1 //===- lib/MC/ELFObjectWriter.cpp - ELF File Writer -----------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements ELF object file writer information.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/MC/MCELFObjectWriter.h"
15 #include "llvm/ADT/STLExtras.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/ADT/SmallString.h"
18 #include "llvm/ADT/StringMap.h"
19 #include "llvm/MC/MCAsmBackend.h"
20 #include "llvm/MC/MCAsmInfo.h"
21 #include "llvm/MC/MCAsmLayout.h"
22 #include "llvm/MC/MCAssembler.h"
23 #include "llvm/MC/MCContext.h"
24 #include "llvm/MC/MCELF.h"
25 #include "llvm/MC/MCELFSymbolFlags.h"
26 #include "llvm/MC/MCExpr.h"
27 #include "llvm/MC/MCFixupKindInfo.h"
28 #include "llvm/MC/MCObjectWriter.h"
29 #include "llvm/MC/MCSectionELF.h"
30 #include "llvm/MC/MCValue.h"
31 #include "llvm/MC/StringTableBuilder.h"
32 #include "llvm/Support/Compression.h"
33 #include "llvm/Support/Debug.h"
34 #include "llvm/Support/ELF.h"
35 #include "llvm/Support/Endian.h"
36 #include "llvm/Support/ErrorHandling.h"
41 #define DEBUG_TYPE "reloc-info"
45 typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
47 class ELFObjectWriter;
49 class SymbolTableWriter {
50 ELFObjectWriter &EWriter;
53 // indexes we are going to write to .symtab_shndx.
54 std::vector<uint32_t> ShndxIndexes;
56 // The numbel of symbols written so far.
59 void createSymtabShndx();
61 template <typename T> void write(T Value);
64 SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit);
66 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
67 uint8_t other, uint32_t shndx, bool Reserved);
69 ArrayRef<uint32_t> getShndxIndexes() const { return ShndxIndexes; }
72 class ELFObjectWriter : public MCObjectWriter {
73 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
74 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
75 static uint64_t SymbolValue(const MCSymbol &Sym, const MCAsmLayout &Layout);
76 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbol &Symbol,
77 bool Used, bool Renamed);
78 static bool isLocal(const MCSymbol &Symbol, bool isUsedInReloc);
80 /// Helper struct for containing some precomputed information on symbols.
81 struct ELFSymbolData {
82 const MCSymbol *Symbol;
84 uint32_t SectionIndex;
87 // Support lexicographic sorting.
88 bool operator<(const ELFSymbolData &RHS) const {
89 unsigned LHSType = MCELF::GetType(Symbol->getData());
90 unsigned RHSType = MCELF::GetType(RHS.Symbol->getData());
91 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
93 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
95 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
96 return SectionIndex < RHS.SectionIndex;
97 return Name < RHS.Name;
101 /// The target specific ELF writer instance.
102 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
104 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
105 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
106 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
108 llvm::DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>>
110 StringTableBuilder ShStrTabBuilder;
113 /// @name Symbol Table Data
116 StringTableBuilder StrTabBuilder;
117 std::vector<uint64_t> FileSymbolData;
118 std::vector<ELFSymbolData> LocalSymbolData;
119 std::vector<ELFSymbolData> ExternalSymbolData;
120 std::vector<ELFSymbolData> UndefinedSymbolData;
126 // This holds the symbol table index of the last local symbol.
127 unsigned LastLocalSymbolIndex;
128 // This holds the .strtab section index.
129 unsigned StringTableIndex;
130 // This holds the .symtab section index.
131 unsigned SymbolTableIndex;
133 unsigned ShstrtabIndex;
135 // Sections in the order they are to be output in the section table.
136 std::vector<MCSectionELF *> SectionTable;
137 unsigned addToSectionTable(MCSectionELF *Sec);
139 // TargetObjectWriter wrappers.
140 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
141 bool hasRelocationAddend() const {
142 return TargetObjectWriter->hasRelocationAddend();
144 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
145 bool IsPCRel) const {
146 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
150 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
152 : MCObjectWriter(OS, IsLittleEndian), TargetObjectWriter(MOTW),
155 void reset() override {
157 WeakrefUsedInReloc.clear();
160 ShStrTabBuilder.clear();
161 StrTabBuilder.clear();
162 FileSymbolData.clear();
163 LocalSymbolData.clear();
164 ExternalSymbolData.clear();
165 UndefinedSymbolData.clear();
167 SectionTable.clear();
168 MCObjectWriter::reset();
171 ~ELFObjectWriter() override;
173 void WriteWord(uint64_t W) {
180 template <typename T> void write(T Val) {
182 support::endian::Writer<support::little>(OS).write(Val);
184 support::endian::Writer<support::big>(OS).write(Val);
187 void writeHeader(const MCAssembler &Asm);
189 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
190 const MCAsmLayout &Layout);
192 // Start and end offset of each section
193 typedef std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>
196 void WriteSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
197 SectionOffsetsTy &SectionOffsets);
199 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
200 const MCSymbolRefExpr *RefA,
201 const MCSymbol *Sym, uint64_t C,
202 unsigned Type) const;
204 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
205 const MCFragment *Fragment, const MCFixup &Fixup,
206 MCValue Target, bool &IsPCRel,
207 uint64_t &FixedValue) override;
209 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
212 // Map from a signature symbol to the group section index
213 typedef DenseMap<const MCSymbol *, unsigned> RevGroupMapTy;
215 /// Compute the symbol table data
217 /// \param Asm - The assembler.
