156 std::unique_ptr<GotPltSection<ELFT>> GotPlt;
157 std::unique_ptr<HashTableSection<ELFT>> HashTab;
158 std::unique_ptr<RelocationSection<ELFT>> RelaPlt;
159 std::unique_ptr<StringTableSection<ELFT>> StrTab;
160 std::unique_ptr<SymbolTableSection<ELFT>> SymTabSec;
161 std::unique_ptr<OutputSection<ELFT>> MipsRldMap;
162 std::unique_ptr<VersionDefinitionSection<ELFT>> VerDef;
164 if (Config->BuildId == BuildIdKind::Fnv1)
165 BuildId.reset(new BuildIdFnv1<ELFT>);
166 else if (Config->BuildId == BuildIdKind::Md5)
167 BuildId.reset(new BuildIdMd5<ELFT>);
168 else if (Config->BuildId == BuildIdKind::Sha1)
169 BuildId.reset(new BuildIdSha1<ELFT>);
170 else if (Config->BuildId == BuildIdKind::Hexstring)
171 BuildId.reset(new BuildIdHexstring<ELFT>);
173 if (Config->EhFrameHdr)
174 EhFrameHdr.reset(new EhFrameHeader<ELFT>);
177 GnuHashTab.reset(new GnuHashTableSection<ELFT>);
178 if (Config->SysvHash)
179 HashTab.reset(new HashTableSection<ELFT>);
180 StringRef S = Config->Rela ? ".rela.plt" : ".rel.plt";
181 GotPlt.reset(new GotPltSection<ELFT>);
182 RelaPlt.reset(new RelocationSection<ELFT>(S, false /*Sort*/));
183 if (!Config->StripAll) {
184 StrTab.reset(new StringTableSection<ELFT>(".strtab", false));
185 SymTabSec.reset(new SymbolTableSection<ELFT>(*StrTab));
187 if (Config->EMachine == EM_MIPS && !Config->Shared) {
188 // This is a MIPS specific section to hold a space within the data segment
189 // of executable file which is pointed to by the DT_MIPS_RLD_MAP entry.
190 // See "Dynamic section" in Chapter 5 in the following document:
191 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
192 MipsRldMap.reset(new OutputSection<ELFT>(".rld_map", SHT_PROGBITS,
193 SHF_ALLOC | SHF_WRITE));
194 MipsRldMap->setSize(sizeof(uintX_t));
195 MipsRldMap->updateAlignment(sizeof(uintX_t));
197 if (!Config->VersionDefinitions.empty())
198 VerDef.reset(new VersionDefinitionSection<ELFT>());
200 Out<ELFT>::Bss = &Bss;
201 Out<ELFT>::BuildId = BuildId.get();
202 Out<ELFT>::DynStrTab = &DynStrTab;
203 Out<ELFT>::DynSymTab = &DynSymTab;
204 Out<ELFT>::Dynamic = &Dynamic;
205 Out<ELFT>::EhFrame = &EhFrame;
206 Out<ELFT>::EhFrameHdr = EhFrameHdr.get();
207 Out<ELFT>::GnuHashTab = GnuHashTab.get();
208 Out<ELFT>::Got = &Got;
209 Out<ELFT>::GotPlt = GotPlt.get();
210 Out<ELFT>::HashTab = HashTab.get();
211 Out<ELFT>::Interp = &Interp;
212 Out<ELFT>::Plt = &Plt;
213 Out<ELFT>::RelaDyn = &RelaDyn;
214 Out<ELFT>::RelaPlt = RelaPlt.get();
215 Out<ELFT>::ShStrTab = &ShStrTab;
216 Out<ELFT>::StrTab = StrTab.get();
217 Out<ELFT>::SymTab = SymTabSec.get();
218 Out<ELFT>::VerDef = VerDef.get();
219 Out<ELFT>::VerSym = &VerSym;
220 Out<ELFT>::VerNeed = &VerNeed;
221 Out<ELFT>::MipsRldMap = MipsRldMap.get();
222 Out<ELFT>::Opd = nullptr;
223 Out<ELFT>::OpdBuf = nullptr;
224 Out<ELFT>::TlsPhdr = nullptr;
225 Out<ELFT>::ElfHeader = &ElfHeader;
226 Out<ELFT>::ProgramHeaders = &ProgramHeaders;
228 Writer<ELFT>(*Symtab).run();
231 // The main function of the writer.
232 template <class ELFT> void Writer<ELFT>::run() {
233 if (!Config->DiscardAll)
235 addReservedSymbols();
240 if (Config->Relocatable) {
245 if (ScriptConfig->DoLayout) {
246 Script<ELFT>::X->assignAddresses(OutputSections);
248 fixSectionAlignments();
253 fixAbsoluteSymbols();
264 if (auto EC = Buffer->commit())
265 error(EC, "failed to write to the output file");
268 template <class ELFT>
269 static void reportUndefined(SymbolTable<ELFT> &Symtab, SymbolBody *Sym) {
270 if (Config->UnresolvedSymbols == UnresolvedPolicy::Ignore)
273 if (Config->Shared && Sym->symbol()->Visibility == STV_DEFAULT &&
274 Config->UnresolvedSymbols != UnresolvedPolicy::NoUndef)
277 std::string Msg = "undefined symbol: " + Sym->getName().str();
279 Msg += " in " + getFilename(Sym->File);
280 if (Config->UnresolvedSymbols == UnresolvedPolicy::Warn)
286 template <class ELFT>
287 static bool shouldKeepInSymtab(InputSectionBase<ELFT> *Sec, StringRef SymName,
288 const SymbolBody &B) {
292 // We keep sections in symtab for relocatable output.
294 return Config->Relocatable;
296 // If sym references a section in a discarded group, don't keep it.
297 if (Sec == &InputSection<ELFT>::Discarded)
300 if (Config->DiscardNone)
303 // In ELF assembly .L symbols are normally discarded by the assembler.
