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 Script->assignAddresses();
432 // If -compressed-debug-sections is specified, we need to compress
433 // .debug_* sections. Do it right now because it changes the size of
435 for (OutputSection *Sec : OutputSections)
436 Sec->maybeCompress<ELFT>();
438 Script->allocateHeaders(Phdrs);
440 // Remove empty PT_LOAD to avoid causing the dynamic linker to try to mmap a
441 // 0 sized region. This has to be done late since only after assignAddresses
442 // we know the size of the sections.
445 if (!Config->OFormatBinary)
448 assignFileOffsetsBinary();
452 if (Config->Relocatable) {
453 for (OutputSection *Sec : OutputSections)
457 // It does not make sense try to open the file if we have error already.
460 // Write the result down to a file.
465 if (!Config->OFormatBinary) {
470 writeSectionsBinary();
473 // Backfill .note.gnu.build-id section content. This is done at last
474 // because the content is usually a hash value of the entire output file.
479 // Handle -Map option.
484 if (auto E = Buffer->commit())
485 error("failed to write to the output file: " + toString(std::move(E)));
488 static bool shouldKeepInSymtab(SectionBase *Sec, StringRef SymName,
493 // If sym references a section in a discarded group, don't keep it.
494 if (Sec == &InputSection::Discarded)
497 if (Config->Discard == DiscardPolicy::None)
500 // In ELF assembly .L symbols are normally discarded by the assembler.
501 // If the assembler fails to do so, the linker discards them if
502 // * --discard-locals is used.
503 // * The symbol is in a SHF_MERGE section, which is normally the reason for
504 // the assembler keeping the .L symbol.
505 if (!SymName.startswith(".L") && !SymName.empty())
508 if (Config->Discard == DiscardPolicy::Locals)
511 return !Sec || !(Sec->Flags & SHF_MERGE);
514 static bool includeInSymtab(const Symbol &B) {
515 if (!B.isLocal() && !B.IsUsedInRegularObj)
518 if (auto *D = dyn_cast<Defined>(&B)) {
519 // Always include absolute symbols.
520 SectionBase *Sec = D->Section;
524 // Exclude symbols pointing to garbage-collected sections.
525 if (isa<InputSectionBase>(Sec) && !Sec->Live)
527 if (auto *S = dyn_cast<MergeInputSection>(Sec))
528 if (!S->getSectionPiece(D->Value)->Live)
535 // Local symbols are not in the linker's symbol table. This function scans
536 // each object file's symbol table to copy local symbols to the output.
537 template <class ELFT> void Writer<ELFT>::copyLocalSymbols() {
540 for (InputFile *File : ObjectFiles) {
541 ObjFile<ELFT> *F = cast<ObjFile<ELFT>>(File);
542 for (Symbol *B : F->getLocalSymbols()) {
545 ": broken object: getLocalSymbols returns a non-local symbol");
546 auto *DR = dyn_cast<Defined>(B);
548 // No reason to keep local undefined symbol in symtab.
551 if (!includeInSymtab(*B))
554 SectionBase *Sec = DR->Section;
555 if (!shouldKeepInSymtab(Sec, B->getName(), *B))
557 InX::SymTab->addSymbol(B);
562 template <class ELFT> void Writer<ELFT>::addSectionSymbols() {
563 // Create a section symbol for each output section so that we can represent
564 // relocations that point to the section. If we know that no relocation is
565 // referring to a section (that happens if the section is a synthetic one), we
566 // don't create a section symbol for that section.
567 for (BaseCommand *Base : Script->SectionCommands) {
568 auto *Sec = dyn_cast<OutputSection>(Base);
571 auto I = llvm::find_if(Sec->SectionCommands, [](BaseCommand *Base) {
572 if (auto *ISD = dyn_cast<InputSectionDescription>(Base))
573 return !ISD->Sections.empty();
576 if (I == Sec->SectionCommands.end())
578 InputSection *IS = cast<InputSectionDescription>(*I)->Sections[0];
580 // Relocations are not using REL[A] section symbols.
581 if (IS->Type == SHT_REL || IS->Type == SHT_RELA)
584 // Unlike other synthetic sections, mergeable output sections contain data
585 // copied from input sections, and there may be a relocation pointing to its
586 // contents if -r or -emit-reloc are given.
587 if (isa<SyntheticSection>(IS) && !(IS->Flags & SHF_MERGE))
591 make<Defined>(IS->File, "", STB_LOCAL, /*StOther=*/0, STT_SECTION,
592 /*Value=*/0, /*Size=*/0, IS);
593 InX::SymTab->addSymbol(Sym);
597 // Today's loaders have a feature to make segments read-only after
598 // processing dynamic relocations to enhance security. PT_GNU_RELRO
599 // is defined for that.
601 // This function returns true if a section needs to be put into a
602 // PT_GNU_RELRO segment.
603 static bool isRelroSection(const OutputSection *Sec) {
607 uint64_t Flags = Sec->Flags;
609 // Non-allocatable or non-writable sections don't need RELRO because
610 // they are not writable or not even mapped to memory in the first place.
611 // RELRO is for sections that are essentially read-only but need to
612 // be writable only at process startup to allow dynamic linker to
613 // apply relocations.
614 if (!(Flags & SHF_ALLOC) || !(Flags & SHF_WRITE))
617 // Once initialized, TLS data segments are used as data templates
618 // for a thread-local storage. For each new thread, runtime
619 // allocates memory for a TLS and copy templates there. No thread
620 // are supposed to use templates directly. Thus, it can be in RELRO.
624 // .init_array, .preinit_array and .fini_array contain pointers to
625 // functions that are executed on process startup or exit. These
626 // pointers are set by the static linker, and they are not expected
627 // to change at runtime. But if you are an attacker, you could do
628 // interesting things by manipulating pointers in .fini_array, for
629 // example. So they are put into RELRO.
630 uint32_t Type = Sec->Type;
631 if (Type == SHT_INIT_ARRAY || Type == SHT_FINI_ARRAY ||
632 Type == SHT_PREINIT_ARRAY)
635 // .got contains pointers to external symbols. They are resolved by
636 // the dynamic linker when a module is loaded into memory, and after
637 // that they are not expected to change. So, it can be in RELRO.
638 if (InX::Got && Sec == InX::Got->getParent())
641 // .got.plt contains pointers to external function symbols. They are
642 // by default resolved lazily, so we usually cannot put it into RELRO.
643 // However, if "-z now" is given, the lazy symbol resolution is
644 // disabled, which enables us to put it into RELRO.
645 if (Sec == InX::GotPlt->getParent())
648 // .dynamic section contains data for the dynamic linker, and
649 // there's no need to write to it at runtime, so it's better to put
651 if (Sec == InX::Dynamic->getParent())
654 // Sections with some special names are put into RELRO. This is a
655 // bit unfortunate because section names shouldn't be significant in
656 // ELF in spirit. But in reality many linker features depend on
657 // magic section names.
658 StringRef S = Sec->Name;
659 return S == ".data.rel.ro" || S == ".bss.rel.ro" || S == ".ctors" ||
660 S == ".dtors" || S == ".jcr" || S == ".eh_frame" ||
661 S == ".openbsd.randomdata";
664 // We compute a rank for each section. The rank indicates where the
665 // section should be placed in the file. Instead of using simple
666 // numbers (0,1,2...), we use a series of flags. One for each decision
667 // point when placing the section.
668 // Using flags has two key properties:
669 // * It is easy to check if a give branch was taken.
670 // * It is easy two see how similar two ranks are (see getRankProximity).
672 RF_NOT_ADDR_SET = 1 << 16,
673 RF_NOT_INTERP = 1 << 15,
674 RF_NOT_ALLOC = 1 << 14,
676 RF_EXEC_WRITE = 1 << 12,
678 RF_NON_TLS_BSS = 1 << 10,
679 RF_NON_TLS_BSS_RO = 1 << 9,
682 RF_PPC_NOT_TOCBSS = 1 << 6,
684 RF_PPC_TOCL = 1 << 4,
686 RF_PPC_BRANCH_LT = 1 << 2,
687 RF_MIPS_GPREL = 1 << 1,
688 RF_MIPS_NOT_GOT = 1 << 0
691 static unsigned getSectionRank(const OutputSection *Sec) {
694 // We want to put section specified by -T option first, so we
695 // can start assigning VA starting from them later.
