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 setReservedSymbolSections();
59 std::vector<PhdrEntry *> createPhdrs();
60 void removeEmptyPTLoad();
61 void addPtArmExid(std::vector<PhdrEntry *> &Phdrs);
62 void assignFileOffsets();
63 void assignFileOffsetsBinary();
65 void fixSectionAlignments();
67 void writeTrapInstr();
70 void writeSectionsBinary();
73 std::unique_ptr<FileOutputBuffer> &Buffer;
75 void addRelIpltSymbols();
76 void addStartEndSymbols();
77 void addStartStopSymbols(OutputSection *Sec);
78 uint64_t getEntryAddr();
80 std::vector<PhdrEntry *> Phdrs;
83 uint64_t SectionHeaderOff;
85 bool HasGotBaseSym = false;
87 } // anonymous namespace
89 StringRef elf::getOutputSectionName(InputSectionBase *S) {
90 // ".zdebug_" is a prefix for ZLIB-compressed sections.
91 // Because we decompressed input sections, we want to remove 'z'.
92 if (S->Name.startswith(".zdebug_"))
93 return Saver.save("." + S->Name.substr(2));
95 if (Config->Relocatable)
98 // This is for --emit-relocs. If .text.foo is emitted as .text.bar, we want
99 // to emit .rela.text.foo as .rela.text.bar for consistency (this is not
100 // technically required, but not doing it is odd). This code guarantees that.
101 if ((S->Type == SHT_REL || S->Type == SHT_RELA) &&
102 !isa<SyntheticSection>(S)) {
104 cast<InputSection>(S)->getRelocatedSection()->getOutputSection();
105 if (S->Type == SHT_RELA)
106 return Saver.save(".rela" + Out->Name);
107 return Saver.save(".rel" + Out->Name);
111 {".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.rel.ro.",
112 ".bss.", ".init_array.", ".fini_array.", ".ctors.", ".dtors.", ".tbss.",
113 ".gcc_except_table.", ".tdata.", ".ARM.exidx.", ".ARM.extab."}) {
114 StringRef Prefix = V.drop_back();
115 if (S->Name.startswith(V) || S->Name == Prefix)
119 // CommonSection is identified as "COMMON" in linker scripts.
120 // By default, it should go to .bss section.
121 if (S->Name == "COMMON")
127 static bool needsInterpSection() {
128 return !SharedFiles.empty() && !Config->DynamicLinker.empty() &&
129 Script->needsInterpSection();
132 template <class ELFT> void elf::writeResult() { Writer<ELFT>().run(); }
134 template <class ELFT> void Writer<ELFT>::removeEmptyPTLoad() {
135 llvm::erase_if(Phdrs, [&](const PhdrEntry *P) {
136 if (P->p_type != PT_LOAD)
140 uint64_t Size = P->LastSec->Addr + P->LastSec->Size - P->FirstSec->Addr;
145 template <class ELFT> static void combineEhFrameSections() {
146 for (InputSectionBase *&S : InputSections) {
147 EhInputSection *ES = dyn_cast<EhInputSection>(S);
148 if (!ES || !ES->Live)
151 InX::EhFrame->addSection<ELFT>(ES);
155 std::vector<InputSectionBase *> &V = InputSections;
156 V.erase(std::remove(V.begin(), V.end(), nullptr), V.end());
159 static Defined *addOptionalRegular(StringRef Name, SectionBase *Sec,
160 uint64_t Val, uint8_t StOther = STV_HIDDEN,
161 uint8_t Binding = STB_GLOBAL) {
162 Symbol *S = Symtab->find(Name);
163 if (!S || S->isDefined())
165 Symbol *Sym = Symtab->addRegular(Name, StOther, STT_NOTYPE, Val,
166 /*Size=*/0, Binding, Sec,
168 return cast<Defined>(Sym);
171 // The linker is expected to define some symbols depending on
172 // the linking result. This function defines such symbols.
173 void elf::addReservedSymbols() {
174 if (Config->EMachine == EM_MIPS) {
175 // Define _gp for MIPS. st_value of _gp symbol will be updated by Writer
176 // so that it points to an absolute address which by default is relative
177 // to GOT. Default offset is 0x7ff0.
178 // See "Global Data Symbols" in Chapter 6 in the following document:
179 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
180 ElfSym::MipsGp = Symtab->addAbsolute("_gp", STV_HIDDEN, STB_GLOBAL);
182 // On MIPS O32 ABI, _gp_disp is a magic symbol designates offset between
183 // start of function and 'gp' pointer into GOT.
184 if (Symtab->find("_gp_disp"))
186 Symtab->addAbsolute("_gp_disp", STV_HIDDEN, STB_GLOBAL);
188 // The __gnu_local_gp is a magic symbol equal to the current value of 'gp'
189 // pointer. This symbol is used in the code generated by .cpload pseudo-op
190 // in case of using -mno-shared option.
191 // https://sourceware.org/ml/binutils/2004-12/msg00094.html
192 if (Symtab->find("__gnu_local_gp"))
193 ElfSym::MipsLocalGp =
194 Symtab->addAbsolute("__gnu_local_gp", STV_HIDDEN, STB_GLOBAL);
197 ElfSym::GlobalOffsetTable = addOptionalRegular(
198 "_GLOBAL_OFFSET_TABLE_", Out::ElfHeader, Target->GotBaseSymOff);
200 // __ehdr_start is the location of ELF file headers. Note that we define
201 // this symbol unconditionally even when using a linker script, which
202 // differs from the behavior implemented by GNU linker which only define
203 // this symbol if ELF headers are in the memory mapped segment.
204 // __executable_start is not documented, but the expectation of at
205 // least the android libc is that it points to the elf header too.
206 // __dso_handle symbol is passed to cxa_finalize as a marker to identify
207 // each DSO. The address of the symbol doesn't matter as long as they are
208 // different in different DSOs, so we chose the start address of the DSO.
209 for (const char *Name :
210 {"__ehdr_start", "__executable_start", "__dso_handle"})
211 addOptionalRegular(Name, Out::ElfHeader, 0, STV_HIDDEN);
213 // If linker script do layout we do not need to create any standart symbols.
214 if (Script->HasSectionsCommand)
217 auto Add = [](StringRef S, int64_t Pos) {
218 return addOptionalRegular(S, Out::ElfHeader, Pos, STV_DEFAULT);
221 ElfSym::Bss = Add("__bss_start", 0);
222 ElfSym::End1 = Add("end", -1);
223 ElfSym::End2 = Add("_end", -1);
224 ElfSym::Etext1 = Add("etext", -1);
225 ElfSym::Etext2 = Add("_etext", -1);
226 ElfSym::Edata1 = Add("edata", -1);
227 ElfSym::Edata2 = Add("_edata", -1);
230 static OutputSection *findSection(StringRef Name) {
231 for (BaseCommand *Base : Script->SectionCommands)
232 if (auto *Sec = dyn_cast<OutputSection>(Base))
233 if (Sec->Name == Name)
238 // Initialize Out members.
239 template <class ELFT> static void createSyntheticSections() {
240 // Initialize all pointers with NULL. This is needed because
241 // you can call lld::elf::main more than once as a library.
242 memset(&Out::First, 0, sizeof(Out));
244 auto Add = [](InputSectionBase *Sec) { InputSections.push_back(Sec); };
246 InX::DynStrTab = make<StringTableSection>(".dynstr", true);
247 InX::Dynamic = make<DynamicSection<ELFT>>();
248 if (Config->AndroidPackDynRelocs) {
249 InX::RelaDyn = make<AndroidPackedRelocationSection<ELFT>>(
250 Config->IsRela ? ".rela.dyn" : ".rel.dyn");
252 InX::RelaDyn = make<RelocationSection<ELFT>>(
253 Config->IsRela ? ".rela.dyn" : ".rel.dyn", Config->ZCombreloc);
255 InX::ShStrTab = make<StringTableSection>(".shstrtab", false);
257 Out::ProgramHeaders = make<OutputSection>("", 0, SHF_ALLOC);
258 Out::ProgramHeaders->Alignment = Config->Wordsize;
260 if (needsInterpSection()) {
261 InX::Interp = createInterpSection();
264 InX::Interp = nullptr;
267 if (Config->Strip != StripPolicy::All) {
268 InX::StrTab = make<StringTableSection>(".strtab", false);
269 InX::SymTab = make<SymbolTableSection<ELFT>>(*InX::StrTab);
272 if (Config->BuildId != BuildIdKind::None) {
273 InX::BuildId = make<BuildIdSection>();
277 InX::Bss = make<BssSection>(".bss", 0, 1);
280 // If there is a SECTIONS command and a .data.rel.ro section name use name
281 // .data.rel.ro.bss so that we match in the .data.rel.ro output section.
282 // This makes sure our relro is contiguous.
284 Script->HasSectionsCommand && findSection(".data.rel.ro");
285 InX::BssRelRo = make<BssSection>(
286 HasDataRelRo ? ".data.rel.ro.bss" : ".bss.rel.ro", 0, 1);
289 // Add MIPS-specific sections.