304 // If the assembler fails to do so, the linker discards them if
305 // * --discard-locals is used.
306 // * The symbol is in a SHF_MERGE section, which is normally the reason for
307 // the assembler keeping the .L symbol.
308 if (!SymName.startswith(".L") && !SymName.empty())
311 if (Config->DiscardLocals)
314 return !(Sec->getSectionHdr()->sh_flags & SHF_MERGE);
317 template <class ELFT> static bool includeInSymtab(const SymbolBody &B) {
318 if (!B.isLocal() && !B.symbol()->IsUsedInRegularObj)
321 if (auto *D = dyn_cast<DefinedRegular<ELFT>>(&B)) {
322 // Always include absolute symbols.
325 // Exclude symbols pointing to garbage-collected sections.
326 if (!D->Section->Live)
328 if (auto *S = dyn_cast<MergeInputSection<ELFT>>(D->Section))
329 if (!S->getSectionPiece(D->Value)->Live)
335 // Local symbols are not in the linker's symbol table. This function scans
336 // each object file's symbol table to copy local symbols to the output.
337 template <class ELFT> void Writer<ELFT>::copyLocalSymbols() {
338 if (!Out<ELFT>::SymTab)
340 for (const std::unique_ptr<elf::ObjectFile<ELFT>> &F :
341 Symtab.getObjectFiles()) {
342 const char *StrTab = F->getStringTable().data();
343 for (SymbolBody *B : F->getLocalSymbols()) {
344 auto *DR = dyn_cast<DefinedRegular<ELFT>>(B);
345 // No reason to keep local undefined symbol in symtab.
348 if (!includeInSymtab<ELFT>(*B))
350 StringRef SymName(StrTab + B->getNameOffset());
351 InputSectionBase<ELFT> *Sec = DR->Section;
352 if (!shouldKeepInSymtab<ELFT>(Sec, SymName, *B))
354 ++Out<ELFT>::SymTab->NumLocals;
355 if (Config->Relocatable)
356 B->DynsymIndex = Out<ELFT>::SymTab->NumLocals;
357 F->KeptLocalSyms.push_back(
358 std::make_pair(DR, Out<ELFT>::SymTab->StrTabSec.addString(SymName)));
363 // PPC64 has a number of special SHT_PROGBITS+SHF_ALLOC+SHF_WRITE sections that
364 // we would like to make sure appear is a specific order to maximize their
365 // coverage by a single signed 16-bit offset from the TOC base pointer.
366 // Conversely, the special .tocbss section should be first among all SHT_NOBITS
367 // sections. This will put it next to the loaded special PPC64 sections (and,
368 // thus, within reach of the TOC base pointer).
369 static int getPPC64SectionRank(StringRef SectionName) {
370 return StringSwitch<int>(SectionName)
372 .Case(".branch_lt", 2)
379 template <class ELFT> static bool isRelroSection(OutputSectionBase<ELFT> *Sec) {
382 typename ELFT::uint Flags = Sec->getFlags();
383 if (!(Flags & SHF_ALLOC) || !(Flags & SHF_WRITE))
387 uint32_t Type = Sec->getType();
388 if (Type == SHT_INIT_ARRAY || Type == SHT_FINI_ARRAY ||
389 Type == SHT_PREINIT_ARRAY)
391 if (Sec == Out<ELFT>::GotPlt)
393 if (Sec == Out<ELFT>::Dynamic || Sec == Out<ELFT>::Got)
395 StringRef S = Sec->getName();
396 return S == ".data.rel.ro" || S == ".ctors" || S == ".dtors" || S == ".jcr" ||
400 // Output section ordering is determined by this function.
401 template <class ELFT>
402 static bool compareSections(OutputSectionBase<ELFT> *A,
403 OutputSectionBase<ELFT> *B) {
404 typedef typename ELFT::uint uintX_t;
406 int Comp = Script<ELFT>::X->compareSections(A->getName(), B->getName());
410 uintX_t AFlags = A->getFlags();
411 uintX_t BFlags = B->getFlags();
413 // Allocatable sections go first to reduce the total PT_LOAD size and
414 // so debug info doesn't change addresses in actual code.
415 bool AIsAlloc = AFlags & SHF_ALLOC;
416 bool BIsAlloc = BFlags & SHF_ALLOC;
417 if (AIsAlloc != BIsAlloc)
420 // We don't have any special requirements for the relative order of
421 // two non allocatable sections.
425 // We want the read only sections first so that they go in the PT_LOAD
426 // covering the program headers at the start of the file.
427 bool AIsWritable = AFlags & SHF_WRITE;
428 bool BIsWritable = BFlags & SHF_WRITE;
429 if (AIsWritable != BIsWritable)
432 // For a corresponding reason, put non exec sections first (the program
433 // header PT_LOAD is not executable).
434 bool AIsExec = AFlags & SHF_EXECINSTR;
435 bool BIsExec = BFlags & SHF_EXECINSTR;
436 if (AIsExec != BIsExec)
439 // If we got here we know that both A and B are in the same PT_LOAD.
441 // The TLS initialization block needs to be a single contiguous block in a R/W
442 // PT_LOAD, so stick TLS sections directly before R/W sections. The TLS NOBITS
443 // sections are placed here as they don't take up virtual address space in the
445 bool AIsTls = AFlags & SHF_TLS;
446 bool BIsTls = BFlags & SHF_TLS;
447 if (AIsTls != BIsTls)
450 // The next requirement we have is to put nobits sections last. The
451 // reason is that the only thing the dynamic linker will see about
452 // them is a p_memsz that is larger than p_filesz. Seeing that it
453 // zeros the end of the PT_LOAD, so that has to correspond to the
455 bool AIsNoBits = A->getType() == SHT_NOBITS;
456 bool BIsNoBits = B->getType() == SHT_NOBITS;
457 if (AIsNoBits != BIsNoBits)
460 // We place RelRo section before plain r/w ones.