218 /// \param SectionIndexMap - Maps a section to its index.
219 /// \param RevGroupMap - Maps a signature symbol to the group section.
220 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
221 const SectionIndexMapTy &SectionIndexMap,
222 const RevGroupMapTy &RevGroupMap);
224 MCSectionELF *createRelocationSection(MCAssembler &Asm,
225 const MCSectionELF &Sec);
227 const MCSectionELF *createSectionHeaderStringTable();
228 const MCSectionELF *createStringTable(MCContext &Ctx);
230 void ExecutePostLayoutBinding(MCAssembler &Asm,
231 const MCAsmLayout &Layout) override;
233 void writeSectionHeader(const MCAssembler &Asm, const MCAsmLayout &Layout,
234 const SectionIndexMapTy &SectionIndexMap,
235 const SectionOffsetsTy &SectionOffsets);
237 void writeSectionData(const MCAssembler &Asm, const MCSectionData &SD,
238 const MCAsmLayout &Layout);
240 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
241 uint64_t Address, uint64_t Offset, uint64_t Size,
242 uint32_t Link, uint32_t Info, uint64_t Alignment,
245 void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
247 bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
248 const MCSymbol &SymA,
249 const MCFragment &FB,
251 bool IsPCRel) const override;
253 bool isWeak(const MCSymbol &Sym) const override;
255 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
256 void writeSection(const SectionIndexMapTy &SectionIndexMap,
257 uint32_t GroupSymbolIndex, uint64_t Offset, uint64_t Size,
258 const MCSectionELF &Section);
262 unsigned ELFObjectWriter::addToSectionTable(MCSectionELF *Sec) {
263 SectionTable.push_back(Sec);
264 ShStrTabBuilder.add(Sec->getSectionName());
265 return SectionTable.size();
268 void SymbolTableWriter::createSymtabShndx() {
269 if (!ShndxIndexes.empty())
272 ShndxIndexes.resize(NumWritten);
275 template <typename T> void SymbolTableWriter::write(T Value) {
276 EWriter.write(Value);
279 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
280 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
282 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
283 uint64_t size, uint8_t other,
284 uint32_t shndx, bool Reserved) {
285 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
290 if (!ShndxIndexes.empty()) {
292 ShndxIndexes.push_back(shndx);
294 ShndxIndexes.push_back(0);
297 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
300 write(name); // st_name
301 write(info); // st_info
302 write(other); // st_other
303 write(Index); // st_shndx
304 write(value); // st_value
305 write(size); // st_size
307 write(name); // st_name
308 write(uint32_t(value)); // st_value
309 write(uint32_t(size)); // st_size
310 write(info); // st_info
311 write(other); // st_other
312 write(Index); // st_shndx
318 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
319 const MCFixupKindInfo &FKI =
320 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
322 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
325 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
329 case MCSymbolRefExpr::VK_GOT:
330 case MCSymbolRefExpr::VK_PLT:
331 case MCSymbolRefExpr::VK_GOTPCREL:
332 case MCSymbolRefExpr::VK_GOTOFF:
333 case MCSymbolRefExpr::VK_TPOFF:
334 case MCSymbolRefExpr::VK_TLSGD:
335 case MCSymbolRefExpr::VK_GOTTPOFF:
336 case MCSymbolRefExpr::VK_INDNTPOFF:
337 case MCSymbolRefExpr::VK_NTPOFF:
338 case MCSymbolRefExpr::VK_GOTNTPOFF:
339 case MCSymbolRefExpr::VK_TLSLDM:
340 case MCSymbolRefExpr::VK_DTPOFF:
341 case MCSymbolRefExpr::VK_TLSLD:
346 ELFObjectWriter::~ELFObjectWriter()
349 // Emit the ELF header.
350 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
356 // emitWord method behaves differently for ELF32 and ELF64, writing
357 // 4 bytes in the former and 8 in the latter.
359 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
361 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
364 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
366 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
368 Write8(TargetObjectWriter->getOSABI());
369 Write8(0); // e_ident[EI_ABIVERSION]
371 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
373 Write16(ELF::ET_REL); // e_type
375 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
377 Write32(ELF::EV_CURRENT); // e_version
378 WriteWord(0); // e_entry, no entry point in .o file
379 WriteWord(0); // e_phoff, no program header for .o
380 WriteWord(0); // e_shoff = sec hdr table off in bytes
382 // e_flags = whatever the target wants
383 Write32(Asm.getELFHeaderEFlags());
385 // e_ehsize = ELF header size
386 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
388 Write16(0); // e_phentsize = prog header entry size
389 Write16(0); // e_phnum = # prog header entries = 0
391 // e_shentsize = Section header entry size
392 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
394 // e_shnum = # of section header ents
397 // e_shstrndx = Section # of '.shstrtab'
398 assert(ShstrtabIndex < ELF::SHN_LORESERVE);
399 Write16(ShstrtabIndex);
402 uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
403 const MCAsmLayout &Layout) {
404 MCSymbolData &Data = Sym.getData();
405 if (Data.isCommon() && Data.isExternal())
406 return Data.getCommonAlignment();
409 if (!Layout.getSymbolOffset(Sym, Res))
412 if (Layout.getAssembler().isThumbFunc(&Sym))
418 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
419 const MCAsmLayout &Layout) {
420 // The presence of symbol versions causes undefined symbols and
421 // versions declared with @@@ to be renamed.
