1 //===- Writer.cpp ---------------------------------------------------------===//
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
11 #include "AArch64ErrataFix.h"
13 #include "Filesystem.h"
14 #include "LinkerScript.h"
16 #include "OutputSections.h"
17 #include "Relocations.h"
19 #include "SymbolTable.h"
21 #include "SyntheticSections.h"
23 #include "lld/Common/Memory.h"
24 #include "lld/Common/Threads.h"
25 #include "llvm/ADT/StringMap.h"
26 #include "llvm/ADT/StringSwitch.h"
30 using namespace llvm::ELF;
31 using namespace llvm::object;
32 using namespace llvm::support;
33 using namespace llvm::support::endian;
36 using namespace lld::elf;
39 // The writer writes a SymbolTable result to a file.
40 template <class ELFT> class Writer {
42 Writer() : Buffer(errorHandler().OutputBuffer) {}
43 typedef typename ELFT::Shdr Elf_Shdr;
44 typedef typename ELFT::Ehdr Elf_Ehdr;
45 typedef typename ELFT::Phdr Elf_Phdr;
50 void copyLocalSymbols();
51 void addSectionSymbols();
52 void forEachRelSec(std::function<void(InputSectionBase &)> Fn);
54 void resolveShfLinkOrder();
55 void sortInputSections();
56 void finalizeSections();
57 void addPredefinedSections();
58 void setReservedSymbolSections();
60 std::vector<PhdrEntry *> createPhdrs();
61 void removeEmptyPTLoad();
62 void addPtArmExid(std::vector<PhdrEntry *> &Phdrs);
63 void assignFileOffsets();
64 void assignFileOffsetsBinary();
66 void fixSectionAlignments();
68 void writeTrapInstr();
71 void writeSectionsBinary();
74 std::unique_ptr<FileOutputBuffer> &Buffer;
76 void addRelIpltSymbols();
77 void addStartEndSymbols();
78 void addStartStopSymbols(OutputSection *Sec);
79 uint64_t getEntryAddr();
81 std::vector<PhdrEntry *> Phdrs;
84 uint64_t SectionHeaderOff;
86 bool HasGotBaseSym = false;
88 } // anonymous namespace
90 StringRef elf::getOutputSectionName(InputSectionBase *S) {
91 // ".zdebug_" is a prefix for ZLIB-compressed sections.
92 // Because we decompressed input sections, we want to remove 'z'.
93 if (S->Name.startswith(".zdebug_"))
94 return Saver.save("." + S->Name.substr(2));
96 if (Config->Relocatable)
99 // This is for --emit-relocs. If .text.foo is emitted as .text.bar, we want
100 // to emit .rela.text.foo as .rela.text.bar for consistency (this is not
101 // technically required, but not doing it is odd). This code guarantees that.
102 if ((S->Type == SHT_REL || S->Type == SHT_RELA) &&
103 !isa<SyntheticSection>(S)) {
105 cast<InputSection>(S)->getRelocatedSection()->getOutputSection();
106 if (S->Type == SHT_RELA)
107 return Saver.save(".rela" + Out->Name);
108 return Saver.save(".rel" + Out->Name);
112 {".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.rel.ro.",
113 ".bss.", ".init_array.", ".fini_array.", ".ctors.", ".dtors.", ".tbss.",
114 ".gcc_except_table.", ".tdata.", ".ARM.exidx.", ".ARM.extab."}) {
115 StringRef Prefix = V.drop_back();
116 if (S->Name.startswith(V) || S->Name == Prefix)
120 // CommonSection is identified as "COMMON" in linker scripts.
121 // By default, it should go to .bss section.
122 if (S->Name == "COMMON")
128 static bool needsInterpSection() {
129 return !SharedFiles.empty() && !Config->DynamicLinker.empty() &&
130 Script->needsInterpSection();
133 template <class ELFT> void elf::writeResult() { Writer<ELFT>().run(); }
135 template <class ELFT> void Writer<ELFT>::removeEmptyPTLoad() {
136 llvm::erase_if(Phdrs, [&](const PhdrEntry *P) {
137 if (P->p_type != PT_LOAD)
141 uint64_t Size = P->LastSec->Addr + P->LastSec->Size - P->FirstSec->Addr;
146 template <class ELFT> static void combineEhFrameSections() {
147 for (InputSectionBase *&S : InputSections) {
148 EhInputSection *ES = dyn_cast<EhInputSection>(S);
149 if (!ES || !ES->Live)
152 InX::EhFrame->addSection<ELFT>(ES);
156 std::vector<InputSectionBase *> &V = InputSections;
157 V.erase(std::remove(V.begin(), V.end(), nullptr), V.end());
160 template <class ELFT>
161 static Defined *addOptionalRegular(StringRef Name, SectionBase *Sec,
162 uint64_t Val, uint8_t StOther = STV_HIDDEN,
163 uint8_t Binding = STB_GLOBAL) {
164 Symbol *S = Symtab->find(Name);
165 if (!S || S->isDefined())
167 Symbol *Sym = Symtab->addRegular<ELFT>(Name, StOther, STT_NOTYPE, Val,
168 /*Size=*/0, Binding, Sec,
170 return cast<Defined>(Sym);
173 // The linker is expected to define some symbols depending on
174 // the linking result. This function defines such symbols.
175 template <class ELFT> void elf::addReservedSymbols() {
176 if (Config->EMachine == EM_MIPS) {
177 // Define _gp for MIPS. st_value of _gp symbol will be updated by Writer
178 // so that it points to an absolute address which by default is relative
179 // to GOT. Default offset is 0x7ff0.
180 // See "Global Data Symbols" in Chapter 6 in the following document:
181 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
182 ElfSym::MipsGp = Symtab->addAbsolute<ELFT>("_gp", STV_HIDDEN, STB_GLOBAL);
184 // On MIPS O32 ABI, _gp_disp is a magic symbol designates offset between
185 // start of function and 'gp' pointer into GOT.
186 if (Symtab->find("_gp_disp"))
188 Symtab->addAbsolute<ELFT>("_gp_disp", STV_HIDDEN, STB_GLOBAL);
190 // The __gnu_local_gp is a magic symbol equal to the current value of 'gp'
191 // pointer. This symbol is used in the code generated by .cpload pseudo-op
192 // in case of using -mno-shared option.
193 // https://sourceware.org/ml/binutils/2004-12/msg00094.html
194 if (Symtab->find("__gnu_local_gp"))
195 ElfSym::MipsLocalGp =
196 Symtab->addAbsolute<ELFT>("__gnu_local_gp", STV_HIDDEN, STB_GLOBAL);
199 ElfSym::GlobalOffsetTable = addOptionalRegular<ELFT>(
200 "_GLOBAL_OFFSET_TABLE_", Out::ElfHeader, Target->GotBaseSymOff);
202 // __ehdr_start is the location of ELF file headers. Note that we define
203 // this symbol unconditionally even when using a linker script, which
204 // differs from the behavior implemented by GNU linker which only define
205 // this symbol if ELF headers are in the memory mapped segment.
206 // __executable_start is not documented, but the expectation of at
207 // least the android libc is that it points to the elf header too.
208 // __dso_handle symbol is passed to cxa_finalize as a marker to identify
209 // each DSO. The address of the symbol doesn't matter as long as they are
210 // different in different DSOs, so we chose the start address of the DSO.
211 for (const char *Name :
212 {"__ehdr_start", "__executable_start", "__dso_handle"})
213 addOptionalRegular<ELFT>(Name, Out::ElfHeader, 0, STV_HIDDEN);
215 // If linker script do layout we do not need to create any standart symbols.
216 if (Script->HasSectionsCommand)
219 auto Add = [](StringRef S, int64_t Pos) {
220 return addOptionalRegular<ELFT>(S, Out::ElfHeader, Pos, STV_DEFAULT);
223 ElfSym::Bss = Add("__bss_start", 0);
224 ElfSym::End1 = Add("end", -1);
225 ElfSym::End2 = Add("_end", -1);
226 ElfSym::Etext1 = Add("etext", -1);
227 ElfSym::Etext2 = Add("_etext", -1);
228 ElfSym::Edata1 = Add("edata", -1);
229 ElfSym::Edata2 = Add("_edata", -1);
232 static OutputSection *findSection(StringRef Name) {
233 for (BaseCommand *Base : Script->SectionCommands)
234 if (auto *Sec = dyn_cast<OutputSection>(Base))
235 if (Sec->Name == Name)
240 // Initialize Out members.
241 template <class ELFT> static void createSyntheticSections() {
242 // Initialize all pointers with NULL. This is needed because
243 // you can call lld::elf::main more than once as a library.
244 memset(&Out::First, 0, sizeof(Out));
246 auto Add = [](InputSectionBase *Sec) { InputSections.push_back(Sec); };
248 InX::DynStrTab = make<StringTableSection>(".dynstr", true);
249 InX::Dynamic = make<DynamicSection<ELFT>>();
250 if (Config->AndroidPackDynRelocs) {
251 InX::RelaDyn = make<AndroidPackedRelocationSection<ELFT>>(
252 Config->IsRela ? ".rela.dyn" : ".rel.dyn");
254 InX::RelaDyn = make<RelocationSection<ELFT>>(
255 Config->IsRela ? ".rela.dyn" : ".rel.dyn", Config->ZCombreloc);
257 InX::ShStrTab = make<StringTableSection>(".shstrtab", false);
259 Out::ProgramHeaders = make<OutputSection>("", 0, SHF_ALLOC);
260 Out::ProgramHeaders->Alignment = Config->Wordsize;
262 if (needsInterpSection()) {
263 InX::Interp = createInterpSection();
266 InX::Interp = nullptr;
269 if (Config->Strip != StripPolicy::All) {
270 InX::StrTab = make<StringTableSection>(".strtab", false);
271 InX::SymTab = make<SymbolTableSection<ELFT>>(*InX::StrTab);
274 if (Config->BuildId != BuildIdKind::None) {
275 InX::BuildId = make<BuildIdSection>();
279 InX::Bss = make<BssSection>(".bss", 0, 1);
282 // If there is a SECTIONS command and a .data.rel.ro section name use name
283 // .data.rel.ro.bss so that we match in the .data.rel.ro output section.