461 bool AIsRelRo = isRelroSection(A);
462 bool BIsRelRo = isRelroSection(B);
463 if (AIsRelRo != BIsRelRo)
466 // Some architectures have additional ordering restrictions for sections
467 // within the same PT_LOAD.
468 if (Config->EMachine == EM_PPC64)
469 return getPPC64SectionRank(A->getName()) <
470 getPPC64SectionRank(B->getName());
475 // Until this function is called, common symbols do not belong to any section.
476 // This function adds them to end of BSS section.
477 template <class ELFT>
478 void Writer<ELFT>::addCommonSymbols(std::vector<DefinedCommon *> &Syms) {
482 // Sort the common symbols by alignment as an heuristic to pack them better.
483 std::stable_sort(Syms.begin(), Syms.end(),
484 [](const DefinedCommon *A, const DefinedCommon *B) {
485 return A->Alignment > B->Alignment;
488 uintX_t Off = Out<ELFT>::Bss->getSize();
489 for (DefinedCommon *C : Syms) {
490 Off = alignTo(Off, C->Alignment);
491 Out<ELFT>::Bss->updateAlignment(C->Alignment);
492 C->OffsetInBss = Off;
496 Out<ELFT>::Bss->setSize(Off);
499 template <class ELFT>
500 static Symbol *addOptionalSynthetic(SymbolTable<ELFT> &Table, StringRef Name,
501 OutputSectionBase<ELFT> *Sec,
502 typename ELFT::uint Val) {
503 SymbolBody *S = Table.find(Name);
506 if (!S->isUndefined() && !S->isShared())
508 return Table.addSynthetic(Name, Sec, Val);
511 // The beginning and the ending of .rel[a].plt section are marked
512 // with __rel[a]_iplt_{start,end} symbols if it is a statically linked
513 // executable. The runtime needs these symbols in order to resolve
514 // all IRELATIVE relocs on startup. For dynamic executables, we don't
515 // need these symbols, since IRELATIVE relocs are resolved through GOT
516 // and PLT. For details, see http://www.airs.com/blog/archives/403.
517 template <class ELFT> void Writer<ELFT>::addRelIpltSymbols() {
518 if (isOutputDynamic() || !Out<ELFT>::RelaPlt)
520 StringRef S = Config->Rela ? "__rela_iplt_start" : "__rel_iplt_start";
521 addOptionalSynthetic(Symtab, S, Out<ELFT>::RelaPlt, 0);
523 S = Config->Rela ? "__rela_iplt_end" : "__rel_iplt_end";
524 addOptionalSynthetic(Symtab, S, Out<ELFT>::RelaPlt,
525 DefinedSynthetic<ELFT>::SectionEnd);
528 // The linker is expected to define some symbols depending on
529 // the linking result. This function defines such symbols.
530 template <class ELFT> void Writer<ELFT>::addReservedSymbols() {
531 if (Config->EMachine == EM_MIPS) {
532 // Define _gp for MIPS. st_value of _gp symbol will be updated by Writer
533 // so that it points to an absolute address which is relative to GOT.
534 // See "Global Data Symbols" in Chapter 6 in the following document:
535 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
536 Symtab.addSynthetic("_gp", Out<ELFT>::Got, MipsGPOffset);
538 // On MIPS O32 ABI, _gp_disp is a magic symbol designates offset between
539 // start of function and 'gp' pointer into GOT.
541 addOptionalSynthetic(Symtab, "_gp_disp", Out<ELFT>::Got, MipsGPOffset);
543 ElfSym<ELFT>::MipsGpDisp = Sym->body();
545 // The __gnu_local_gp is a magic symbol equal to the current value of 'gp'
546 // pointer. This symbol is used in the code generated by .cpload pseudo-op
547 // in case of using -mno-shared option.
548 // https://sourceware.org/ml/binutils/2004-12/msg00094.html
549 addOptionalSynthetic(Symtab, "__gnu_local_gp", Out<ELFT>::Got,
553 // In the assembly for 32 bit x86 the _GLOBAL_OFFSET_TABLE_ symbol
554 // is magical and is used to produce a R_386_GOTPC relocation.
555 // The R_386_GOTPC relocation value doesn't actually depend on the
556 // symbol value, so it could use an index of STN_UNDEF which, according
557 // to the spec, means the symbol value is 0.
558 // Unfortunately both gas and MC keep the _GLOBAL_OFFSET_TABLE_ symbol in
560 // The situation is even stranger on x86_64 where the assembly doesn't
561 // need the magical symbol, but gas still puts _GLOBAL_OFFSET_TABLE_ as
562 // an undefined symbol in the .o files.
563 // Given that the symbol is effectively unused, we just create a dummy
564 // hidden one to avoid the undefined symbol error.
565 if (!Config->Relocatable)
566 Symtab.addIgnored("_GLOBAL_OFFSET_TABLE_");
568 // __tls_get_addr is defined by the dynamic linker for dynamic ELFs. For
569 // static linking the linker is required to optimize away any references to
570 // __tls_get_addr, so it's not defined anywhere. Create a hidden definition
571 // to avoid the undefined symbol error.
572 if (!isOutputDynamic())
573 Symtab.addIgnored("__tls_get_addr");
575 auto Define = [this](StringRef S, DefinedRegular<ELFT> *&Sym1,
576 DefinedRegular<ELFT> *&Sym2) {
577 Sym1 = Symtab.addIgnored(S, STV_DEFAULT);
579 // The name without the underscore is not a reserved name,
580 // so it is defined only when there is a reference against it.