423 for (const MCSymbol &Alias : Asm.symbols()) {
424 MCSymbolData &OriginalData = Alias.getData();
427 if (!Alias.isVariable())
429 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
432 const MCSymbol &Symbol = Ref->getSymbol();
433 MCSymbolData &SD = Asm.getSymbolData(Symbol);
435 StringRef AliasName = Alias.getName();
436 size_t Pos = AliasName.find('@');
437 if (Pos == StringRef::npos)
440 // Aliases defined with .symvar copy the binding from the symbol they alias.
441 // This is the first place we are able to copy this information.
442 OriginalData.setExternal(SD.isExternal());
443 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
445 StringRef Rest = AliasName.substr(Pos);
446 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
449 // FIXME: produce a better error message.
450 if (Symbol.isUndefined() && Rest.startswith("@@") &&
451 !Rest.startswith("@@@"))
452 report_fatal_error("A @@ version cannot be undefined");
454 Renames.insert(std::make_pair(&Symbol, &Alias));
458 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
459 uint8_t Type = newType;
461 // Propagation rules:
462 // IFUNC > FUNC > OBJECT > NOTYPE
463 // TLS_OBJECT > OBJECT > NOTYPE
465 // dont let the new type degrade the old type
469 case ELF::STT_GNU_IFUNC:
470 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
471 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
472 Type = ELF::STT_GNU_IFUNC;
475 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
476 Type == ELF::STT_TLS)
477 Type = ELF::STT_FUNC;
479 case ELF::STT_OBJECT:
480 if (Type == ELF::STT_NOTYPE)
481 Type = ELF::STT_OBJECT;
484 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
485 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
493 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
494 const MCAsmLayout &Layout) {
495 MCSymbolData &OrigData = MSD.Symbol->getData();
496 assert((!OrigData.getFragment() ||
497 (&OrigData.getFragment()->getParent()->getSection() ==
498 &MSD.Symbol->getSection())) &&
499 "The symbol's section doesn't match the fragment's symbol");
500 const MCSymbol *Base = Layout.getBaseSymbol(*MSD.Symbol);
502 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
504 bool IsReserved = !Base || OrigData.isCommon();
506 // Binding and Type share the same byte as upper and lower nibbles
507 uint8_t Binding = MCELF::GetBinding(OrigData);
508 uint8_t Type = MCELF::GetType(OrigData);
509 MCSymbolData *BaseSD = nullptr;
511 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
512 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
514 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
516 // Other and Visibility share the same byte with Visibility using the lower
518 uint8_t Visibility = MCELF::GetVisibility(OrigData);
519 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
522 uint64_t Value = SymbolValue(*MSD.Symbol, Layout);
525 const MCExpr *ESize = OrigData.getSize();
527 ESize = BaseSD->getSize();
531 if (!ESize->evaluateKnownAbsolute(Res, Layout))
532 report_fatal_error("Size expression must be absolute.");
536 // Write out the symbol table entry
537 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
538 MSD.SectionIndex, IsReserved);
541 void ELFObjectWriter::WriteSymbolTable(MCAssembler &Asm,
542 const MCAsmLayout &Layout,
543 SectionOffsetsTy &SectionOffsets) {
545 MCContext &Ctx = Asm.getContext();
547 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
550 MCSectionELF *SymtabSection =
551 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
552 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
553 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
554 SymbolTableIndex = addToSectionTable(SymtabSection);
556 // The string table must be emitted first because we need the index
557 // into the string table for all the symbol names.
559 SymbolTableWriter Writer(*this, is64Bit());
561 uint64_t Padding = OffsetToAlignment(OS.tell(), SymtabSD.getAlignment());
564 uint64_t SecStart = OS.tell();
566 // The first entry is the undefined symbol entry.
567 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
569 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
570 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
571 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
574 // Write the symbol table entries.