284 // This makes sure our relro is contiguous.
286 Script->HasSectionsCommand && findSection(".data.rel.ro");
287 InX::BssRelRo = make<BssSection>(
288 HasDataRelRo ? ".data.rel.ro.bss" : ".bss.rel.ro", 0, 1);
291 // Add MIPS-specific sections.
292 if (Config->EMachine == EM_MIPS) {
293 if (!Config->Shared && Config->HasDynSymTab) {
294 InX::MipsRldMap = make<MipsRldMapSection>();
295 Add(InX::MipsRldMap);
297 if (auto *Sec = MipsAbiFlagsSection<ELFT>::create())
299 if (auto *Sec = MipsOptionsSection<ELFT>::create())
301 if (auto *Sec = MipsReginfoSection<ELFT>::create())
305 if (Config->HasDynSymTab) {
306 InX::DynSymTab = make<SymbolTableSection<ELFT>>(*InX::DynStrTab);
309 In<ELFT>::VerSym = make<VersionTableSection<ELFT>>();
310 Add(In<ELFT>::VerSym);
312 if (!Config->VersionDefinitions.empty()) {
313 In<ELFT>::VerDef = make<VersionDefinitionSection<ELFT>>();
314 Add(In<ELFT>::VerDef);
317 In<ELFT>::VerNeed = make<VersionNeedSection<ELFT>>();
318 Add(In<ELFT>::VerNeed);
320 if (Config->GnuHash) {
321 InX::GnuHashTab = make<GnuHashTableSection>();
322 Add(InX::GnuHashTab);
325 if (Config->SysvHash) {
326 InX::HashTab = make<HashTableSection>();
335 // Add .got. MIPS' .got is so different from the other archs,
336 // it has its own class.
337 if (Config->EMachine == EM_MIPS) {
338 InX::MipsGot = make<MipsGotSection>();
341 InX::Got = make<GotSection>();
345 InX::GotPlt = make<GotPltSection>();
347 InX::IgotPlt = make<IgotPltSection>();
350 if (Config->GdbIndex) {
351 InX::GdbIndex = createGdbIndex<ELFT>();
355 // We always need to add rel[a].plt to output if it has entries.
356 // Even for static linking it can contain R_[*]_IRELATIVE relocations.
357 InX::RelaPlt = make<RelocationSection<ELFT>>(
358 Config->IsRela ? ".rela.plt" : ".rel.plt", false /*Sort*/);
361 // The RelaIplt immediately follows .rel.plt (.rel.dyn for ARM) to ensure
362 // that the IRelative relocations are processed last by the dynamic loader.
363 // We cannot place the iplt section in .rel.dyn when Android relocation
364 // packing is enabled because that would cause a section type mismatch.
365 // However, because the Android dynamic loader reads .rel.plt after .rel.dyn,
366 // we can get the desired behaviour by placing the iplt section in .rel.plt.
367 InX::RelaIplt = make<RelocationSection<ELFT>>(
368 (Config->EMachine == EM_ARM && !Config->AndroidPackDynRelocs)
370 : InX::RelaPlt->Name,
374 InX::Plt = make<PltSection>(Target->PltHeaderSize);
376 InX::Iplt = make<PltSection>(0);
379 if (!Config->Relocatable) {
380 if (Config->EhFrameHdr) {
381 InX::EhFrameHdr = make<EhFrameHeader>();
382 Add(InX::EhFrameHdr);
384 InX::EhFrame = make<EhFrameSection>();
395 // The main function of the writer.
396 template <class ELFT> void Writer<ELFT>::run() {
397 // Create linker-synthesized sections such as .got or .plt.
398 // Such sections are of type input section.
399 createSyntheticSections<ELFT>();
401 if (!Config->Relocatable)
402 combineEhFrameSections<ELFT>();
404 // We want to process linker script commands. When SECTIONS command
405 // is given we let it create sections.
406 Script->processSectionCommands();
408 // Linker scripts controls how input sections are assigned to output sections.
409 // Input sections that were not handled by scripts are called "orphans", and
410 // they are assigned to output sections by the default rule. Process that.
411 Script->addOrphanSections();
413 if (Config->Discard != DiscardPolicy::All)
416 if (Config->CopyRelocs)
419 // Now that we have a complete set of output sections. This function
420 // completes section contents. For example, we need to add strings
421 // to the string table, and add entries to .got and .plt.
422 // finalizeSections does that.
427 // If -compressed-debug-sections is specified, we need to compress
428 // .debug_* sections. Do it right now because it changes the size of
430 parallelForEach(OutputSections,
431 [](OutputSection *Sec) { Sec->maybeCompress<ELFT>(); });
433 Script->assignAddresses();
434 Script->allocateHeaders(Phdrs);
436 // Remove empty PT_LOAD to avoid causing the dynamic linker to try to mmap a
437 // 0 sized region. This has to be done late since only after assignAddresses
438 // we know the size of the sections.
441 if (!Config->OFormatBinary)
444 assignFileOffsetsBinary();
448 if (Config->Relocatable) {
449 for (OutputSection *Sec : OutputSections)
453 // It does not make sense try to open the file if we have error already.
456 // Write the result down to a file.
461 if (!Config->OFormatBinary) {
466 writeSectionsBinary();
469 // Backfill .note.gnu.build-id section content. This is done at last
470 // because the content is usually a hash value of the entire output file.
475 // Handle -Map option.
480 if (auto E = Buffer->commit())
481 error("failed to write to the output file: " + toString(std::move(E)));
484 static bool shouldKeepInSymtab(SectionBase *Sec, StringRef SymName,
486 if (B.isFile() || B.isSection())
489 // If sym references a section in a discarded group, don't keep it.
490 if (Sec == &InputSection::Discarded)
493 if (Config->Discard == DiscardPolicy::None)
496 // In ELF assembly .L symbols are normally discarded by the assembler.
497 // If the assembler fails to do so, the linker discards them if
498 // * --discard-locals is used.
499 // * The symbol is in a SHF_MERGE section, which is normally the reason for
500 // the assembler keeping the .L symbol.
501 if (!SymName.startswith(".L") && !SymName.empty())
504 if (Config->Discard == DiscardPolicy::Locals)
507 return !Sec || !(Sec->Flags & SHF_MERGE);
510 static bool includeInSymtab(const Symbol &B) {
511 if (!B.isLocal() && !B.IsUsedInRegularObj)
514 if (auto *D = dyn_cast<Defined>(&B)) {
515 // Always include absolute symbols.
516 SectionBase *Sec = D->Section;
520 // Exclude symbols pointing to garbage-collected sections.
521 if (isa<InputSectionBase>(Sec) && !Sec->Live)
523 if (auto *S = dyn_cast<MergeInputSection>(Sec))
524 if (!S->getSectionPiece(D->Value)->Live)
531 // Local symbols are not in the linker's symbol table. This function scans
532 // each object file's symbol table to copy local symbols to the output.
533 template <class ELFT> void Writer<ELFT>::copyLocalSymbols() {
536 for (InputFile *File : ObjectFiles) {
537 ObjFile<ELFT> *F = cast<ObjFile<ELFT>>(File);
538 for (Symbol *B : F->getLocalSymbols()) {
541 ": broken object: getLocalSymbols returns a non-local symbol");
542 auto *DR = dyn_cast<Defined>(B);
544 // No reason to keep local undefined symbol in symtab.
547 if (!includeInSymtab(*B))
550 SectionBase *Sec = DR->Section;
551 if (!shouldKeepInSymtab(Sec, B->getName(), *B))
553 InX::SymTab->addSymbol(B);
558 template <class ELFT> void Writer<ELFT>::addSectionSymbols() {
559 // Create a section symbol for each output section so that we can represent
560 // relocations that point to the section. If we know that no relocation is
561 // referring to a section (that happens if the section is a synthetic one), we
562 // don't create a section symbol for that section.
563 for (BaseCommand *Base : Script->SectionCommands) {
564 auto *Sec = dyn_cast<OutputSection>(Base);
567 auto I = llvm::find_if(Sec->SectionCommands, [](BaseCommand *Base) {
568 if (auto *ISD = dyn_cast<InputSectionDescription>(Base))
569 return !ISD->Sections.empty();
572 if (I == Sec->SectionCommands.end())
574 InputSection *IS = cast<InputSectionDescription>(*I)->Sections[0];
576 // Relocations are not using REL[A] section symbols.
577 if (IS->Type == SHT_REL || IS->Type == SHT_RELA)
580 // Unlike other synthetic sections, mergeable output sections contain data
581 // copied from input sections, and there may be a relocation pointing to its
582 // contents if -r or -emit-reloc are given.
583 if (isa<SyntheticSection>(IS) && !(IS->Flags & SHF_MERGE))
587 make<Defined>(IS->File, "", STB_LOCAL, /*StOther=*/0, STT_SECTION,
588 /*Value=*/0, /*Size=*/0, IS);
589 InX::SymTab->addSymbol(Sym);
593 // Today's loaders have a feature to make segments read-only after
594 // processing dynamic relocations to enhance security. PT_GNU_RELRO
595 // is defined for that.
597 // This function returns true if a section needs to be put into a
598 // PT_GNU_RELRO segment.
