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(MCSymbolData &Data, const MCAsmLayout &Layout);
76 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data,
77 bool Used, bool Renamed);
78 static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
80 /// Helper struct for containing some precomputed information on symbols.
81 struct ELFSymbolData {
82 MCSymbolData *SymbolData;
84 uint32_t SectionIndex;
87 // Support lexicographic sorting.
88 bool operator<(const ELFSymbolData &RHS) const {
89 unsigned LHSType = MCELF::GetType(*SymbolData);
90 unsigned RHSType = MCELF::GetType(*RHS.SymbolData);
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<const MCSectionELF *> SectionTable;
137 unsigned addToSectionTable(const 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();
166 MCObjectWriter::reset();
169 ~ELFObjectWriter() override;
171 void WriteWord(uint64_t W) {
178 template <typename T> void write(T Val) {
180 support::endian::Writer<support::little>(OS).write(Val);
182 support::endian::Writer<support::big>(OS).write(Val);
185 void writeHeader(const MCAssembler &Asm);
187 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
188 const MCAsmLayout &Layout);
190 // Start and end offset of each section
191 typedef std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>
194 void WriteSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
195 SectionOffsetsTy &SectionOffsets);
197 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
198 const MCSymbolRefExpr *RefA,
199 const MCSymbolData *SD, uint64_t C,
200 unsigned Type) const;
202 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
203 const MCFragment *Fragment, const MCFixup &Fixup,
204 MCValue Target, bool &IsPCRel,
205 uint64_t &FixedValue) override;
207 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
210 // Map from a signature symbol to the group section index
211 typedef DenseMap<const MCSymbol *, unsigned> RevGroupMapTy;
213 /// Compute the symbol table data
215 /// \param Asm - The assembler.
216 /// \param SectionIndexMap - Maps a section to its index.
217 /// \param RevGroupMap - Maps a signature symbol to the group section.
218 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
219 const SectionIndexMapTy &SectionIndexMap,
220 const RevGroupMapTy &RevGroupMap);
222 const MCSectionELF *createRelocationSection(MCAssembler &Asm,
223 const MCSectionELF &Sec);
225 const MCSectionELF *createSectionHeaderStringTable();
226 const MCSectionELF *createStringTable(MCContext &Ctx);
228 void ExecutePostLayoutBinding(MCAssembler &Asm,
229 const MCAsmLayout &Layout) override;
231 void writeSectionHeader(MCAssembler &Asm, const MCAsmLayout &Layout,
232 const SectionIndexMapTy &SectionIndexMap,
233 const SectionOffsetsTy &SectionOffsets);
235 void writeSectionData(const MCAssembler &Asm, const MCSectionData &SD,
236 const MCAsmLayout &Layout);
238 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
239 uint64_t Address, uint64_t Offset, uint64_t Size,
240 uint32_t Link, uint32_t Info, uint64_t Alignment,
243 void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
246 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
247 const MCSymbolData &DataA,
248 const MCFragment &FB,
250 bool IsPCRel) const override;
252 bool isWeak(const MCSymbolData &SD) const override;
254 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
255 void writeSection(MCAssembler &Asm,
256 const SectionIndexMapTy &SectionIndexMap,
257 uint32_t GroupSymbolIndex,
258 uint64_t Offset, uint64_t Size, uint64_t Alignment,
259 const MCSectionELF &Section);
263 unsigned ELFObjectWriter::addToSectionTable(const MCSectionELF *Sec) {
264 SectionTable.push_back(Sec);
265 ShStrTabBuilder.add(Sec->getSectionName());
266 return SectionTable.size();
269 void SymbolTableWriter::createSymtabShndx() {
270 if (!ShndxIndexes.empty())
273 ShndxIndexes.resize(NumWritten);
276 template <typename T> void SymbolTableWriter::write(T Value) {
277 EWriter.write(Value);
280 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
281 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
283 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
284 uint64_t size, uint8_t other,
285 uint32_t shndx, bool Reserved) {
286 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
291 if (!ShndxIndexes.empty()) {
293 ShndxIndexes.push_back(shndx);
295 ShndxIndexes.push_back(0);
298 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
