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();
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 MCSymbolData *SD, 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 const 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(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);
248 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
249 const MCSymbolData &DataA,
250 const MCFragment &FB,
252 bool IsPCRel) const override;
254 bool isWeak(const MCSymbolData &SD) const override;
256 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
257 void writeSection(MCAssembler &Asm,
258 const SectionIndexMapTy &SectionIndexMap,
259 uint32_t GroupSymbolIndex,
260 uint64_t Offset, uint64_t Size, uint64_t Alignment,
261 const MCSectionELF &Section);
265 unsigned ELFObjectWriter::addToSectionTable(const MCSectionELF *Sec) {
266 SectionTable.push_back(Sec);
267 ShStrTabBuilder.add(Sec->getSectionName());
268 return SectionTable.size();
271 void SymbolTableWriter::createSymtabShndx() {
272 if (!ShndxIndexes.empty())
275 ShndxIndexes.resize(NumWritten);
278 template <typename T> void SymbolTableWriter::write(T Value) {
279 EWriter.write(Value);
282 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
283 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
285 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
286 uint64_t size, uint8_t other,
287 uint32_t shndx, bool Reserved) {
288 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
293 if (!ShndxIndexes.empty()) {
295 ShndxIndexes.push_back(shndx);
297 ShndxIndexes.push_back(0);
300 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
303 write(name); // st_name
304 write(info); // st_info
305 write(other); // st_other
306 write(Index); // st_shndx
307 write(value); // st_value
308 write(size); // st_size
310 write(name); // st_name
311 write(uint32_t(value)); // st_value
312 write(uint32_t(size)); // st_size
313 write(info); // st_info
314 write(other); // st_other
315 write(Index); // st_shndx
321 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
322 const MCFixupKindInfo &FKI =
323 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
325 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
328 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
332 case MCSymbolRefExpr::VK_GOT:
333 case MCSymbolRefExpr::VK_PLT:
334 case MCSymbolRefExpr::VK_GOTPCREL:
335 case MCSymbolRefExpr::VK_GOTOFF:
336 case MCSymbolRefExpr::VK_TPOFF:
337 case MCSymbolRefExpr::VK_TLSGD:
338 case MCSymbolRefExpr::VK_GOTTPOFF:
339 case MCSymbolRefExpr::VK_INDNTPOFF:
340 case MCSymbolRefExpr::VK_NTPOFF:
341 case MCSymbolRefExpr::VK_GOTNTPOFF:
342 case MCSymbolRefExpr::VK_TLSLDM:
343 case MCSymbolRefExpr::VK_DTPOFF:
344 case MCSymbolRefExpr::VK_TLSLD:
349 ELFObjectWriter::~ELFObjectWriter()
352 // Emit the ELF header.
353 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
359 // emitWord method behaves differently for ELF32 and ELF64, writing
360 // 4 bytes in the former and 8 in the latter.
362 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
364 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
367 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
369 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
371 Write8(TargetObjectWriter->getOSABI());
372 Write8(0); // e_ident[EI_ABIVERSION]
374 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
376 Write16(ELF::ET_REL); // e_type
378 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
380 Write32(ELF::EV_CURRENT); // e_version
381 WriteWord(0); // e_entry, no entry point in .o file
382 WriteWord(0); // e_phoff, no program header for .o
383 WriteWord(0); // e_shoff = sec hdr table off in bytes
385 // e_flags = whatever the target wants
386 Write32(Asm.getELFHeaderEFlags());
388 // e_ehsize = ELF header size
389 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
391 Write16(0); // e_phentsize = prog header entry size
392 Write16(0); // e_phnum = # prog header entries = 0
394 // e_shentsize = Section header entry size
395 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
397 // e_shnum = # of section header ents
400 // e_shstrndx = Section # of '.shstrtab'
401 assert(ShstrtabIndex < ELF::SHN_LORESERVE);
402 Write16(ShstrtabIndex);
405 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
406 const MCAsmLayout &Layout) {
407 if (Data.isCommon() && Data.isExternal())
408 return Data.getCommonAlignment();
411 if (!Layout.getSymbolOffset(&Data, Res))
414 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
420 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
421 const MCAsmLayout &Layout) {
422 // The presence of symbol versions causes undefined symbols and
423 // versions declared with @@@ to be renamed.