599 static bool isRelroSection(const OutputSection *Sec) {
603 uint64_t Flags = Sec->Flags;
605 // Non-allocatable or non-writable sections don't need RELRO because
606 // they are not writable or not even mapped to memory in the first place.
607 // RELRO is for sections that are essentially read-only but need to
608 // be writable only at process startup to allow dynamic linker to
609 // apply relocations.
610 if (!(Flags & SHF_ALLOC) || !(Flags & SHF_WRITE))
613 // Once initialized, TLS data segments are used as data templates
614 // for a thread-local storage. For each new thread, runtime
615 // allocates memory for a TLS and copy templates there. No thread
616 // are supposed to use templates directly. Thus, it can be in RELRO.
620 // .init_array, .preinit_array and .fini_array contain pointers to
621 // functions that are executed on process startup or exit. These
622 // pointers are set by the static linker, and they are not expected
623 // to change at runtime. But if you are an attacker, you could do
624 // interesting things by manipulating pointers in .fini_array, for
625 // example. So they are put into RELRO.
626 uint32_t Type = Sec->Type;
627 if (Type == SHT_INIT_ARRAY || Type == SHT_FINI_ARRAY ||
628 Type == SHT_PREINIT_ARRAY)
631 // .got contains pointers to external symbols. They are resolved by
632 // the dynamic linker when a module is loaded into memory, and after
633 // that they are not expected to change. So, it can be in RELRO.
634 if (InX::Got && Sec == InX::Got->getParent())
637 // .got.plt contains pointers to external function symbols. They are
638 // by default resolved lazily, so we usually cannot put it into RELRO.
639 // However, if "-z now" is given, the lazy symbol resolution is
640 // disabled, which enables us to put it into RELRO.
641 if (Sec == InX::GotPlt->getParent())
644 // .dynamic section contains data for the dynamic linker, and
645 // there's no need to write to it at runtime, so it's better to put
647 if (Sec == InX::Dynamic->getParent())
650 // Sections with some special names are put into RELRO. This is a
651 // bit unfortunate because section names shouldn't be significant in
652 // ELF in spirit. But in reality many linker features depend on
653 // magic section names.
654 StringRef S = Sec->Name;
655 return S == ".data.rel.ro" || S == ".bss.rel.ro" || S == ".ctors" ||
656 S == ".dtors" || S == ".jcr" || S == ".eh_frame" ||
657 S == ".openbsd.randomdata";
660 // We compute a rank for each section. The rank indicates where the
661 // section should be placed in the file. Instead of using simple
662 // numbers (0,1,2...), we use a series of flags. One for each decision
663 // point when placing the section.
664 // Using flags has two key properties:
665 // * It is easy to check if a give branch was taken.
666 // * It is easy two see how similar two ranks are (see getRankProximity).
668 RF_NOT_ADDR_SET = 1 << 16,
669 RF_NOT_INTERP = 1 << 15,
670 RF_NOT_ALLOC = 1 << 14,
672 RF_EXEC_WRITE = 1 << 12,
674 RF_NON_TLS_BSS = 1 << 10,
675 RF_NON_TLS_BSS_RO = 1 << 9,
678 RF_PPC_NOT_TOCBSS = 1 << 6,
680 RF_PPC_TOCL = 1 << 4,
682 RF_PPC_BRANCH_LT = 1 << 2,
683 RF_MIPS_GPREL = 1 << 1,
684 RF_MIPS_NOT_GOT = 1 << 0
687 static unsigned getSectionRank(const OutputSection *Sec) {
690 // We want to put section specified by -T option first, so we
691 // can start assigning VA starting from them later.
692 if (Config->SectionStartMap.count(Sec->Name))
694 Rank |= RF_NOT_ADDR_SET;
696 // Put .interp first because some loaders want to see that section
697 // on the first page of the executable file when loaded into memory.
698 if (Sec->Name == ".interp")
700 Rank |= RF_NOT_INTERP;
702 // Allocatable sections go first to reduce the total PT_LOAD size and
703 // so debug info doesn't change addresses in actual code.
704 if (!(Sec->Flags & SHF_ALLOC))
705 return Rank | RF_NOT_ALLOC;
707 // Sort sections based on their access permission in the following
708 // order: R, RX, RWX, RW. This order is based on the following
710 // * Read-only sections come first such that they go in the
711 // PT_LOAD covering the program headers at the start of the file.
712 // * Read-only, executable sections come next, unless the
713 // -no-rosegment option is used.
714 // * Writable, executable sections follow such that .plt on
715 // architectures where it needs to be writable will be placed
716 // between .text and .data.
717 // * Writable sections come last, such that .bss lands at the very
718 // end of the last PT_LOAD.
719 bool IsExec = Sec->Flags & SHF_EXECINSTR;
720 bool IsWrite = Sec->Flags & SHF_WRITE;
724 Rank |= RF_EXEC_WRITE;
725 else if (!Config->SingleRoRx)
732 // If we got here we know that both A and B are in the same PT_LOAD.
734 bool IsTls = Sec->Flags & SHF_TLS;
735 bool IsNoBits = Sec->Type == SHT_NOBITS;
737 // The first requirement we have is to put (non-TLS) nobits sections last. The
738 // reason is that the only thing the dynamic linker will see about them is a
739 // p_memsz that is larger than p_filesz. Seeing that it zeros the end of the
740 // PT_LOAD, so that has to correspond to the nobits sections.
741 bool IsNonTlsNoBits = IsNoBits && !IsTls;
743 Rank |= RF_NON_TLS_BSS;
745 // We place nobits RelRo sections before plain r/w ones, and non-nobits RelRo
746 // sections after r/w ones, so that the RelRo sections are contiguous.
747 bool IsRelRo = isRelroSection(Sec);
748 if (IsNonTlsNoBits && !IsRelRo)
749 Rank |= RF_NON_TLS_BSS_RO;
750 if (!IsNonTlsNoBits && IsRelRo)
751 Rank |= RF_NON_TLS_BSS_RO;
753 // The TLS initialization block needs to be a single contiguous block in a R/W
754 // PT_LOAD, so stick TLS sections directly before the other RelRo R/W
755 // sections. The TLS NOBITS sections are placed here as they don't take up
756 // virtual address space in the PT_LOAD.
760 // Within the TLS initialization block, the non-nobits sections need to appear
765 // Some architectures have additional ordering restrictions for sections
766 // within the same PT_LOAD.
767 if (Config->EMachine == EM_PPC64) {
768 // PPC64 has a number of special SHT_PROGBITS+SHF_ALLOC+SHF_WRITE sections
769 // that we would like to make sure appear is a specific order to maximize
770 // their coverage by a single signed 16-bit offset from the TOC base
771 // pointer. Conversely, the special .tocbss section should be first among
772 // all SHT_NOBITS sections. This will put it next to the loaded special
773 // PPC64 sections (and, thus, within reach of the TOC base pointer).
774 StringRef Name = Sec->Name;
775 if (Name != ".tocbss")
776 Rank |= RF_PPC_NOT_TOCBSS;
787 if (Name == ".branch_lt")
788 Rank |= RF_PPC_BRANCH_LT;
790 if (Config->EMachine == EM_MIPS) {
791 // All sections with SHF_MIPS_GPREL flag should be grouped together
792 // because data in these sections is addressable with a gp relative address.
793 if (Sec->Flags & SHF_MIPS_GPREL)
794 Rank |= RF_MIPS_GPREL;
796 if (Sec->Name != ".got")
797 Rank |= RF_MIPS_NOT_GOT;
803 static bool compareSections(const BaseCommand *ACmd, const BaseCommand *BCmd) {
804 const OutputSection *A = cast<OutputSection>(ACmd);
805 const OutputSection *B = cast<OutputSection>(BCmd);
806 if (A->SortRank != B->SortRank)
807 return A->SortRank < B->SortRank;
808 if (!(A->SortRank & RF_NOT_ADDR_SET))
809 return Config->SectionStartMap.lookup(A->Name) <
810 Config->SectionStartMap.lookup(B->Name);
814 void PhdrEntry::add(OutputSection *Sec) {
818 p_align = std::max(p_align, Sec->Alignment);
819 if (p_type == PT_LOAD)
823 // The beginning and the ending of .rel[a].plt section are marked
824 // with __rel[a]_iplt_{start,end} symbols if it is a statically linked
825 // executable. The runtime needs these symbols in order to resolve
826 // all IRELATIVE relocs on startup. For dynamic executables, we don't
827 // need these symbols, since IRELATIVE relocs are resolved through GOT
828 // and PLT. For details, see http://www.airs.com/blog/archives/403.
829 template <class ELFT> void Writer<ELFT>::addRelIpltSymbols() {
832 StringRef S = Config->IsRela ? "__rela_iplt_start" : "__rel_iplt_start";
833 addOptionalRegular<ELFT>(S, InX::RelaIplt, 0, STV_HIDDEN, STB_WEAK);
835 S = Config->IsRela ? "__rela_iplt_end" : "__rel_iplt_end";
836 addOptionalRegular<ELFT>(S, InX::RelaIplt, -1, STV_HIDDEN, STB_WEAK);
839 template <class ELFT>
840 void Writer<ELFT>::forEachRelSec(std::function<void(InputSectionBase &)> Fn) {
841 // Scan all relocations. Each relocation goes through a series
842 // of tests to determine if it needs special treatment, such as
843 // creating GOT, PLT, copy relocations, etc.
844 // Note that relocations for non-alloc sections are directly
845 // processed by InputSection::relocateNonAlloc.