575 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
577 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
578 ELFSymbolData &MSD = LocalSymbolData[i];
579 WriteSymbol(Writer, MSD, Layout);
582 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
583 ELFSymbolData &MSD = ExternalSymbolData[i];
584 MCSymbolData &Data = MSD.Symbol->getData();
585 assert(((Data.getFlags() & ELF_STB_Global) ||
586 (Data.getFlags() & ELF_STB_Weak)) &&
587 "External symbol requires STB_GLOBAL or STB_WEAK flag");
588 WriteSymbol(Writer, MSD, Layout);
589 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
590 LastLocalSymbolIndex++;
593 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
594 ELFSymbolData &MSD = UndefinedSymbolData[i];
595 MCSymbolData &Data = MSD.Symbol->getData();
596 WriteSymbol(Writer, MSD, Layout);
597 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
598 LastLocalSymbolIndex++;
601 uint64_t SecEnd = OS.tell();
602 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
604 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
605 if (ShndxIndexes.empty())
608 SecStart = OS.tell();
609 MCSectionELF *SymtabShndxSection =
610 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
611 addToSectionTable(SymtabShndxSection);
612 MCSectionData *SymtabShndxSD =
613 &Asm.getOrCreateSectionData(*SymtabShndxSection);
614 SymtabShndxSD->setAlignment(4);
615 for (uint32_t Index : ShndxIndexes)
618 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
621 // It is always valid to create a relocation with a symbol. It is preferable
622 // to use a relocation with a section if that is possible. Using the section
623 // allows us to omit some local symbols from the symbol table.
624 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
625 const MCSymbolRefExpr *RefA,
626 const MCSymbol *Sym, uint64_t C,
627 unsigned Type) const {
628 MCSymbolData *SD = Sym ? &Sym->getData() : nullptr;
630 // A PCRel relocation to an absolute value has no symbol (or section). We
631 // represent that with a relocation to a null section.
635 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
639 // The .odp creation emits a relocation against the symbol ".TOC." which
640 // create a R_PPC64_TOC relocation. However the relocation symbol name
641 // in final object creation should be NULL, since the symbol does not
642 // really exist, it is just the reference to TOC base for the current
643 // object file. Since the symbol is undefined, returning false results
644 // in a relocation with a null section which is the desired result.
645 case MCSymbolRefExpr::VK_PPC_TOCBASE:
648 // These VariantKind cause the relocation to refer to something other than
649 // the symbol itself, like a linker generated table. Since the address of
650 // symbol is not relevant, we cannot replace the symbol with the
651 // section and patch the difference in the addend.
652 case MCSymbolRefExpr::VK_GOT:
653 case MCSymbolRefExpr::VK_PLT:
654 case MCSymbolRefExpr::VK_GOTPCREL:
655 case MCSymbolRefExpr::VK_Mips_GOT:
656 case MCSymbolRefExpr::VK_PPC_GOT_LO:
657 case MCSymbolRefExpr::VK_PPC_GOT_HI:
658 case MCSymbolRefExpr::VK_PPC_GOT_HA:
662 // An undefined symbol is not in any section, so the relocation has to point
663 // to the symbol itself.
664 assert(Sym && "Expected a symbol");
665 if (Sym->isUndefined())
668 unsigned Binding = MCELF::GetBinding(*SD);
671 llvm_unreachable("Invalid Binding");
675 // If the symbol is weak, it might be overridden by a symbol in another
676 // file. The relocation has to point to the symbol so that the linker
679 case ELF::STB_GLOBAL:
680 // Global ELF symbols can be preempted by the dynamic linker. The relocation
681 // has to point to the symbol for a reason analogous to the STB_WEAK case.
685 // If a relocation points to a mergeable section, we have to be careful.
686 // If the offset is zero, a relocation with the section will encode the
687 // same information. With a non-zero offset, the situation is different.
688 // For example, a relocation can point 42 bytes past the end of a string.
689 // If we change such a relocation to use the section, the linker would think
690 // that it pointed to another string and subtracting 42 at runtime will
691 // produce the wrong value.
692 auto &Sec = cast<MCSectionELF>(Sym->getSection());
693 unsigned Flags = Sec.getFlags();
694 if (Flags & ELF::SHF_MERGE) {
698 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
699 // only handle section relocations to mergeable sections if using RELA.
700 if (!hasRelocationAddend())
704 // Most TLS relocations use a got, so they need the symbol. Even those that
705 // are just an offset (@tpoff), require a symbol in gold versions before
706 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
707 // http://sourceware.org/PR16773.
708 if (Flags & ELF::SHF_TLS)
711 // If the symbol is a thumb function the final relocation must set the lowest
712 // bit. With a symbol that is done by just having the symbol have that bit
713 // set, so we would lose the bit if we relocated with the section.
714 // FIXME: We could use the section but add the bit to the relocation value.
715 if (Asm.isThumbFunc(Sym))
718 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
723 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
724 const MCSymbol &Sym = Ref.getSymbol();
726 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
729 if (!Sym.isVariable())
732 const MCExpr *Expr = Sym.getVariableValue();
733 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
737 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
738 return &Inner->getSymbol();
742 // True if the assembler knows nothing about the final value of the symbol.
743 // This doesn't cover the comdat issues, since in those cases the assembler
744 // can at least know that all symbols in the section will move together.