425 for (MCSymbolData &OriginalData : Asm.symbols()) {
426 const MCSymbol &Alias = OriginalData.getSymbol();
429 if (!Alias.isVariable())
431 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
434 const MCSymbol &Symbol = Ref->getSymbol();
435 MCSymbolData &SD = Asm.getSymbolData(Symbol);
437 StringRef AliasName = Alias.getName();
438 size_t Pos = AliasName.find('@');
439 if (Pos == StringRef::npos)
442 // Aliases defined with .symvar copy the binding from the symbol they alias.
443 // This is the first place we are able to copy this information.
444 OriginalData.setExternal(SD.isExternal());
445 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
447 StringRef Rest = AliasName.substr(Pos);
448 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
451 // FIXME: produce a better error message.
452 if (Symbol.isUndefined() && Rest.startswith("@@") &&
453 !Rest.startswith("@@@"))
454 report_fatal_error("A @@ version cannot be undefined");
456 Renames.insert(std::make_pair(&Symbol, &Alias));
460 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
461 uint8_t Type = newType;
463 // Propagation rules:
464 // IFUNC > FUNC > OBJECT > NOTYPE
465 // TLS_OBJECT > OBJECT > NOTYPE
467 // dont let the new type degrade the old type
471 case ELF::STT_GNU_IFUNC:
472 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
473 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
474 Type = ELF::STT_GNU_IFUNC;
477 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
478 Type == ELF::STT_TLS)
479 Type = ELF::STT_FUNC;
481 case ELF::STT_OBJECT:
482 if (Type == ELF::STT_NOTYPE)
483 Type = ELF::STT_OBJECT;
486 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
487 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
495 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
496 const MCAsmLayout &Layout) {
497 MCSymbolData &OrigData = *MSD.SymbolData;
498 assert((!OrigData.getFragment() ||
499 (&OrigData.getFragment()->getParent()->getSection() ==
500 &OrigData.getSymbol().getSection())) &&
501 "The symbol's section doesn't match the fragment's symbol");
502 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
504 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
506 bool IsReserved = !Base || OrigData.isCommon();
508 // Binding and Type share the same byte as upper and lower nibbles
509 uint8_t Binding = MCELF::GetBinding(OrigData);
510 uint8_t Type = MCELF::GetType(OrigData);
511 MCSymbolData *BaseSD = nullptr;
513 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
514 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
516 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
518 // Other and Visibility share the same byte with Visibility using the lower
520 uint8_t Visibility = MCELF::GetVisibility(OrigData);
521 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
524 uint64_t Value = SymbolValue(OrigData, Layout);
527 const MCExpr *ESize = OrigData.getSize();
529 ESize = BaseSD->getSize();
533 if (!ESize->evaluateKnownAbsolute(Res, Layout))
534 report_fatal_error("Size expression must be absolute.");
538 // Write out the symbol table entry
539 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
540 MSD.SectionIndex, IsReserved);
543 void ELFObjectWriter::WriteSymbolTable(MCAssembler &Asm,
544 const MCAsmLayout &Layout,
545 SectionOffsetsTy &SectionOffsets) {
547 MCContext &Ctx = Asm.getContext();
549 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
552 const MCSectionELF *SymtabSection =
553 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
554 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
555 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
556 SymbolTableIndex = addToSectionTable(SymtabSection);
558 // The string table must be emitted first because we need the index
559 // into the string table for all the symbol names.
561 SymbolTableWriter Writer(*this, is64Bit());
563 uint64_t Padding = OffsetToAlignment(OS.tell(), SymtabSD.getAlignment());
566 uint64_t SecStart = OS.tell();
568 // The first entry is the undefined symbol entry.
569 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
571 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
572 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
573 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
576 // Write the symbol table entries.