696 if (Config->SectionStartMap.count(Sec->Name))
698 Rank |= RF_NOT_ADDR_SET;
700 // Put .interp first because some loaders want to see that section
701 // on the first page of the executable file when loaded into memory.
702 if (Sec->Name == ".interp")
704 Rank |= RF_NOT_INTERP;
706 // Allocatable sections go first to reduce the total PT_LOAD size and
707 // so debug info doesn't change addresses in actual code.
708 if (!(Sec->Flags & SHF_ALLOC))
709 return Rank | RF_NOT_ALLOC;
711 // Sort sections based on their access permission in the following
712 // order: R, RX, RWX, RW. This order is based on the following
714 // * Read-only sections come first such that they go in the
715 // PT_LOAD covering the program headers at the start of the file.
716 // * Read-only, executable sections come next, unless the
717 // -no-rosegment option is used.
718 // * Writable, executable sections follow such that .plt on
719 // architectures where it needs to be writable will be placed
720 // between .text and .data.
721 // * Writable sections come last, such that .bss lands at the very
722 // end of the last PT_LOAD.
723 bool IsExec = Sec->Flags & SHF_EXECINSTR;
724 bool IsWrite = Sec->Flags & SHF_WRITE;
728 Rank |= RF_EXEC_WRITE;
729 else if (!Config->SingleRoRx)
736 // If we got here we know that both A and B are in the same PT_LOAD.
738 bool IsTls = Sec->Flags & SHF_TLS;
739 bool IsNoBits = Sec->Type == SHT_NOBITS;
741 // The first requirement we have is to put (non-TLS) nobits sections last. The
742 // reason is that the only thing the dynamic linker will see about them is a
743 // p_memsz that is larger than p_filesz. Seeing that it zeros the end of the
744 // PT_LOAD, so that has to correspond to the nobits sections.
745 bool IsNonTlsNoBits = IsNoBits && !IsTls;
747 Rank |= RF_NON_TLS_BSS;
749 // We place nobits RelRo sections before plain r/w ones, and non-nobits RelRo
750 // sections after r/w ones, so that the RelRo sections are contiguous.
751 bool IsRelRo = isRelroSection(Sec);
752 if (IsNonTlsNoBits && !IsRelRo)
753 Rank |= RF_NON_TLS_BSS_RO;
754 if (!IsNonTlsNoBits && IsRelRo)
755 Rank |= RF_NON_TLS_BSS_RO;
757 // The TLS initialization block needs to be a single contiguous block in a R/W
758 // PT_LOAD, so stick TLS sections directly before the other RelRo R/W
759 // sections. The TLS NOBITS sections are placed here as they don't take up
760 // virtual address space in the PT_LOAD.
764 // Within the TLS initialization block, the non-nobits sections need to appear
769 // Some architectures have additional ordering restrictions for sections
770 // within the same PT_LOAD.
771 if (Config->EMachine == EM_PPC64) {
772 // PPC64 has a number of special SHT_PROGBITS+SHF_ALLOC+SHF_WRITE sections
773 // that we would like to make sure appear is a specific order to maximize
774 // their coverage by a single signed 16-bit offset from the TOC base
775 // pointer. Conversely, the special .tocbss section should be first among
776 // all SHT_NOBITS sections. This will put it next to the loaded special
777 // PPC64 sections (and, thus, within reach of the TOC base pointer).
778 StringRef Name = Sec->Name;
779 if (Name != ".tocbss")
780 Rank |= RF_PPC_NOT_TOCBSS;
791 if (Name == ".branch_lt")
792 Rank |= RF_PPC_BRANCH_LT;
794 if (Config->EMachine == EM_MIPS) {
795 // All sections with SHF_MIPS_GPREL flag should be grouped together
796 // because data in these sections is addressable with a gp relative address.
797 if (Sec->Flags & SHF_MIPS_GPREL)
798 Rank |= RF_MIPS_GPREL;
800 if (Sec->Name != ".got")
801 Rank |= RF_MIPS_NOT_GOT;
807 static bool compareSections(const BaseCommand *ACmd, const BaseCommand *BCmd) {
808 const OutputSection *A = cast<OutputSection>(ACmd);
809 const OutputSection *B = cast<OutputSection>(BCmd);
810 if (A->SortRank != B->SortRank)
811 return A->SortRank < B->SortRank;
812 if (!(A->SortRank & RF_NOT_ADDR_SET))
813 return Config->SectionStartMap.lookup(A->Name) <
814 Config->SectionStartMap.lookup(B->Name);
818 void PhdrEntry::add(OutputSection *Sec) {
822 p_align = std::max(p_align, Sec->Alignment);
823 if (p_type == PT_LOAD)
826 ASectionHasLMA = true;
829 // The beginning and the ending of .rel[a].plt section are marked
830 // with __rel[a]_iplt_{start,end} symbols if it is a statically linked
831 // executable. The runtime needs these symbols in order to resolve
832 // all IRELATIVE relocs on startup. For dynamic executables, we don't
833 // need these symbols, since IRELATIVE relocs are resolved through GOT
834 // and PLT. For details, see http://www.airs.com/blog/archives/403.
835 template <class ELFT> void Writer<ELFT>::addRelIpltSymbols() {
838 StringRef S = Config->IsRela ? "__rela_iplt_start" : "__rel_iplt_start";
839 addOptionalRegular(S, InX::RelaIplt, 0, STV_HIDDEN, STB_WEAK);
841 S = Config->IsRela ? "__rela_iplt_end" : "__rel_iplt_end";
842 addOptionalRegular(S, InX::RelaIplt, -1, STV_HIDDEN, STB_WEAK);
845 template <class ELFT>
846 void Writer<ELFT>::forEachRelSec(std::function<void(InputSectionBase &)> Fn) {
847 // Scan all relocations. Each relocation goes through a series
848 // of tests to determine if it needs special treatment, such as
849 // creating GOT, PLT, copy relocations, etc.
850 // Note that relocations for non-alloc sections are directly
851 // processed by InputSection::relocateNonAlloc.
852 for (InputSectionBase *IS : InputSections)
853 if (IS->Live && isa<InputSection>(IS) && (IS->Flags & SHF_ALLOC))
855 for (EhInputSection *ES : InX::EhFrame->Sections)
859 // This function generates assignments for predefined symbols (e.g. _end or
860 // _etext) and inserts them into the commands sequence to be processed at the
861 // appropriate time. This ensures that the value is going to be correct by the
862 // time any references to these symbols are processed and is equivalent to
863 // defining these symbols explicitly in the linker script.
864 template <class ELFT> void Writer<ELFT>::setReservedSymbolSections() {
865 if (ElfSym::GlobalOffsetTable) {
866 // The _GLOBAL_OFFSET_TABLE_ symbol is defined by target convention to
867 // be at some offset from the base of the .got section, usually 0 or the end
869 InputSection *GotSection = InX::MipsGot ? cast<InputSection>(InX::MipsGot)
870 : cast<InputSection>(InX::Got);
871 ElfSym::GlobalOffsetTable->Section = GotSection;
874 PhdrEntry *Last = nullptr;
875 PhdrEntry *LastRO = nullptr;
877 for (PhdrEntry *P : Phdrs) {
878 if (P->p_type != PT_LOAD)
881 if (!(P->p_flags & PF_W))
886 // _etext is the first location after the last read-only loadable segment.
888 ElfSym::Etext1->Section = LastRO->LastSec;
890 ElfSym::Etext2->Section = LastRO->LastSec;
894 // _edata points to the end of the last mapped initialized section.