290 if (Config->EMachine == EM_MIPS) {
291 if (!Config->Shared && Config->HasDynSymTab) {
292 InX::MipsRldMap = make<MipsRldMapSection>();
293 Add(InX::MipsRldMap);
295 if (auto *Sec = MipsAbiFlagsSection<ELFT>::create())
297 if (auto *Sec = MipsOptionsSection<ELFT>::create())
299 if (auto *Sec = MipsReginfoSection<ELFT>::create())
303 if (Config->HasDynSymTab) {
304 InX::DynSymTab = make<SymbolTableSection<ELFT>>(*InX::DynStrTab);
307 In<ELFT>::VerSym = make<VersionTableSection<ELFT>>();
308 Add(In<ELFT>::VerSym);
310 if (!Config->VersionDefinitions.empty()) {
311 In<ELFT>::VerDef = make<VersionDefinitionSection<ELFT>>();
312 Add(In<ELFT>::VerDef);
315 In<ELFT>::VerNeed = make<VersionNeedSection<ELFT>>();
316 Add(In<ELFT>::VerNeed);
318 if (Config->GnuHash) {
319 InX::GnuHashTab = make<GnuHashTableSection>();
320 Add(InX::GnuHashTab);
323 if (Config->SysvHash) {
324 InX::HashTab = make<HashTableSection>();
333 // Add .got. MIPS' .got is so different from the other archs,
334 // it has its own class.
335 if (Config->EMachine == EM_MIPS) {
336 InX::MipsGot = make<MipsGotSection>();
339 InX::Got = make<GotSection>();
343 InX::GotPlt = make<GotPltSection>();
345 InX::IgotPlt = make<IgotPltSection>();
348 if (Config->GdbIndex) {
349 InX::GdbIndex = createGdbIndex<ELFT>();
353 // We always need to add rel[a].plt to output if it has entries.
354 // Even for static linking it can contain R_[*]_IRELATIVE relocations.
355 InX::RelaPlt = make<RelocationSection<ELFT>>(
356 Config->IsRela ? ".rela.plt" : ".rel.plt", false /*Sort*/);
359 // The RelaIplt immediately follows .rel.plt (.rel.dyn for ARM) to ensure
360 // that the IRelative relocations are processed last by the dynamic loader.
361 // We cannot place the iplt section in .rel.dyn when Android relocation
362 // packing is enabled because that would cause a section type mismatch.
363 // However, because the Android dynamic loader reads .rel.plt after .rel.dyn,
364 // we can get the desired behaviour by placing the iplt section in .rel.plt.
365 InX::RelaIplt = make<RelocationSection<ELFT>>(
366 (Config->EMachine == EM_ARM && !Config->AndroidPackDynRelocs)
368 : InX::RelaPlt->Name,
372 InX::Plt = make<PltSection>(Target->PltHeaderSize);
374 InX::Iplt = make<PltSection>(0);
377 if (!Config->Relocatable) {
378 if (Config->EhFrameHdr) {
379 InX::EhFrameHdr = make<EhFrameHeader>();
380 Add(InX::EhFrameHdr);
382 InX::EhFrame = make<EhFrameSection>();
392 if (Config->EMachine == EM_ARM && !Config->Relocatable)
393 // Add a sentinel to terminate .ARM.exidx. It helps an unwinder
394 // to find the exact address range of the last entry.
395 Add(make<ARMExidxSentinelSection>());
398 // The main function of the writer.
399 template <class ELFT> void Writer<ELFT>::run() {
400 // Create linker-synthesized sections such as .got or .plt.
401 // Such sections are of type input section.
402 createSyntheticSections<ELFT>();
404 if (!Config->Relocatable)
405 combineEhFrameSections<ELFT>();
407 // We want to process linker script commands. When SECTIONS command
408 // is given we let it create sections.
409 Script->processSectionCommands();
411 // Linker scripts controls how input sections are assigned to output sections.
412 // Input sections that were not handled by scripts are called "orphans", and
413 // they are assigned to output sections by the default rule. Process that.
414 Script->addOrphanSections();
416 if (Config->Discard != DiscardPolicy::All)
419 if (Config->CopyRelocs)
422 // Now that we have a complete set of output sections. This function
423 // completes section contents. For example, we need to add strings
424 // to the string table, and add entries to .got and .plt.
425 // finalizeSections does that.
430 // If -compressed-debug-sections is specified, we need to compress
431 // .debug_* sections. Do it right now because it changes the size of
433 parallelForEach(OutputSections,
434 [](OutputSection *Sec) { Sec->maybeCompress<ELFT>(); });
436 Script->assignAddresses();
437 Script->allocateHeaders(Phdrs);
439 // Remove empty PT_LOAD to avoid causing the dynamic linker to try to mmap a
440 // 0 sized region. This has to be done late since only after assignAddresses
441 // we know the size of the sections.
444 if (!Config->OFormatBinary)
447 assignFileOffsetsBinary();
451 if (Config->Relocatable) {
452 for (OutputSection *Sec : OutputSections)
456 // It does not make sense try to open the file if we have error already.
459 // Write the result down to a file.
464 if (!Config->OFormatBinary) {
469 writeSectionsBinary();
472 // Backfill .note.gnu.build-id section content. This is done at last
473 // because the content is usually a hash value of the entire output file.
478 // Handle -Map option.
483 if (auto E = Buffer->commit())
484 error("failed to write to the output file: " + toString(std::move(E)));
487 static bool shouldKeepInSymtab(SectionBase *Sec, StringRef SymName,
489 if (B.isFile() || B.isSection())
492 // If sym references a section in a discarded group, don't keep it.
493 if (Sec == &InputSection::Discarded)
496 if (Config->Discard == DiscardPolicy::None)
499 // In ELF assembly .L symbols are normally discarded by the assembler.
500 // If the assembler fails to do so, the linker discards them if
501 // * --discard-locals is used.
502 // * The symbol is in a SHF_MERGE section, which is normally the reason for
503 // the assembler keeping the .L symbol.
504 if (!SymName.startswith(".L") && !SymName.empty())
507 if (Config->Discard == DiscardPolicy::Locals)
510 return !Sec || !(Sec->Flags & SHF_MERGE);
513 static bool includeInSymtab(const Symbol &B) {
514 if (!B.isLocal() && !B.IsUsedInRegularObj)
517 if (auto *D = dyn_cast<Defined>(&B)) {
518 // Always include absolute symbols.
519 SectionBase *Sec = D->Section;
523 // Exclude symbols pointing to garbage-collected sections.
524 if (isa<InputSectionBase>(Sec) && !Sec->Live)
526 if (auto *S = dyn_cast<MergeInputSection>(Sec))
527 if (!S->getSectionPiece(D->Value)->Live)
534 // Local symbols are not in the linker's symbol table. This function scans
535 // each object file's symbol table to copy local symbols to the output.
536 template <class ELFT> void Writer<ELFT>::copyLocalSymbols() {
539 for (InputFile *File : ObjectFiles) {
540 ObjFile<ELFT> *F = cast<ObjFile<ELFT>>(File);
541 for (Symbol *B : F->getLocalSymbols()) {
544 ": broken object: getLocalSymbols returns a non-local symbol");
545 auto *DR = dyn_cast<Defined>(B);
547 // No reason to keep local undefined symbol in symtab.
550 if (!includeInSymtab(*B))
553 SectionBase *Sec = DR->Section;
554 if (!shouldKeepInSymtab(Sec, B->getName(), *B))
556 InX::SymTab->addSymbol(B);
561 template <class ELFT> void Writer<ELFT>::addSectionSymbols() {
562 // Create a section symbol for each output section so that we can represent
563 // relocations that point to the section. If we know that no relocation is
564 // referring to a section (that happens if the section is a synthetic one), we
565 // don't create a section symbol for that section.
566 for (BaseCommand *Base : Script->SectionCommands) {
567 auto *Sec = dyn_cast<OutputSection>(Base);
570 auto I = llvm::find_if(Sec->SectionCommands, [](BaseCommand *Base) {
571 if (auto *ISD = dyn_cast<InputSectionDescription>(Base))
572 return !ISD->Sections.empty();
575 if (I == Sec->SectionCommands.end())
577 InputSection *IS = cast<InputSectionDescription>(*I)->Sections[0];
579 // Relocations are not using REL[A] section symbols.
580 if (IS->Type == SHT_REL || IS->Type == SHT_RELA)
583 // Unlike other synthetic sections, mergeable output sections contain data
584 // copied from input sections, and there may be a relocation pointing to its
585 // contents if -r or -emit-reloc are given.
586 if (isa<SyntheticSection>(IS) && !(IS->Flags & SHF_MERGE))
590 make<Defined>(IS->File, "", STB_LOCAL, /*StOther=*/0, STT_SECTION,
591 /*Value=*/0, /*Size=*/0, IS);
592 InX::SymTab->addSymbol(Sym);
596 // Today's loaders have a feature to make segments read-only after
597 // processing dynamic relocations to enhance security. PT_GNU_RELRO
598 // is defined for that.
600 // This function returns true if a section needs to be put into a
601 // PT_GNU_RELRO segment.
602 static bool isRelroSection(const OutputSection *Sec) {
606 uint64_t Flags = Sec->Flags;
608 // Non-allocatable or non-writable sections don't need RELRO because
609 // they are not writable or not even mapped to memory in the first place.
610 // RELRO is for sections that are essentially read-only but need to
611 // be writable only at process startup to allow dynamic linker to
612 // apply relocations.
613 if (!(Flags & SHF_ALLOC) || !(Flags & SHF_WRITE))
616 // Once initialized, TLS data segments are used as data templates
617 // for a thread-local storage. For each new thread, runtime
618 // allocates memory for a TLS and copy templates there. No thread
619 // are supposed to use templates directly. Thus, it can be in RELRO.
623 // .init_array, .preinit_array and .fini_array contain pointers to
624 // functions that are executed on process startup or exit. These
625 // pointers are set by the static linker, and they are not expected
626 // to change at runtime. But if you are an attacker, you could do
627 // interesting things by manipulating pointers in .fini_array, for
628 // example. So they are put into RELRO.