581 assert(S.startswith("_"));
583 if (SymbolBody *B = Symtab.find(S))
584 if (B->isUndefined())
585 Sym2 = Symtab.addAbsolute(S, STV_DEFAULT);
588 Define("_end", ElfSym<ELFT>::End, ElfSym<ELFT>::End2);
589 Define("_etext", ElfSym<ELFT>::Etext, ElfSym<ELFT>::Etext2);
590 Define("_edata", ElfSym<ELFT>::Edata, ElfSym<ELFT>::Edata2);
593 // Sort input sections by section name suffixes for
594 // __attribute__((init_priority(N))).
595 template <class ELFT> static void sortInitFini(OutputSectionBase<ELFT> *S) {
597 reinterpret_cast<OutputSection<ELFT> *>(S)->sortInitFini();
600 // Sort input sections by the special rule for .ctors and .dtors.
601 template <class ELFT> static void sortCtorsDtors(OutputSectionBase<ELFT> *S) {
603 reinterpret_cast<OutputSection<ELFT> *>(S)->sortCtorsDtors();
606 // Create output section objects and add them to OutputSections.
607 template <class ELFT> void Writer<ELFT>::createSections() {
608 // Create output sections for input object file sections.
609 std::vector<OutputSectionBase<ELFT> *> RegularSections;
610 OutputSectionFactory<ELFT> Factory;
611 for (const std::unique_ptr<elf::ObjectFile<ELFT>> &F :
612 Symtab.getObjectFiles()) {
613 for (InputSectionBase<ELFT> *C : F->getSections()) {
614 if (isDiscarded(C)) {
615 reportDiscarded(C, F);
618 OutputSectionBase<ELFT> *Sec;
620 std::tie(Sec, IsNew) = Factory.create(C, getOutputSectionName(C));
622 OwningSections.emplace_back(Sec);
623 OutputSections.push_back(Sec);
624 RegularSections.push_back(Sec);
630 // If we have a .opd section (used under PPC64 for function descriptors),
631 // store a pointer to it here so that we can use it later when processing
633 Out<ELFT>::Opd = Factory.lookup(".opd", SHT_PROGBITS, SHF_WRITE | SHF_ALLOC);
635 Out<ELFT>::Dynamic->PreInitArraySec = Factory.lookup(
636 ".preinit_array", SHT_PREINIT_ARRAY, SHF_WRITE | SHF_ALLOC);
637 Out<ELFT>::Dynamic->InitArraySec =
638 Factory.lookup(".init_array", SHT_INIT_ARRAY, SHF_WRITE | SHF_ALLOC);
639 Out<ELFT>::Dynamic->FiniArraySec =
640 Factory.lookup(".fini_array", SHT_FINI_ARRAY, SHF_WRITE | SHF_ALLOC);
642 // Sort section contents for __attribute__((init_priority(N)).
643 sortInitFini(Out<ELFT>::Dynamic->InitArraySec);
644 sortInitFini(Out<ELFT>::Dynamic->FiniArraySec);
645 sortCtorsDtors(Factory.lookup(".ctors", SHT_PROGBITS, SHF_WRITE | SHF_ALLOC));
646 sortCtorsDtors(Factory.lookup(".dtors", SHT_PROGBITS, SHF_WRITE | SHF_ALLOC));
648 // The linker needs to define SECNAME_start, SECNAME_end and SECNAME_stop
649 // symbols for sections, so that the runtime can get the start and end
650 // addresses of each section by section name. Add such symbols.
651 if (!Config->Relocatable) {
652 addStartEndSymbols();
653 for (OutputSectionBase<ELFT> *Sec : RegularSections)
654 addStartStopSymbols(Sec);
657 // Add _DYNAMIC symbol. Unlike GNU gold, our _DYNAMIC symbol has no type.
658 // It should be okay as no one seems to care about the type.
659 // Even the author of gold doesn't remember why gold behaves that way.
660 // https://sourceware.org/ml/binutils/2002-03/msg00360.html
661 if (isOutputDynamic())
662 Symtab.addSynthetic("_DYNAMIC", Out<ELFT>::Dynamic, 0);
664 // Define __rel[a]_iplt_{start,end} symbols if needed.
667 // Add scripted symbols with zero values now.
668 // Real values will be assigned later
669 Script<ELFT>::X->addScriptedSymbols();
671 if (!Out<ELFT>::EhFrame->empty()) {
672 OutputSections.push_back(Out<ELFT>::EhFrame);
673 Out<ELFT>::EhFrame->finalize();
676 // Scan relocations. This must be done after every symbol is declared so that
677 // we can correctly decide if a dynamic relocation is needed.
678 for (const std::unique_ptr<elf::ObjectFile<ELFT>> &F :
679 Symtab.getObjectFiles()) {
680 for (InputSectionBase<ELFT> *C : F->getSections()) {
683 if (auto *S = dyn_cast<InputSection<ELFT>>(C)) {
687 if (auto *S = dyn_cast<EhInputSection<ELFT>>(C))
689 scanRelocations(*S, *S->RelocSection);
693 for (OutputSectionBase<ELFT> *Sec : OutputSections)
694 Sec->assignOffsets();
696 // Now that we have defined all possible symbols including linker-
697 // synthesized ones. Visit all symbols to give the finishing touches.
698 std::vector<DefinedCommon *> CommonSymbols;
699 for (Symbol *S : Symtab.getSymbols()) {
700 SymbolBody *Body = S->body();
702 // We only report undefined symbols in regular objects. This means that we
703 // will accept an undefined reference in bitcode if it can be optimized out.
704 if (S->IsUsedInRegularObj && Body->isUndefined() && !S->isWeak())
705 reportUndefined<ELFT>(Symtab, Body);
707 if (auto *C = dyn_cast<DefinedCommon>(Body))
708 CommonSymbols.push_back(C);
710 if (!includeInSymtab<ELFT>(*Body))
712 if (Out<ELFT>::SymTab)
713 Out<ELFT>::SymTab->addSymbol(Body);
715 if (isOutputDynamic() && S->includeInDynsym()) {
716 Out<ELFT>::DynSymTab->addSymbol(Body);
717 if (auto *SS = dyn_cast<SharedSymbol<ELFT>>(Body))
718 if (SS->file()->isNeeded())
719 Out<ELFT>::VerNeed->addSymbol(SS);
723 // Do not proceed if there was an undefined symbol.