301 write(name); // st_name
302 write(info); // st_info
303 write(other); // st_other
304 write(Index); // st_shndx
305 write(value); // st_value
306 write(size); // st_size
308 write(name); // st_name
309 write(uint32_t(value)); // st_value
310 write(uint32_t(size)); // st_size
311 write(info); // st_info
312 write(other); // st_other
313 write(Index); // st_shndx
319 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
320 const MCFixupKindInfo &FKI =
321 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
323 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
326 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
330 case MCSymbolRefExpr::VK_GOT:
331 case MCSymbolRefExpr::VK_PLT:
332 case MCSymbolRefExpr::VK_GOTPCREL:
333 case MCSymbolRefExpr::VK_GOTOFF:
334 case MCSymbolRefExpr::VK_TPOFF:
335 case MCSymbolRefExpr::VK_TLSGD:
336 case MCSymbolRefExpr::VK_GOTTPOFF:
337 case MCSymbolRefExpr::VK_INDNTPOFF:
338 case MCSymbolRefExpr::VK_NTPOFF:
339 case MCSymbolRefExpr::VK_GOTNTPOFF:
340 case MCSymbolRefExpr::VK_TLSLDM:
341 case MCSymbolRefExpr::VK_DTPOFF:
342 case MCSymbolRefExpr::VK_TLSLD:
347 ELFObjectWriter::~ELFObjectWriter()
350 // Emit the ELF header.
351 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
357 // emitWord method behaves differently for ELF32 and ELF64, writing
358 // 4 bytes in the former and 8 in the latter.
360 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
362 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
365 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
367 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
369 Write8(TargetObjectWriter->getOSABI());
370 Write8(0); // e_ident[EI_ABIVERSION]
372 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
374 Write16(ELF::ET_REL); // e_type
376 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
378 Write32(ELF::EV_CURRENT); // e_version
379 WriteWord(0); // e_entry, no entry point in .o file
380 WriteWord(0); // e_phoff, no program header for .o
381 WriteWord(0); // e_shoff = sec hdr table off in bytes
383 // e_flags = whatever the target wants
384 Write32(Asm.getELFHeaderEFlags());
386 // e_ehsize = ELF header size
387 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
389 Write16(0); // e_phentsize = prog header entry size
390 Write16(0); // e_phnum = # prog header entries = 0
392 // e_shentsize = Section header entry size
393 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
395 // e_shnum = # of section header ents
398 // e_shstrndx = Section # of '.shstrtab'
399 assert(ShstrtabIndex < ELF::SHN_LORESERVE);
400 Write16(ShstrtabIndex);
403 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
404 const MCAsmLayout &Layout) {
405 if (Data.isCommon() && Data.isExternal())
406 return Data.getCommonAlignment();
409 if (!Layout.getSymbolOffset(&Data, Res))
412 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
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 (MCSymbolData &OriginalData : Asm.symbols()) {
424 const MCSymbol &Alias = OriginalData.getSymbol();
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.SymbolData;
496 assert((!OrigData.getFragment() ||
497 (&OrigData.getFragment()->getParent()->getSection() ==
498 &OrigData.getSymbol().getSection())) &&
499 "The symbol's section doesn't match the fragment's symbol");
500 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
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(OrigData, 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 const 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.SymbolData;
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.SymbolData;
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 const 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 MCSymbolData *SD,
628 unsigned Type) const {
629 // A PCRel relocation to an absolute value has no symbol (or section). We
630 // represent that with a relocation to a null section.
634 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
638 // The .odp creation emits a relocation against the symbol ".TOC." which
639 // create a R_PPC64_TOC relocation. However the relocation symbol name
640 // in final object creation should be NULL, since the symbol does not
641 // really exist, it is just the reference to TOC base for the current
642 // object file. Since the symbol is undefined, returning false results
643 // in a relocation with a null section which is the desired result.