629 uint32_t Type = Sec->Type;
630 if (Type == SHT_INIT_ARRAY || Type == SHT_FINI_ARRAY ||
631 Type == SHT_PREINIT_ARRAY)
634 // .got contains pointers to external symbols. They are resolved by
635 // the dynamic linker when a module is loaded into memory, and after
636 // that they are not expected to change. So, it can be in RELRO.
637 if (InX::Got && Sec == InX::Got->getParent())
640 // .got.plt contains pointers to external function symbols. They are
641 // by default resolved lazily, so we usually cannot put it into RELRO.
642 // However, if "-z now" is given, the lazy symbol resolution is
643 // disabled, which enables us to put it into RELRO.
644 if (Sec == InX::GotPlt->getParent())
647 // .dynamic section contains data for the dynamic linker, and
648 // there's no need to write to it at runtime, so it's better to put
650 if (Sec == InX::Dynamic->getParent())
653 // Sections with some special names are put into RELRO. This is a
654 // bit unfortunate because section names shouldn't be significant in
655 // ELF in spirit. But in reality many linker features depend on
656 // magic section names.
657 StringRef S = Sec->Name;
658 return S == ".data.rel.ro" || S == ".bss.rel.ro" || S == ".ctors" ||
659 S == ".dtors" || S == ".jcr" || S == ".eh_frame" ||
660 S == ".openbsd.randomdata";
663 // We compute a rank for each section. The rank indicates where the
664 // section should be placed in the file. Instead of using simple
665 // numbers (0,1,2...), we use a series of flags. One for each decision
666 // point when placing the section.
667 // Using flags has two key properties:
668 // * It is easy to check if a give branch was taken.
669 // * It is easy two see how similar two ranks are (see getRankProximity).
671 RF_NOT_ADDR_SET = 1 << 16,
672 RF_NOT_INTERP = 1 << 15,
673 RF_NOT_ALLOC = 1 << 14,
675 RF_EXEC_WRITE = 1 << 12,
677 RF_NON_TLS_BSS = 1 << 10,
678 RF_NON_TLS_BSS_RO = 1 << 9,
681 RF_PPC_NOT_TOCBSS = 1 << 6,
683 RF_PPC_TOCL = 1 << 4,
685 RF_PPC_BRANCH_LT = 1 << 2,
686 RF_MIPS_GPREL = 1 << 1,
687 RF_MIPS_NOT_GOT = 1 << 0
690 static unsigned getSectionRank(const OutputSection *Sec) {
693 // We want to put section specified by -T option first, so we
694 // can start assigning VA starting from them later.
695 if (Config->SectionStartMap.count(Sec->Name))
697 Rank |= RF_NOT_ADDR_SET;
699 // Put .interp first because some loaders want to see that section
700 // on the first page of the executable file when loaded into memory.
701 if (Sec->Name == ".interp")
703 Rank |= RF_NOT_INTERP;
705 // Allocatable sections go first to reduce the total PT_LOAD size and
706 // so debug info doesn't change addresses in actual code.
707 if (!(Sec->Flags & SHF_ALLOC))
708 return Rank | RF_NOT_ALLOC;
710 // Sort sections based on their access permission in the following
711 // order: R, RX, RWX, RW. This order is based on the following
713 // * Read-only sections come first such that they go in the
714 // PT_LOAD covering the program headers at the start of the file.
715 // * Read-only, executable sections come next, unless the
716 // -no-rosegment option is used.
717 // * Writable, executable sections follow such that .plt on
718 // architectures where it needs to be writable will be placed
719 // between .text and .data.
720 // * Writable sections come last, such that .bss lands at the very
721 // end of the last PT_LOAD.
722 bool IsExec = Sec->Flags & SHF_EXECINSTR;
723 bool IsWrite = Sec->Flags & SHF_WRITE;
727 Rank |= RF_EXEC_WRITE;
728 else if (!Config->SingleRoRx)
735 // If we got here we know that both A and B are in the same PT_LOAD.
737 bool IsTls = Sec->Flags & SHF_TLS;
738 bool IsNoBits = Sec->Type == SHT_NOBITS;
740 // The first requirement we have is to put (non-TLS) nobits sections last. The
741 // reason is that the only thing the dynamic linker will see about them is a
742 // p_memsz that is larger than p_filesz. Seeing that it zeros the end of the
743 // PT_LOAD, so that has to correspond to the nobits sections.
744 bool IsNonTlsNoBits = IsNoBits && !IsTls;
746 Rank |= RF_NON_TLS_BSS;
748 // We place nobits RelRo sections before plain r/w ones, and non-nobits RelRo
749 // sections after r/w ones, so that the RelRo sections are contiguous.
750 bool IsRelRo = isRelroSection(Sec);
751 if (IsNonTlsNoBits && !IsRelRo)
752 Rank |= RF_NON_TLS_BSS_RO;
753 if (!IsNonTlsNoBits && IsRelRo)
754 Rank |= RF_NON_TLS_BSS_RO;
756 // The TLS initialization block needs to be a single contiguous block in a R/W
757 // PT_LOAD, so stick TLS sections directly before the other RelRo R/W
758 // sections. The TLS NOBITS sections are placed here as they don't take up
759 // virtual address space in the PT_LOAD.
763 // Within the TLS initialization block, the non-nobits sections need to appear
768 // Some architectures have additional ordering restrictions for sections
769 // within the same PT_LOAD.
770 if (Config->EMachine == EM_PPC64) {
771 // PPC64 has a number of special SHT_PROGBITS+SHF_ALLOC+SHF_WRITE sections
772 // that we would like to make sure appear is a specific order to maximize
773 // their coverage by a single signed 16-bit offset from the TOC base
774 // pointer. Conversely, the special .tocbss section should be first among
775 // all SHT_NOBITS sections. This will put it next to the loaded special
776 // PPC64 sections (and, thus, within reach of the TOC base pointer).
777 StringRef Name = Sec->Name;
778 if (Name != ".tocbss")
779 Rank |= RF_PPC_NOT_TOCBSS;
790 if (Name == ".branch_lt")
791 Rank |= RF_PPC_BRANCH_LT;
793 if (Config->EMachine == EM_MIPS) {
794 // All sections with SHF_MIPS_GPREL flag should be grouped together
795 // because data in these sections is addressable with a gp relative address.
796 if (Sec->Flags & SHF_MIPS_GPREL)
797 Rank |= RF_MIPS_GPREL;
799 if (Sec->Name != ".got")
800 Rank |= RF_MIPS_NOT_GOT;
806 static bool compareSections(const BaseCommand *ACmd, const BaseCommand *BCmd) {
807 const OutputSection *A = cast<OutputSection>(ACmd);
808 const OutputSection *B = cast<OutputSection>(BCmd);
809 if (A->SortRank != B->SortRank)
810 return A->SortRank < B->SortRank;
811 if (!(A->SortRank & RF_NOT_ADDR_SET))
812 return Config->SectionStartMap.lookup(A->Name) <
813 Config->SectionStartMap.lookup(B->Name);
817 void PhdrEntry::add(OutputSection *Sec) {
821 p_align = std::max(p_align, Sec->Alignment);
822 if (p_type == PT_LOAD)
826 // The beginning and the ending of .rel[a].plt section are marked
827 // with __rel[a]_iplt_{start,end} symbols if it is a statically linked
828 // executable. The runtime needs these symbols in order to resolve
829 // all IRELATIVE relocs on startup. For dynamic executables, we don't
830 // need these symbols, since IRELATIVE relocs are resolved through GOT
831 // and PLT. For details, see http://www.airs.com/blog/archives/403.
832 template <class ELFT> void Writer<ELFT>::addRelIpltSymbols() {
835 StringRef S = Config->IsRela ? "__rela_iplt_start" : "__rel_iplt_start";
836 addOptionalRegular(S, InX::RelaIplt, 0, STV_HIDDEN, STB_WEAK);
838 S = Config->IsRela ? "__rela_iplt_end" : "__rel_iplt_end";
839 addOptionalRegular(S, InX::RelaIplt, -1, STV_HIDDEN, STB_WEAK);
842 template <class ELFT>
843 void Writer<ELFT>::forEachRelSec(std::function<void(InputSectionBase &)> Fn) {
844 // Scan all relocations. Each relocation goes through a series
845 // of tests to determine if it needs special treatment, such as
846 // creating GOT, PLT, copy relocations, etc.
847 // Note that relocations for non-alloc sections are directly
848 // processed by InputSection::relocateNonAlloc.
849 for (InputSectionBase *IS : InputSections)
850 if (IS->Live && isa<InputSection>(IS) && (IS->Flags & SHF_ALLOC))
852 for (EhInputSection *ES : InX::EhFrame->Sections)
856 // This function generates assignments for predefined symbols (e.g. _end or
857 // _etext) and inserts them into the commands sequence to be processed at the
858 // appropriate time. This ensures that the value is going to be correct by the
859 // time any references to these symbols are processed and is equivalent to
860 // defining these symbols explicitly in the linker script.
861 template <class ELFT> void Writer<ELFT>::setReservedSymbolSections() {
862 if (ElfSym::GlobalOffsetTable) {
863 // The _GLOBAL_OFFSET_TABLE_ symbol is defined by target convention to
864 // be at some offset from the base of the .got section, usually 0 or the end
866 InputSection *GotSection = InX::MipsGot ? cast<InputSection>(InX::MipsGot)
867 : cast<InputSection>(InX::Got);
868 ElfSym::GlobalOffsetTable->Section = GotSection;
871 PhdrEntry *Last = nullptr;
872 PhdrEntry *LastRO = nullptr;
874 for (PhdrEntry *P : Phdrs) {
875 if (P->p_type != PT_LOAD)
878 if (!(P->p_flags & PF_W))
883 // _etext is the first location after the last read-only loadable segment.