727 addCommonSymbols(CommonSymbols);
729 // So far we have added sections from input object files.
730 // This function adds linker-created Out<ELFT>::* sections.
731 addPredefinedSections();
733 std::stable_sort(OutputSections.begin(), OutputSections.end(),
734 compareSections<ELFT>);
737 for (OutputSectionBase<ELFT> *Sec : OutputSections) {
738 Sec->SectionIndex = I++;
739 Sec->setSHName(Out<ELFT>::ShStrTab->addString(Sec->getName()));
742 // Finalizers fix each section's size.
743 // .dynsym is finalized early since that may fill up .gnu.hash.
744 if (isOutputDynamic())
745 Out<ELFT>::DynSymTab->finalize();
747 // Fill other section headers. The dynamic table is finalized
748 // at the end because some tags like RELSZ depend on result
749 // of finalizing other sections. The dynamic string table is
750 // finalized once the .dynamic finalizer has added a few last
751 // strings. See DynamicSection::finalize()
752 for (OutputSectionBase<ELFT> *Sec : OutputSections)
753 if (Sec != Out<ELFT>::DynStrTab && Sec != Out<ELFT>::Dynamic)
756 if (isOutputDynamic())
757 Out<ELFT>::Dynamic->finalize();
759 // Now that all output offsets are fixed. Finalize mergeable sections
760 // to fix their maps from input offsets to output offsets.
761 for (OutputSectionBase<ELFT> *Sec : OutputSections)
762 Sec->finalizePieces();
765 template <class ELFT> bool Writer<ELFT>::needsGot() {
766 if (!Out<ELFT>::Got->empty())
769 // We add the .got section to the result for dynamic MIPS target because
770 // its address and properties are mentioned in the .dynamic section.
771 if (Config->EMachine == EM_MIPS)
774 // If we have a relocation that is relative to GOT (such as GOTOFFREL),
775 // we need to emit a GOT even if it's empty.
776 return Out<ELFT>::Got->HasGotOffRel;
779 // This function add Out<ELFT>::* sections to OutputSections.
780 template <class ELFT> void Writer<ELFT>::addPredefinedSections() {
781 auto Add = [&](OutputSectionBase<ELFT> *C) {
783 OutputSections.push_back(C);
786 // A core file does not usually contain unmodified segments except
787 // the first page of the executable. Add the build ID section to beginning of
788 // the file so that the section is included in the first page.
789 if (Out<ELFT>::BuildId)
790 OutputSections.insert(OutputSections.begin(), Out<ELFT>::BuildId);
792 // Add .interp at first because some loaders want to see that section
793 // on the first page of the executable file when loaded into memory.
794 if (needsInterpSection())
795 OutputSections.insert(OutputSections.begin(), Out<ELFT>::Interp);
797 // This order is not the same as the final output order
798 // because we sort the sections using their attributes below.
799 Add(Out<ELFT>::SymTab);
800 Add(Out<ELFT>::ShStrTab);
801 Add(Out<ELFT>::StrTab);
802 if (isOutputDynamic()) {
803 Add(Out<ELFT>::DynSymTab);
805 bool HasVerNeed = Out<ELFT>::VerNeed->getNeedNum() != 0;
806 if (Out<ELFT>::VerDef || HasVerNeed)
807 Add(Out<ELFT>::VerSym);
808 Add(Out<ELFT>::VerDef);
810 Add(Out<ELFT>::VerNeed);
812 Add(Out<ELFT>::GnuHashTab);
813 Add(Out<ELFT>::HashTab);
814 Add(Out<ELFT>::Dynamic);
815 Add(Out<ELFT>::DynStrTab);
816 if (Out<ELFT>::RelaDyn->hasRelocs())
817 Add(Out<ELFT>::RelaDyn);
818 Add(Out<ELFT>::MipsRldMap);
821 // We always need to add rel[a].plt to output if it has entries.
822 // Even during static linking it can contain R_[*]_IRELATIVE relocations.
823 if (Out<ELFT>::RelaPlt && Out<ELFT>::RelaPlt->hasRelocs()) {
824 Add(Out<ELFT>::RelaPlt);
825 Out<ELFT>::RelaPlt->Static = !isOutputDynamic();
830 if (Out<ELFT>::GotPlt && !Out<ELFT>::GotPlt->empty())
831 Add(Out<ELFT>::GotPlt);
832 if (!Out<ELFT>::Plt->empty())
834 if (!Out<ELFT>::EhFrame->empty())
835 Add(Out<ELFT>::EhFrameHdr);
836 if (Out<ELFT>::Bss->getSize() > 0)
840 // The linker is expected to define SECNAME_start and SECNAME_end
841 // symbols for a few sections. This function defines them.
842 template <class ELFT> void Writer<ELFT>::addStartEndSymbols() {
843 auto Define = [&](StringRef Start, StringRef End,
844 OutputSectionBase<ELFT> *OS) {
846 this->Symtab.addSynthetic(Start, OS, 0);
847 this->Symtab.addSynthetic(End, OS, DefinedSynthetic<ELFT>::SectionEnd);
849 addOptionalSynthetic(this->Symtab, Start,
850 (OutputSectionBase<ELFT> *)nullptr, 0);
851 addOptionalSynthetic(this->Symtab, End,
852 (OutputSectionBase<ELFT> *)nullptr, 0);
856 Define("__preinit_array_start", "__preinit_array_end",
857 Out<ELFT>::Dynamic->PreInitArraySec);
858 Define("__init_array_start", "__init_array_end",
859 Out<ELFT>::Dynamic->InitArraySec);
860 Define("__fini_array_start", "__fini_array_end",
861 Out<ELFT>::Dynamic->FiniArraySec);
864 // If a section name is valid as a C identifier (which is rare because of
865 // the leading '.'), linkers are expected to define __start_<secname> and
866 // __stop_<secname> symbols. They are at beginning and end of the section,
867 // respectively. This is not requested by the ELF standard, but GNU ld and
868 // gold provide the feature, and used by many programs.