577 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
579 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
580 ELFSymbolData &MSD = LocalSymbolData[i];
581 WriteSymbol(Writer, MSD, Layout);
584 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
585 ELFSymbolData &MSD = ExternalSymbolData[i];
586 MCSymbolData &Data = *MSD.SymbolData;
587 assert(((Data.getFlags() & ELF_STB_Global) ||
588 (Data.getFlags() & ELF_STB_Weak)) &&
589 "External symbol requires STB_GLOBAL or STB_WEAK flag");
590 WriteSymbol(Writer, MSD, Layout);
591 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
592 LastLocalSymbolIndex++;
595 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
596 ELFSymbolData &MSD = UndefinedSymbolData[i];
597 MCSymbolData &Data = *MSD.SymbolData;
598 WriteSymbol(Writer, MSD, Layout);
599 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
600 LastLocalSymbolIndex++;
603 uint64_t SecEnd = OS.tell();
604 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
606 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
607 if (ShndxIndexes.empty())
610 SecStart = OS.tell();
611 const MCSectionELF *SymtabShndxSection =
612 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
613 addToSectionTable(SymtabShndxSection);
614 MCSectionData *SymtabShndxSD =
615 &Asm.getOrCreateSectionData(*SymtabShndxSection);
616 SymtabShndxSD->setAlignment(4);
617 for (uint32_t Index : ShndxIndexes)
620 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
623 // It is always valid to create a relocation with a symbol. It is preferable
624 // to use a relocation with a section if that is possible. Using the section
625 // allows us to omit some local symbols from the symbol table.
626 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
627 const MCSymbolRefExpr *RefA,
628 const MCSymbolData *SD,
630 unsigned Type) const {
631 // A PCRel relocation to an absolute value has no symbol (or section). We
632 // represent that with a relocation to a null section.
636 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
640 // The .odp creation emits a relocation against the symbol ".TOC." which
641 // create a R_PPC64_TOC relocation. However the relocation symbol name
642 // in final object creation should be NULL, since the symbol does not
643 // really exist, it is just the reference to TOC base for the current
644 // object file. Since the symbol is undefined, returning false results
645 // in a relocation with a null section which is the desired result.
646 case MCSymbolRefExpr::VK_PPC_TOCBASE:
649 // These VariantKind cause the relocation to refer to something other than
650 // the symbol itself, like a linker generated table. Since the address of
651 // symbol is not relevant, we cannot replace the symbol with the
652 // section and patch the difference in the addend.
653 case MCSymbolRefExpr::VK_GOT:
654 case MCSymbolRefExpr::VK_PLT:
655 case MCSymbolRefExpr::VK_GOTPCREL:
656 case MCSymbolRefExpr::VK_Mips_GOT:
657 case MCSymbolRefExpr::VK_PPC_GOT_LO:
658 case MCSymbolRefExpr::VK_PPC_GOT_HI:
659 case MCSymbolRefExpr::VK_PPC_GOT_HA:
663 // An undefined symbol is not in any section, so the relocation has to point
664 // to the symbol itself.
665 const MCSymbol &Sym = SD->getSymbol();
666 if (Sym.isUndefined())
669 unsigned Binding = MCELF::GetBinding(*SD);
672 llvm_unreachable("Invalid Binding");
676 // If the symbol is weak, it might be overridden by a symbol in another
677 // file. The relocation has to point to the symbol so that the linker
680 case ELF::STB_GLOBAL:
681 // Global ELF symbols can be preempted by the dynamic linker. The relocation
682 // has to point to the symbol for a reason analogous to the STB_WEAK case.
686 // If a relocation points to a mergeable section, we have to be careful.
687 // If the offset is zero, a relocation with the section will encode the
688 // same information. With a non-zero offset, the situation is different.
689 // For example, a relocation can point 42 bytes past the end of a string.
690 // If we change such a relocation to use the section, the linker would think
691 // that it pointed to another string and subtracting 42 at runtime will
692 // produce the wrong value.
693 auto &Sec = cast<MCSectionELF>(Sym.getSection());
694 unsigned Flags = Sec.getFlags();
695 if (Flags & ELF::SHF_MERGE) {
699 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
700 // only handle section relocations to mergeable sections if using RELA.
701 if (!hasRelocationAddend())
705 // Most TLS relocations use a got, so they need the symbol. Even those that
706 // are just an offset (@tpoff), require a symbol in gold versions before
707 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
708 // http://sourceware.org/PR16773.
709 if (Flags & ELF::SHF_TLS)
712 // If the symbol is a thumb function the final relocation must set the lowest
713 // bit. With a symbol that is done by just having the symbol have that bit
714 // set, so we would lose the bit if we relocated with the section.