745 static bool isWeak(const MCSymbolData &D) {
746 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
749 switch (MCELF::GetBinding(D)) {
751 llvm_unreachable("Unknown binding");
754 case ELF::STB_GLOBAL:
757 case ELF::STB_GNU_UNIQUE:
762 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
763 const MCAsmLayout &Layout,
764 const MCFragment *Fragment,
765 const MCFixup &Fixup, MCValue Target,
766 bool &IsPCRel, uint64_t &FixedValue) {
767 const MCSectionData *FixupSectionD = Fragment->getParent();
768 const MCSectionELF &FixupSection =
769 cast<MCSectionELF>(FixupSectionD->getSection());
770 uint64_t C = Target.getConstant();
771 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
773 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
774 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
775 "Should not have constructed this");
777 // Let A, B and C being the components of Target and R be the location of
778 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
779 // If it is pcrel, we want to compute (A - B + C - R).
781 // In general, ELF has no relocations for -B. It can only represent (A + C)
782 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
783 // replace B to implement it: (A - R - K + C)
785 Asm.getContext().reportFatalError(
787 "No relocation available to represent this relative expression");
789 const MCSymbol &SymB = RefB->getSymbol();
791 if (SymB.isUndefined())
792 Asm.getContext().reportFatalError(
794 Twine("symbol '") + SymB.getName() +
795 "' can not be undefined in a subtraction expression");
797 assert(!SymB.isAbsolute() && "Should have been folded");
798 const MCSection &SecB = SymB.getSection();
799 if (&SecB != &FixupSection)
800 Asm.getContext().reportFatalError(
801 Fixup.getLoc(), "Cannot represent a difference across sections");
803 if (::isWeak(SymB.getData()))
804 Asm.getContext().reportFatalError(
805 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
807 uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
808 uint64_t K = SymBOffset - FixupOffset;
813 // We either rejected the fixup or folded B into C at this point.
814 const MCSymbolRefExpr *RefA = Target.getSymA();
815 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
817 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
818 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymA, C, Type);
819 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
820 C += Layout.getSymbolOffset(*SymA);
823 if (hasRelocationAddend()) {
830 // FIXME: What is this!?!?
831 MCSymbolRefExpr::VariantKind Modifier =
832 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
833 if (RelocNeedsGOT(Modifier))
836 if (!RelocateWithSymbol) {
837 const MCSection *SecA =
838 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
839 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
840 MCSymbol *SectionSymbol =
841 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
843 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
844 Relocations[&FixupSection].push_back(Rec);
849 if (const MCSymbol *R = Renames.lookup(SymA))
852 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
853 WeakrefUsedInReloc.insert(WeakRef);
855 UsedInReloc.insert(SymA);
857 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
858 Relocations[&FixupSection].push_back(Rec);
864 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
866 const MCSymbolData &SD = Asm.getSymbolData(*S);
867 return SD.getIndex();
870 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
871 const MCSymbol &Symbol, bool Used,
873 const MCSymbolData &Data = Symbol.getData();
874 if (Symbol.isVariable()) {
875 const MCExpr *Expr = Symbol.getVariableValue();
876 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
877 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
888 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
891 if (Symbol.isVariable()) {
892 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
893 if (Base && Base->isUndefined())
897 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
898 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
901 if (Symbol.isTemporary())
907 bool ELFObjectWriter::isLocal(const MCSymbol &Symbol, bool isUsedInReloc) {
908 const MCSymbolData &Data = Symbol.getData();
909 if (Data.isExternal())
912 if (Symbol.isDefined())
921 void ELFObjectWriter::computeSymbolTable(
922 MCAssembler &Asm, const MCAsmLayout &Layout,
923 const SectionIndexMapTy &SectionIndexMap,
924 const RevGroupMapTy &RevGroupMap) {
925 // FIXME: Is this the correct place to do this?
926 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
928 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
929 MCSymbol *Sym = Asm.getContext().getOrCreateSymbol(Name);
930 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
931 Data.setExternal(true);
932 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
935 // Add the data for the symbols.
936 for (const MCSymbol &Symbol : Asm.symbols()) {
937 MCSymbolData &SD = Symbol.getData();
939 bool Used = UsedInReloc.count(&Symbol);
940 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
941 bool isSignature = RevGroupMap.count(&Symbol);
943 if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
944 Renames.count(&Symbol)))
948 MSD.Symbol = &Symbol;
949 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
951 // Undefined symbols are global, but this is the first place we
952 // are able to set it.
953 bool Local = isLocal(Symbol, Used);
954 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
956 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
957 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
958 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
962 MSD.SectionIndex = ELF::SHN_ABS;
963 } else if (SD.isCommon()) {
965 MSD.SectionIndex = ELF::SHN_COMMON;
966 } else if (BaseSymbol->isUndefined()) {
967 if (isSignature && !Used)
968 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
970 MSD.SectionIndex = ELF::SHN_UNDEF;
971 if (!Used && WeakrefUsed)
972 MCELF::SetBinding(SD, ELF::STB_WEAK);
974 const MCSectionELF &Section =
975 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
976 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
977 assert(MSD.SectionIndex && "Invalid section index!");
980 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
983 // FIXME: All name handling should be done before we get to the writer,
984 // including dealing with GNU-style version suffixes. Fixing this isn't
987 // We thus have to be careful to not perform the symbol version replacement
990 // The ELF format is used on Windows by the MCJIT engine. Thus, on
991 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
992 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
993 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
994 // the EFLObjectWriter should not interpret the "@@@" sub-string as
995 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
996 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
997 // "__imp_?" or "__imp_@?".