869 template <class ELFT>
870 void Writer<ELFT>::addStartStopSymbols(OutputSectionBase<ELFT> *Sec) {
871 StringRef S = Sec->getName();
872 if (!isValidCIdentifier(S))
874 StringSaver Saver(Alloc);
875 StringRef Start = Saver.save("__start_" + S);
876 StringRef Stop = Saver.save("__stop_" + S);
877 if (SymbolBody *B = Symtab.find(Start))
878 if (B->isUndefined())
879 Symtab.addSynthetic(Start, Sec, 0);
880 if (SymbolBody *B = Symtab.find(Stop))
881 if (B->isUndefined())
882 Symtab.addSynthetic(Stop, Sec, DefinedSynthetic<ELFT>::SectionEnd);
885 template <class ELFT> static bool needsPtLoad(OutputSectionBase<ELFT> *Sec) {
886 if (!(Sec->getFlags() & SHF_ALLOC))
889 // Don't allocate VA space for TLS NOBITS sections. The PT_TLS PHDR is
890 // responsible for allocating space for them, not the PT_LOAD that
891 // contains the TLS initialization image.
892 if (Sec->getFlags() & SHF_TLS && Sec->getType() == SHT_NOBITS)
897 static uint32_t toPhdrFlags(uint64_t Flags) {
899 if (Flags & SHF_WRITE)
901 if (Flags & SHF_EXECINSTR)
906 // Decide which program headers to create and which sections to include in each
908 template <class ELFT> void Writer<ELFT>::createPhdrs() {
909 auto AddHdr = [this](unsigned Type, unsigned Flags) {
910 return &*Phdrs.emplace(Phdrs.end(), Type, Flags);
913 auto AddSec = [](Phdr &Hdr, OutputSectionBase<ELFT> *Sec) {
917 Hdr.H.p_align = std::max<uintX_t>(Hdr.H.p_align, Sec->getAlignment());
920 // The first phdr entry is PT_PHDR which describes the program header itself.
921 Phdr &Hdr = *AddHdr(PT_PHDR, PF_R);
922 AddSec(Hdr, Out<ELFT>::ProgramHeaders);
924 // PT_INTERP must be the second entry if exists.
925 if (needsInterpSection()) {
926 Phdr &Hdr = *AddHdr(PT_INTERP, toPhdrFlags(Out<ELFT>::Interp->getFlags()));
927 AddSec(Hdr, Out<ELFT>::Interp);
930 // Add the first PT_LOAD segment for regular output sections.
931 uintX_t Flags = PF_R;
932 Phdr *Load = AddHdr(PT_LOAD, Flags);
933 AddSec(*Load, Out<ELFT>::ElfHeader);
934 AddSec(*Load, Out<ELFT>::ProgramHeaders);
936 Phdr TlsHdr(PT_TLS, PF_R);
937 Phdr RelRo(PT_GNU_RELRO, PF_R);
938 Phdr Note(PT_NOTE, PF_R);
939 for (OutputSectionBase<ELFT> *Sec : OutputSections) {
940 if (!(Sec->getFlags() & SHF_ALLOC))
943 // If we meet TLS section then we create TLS header
944 // and put all TLS sections inside for futher use when
946 if (Sec->getFlags() & SHF_TLS)
949 if (!needsPtLoad<ELFT>(Sec))
952 // If flags changed then we want new load segment.
953 uintX_t NewFlags = toPhdrFlags(Sec->getFlags());
954 if (Flags != NewFlags) {
955 Load = AddHdr(PT_LOAD, NewFlags);
961 if (isRelroSection(Sec))
963 if (Sec->getType() == SHT_NOTE)
967 // Add the TLS segment unless it's empty.
969 Phdrs.push_back(std::move(TlsHdr));
971 // Add an entry for .dynamic.
972 if (isOutputDynamic()) {
973 Phdr &H = *AddHdr(PT_DYNAMIC, toPhdrFlags(Out<ELFT>::Dynamic->getFlags()));
974 AddSec(H, Out<ELFT>::Dynamic);
977 // PT_GNU_RELRO includes all sections that should be marked as
978 // read-only by dynamic linker after proccessing relocations.
980 Phdrs.push_back(std::move(RelRo));
982 // PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
983 if (!Out<ELFT>::EhFrame->empty() && Out<ELFT>::EhFrameHdr) {
984 Phdr &Hdr = *AddHdr(PT_GNU_EH_FRAME,
985 toPhdrFlags(Out<ELFT>::EhFrameHdr->getFlags()));
986 AddSec(Hdr, Out<ELFT>::EhFrameHdr);
989 // PT_GNU_STACK is a special section to tell the loader to make the
990 // pages for the stack non-executable.
991 if (!Config->ZExecStack)
992 AddHdr(PT_GNU_STACK, PF_R | PF_W);
995 Phdrs.push_back(std::move(Note));
997 Out<ELFT>::ProgramHeaders->setSize(sizeof(Elf_Phdr) * Phdrs.size());
1000 // The first section of each PT_LOAD and the first section after PT_GNU_RELRO
1001 // have to be page aligned so that the dynamic linker can set the permissions.
1002 template <class ELFT> void Writer<ELFT>::fixSectionAlignments() {
1003 for (const Phdr &P : Phdrs)
1004 if (P.H.p_type == PT_LOAD)
1005 P.First->PageAlign = true;
1007 for (const Phdr &P : Phdrs) {
1008 if (P.H.p_type != PT_GNU_RELRO)
1010 // Find the first section after PT_GNU_RELRO. If it is in a PT_LOAD we
1011 // have to align it to a page.