895 OutputSection *Edata = nullptr;
896 for (OutputSection *OS : OutputSections) {
897 if (OS->Type != SHT_NOBITS)
899 if (OS == Last->LastSec)
904 ElfSym::Edata1->Section = Edata;
906 ElfSym::Edata2->Section = Edata;
908 // _end is the first location after the uninitialized data region.
910 ElfSym::End1->Section = Last->LastSec;
912 ElfSym::End2->Section = Last->LastSec;
916 ElfSym::Bss->Section = findSection(".bss");
918 // Setup MIPS _gp_disp/__gnu_local_gp symbols which should
919 // be equal to the _gp symbol's value.
920 if (ElfSym::MipsGp) {
921 // Find GP-relative section with the lowest address
922 // and use this address to calculate default _gp value.
923 for (OutputSection *OS : OutputSections) {
924 if (OS->Flags & SHF_MIPS_GPREL) {
925 ElfSym::MipsGp->Section = OS;
926 ElfSym::MipsGp->Value = 0x7ff0;
933 // We want to find how similar two ranks are.
934 // The more branches in getSectionRank that match, the more similar they are.
935 // Since each branch corresponds to a bit flag, we can just use
936 // countLeadingZeros.
937 static int getRankProximityAux(OutputSection *A, OutputSection *B) {
938 return countLeadingZeros(A->SortRank ^ B->SortRank);
941 static int getRankProximity(OutputSection *A, BaseCommand *B) {
942 if (auto *Sec = dyn_cast<OutputSection>(B))
944 return getRankProximityAux(A, Sec);
948 // When placing orphan sections, we want to place them after symbol assignments
949 // so that an orphan after
953 // doesn't break the intended meaning of the begin/end symbols.
954 // We don't want to go over sections since findOrphanPos is the
955 // one in charge of deciding the order of the sections.
956 // We don't want to go over changes to '.', since doing so in
957 // rx_sec : { *(rx_sec) }
958 // . = ALIGN(0x1000);
959 // /* The RW PT_LOAD starts here*/
960 // rw_sec : { *(rw_sec) }
961 // would mean that the RW PT_LOAD would become unaligned.
962 static bool shouldSkip(BaseCommand *Cmd) {
963 if (isa<OutputSection>(Cmd))
965 if (auto *Assign = dyn_cast<SymbolAssignment>(Cmd))
966 return Assign->Name != ".";
970 // We want to place orphan sections so that they share as much
971 // characteristics with their neighbors as possible. For example, if
972 // both are rw, or both are tls.
973 template <typename ELFT>
974 static std::vector<BaseCommand *>::iterator
975 findOrphanPos(std::vector<BaseCommand *>::iterator B,
976 std::vector<BaseCommand *>::iterator E) {
977 OutputSection *Sec = cast<OutputSection>(*E);
979 // Find the first element that has as close a rank as possible.
980 auto I = std::max_element(B, E, [=](BaseCommand *A, BaseCommand *B) {
981 return getRankProximity(Sec, A) < getRankProximity(Sec, B);
986 // Consider all existing sections with the same proximity.
987 int Proximity = getRankProximity(Sec, *I);
988 for (; I != E; ++I) {
989 auto *CurSec = dyn_cast<OutputSection>(*I);
990 if (!CurSec || !CurSec->Live)
992 if (getRankProximity(Sec, CurSec) != Proximity ||
993 Sec->SortRank < CurSec->SortRank)
997 auto IsLiveSection = [](BaseCommand *Cmd) {
998 auto *OS = dyn_cast<OutputSection>(Cmd);
999 return OS && OS->Live;
1002 auto J = std::find_if(llvm::make_reverse_iterator(I),
1003 llvm::make_reverse_iterator(B), IsLiveSection);
1006 // As a special case, if the orphan section is the last section, put
1007 // it at the very end, past any other commands.
1008 // This matches bfd's behavior and is convenient when the linker script fully
1009 // specifies the start of the file, but doesn't care about the end (the non
1010 // alloc sections for example).
1011 auto NextSec = std::find_if(I, E, IsLiveSection);
1015 while (I != E && shouldSkip(*I))
1020 // If no layout was provided by linker script, we want to apply default
1021 // sorting for special input sections and handle --symbol-ordering-file.
1022 template <class ELFT> void Writer<ELFT>::sortInputSections() {
1023 assert(!Script->HasSectionsCommand);
1025 // Sort input sections by priority using the list provided
1026 // by --symbol-ordering-file.
1027 DenseMap<SectionBase *, int> Order = buildSectionOrder();
1029 for (BaseCommand *Base : Script->SectionCommands)
1030 if (auto *Sec = dyn_cast<OutputSection>(Base))
1032 Sec->sort([&](InputSectionBase *S) { return Order.lookup(S); });
1034 // Sort input sections by section name suffixes for
1035 // __attribute__((init_priority(N))).
1036 if (OutputSection *Sec = findSection(".init_array"))
1037 Sec->sortInitFini();
1038 if (OutputSection *Sec = findSection(".fini_array"))
1039 Sec->sortInitFini();
1041 // Sort input sections by the special rule for .ctors and .dtors.
1042 if (OutputSection *Sec = findSection(".ctors"))
1043 Sec->sortCtorsDtors();
1044 if (OutputSection *Sec = findSection(".dtors"))
1045 Sec->sortCtorsDtors();
1048 template <class ELFT> void Writer<ELFT>::sortSections() {
1049 Script->adjustSectionsBeforeSorting();
1051 // Don't sort if using -r. It is not necessary and we want to preserve the
1052 // relative order for SHF_LINK_ORDER sections.
1053 if (Config->Relocatable)
1056 for (BaseCommand *Base : Script->SectionCommands)
1057 if (auto *Sec = dyn_cast<OutputSection>(Base))
1058 Sec->SortRank = getSectionRank(Sec);
1060 if (!Script->HasSectionsCommand) {
1061 sortInputSections();
1063 // We know that all the OutputSections are contiguous in this case.
1064 auto E = Script->SectionCommands.end();
1065 auto I = Script->SectionCommands.begin();
1066 auto IsSection = [](BaseCommand *Base) { return isa<OutputSection>(Base); };
1067 I = std::find_if(I, E, IsSection);
1068 E = std::find_if(llvm::make_reverse_iterator(E),
1069 llvm::make_reverse_iterator(I), IsSection)
1071 std::stable_sort(I, E, compareSections);
1075 // Orphan sections are sections present in the input files which are
1076 // not explicitly placed into the output file by the linker script.
1078 // The sections in the linker script are already in the correct
1079 // order. We have to figuere out where to insert the orphan
1082 // The order of the sections in the script is arbitrary and may not agree with
1083 // compareSections. This means that we cannot easily define a strict weak
1084 // ordering. To see why, consider a comparison of a section in the script and
1085 // one not in the script. We have a two simple options:
1086 // * Make them equivalent (a is not less than b, and b is not less than a).
1087 // The problem is then that equivalence has to be transitive and we can
1088 // have sections a, b and c with only b in a script and a less than c
1089 // which breaks this property.
1090 // * Use compareSectionsNonScript. Given that the script order doesn't have
1091 // to match, we can end up with sections a, b, c, d where b and c are in the
1092 // script and c is compareSectionsNonScript less than b. In which case d
1093 // can be equivalent to c, a to b and d < a. As a concrete example:
1094 // .a (rx) # not in script
1095 // .b (rx) # in script
1096 // .c (ro) # in script
1097 // .d (ro) # not in script
1099 // The way we define an order then is:
1100 // * Sort only the orphan sections. They are in the end right now.
1101 // * Move each orphan section to its preferred position. We try
1102 // to put each section in the last position where it it can share
1105 // There is some ambiguity as to where exactly a new entry should be
1106 // inserted, because Commands contains not only output section
1107 // commands but also other types of commands such as symbol assignment
1108 // expressions. There's no correct answer here due to the lack of the
1109 // formal specification of the linker script. We use heuristics to
1110 // determine whether a new output command should be added before or
1111 // after another commands. For the details, look at shouldSkip
1114 auto I = Script->SectionCommands.begin();
1115 auto E = Script->SectionCommands.end();
1116 auto NonScriptI = std::find_if(I, E, [](BaseCommand *Base) {
1117 if (auto *Sec = dyn_cast<OutputSection>(Base))
1118 return Sec->Live && Sec->SectionIndex == INT_MAX;
1122 // Sort the orphan sections.