885 ElfSym::Etext1->Section = LastRO->LastSec;
887 ElfSym::Etext2->Section = LastRO->LastSec;
891 // _edata points to the end of the last mapped initialized section.
892 OutputSection *Edata = nullptr;
893 for (OutputSection *OS : OutputSections) {
894 if (OS->Type != SHT_NOBITS)
896 if (OS == Last->LastSec)
901 ElfSym::Edata1->Section = Edata;
903 ElfSym::Edata2->Section = Edata;
905 // _end is the first location after the uninitialized data region.
907 ElfSym::End1->Section = Last->LastSec;
909 ElfSym::End2->Section = Last->LastSec;
913 ElfSym::Bss->Section = findSection(".bss");
915 // Setup MIPS _gp_disp/__gnu_local_gp symbols which should
916 // be equal to the _gp symbol's value.
917 if (ElfSym::MipsGp) {
918 // Find GP-relative section with the lowest address
919 // and use this address to calculate default _gp value.
920 for (OutputSection *OS : OutputSections) {
921 if (OS->Flags & SHF_MIPS_GPREL) {
922 ElfSym::MipsGp->Section = OS;
923 ElfSym::MipsGp->Value = 0x7ff0;
930 // We want to find how similar two ranks are.
931 // The more branches in getSectionRank that match, the more similar they are.
932 // Since each branch corresponds to a bit flag, we can just use
933 // countLeadingZeros.
934 static int getRankProximityAux(OutputSection *A, OutputSection *B) {
935 return countLeadingZeros(A->SortRank ^ B->SortRank);
938 static int getRankProximity(OutputSection *A, BaseCommand *B) {
939 if (auto *Sec = dyn_cast<OutputSection>(B))
941 return getRankProximityAux(A, Sec);
945 // When placing orphan sections, we want to place them after symbol assignments
946 // so that an orphan after
950 // doesn't break the intended meaning of the begin/end symbols.
951 // We don't want to go over sections since findOrphanPos is the
952 // one in charge of deciding the order of the sections.
953 // We don't want to go over changes to '.', since doing so in
954 // rx_sec : { *(rx_sec) }
955 // . = ALIGN(0x1000);
956 // /* The RW PT_LOAD starts here*/
957 // rw_sec : { *(rw_sec) }
958 // would mean that the RW PT_LOAD would become unaligned.
959 static bool shouldSkip(BaseCommand *Cmd) {
960 if (isa<OutputSection>(Cmd))
962 if (auto *Assign = dyn_cast<SymbolAssignment>(Cmd))
963 return Assign->Name != ".";
967 // We want to place orphan sections so that they share as much
968 // characteristics with their neighbors as possible. For example, if
969 // both are rw, or both are tls.
970 template <typename ELFT>
971 static std::vector<BaseCommand *>::iterator
972 findOrphanPos(std::vector<BaseCommand *>::iterator B,
973 std::vector<BaseCommand *>::iterator E) {
974 OutputSection *Sec = cast<OutputSection>(*E);
976 // Find the first element that has as close a rank as possible.
977 auto I = std::max_element(B, E, [=](BaseCommand *A, BaseCommand *B) {
978 return getRankProximity(Sec, A) < getRankProximity(Sec, B);
983 // Consider all existing sections with the same proximity.
984 int Proximity = getRankProximity(Sec, *I);
985 for (; I != E; ++I) {
986 auto *CurSec = dyn_cast<OutputSection>(*I);
987 if (!CurSec || !CurSec->Live)
989 if (getRankProximity(Sec, CurSec) != Proximity ||
990 Sec->SortRank < CurSec->SortRank)
994 auto IsLiveSection = [](BaseCommand *Cmd) {
995 auto *OS = dyn_cast<OutputSection>(Cmd);
996 return OS && OS->Live;
999 auto J = std::find_if(llvm::make_reverse_iterator(I),
1000 llvm::make_reverse_iterator(B), IsLiveSection);
1003 // As a special case, if the orphan section is the last section, put
1004 // it at the very end, past any other commands.
1005 // This matches bfd's behavior and is convenient when the linker script fully
1006 // specifies the start of the file, but doesn't care about the end (the non
1007 // alloc sections for example).
1008 auto NextSec = std::find_if(I, E, IsLiveSection);
1012 while (I != E && shouldSkip(*I))
1017 // If no layout was provided by linker script, we want to apply default
1018 // sorting for special input sections and handle --symbol-ordering-file.
1019 template <class ELFT> void Writer<ELFT>::sortInputSections() {
1020 assert(!Script->HasSectionsCommand);
1022 // Sort input sections by priority using the list provided
1023 // by --symbol-ordering-file.
1024 DenseMap<SectionBase *, int> Order = buildSectionOrder();
1026 for (BaseCommand *Base : Script->SectionCommands)
1027 if (auto *Sec = dyn_cast<OutputSection>(Base))
1029 Sec->sort([&](InputSectionBase *S) { return Order.lookup(S); });
1031 // Sort input sections by section name suffixes for
1032 // __attribute__((init_priority(N))).
1033 if (OutputSection *Sec = findSection(".init_array"))
1034 Sec->sortInitFini();
1035 if (OutputSection *Sec = findSection(".fini_array"))
1036 Sec->sortInitFini();
1038 // Sort input sections by the special rule for .ctors and .dtors.
1039 if (OutputSection *Sec = findSection(".ctors"))
1040 Sec->sortCtorsDtors();
1041 if (OutputSection *Sec = findSection(".dtors"))
1042 Sec->sortCtorsDtors();
1045 template <class ELFT> void Writer<ELFT>::sortSections() {
1046 Script->adjustSectionsBeforeSorting();
1048 // Don't sort if using -r. It is not necessary and we want to preserve the
1049 // relative order for SHF_LINK_ORDER sections.
1050 if (Config->Relocatable)
1053 for (BaseCommand *Base : Script->SectionCommands)
1054 if (auto *Sec = dyn_cast<OutputSection>(Base))
1055 Sec->SortRank = getSectionRank(Sec);
1057 if (!Script->HasSectionsCommand) {
1058 sortInputSections();
1060 // We know that all the OutputSections are contiguous in this case.
1061 auto E = Script->SectionCommands.end();
1062 auto I = Script->SectionCommands.begin();
1063 auto IsSection = [](BaseCommand *Base) { return isa<OutputSection>(Base); };
1064 I = std::find_if(I, E, IsSection);
1065 E = std::find_if(llvm::make_reverse_iterator(E),
1066 llvm::make_reverse_iterator(I), IsSection)
1068 std::stable_sort(I, E, compareSections);
1072 // Orphan sections are sections present in the input files which are
1073 // not explicitly placed into the output file by the linker script.
1075 // The sections in the linker script are already in the correct
1076 // order. We have to figuere out where to insert the orphan
1079 // The order of the sections in the script is arbitrary and may not agree with
1080 // compareSections. This means that we cannot easily define a strict weak
1081 // ordering. To see why, consider a comparison of a section in the script and
1082 // one not in the script. We have a two simple options:
1083 // * Make them equivalent (a is not less than b, and b is not less than a).
1084 // The problem is then that equivalence has to be transitive and we can
1085 // have sections a, b and c with only b in a script and a less than c
1086 // which breaks this property.
1087 // * Use compareSectionsNonScript. Given that the script order doesn't have
1088 // to match, we can end up with sections a, b, c, d where b and c are in the
1089 // script and c is compareSectionsNonScript less than b. In which case d
1090 // can be equivalent to c, a to b and d < a. As a concrete example:
1091 // .a (rx) # not in script
1092 // .b (rx) # in script
1093 // .c (ro) # in script
1094 // .d (ro) # not in script
1096 // The way we define an order then is:
1097 // * Sort only the orphan sections. They are in the end right now.
1098 // * Move each orphan section to its preferred position. We try
1099 // to put each section in the last position where it it can share
1102 // There is some ambiguity as to where exactly a new entry should be
1103 // inserted, because Commands contains not only output section
1104 // commands but also other types of commands such as symbol assignment
1105 // expressions. There's no correct answer here due to the lack of the
1106 // formal specification of the linker script. We use heuristics to
1107 // determine whether a new output command should be added before or
1108 // after another commands. For the details, look at shouldSkip
1111 auto I = Script->SectionCommands.begin();
1112 auto E = Script->SectionCommands.end();
1113 auto NonScriptI = std::find_if(I, E, [](BaseCommand *Base) {
1114 if (auto *Sec = dyn_cast<OutputSection>(Base))
1115 return Sec->Live && Sec->SectionIndex == INT_MAX;
1119 // Sort the orphan sections.
1120 std::stable_sort(NonScriptI, E, compareSections);
1122 // As a horrible special case, skip the first . assignment if it is before any
1123 // section. We do this because it is common to set a load address by starting
1124 // the script with ". = 0xabcd" and the expectation is that every section is
1126 auto FirstSectionOrDotAssignment =
1127 std::find_if(I, E, [](BaseCommand *Cmd) { return !shouldSkip(Cmd); });
1128 if (FirstSectionOrDotAssignment != E &&
1129 isa<SymbolAssignment>(**FirstSectionOrDotAssignment))
1130 ++FirstSectionOrDotAssignment;
1131 I = FirstSectionOrDotAssignment;
1133 while (NonScriptI != E) {
1134 auto Pos = findOrphanPos<ELFT>(I, NonScriptI);
1135 OutputSection *Orphan = cast<OutputSection>(*NonScriptI);
1137 // As an optimization, find all sections with the same sort rank
1138 // and insert them with one rotate.