715 // FIXME: We could use the section but add the bit to the relocation value.
716 if (Asm.isThumbFunc(&Sym))
719 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
724 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
725 const MCSymbol &Sym = Ref.getSymbol();
727 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
730 if (!Sym.isVariable())
733 const MCExpr *Expr = Sym.getVariableValue();
734 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
738 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
739 return &Inner->getSymbol();
743 // True if the assembler knows nothing about the final value of the symbol.
744 // This doesn't cover the comdat issues, since in those cases the assembler
745 // can at least know that all symbols in the section will move together.
746 static bool isWeak(const MCSymbolData &D) {
747 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
750 switch (MCELF::GetBinding(D)) {
752 llvm_unreachable("Unknown binding");
755 case ELF::STB_GLOBAL:
758 case ELF::STB_GNU_UNIQUE:
763 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
764 const MCAsmLayout &Layout,
765 const MCFragment *Fragment,
766 const MCFixup &Fixup, MCValue Target,
767 bool &IsPCRel, uint64_t &FixedValue) {
768 const MCSectionData *FixupSectionD = Fragment->getParent();
769 const MCSectionELF &FixupSection =
770 cast<MCSectionELF>(FixupSectionD->getSection());
771 uint64_t C = Target.getConstant();
772 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
774 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
775 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
776 "Should not have constructed this");
778 // Let A, B and C being the components of Target and R be the location of
779 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
780 // If it is pcrel, we want to compute (A - B + C - R).
782 // In general, ELF has no relocations for -B. It can only represent (A + C)
783 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
784 // replace B to implement it: (A - R - K + C)
786 Asm.getContext().FatalError(
788 "No relocation available to represent this relative expression");
790 const MCSymbol &SymB = RefB->getSymbol();
792 if (SymB.isUndefined())
793 Asm.getContext().FatalError(
795 Twine("symbol '") + SymB.getName() +
796 "' can not be undefined in a subtraction expression");
798 assert(!SymB.isAbsolute() && "Should have been folded");
799 const MCSection &SecB = SymB.getSection();
800 if (&SecB != &FixupSection)
801 Asm.getContext().FatalError(
802 Fixup.getLoc(), "Cannot represent a difference across sections");
804 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
806 Asm.getContext().FatalError(
807 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
809 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
810 uint64_t K = SymBOffset - FixupOffset;
815 // We either rejected the fixup or folded B into C at this point.
816 const MCSymbolRefExpr *RefA = Target.getSymA();
817 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
818 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
820 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
821 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
822 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
823 C += Layout.getSymbolOffset(SymAD);
826 if (hasRelocationAddend()) {
833 // FIXME: What is this!?!?
834 MCSymbolRefExpr::VariantKind Modifier =
835 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
836 if (RelocNeedsGOT(Modifier))
839 if (!RelocateWithSymbol) {
840 const MCSection *SecA =
841 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
842 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
843 MCSymbol *SectionSymbol =
844 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
846 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
847 Relocations[&FixupSection].push_back(Rec);
852 if (const MCSymbol *R = Renames.lookup(SymA))
855 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
856 WeakrefUsedInReloc.insert(WeakRef);
858 UsedInReloc.insert(SymA);
860 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
861 Relocations[&FixupSection].push_back(Rec);
867 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
869 const MCSymbolData &SD = Asm.getSymbolData(*S);
870 return SD.getIndex();
873 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
874 const MCSymbolData &Data, bool Used,
876 const MCSymbol &Symbol = Data.getSymbol();
877 if (Symbol.isVariable()) {
878 const MCExpr *Expr = Symbol.getVariableValue();
879 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
880 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
891 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
894 if (Symbol.isVariable()) {
895 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
896 if (Base && Base->isUndefined())
900 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
901 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
904 if (Symbol.isTemporary())
910 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
911 if (Data.isExternal())
914 const MCSymbol &Symbol = Data.getSymbol();
915 if (Symbol.isDefined())
924 void ELFObjectWriter::computeSymbolTable(
925 MCAssembler &Asm, const MCAsmLayout &Layout,
926 const SectionIndexMapTy &SectionIndexMap,
927 const RevGroupMapTy &RevGroupMap) {
928 // FIXME: Is this the correct place to do this?