999 // It would have been interesting to perform the MS mangling prefix check
1000 // only when the target triple is of the form *-pc-windows-elf. But, it
1001 // seems that this information is not easily accessible from the
1003 StringRef Name = Symbol.getName();
1004 if (!Name.startswith("?") && !Name.startswith("@?") &&
1005 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1006 // This symbol isn't following the MSVC C++ name mangling convention. We
1007 // can thus safely interpret the @@@ in symbol names as specifying symbol
1009 SmallString<32> Buf;
1010 size_t Pos = Name.find("@@@");
1011 if (Pos != StringRef::npos) {
1012 Buf += Name.substr(0, Pos);
1013 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1014 Buf += Name.substr(Pos + Skip);
1019 // Sections have their own string table
1020 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1021 MSD.Name = StrTabBuilder.add(Name);
1023 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1024 UndefinedSymbolData.push_back(MSD);
1026 LocalSymbolData.push_back(MSD);
1028 ExternalSymbolData.push_back(MSD);
1031 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1032 StrTabBuilder.add(*i);
1034 StrTabBuilder.finalize(StringTableBuilder::ELF);
1036 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1037 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1039 for (ELFSymbolData &MSD : LocalSymbolData)
1040 MSD.StringIndex = MCELF::GetType(MSD.Symbol->getData()) == ELF::STT_SECTION
1042 : StrTabBuilder.getOffset(MSD.Name);
1043 for (ELFSymbolData &MSD : ExternalSymbolData)
1044 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1045 for (ELFSymbolData& MSD : UndefinedSymbolData)
1046 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1048 // Symbols are required to be in lexicographic order.
1049 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1050 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1051 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1053 // Set the symbol indices. Local symbols must come before all other
1054 // symbols with non-local bindings.
1055 unsigned Index = FileSymbolData.size() + 1;
1056 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1057 LocalSymbolData[i].Symbol->getData().setIndex(Index++);
1059 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1060 ExternalSymbolData[i].Symbol->getData().setIndex(Index++);
1061 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1062 UndefinedSymbolData[i].Symbol->getData().setIndex(Index++);
1066 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1067 const MCSectionELF &Sec) {
1068 if (Relocations[&Sec].empty())
1071 MCContext &Ctx = Asm.getContext();
1072 const StringRef SectionName = Sec.getSectionName();
1073 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1074 RelaSectionName += SectionName;
1077 if (hasRelocationAddend())
1078 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1080 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1083 if (Sec.getFlags() & ELF::SHF_GROUP)
1084 Flags = ELF::SHF_GROUP;
1086 MCSectionELF *RelaSection = Ctx.createELFRelSection(
1087 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1088 Flags, EntrySize, Sec.getGroup(), &Sec);
1089 MCSectionData &RelSD = Asm.getOrCreateSectionData(*RelaSection);
1090 RelSD.setAlignment(is64Bit() ? 8 : 4);
1094 static SmallVector<char, 128>
1095 getUncompressedData(const MCAsmLayout &Layout,
1096 const MCSectionData::FragmentListType &Fragments) {
1097 SmallVector<char, 128> UncompressedData;
1098 for (const MCFragment &F : Fragments) {
1099 const SmallVectorImpl<char> *Contents;
1100 switch (F.getKind()) {
1101 case MCFragment::FT_Data:
1102 Contents = &cast<MCDataFragment>(F).getContents();
1104 case MCFragment::FT_Dwarf:
1105 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1107 case MCFragment::FT_DwarfFrame:
1108 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1112 "Not expecting any other fragment types in a debug_* section");
1114 UncompressedData.append(Contents->begin(), Contents->end());
1116 return UncompressedData;
1119 // Include the debug info compression header:
1120 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1121 // useful for consumers to preallocate a buffer to decompress into.
1123 prependCompressionHeader(uint64_t Size,
1124 SmallVectorImpl<char> &CompressedContents) {
1125 const StringRef Magic = "ZLIB";
1126 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1128 if (sys::IsLittleEndianHost)
1129 sys::swapByteOrder(Size);
1130 CompressedContents.insert(CompressedContents.begin(),
1131 Magic.size() + sizeof(Size), 0);
1132 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1133 std::copy(reinterpret_cast<char *>(&Size),
1134 reinterpret_cast<char *>(&Size + 1),
1135 CompressedContents.begin() + Magic.size());
1139 void ELFObjectWriter::writeSectionData(const MCAssembler &Asm,
1140 const MCSectionData &SD,
1141 const MCAsmLayout &Layout) {
1142 MCSectionELF &Section = static_cast<MCSectionELF &>(SD.getSection());
1143 StringRef SectionName = Section.getSectionName();
1145 // Compressing debug_frame requires handling alignment fragments which is
1146 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1147 // for writing to arbitrary buffers) for little benefit.
1148 if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
1149 !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
1150 Asm.writeSectionData(&SD, Layout);
1154 // Gather the uncompressed data from all the fragments.