1139 unsigned Rank = Orphan->SortRank;
1140 auto End = std::find_if(NonScriptI + 1, E, [=](BaseCommand *Cmd) {
1141 return cast<OutputSection>(Cmd)->SortRank != Rank;
1143 std::rotate(Pos, NonScriptI, End);
1147 Script->adjustSectionsAfterSorting();
1150 static bool compareByFilePosition(InputSection *A, InputSection *B) {
1151 // Synthetic, i. e. a sentinel section, should go last.
1152 if (A->kind() == InputSectionBase::Synthetic ||
1153 B->kind() == InputSectionBase::Synthetic)
1154 return A->kind() != InputSectionBase::Synthetic;
1155 InputSection *LA = A->getLinkOrderDep();
1156 InputSection *LB = B->getLinkOrderDep();
1157 OutputSection *AOut = LA->getParent();
1158 OutputSection *BOut = LB->getParent();
1160 return AOut->SectionIndex < BOut->SectionIndex;
1161 return LA->OutSecOff < LB->OutSecOff;
1164 // This function is used by the --merge-exidx-entries to detect duplicate
1165 // .ARM.exidx sections. It is Arm only.
1167 // The .ARM.exidx section is of the form:
1168 // | PREL31 offset to function | Unwind instructions for function |
1169 // where the unwind instructions are either a small number of unwind
1170 // instructions inlined into the table entry, the special CANT_UNWIND value of
1171 // 0x1 or a PREL31 offset into a .ARM.extab Section that contains unwind
1174 // We return true if all the unwind instructions in the .ARM.exidx entries of
1175 // Cur can be merged into the last entry of Prev.
1176 static bool isDuplicateArmExidxSec(InputSection *Prev, InputSection *Cur) {
1178 // References to .ARM.Extab Sections have bit 31 clear and are not the
1179 // special EXIDX_CANTUNWIND bit-pattern.
1180 auto IsExtabRef = [](uint32_t Unwind) {
1181 return (Unwind & 0x80000000) == 0 && Unwind != 0x1;
1189 // Get the last table Entry from the previous .ARM.exidx section.
1190 const ExidxEntry &PrevEntry = *reinterpret_cast<const ExidxEntry *>(
1191 Prev->Data.data() + Prev->getSize() - sizeof(ExidxEntry));
1192 if (IsExtabRef(PrevEntry.Unwind))
1195 // We consider the unwind instructions of an .ARM.exidx table entry
1196 // a duplicate if the previous unwind instructions if:
1197 // - Both are the special EXIDX_CANTUNWIND.
1198 // - Both are the same inline unwind instructions.
1199 // We do not attempt to follow and check links into .ARM.extab tables as
1200 // consecutive identical entries are rare and the effort to check that they
1201 // are identical is high.
1203 if (isa<SyntheticSection>(Cur))
1204 // Exidx sentinel section has implicit EXIDX_CANTUNWIND;
1205 return PrevEntry.Unwind == 0x1;
1207 ArrayRef<const ExidxEntry> Entries(
1208 reinterpret_cast<const ExidxEntry *>(Cur->Data.data()),
1209 Cur->getSize() / sizeof(ExidxEntry));
1210 for (const ExidxEntry &Entry : Entries)
1211 if (IsExtabRef(Entry.Unwind) || Entry.Unwind != PrevEntry.Unwind)
1213 // All table entries in this .ARM.exidx Section can be merged into the
1214 // previous Section.
1218 template <class ELFT> void Writer<ELFT>::resolveShfLinkOrder() {
1219 for (OutputSection *Sec : OutputSections) {
1220 if (!(Sec->Flags & SHF_LINK_ORDER))
1223 // Link order may be distributed across several InputSectionDescriptions
1224 // but sort must consider them all at once.
1225 std::vector<InputSection **> ScriptSections;
1226 std::vector<InputSection *> Sections;
1227 for (BaseCommand *Base : Sec->SectionCommands) {
1228 if (auto *ISD = dyn_cast<InputSectionDescription>(Base)) {
1229 for (InputSection *&IS : ISD->Sections) {
1230 ScriptSections.push_back(&IS);
1231 Sections.push_back(IS);
1235 std::stable_sort(Sections.begin(), Sections.end(), compareByFilePosition);
1237 if (!Config->Relocatable && Config->EMachine == EM_ARM &&
1238 Sec->Type == SHT_ARM_EXIDX) {
1240 if (!Sections.empty() && isa<ARMExidxSentinelSection>(Sections.back())) {
1241 assert(Sections.size() >= 2 &&
1242 "We should create a sentinel section only if there are "
1243 "alive regular exidx sections.");
1244 // The last executable section is required to fill the sentinel.
1245 // Remember it here so that we don't have to find it again.
1246 auto *Sentinel = cast<ARMExidxSentinelSection>(Sections.back());
1247 Sentinel->Highest = Sections[Sections.size() - 2]->getLinkOrderDep();
1250 if (Config->MergeArmExidx) {
1251 // The EHABI for the Arm Architecture permits consecutive identical
1252 // table entries to be merged. We use a simple implementation that
1253 // removes a .ARM.exidx Input Section if it can be merged into the
1254 // previous one. This does not require any rewriting of InputSection
1255 // contents but misses opportunities for fine grained deduplication
1256 // where only a subset of the InputSection contents can be merged.
1259 // The last one is a sentinel entry which should not be removed.
1260 int N = Sections.size() - 1;
1262 if (isDuplicateArmExidxSec(Sections[Prev], Sections[Cur]))
1263 Sections[Cur] = nullptr;
1271 for (int I = 0, N = Sections.size(); I < N; ++I)
1272 *ScriptSections[I] = Sections[I];
1274 // Remove the Sections we marked as duplicate earlier.
1275 for (BaseCommand *Base : Sec->SectionCommands)
1276 if (auto *ISD = dyn_cast<InputSectionDescription>(Base))
1277 ISD->Sections.erase(
1278 std::remove(ISD->Sections.begin(), ISD->Sections.end(), nullptr),
1279 ISD->Sections.end());
1283 static void applySynthetic(const std::vector<SyntheticSection *> &Sections,
1284 std::function<void(SyntheticSection *)> Fn) {
1285 for (SyntheticSection *SS : Sections)
1286 if (SS && SS->getParent() && !SS->empty())
1290 // In order to allow users to manipulate linker-synthesized sections,
1291 // we had to add synthetic sections to the input section list early,
1292 // even before we make decisions whether they are needed. This allows
1293 // users to write scripts like this: ".mygot : { .got }".
1295 // Doing it has an unintended side effects. If it turns out that we
1296 // don't need a .got (for example) at all because there's no
1297 // relocation that needs a .got, we don't want to emit .got.
1299 // To deal with the above problem, this function is called after
1300 // scanRelocations is called to remove synthetic sections that turn
1302 static void removeUnusedSyntheticSections() {
1303 // All input synthetic sections that can be empty are placed after
1304 // all regular ones. We iterate over them all and exit at first
1306 for (InputSectionBase *S : llvm::reverse(InputSections)) {
1307 SyntheticSection *SS = dyn_cast<SyntheticSection>(S);
1310 OutputSection *OS = SS->getParent();
1311 if (!SS->empty() || !OS)
1314 std::vector<BaseCommand *>::iterator Empty = OS->SectionCommands.end();
1315 for (auto I = OS->SectionCommands.begin(), E = OS->SectionCommands.end();
1317 BaseCommand *B = *I;
1318 if (auto *ISD = dyn_cast<InputSectionDescription>(B)) {
1319 llvm::erase_if(ISD->Sections,
1320 [=](InputSection *IS) { return IS == SS; });
1321 if (ISD->Sections.empty())
1325 if (Empty != OS->SectionCommands.end())
1326 OS->SectionCommands.erase(Empty);
1328 // If there are no other sections in the output section, remove it from the
1330 if (OS->SectionCommands.empty())
1335 // Returns true if a symbol can be replaced at load-time by a symbol
1336 // with the same name defined in other ELF executable or DSO.
1337 static bool computeIsPreemptible(const Symbol &B) {
1338 assert(!B.isLocal());
1339 // Only symbols that appear in dynsym can be preempted.
1340 if (!B.includeInDynsym())
1343 // Only default visibility symbols can be preempted.
1344 if (B.Visibility != STV_DEFAULT)
1347 // At this point copy relocations have not been created yet, so any
1348 // symbol that is not defined locally is preemptible.
1352 // If we have a dynamic list it specifies which local symbols are preemptible.
1353 if (Config->HasDynamicList)
1356 if (!Config->Shared)
1359 // -Bsymbolic means that definitions are not preempted.
1360 if (Config->Bsymbolic || (Config->BsymbolicFunctions && B.isFunc()))
1365 // Create output section objects and add them to OutputSections.
1366 template <class ELFT> void Writer<ELFT>::finalizeSections() {
1367 Out::DebugInfo = findSection(".debug_info");
1368 Out::PreinitArray = findSection(".preinit_array");
1369 Out::InitArray = findSection(".init_array");
1370 Out::FiniArray = findSection(".fini_array");
1372 // The linker needs to define SECNAME_start, SECNAME_end and SECNAME_stop
1373 // symbols for sections, so that the runtime can get the start and end
1374 // addresses of each section by section name. Add such symbols.