929 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
931 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
932 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
933 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
934 Data.setExternal(true);
935 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
938 // Add the data for the symbols.
939 for (MCSymbolData &SD : Asm.symbols()) {
940 const MCSymbol &Symbol = SD.getSymbol();
942 bool Used = UsedInReloc.count(&Symbol);
943 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
944 bool isSignature = RevGroupMap.count(&Symbol);
946 if (!isInSymtab(Layout, SD,
947 Used || WeakrefUsed || isSignature,
948 Renames.count(&Symbol)))
952 MSD.SymbolData = &SD;
953 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
955 // Undefined symbols are global, but this is the first place we
956 // are able to set it.
957 bool Local = isLocal(SD, Used);
958 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
960 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
961 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
962 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
966 MSD.SectionIndex = ELF::SHN_ABS;
967 } else if (SD.isCommon()) {
969 MSD.SectionIndex = ELF::SHN_COMMON;
970 } else if (BaseSymbol->isUndefined()) {
971 if (isSignature && !Used)
972 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
974 MSD.SectionIndex = ELF::SHN_UNDEF;
975 if (!Used && WeakrefUsed)
976 MCELF::SetBinding(SD, ELF::STB_WEAK);
978 const MCSectionELF &Section =
979 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
980 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
981 assert(MSD.SectionIndex && "Invalid section index!");
984 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
987 // FIXME: All name handling should be done before we get to the writer,
988 // including dealing with GNU-style version suffixes. Fixing this isn't
991 // We thus have to be careful to not perform the symbol version replacement
994 // The ELF format is used on Windows by the MCJIT engine. Thus, on
995 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
996 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
997 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
998 // the EFLObjectWriter should not interpret the "@@@" sub-string as
999 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1000 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1001 // "__imp_?" or "__imp_@?".
1003 // It would have been interesting to perform the MS mangling prefix check
1004 // only when the target triple is of the form *-pc-windows-elf. But, it
1005 // seems that this information is not easily accessible from the
1007 StringRef Name = Symbol.getName();
1008 if (!Name.startswith("?") && !Name.startswith("@?") &&
1009 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1010 // This symbol isn't following the MSVC C++ name mangling convention. We
1011 // can thus safely interpret the @@@ in symbol names as specifying symbol
1013 SmallString<32> Buf;
1014 size_t Pos = Name.find("@@@");
1015 if (Pos != StringRef::npos) {
1016 Buf += Name.substr(0, Pos);
1017 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1018 Buf += Name.substr(Pos + Skip);
1023 // Sections have their own string table
1024 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1025 MSD.Name = StrTabBuilder.add(Name);
1027 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1028 UndefinedSymbolData.push_back(MSD);
1030 LocalSymbolData.push_back(MSD);
1032 ExternalSymbolData.push_back(MSD);
1035 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1036 StrTabBuilder.add(*i);
1038 StrTabBuilder.finalize(StringTableBuilder::ELF);
1040 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1041 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1043 for (ELFSymbolData &MSD : LocalSymbolData)
1044 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1046 : StrTabBuilder.getOffset(MSD.Name);
1047 for (ELFSymbolData &MSD : ExternalSymbolData)
1048 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1049 for (ELFSymbolData& MSD : UndefinedSymbolData)
1050 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1052 // Symbols are required to be in lexicographic order.
1053 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1054 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1055 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1057 // Set the symbol indices. Local symbols must come before all other
1058 // symbols with non-local bindings.