1123 std::stable_sort(NonScriptI, E, compareSections);
1125 // As a horrible special case, skip the first . assignment if it is before any
1126 // section. We do this because it is common to set a load address by starting
1127 // the script with ". = 0xabcd" and the expectation is that every section is
1129 auto FirstSectionOrDotAssignment =
1130 std::find_if(I, E, [](BaseCommand *Cmd) { return !shouldSkip(Cmd); });
1131 if (FirstSectionOrDotAssignment != E &&
1132 isa<SymbolAssignment>(**FirstSectionOrDotAssignment))
1133 ++FirstSectionOrDotAssignment;
1134 I = FirstSectionOrDotAssignment;
1136 while (NonScriptI != E) {
1137 auto Pos = findOrphanPos<ELFT>(I, NonScriptI);
1138 OutputSection *Orphan = cast<OutputSection>(*NonScriptI);
1140 // As an optimization, find all sections with the same sort rank
1141 // and insert them with one rotate.
1142 unsigned Rank = Orphan->SortRank;
1143 auto End = std::find_if(NonScriptI + 1, E, [=](BaseCommand *Cmd) {
1144 return cast<OutputSection>(Cmd)->SortRank != Rank;
1146 std::rotate(Pos, NonScriptI, End);
1150 Script->adjustSectionsAfterSorting();
1153 static bool compareByFilePosition(InputSection *A, InputSection *B) {
1154 // Synthetic, i. e. a sentinel section, should go last.
1155 if (A->kind() == InputSectionBase::Synthetic ||
1156 B->kind() == InputSectionBase::Synthetic)
1157 return A->kind() != InputSectionBase::Synthetic;
1158 InputSection *LA = A->getLinkOrderDep();
1159 InputSection *LB = B->getLinkOrderDep();
1160 OutputSection *AOut = LA->getParent();
1161 OutputSection *BOut = LB->getParent();
1163 return AOut->SectionIndex < BOut->SectionIndex;
1164 return LA->OutSecOff < LB->OutSecOff;
1167 // This function is used by the --merge-exidx-entries to detect duplicate
1168 // .ARM.exidx sections. It is Arm only.
1170 // The .ARM.exidx section is of the form:
1171 // | PREL31 offset to function | Unwind instructions for function |
1172 // where the unwind instructions are either a small number of unwind
1173 // instructions inlined into the table entry, the special CANT_UNWIND value of
1174 // 0x1 or a PREL31 offset into a .ARM.extab Section that contains unwind
1177 // We return true if all the unwind instructions in the .ARM.exidx entries of
1178 // Cur can be merged into the last entry of Prev.
1179 static bool isDuplicateArmExidxSec(InputSection *Prev, InputSection *Cur) {
1181 // References to .ARM.Extab Sections have bit 31 clear and are not the
1182 // special EXIDX_CANTUNWIND bit-pattern.
1183 auto IsExtabRef = [](uint32_t Unwind) {
1184 return (Unwind & 0x80000000) == 0 && Unwind != 0x1;
1192 // Get the last table Entry from the previous .ARM.exidx section.
1193 const ExidxEntry &PrevEntry = *reinterpret_cast<const ExidxEntry *>(
1194 Prev->Data.data() + Prev->getSize() - sizeof(ExidxEntry));
1195 if (IsExtabRef(PrevEntry.Unwind))
1198 // We consider the unwind instructions of an .ARM.exidx table entry
1199 // a duplicate if the previous unwind instructions if:
1200 // - Both are the special EXIDX_CANTUNWIND.
1201 // - Both are the same inline unwind instructions.
1202 // We do not attempt to follow and check links into .ARM.extab tables as
1203 // consecutive identical entries are rare and the effort to check that they
1204 // are identical is high.
1206 if (isa<SyntheticSection>(Cur))
1207 // Exidx sentinel section has implicit EXIDX_CANTUNWIND;
1208 return PrevEntry.Unwind == 0x1;
1210 ArrayRef<const ExidxEntry> Entries(
1211 reinterpret_cast<const ExidxEntry *>(Cur->Data.data()),
1212 Cur->getSize() / sizeof(ExidxEntry));
1213 for (const ExidxEntry &Entry : Entries)
1214 if (IsExtabRef(Entry.Unwind) || Entry.Unwind != PrevEntry.Unwind)
1216 // All table entries in this .ARM.exidx Section can be merged into the
1217 // previous Section.
1221 template <class ELFT> void Writer<ELFT>::resolveShfLinkOrder() {
1222 for (OutputSection *Sec : OutputSections) {
1223 if (!(Sec->Flags & SHF_LINK_ORDER))
1226 // Link order may be distributed across several InputSectionDescriptions
1227 // but sort must consider them all at once.
1228 std::vector<InputSection **> ScriptSections;
1229 std::vector<InputSection *> Sections;
1230 for (BaseCommand *Base : Sec->SectionCommands) {
1231 if (auto *ISD = dyn_cast<InputSectionDescription>(Base)) {
1232 for (InputSection *&IS : ISD->Sections) {
1233 ScriptSections.push_back(&IS);
1234 Sections.push_back(IS);
1238 std::stable_sort(Sections.begin(), Sections.end(), compareByFilePosition);
1240 if (!Config->Relocatable && Config->EMachine == EM_ARM &&
1241 Sec->Type == SHT_ARM_EXIDX) {
1243 if (!Sections.empty() && isa<ARMExidxSentinelSection>(Sections.back())) {
1244 assert(Sections.size() >= 2 &&
1245 "We should create a sentinel section only if there are "
1246 "alive regular exidx sections.");
1247 // The last executable section is required to fill the sentinel.
1248 // Remember it here so that we don't have to find it again.
1249 auto *Sentinel = cast<ARMExidxSentinelSection>(Sections.back());
1250 Sentinel->Highest = Sections[Sections.size() - 2]->getLinkOrderDep();
1253 if (Config->MergeArmExidx) {
1254 // The EHABI for the Arm Architecture permits consecutive identical
1255 // table entries to be merged. We use a simple implementation that
1256 // removes a .ARM.exidx Input Section if it can be merged into the
1257 // previous one. This does not require any rewriting of InputSection
1258 // contents but misses opportunities for fine grained deduplication
1259 // where only a subset of the InputSection contents can be merged.
1262 // The last one is a sentinel entry which should not be removed.
1263 int N = Sections.size() - 1;
1265 if (isDuplicateArmExidxSec(Sections[Prev], Sections[Cur]))
1266 Sections[Cur] = nullptr;
1274 for (int I = 0, N = Sections.size(); I < N; ++I)
1275 *ScriptSections[I] = Sections[I];
1277 // Remove the Sections we marked as duplicate earlier.
1278 for (BaseCommand *Base : Sec->SectionCommands)
1279 if (auto *ISD = dyn_cast<InputSectionDescription>(Base))
1280 ISD->Sections.erase(
1281 std::remove(ISD->Sections.begin(), ISD->Sections.end(), nullptr),
1282 ISD->Sections.end());
1286 static void applySynthetic(const std::vector<SyntheticSection *> &Sections,
1287 std::function<void(SyntheticSection *)> Fn) {
1288 for (SyntheticSection *SS : Sections)
1289 if (SS && SS->getParent() && !SS->empty())
1293 // In order to allow users to manipulate linker-synthesized sections,
1294 // we had to add synthetic sections to the input section list early,
1295 // even before we make decisions whether they are needed. This allows
1296 // users to write scripts like this: ".mygot : { .got }".
1298 // Doing it has an unintended side effects. If it turns out that we
1299 // don't need a .got (for example) at all because there's no
1300 // relocation that needs a .got, we don't want to emit .got.