644 case MCSymbolRefExpr::VK_PPC_TOCBASE:
647 // These VariantKind cause the relocation to refer to something other than
648 // the symbol itself, like a linker generated table. Since the address of
649 // symbol is not relevant, we cannot replace the symbol with the
650 // section and patch the difference in the addend.
651 case MCSymbolRefExpr::VK_GOT:
652 case MCSymbolRefExpr::VK_PLT:
653 case MCSymbolRefExpr::VK_GOTPCREL:
654 case MCSymbolRefExpr::VK_Mips_GOT:
655 case MCSymbolRefExpr::VK_PPC_GOT_LO:
656 case MCSymbolRefExpr::VK_PPC_GOT_HI:
657 case MCSymbolRefExpr::VK_PPC_GOT_HA:
661 // An undefined symbol is not in any section, so the relocation has to point
662 // to the symbol itself.
663 const MCSymbol &Sym = SD->getSymbol();
664 if (Sym.isUndefined())
667 unsigned Binding = MCELF::GetBinding(*SD);
670 llvm_unreachable("Invalid Binding");
674 // If the symbol is weak, it might be overridden by a symbol in another
675 // file. The relocation has to point to the symbol so that the linker
678 case ELF::STB_GLOBAL:
679 // Global ELF symbols can be preempted by the dynamic linker. The relocation
680 // has to point to the symbol for a reason analogous to the STB_WEAK case.
684 // If a relocation points to a mergeable section, we have to be careful.
685 // If the offset is zero, a relocation with the section will encode the
686 // same information. With a non-zero offset, the situation is different.
687 // For example, a relocation can point 42 bytes past the end of a string.
688 // If we change such a relocation to use the section, the linker would think
689 // that it pointed to another string and subtracting 42 at runtime will
690 // produce the wrong value.
691 auto &Sec = cast<MCSectionELF>(Sym.getSection());
692 unsigned Flags = Sec.getFlags();
693 if (Flags & ELF::SHF_MERGE) {
697 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
698 // only handle section relocations to mergeable sections if using RELA.
699 if (!hasRelocationAddend())
703 // Most TLS relocations use a got, so they need the symbol. Even those that
704 // are just an offset (@tpoff), require a symbol in gold versions before
705 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
706 // http://sourceware.org/PR16773.
707 if (Flags & ELF::SHF_TLS)
710 // If the symbol is a thumb function the final relocation must set the lowest
711 // bit. With a symbol that is done by just having the symbol have that bit
712 // set, so we would lose the bit if we relocated with the section.
713 // FIXME: We could use the section but add the bit to the relocation value.
714 if (Asm.isThumbFunc(&Sym))
717 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
722 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
723 const MCSymbol &Sym = Ref.getSymbol();
725 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
728 if (!Sym.isVariable())
731 const MCExpr *Expr = Sym.getVariableValue();
732 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
736 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
737 return &Inner->getSymbol();
741 // True if the assembler knows nothing about the final value of the symbol.
742 // This doesn't cover the comdat issues, since in those cases the assembler
743 // can at least know that all symbols in the section will move together.
744 static bool isWeak(const MCSymbolData &D) {
745 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
748 switch (MCELF::GetBinding(D)) {
750 llvm_unreachable("Unknown binding");
753 case ELF::STB_GLOBAL:
756 case ELF::STB_GNU_UNIQUE:
761 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
762 const MCAsmLayout &Layout,
763 const MCFragment *Fragment,
764 const MCFixup &Fixup, MCValue Target,
765 bool &IsPCRel, uint64_t &FixedValue) {
766 const MCSectionData *FixupSectionD = Fragment->getParent();
767 const MCSectionELF &FixupSection =
768 cast<MCSectionELF>(FixupSectionD->getSection());
769 uint64_t C = Target.getConstant();
770 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
772 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
773 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
774 "Should not have constructed this");
776 // Let A, B and C being the components of Target and R be the location of
777 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
778 // If it is pcrel, we want to compute (A - B + C - R).