846 for (InputSectionBase *IS : InputSections)
847 if (IS->Live && isa<InputSection>(IS) && (IS->Flags & SHF_ALLOC))
849 for (EhInputSection *ES : InX::EhFrame->Sections)
853 // This function generates assignments for predefined symbols (e.g. _end or
854 // _etext) and inserts them into the commands sequence to be processed at the
855 // appropriate time. This ensures that the value is going to be correct by the
856 // time any references to these symbols are processed and is equivalent to
857 // defining these symbols explicitly in the linker script.
858 template <class ELFT> void Writer<ELFT>::setReservedSymbolSections() {
859 if (ElfSym::GlobalOffsetTable) {
860 // The _GLOBAL_OFFSET_TABLE_ symbol is defined by target convention to
861 // be at some offset from the base of the .got section, usually 0 or the end
863 InputSection *GotSection = InX::MipsGot ? cast<InputSection>(InX::MipsGot)
864 : cast<InputSection>(InX::Got);
865 ElfSym::GlobalOffsetTable->Section = GotSection;
868 PhdrEntry *Last = nullptr;
869 PhdrEntry *LastRO = nullptr;
871 for (PhdrEntry *P : Phdrs) {
872 if (P->p_type != PT_LOAD)
875 if (!(P->p_flags & PF_W))
880 // _etext is the first location after the last read-only loadable segment.
882 ElfSym::Etext1->Section = LastRO->LastSec;
884 ElfSym::Etext2->Section = LastRO->LastSec;
888 // _edata points to the end of the last mapped initialized section.
889 OutputSection *Edata = nullptr;
890 for (OutputSection *OS : OutputSections) {
891 if (OS->Type != SHT_NOBITS)
893 if (OS == Last->LastSec)
898 ElfSym::Edata1->Section = Edata;
900 ElfSym::Edata2->Section = Edata;
902 // _end is the first location after the uninitialized data region.
904 ElfSym::End1->Section = Last->LastSec;
906 ElfSym::End2->Section = Last->LastSec;
910 ElfSym::Bss->Section = findSection(".bss");
912 // Setup MIPS _gp_disp/__gnu_local_gp symbols which should
913 // be equal to the _gp symbol's value.
914 if (ElfSym::MipsGp) {
915 // Find GP-relative section with the lowest address
916 // and use this address to calculate default _gp value.
917 for (OutputSection *OS : OutputSections) {
918 if (OS->Flags & SHF_MIPS_GPREL) {
919 ElfSym::MipsGp->Section = OS;
920 ElfSym::MipsGp->Value = 0x7ff0;
927 // We want to find how similar two ranks are.
928 // The more branches in getSectionRank that match, the more similar they are.
929 // Since each branch corresponds to a bit flag, we can just use
930 // countLeadingZeros.
931 static int getRankProximityAux(OutputSection *A, OutputSection *B) {
932 return countLeadingZeros(A->SortRank ^ B->SortRank);
935 static int getRankProximity(OutputSection *A, BaseCommand *B) {
936 if (auto *Sec = dyn_cast<OutputSection>(B))
938 return getRankProximityAux(A, Sec);
942 // When placing orphan sections, we want to place them after symbol assignments
943 // so that an orphan after
947 // doesn't break the intended meaning of the begin/end symbols.
948 // We don't want to go over sections since findOrphanPos is the
949 // one in charge of deciding the order of the sections.
950 // We don't want to go over changes to '.', since doing so in
951 // rx_sec : { *(rx_sec) }
952 // . = ALIGN(0x1000);
953 // /* The RW PT_LOAD starts here*/
954 // rw_sec : { *(rw_sec) }
955 // would mean that the RW PT_LOAD would become unaligned.
956 static bool shouldSkip(BaseCommand *Cmd) {
957 if (isa<OutputSection>(Cmd))
959 if (auto *Assign = dyn_cast<SymbolAssignment>(Cmd))
960 return Assign->Name != ".";
964 // We want to place orphan sections so that they share as much
965 // characteristics with their neighbors as possible. For example, if
966 // both are rw, or both are tls.
967 template <typename ELFT>
968 static std::vector<BaseCommand *>::iterator
969 findOrphanPos(std::vector<BaseCommand *>::iterator B,
970 std::vector<BaseCommand *>::iterator E) {
971 OutputSection *Sec = cast<OutputSection>(*E);
973 // Find the first element that has as close a rank as possible.
974 auto I = std::max_element(B, E, [=](BaseCommand *A, BaseCommand *B) {
975 return getRankProximity(Sec, A) < getRankProximity(Sec, B);
980 // Consider all existing sections with the same proximity.
981 int Proximity = getRankProximity(Sec, *I);
982 for (; I != E; ++I) {
983 auto *CurSec = dyn_cast<OutputSection>(*I);
984 if (!CurSec || !CurSec->Live)
986 if (getRankProximity(Sec, CurSec) != Proximity ||
987 Sec->SortRank < CurSec->SortRank)
991 auto IsLiveSection = [](BaseCommand *Cmd) {
992 auto *OS = dyn_cast<OutputSection>(Cmd);
993 return OS && OS->Live;
996 auto J = std::find_if(llvm::make_reverse_iterator(I),
997 llvm::make_reverse_iterator(B), IsLiveSection);
1000 // As a special case, if the orphan section is the last section, put
1001 // it at the very end, past any other commands.
1002 // This matches bfd's behavior and is convenient when the linker script fully
1003 // specifies the start of the file, but doesn't care about the end (the non
1004 // alloc sections for example).
1005 auto NextSec = std::find_if(I, E, IsLiveSection);
1009 while (I != E && shouldSkip(*I))
1014 // If no layout was provided by linker script, we want to apply default
1015 // sorting for special input sections and handle --symbol-ordering-file.
1016 template <class ELFT> void Writer<ELFT>::sortInputSections() {
1017 assert(!Script->HasSectionsCommand);
1019 // Sort input sections by priority using the list provided
1020 // by --symbol-ordering-file.
1021 DenseMap<SectionBase *, int> Order = buildSectionOrder();
1023 for (BaseCommand *Base : Script->SectionCommands)
1024 if (auto *Sec = dyn_cast<OutputSection>(Base))
1026 Sec->sort([&](InputSectionBase *S) { return Order.lookup(S); });
1028 // Sort input sections by section name suffixes for
1029 // __attribute__((init_priority(N))).
1030 if (OutputSection *Sec = findSection(".init_array"))
1031 Sec->sortInitFini();
1032 if (OutputSection *Sec = findSection(".fini_array"))
1033 Sec->sortInitFini();
1035 // Sort input sections by the special rule for .ctors and .dtors.
1036 if (OutputSection *Sec = findSection(".ctors"))
1037 Sec->sortCtorsDtors();
1038 if (OutputSection *Sec = findSection(".dtors"))
1039 Sec->sortCtorsDtors();
1042 template <class ELFT> void Writer<ELFT>::sortSections() {
1043 Script->adjustSectionsBeforeSorting();
1045 // Don't sort if using -r. It is not necessary and we want to preserve the
1046 // relative order for SHF_LINK_ORDER sections.
1047 if (Config->Relocatable)
1050 for (BaseCommand *Base : Script->SectionCommands)
1051 if (auto *Sec = dyn_cast<OutputSection>(Base))
1052 Sec->SortRank = getSectionRank(Sec);
1054 if (!Script->HasSectionsCommand) {
1055 sortInputSections();
1057 // We know that all the OutputSections are contiguous in this case.
1058 auto E = Script->SectionCommands.end();
1059 auto I = Script->SectionCommands.begin();
1060 auto IsSection = [](BaseCommand *Base) { return isa<OutputSection>(Base); };
1061 I = std::find_if(I, E, IsSection);
1062 E = std::find_if(llvm::make_reverse_iterator(E),
1063 llvm::make_reverse_iterator(I), IsSection)
1065 std::stable_sort(I, E, compareSections);
1069 // Orphan sections are sections present in the input files which are
1070 // not explicitly placed into the output file by the linker script.
1072 // The sections in the linker script are already in the correct
1073 // order. We have to figuere out where to insert the orphan
1076 // The order of the sections in the script is arbitrary and may not agree with
1077 // compareSections. This means that we cannot easily define a strict weak
1078 // ordering. To see why, consider a comparison of a section in the script and
1079 // one not in the script. We have a two simple options:
1080 // * Make them equivalent (a is not less than b, and b is not less than a).
1081 // The problem is then that equivalence has to be transitive and we can
1082 // have sections a, b and c with only b in a script and a less than c
1083 // which breaks this property.
1084 // * Use compareSectionsNonScript. Given that the script order doesn't have
1085 // to match, we can end up with sections a, b, c, d where b and c are in the
1086 // script and c is compareSectionsNonScript less than b. In which case d
1087 // can be equivalent to c, a to b and d < a. As a concrete example:
1088 // .a (rx) # not in script
1089 // .b (rx) # in script
1090 // .c (ro) # in script
1091 // .d (ro) # not in script
1093 // The way we define an order then is:
1094 // * Sort only the orphan sections. They are in the end right now.
1095 // * Move each orphan section to its preferred position. We try
1096 // to put each section in the last position where it it can share
1099 // There is some ambiguity as to where exactly a new entry should be
1100 // inserted, because Commands contains not only output section
1101 // commands but also other types of commands such as symbol assignment
1102 // expressions. There's no correct answer here due to the lack of the
1103 // formal specification of the linker script. We use heuristics to
1104 // determine whether a new output command should be added before or
1105 // after another commands. For the details, look at shouldSkip
1108 auto I = Script->SectionCommands.begin();
1109 auto E = Script->SectionCommands.end();
1110 auto NonScriptI = std::find_if(I, E, [](BaseCommand *Base) {
1111 if (auto *Sec = dyn_cast<OutputSection>(Base))
1112 return Sec->Live && Sec->SectionIndex == INT_MAX;
1116 // Sort the orphan sections.