1155 const MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1156 SmallVector<char, 128> UncompressedData =
1157 getUncompressedData(Layout, Fragments);
1159 SmallVector<char, 128> CompressedContents;
1160 zlib::Status Success = zlib::compress(
1161 StringRef(UncompressedData.data(), UncompressedData.size()),
1162 CompressedContents);
1163 if (Success != zlib::StatusOK) {
1164 Asm.writeSectionData(&SD, Layout);
1168 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
1169 Asm.writeSectionData(&SD, Layout);
1172 Asm.getContext().renameELFSection(&Section,
1173 (".z" + SectionName.drop_front(1)).str());
1174 OS << CompressedContents;
1177 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1178 uint64_t Flags, uint64_t Address,
1179 uint64_t Offset, uint64_t Size,
1180 uint32_t Link, uint32_t Info,
1182 uint64_t EntrySize) {
1183 Write32(Name); // sh_name: index into string table
1184 Write32(Type); // sh_type
1185 WriteWord(Flags); // sh_flags
1186 WriteWord(Address); // sh_addr
1187 WriteWord(Offset); // sh_offset
1188 WriteWord(Size); // sh_size
1189 Write32(Link); // sh_link
1190 Write32(Info); // sh_info
1191 WriteWord(Alignment); // sh_addralign
1192 WriteWord(EntrySize); // sh_entsize
1195 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1196 const MCSectionELF &Sec) {
1197 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1199 // Sort the relocation entries. Most targets just sort by Offset, but some
1200 // (e.g., MIPS) have additional constraints.
1201 TargetObjectWriter->sortRelocs(Asm, Relocs);
1203 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1204 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1206 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1209 write(Entry.Offset);
1210 if (TargetObjectWriter->isN64()) {
1211 write(uint32_t(Index));
1213 write(TargetObjectWriter->getRSsym(Entry.Type));
1214 write(TargetObjectWriter->getRType3(Entry.Type));
1215 write(TargetObjectWriter->getRType2(Entry.Type));
1216 write(TargetObjectWriter->getRType(Entry.Type));
1218 struct ELF::Elf64_Rela ERE64;
1219 ERE64.setSymbolAndType(Index, Entry.Type);
1220 write(ERE64.r_info);
1222 if (hasRelocationAddend())
1223 write(Entry.Addend);
1225 write(uint32_t(Entry.Offset));
1227 struct ELF::Elf32_Rela ERE32;
1228 ERE32.setSymbolAndType(Index, Entry.Type);
1229 write(ERE32.r_info);
1231 if (hasRelocationAddend())
1232 write(uint32_t(Entry.Addend));
1237 const MCSectionELF *ELFObjectWriter::createSectionHeaderStringTable() {
1238 const MCSectionELF *ShstrtabSection = SectionTable[ShstrtabIndex - 1];
1239 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1240 OS << ShStrTabBuilder.data();
1241 return ShstrtabSection;
1244 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1245 MCSectionELF *StrtabSection =
1246 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1247 StringTableIndex = addToSectionTable(StrtabSection);
1248 OS << StrTabBuilder.data();
1249 return StrtabSection;
1252 void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
1253 uint32_t GroupSymbolIndex, uint64_t Offset,
1254 uint64_t Size, const MCSectionELF &Section) {
1255 uint64_t sh_link = 0;
1256 uint64_t sh_info = 0;
1258 switch(Section.getType()) {
1263 case ELF::SHT_DYNAMIC:
1264 llvm_unreachable("SHT_DYNAMIC in a relocatable object");
1267 case ELF::SHT_RELA: {
1268 sh_link = SymbolTableIndex;
1269 assert(sh_link && ".symtab not found");
1270 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1271 sh_info = SectionIndexMap.lookup(InfoSection);
1275 case ELF::SHT_SYMTAB:
1276 case ELF::SHT_DYNSYM:
1277 sh_link = StringTableIndex;
1278 sh_info = LastLocalSymbolIndex;
1281 case ELF::SHT_SYMTAB_SHNDX:
1282 sh_link = SymbolTableIndex;
1285 case ELF::SHT_GROUP:
1286 sh_link = SymbolTableIndex;
1287 sh_info = GroupSymbolIndex;
1291 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1292 Section.getType() == ELF::SHT_ARM_EXIDX)
1293 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1295 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1296 Section.getType(), Section.getFlags(), 0, Offset, Size,
1297 sh_link, sh_info, Section.getAlignment(),
1298 Section.getEntrySize());
1301 void ELFObjectWriter::writeSectionHeader(
1302 const MCAssembler &Asm, const MCAsmLayout &Layout,
1303 const SectionIndexMapTy &SectionIndexMap,
1304 const SectionOffsetsTy &SectionOffsets) {
1305 const unsigned NumSections = SectionTable.size();
1307 // Null section first.