780 // In general, ELF has no relocations for -B. It can only represent (A + C)
781 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
782 // replace B to implement it: (A - R - K + C)
784 Asm.getContext().FatalError(
786 "No relocation available to represent this relative expression");
788 const MCSymbol &SymB = RefB->getSymbol();
790 if (SymB.isUndefined())
791 Asm.getContext().FatalError(
793 Twine("symbol '") + SymB.getName() +
794 "' can not be undefined in a subtraction expression");
796 assert(!SymB.isAbsolute() && "Should have been folded");
797 const MCSection &SecB = SymB.getSection();
798 if (&SecB != &FixupSection)
799 Asm.getContext().FatalError(
800 Fixup.getLoc(), "Cannot represent a difference across sections");
802 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
804 Asm.getContext().FatalError(
805 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
807 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
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;
816 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
818 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
819 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
820 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
821 C += Layout.getSymbolOffset(SymAD);
824 if (hasRelocationAddend()) {
831 // FIXME: What is this!?!?
832 MCSymbolRefExpr::VariantKind Modifier =
833 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
834 if (RelocNeedsGOT(Modifier))
837 if (!RelocateWithSymbol) {
838 const MCSection *SecA =
839 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
840 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
841 MCSymbol *SectionSymbol =
842 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
844 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
845 Relocations[&FixupSection].push_back(Rec);
850 if (const MCSymbol *R = Renames.lookup(SymA))
853 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
854 WeakrefUsedInReloc.insert(WeakRef);
856 UsedInReloc.insert(SymA);
858 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
859 Relocations[&FixupSection].push_back(Rec);
865 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
867 const MCSymbolData &SD = Asm.getSymbolData(*S);
868 return SD.getIndex();
871 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
872 const MCSymbolData &Data, bool Used,
874 const MCSymbol &Symbol = Data.getSymbol();
875 if (Symbol.isVariable()) {
876 const MCExpr *Expr = Symbol.getVariableValue();
877 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
878 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
889 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
892 if (Symbol.isVariable()) {
893 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
894 if (Base && Base->isUndefined())
898 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
899 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
902 if (Symbol.isTemporary())
908 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
909 if (Data.isExternal())
912 const MCSymbol &Symbol = Data.getSymbol();
913 if (Symbol.isDefined())
922 void ELFObjectWriter::computeSymbolTable(
923 MCAssembler &Asm, const MCAsmLayout &Layout,
924 const SectionIndexMapTy &SectionIndexMap,
925 const RevGroupMapTy &RevGroupMap) {
926 // FIXME: Is this the correct place to do this?
927 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
929 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
930 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
931 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
932 Data.setExternal(true);
933 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
936 // Add the data for the symbols.
937 for (MCSymbolData &SD : Asm.symbols()) {
938 const MCSymbol &Symbol = SD.getSymbol();
940 bool Used = UsedInReloc.count(&Symbol);
941 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
942 bool isSignature = RevGroupMap.count(&Symbol);
944 if (!isInSymtab(Layout, SD,
945 Used || WeakrefUsed || isSignature,
946 Renames.count(&Symbol)))
950 MSD.SymbolData = &SD;
951 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
953 // Undefined symbols are global, but this is the first place we
954 // are able to set it.