1117 std::stable_sort(NonScriptI, E, compareSections);
1119 // As a horrible special case, skip the first . assignment if it is before any
1120 // section. We do this because it is common to set a load address by starting
1121 // the script with ". = 0xabcd" and the expectation is that every section is
1123 auto FirstSectionOrDotAssignment =
1124 std::find_if(I, E, [](BaseCommand *Cmd) { return !shouldSkip(Cmd); });
1125 if (FirstSectionOrDotAssignment != E &&
1126 isa<SymbolAssignment>(**FirstSectionOrDotAssignment))
1127 ++FirstSectionOrDotAssignment;
1128 I = FirstSectionOrDotAssignment;
1130 while (NonScriptI != E) {
1131 auto Pos = findOrphanPos<ELFT>(I, NonScriptI);
1132 OutputSection *Orphan = cast<OutputSection>(*NonScriptI);
1134 // As an optimization, find all sections with the same sort rank
1135 // and insert them with one rotate.
1136 unsigned Rank = Orphan->SortRank;
1137 auto End = std::find_if(NonScriptI + 1, E, [=](BaseCommand *Cmd) {
1138 return cast<OutputSection>(Cmd)->SortRank != Rank;
1140 std::rotate(Pos, NonScriptI, End);
1144 Script->adjustSectionsAfterSorting();
1147 static bool compareByFilePosition(InputSection *A, InputSection *B) {
1148 // Synthetic doesn't have link order dependecy, stable_sort will keep it last
1149 if (A->kind() == InputSectionBase::Synthetic ||
1150 B->kind() == InputSectionBase::Synthetic)
1152 InputSection *LA = A->getLinkOrderDep();
1153 InputSection *LB = B->getLinkOrderDep();
1154 OutputSection *AOut = LA->getParent();
1155 OutputSection *BOut = LB->getParent();
1157 return AOut->SectionIndex < BOut->SectionIndex;
1158 return LA->OutSecOff < LB->OutSecOff;
1161 // This function is used by the --merge-exidx-entries to detect duplicate
1162 // .ARM.exidx sections. It is Arm only.
1164 // The .ARM.exidx section is of the form:
1165 // | PREL31 offset to function | Unwind instructions for function |
1166 // where the unwind instructions are either a small number of unwind
1167 // instructions inlined into the table entry, the special CANT_UNWIND value of
1168 // 0x1 or a PREL31 offset into a .ARM.extab Section that contains unwind
1171 // We return true if all the unwind instructions in the .ARM.exidx entries of
1172 // Cur can be merged into the last entry of Prev.
1173 static bool isDuplicateArmExidxSec(InputSection *Prev, InputSection *Cur) {
1175 // References to .ARM.Extab Sections have bit 31 clear and are not the
1176 // special EXIDX_CANTUNWIND bit-pattern.
1177 auto IsExtabRef = [](uint32_t Unwind) {
1178 return (Unwind & 0x80000000) == 0 && Unwind != 0x1;
1186 // Get the last table Entry from the previous .ARM.exidx section.
1187 const ExidxEntry &PrevEntry = *reinterpret_cast<const ExidxEntry *>(
1188 Prev->Data.data() + Prev->getSize() - sizeof(ExidxEntry));
1189 if (IsExtabRef(PrevEntry.Unwind))
1192 // We consider the unwind instructions of an .ARM.exidx table entry
1193 // a duplicate if the previous unwind instructions if:
1194 // - Both are the special EXIDX_CANTUNWIND.
1195 // - Both are the same inline unwind instructions.
1196 // We do not attempt to follow and check links into .ARM.extab tables as
1197 // consecutive identical entries are rare and the effort to check that they
1198 // are identical is high.
1200 if (isa<SyntheticSection>(Cur))
1201 // Exidx sentinel section has implicit EXIDX_CANTUNWIND;
1202 return PrevEntry.Unwind == 0x1;
1204 ArrayRef<const ExidxEntry> Entries(
1205 reinterpret_cast<const ExidxEntry *>(Cur->Data.data()),
1206 Cur->getSize() / sizeof(ExidxEntry));
1207 for (const ExidxEntry &Entry : Entries)
1208 if (IsExtabRef(Entry.Unwind) || Entry.Unwind != PrevEntry.Unwind)
1210 // All table entries in this .ARM.exidx Section can be merged into the
1211 // previous Section.
1215 template <class ELFT> void Writer<ELFT>::resolveShfLinkOrder() {
1216 for (OutputSection *Sec : OutputSections) {
1217 if (!(Sec->Flags & SHF_LINK_ORDER))
1220 // Link order may be distributed across several InputSectionDescriptions
1221 // but sort must consider them all at once.
1222 std::vector<InputSection **> ScriptSections;
1223 std::vector<InputSection *> Sections;
1224 for (BaseCommand *Base : Sec->SectionCommands) {
1225 if (auto *ISD = dyn_cast<InputSectionDescription>(Base)) {
1226 for (InputSection *&IS : ISD->Sections) {
1227 ScriptSections.push_back(&IS);
1228 Sections.push_back(IS);
1232 std::stable_sort(Sections.begin(), Sections.end(), compareByFilePosition);
1234 if (Config->MergeArmExidx && !Config->Relocatable &&
1235 Config->EMachine == EM_ARM && Sec->Type == SHT_ARM_EXIDX) {
1236 // The EHABI for the Arm Architecture permits consecutive identical
1237 // table entries to be merged. We use a simple implementation that
1238 // removes a .ARM.exidx Input Section if it can be merged into the
1239 // previous one. This does not require any rewriting of InputSection
1240 // contents but misses opportunities for fine grained deduplication where
1241 // only a subset of the InputSection contents can be merged.
1244 int N = Sections.size();
1246 if (isDuplicateArmExidxSec(Sections[Prev], Sections[Cur]))
1247 Sections[Cur] = nullptr;
1254 for (int I = 0, N = Sections.size(); I < N; ++I)
1255 *ScriptSections[I] = Sections[I];
1257 // Remove the Sections we marked as duplicate earlier.
1258 for (BaseCommand *Base : Sec->SectionCommands)
1259 if (auto *ISD = dyn_cast<InputSectionDescription>(Base))
1260 ISD->Sections.erase(
1261 std::remove(ISD->Sections.begin(), ISD->Sections.end(), nullptr),
1262 ISD->Sections.end());
1266 static void applySynthetic(const std::vector<SyntheticSection *> &Sections,
1267 std::function<void(SyntheticSection *)> Fn) {
1268 for (SyntheticSection *SS : Sections)
1269 if (SS && SS->getParent() && !SS->empty())
1273 // In order to allow users to manipulate linker-synthesized sections,
1274 // we had to add synthetic sections to the input section list early,
1275 // even before we make decisions whether they are needed. This allows
1276 // users to write scripts like this: ".mygot : { .got }".
1278 // Doing it has an unintended side effects. If it turns out that we
1279 // don't need a .got (for example) at all because there's no
1280 // relocation that needs a .got, we don't want to emit .got.
1282 // To deal with the above problem, this function is called after
1283 // scanRelocations is called to remove synthetic sections that turn
1285 static void removeUnusedSyntheticSections() {
1286 // All input synthetic sections that can be empty are placed after
1287 // all regular ones. We iterate over them all and exit at first
1289 for (InputSectionBase *S : llvm::reverse(InputSections)) {
1290 SyntheticSection *SS = dyn_cast<SyntheticSection>(S);
1293 OutputSection *OS = SS->getParent();
1294 if (!SS->empty() || !OS)
1297 std::vector<BaseCommand *>::iterator Empty = OS->SectionCommands.end();
1298 for (auto I = OS->SectionCommands.begin(), E = OS->SectionCommands.end();
1300 BaseCommand *B = *I;
1301 if (auto *ISD = dyn_cast<InputSectionDescription>(B)) {
1302 llvm::erase_if(ISD->Sections,
1303 [=](InputSection *IS) { return IS == SS; });
1304 if (ISD->Sections.empty())
1308 if (Empty != OS->SectionCommands.end())
1309 OS->SectionCommands.erase(Empty);
1311 // If there are no other sections in the output section, remove it from the
1313 if (OS->SectionCommands.empty())
1318 // Returns true if a symbol can be replaced at load-time by a symbol
1319 // with the same name defined in other ELF executable or DSO.
1320 static bool computeIsPreemptible(const Symbol &B) {
1321 assert(!B.isLocal());
1322 // Only symbols that appear in dynsym can be preempted.
1323 if (!B.includeInDynsym())
1326 // Only default visibility symbols can be preempted.
1327 if (B.Visibility != STV_DEFAULT)
1330 // At this point copy relocations have not been created yet, so any
1331 // symbol that is not defined locally is preemptible.
1335 // If we have a dynamic list it specifies which local symbols are preemptible.
1336 if (Config->HasDynamicList)
1339 if (!Config->Shared)
1342 // -Bsymbolic means that definitions are not preempted.
1343 if (Config->Bsymbolic || (Config->BsymbolicFunctions && B.isFunc()))
1348 // Create output section objects and add them to OutputSections.
1349 template <class ELFT> void Writer<ELFT>::finalizeSections() {
1350 Out::DebugInfo = findSection(".debug_info");
1351 Out::PreinitArray = findSection(".preinit_array");
1352 Out::InitArray = findSection(".init_array");
1353 Out::FiniArray = findSection(".fini_array");
1355 // The linker needs to define SECNAME_start, SECNAME_end and SECNAME_stop
1356 // symbols for sections, so that the runtime can get the start and end
1357 // addresses of each section by section name. Add such symbols.
1358 if (!Config->Relocatable) {
1359 addStartEndSymbols();
1360 for (BaseCommand *Base : Script->SectionCommands)
1361 if (auto *Sec = dyn_cast<OutputSection>(Base))
1362 addStartStopSymbols(Sec);
1365 // Add _DYNAMIC symbol. Unlike GNU gold, our _DYNAMIC symbol has no type.