1302 // To deal with the above problem, this function is called after
1303 // scanRelocations is called to remove synthetic sections that turn
1305 static void removeUnusedSyntheticSections() {
1306 // All input synthetic sections that can be empty are placed after
1307 // all regular ones. We iterate over them all and exit at first
1309 for (InputSectionBase *S : llvm::reverse(InputSections)) {
1310 SyntheticSection *SS = dyn_cast<SyntheticSection>(S);
1313 OutputSection *OS = SS->getParent();
1314 if (!SS->empty() || !OS)
1317 std::vector<BaseCommand *>::iterator Empty = OS->SectionCommands.end();
1318 for (auto I = OS->SectionCommands.begin(), E = OS->SectionCommands.end();
1320 BaseCommand *B = *I;
1321 if (auto *ISD = dyn_cast<InputSectionDescription>(B)) {
1322 llvm::erase_if(ISD->Sections,
1323 [=](InputSection *IS) { return IS == SS; });
1324 if (ISD->Sections.empty())
1328 if (Empty != OS->SectionCommands.end())
1329 OS->SectionCommands.erase(Empty);
1331 // If there are no other sections in the output section, remove it from the
1333 if (OS->SectionCommands.empty())
1338 // Returns true if a symbol can be replaced at load-time by a symbol
1339 // with the same name defined in other ELF executable or DSO.
1340 static bool computeIsPreemptible(const Symbol &B) {
1341 assert(!B.isLocal());
1342 // Only symbols that appear in dynsym can be preempted.
1343 if (!B.includeInDynsym())
1346 // Only default visibility symbols can be preempted.
1347 if (B.Visibility != STV_DEFAULT)
1350 // At this point copy relocations have not been created yet, so any
1351 // symbol that is not defined locally is preemptible.
1355 // If we have a dynamic list it specifies which local symbols are preemptible.
1356 if (Config->HasDynamicList)
1359 if (!Config->Shared)
1362 // -Bsymbolic means that definitions are not preempted.
1363 if (Config->Bsymbolic || (Config->BsymbolicFunctions && B.isFunc()))
1368 // Create output section objects and add them to OutputSections.
1369 template <class ELFT> void Writer<ELFT>::finalizeSections() {
1370 Out::DebugInfo = findSection(".debug_info");
1371 Out::PreinitArray = findSection(".preinit_array");
1372 Out::InitArray = findSection(".init_array");
1373 Out::FiniArray = findSection(".fini_array");
1375 // The linker needs to define SECNAME_start, SECNAME_end and SECNAME_stop
1376 // symbols for sections, so that the runtime can get the start and end
1377 // addresses of each section by section name. Add such symbols.
1378 if (!Config->Relocatable) {
1379 addStartEndSymbols();
1380 for (BaseCommand *Base : Script->SectionCommands)
1381 if (auto *Sec = dyn_cast<OutputSection>(Base))
1382 addStartStopSymbols(Sec);
1385 // Add _DYNAMIC symbol. Unlike GNU gold, our _DYNAMIC symbol has no type.
1386 // It should be okay as no one seems to care about the type.
1387 // Even the author of gold doesn't remember why gold behaves that way.
1388 // https://sourceware.org/ml/binutils/2002-03/msg00360.html
1390 Symtab->addRegular("_DYNAMIC", STV_HIDDEN, STT_NOTYPE, 0 /*Value*/,
1391 /*Size=*/0, STB_WEAK, InX::Dynamic,
1394 // Define __rel[a]_iplt_{start,end} symbols if needed.
1395 addRelIpltSymbols();
1397 // This responsible for splitting up .eh_frame section into
1398 // pieces. The relocation scan uses those pieces, so this has to be
1400 applySynthetic({InX::EhFrame},
1401 [](SyntheticSection *SS) { SS->finalizeContents(); });
1403 for (Symbol *S : Symtab->getSymbols()) {
1404 S->IsPreemptible |= computeIsPreemptible(*S);
1405 if (S->isGnuIFunc() && Config->ZIfuncnoplt)
1406 S->ExportDynamic = true;
1409 // Scan relocations. This must be done after every symbol is declared so that
1410 // we can correctly decide if a dynamic relocation is needed.
1411 if (!Config->Relocatable)
1412 forEachRelSec(scanRelocations<ELFT>);
1414 if (InX::Plt && !InX::Plt->empty())
1415 InX::Plt->addSymbols();
1416 if (InX::Iplt && !InX::Iplt->empty())
1417 InX::Iplt->addSymbols();
1419 // Now that we have defined all possible global symbols including linker-
1420 // synthesized ones. Visit all symbols to give the finishing touches.
1421 for (Symbol *Sym : Symtab->getSymbols()) {
1422 if (!includeInSymtab(*Sym))
1425 InX::SymTab->addSymbol(Sym);
1427 if (InX::DynSymTab && Sym->includeInDynsym()) {
1428 InX::DynSymTab->addSymbol(Sym);
1429 if (auto *SS = dyn_cast<SharedSymbol>(Sym))
1430 if (cast<SharedFile<ELFT>>(Sym->File)->IsNeeded)
1431 In<ELFT>::VerNeed->addSymbol(SS);
1435 // Do not proceed if there was an undefined symbol.
1439 removeUnusedSyntheticSections();
1442 Script->removeEmptyCommands();
1444 // Now that we have the final list, create a list of all the
1445 // OutputSections for convenience.
1446 for (BaseCommand *Base : Script->SectionCommands)
1447 if (auto *Sec = dyn_cast<OutputSection>(Base))
1448 OutputSections.push_back(Sec);
1450 // Prefer command line supplied address over other constraints.
1451 for (OutputSection *Sec : OutputSections) {
1452 auto I = Config->SectionStartMap.find(Sec->Name);
1453 if (I != Config->SectionStartMap.end())
1454 Sec->AddrExpr = [=] { return I->second; };
1457 // This is a bit of a hack. A value of 0 means undef, so we set it
1458 // to 1 t make __ehdr_start defined. The section number is not
1459 // particularly relevant.
1460 Out::ElfHeader->SectionIndex = 1;
1463 for (OutputSection *Sec : OutputSections) {
1464 Sec->SectionIndex = I++;
1465 Sec->ShName = InX::ShStrTab->addString(Sec->Name);
1468 // Binary and relocatable output does not have PHDRS.
1469 // The headers have to be created before finalize as that can influence the
1470 // image base and the dynamic section on mips includes the image base.
1471 if (!Config->Relocatable && !Config->OFormatBinary) {
1472 Phdrs = Script->hasPhdrsCommands() ? Script->createPhdrs() : createPhdrs();
1473 addPtArmExid(Phdrs);
1474 Out::ProgramHeaders->Size = sizeof(Elf_Phdr) * Phdrs.size();
1477 // Some symbols are defined in term of program headers. Now that we
1478 // have the headers, we can find out which sections they point to.
1479 setReservedSymbolSections();
1481 // Dynamic section must be the last one in this list and dynamic
1482 // symbol table section (DynSymTab) must be the first one.
1484 {InX::DynSymTab, InX::Bss, InX::BssRelRo, InX::GnuHashTab,
1485 InX::HashTab, InX::SymTab, InX::ShStrTab, InX::StrTab,
1486 In<ELFT>::VerDef, InX::DynStrTab, InX::Got, InX::MipsGot,
1487 InX::IgotPlt, InX::GotPlt, InX::RelaDyn, InX::RelaIplt,
1488 InX::RelaPlt, InX::Plt, InX::Iplt, InX::EhFrameHdr,
1489 In<ELFT>::VerSym, In<ELFT>::VerNeed, InX::Dynamic},
1490 [](SyntheticSection *SS) { SS->finalizeContents(); });
1492 if (!Script->HasSectionsCommand && !Config->Relocatable)
1493 fixSectionAlignments();
1495 // After link order processing .ARM.exidx sections can be deduplicated, which
1496 // needs to be resolved before any other address dependent operation.