955 bool Local = isLocal(SD, Used);
956 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
958 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
959 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
960 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
964 MSD.SectionIndex = ELF::SHN_ABS;
965 } else if (SD.isCommon()) {
967 MSD.SectionIndex = ELF::SHN_COMMON;
968 } else if (BaseSymbol->isUndefined()) {
969 if (isSignature && !Used)
970 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
972 MSD.SectionIndex = ELF::SHN_UNDEF;
973 if (!Used && WeakrefUsed)
974 MCELF::SetBinding(SD, ELF::STB_WEAK);
976 const MCSectionELF &Section =
977 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
978 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
979 assert(MSD.SectionIndex && "Invalid section index!");
982 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
985 // FIXME: All name handling should be done before we get to the writer,
986 // including dealing with GNU-style version suffixes. Fixing this isn't
989 // We thus have to be careful to not perform the symbol version replacement
992 // The ELF format is used on Windows by the MCJIT engine. Thus, on
993 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
994 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
995 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
996 // the EFLObjectWriter should not interpret the "@@@" sub-string as
997 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
998 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
999 // "__imp_?" or "__imp_@?".
1001 // It would have been interesting to perform the MS mangling prefix check
1002 // only when the target triple is of the form *-pc-windows-elf. But, it
1003 // seems that this information is not easily accessible from the
1005 StringRef Name = Symbol.getName();
1006 if (!Name.startswith("?") && !Name.startswith("@?") &&
1007 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1008 // This symbol isn't following the MSVC C++ name mangling convention. We
1009 // can thus safely interpret the @@@ in symbol names as specifying symbol
1011 SmallString<32> Buf;
1012 size_t Pos = Name.find("@@@");
1013 if (Pos != StringRef::npos) {
1014 Buf += Name.substr(0, Pos);
1015 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1016 Buf += Name.substr(Pos + Skip);
1021 // Sections have their own string table
1022 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1023 MSD.Name = StrTabBuilder.add(Name);
1025 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1026 UndefinedSymbolData.push_back(MSD);
1028 LocalSymbolData.push_back(MSD);
1030 ExternalSymbolData.push_back(MSD);
1033 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1034 StrTabBuilder.add(*i);
1036 StrTabBuilder.finalize(StringTableBuilder::ELF);
1038 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1039 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1041 for (ELFSymbolData &MSD : LocalSymbolData)
1042 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1044 : StrTabBuilder.getOffset(MSD.Name);
1045 for (ELFSymbolData &MSD : ExternalSymbolData)
1046 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1047 for (ELFSymbolData& MSD : UndefinedSymbolData)
1048 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1050 // Symbols are required to be in lexicographic order.
1051 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1052 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1053 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1055 // Set the symbol indices. Local symbols must come before all other
1056 // symbols with non-local bindings.
1057 unsigned Index = FileSymbolData.size() + 1;
1058 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1059 LocalSymbolData[i].SymbolData->setIndex(Index++);
1061 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1062 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1063 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1064 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1067 const MCSectionELF *
1068 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1069 const MCSectionELF &Sec) {
1070 if (Relocations[&Sec].empty())
1073 MCContext &Ctx = Asm.getContext();
1074 const StringRef SectionName = Sec.getSectionName();
1075 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1076 RelaSectionName += SectionName;
1079 if (hasRelocationAddend())
1080 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1082 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1085 if (Sec.getFlags() & ELF::SHF_GROUP)
1086 Flags = ELF::SHF_GROUP;
1088 const MCSectionELF *RelaSection = Ctx.createELFRelSection(
1089 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1090 Flags, EntrySize, Sec.getGroup(), &Sec);
1091 MCSectionData &RelSD = Asm.getOrCreateSectionData(*RelaSection);
1092 RelSD.setAlignment(is64Bit() ? 8 : 4);
1096 static SmallVector<char, 128>
1097 getUncompressedData(const MCAsmLayout &Layout,
1098 const MCSectionData::FragmentListType &Fragments) {
1099 SmallVector<char, 128> UncompressedData;
1100 for (const MCFragment &F : Fragments) {
1101 const SmallVectorImpl<char> *Contents;
1102 switch (F.getKind()) {
1103 case MCFragment::FT_Data:
1104 Contents = &cast<MCDataFragment>(F).getContents();
1106 case MCFragment::FT_Dwarf:
1107 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1109 case MCFragment::FT_DwarfFrame:
1110 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1114 "Not expecting any other fragment types in a debug_* section");
1116 UncompressedData.append(Contents->begin(), Contents->end());
1118 return UncompressedData;
1121 // Include the debug info compression header:
1122 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1123 // useful for consumers to preallocate a buffer to decompress into.