1366 // It should be okay as no one seems to care about the type.
1367 // Even the author of gold doesn't remember why gold behaves that way.
1368 // https://sourceware.org/ml/binutils/2002-03/msg00360.html
1370 Symtab->addRegular<ELFT>("_DYNAMIC", STV_HIDDEN, STT_NOTYPE, 0 /*Value*/,
1371 /*Size=*/0, STB_WEAK, InX::Dynamic,
1374 // Define __rel[a]_iplt_{start,end} symbols if needed.
1375 addRelIpltSymbols();
1377 // This responsible for splitting up .eh_frame section into
1378 // pieces. The relocation scan uses those pieces, so this has to be
1380 applySynthetic({InX::EhFrame},
1381 [](SyntheticSection *SS) { SS->finalizeContents(); });
1383 for (Symbol *S : Symtab->getSymbols())
1384 S->IsPreemptible |= computeIsPreemptible(*S);
1386 // Scan relocations. This must be done after every symbol is declared so that
1387 // we can correctly decide if a dynamic relocation is needed.
1388 if (!Config->Relocatable)
1389 forEachRelSec(scanRelocations<ELFT>);
1391 if (InX::Plt && !InX::Plt->empty())
1392 InX::Plt->addSymbols();
1393 if (InX::Iplt && !InX::Iplt->empty())
1394 InX::Iplt->addSymbols();
1396 // Now that we have defined all possible global symbols including linker-
1397 // synthesized ones. Visit all symbols to give the finishing touches.
1398 for (Symbol *Sym : Symtab->getSymbols()) {
1399 if (!includeInSymtab(*Sym))
1402 InX::SymTab->addSymbol(Sym);
1404 if (InX::DynSymTab && Sym->includeInDynsym()) {
1405 InX::DynSymTab->addSymbol(Sym);
1406 if (auto *SS = dyn_cast<SharedSymbol>(Sym))
1407 if (cast<SharedFile<ELFT>>(Sym->File)->IsNeeded)
1408 In<ELFT>::VerNeed->addSymbol(SS);
1412 // Do not proceed if there was an undefined symbol.
1416 addPredefinedSections();
1417 removeUnusedSyntheticSections();
1420 Script->removeEmptyCommands();
1422 // Now that we have the final list, create a list of all the
1423 // OutputSections for convenience.
1424 for (BaseCommand *Base : Script->SectionCommands)
1425 if (auto *Sec = dyn_cast<OutputSection>(Base))
1426 OutputSections.push_back(Sec);
1428 // Prefer command line supplied address over other constraints.
1429 for (OutputSection *Sec : OutputSections) {
1430 auto I = Config->SectionStartMap.find(Sec->Name);
1431 if (I != Config->SectionStartMap.end())
1432 Sec->AddrExpr = [=] { return I->second; };
1435 // This is a bit of a hack. A value of 0 means undef, so we set it
1436 // to 1 t make __ehdr_start defined. The section number is not
1437 // particularly relevant.
1438 Out::ElfHeader->SectionIndex = 1;
1441 for (OutputSection *Sec : OutputSections) {
1442 Sec->SectionIndex = I++;
1443 Sec->ShName = InX::ShStrTab->addString(Sec->Name);
1446 // Binary and relocatable output does not have PHDRS.
1447 // The headers have to be created before finalize as that can influence the
1448 // image base and the dynamic section on mips includes the image base.
1449 if (!Config->Relocatable && !Config->OFormatBinary) {
1450 Phdrs = Script->hasPhdrsCommands() ? Script->createPhdrs() : createPhdrs();
1451 addPtArmExid(Phdrs);
1452 Out::ProgramHeaders->Size = sizeof(Elf_Phdr) * Phdrs.size();
1455 // Some symbols are defined in term of program headers. Now that we
1456 // have the headers, we can find out which sections they point to.
1457 setReservedSymbolSections();
1459 // Dynamic section must be the last one in this list and dynamic
1460 // symbol table section (DynSymTab) must be the first one.
1462 {InX::DynSymTab, InX::Bss, InX::BssRelRo, InX::GnuHashTab,
1463 InX::HashTab, InX::SymTab, InX::ShStrTab, InX::StrTab,
1464 In<ELFT>::VerDef, InX::DynStrTab, InX::Got, InX::MipsGot,
1465 InX::IgotPlt, InX::GotPlt, InX::RelaDyn, InX::RelaIplt,
1466 InX::RelaPlt, InX::Plt, InX::Iplt, InX::EhFrameHdr,
1467 In<ELFT>::VerSym, In<ELFT>::VerNeed, InX::Dynamic},
1468 [](SyntheticSection *SS) { SS->finalizeContents(); });
1470 if (!Script->HasSectionsCommand && !Config->Relocatable)
1471 fixSectionAlignments();
1473 // After link order processing .ARM.exidx sections can be deduplicated, which
1474 // needs to be resolved before any other address dependent operation.
1475 resolveShfLinkOrder();
1477 // Some architectures need to generate content that depends on the address
1478 // of InputSections. For example some architectures use small displacements
1479 // for jump instructions that is is the linker's responsibility for creating
1480 // range extension thunks for. As the generation of the content may also
1481 // alter InputSection addresses we must converge to a fixed point.
1482 if (Target->NeedsThunks || Config->AndroidPackDynRelocs) {
1484 AArch64Err843419Patcher A64P;
1487 Script->assignAddresses();
1489 if (Target->NeedsThunks)
1490 Changed |= TC.createThunks(OutputSections);
1491 if (Config->FixCortexA53Errata843419) {
1493 Script->assignAddresses();
1494 Changed |= A64P.createFixes();
1497 InX::MipsGot->updateAllocSize();
1498 Changed |= InX::RelaDyn->updateAllocSize();
1502 // Fill other section headers. The dynamic table is finalized
1503 // at the end because some tags like RELSZ depend on result
1504 // of finalizing other sections.
1505 for (OutputSection *Sec : OutputSections)
1506 Sec->finalize<ELFT>();
1508 // createThunks may have added local symbols to the static symbol table
1509 applySynthetic({InX::SymTab},
1510 [](SyntheticSection *SS) { SS->postThunkContents(); });
1513 template <class ELFT> void Writer<ELFT>::addPredefinedSections() {
1514 // ARM ABI requires .ARM.exidx to be terminated by some piece of data.
1515 // We have the terminater synthetic section class. Add that at the end.
1516 OutputSection *Cmd = findSection(".ARM.exidx");
1517 if (!Cmd || !Cmd->Live || Config->Relocatable)
1520 auto *Sentinel = make<ARMExidxSentinelSection>();
1521 Cmd->addSection(Sentinel);
1524 // The linker is expected to define SECNAME_start and SECNAME_end
1525 // symbols for a few sections. This function defines them.
1526 template <class ELFT> void Writer<ELFT>::addStartEndSymbols() {
1527 auto Define = [&](StringRef Start, StringRef End, OutputSection *OS) {
1528 // These symbols resolve to the image base if the section does not exist.
1529 // A special value -1 indicates end of the section.
1531 addOptionalRegular<ELFT>(Start, OS, 0);
1532 addOptionalRegular<ELFT>(End, OS, -1);
1535 OS = Out::ElfHeader;
1536 addOptionalRegular<ELFT>(Start, OS, 0);
1537 addOptionalRegular<ELFT>(End, OS, 0);
1541 Define("__preinit_array_start", "__preinit_array_end", Out::PreinitArray);
1542 Define("__init_array_start", "__init_array_end", Out::InitArray);
1543 Define("__fini_array_start", "__fini_array_end", Out::FiniArray);
1545 if (OutputSection *Sec = findSection(".ARM.exidx"))
1546 Define("__exidx_start", "__exidx_end", Sec);
1549 // If a section name is valid as a C identifier (which is rare because of
1550 // the leading '.'), linkers are expected to define __start_<secname> and
1551 // __stop_<secname> symbols. They are at beginning and end of the section,
1552 // respectively. This is not requested by the ELF standard, but GNU ld and
1553 // gold provide the feature, and used by many programs.
1554 template <class ELFT>
1555 void Writer<ELFT>::addStartStopSymbols(OutputSection *Sec) {
1556 StringRef S = Sec->Name;
1557 if (!isValidCIdentifier(S))
1559 addOptionalRegular<ELFT>(Saver.save("__start_" + S), Sec, 0, STV_DEFAULT);
1560 addOptionalRegular<ELFT>(Saver.save("__stop_" + S), Sec, -1, STV_DEFAULT);
1563 static bool needsPtLoad(OutputSection *Sec) {
1564 if (!(Sec->Flags & SHF_ALLOC))
1567 // Don't allocate VA space for TLS NOBITS sections. The PT_TLS PHDR is
1568 // responsible for allocating space for them, not the PT_LOAD that
1569 // contains the TLS initialization image.
1570 if (Sec->Flags & SHF_TLS && Sec->Type == SHT_NOBITS)
1575 // Linker scripts are responsible for aligning addresses. Unfortunately, most
1576 // linker scripts are designed for creating two PT_LOADs only, one RX and one
1577 // RW. This means that there is no alignment in the RO to RX transition and we
1578 // cannot create a PT_LOAD there.
1579 static uint64_t computeFlags(uint64_t Flags) {
1581 return PF_R | PF_W | PF_X;
1582 if (Config->SingleRoRx && !(Flags & PF_W))
1583 return Flags | PF_X;
1587 // Decide which program headers to create and which sections to include in each
1589 template <class ELFT> std::vector<PhdrEntry *> Writer<ELFT>::createPhdrs() {
1590 std::vector<PhdrEntry *> Ret;
1591 auto AddHdr = [&](unsigned Type, unsigned Flags) -> PhdrEntry * {
1592 Ret.push_back(make<PhdrEntry>(Type, Flags));
1596 // The first phdr entry is PT_PHDR which describes the program header itself.