1012 auto End = OutputSections.end();
1013 auto I = std::find(OutputSections.begin(), End, P.Last);
1014 if (I == End || (I + 1) == End)
1016 OutputSectionBase<ELFT> *Sec = *(I + 1);
1017 if (needsPtLoad(Sec))
1018 Sec->PageAlign = true;
1022 // We should set file offsets and VAs for elf header and program headers
1023 // sections. These are special, we do not include them into output sections
1024 // list, but have them to simplify the code.
1025 template <class ELFT> void Writer<ELFT>::fixHeaders() {
1026 uintX_t BaseVA = ScriptConfig->DoLayout ? 0 : Config->ImageBase;
1027 Out<ELFT>::ElfHeader->setVA(BaseVA);
1028 uintX_t Off = Out<ELFT>::ElfHeader->getSize();
1029 Out<ELFT>::ProgramHeaders->setVA(Off + BaseVA);
1032 // Assign VAs (addresses at run-time) to output sections.
1033 template <class ELFT> void Writer<ELFT>::assignAddresses() {
1034 uintX_t VA = Config->ImageBase + Out<ELFT>::ElfHeader->getSize() +
1035 Out<ELFT>::ProgramHeaders->getSize();
1037 uintX_t ThreadBssOffset = 0;
1038 for (OutputSectionBase<ELFT> *Sec : OutputSections) {
1039 uintX_t Alignment = Sec->getAlignment();
1041 Alignment = std::max<uintX_t>(Alignment, Target->PageSize);
1043 // We only assign VAs to allocated sections.
1044 if (needsPtLoad<ELFT>(Sec)) {
1045 VA = alignTo(VA, Alignment);
1047 VA += Sec->getSize();
1048 } else if (Sec->getFlags() & SHF_TLS && Sec->getType() == SHT_NOBITS) {
1049 uintX_t TVA = VA + ThreadBssOffset;
1050 TVA = alignTo(TVA, Alignment);
1052 ThreadBssOffset = TVA - VA + Sec->getSize();
1057 // Adjusts the file alignment for a given output section and returns
1058 // its new file offset. The file offset must be the same with its
1059 // virtual address (modulo the page size) so that the loader can load
1060 // executables without any address adjustment.
1061 template <class ELFT, class uintX_t>
1062 static uintX_t getFileAlignment(uintX_t Off, OutputSectionBase<ELFT> *Sec) {
1063 uintX_t Alignment = Sec->getAlignment();
1065 Alignment = std::max<uintX_t>(Alignment, Target->PageSize);
1066 Off = alignTo(Off, Alignment);
1068 // Relocatable output does not have program headers
1069 // and does not need any other offset adjusting.
1070 if (Config->Relocatable || !(Sec->getFlags() & SHF_ALLOC))
1072 return alignTo(Off, Target->PageSize, Sec->getVA());
1075 // Assign file offsets to output sections.
1076 template <class ELFT> void Writer<ELFT>::assignFileOffsets() {
1079 auto Set = [&](OutputSectionBase<ELFT> *Sec) {
1080 if (Sec->getType() == SHT_NOBITS) {
1081 Sec->setFileOffset(Off);
1085 Off = getFileAlignment<ELFT>(Off, Sec);
1086 Sec->setFileOffset(Off);
1087 Off += Sec->getSize();
1090 Set(Out<ELFT>::ElfHeader);
1091 Set(Out<ELFT>::ProgramHeaders);
1092 for (OutputSectionBase<ELFT> *Sec : OutputSections)
1095 SectionHeaderOff = alignTo(Off, sizeof(uintX_t));
1096 FileSize = SectionHeaderOff + (OutputSections.size() + 1) * sizeof(Elf_Shdr);
1099 // Finalize the program headers. We call this function after we assign
1100 // file offsets and VAs to all sections.
1101 template <class ELFT> void Writer<ELFT>::setPhdrs() {
1102 for (Phdr &P : Phdrs) {
1104 OutputSectionBase<ELFT> *First = P.First;
1105 OutputSectionBase<ELFT> *Last = P.Last;
1107 H.p_filesz = Last->getFileOff() - First->getFileOff();
1108 if (Last->getType() != SHT_NOBITS)
1109 H.p_filesz += Last->getSize();
1110 H.p_memsz = Last->getVA() + Last->getSize() - First->getVA();
1111 H.p_offset = First->getFileOff();
1112 H.p_vaddr = First->getVA();
1114 if (H.p_type == PT_LOAD)
1115 H.p_align = Target->PageSize;
1116 else if (H.p_type == PT_GNU_RELRO)
1118 H.p_paddr = H.p_vaddr;
1120 // The TLS pointer goes after PT_TLS. At least glibc will align it,
1121 // so round up the size to make sure the offsets are correct.
1122 if (H.p_type == PT_TLS) {
1123 Out<ELFT>::TlsPhdr = &H;
1124 H.p_memsz = alignTo(H.p_memsz, H.p_align);
1129 static uint32_t getMipsEFlags(bool Is64Bits) {
1130 // FIXME: In fact ELF flags depends on ELF flags of input object files
1131 // and selected emulation. For now just use hard coded values.
1133 return EF_MIPS_CPIC | EF_MIPS_PIC | EF_MIPS_ARCH_64R2;
1135 uint32_t V = EF_MIPS_CPIC | EF_MIPS_ABI_O32 | EF_MIPS_ARCH_32R2;
1141 template <class ELFT> static typename ELFT::uint getEntryAddr() {
1142 if (Symbol *S = Config->EntrySym)
1143 return S->body()->getVA<ELFT>();
1144 if (Config->EntryAddr != uint64_t(-1))
1145 return Config->EntryAddr;
1149 template <class ELFT> static uint8_t getELFEncoding() {
1150 if (ELFT::TargetEndianness == llvm::support::little)
1155 static uint16_t getELFType() {
1158 if (Config->Relocatable)
1163 // This function is called after we have assigned address and size
1164 // to each section. This function fixes some predefined absolute
1165 // symbol values that depend on section address and size.