1308 uint64_t FirstSectionSize =
1309 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1310 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1312 for (MCSectionELF *Section : SectionTable) {
1313 uint32_t GroupSymbolIndex;
1314 unsigned Type = Section->getType();
1315 if (Type != ELF::SHT_GROUP)
1316 GroupSymbolIndex = 0;
1318 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section->getGroup());
1320 const std::pair<uint64_t, uint64_t> &Offsets =
1321 SectionOffsets.find(Section)->second;
1323 if (Type == ELF::SHT_NOBITS) {
1324 const MCSectionData &SD = Asm.getSectionData(*Section);
1325 Size = Layout.getSectionAddressSize(&SD);
1327 Size = Offsets.second - Offsets.first;
1330 writeSection(SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1335 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1336 const MCAsmLayout &Layout) {
1337 MCContext &Ctx = Asm.getContext();
1338 MCSectionELF *ShstrtabSection =
1339 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1340 ShstrtabIndex = addToSectionTable(ShstrtabSection);
1342 RevGroupMapTy RevGroupMap;
1343 SectionIndexMapTy SectionIndexMap;
1345 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1347 // Write out the ELF header ...
1350 // ... then the sections ...
1351 SectionOffsetsTy SectionOffsets;
1352 bool ComputedSymtab = false;
1353 for (const MCSectionData &SD : Asm) {
1354 MCSectionELF &Section = static_cast<MCSectionELF &>(SD.getSection());
1356 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1357 WriteZeros(Padding);
1359 // Remember the offset into the file for this section.
1360 uint64_t SecStart = OS.tell();
1362 const MCSymbol *SignatureSymbol = Section.getGroup();
1363 unsigned Type = Section.getType();
1364 if (Type == ELF::SHT_GROUP) {
1365 assert(SignatureSymbol);
1366 write(uint32_t(ELF::GRP_COMDAT));
1367 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1368 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1371 } else if (Type == ELF::SHT_REL || Type == ELF::SHT_RELA) {
1372 if (!ComputedSymtab) {
1373 // Compute symbol table information.
1374 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1375 ComputedSymtab = true;
1377 writeRelocations(Asm, *Section.getAssociatedSection());
1379 writeSectionData(Asm, SD, Layout);
1382 uint64_t SecEnd = OS.tell();
1383 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1385 if (Type == ELF::SHT_GROUP || Type == ELF::SHT_REL || Type == ELF::SHT_RELA)
1388 MCSectionELF *RelSection = createRelocationSection(Asm, Section);
1390 if (SignatureSymbol) {
1391 Asm.getOrCreateSymbolData(*SignatureSymbol);
1392 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1394 MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1395 GroupIdx = addToSectionTable(Group);
1396 MCSectionData *GroupD = &Asm.getOrCreateSectionData(*Group);
1397 GroupD->setAlignment(4);
1399 GroupMembers[SignatureSymbol].push_back(&Section);
1401 GroupMembers[SignatureSymbol].push_back(RelSection);
1404 SectionIndexMap[&Section] = addToSectionTable(&Section);
1406 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1409 if (!ComputedSymtab) {
1410 // Compute symbol table information.
1411 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1412 ComputedSymtab = true;
1415 WriteSymbolTable(Asm, Layout, SectionOffsets);
1418 uint64_t SecStart = OS.tell();
1419 const MCSectionELF *Sec = createStringTable(Ctx);
1420 uint64_t SecEnd = OS.tell();
1421 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1425 uint64_t SecStart = OS.tell();
1426 const MCSectionELF *Sec = createSectionHeaderStringTable();
1427 uint64_t SecEnd = OS.tell();
1428 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1431 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1432 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1433 WriteZeros(Padding);
1435 const unsigned SectionHeaderOffset = OS.tell();
1437 // ... then the section header table ...
1438 writeSectionHeader(Asm, Layout, SectionIndexMap, SectionOffsets);
1440 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1441 ? (uint16_t)ELF::SHN_UNDEF
1442 : SectionTable.size() + 1;
1443 if (sys::IsLittleEndianHost != IsLittleEndian)
1444 sys::swapByteOrder(NumSections);
1445 unsigned NumSectionsOffset;
1448 uint64_t Val = SectionHeaderOffset;
1449 if (sys::IsLittleEndianHost != IsLittleEndian)
1450 sys::swapByteOrder(Val);
1451 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1452 offsetof(ELF::Elf64_Ehdr, e_shoff));
1453 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1455 uint32_t Val = SectionHeaderOffset;
1456 if (sys::IsLittleEndianHost != IsLittleEndian)
1457 sys::swapByteOrder(Val);
1458 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1459 offsetof(ELF::Elf32_Ehdr, e_shoff));
1460 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1462 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1466 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1467 const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
1468 bool InSet, bool IsPCRel) const {
1471 if (::isWeak(SymA.getData()))
1474 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
1478 bool ELFObjectWriter::isWeak(const MCSymbol &Sym) const {
1479 const MCSymbolData &SD = Sym.getData();
1483 // It is invalid to replace a reference to a global in a comdat
1484 // with a reference to a local since out of comdat references
1485 // to a local are forbidden.
1486 // We could try to return false for more cases, like the reference
1487 // being in the same comdat or Sym being an alias to another global,
1488 // but it is not clear if it is worth the effort.
1489 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1492 if (!Sym.isInSection())
1495 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1496 return Sec.getGroup();
1499 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1500 raw_pwrite_stream &OS,
1501 bool IsLittleEndian) {
1502 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);