1597 AddHdr(PT_PHDR, PF_R)->add(Out::ProgramHeaders);
1599 // PT_INTERP must be the second entry if exists.
1600 if (OutputSection *Cmd = findSection(".interp"))
1601 AddHdr(PT_INTERP, Cmd->getPhdrFlags())->add(Cmd);
1603 // Add the first PT_LOAD segment for regular output sections.
1604 uint64_t Flags = computeFlags(PF_R);
1605 PhdrEntry *Load = AddHdr(PT_LOAD, Flags);
1607 // Add the headers. We will remove them if they don't fit.
1608 Load->add(Out::ElfHeader);
1609 Load->add(Out::ProgramHeaders);
1611 for (OutputSection *Sec : OutputSections) {
1612 if (!(Sec->Flags & SHF_ALLOC))
1614 if (!needsPtLoad(Sec))
1617 // Segments are contiguous memory regions that has the same attributes
1618 // (e.g. executable or writable). There is one phdr for each segment.
1619 // Therefore, we need to create a new phdr when the next section has
1620 // different flags or is loaded at a discontiguous address using AT linker
1622 uint64_t NewFlags = computeFlags(Sec->getPhdrFlags());
1623 if (Sec->LMAExpr || Flags != NewFlags) {
1624 Load = AddHdr(PT_LOAD, NewFlags);
1631 // Add a TLS segment if any.
1632 PhdrEntry *TlsHdr = make<PhdrEntry>(PT_TLS, PF_R);
1633 for (OutputSection *Sec : OutputSections)
1634 if (Sec->Flags & SHF_TLS)
1636 if (TlsHdr->FirstSec)
1637 Ret.push_back(TlsHdr);
1639 // Add an entry for .dynamic.
1641 AddHdr(PT_DYNAMIC, InX::Dynamic->getParent()->getPhdrFlags())
1642 ->add(InX::Dynamic->getParent());
1644 // PT_GNU_RELRO includes all sections that should be marked as
1645 // read-only by dynamic linker after proccessing relocations.
1646 // Current dynamic loaders only support one PT_GNU_RELRO PHDR, give
1647 // an error message if more than one PT_GNU_RELRO PHDR is required.
1648 PhdrEntry *RelRo = make<PhdrEntry>(PT_GNU_RELRO, PF_R);
1649 bool InRelroPhdr = false;
1650 bool IsRelroFinished = false;
1651 for (OutputSection *Sec : OutputSections) {
1652 if (!needsPtLoad(Sec))
1654 if (isRelroSection(Sec)) {
1656 if (!IsRelroFinished)
1659 error("section: " + Sec->Name + " is not contiguous with other relro" +
1661 } else if (InRelroPhdr) {
1662 InRelroPhdr = false;
1663 IsRelroFinished = true;
1666 if (RelRo->FirstSec)
1667 Ret.push_back(RelRo);
1669 // PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
1670 if (!InX::EhFrame->empty() && InX::EhFrameHdr && InX::EhFrame->getParent() &&
1671 InX::EhFrameHdr->getParent())
1672 AddHdr(PT_GNU_EH_FRAME, InX::EhFrameHdr->getParent()->getPhdrFlags())
1673 ->add(InX::EhFrameHdr->getParent());
1675 // PT_OPENBSD_RANDOMIZE is an OpenBSD-specific feature. That makes
1676 // the dynamic linker fill the segment with random data.
1677 if (OutputSection *Cmd = findSection(".openbsd.randomdata"))
1678 AddHdr(PT_OPENBSD_RANDOMIZE, Cmd->getPhdrFlags())->add(Cmd);
1680 // PT_GNU_STACK is a special section to tell the loader to make the
1681 // pages for the stack non-executable. If you really want an executable
1682 // stack, you can pass -z execstack, but that's not recommended for
1683 // security reasons.
1685 if (Config->ZExecstack)
1686 Perm = PF_R | PF_W | PF_X;
1689 AddHdr(PT_GNU_STACK, Perm)->p_memsz = Config->ZStackSize;
1691 // PT_OPENBSD_WXNEEDED is a OpenBSD-specific header to mark the executable
1692 // is expected to perform W^X violations, such as calling mprotect(2) or
1693 // mmap(2) with PROT_WRITE | PROT_EXEC, which is prohibited by default on
1695 if (Config->ZWxneeded)
1696 AddHdr(PT_OPENBSD_WXNEEDED, PF_X);
1698 // Create one PT_NOTE per a group of contiguous .note sections.
1699 PhdrEntry *Note = nullptr;
1700 for (OutputSection *Sec : OutputSections) {
1701 if (Sec->Type == SHT_NOTE) {
1702 if (!Note || Sec->LMAExpr)
1703 Note = AddHdr(PT_NOTE, PF_R);
1712 template <class ELFT>
1713 void Writer<ELFT>::addPtArmExid(std::vector<PhdrEntry *> &Phdrs) {
1714 if (Config->EMachine != EM_ARM)
1716 auto I = llvm::find_if(OutputSections, [](OutputSection *Cmd) {
1717 return Cmd->Type == SHT_ARM_EXIDX;
1719 if (I == OutputSections.end())
1722 // PT_ARM_EXIDX is the ARM EHABI equivalent of PT_GNU_EH_FRAME
1723 PhdrEntry *ARMExidx = make<PhdrEntry>(PT_ARM_EXIDX, PF_R);
1725 Phdrs.push_back(ARMExidx);
1728 // The first section of each PT_LOAD, the first section in PT_GNU_RELRO and the
1729 // first section after PT_GNU_RELRO have to be page aligned so that the dynamic
1730 // linker can set the permissions.
1731 template <class ELFT> void Writer<ELFT>::fixSectionAlignments() {
1732 auto PageAlign = [](OutputSection *Cmd) {
1733 if (Cmd && !Cmd->AddrExpr)
1734 Cmd->AddrExpr = [=] {
1735 return alignTo(Script->getDot(), Config->MaxPageSize);
1739 for (const PhdrEntry *P : Phdrs)
1740 if (P->p_type == PT_LOAD && P->FirstSec)
1741 PageAlign(P->FirstSec);
1743 for (const PhdrEntry *P : Phdrs) {
1744 if (P->p_type != PT_GNU_RELRO)
1747 PageAlign(P->FirstSec);
1748 // Find the first section after PT_GNU_RELRO. If it is in a PT_LOAD we
1749 // have to align it to a page.
1750 auto End = OutputSections.end();
1751 auto I = std::find(OutputSections.begin(), End, P->LastSec);
1752 if (I == End || (I + 1) == End)
1754 OutputSection *Cmd = (*(I + 1));
1755 if (needsPtLoad(Cmd))
1760 // Adjusts the file alignment for a given output section and returns
1761 // its new file offset. The file offset must be the same with its
1762 // virtual address (modulo the page size) so that the loader can load
1763 // executables without any address adjustment.
1764 static uint64_t getFileAlignment(uint64_t Off, OutputSection *Cmd) {
1765 // If the section is not in a PT_LOAD, we just have to align it.
1767 return alignTo(Off, Cmd->Alignment);
1769 OutputSection *First = Cmd->PtLoad->FirstSec;
1770 // The first section in a PT_LOAD has to have congruent offset and address
1771 // module the page size.
1773 return alignTo(Off, std::max<uint64_t>(Cmd->Alignment, Config->MaxPageSize),
1776 // If two sections share the same PT_LOAD the file offset is calculated
1777 // using this formula: Off2 = Off1 + (VA2 - VA1).
1778 return First->Offset + Cmd->Addr - First->Addr;
1781 static uint64_t setOffset(OutputSection *Cmd, uint64_t Off) {
1782 if (Cmd->Type == SHT_NOBITS) {
1787 Off = getFileAlignment(Off, Cmd);
1789 return Off + Cmd->Size;
1792 template <class ELFT> void Writer<ELFT>::assignFileOffsetsBinary() {
1794 for (OutputSection *Sec : OutputSections)
1795 if (Sec->Flags & SHF_ALLOC)
1796 Off = setOffset(Sec, Off);
1797 FileSize = alignTo(Off, Config->Wordsize);
1800 // Assign file offsets to output sections.
1801 template <class ELFT> void Writer<ELFT>::assignFileOffsets() {
1803 Off = setOffset(Out::ElfHeader, Off);
1804 Off = setOffset(Out::ProgramHeaders, Off);
1806 PhdrEntry *LastRX = nullptr;
1807 for (PhdrEntry *P : Phdrs)
1808 if (P->p_type == PT_LOAD && (P->p_flags & PF_X))
1811 for (OutputSection *Sec : OutputSections) {
1812 Off = setOffset(Sec, Off);
1813 if (Script->HasSectionsCommand)
1815 // If this is a last section of the last executable segment and that
1816 // segment is the last loadable segment, align the offset of the
1817 // following section to avoid loading non-segments parts of the file.
1818 if (LastRX && LastRX->LastSec == Sec)
1819 Off = alignTo(Off, Target->PageSize);
1822 SectionHeaderOff = alignTo(Off, Config->Wordsize);
1823 FileSize = SectionHeaderOff + (OutputSections.size() + 1) * sizeof(Elf_Shdr);
1826 // Finalize the program headers. We call this function after we assign
1827 // file offsets and VAs to all sections.