1125 prependCompressionHeader(uint64_t Size,
1126 SmallVectorImpl<char> &CompressedContents) {
1127 const StringRef Magic = "ZLIB";
1128 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1130 if (sys::IsLittleEndianHost)
1131 sys::swapByteOrder(Size);
1132 CompressedContents.insert(CompressedContents.begin(),
1133 Magic.size() + sizeof(Size), 0);
1134 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1135 std::copy(reinterpret_cast<char *>(&Size),
1136 reinterpret_cast<char *>(&Size + 1),
1137 CompressedContents.begin() + Magic.size());
1141 void ELFObjectWriter::writeSectionData(const MCAssembler &Asm,
1142 const MCSectionData &SD,
1143 const MCAsmLayout &Layout) {
1144 const MCSectionELF &Section =
1145 static_cast<const MCSectionELF &>(SD.getSection());
1146 StringRef SectionName = Section.getSectionName();
1148 // Compressing debug_frame requires handling alignment fragments which is
1149 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1150 // for writing to arbitrary buffers) for little benefit.
1151 if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
1152 !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
1153 Asm.writeSectionData(&SD, Layout);
1157 // Gather the uncompressed data from all the fragments.
1158 const MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1159 SmallVector<char, 128> UncompressedData =
1160 getUncompressedData(Layout, Fragments);
1162 SmallVector<char, 128> CompressedContents;
1163 zlib::Status Success = zlib::compress(
1164 StringRef(UncompressedData.data(), UncompressedData.size()),
1165 CompressedContents);
1166 if (Success != zlib::StatusOK) {
1167 Asm.writeSectionData(&SD, Layout);
1171 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
1172 Asm.writeSectionData(&SD, Layout);
1175 Asm.getContext().renameELFSection(&Section,
1176 (".z" + SectionName.drop_front(1)).str());
1177 OS << CompressedContents;
1180 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1181 uint64_t Flags, uint64_t Address,
1182 uint64_t Offset, uint64_t Size,
1183 uint32_t Link, uint32_t Info,
1185 uint64_t EntrySize) {
1186 Write32(Name); // sh_name: index into string table
1187 Write32(Type); // sh_type
1188 WriteWord(Flags); // sh_flags
1189 WriteWord(Address); // sh_addr
1190 WriteWord(Offset); // sh_offset
1191 WriteWord(Size); // sh_size
1192 Write32(Link); // sh_link
1193 Write32(Info); // sh_info
1194 WriteWord(Alignment); // sh_addralign
1195 WriteWord(EntrySize); // sh_entsize
1198 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1199 const MCSectionELF &Sec) {
1200 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1202 // Sort the relocation entries. Most targets just sort by Offset, but some
1203 // (e.g., MIPS) have additional constraints.