1059 unsigned Index = FileSymbolData.size() + 1;
1060 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1061 LocalSymbolData[i].SymbolData->setIndex(Index++);
1063 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1064 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1065 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1066 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1069 const MCSectionELF *
1070 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1071 const MCSectionELF &Sec) {
1072 if (Relocations[&Sec].empty())
1075 MCContext &Ctx = Asm.getContext();
1076 const StringRef SectionName = Sec.getSectionName();
1077 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1078 RelaSectionName += SectionName;
1081 if (hasRelocationAddend())
1082 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1084 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1087 if (Sec.getFlags() & ELF::SHF_GROUP)
1088 Flags = ELF::SHF_GROUP;
1090 const MCSectionELF *RelaSection = Ctx.createELFRelSection(
1091 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1092 Flags, EntrySize, Sec.getGroup(), &Sec);
1093 MCSectionData &RelSD = Asm.getOrCreateSectionData(*RelaSection);
1094 RelSD.setAlignment(is64Bit() ? 8 : 4);
1098 static SmallVector<char, 128>
1099 getUncompressedData(const MCAsmLayout &Layout,
1100 const MCSectionData::FragmentListType &Fragments) {
1101 SmallVector<char, 128> UncompressedData;
1102 for (const MCFragment &F : Fragments) {
1103 const SmallVectorImpl<char> *Contents;
1104 switch (F.getKind()) {
1105 case MCFragment::FT_Data:
1106 Contents = &cast<MCDataFragment>(F).getContents();
1108 case MCFragment::FT_Dwarf:
1109 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1111 case MCFragment::FT_DwarfFrame:
1112 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1116 "Not expecting any other fragment types in a debug_* section");
1118 UncompressedData.append(Contents->begin(), Contents->end());
1120 return UncompressedData;
1123 // Include the debug info compression header:
1124 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1125 // useful for consumers to preallocate a buffer to decompress into.
1127 prependCompressionHeader(uint64_t Size,
1128 SmallVectorImpl<char> &CompressedContents) {
1129 const StringRef Magic = "ZLIB";
1130 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1132 if (sys::IsLittleEndianHost)
1133 sys::swapByteOrder(Size);
1134 CompressedContents.insert(CompressedContents.begin(),
1135 Magic.size() + sizeof(Size), 0);
1136 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1137 std::copy(reinterpret_cast<char *>(&Size),
1138 reinterpret_cast<char *>(&Size + 1),
1139 CompressedContents.begin() + Magic.size());
1143 void ELFObjectWriter::writeSectionData(const MCAssembler &Asm,
1144 const MCSectionData &SD,
1145 const MCAsmLayout &Layout) {
1146 const MCSectionELF &Section =
1147 static_cast<const MCSectionELF &>(SD.getSection());
1148 StringRef SectionName = Section.getSectionName();
1150 // Compressing debug_frame requires handling alignment fragments which is
1151 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1152 // for writing to arbitrary buffers) for little benefit.
1153 if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
1154 !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
1155 Asm.writeSectionData(&SD, Layout);
1159 // Gather the uncompressed data from all the fragments.
1160 const MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1161 SmallVector<char, 128> UncompressedData =
1162 getUncompressedData(Layout, Fragments);
1164 SmallVector<char, 128> CompressedContents;
1165 zlib::Status Success = zlib::compress(
1166 StringRef(UncompressedData.data(), UncompressedData.size()),
1167 CompressedContents);
1168 if (Success != zlib::StatusOK) {
1169 Asm.writeSectionData(&SD, Layout);
1173 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
1174 Asm.writeSectionData(&SD, Layout);
1177 Asm.getContext().renameELFSection(&Section,
1178 (".z" + SectionName.drop_front(1)).str());
1179 OS << CompressedContents;
1182 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1183 uint64_t Flags, uint64_t Address,
1184 uint64_t Offset, uint64_t Size,
1185 uint32_t Link, uint32_t Info,
1187 uint64_t EntrySize) {
1188 Write32(Name); // sh_name: index into string table
1189 Write32(Type); // sh_type
1190 WriteWord(Flags); // sh_flags
1191 WriteWord(Address); // sh_addr
1192 WriteWord(Offset); // sh_offset
1193 WriteWord(Size); // sh_size
1194 Write32(Link); // sh_link
1195 Write32(Info); // sh_info
1196 WriteWord(Alignment); // sh_addralign
1197 WriteWord(EntrySize); // sh_entsize
1200 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1201 const MCSectionELF &Sec) {
1202 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1204 // Sort the relocation entries. Most targets just sort by Offset, but some
1205 // (e.g., MIPS) have additional constraints.