1828 template <class ELFT> void Writer<ELFT>::setPhdrs() {
1829 for (PhdrEntry *P : Phdrs) {
1830 OutputSection *First = P->FirstSec;
1831 OutputSection *Last = P->LastSec;
1833 P->p_filesz = Last->Offset - First->Offset;
1834 if (Last->Type != SHT_NOBITS)
1835 P->p_filesz += Last->Size;
1836 P->p_memsz = Last->Addr + Last->Size - First->Addr;
1837 P->p_offset = First->Offset;
1838 P->p_vaddr = First->Addr;
1840 P->p_paddr = First->getLMA();
1842 if (P->p_type == PT_LOAD)
1843 P->p_align = std::max<uint64_t>(P->p_align, Config->MaxPageSize);
1844 else if (P->p_type == PT_GNU_RELRO) {
1846 // The glibc dynamic loader rounds the size down, so we need to round up
1847 // to protect the last page. This is a no-op on FreeBSD which always
1849 P->p_memsz = alignTo(P->p_memsz, Target->PageSize);
1852 // The TLS pointer goes after PT_TLS. At least glibc will align it,
1853 // so round up the size to make sure the offsets are correct.
1854 if (P->p_type == PT_TLS) {
1857 P->p_memsz = alignTo(P->p_memsz, P->p_align);
1862 // The entry point address is chosen in the following ways.
1864 // 1. the '-e' entry command-line option;
1865 // 2. the ENTRY(symbol) command in a linker control script;
1866 // 3. the value of the symbol _start, if present;
1867 // 4. the number represented by the entry symbol, if it is a number;
1868 // 5. the address of the first byte of the .text section, if present;
1869 // 6. the address 0.
1870 template <class ELFT> uint64_t Writer<ELFT>::getEntryAddr() {
1872 if (Symbol *B = Symtab->find(Config->Entry))
1877 if (to_integer(Config->Entry, Addr))
1881 if (OutputSection *Sec = findSection(".text")) {
1882 if (Config->WarnMissingEntry)
1883 warn("cannot find entry symbol " + Config->Entry + "; defaulting to 0x" +
1884 utohexstr(Sec->Addr));
1889 if (Config->WarnMissingEntry)
1890 warn("cannot find entry symbol " + Config->Entry +
1891 "; not setting start address");
1895 static uint16_t getELFType() {
1898 if (Config->Relocatable)
1903 template <class ELFT> void Writer<ELFT>::writeHeader() {
1904 uint8_t *Buf = Buffer->getBufferStart();
1905 memcpy(Buf, "\177ELF", 4);
1907 // Write the ELF header.
1908 auto *EHdr = reinterpret_cast<Elf_Ehdr *>(Buf);
1909 EHdr->e_ident[EI_CLASS] = Config->Is64 ? ELFCLASS64 : ELFCLASS32;
1910 EHdr->e_ident[EI_DATA] = Config->IsLE ? ELFDATA2LSB : ELFDATA2MSB;
1911 EHdr->e_ident[EI_VERSION] = EV_CURRENT;
1912 EHdr->e_ident[EI_OSABI] = Config->OSABI;
1913 EHdr->e_type = getELFType();
1914 EHdr->e_machine = Config->EMachine;
1915 EHdr->e_version = EV_CURRENT;
1916 EHdr->e_entry = getEntryAddr();
1917 EHdr->e_shoff = SectionHeaderOff;
1918 EHdr->e_flags = Config->EFlags;
1919 EHdr->e_ehsize = sizeof(Elf_Ehdr);
1920 EHdr->e_phnum = Phdrs.size();
1921 EHdr->e_shentsize = sizeof(Elf_Shdr);
1922 EHdr->e_shnum = OutputSections.size() + 1;
1923 EHdr->e_shstrndx = InX::ShStrTab->getParent()->SectionIndex;
1925 if (!Config->Relocatable) {
1926 EHdr->e_phoff = sizeof(Elf_Ehdr);
1927 EHdr->e_phentsize = sizeof(Elf_Phdr);
1930 // Write the program header table.
1931 auto *HBuf = reinterpret_cast<Elf_Phdr *>(Buf + EHdr->e_phoff);
1932 for (PhdrEntry *P : Phdrs) {
1933 HBuf->p_type = P->p_type;
1934 HBuf->p_flags = P->p_flags;
1935 HBuf->p_offset = P->p_offset;
1936 HBuf->p_vaddr = P->p_vaddr;
1937 HBuf->p_paddr = P->p_paddr;
1938 HBuf->p_filesz = P->p_filesz;
1939 HBuf->p_memsz = P->p_memsz;
1940 HBuf->p_align = P->p_align;
1944 // Write the section header table. Note that the first table entry is null.
1945 auto *SHdrs = reinterpret_cast<Elf_Shdr *>(Buf + EHdr->e_shoff);
1946 for (OutputSection *Sec : OutputSections)
1947 Sec->writeHeaderTo<ELFT>(++SHdrs);
1950 // Open a result file.
1951 template <class ELFT> void Writer<ELFT>::openFile() {
1952 if (!Config->Is64 && FileSize > UINT32_MAX) {
1953 error("output file too large: " + Twine(FileSize) + " bytes");
1957 unlinkAsync(Config->OutputFile);
1959 if (!Config->Relocatable)
1960 Flags = FileOutputBuffer::F_executable;
1961 Expected<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
1962 FileOutputBuffer::create(Config->OutputFile, FileSize, Flags);
1965 error("failed to open " + Config->OutputFile + ": " +
1966 llvm::toString(BufferOrErr.takeError()));
1968 Buffer = std::move(*BufferOrErr);
1971 template <class ELFT> void Writer<ELFT>::writeSectionsBinary() {
1972 uint8_t *Buf = Buffer->getBufferStart();
1973 for (OutputSection *Sec : OutputSections)
1974 if (Sec->Flags & SHF_ALLOC)
1975 Sec->writeTo<ELFT>(Buf + Sec->Offset);
1978 static void fillTrap(uint8_t *I, uint8_t *End) {
1979 for (; I + 4 <= End; I += 4)
1980 memcpy(I, &Target->TrapInstr, 4);
1983 // Fill the last page of executable segments with trap instructions
1984 // instead of leaving them as zero. Even though it is not required by any
1985 // standard, it is in general a good thing to do for security reasons.
1987 // We'll leave other pages in segments as-is because the rest will be
1988 // overwritten by output sections.
1989 template <class ELFT> void Writer<ELFT>::writeTrapInstr() {
1990 if (Script->HasSectionsCommand)
1993 // Fill the last page.
1994 uint8_t *Buf = Buffer->getBufferStart();
1995 for (PhdrEntry *P : Phdrs)
1996 if (P->p_type == PT_LOAD && (P->p_flags & PF_X))
1997 fillTrap(Buf + alignDown(P->p_offset + P->p_filesz, Target->PageSize),
1998 Buf + alignTo(P->p_offset + P->p_filesz, Target->PageSize));
2000 // Round up the file size of the last segment to the page boundary iff it is
2001 // an executable segment to ensure that other tools don't accidentally
2002 // trim the instruction padding (e.g. when stripping the file).
2003 PhdrEntry *Last = nullptr;
2004 for (PhdrEntry *P : Phdrs)
2005 if (P->p_type == PT_LOAD)
2008 if (Last && (Last->p_flags & PF_X))
2009 Last->p_memsz = Last->p_filesz = alignTo(Last->p_filesz, Target->PageSize);
2012 // Write section contents to a mmap'ed file.
2013 template <class ELFT> void Writer<ELFT>::writeSections() {
2014 uint8_t *Buf = Buffer->getBufferStart();
2016 // PPC64 needs to process relocations in the .opd section
2017 // before processing relocations in code-containing sections.
2018 if (auto *OpdCmd = findSection(".opd")) {
2020 Out::OpdBuf = Buf + Out::Opd->Offset;
2021 OpdCmd->template writeTo<ELFT>(Buf + Out::Opd->Offset);
2024 OutputSection *EhFrameHdr = nullptr;
2025 if (InX::EhFrameHdr && !InX::EhFrameHdr->empty())
2026 EhFrameHdr = InX::EhFrameHdr->getParent();
2028 // In -r or -emit-relocs mode, write the relocation sections first as in
2029 // ELf_Rel targets we might find out that we need to modify the relocated
2030 // section while doing it.
2031 for (OutputSection *Sec : OutputSections)
2032 if (Sec->Type == SHT_REL || Sec->Type == SHT_RELA)
2033 Sec->writeTo<ELFT>(Buf + Sec->Offset);
2035 for (OutputSection *Sec : OutputSections)
2036 if (Sec != Out::Opd && Sec != EhFrameHdr && Sec->Type != SHT_REL &&
2037 Sec->Type != SHT_RELA)
2038 Sec->writeTo<ELFT>(Buf + Sec->Offset);
2040 // The .eh_frame_hdr depends on .eh_frame section contents, therefore
2041 // it should be written after .eh_frame is written.
2043 EhFrameHdr->writeTo<ELFT>(Buf + EhFrameHdr->Offset);
2046 template <class ELFT> void Writer<ELFT>::writeBuildId() {
2047 if (!InX::BuildId || !InX::BuildId->getParent())
2050 // Compute a hash of all sections of the output file.
2051 uint8_t *Start = Buffer->getBufferStart();
2052 uint8_t *End = Start + FileSize;
2053 InX::BuildId->writeBuildId({Start, End});
2056 template void elf::writeResult<ELF32LE>();
2057 template void elf::writeResult<ELF32BE>();
2058 template void elf::writeResult<ELF64LE>();
2059 template void elf::writeResult<ELF64BE>();
2061 template void elf::addReservedSymbols<ELF32LE>();
2062 template void elf::addReservedSymbols<ELF32BE>();
2063 template void elf::addReservedSymbols<ELF64LE>();
2064 template void elf::addReservedSymbols<ELF64BE>();