1204 TargetObjectWriter->sortRelocs(Asm, Relocs);
1206 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1207 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1209 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1212 write(Entry.Offset);
1213 if (TargetObjectWriter->isN64()) {
1214 write(uint32_t(Index));
1216 write(TargetObjectWriter->getRSsym(Entry.Type));
1217 write(TargetObjectWriter->getRType3(Entry.Type));
1218 write(TargetObjectWriter->getRType2(Entry.Type));
1219 write(TargetObjectWriter->getRType(Entry.Type));
1221 struct ELF::Elf64_Rela ERE64;
1222 ERE64.setSymbolAndType(Index, Entry.Type);
1223 write(ERE64.r_info);
1225 if (hasRelocationAddend())
1226 write(Entry.Addend);
1228 write(uint32_t(Entry.Offset));
1230 struct ELF::Elf32_Rela ERE32;
1231 ERE32.setSymbolAndType(Index, Entry.Type);
1232 write(ERE32.r_info);
1234 if (hasRelocationAddend())
1235 write(uint32_t(Entry.Addend));
1240 const MCSectionELF *ELFObjectWriter::createSectionHeaderStringTable() {
1241 const MCSectionELF *ShstrtabSection = SectionTable[ShstrtabIndex - 1];
1242 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1243 OS << ShStrTabBuilder.data();
1244 return ShstrtabSection;
1247 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1248 const MCSectionELF *StrtabSection =
1249 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1250 StringTableIndex = addToSectionTable(StrtabSection);
1251 OS << StrTabBuilder.data();
1252 return StrtabSection;
1255 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1256 const SectionIndexMapTy &SectionIndexMap,
1257 uint32_t GroupSymbolIndex,
1258 uint64_t Offset, uint64_t Size,
1260 const MCSectionELF &Section) {
1261 uint64_t sh_link = 0;
1262 uint64_t sh_info = 0;
1264 switch(Section.getType()) {
1269 case ELF::SHT_DYNAMIC:
1270 llvm_unreachable("SHT_DYNAMIC in a relocatable object");
1273 case ELF::SHT_RELA: {
1274 sh_link = SymbolTableIndex;
1275 assert(sh_link && ".symtab not found");
1276 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1277 sh_info = SectionIndexMap.lookup(InfoSection);
1281 case ELF::SHT_SYMTAB:
1282 case ELF::SHT_DYNSYM:
1283 sh_link = StringTableIndex;
1284 sh_info = LastLocalSymbolIndex;
1287 case ELF::SHT_SYMTAB_SHNDX:
1288 sh_link = SymbolTableIndex;
1291 case ELF::SHT_GROUP:
1292 sh_link = SymbolTableIndex;
1293 sh_info = GroupSymbolIndex;
1297 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1298 Section.getType() == ELF::SHT_ARM_EXIDX)
1299 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1301 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1303 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1304 Alignment, Section.getEntrySize());
1307 void ELFObjectWriter::writeSectionHeader(
1308 MCAssembler &Asm, const MCAsmLayout &Layout,
1309 const SectionIndexMapTy &SectionIndexMap,
1310 const SectionOffsetsTy &SectionOffsets) {
1311 const unsigned NumSections = SectionTable.size();
1313 // Null section first.
1314 uint64_t FirstSectionSize =
1315 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1316 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1318 for (const MCSectionELF *Section : SectionTable) {
1319 const MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1320 uint32_t GroupSymbolIndex;
1321 unsigned Type = Section->getType();
1322 if (Type != ELF::SHT_GROUP)
1323 GroupSymbolIndex = 0;
1325 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section->getGroup());
1327 const std::pair<uint64_t, uint64_t> &Offsets =
1328 SectionOffsets.find(Section)->second;
1329 uint64_t Size = Type == ELF::SHT_NOBITS ? Layout.getSectionAddressSize(&SD)
1330 : Offsets.second - Offsets.first;
1332 writeSection(Asm, SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1333 SD.getAlignment(), *Section);
1337 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1338 const MCAsmLayout &Layout) {
1339 MCContext &Ctx = Asm.getContext();
1340 const MCSectionELF *ShstrtabSection =
1341 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1342 ShstrtabIndex = addToSectionTable(ShstrtabSection);
1344 RevGroupMapTy RevGroupMap;
1345 SectionIndexMapTy SectionIndexMap;
1347 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1349 // Write out the ELF header ...
1352 // ... then the sections ...
1353 SectionOffsetsTy SectionOffsets;
1354 bool ComputedSymtab = false;
1355 for (const MCSectionData &SD : Asm) {
1356 const MCSectionELF &Section =
1357 static_cast<const MCSectionELF &>(SD.getSection());
1359 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1360 WriteZeros(Padding);
1362 // Remember the offset into the file for this section.