1375 if (!Config->Relocatable) {
1376 addStartEndSymbols();
1377 for (BaseCommand *Base : Script->SectionCommands)
1378 if (auto *Sec = dyn_cast<OutputSection>(Base))
1379 addStartStopSymbols(Sec);
1382 // Add _DYNAMIC symbol. Unlike GNU gold, our _DYNAMIC symbol has no type.
1383 // It should be okay as no one seems to care about the type.
1384 // Even the author of gold doesn't remember why gold behaves that way.
1385 // https://sourceware.org/ml/binutils/2002-03/msg00360.html
1387 Symtab->addRegular("_DYNAMIC", STV_HIDDEN, STT_NOTYPE, 0 /*Value*/,
1388 /*Size=*/0, STB_WEAK, InX::Dynamic,
1391 // Define __rel[a]_iplt_{start,end} symbols if needed.
1392 addRelIpltSymbols();
1394 // This responsible for splitting up .eh_frame section into
1395 // pieces. The relocation scan uses those pieces, so this has to be
1397 applySynthetic({InX::EhFrame},
1398 [](SyntheticSection *SS) { SS->finalizeContents(); });
1400 for (Symbol *S : Symtab->getSymbols())
1401 S->IsPreemptible |= computeIsPreemptible(*S);
1403 // Scan relocations. This must be done after every symbol is declared so that
1404 // we can correctly decide if a dynamic relocation is needed.
1405 if (!Config->Relocatable)
1406 forEachRelSec(scanRelocations<ELFT>);
1408 if (InX::Plt && !InX::Plt->empty())
1409 InX::Plt->addSymbols();
1410 if (InX::Iplt && !InX::Iplt->empty())
1411 InX::Iplt->addSymbols();
1413 // Now that we have defined all possible global symbols including linker-
1414 // synthesized ones. Visit all symbols to give the finishing touches.
1415 for (Symbol *Sym : Symtab->getSymbols()) {
1416 if (!includeInSymtab(*Sym))
1419 InX::SymTab->addSymbol(Sym);
1421 if (InX::DynSymTab && Sym->includeInDynsym()) {
1422 InX::DynSymTab->addSymbol(Sym);
1423 if (auto *SS = dyn_cast<SharedSymbol>(Sym))
1424 if (cast<SharedFile<ELFT>>(Sym->File)->IsNeeded)
1425 In<ELFT>::VerNeed->addSymbol(SS);
1429 // Do not proceed if there was an undefined symbol.
1433 removeUnusedSyntheticSections();
1436 Script->removeEmptyCommands();
1438 // Now that we have the final list, create a list of all the
1439 // OutputSections for convenience.
1440 for (BaseCommand *Base : Script->SectionCommands)
1441 if (auto *Sec = dyn_cast<OutputSection>(Base))
1442 OutputSections.push_back(Sec);
1444 // Prefer command line supplied address over other constraints.
1445 for (OutputSection *Sec : OutputSections) {
1446 auto I = Config->SectionStartMap.find(Sec->Name);
1447 if (I != Config->SectionStartMap.end())
1448 Sec->AddrExpr = [=] { return I->second; };
1451 // This is a bit of a hack. A value of 0 means undef, so we set it
1452 // to 1 t make __ehdr_start defined. The section number is not
1453 // particularly relevant.
1454 Out::ElfHeader->SectionIndex = 1;
1457 for (OutputSection *Sec : OutputSections) {
1458 Sec->SectionIndex = I++;
1459 Sec->ShName = InX::ShStrTab->addString(Sec->Name);
1462 // Binary and relocatable output does not have PHDRS.
1463 // The headers have to be created before finalize as that can influence the
1464 // image base and the dynamic section on mips includes the image base.
1465 if (!Config->Relocatable && !Config->OFormatBinary) {
1466 Phdrs = Script->hasPhdrsCommands() ? Script->createPhdrs() : createPhdrs();
1467 addPtArmExid(Phdrs);
1468 Out::ProgramHeaders->Size = sizeof(Elf_Phdr) * Phdrs.size();
1471 // Some symbols are defined in term of program headers. Now that we
1472 // have the headers, we can find out which sections they point to.
1473 setReservedSymbolSections();
1475 // Dynamic section must be the last one in this list and dynamic
1476 // symbol table section (DynSymTab) must be the first one.
1478 {InX::DynSymTab, InX::Bss, InX::BssRelRo, InX::GnuHashTab,
1479 InX::HashTab, InX::SymTab, InX::ShStrTab, InX::StrTab,
1480 In<ELFT>::VerDef, InX::DynStrTab, InX::Got, InX::MipsGot,
1481 InX::IgotPlt, InX::GotPlt, InX::RelaDyn, InX::RelaIplt,
1482 InX::RelaPlt, InX::Plt, InX::Iplt, InX::EhFrameHdr,
1483 In<ELFT>::VerSym, In<ELFT>::VerNeed, InX::Dynamic},
1484 [](SyntheticSection *SS) { SS->finalizeContents(); });
1486 if (!Script->HasSectionsCommand && !Config->Relocatable)
1487 fixSectionAlignments();
1489 // After link order processing .ARM.exidx sections can be deduplicated, which
1490 // needs to be resolved before any other address dependent operation.
1491 resolveShfLinkOrder();
1493 // Some architectures need to generate content that depends on the address
1494 // of InputSections. For example some architectures use small displacements
1495 // for jump instructions that is is the linker's responsibility for creating
1496 // range extension thunks for. As the generation of the content may also
1497 // alter InputSection addresses we must converge to a fixed point.
1498 if (Target->NeedsThunks || Config->AndroidPackDynRelocs) {
1500 AArch64Err843419Patcher A64P;
1503 Script->assignAddresses();
1505 if (Target->NeedsThunks)
1506 Changed |= TC.createThunks(OutputSections);
1507 if (Config->FixCortexA53Errata843419) {
1509 Script->assignAddresses();
1510 Changed |= A64P.createFixes();
1513 InX::MipsGot->updateAllocSize();
1514 Changed |= InX::RelaDyn->updateAllocSize();
1518 // Fill other section headers. The dynamic table is finalized
1519 // at the end because some tags like RELSZ depend on result
1520 // of finalizing other sections.
1521 for (OutputSection *Sec : OutputSections)
1522 Sec->finalize<ELFT>();
1524 // createThunks may have added local symbols to the static symbol table
1525 applySynthetic({InX::SymTab},
1526 [](SyntheticSection *SS) { SS->postThunkContents(); });
1529 // The linker is expected to define SECNAME_start and SECNAME_end
1530 // symbols for a few sections. This function defines them.
1531 template <class ELFT> void Writer<ELFT>::addStartEndSymbols() {
1532 auto Define = [&](StringRef Start, StringRef End, OutputSection *OS) {
1533 // These symbols resolve to the image base if the section does not exist.
1534 // A special value -1 indicates end of the section.
1536 addOptionalRegular(Start, OS, 0);
1537 addOptionalRegular(End, OS, -1);
1540 OS = Out::ElfHeader;
1541 addOptionalRegular(Start, OS, 0);
1542 addOptionalRegular(End, OS, 0);
1546 Define("__preinit_array_start", "__preinit_array_end", Out::PreinitArray);
1547 Define("__init_array_start", "__init_array_end", Out::InitArray);
1548 Define("__fini_array_start", "__fini_array_end", Out::FiniArray);
1550 if (OutputSection *Sec = findSection(".ARM.exidx"))
1551 Define("__exidx_start", "__exidx_end", Sec);
1554 // If a section name is valid as a C identifier (which is rare because of
1555 // the leading '.'), linkers are expected to define __start_<secname> and
1556 // __stop_<secname> symbols. They are at beginning and end of the section,
1557 // respectively. This is not requested by the ELF standard, but GNU ld and
1558 // gold provide the feature, and used by many programs.
1559 template <class ELFT>
1560 void Writer<ELFT>::addStartStopSymbols(OutputSection *Sec) {
1561 StringRef S = Sec->Name;
1562 if (!isValidCIdentifier(S))
1564 addOptionalRegular(Saver.save("__start_" + S), Sec, 0, STV_DEFAULT);
1565 addOptionalRegular(Saver.save("__stop_" + S), Sec, -1, STV_DEFAULT);
1568 static bool needsPtLoad(OutputSection *Sec) {
1569 if (!(Sec->Flags & SHF_ALLOC))
1572 // Don't allocate VA space for TLS NOBITS sections. The PT_TLS PHDR is
1573 // responsible for allocating space for them, not the PT_LOAD that
1574 // contains the TLS initialization image.
1575 if (Sec->Flags & SHF_TLS && Sec->Type == SHT_NOBITS)
1580 // Linker scripts are responsible for aligning addresses. Unfortunately, most
1581 // linker scripts are designed for creating two PT_LOADs only, one RX and one
1582 // RW. This means that there is no alignment in the RO to RX transition and we
1583 // cannot create a PT_LOAD there.
1584 static uint64_t computeFlags(uint64_t Flags) {
1586 return PF_R | PF_W | PF_X;
1587 if (Config->SingleRoRx && !(Flags & PF_W))
1588 return Flags | PF_X;
1592 // Decide which program headers to create and which sections to include in each
1594 template <class ELFT> std::vector<PhdrEntry *> Writer<ELFT>::createPhdrs() {
1595 std::vector<PhdrEntry *> Ret;
1596 auto AddHdr = [&](unsigned Type, unsigned Flags) -> PhdrEntry * {
1597 Ret.push_back(make<PhdrEntry>(Type, Flags));
1601 // The first phdr entry is PT_PHDR which describes the program header itself.