1497 resolveShfLinkOrder();
1499 // Some architectures need to generate content that depends on the address
1500 // of InputSections. For example some architectures use small displacements
1501 // for jump instructions that is is the linker's responsibility for creating
1502 // range extension thunks for. As the generation of the content may also
1503 // alter InputSection addresses we must converge to a fixed point.
1504 if (Target->NeedsThunks || Config->AndroidPackDynRelocs) {
1506 AArch64Err843419Patcher A64P;
1509 Script->assignAddresses();
1511 if (Target->NeedsThunks)
1512 Changed |= TC.createThunks(OutputSections);
1513 if (Config->FixCortexA53Errata843419) {
1515 Script->assignAddresses();
1516 Changed |= A64P.createFixes();
1519 InX::MipsGot->updateAllocSize();
1520 Changed |= InX::RelaDyn->updateAllocSize();
1524 // Fill other section headers. The dynamic table is finalized
1525 // at the end because some tags like RELSZ depend on result
1526 // of finalizing other sections.
1527 for (OutputSection *Sec : OutputSections)
1528 Sec->finalize<ELFT>();
1530 // createThunks may have added local symbols to the static symbol table
1531 applySynthetic({InX::SymTab},
1532 [](SyntheticSection *SS) { SS->postThunkContents(); });
1535 // The linker is expected to define SECNAME_start and SECNAME_end
1536 // symbols for a few sections. This function defines them.
1537 template <class ELFT> void Writer<ELFT>::addStartEndSymbols() {
1538 auto Define = [&](StringRef Start, StringRef End, OutputSection *OS) {
1539 // These symbols resolve to the image base if the section does not exist.
1540 // A special value -1 indicates end of the section.
1542 addOptionalRegular(Start, OS, 0);
1543 addOptionalRegular(End, OS, -1);
1546 OS = Out::ElfHeader;
1547 addOptionalRegular(Start, OS, 0);
1548 addOptionalRegular(End, OS, 0);
1552 Define("__preinit_array_start", "__preinit_array_end", Out::PreinitArray);
1553 Define("__init_array_start", "__init_array_end", Out::InitArray);
1554 Define("__fini_array_start", "__fini_array_end", Out::FiniArray);
1556 if (OutputSection *Sec = findSection(".ARM.exidx"))
1557 Define("__exidx_start", "__exidx_end", Sec);
1560 // If a section name is valid as a C identifier (which is rare because of
1561 // the leading '.'), linkers are expected to define __start_<secname> and
1562 // __stop_<secname> symbols. They are at beginning and end of the section,
1563 // respectively. This is not requested by the ELF standard, but GNU ld and
1564 // gold provide the feature, and used by many programs.
1565 template <class ELFT>
1566 void Writer<ELFT>::addStartStopSymbols(OutputSection *Sec) {
1567 StringRef S = Sec->Name;
1568 if (!isValidCIdentifier(S))
1570 addOptionalRegular(Saver.save("__start_" + S), Sec, 0, STV_DEFAULT);
1571 addOptionalRegular(Saver.save("__stop_" + S), Sec, -1, STV_DEFAULT);
1574 static bool needsPtLoad(OutputSection *Sec) {
1575 if (!(Sec->Flags & SHF_ALLOC))
1578 // Don't allocate VA space for TLS NOBITS sections. The PT_TLS PHDR is
1579 // responsible for allocating space for them, not the PT_LOAD that
1580 // contains the TLS initialization image.
1581 if (Sec->Flags & SHF_TLS && Sec->Type == SHT_NOBITS)
1586 // Linker scripts are responsible for aligning addresses. Unfortunately, most
1587 // linker scripts are designed for creating two PT_LOADs only, one RX and one
1588 // RW. This means that there is no alignment in the RO to RX transition and we
1589 // cannot create a PT_LOAD there.
1590 static uint64_t computeFlags(uint64_t Flags) {
1592 return PF_R | PF_W | PF_X;
1593 if (Config->SingleRoRx && !(Flags & PF_W))
1594 return Flags | PF_X;
1598 // Decide which program headers to create and which sections to include in each
1600 template <class ELFT> std::vector<PhdrEntry *> Writer<ELFT>::createPhdrs() {
1601 std::vector<PhdrEntry *> Ret;
1602 auto AddHdr = [&](unsigned Type, unsigned Flags) -> PhdrEntry * {
1603 Ret.push_back(make<PhdrEntry>(Type, Flags));
1607 // The first phdr entry is PT_PHDR which describes the program header itself.
1608 AddHdr(PT_PHDR, PF_R)->add(Out::ProgramHeaders);
1610 // PT_INTERP must be the second entry if exists.
1611 if (OutputSection *Cmd = findSection(".interp"))
1612 AddHdr(PT_INTERP, Cmd->getPhdrFlags())->add(Cmd);
1614 // Add the first PT_LOAD segment for regular output sections.
1615 uint64_t Flags = computeFlags(PF_R);
1616 PhdrEntry *Load = AddHdr(PT_LOAD, Flags);
1618 // Add the headers. We will remove them if they don't fit.
1619 Load->add(Out::ElfHeader);
1620 Load->add(Out::ProgramHeaders);
1622 for (OutputSection *Sec : OutputSections) {
1623 if (!(Sec->Flags & SHF_ALLOC))
1625 if (!needsPtLoad(Sec))
1628 // Segments are contiguous memory regions that has the same attributes
1629 // (e.g. executable or writable). There is one phdr for each segment.
1630 // Therefore, we need to create a new phdr when the next section has
1631 // different flags or is loaded at a discontiguous address using AT linker
1633 uint64_t NewFlags = computeFlags(Sec->getPhdrFlags());
1634 if ((Sec->LMAExpr && Load->ASectionHasLMA) ||
1635 Sec->MemRegion != Load->FirstSec->MemRegion || Flags != NewFlags) {
1637 Load = AddHdr(PT_LOAD, NewFlags);
1644 // Add a TLS segment if any.
1645 PhdrEntry *TlsHdr = make<PhdrEntry>(PT_TLS, PF_R);
1646 for (OutputSection *Sec : OutputSections)
1647 if (Sec->Flags & SHF_TLS)
1649 if (TlsHdr->FirstSec)
1650 Ret.push_back(TlsHdr);
1652 // Add an entry for .dynamic.
1654 AddHdr(PT_DYNAMIC, InX::Dynamic->getParent()->getPhdrFlags())
1655 ->add(InX::Dynamic->getParent());
1657 // PT_GNU_RELRO includes all sections that should be marked as
1658 // read-only by dynamic linker after proccessing relocations.
1659 // Current dynamic loaders only support one PT_GNU_RELRO PHDR, give
1660 // an error message if more than one PT_GNU_RELRO PHDR is required.
1661 PhdrEntry *RelRo = make<PhdrEntry>(PT_GNU_RELRO, PF_R);
1662 bool InRelroPhdr = false;
1663 bool IsRelroFinished = false;
1664 for (OutputSection *Sec : OutputSections) {
1665 if (!needsPtLoad(Sec))
1667 if (isRelroSection(Sec)) {
1669 if (!IsRelroFinished)
1672 error("section: " + Sec->Name + " is not contiguous with other relro" +
1674 } else if (InRelroPhdr) {
1675 InRelroPhdr = false;
1676 IsRelroFinished = true;
1679 if (RelRo->FirstSec)
1680 Ret.push_back(RelRo);
1682 // PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
1683 if (!InX::EhFrame->empty() && InX::EhFrameHdr && InX::EhFrame->getParent() &&
1684 InX::EhFrameHdr->getParent())
1685 AddHdr(PT_GNU_EH_FRAME, InX::EhFrameHdr->getParent()->getPhdrFlags())
1686 ->add(InX::EhFrameHdr->getParent());
1688 // PT_OPENBSD_RANDOMIZE is an OpenBSD-specific feature. That makes
1689 // the dynamic linker fill the segment with random data.