1363 uint64_t SecStart = OS.tell();
1365 const MCSymbol *SignatureSymbol = Section.getGroup();
1366 unsigned Type = Section.getType();
1367 if (Type == ELF::SHT_GROUP) {
1368 assert(SignatureSymbol);
1369 write(uint32_t(ELF::GRP_COMDAT));
1370 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1371 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1374 } else if (Type == ELF::SHT_REL || Type == ELF::SHT_RELA) {
1375 if (!ComputedSymtab) {
1376 // Compute symbol table information.
1377 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1378 ComputedSymtab = true;
1380 writeRelocations(Asm, *Section.getAssociatedSection());
1382 writeSectionData(Asm, SD, Layout);
1385 uint64_t SecEnd = OS.tell();
1386 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1388 if (Type == ELF::SHT_GROUP || Type == ELF::SHT_REL || Type == ELF::SHT_RELA)
1391 const MCSectionELF *RelSection = createRelocationSection(Asm, Section);
1393 if (SignatureSymbol) {
1394 Asm.getOrCreateSymbolData(*SignatureSymbol);
1395 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1397 const MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1398 GroupIdx = addToSectionTable(Group);
1399 MCSectionData *GroupD = &Asm.getOrCreateSectionData(*Group);
1400 GroupD->setAlignment(4);
1402 GroupMembers[SignatureSymbol].push_back(&Section);
1404 GroupMembers[SignatureSymbol].push_back(RelSection);
1407 SectionIndexMap[&Section] = addToSectionTable(&Section);
1409 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1412 if (!ComputedSymtab) {
1413 // Compute symbol table information.
1414 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1415 ComputedSymtab = true;
1418 WriteSymbolTable(Asm, Layout, SectionOffsets);
1421 uint64_t SecStart = OS.tell();
1422 const MCSectionELF *Sec = createStringTable(Ctx);
1423 uint64_t SecEnd = OS.tell();
1424 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1428 uint64_t SecStart = OS.tell();
1429 const MCSectionELF *Sec = createSectionHeaderStringTable();
1430 uint64_t SecEnd = OS.tell();
1431 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1434 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1435 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1436 WriteZeros(Padding);
1438 const unsigned SectionHeaderOffset = OS.tell();
1440 // ... then the section header table ...
1441 writeSectionHeader(Asm, Layout, SectionIndexMap, SectionOffsets);
1443 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1444 ? (uint16_t)ELF::SHN_UNDEF
1445 : SectionTable.size() + 1;
1446 if (sys::IsLittleEndianHost != IsLittleEndian)
1447 sys::swapByteOrder(NumSections);
1448 unsigned NumSectionsOffset;
1451 uint64_t Val = SectionHeaderOffset;
1452 if (sys::IsLittleEndianHost != IsLittleEndian)
1453 sys::swapByteOrder(Val);
1454 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1455 offsetof(ELF::Elf64_Ehdr, e_shoff));
1456 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1458 uint32_t Val = SectionHeaderOffset;
1459 if (sys::IsLittleEndianHost != IsLittleEndian)
1460 sys::swapByteOrder(Val);
1461 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1462 offsetof(ELF::Elf32_Ehdr, e_shoff));
1463 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1465 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1469 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1470 const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
1471 bool InSet, bool IsPCRel) const {
1474 if (::isWeak(DataA))
1477 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
1481 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
1485 // It is invalid to replace a reference to a global in a comdat
1486 // with a reference to a local since out of comdat references
1487 // to a local are forbidden.
1488 // We could try to return false for more cases, like the reference
1489 // being in the same comdat or Sym being an alias to another global,
1490 // but it is not clear if it is worth the effort.
1491 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1494 const MCSymbol &Sym = SD.getSymbol();
1495 if (!Sym.isInSection())
1498 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1499 return Sec.getGroup();
1502 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1503 raw_pwrite_stream &OS,
1504 bool IsLittleEndian) {
1505 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);