1602 AddHdr(PT_PHDR, PF_R)->add(Out::ProgramHeaders);
1604 // PT_INTERP must be the second entry if exists.
1605 if (OutputSection *Cmd = findSection(".interp"))
1606 AddHdr(PT_INTERP, Cmd->getPhdrFlags())->add(Cmd);
1608 // Add the first PT_LOAD segment for regular output sections.
1609 uint64_t Flags = computeFlags(PF_R);
1610 PhdrEntry *Load = AddHdr(PT_LOAD, Flags);
1612 // Add the headers. We will remove them if they don't fit.
1613 Load->add(Out::ElfHeader);
1614 Load->add(Out::ProgramHeaders);
1616 for (OutputSection *Sec : OutputSections) {
1617 if (!(Sec->Flags & SHF_ALLOC))
1619 if (!needsPtLoad(Sec))
1622 // Segments are contiguous memory regions that has the same attributes
1623 // (e.g. executable or writable). There is one phdr for each segment.
1624 // Therefore, we need to create a new phdr when the next section has
1625 // different flags or is loaded at a discontiguous address using AT linker
1627 uint64_t NewFlags = computeFlags(Sec->getPhdrFlags());
1628 if (Sec->LMAExpr || Flags != NewFlags) {
1629 Load = AddHdr(PT_LOAD, NewFlags);
1636 // Add a TLS segment if any.
1637 PhdrEntry *TlsHdr = make<PhdrEntry>(PT_TLS, PF_R);
1638 for (OutputSection *Sec : OutputSections)
1639 if (Sec->Flags & SHF_TLS)
1641 if (TlsHdr->FirstSec)
1642 Ret.push_back(TlsHdr);
1644 // Add an entry for .dynamic.
1646 AddHdr(PT_DYNAMIC, InX::Dynamic->getParent()->getPhdrFlags())
1647 ->add(InX::Dynamic->getParent());
1649 // PT_GNU_RELRO includes all sections that should be marked as
1650 // read-only by dynamic linker after proccessing relocations.
1651 // Current dynamic loaders only support one PT_GNU_RELRO PHDR, give
1652 // an error message if more than one PT_GNU_RELRO PHDR is required.
1653 PhdrEntry *RelRo = make<PhdrEntry>(PT_GNU_RELRO, PF_R);
1654 bool InRelroPhdr = false;
1655 bool IsRelroFinished = false;
1656 for (OutputSection *Sec : OutputSections) {
1657 if (!needsPtLoad(Sec))
1659 if (isRelroSection(Sec)) {
1661 if (!IsRelroFinished)
1664 error("section: " + Sec->Name + " is not contiguous with other relro" +
1666 } else if (InRelroPhdr) {
1667 InRelroPhdr = false;
1668 IsRelroFinished = true;
1671 if (RelRo->FirstSec)
1672 Ret.push_back(RelRo);
1674 // PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
1675 if (!InX::EhFrame->empty() && InX::EhFrameHdr && InX::EhFrame->getParent() &&
1676 InX::EhFrameHdr->getParent())
1677 AddHdr(PT_GNU_EH_FRAME, InX::EhFrameHdr->getParent()->getPhdrFlags())
1678 ->add(InX::EhFrameHdr->getParent());
1680 // PT_OPENBSD_RANDOMIZE is an OpenBSD-specific feature. That makes
1681 // the dynamic linker fill the segment with random data.
1682 if (OutputSection *Cmd = findSection(".openbsd.randomdata"))
1683 AddHdr(PT_OPENBSD_RANDOMIZE, Cmd->getPhdrFlags())->add(Cmd);
1685 // PT_GNU_STACK is a special section to tell the loader to make the
1686 // pages for the stack non-executable. If you really want an executable
1687 // stack, you can pass -z execstack, but that's not recommended for
1688 // security reasons.
1690 if (Config->ZExecstack)
1691 Perm = PF_R | PF_W | PF_X;
1694 AddHdr(PT_GNU_STACK, Perm)->p_memsz = Config->ZStackSize;
1696 // PT_OPENBSD_WXNEEDED is a OpenBSD-specific header to mark the executable
1697 // is expected to perform W^X violations, such as calling mprotect(2) or
1698 // mmap(2) with PROT_WRITE | PROT_EXEC, which is prohibited by default on
1700 if (Config->ZWxneeded)
1701 AddHdr(PT_OPENBSD_WXNEEDED, PF_X);
1703 // Create one PT_NOTE per a group of contiguous .note sections.
1704 PhdrEntry *Note = nullptr;
1705 for (OutputSection *Sec : OutputSections) {
1706 if (Sec->Type == SHT_NOTE) {
1707 if (!Note || Sec->LMAExpr)
1708 Note = AddHdr(PT_NOTE, PF_R);
1717 template <class ELFT>
1718 void Writer<ELFT>::addPtArmExid(std::vector<PhdrEntry *> &Phdrs) {
1719 if (Config->EMachine != EM_ARM)
1721 auto I = llvm::find_if(OutputSections, [](OutputSection *Cmd) {
1722 return Cmd->Type == SHT_ARM_EXIDX;
1724 if (I == OutputSections.end())
1727 // PT_ARM_EXIDX is the ARM EHABI equivalent of PT_GNU_EH_FRAME
1728 PhdrEntry *ARMExidx = make<PhdrEntry>(PT_ARM_EXIDX, PF_R);
1730 Phdrs.push_back(ARMExidx);
1733 // The first section of each PT_LOAD, the first section in PT_GNU_RELRO and the
1734 // first section after PT_GNU_RELRO have to be page aligned so that the dynamic
1735 // linker can set the permissions.
1736 template <class ELFT> void Writer<ELFT>::fixSectionAlignments() {
1737 auto PageAlign = [](OutputSection *Cmd) {
1738 if (Cmd && !Cmd->AddrExpr)
1739 Cmd->AddrExpr = [=] {
1740 return alignTo(Script->getDot(), Config->MaxPageSize);
1744 for (const PhdrEntry *P : Phdrs)
1745 if (P->p_type == PT_LOAD && P->FirstSec)
1746 PageAlign(P->FirstSec);
1748 for (const PhdrEntry *P : Phdrs) {
1749 if (P->p_type != PT_GNU_RELRO)
1752 PageAlign(P->FirstSec);
1753 // Find the first section after PT_GNU_RELRO. If it is in a PT_LOAD we
1754 // have to align it to a page.
1755 auto End = OutputSections.end();
1756 auto I = std::find(OutputSections.begin(), End, P->LastSec);
1757 if (I == End || (I + 1) == End)
1759 OutputSection *Cmd = (*(I + 1));
1760 if (needsPtLoad(Cmd))
1765 // Adjusts the file alignment for a given output section and returns
1766 // its new file offset. The file offset must be the same with its
1767 // virtual address (modulo the page size) so that the loader can load
1768 // executables without any address adjustment.
1769 static uint64_t getFileAlignment(uint64_t Off, OutputSection *Cmd) {
1770 // If the section is not in a PT_LOAD, we just have to align it.
1772 return alignTo(Off, Cmd->Alignment);
1774 OutputSection *First = Cmd->PtLoad->FirstSec;
1775 // The first section in a PT_LOAD has to have congruent offset and address
1776 // module the page size.
1778 return alignTo(Off, std::max<uint64_t>(Cmd->Alignment, Config->MaxPageSize),
1781 // If two sections share the same PT_LOAD the file offset is calculated
1782 // using this formula: Off2 = Off1 + (VA2 - VA1).
1783 return First->Offset + Cmd->Addr - First->Addr;
1786 static uint64_t setOffset(OutputSection *Cmd, uint64_t Off) {
1787 if (Cmd->Type == SHT_NOBITS) {
1792 Off = getFileAlignment(Off, Cmd);
1794 return Off + Cmd->Size;
1797 template <class ELFT> void Writer<ELFT>::assignFileOffsetsBinary() {
1799 for (OutputSection *Sec : OutputSections)
1800 if (Sec->Flags & SHF_ALLOC)
1801 Off = setOffset(Sec, Off);
1802 FileSize = alignTo(Off, Config->Wordsize);
1805 // Assign file offsets to output sections.
1806 template <class ELFT> void Writer<ELFT>::assignFileOffsets() {
1808 Off = setOffset(Out::ElfHeader, Off);
1809 Off = setOffset(Out::ProgramHeaders, Off);
1811 PhdrEntry *LastRX = nullptr;
1812 for (PhdrEntry *P : Phdrs)
1813 if (P->p_type == PT_LOAD && (P->p_flags & PF_X))
1816 for (OutputSection *Sec : OutputSections) {
1817 Off = setOffset(Sec, Off);
1818 if (Script->HasSectionsCommand)
1820 // If this is a last section of the last executable segment and that
1821 // segment is the last loadable segment, align the offset of the
1822 // following section to avoid loading non-segments parts of the file.
1823 if (LastRX && LastRX->LastSec == Sec)
1824 Off = alignTo(Off, Target->PageSize);
1827 SectionHeaderOff = alignTo(Off, Config->Wordsize);
1828 FileSize = SectionHeaderOff + (OutputSections.size() + 1) * sizeof(Elf_Shdr);
1831 // Finalize the program headers. We call this function after we assign
1832 // file offsets and VAs to all sections.