1690 if (OutputSection *Cmd = findSection(".openbsd.randomdata"))
1691 AddHdr(PT_OPENBSD_RANDOMIZE, Cmd->getPhdrFlags())->add(Cmd);
1693 // PT_GNU_STACK is a special section to tell the loader to make the
1694 // pages for the stack non-executable. If you really want an executable
1695 // stack, you can pass -z execstack, but that's not recommended for
1696 // security reasons.
1698 if (Config->ZExecstack)
1699 Perm = PF_R | PF_W | PF_X;
1702 AddHdr(PT_GNU_STACK, Perm)->p_memsz = Config->ZStackSize;
1704 // PT_OPENBSD_WXNEEDED is a OpenBSD-specific header to mark the executable
1705 // is expected to perform W^X violations, such as calling mprotect(2) or
1706 // mmap(2) with PROT_WRITE | PROT_EXEC, which is prohibited by default on
1708 if (Config->ZWxneeded)
1709 AddHdr(PT_OPENBSD_WXNEEDED, PF_X);
1711 // Create one PT_NOTE per a group of contiguous .note sections.
1712 PhdrEntry *Note = nullptr;
1713 for (OutputSection *Sec : OutputSections) {
1714 if (Sec->Type == SHT_NOTE && (Sec->Flags & SHF_ALLOC)) {
1715 if (!Note || Sec->LMAExpr)
1716 Note = AddHdr(PT_NOTE, PF_R);
1725 template <class ELFT>
1726 void Writer<ELFT>::addPtArmExid(std::vector<PhdrEntry *> &Phdrs) {
1727 if (Config->EMachine != EM_ARM)
1729 auto I = llvm::find_if(OutputSections, [](OutputSection *Cmd) {
1730 return Cmd->Type == SHT_ARM_EXIDX;
1732 if (I == OutputSections.end())
1735 // PT_ARM_EXIDX is the ARM EHABI equivalent of PT_GNU_EH_FRAME
1736 PhdrEntry *ARMExidx = make<PhdrEntry>(PT_ARM_EXIDX, PF_R);
1738 Phdrs.push_back(ARMExidx);
1741 // The first section of each PT_LOAD, the first section in PT_GNU_RELRO and the
1742 // first section after PT_GNU_RELRO have to be page aligned so that the dynamic
1743 // linker can set the permissions.
1744 template <class ELFT> void Writer<ELFT>::fixSectionAlignments() {
1745 auto PageAlign = [](OutputSection *Cmd) {
1746 if (Cmd && !Cmd->AddrExpr)
1747 Cmd->AddrExpr = [=] {
1748 return alignTo(Script->getDot(), Config->MaxPageSize);
1752 for (const PhdrEntry *P : Phdrs)
1753 if (P->p_type == PT_LOAD && P->FirstSec)
1754 PageAlign(P->FirstSec);
1756 for (const PhdrEntry *P : Phdrs) {
1757 if (P->p_type != PT_GNU_RELRO)
1760 PageAlign(P->FirstSec);
1761 // Find the first section after PT_GNU_RELRO. If it is in a PT_LOAD we
1762 // have to align it to a page.
1763 auto End = OutputSections.end();
1764 auto I = std::find(OutputSections.begin(), End, P->LastSec);
1765 if (I == End || (I + 1) == End)
1767 OutputSection *Cmd = (*(I + 1));
1768 if (needsPtLoad(Cmd))
1773 // Adjusts the file alignment for a given output section and returns
1774 // its new file offset. The file offset must be the same with its
1775 // virtual address (modulo the page size) so that the loader can load
1776 // executables without any address adjustment.
1777 static uint64_t getFileAlignment(uint64_t Off, OutputSection *Cmd) {
1778 OutputSection *First = Cmd->PtLoad ? Cmd->PtLoad->FirstSec : nullptr;
1779 // The first section in a PT_LOAD has to have congruent offset and address
1780 // module the page size.
1782 return alignTo(Off, std::max<uint64_t>(Cmd->Alignment, Config->MaxPageSize),
1785 // For SHT_NOBITS we don't want the alignment of the section to impact the
1786 // offset of the sections that follow. Since nothing seems to care about the
1787 // sh_offset of the SHT_NOBITS section itself, just ignore it.
1788 if (Cmd->Type == SHT_NOBITS)
1791 // If the section is not in a PT_LOAD, we just have to align it.
1793 return alignTo(Off, Cmd->Alignment);
1795 // If two sections share the same PT_LOAD the file offset is calculated
1796 // using this formula: Off2 = Off1 + (VA2 - VA1).
1797 return First->Offset + Cmd->Addr - First->Addr;
1800 static uint64_t setOffset(OutputSection *Cmd, uint64_t Off) {
1801 Off = getFileAlignment(Off, Cmd);
1804 // For SHT_NOBITS we should not count the size.
1805 if (Cmd->Type == SHT_NOBITS)
1808 return Off + Cmd->Size;
1811 template <class ELFT> void Writer<ELFT>::assignFileOffsetsBinary() {
1813 for (OutputSection *Sec : OutputSections)
1814 if (Sec->Flags & SHF_ALLOC)
1815 Off = setOffset(Sec, Off);
1816 FileSize = alignTo(Off, Config->Wordsize);
1819 // Assign file offsets to output sections.
1820 template <class ELFT> void Writer<ELFT>::assignFileOffsets() {
1822 Off = setOffset(Out::ElfHeader, Off);
1823 Off = setOffset(Out::ProgramHeaders, Off);
1825 PhdrEntry *LastRX = nullptr;
1826 for (PhdrEntry *P : Phdrs)
1827 if (P->p_type == PT_LOAD && (P->p_flags & PF_X))
1830 for (OutputSection *Sec : OutputSections) {
1831 Off = setOffset(Sec, Off);
1832 if (Script->HasSectionsCommand)
1834 // If this is a last section of the last executable segment and that
1835 // segment is the last loadable segment, align the offset of the
1836 // following section to avoid loading non-segments parts of the file.
1837 if (LastRX && LastRX->LastSec == Sec)
1838 Off = alignTo(Off, Target->PageSize);
1841 SectionHeaderOff = alignTo(Off, Config->Wordsize);
1842 FileSize = SectionHeaderOff + (OutputSections.size() + 1) * sizeof(Elf_Shdr);
1845 // Finalize the program headers. We call this function after we assign
1846 // file offsets and VAs to all sections.
1847 template <class ELFT> void Writer<ELFT>::setPhdrs() {
1848 for (PhdrEntry *P : Phdrs) {
1849 OutputSection *First = P->FirstSec;
1850 OutputSection *Last = P->LastSec;
1852 P->p_filesz = Last->Offset - First->Offset;
1853 if (Last->Type != SHT_NOBITS)
1854 P->p_filesz += Last->Size;
1855 P->p_memsz = Last->Addr + Last->Size - First->Addr;
1856 P->p_offset = First->Offset;
1857 P->p_vaddr = First->Addr;
1859 P->p_paddr = First->getLMA();
1861 if (P->p_type == PT_LOAD)
1862 P->p_align = std::max<uint64_t>(P->p_align, Config->MaxPageSize);
1863 else if (P->p_type == PT_GNU_RELRO) {
1865 // The glibc dynamic loader rounds the size down, so we need to round up
1866 // to protect the last page. This is a no-op on FreeBSD which always
1868 P->p_memsz = alignTo(P->p_memsz, Target->PageSize);
1871 // The TLS pointer goes after PT_TLS. At least glibc will align it,
1872 // so round up the size to make sure the offsets are correct.
1873 if (P->p_type == PT_TLS) {
1876 P->p_memsz = alignTo(P->p_memsz, P->p_align);
1881 // The entry point address is chosen in the following ways.
1883 // 1. the '-e' entry command-line option;
1884 // 2. the ENTRY(symbol) command in a linker control script;
1885 // 3. the value of the symbol _start, if present;
1886 // 4. the number represented by the entry symbol, if it is a number;
1887 // 5. the address of the first byte of the .text section, if present;
1888 // 6. the address 0.