1166 template <class ELFT> void Writer<ELFT>::fixAbsoluteSymbols() {
1167 auto Set = [](DefinedRegular<ELFT> *S1, DefinedRegular<ELFT> *S2, uintX_t V) {
1174 // _etext is the first location after the last read-only loadable segment.
1175 // _edata is the first location after the last read-write loadable segment.
1176 // _end is the first location after the uninitialized data region.
1177 for (Phdr &P : Phdrs) {
1179 if (H.p_type != PT_LOAD)
1181 Set(ElfSym<ELFT>::End, ElfSym<ELFT>::End2, H.p_vaddr + H.p_memsz);
1183 uintX_t Val = H.p_vaddr + H.p_filesz;
1184 if (H.p_flags & PF_W)
1185 Set(ElfSym<ELFT>::Edata, ElfSym<ELFT>::Edata2, Val);
1187 Set(ElfSym<ELFT>::Etext, ElfSym<ELFT>::Etext2, Val);
1191 template <class ELFT> void Writer<ELFT>::writeHeader() {
1192 uint8_t *Buf = Buffer->getBufferStart();
1193 memcpy(Buf, "\177ELF", 4);
1195 auto &FirstObj = cast<ELFFileBase<ELFT>>(*Config->FirstElf);
1197 // Write the ELF header.
1198 auto *EHdr = reinterpret_cast<Elf_Ehdr *>(Buf);
1199 EHdr->e_ident[EI_CLASS] = ELFT::Is64Bits ? ELFCLASS64 : ELFCLASS32;
1200 EHdr->e_ident[EI_DATA] = getELFEncoding<ELFT>();
1201 EHdr->e_ident[EI_VERSION] = EV_CURRENT;
1202 EHdr->e_ident[EI_OSABI] = FirstObj.getOSABI();
1203 EHdr->e_type = getELFType();
1204 EHdr->e_machine = FirstObj.EMachine;
1205 EHdr->e_version = EV_CURRENT;
1206 EHdr->e_entry = getEntryAddr<ELFT>();
1207 EHdr->e_shoff = SectionHeaderOff;
1208 EHdr->e_ehsize = sizeof(Elf_Ehdr);
1209 EHdr->e_phnum = Phdrs.size();
1210 EHdr->e_shentsize = sizeof(Elf_Shdr);
1211 EHdr->e_shnum = OutputSections.size() + 1;
1212 EHdr->e_shstrndx = Out<ELFT>::ShStrTab->SectionIndex;
1214 if (Config->EMachine == EM_MIPS)
1215 EHdr->e_flags = getMipsEFlags(ELFT::Is64Bits);
1217 if (!Config->Relocatable) {
1218 EHdr->e_phoff = sizeof(Elf_Ehdr);
1219 EHdr->e_phentsize = sizeof(Elf_Phdr);
1222 // Write the program header table.
1223 auto *HBuf = reinterpret_cast<Elf_Phdr *>(Buf + EHdr->e_phoff);
1224 for (Phdr &P : Phdrs)
1227 // Write the section header table. Note that the first table entry is null.
1228 auto *SHdrs = reinterpret_cast<Elf_Shdr *>(Buf + EHdr->e_shoff);
1229 for (OutputSectionBase<ELFT> *Sec : OutputSections)
1230 Sec->writeHeaderTo(++SHdrs);
1233 template <class ELFT> void Writer<ELFT>::openFile() {
1234 ErrorOr<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
1235 FileOutputBuffer::create(Config->OutputFile, FileSize,
1236 FileOutputBuffer::F_executable);
1237 if (auto EC = BufferOrErr.getError())
1238 error(EC, "failed to open " + Config->OutputFile);
1240 Buffer = std::move(*BufferOrErr);
1243 // Write section contents to a mmap'ed file.
1244 template <class ELFT> void Writer<ELFT>::writeSections() {
1245 uint8_t *Buf = Buffer->getBufferStart();
1247 // PPC64 needs to process relocations in the .opd section before processing
1248 // relocations in code-containing sections.
1249 if (OutputSectionBase<ELFT> *Sec = Out<ELFT>::Opd) {
1250 Out<ELFT>::OpdBuf = Buf + Sec->getFileOff();
1251 Sec->writeTo(Buf + Sec->getFileOff());
1254 for (OutputSectionBase<ELFT> *Sec : OutputSections)
1255 if (Sec != Out<ELFT>::Opd)
1256 Sec->writeTo(Buf + Sec->getFileOff());
1259 template <class ELFT> void Writer<ELFT>::writeBuildId() {
1260 if (!Out<ELFT>::BuildId)
1263 // Compute a hash of all sections except .debug_* sections.
1264 // We skip debug sections because they tend to be very large
1265 // and their contents are very likely to be the same as long as
1266 // other sections are the same.
1267 uint8_t *Start = Buffer->getBufferStart();
1268 uint8_t *Last = Start;
1269 std::vector<ArrayRef<uint8_t>> Regions;
1270 for (OutputSectionBase<ELFT> *Sec : OutputSections) {
1271 uint8_t *End = Start + Sec->getFileOff();
1272 if (!Sec->getName().startswith(".debug_"))
1273 Regions.push_back({Last, End});
1276 Regions.push_back({Last, Start + FileSize});
1277 Out<ELFT>::BuildId->writeBuildId(Regions);
1280 template void elf::writeResult<ELF32LE>(SymbolTable<ELF32LE> *Symtab);
1281 template void elf::writeResult<ELF32BE>(SymbolTable<ELF32BE> *Symtab);
1282 template void elf::writeResult<ELF64LE>(SymbolTable<ELF64LE> *Symtab);
1283 template void elf::writeResult<ELF64BE>(SymbolTable<ELF64BE> *Symtab);