1206 TargetObjectWriter->sortRelocs(Asm, Relocs);
1208 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1209 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1211 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1214 write(Entry.Offset);
1215 if (TargetObjectWriter->isN64()) {
1216 write(uint32_t(Index));
1218 write(TargetObjectWriter->getRSsym(Entry.Type));
1219 write(TargetObjectWriter->getRType3(Entry.Type));
1220 write(TargetObjectWriter->getRType2(Entry.Type));
1221 write(TargetObjectWriter->getRType(Entry.Type));
1223 struct ELF::Elf64_Rela ERE64;
1224 ERE64.setSymbolAndType(Index, Entry.Type);
1225 write(ERE64.r_info);
1227 if (hasRelocationAddend())
1228 write(Entry.Addend);
1230 write(uint32_t(Entry.Offset));
1232 struct ELF::Elf32_Rela ERE32;
1233 ERE32.setSymbolAndType(Index, Entry.Type);
1234 write(ERE32.r_info);
1236 if (hasRelocationAddend())
1237 write(uint32_t(Entry.Addend));
1242 const MCSectionELF *ELFObjectWriter::createSectionHeaderStringTable() {
1243 const MCSectionELF *ShstrtabSection = SectionTable[ShstrtabIndex - 1];
1244 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1245 OS << ShStrTabBuilder.data();
1246 return ShstrtabSection;
1249 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1250 const MCSectionELF *StrtabSection =
1251 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1252 StringTableIndex = addToSectionTable(StrtabSection);
1253 OS << StrTabBuilder.data();
1254 return StrtabSection;
1257 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1258 const SectionIndexMapTy &SectionIndexMap,
1259 uint32_t GroupSymbolIndex,
1260 uint64_t Offset, uint64_t Size,
1262 const MCSectionELF &Section) {
1263 uint64_t sh_link = 0;
1264 uint64_t sh_info = 0;
1266 switch(Section.getType()) {
1271 case ELF::SHT_DYNAMIC:
1272 llvm_unreachable("SHT_DYNAMIC in a relocatable object");
1275 case ELF::SHT_RELA: {
1276 sh_link = SymbolTableIndex;
1277 assert(sh_link && ".symtab not found");
1278 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1279 sh_info = SectionIndexMap.lookup(InfoSection);
1283 case ELF::SHT_SYMTAB:
1284 case ELF::SHT_DYNSYM:
1285 sh_link = StringTableIndex;
1286 sh_info = LastLocalSymbolIndex;
1289 case ELF::SHT_SYMTAB_SHNDX:
1290 sh_link = SymbolTableIndex;
1293 case ELF::SHT_GROUP:
1294 sh_link = SymbolTableIndex;
1295 sh_info = GroupSymbolIndex;
1299 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1300 Section.getType() == ELF::SHT_ARM_EXIDX)
1301 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1303 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1305 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1306 Alignment, Section.getEntrySize());
1309 void ELFObjectWriter::writeSectionHeader(
1310 MCAssembler &Asm, const MCAsmLayout &Layout,
1311 const SectionIndexMapTy &SectionIndexMap,
1312 const SectionOffsetsTy &SectionOffsets) {
1313 const unsigned NumSections = SectionTable.size();
1315 // Null section first.
1316 uint64_t FirstSectionSize =
1317 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1318 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1320 for (const MCSectionELF *Section : SectionTable) {
1321 const MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1322 uint32_t GroupSymbolIndex;
1323 unsigned Type = Section->getType();
1324 if (Type != ELF::SHT_GROUP)
1325 GroupSymbolIndex = 0;
1327 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section->getGroup());
1329 const std::pair<uint64_t, uint64_t> &Offsets =
1330 SectionOffsets.find(Section)->second;
1331 uint64_t Size = Type == ELF::SHT_NOBITS ? Layout.getSectionAddressSize(&SD)
1332 : Offsets.second - Offsets.first;
1334 writeSection(Asm, SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1335 SD.getAlignment(), *Section);
1339 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1340 const MCAsmLayout &Layout) {
1341 MCContext &Ctx = Asm.getContext();
1342 const MCSectionELF *ShstrtabSection =
1343 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1344 ShstrtabIndex = addToSectionTable(ShstrtabSection);
1346 RevGroupMapTy RevGroupMap;
1347 SectionIndexMapTy SectionIndexMap;
1349 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1351 // Write out the ELF header ...
1354 // ... then the sections ...