1833 template <class ELFT> void Writer<ELFT>::setPhdrs() {
1834 for (PhdrEntry *P : Phdrs) {
1835 OutputSection *First = P->FirstSec;
1836 OutputSection *Last = P->LastSec;
1838 P->p_filesz = Last->Offset - First->Offset;
1839 if (Last->Type != SHT_NOBITS)
1840 P->p_filesz += Last->Size;
1841 P->p_memsz = Last->Addr + Last->Size - First->Addr;
1842 P->p_offset = First->Offset;
1843 P->p_vaddr = First->Addr;
1845 P->p_paddr = First->getLMA();
1847 if (P->p_type == PT_LOAD)
1848 P->p_align = std::max<uint64_t>(P->p_align, Config->MaxPageSize);
1849 else if (P->p_type == PT_GNU_RELRO) {
1851 // The glibc dynamic loader rounds the size down, so we need to round up
1852 // to protect the last page. This is a no-op on FreeBSD which always
1854 P->p_memsz = alignTo(P->p_memsz, Target->PageSize);
1857 // The TLS pointer goes after PT_TLS. At least glibc will align it,
1858 // so round up the size to make sure the offsets are correct.
1859 if (P->p_type == PT_TLS) {
1862 P->p_memsz = alignTo(P->p_memsz, P->p_align);
1867 // The entry point address is chosen in the following ways.
1869 // 1. the '-e' entry command-line option;
1870 // 2. the ENTRY(symbol) command in a linker control script;
1871 // 3. the value of the symbol _start, if present;
1872 // 4. the number represented by the entry symbol, if it is a number;
1873 // 5. the address of the first byte of the .text section, if present;
1874 // 6. the address 0.
1875 template <class ELFT> uint64_t Writer<ELFT>::getEntryAddr() {
1877 if (Symbol *B = Symtab->find(Config->Entry))
1882 if (to_integer(Config->Entry, Addr))
1886 if (OutputSection *Sec = findSection(".text")) {
1887 if (Config->WarnMissingEntry)
1888 warn("cannot find entry symbol " + Config->Entry + "; defaulting to 0x" +
1889 utohexstr(Sec->Addr));
1894 if (Config->WarnMissingEntry)
1895 warn("cannot find entry symbol " + Config->Entry +
1896 "; not setting start address");
1900 static uint16_t getELFType() {
1903 if (Config->Relocatable)
1908 template <class ELFT> void Writer<ELFT>::writeHeader() {
1909 uint8_t *Buf = Buffer->getBufferStart();
1910 memcpy(Buf, "\177ELF", 4);
1912 // Write the ELF header.
1913 auto *EHdr = reinterpret_cast<Elf_Ehdr *>(Buf);
1914 EHdr->e_ident[EI_CLASS] = Config->Is64 ? ELFCLASS64 : ELFCLASS32;
1915 EHdr->e_ident[EI_DATA] = Config->IsLE ? ELFDATA2LSB : ELFDATA2MSB;
1916 EHdr->e_ident[EI_VERSION] = EV_CURRENT;
1917 EHdr->e_ident[EI_OSABI] = Config->OSABI;
1918 EHdr->e_type = getELFType();
1919 EHdr->e_machine = Config->EMachine;
1920 EHdr->e_version = EV_CURRENT;
1921 EHdr->e_entry = getEntryAddr();
1922 EHdr->e_shoff = SectionHeaderOff;
1923 EHdr->e_flags = Config->EFlags;
1924 EHdr->e_ehsize = sizeof(Elf_Ehdr);
1925 EHdr->e_phnum = Phdrs.size();
1926 EHdr->e_shentsize = sizeof(Elf_Shdr);
1927 EHdr->e_shnum = OutputSections.size() + 1;
1928 EHdr->e_shstrndx = InX::ShStrTab->getParent()->SectionIndex;
1930 if (!Config->Relocatable) {
1931 EHdr->e_phoff = sizeof(Elf_Ehdr);
1932 EHdr->e_phentsize = sizeof(Elf_Phdr);
1935 // Write the program header table.
1936 auto *HBuf = reinterpret_cast<Elf_Phdr *>(Buf + EHdr->e_phoff);
1937 for (PhdrEntry *P : Phdrs) {
1938 HBuf->p_type = P->p_type;
1939 HBuf->p_flags = P->p_flags;
1940 HBuf->p_offset = P->p_offset;
1941 HBuf->p_vaddr = P->p_vaddr;
1942 HBuf->p_paddr = P->p_paddr;
1943 HBuf->p_filesz = P->p_filesz;
1944 HBuf->p_memsz = P->p_memsz;
1945 HBuf->p_align = P->p_align;
1949 // Write the section header table. Note that the first table entry is null.
1950 auto *SHdrs = reinterpret_cast<Elf_Shdr *>(Buf + EHdr->e_shoff);
1951 for (OutputSection *Sec : OutputSections)
1952 Sec->writeHeaderTo<ELFT>(++SHdrs);
1955 // Open a result file.
1956 template <class ELFT> void Writer<ELFT>::openFile() {
1957 if (!Config->Is64 && FileSize > UINT32_MAX) {
1958 error("output file too large: " + Twine(FileSize) + " bytes");
1962 unlinkAsync(Config->OutputFile);
1964 if (!Config->Relocatable)
1965 Flags = FileOutputBuffer::F_executable;
1966 Expected<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
1967 FileOutputBuffer::create(Config->OutputFile, FileSize, Flags);
1970 error("failed to open " + Config->OutputFile + ": " +
1971 llvm::toString(BufferOrErr.takeError()));
1973 Buffer = std::move(*BufferOrErr);
1976 template <class ELFT> void Writer<ELFT>::writeSectionsBinary() {
1977 uint8_t *Buf = Buffer->getBufferStart();
1978 for (OutputSection *Sec : OutputSections)
1979 if (Sec->Flags & SHF_ALLOC)
1980 Sec->writeTo<ELFT>(Buf + Sec->Offset);
1983 static void fillTrap(uint8_t *I, uint8_t *End) {
1984 for (; I + 4 <= End; I += 4)
1985 memcpy(I, &Target->TrapInstr, 4);
1988 // Fill the last page of executable segments with trap instructions
1989 // instead of leaving them as zero. Even though it is not required by any
1990 // standard, it is in general a good thing to do for security reasons.
1992 // We'll leave other pages in segments as-is because the rest will be
1993 // overwritten by output sections.
1994 template <class ELFT> void Writer<ELFT>::writeTrapInstr() {
1995 if (Script->HasSectionsCommand)
1998 // Fill the last page.
1999 uint8_t *Buf = Buffer->getBufferStart();
2000 for (PhdrEntry *P : Phdrs)
2001 if (P->p_type == PT_LOAD && (P->p_flags & PF_X))
2002 fillTrap(Buf + alignDown(P->p_offset + P->p_filesz, Target->PageSize),
2003 Buf + alignTo(P->p_offset + P->p_filesz, Target->PageSize));
2005 // Round up the file size of the last segment to the page boundary iff it is
2006 // an executable segment to ensure that other tools don't accidentally
2007 // trim the instruction padding (e.g. when stripping the file).
2008 PhdrEntry *Last = nullptr;
2009 for (PhdrEntry *P : Phdrs)
2010 if (P->p_type == PT_LOAD)
2013 if (Last && (Last->p_flags & PF_X))
2014 Last->p_memsz = Last->p_filesz = alignTo(Last->p_filesz, Target->PageSize);
2017 // Write section contents to a mmap'ed file.
2018 template <class ELFT> void Writer<ELFT>::writeSections() {
2019 uint8_t *Buf = Buffer->getBufferStart();
2021 // PPC64 needs to process relocations in the .opd section
2022 // before processing relocations in code-containing sections.
2023 if (auto *OpdCmd = findSection(".opd")) {
2025 Out::OpdBuf = Buf + Out::Opd->Offset;
2026 OpdCmd->template writeTo<ELFT>(Buf + Out::Opd->Offset);
2029 OutputSection *EhFrameHdr = nullptr;
2030 if (InX::EhFrameHdr && !InX::EhFrameHdr->empty())
2031 EhFrameHdr = InX::EhFrameHdr->getParent();
2033 // In -r or -emit-relocs mode, write the relocation sections first as in
2034 // ELf_Rel targets we might find out that we need to modify the relocated
2035 // section while doing it.
2036 for (OutputSection *Sec : OutputSections)
2037 if (Sec->Type == SHT_REL || Sec->Type == SHT_RELA)
2038 Sec->writeTo<ELFT>(Buf + Sec->Offset);
2040 for (OutputSection *Sec : OutputSections)
2041 if (Sec != Out::Opd && Sec != EhFrameHdr && Sec->Type != SHT_REL &&
2042 Sec->Type != SHT_RELA)
2043 Sec->writeTo<ELFT>(Buf + Sec->Offset);
2045 // The .eh_frame_hdr depends on .eh_frame section contents, therefore
2046 // it should be written after .eh_frame is written.
2048 EhFrameHdr->writeTo<ELFT>(Buf + EhFrameHdr->Offset);
2051 template <class ELFT> void Writer<ELFT>::writeBuildId() {
2052 if (!InX::BuildId || !InX::BuildId->getParent())
2055 // Compute a hash of all sections of the output file.
2056 uint8_t *Start = Buffer->getBufferStart();
2057 uint8_t *End = Start + FileSize;
2058 InX::BuildId->writeBuildId({Start, End});
2061 template void elf::writeResult<ELF32LE>();
2062 template void elf::writeResult<ELF32BE>();
2063 template void elf::writeResult<ELF64LE>();
2064 template void elf::writeResult<ELF64BE>();