1889 template <class ELFT> uint64_t Writer<ELFT>::getEntryAddr() {
1891 if (Symbol *B = Symtab->find(Config->Entry))
1896 if (to_integer(Config->Entry, Addr))
1900 if (OutputSection *Sec = findSection(".text")) {
1901 if (Config->WarnMissingEntry)
1902 warn("cannot find entry symbol " + Config->Entry + "; defaulting to 0x" +
1903 utohexstr(Sec->Addr));
1908 if (Config->WarnMissingEntry)
1909 warn("cannot find entry symbol " + Config->Entry +
1910 "; not setting start address");
1914 static uint16_t getELFType() {
1917 if (Config->Relocatable)
1922 template <class ELFT> void Writer<ELFT>::writeHeader() {
1923 uint8_t *Buf = Buffer->getBufferStart();
1924 memcpy(Buf, "\177ELF", 4);
1926 // Write the ELF header.
1927 auto *EHdr = reinterpret_cast<Elf_Ehdr *>(Buf);
1928 EHdr->e_ident[EI_CLASS] = Config->Is64 ? ELFCLASS64 : ELFCLASS32;
1929 EHdr->e_ident[EI_DATA] = Config->IsLE ? ELFDATA2LSB : ELFDATA2MSB;
1930 EHdr->e_ident[EI_VERSION] = EV_CURRENT;
1931 EHdr->e_ident[EI_OSABI] = Config->OSABI;
1932 EHdr->e_type = getELFType();
1933 EHdr->e_machine = Config->EMachine;
1934 EHdr->e_version = EV_CURRENT;
1935 EHdr->e_entry = getEntryAddr();
1936 EHdr->e_shoff = SectionHeaderOff;
1937 EHdr->e_flags = Config->EFlags;
1938 EHdr->e_ehsize = sizeof(Elf_Ehdr);
1939 EHdr->e_phnum = Phdrs.size();
1940 EHdr->e_shentsize = sizeof(Elf_Shdr);
1941 EHdr->e_shnum = OutputSections.size() + 1;
1942 EHdr->e_shstrndx = InX::ShStrTab->getParent()->SectionIndex;
1944 if (!Config->Relocatable) {
1945 EHdr->e_phoff = sizeof(Elf_Ehdr);
1946 EHdr->e_phentsize = sizeof(Elf_Phdr);
1949 // Write the program header table.
1950 auto *HBuf = reinterpret_cast<Elf_Phdr *>(Buf + EHdr->e_phoff);
1951 for (PhdrEntry *P : Phdrs) {
1952 HBuf->p_type = P->p_type;
1953 HBuf->p_flags = P->p_flags;
1954 HBuf->p_offset = P->p_offset;
1955 HBuf->p_vaddr = P->p_vaddr;
1956 HBuf->p_paddr = P->p_paddr;
1957 HBuf->p_filesz = P->p_filesz;
1958 HBuf->p_memsz = P->p_memsz;
1959 HBuf->p_align = P->p_align;
1963 // Write the section header table. Note that the first table entry is null.
1964 auto *SHdrs = reinterpret_cast<Elf_Shdr *>(Buf + EHdr->e_shoff);
1965 for (OutputSection *Sec : OutputSections)
1966 Sec->writeHeaderTo<ELFT>(++SHdrs);
1969 // Open a result file.
1970 template <class ELFT> void Writer<ELFT>::openFile() {
1971 if (!Config->Is64 && FileSize > UINT32_MAX) {
1972 error("output file too large: " + Twine(FileSize) + " bytes");
1976 unlinkAsync(Config->OutputFile);
1978 if (!Config->Relocatable)
1979 Flags = FileOutputBuffer::F_executable;
1980 Expected<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
1981 FileOutputBuffer::create(Config->OutputFile, FileSize, Flags);
1984 error("failed to open " + Config->OutputFile + ": " +
1985 llvm::toString(BufferOrErr.takeError()));
1987 Buffer = std::move(*BufferOrErr);
1990 template <class ELFT> void Writer<ELFT>::writeSectionsBinary() {
1991 uint8_t *Buf = Buffer->getBufferStart();
1992 for (OutputSection *Sec : OutputSections)
1993 if (Sec->Flags & SHF_ALLOC)
1994 Sec->writeTo<ELFT>(Buf + Sec->Offset);
1997 static void fillTrap(uint8_t *I, uint8_t *End) {
1998 for (; I + 4 <= End; I += 4)
1999 memcpy(I, &Target->TrapInstr, 4);
2002 // Fill the last page of executable segments with trap instructions
2003 // instead of leaving them as zero. Even though it is not required by any
2004 // standard, it is in general a good thing to do for security reasons.
2006 // We'll leave other pages in segments as-is because the rest will be
2007 // overwritten by output sections.
2008 template <class ELFT> void Writer<ELFT>::writeTrapInstr() {
2009 if (Script->HasSectionsCommand)
2012 // Fill the last page.
2013 uint8_t *Buf = Buffer->getBufferStart();
2014 for (PhdrEntry *P : Phdrs)
2015 if (P->p_type == PT_LOAD && (P->p_flags & PF_X))
2016 fillTrap(Buf + alignDown(P->p_offset + P->p_filesz, Target->PageSize),
2017 Buf + alignTo(P->p_offset + P->p_filesz, Target->PageSize));
2019 // Round up the file size of the last segment to the page boundary iff it is
2020 // an executable segment to ensure that other tools don't accidentally
2021 // trim the instruction padding (e.g. when stripping the file).
2022 PhdrEntry *Last = nullptr;
2023 for (PhdrEntry *P : Phdrs)
2024 if (P->p_type == PT_LOAD)
2027 if (Last && (Last->p_flags & PF_X))
2028 Last->p_memsz = Last->p_filesz = alignTo(Last->p_filesz, Target->PageSize);
2031 // Write section contents to a mmap'ed file.
2032 template <class ELFT> void Writer<ELFT>::writeSections() {
2033 uint8_t *Buf = Buffer->getBufferStart();
2035 // PPC64 needs to process relocations in the .opd section
2036 // before processing relocations in code-containing sections.
2037 if (auto *OpdCmd = findSection(".opd")) {
2039 Out::OpdBuf = Buf + Out::Opd->Offset;
2040 OpdCmd->template writeTo<ELFT>(Buf + Out::Opd->Offset);
2043 OutputSection *EhFrameHdr = nullptr;
2044 if (InX::EhFrameHdr && !InX::EhFrameHdr->empty())
2045 EhFrameHdr = InX::EhFrameHdr->getParent();
2047 // In -r or -emit-relocs mode, write the relocation sections first as in
2048 // ELf_Rel targets we might find out that we need to modify the relocated
2049 // section while doing it.
2050 for (OutputSection *Sec : OutputSections)
2051 if (Sec->Type == SHT_REL || Sec->Type == SHT_RELA)
2052 Sec->writeTo<ELFT>(Buf + Sec->Offset);
2054 for (OutputSection *Sec : OutputSections)
2055 if (Sec != Out::Opd && Sec != EhFrameHdr && Sec->Type != SHT_REL &&
2056 Sec->Type != SHT_RELA)
2057 Sec->writeTo<ELFT>(Buf + Sec->Offset);
2059 // The .eh_frame_hdr depends on .eh_frame section contents, therefore
2060 // it should be written after .eh_frame is written.
2062 EhFrameHdr->writeTo<ELFT>(Buf + EhFrameHdr->Offset);
2065 template <class ELFT> void Writer<ELFT>::writeBuildId() {
2066 if (!InX::BuildId || !InX::BuildId->getParent())
2069 // Compute a hash of all sections of the output file.
2070 uint8_t *Start = Buffer->getBufferStart();
2071 uint8_t *End = Start + FileSize;
2072 InX::BuildId->writeBuildId({Start, End});
2075 template void elf::writeResult<ELF32LE>();
2076 template void elf::writeResult<ELF32BE>();
2077 template void elf::writeResult<ELF64LE>();
2078 template void elf::writeResult<ELF64BE>();