1355 SectionOffsetsTy SectionOffsets;
1356 bool ComputedSymtab = false;
1357 for (const MCSectionData &SD : Asm) {
1358 const MCSectionELF &Section =
1359 static_cast<const MCSectionELF &>(SD.getSection());
1361 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1362 WriteZeros(Padding);
1364 // Remember the offset into the file for this section.
1365 uint64_t SecStart = OS.tell();
1367 const MCSymbol *SignatureSymbol = Section.getGroup();
1368 unsigned Type = Section.getType();
1369 if (Type == ELF::SHT_GROUP) {
1370 assert(SignatureSymbol);
1371 write(uint32_t(ELF::GRP_COMDAT));
1372 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1373 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1376 } else if (Type == ELF::SHT_REL || Type == ELF::SHT_RELA) {
1377 if (!ComputedSymtab) {
1378 // Compute symbol table information.
1379 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1380 ComputedSymtab = true;
1382 writeRelocations(Asm, *Section.getAssociatedSection());
1384 writeSectionData(Asm, SD, Layout);
1387 uint64_t SecEnd = OS.tell();
1388 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1390 if (Type == ELF::SHT_GROUP || Type == ELF::SHT_REL || Type == ELF::SHT_RELA)
1393 const MCSectionELF *RelSection = createRelocationSection(Asm, Section);
1395 if (SignatureSymbol) {
1396 Asm.getOrCreateSymbolData(*SignatureSymbol);
1397 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1399 const MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1400 GroupIdx = addToSectionTable(Group);
1401 MCSectionData *GroupD = &Asm.getOrCreateSectionData(*Group);
1402 GroupD->setAlignment(4);
1404 GroupMembers[SignatureSymbol].push_back(&Section);
1406 GroupMembers[SignatureSymbol].push_back(RelSection);
1409 SectionIndexMap[&Section] = addToSectionTable(&Section);
1411 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1414 if (!ComputedSymtab) {
1415 // Compute symbol table information.
1416 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1417 ComputedSymtab = true;
1420 WriteSymbolTable(Asm, Layout, SectionOffsets);
1423 uint64_t SecStart = OS.tell();
1424 const MCSectionELF *Sec = createStringTable(Ctx);
1425 uint64_t SecEnd = OS.tell();
1426 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1430 uint64_t SecStart = OS.tell();
1431 const MCSectionELF *Sec = createSectionHeaderStringTable();
1432 uint64_t SecEnd = OS.tell();
1433 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1436 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1437 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1438 WriteZeros(Padding);
1440 const unsigned SectionHeaderOffset = OS.tell();
1442 // ... then the section header table ...
1443 writeSectionHeader(Asm, Layout, SectionIndexMap, SectionOffsets);
1445 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1446 ? (uint16_t)ELF::SHN_UNDEF
1447 : SectionTable.size() + 1;
1448 if (sys::IsLittleEndianHost != IsLittleEndian)
1449 sys::swapByteOrder(NumSections);
1450 unsigned NumSectionsOffset;
1453 uint64_t Val = SectionHeaderOffset;
1454 if (sys::IsLittleEndianHost != IsLittleEndian)
1455 sys::swapByteOrder(Val);
1456 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1457 offsetof(ELF::Elf64_Ehdr, e_shoff));
1458 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1460 uint32_t Val = SectionHeaderOffset;
1461 if (sys::IsLittleEndianHost != IsLittleEndian)
1462 sys::swapByteOrder(Val);
1463 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1464 offsetof(ELF::Elf32_Ehdr, e_shoff));
1465 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1467 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1471 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1472 const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
1473 bool InSet, bool IsPCRel) const {
1476 if (::isWeak(DataA))
1479 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
1483 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
1487 // It is invalid to replace a reference to a global in a comdat
1488 // with a reference to a local since out of comdat references
1489 // to a local are forbidden.
1490 // We could try to return false for more cases, like the reference
1491 // being in the same comdat or Sym being an alias to another global,
1492 // but it is not clear if it is worth the effort.
1493 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1496 const MCSymbol &Sym = SD.getSymbol();
1497 if (!Sym.isInSection())
1500 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1501 return Sec.getGroup();
1504 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1505 raw_pwrite_stream &OS,
1506 bool IsLittleEndian) {
1507 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);