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;
136 // TargetObjectWriter wrappers.
137 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
138 bool hasRelocationAddend() const {
139 return TargetObjectWriter->hasRelocationAddend();
141 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
142 bool IsPCRel) const {
143 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
147 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
149 : MCObjectWriter(OS, IsLittleEndian), TargetObjectWriter(MOTW),
152 void reset() override {
154 WeakrefUsedInReloc.clear();
157 ShStrTabBuilder.clear();
158 StrTabBuilder.clear();
159 FileSymbolData.clear();
160 LocalSymbolData.clear();
161 ExternalSymbolData.clear();
162 UndefinedSymbolData.clear();
163 MCObjectWriter::reset();
166 ~ELFObjectWriter() override;
168 void WriteWord(uint64_t W) {
175 template <typename T> void write(T Val) {
177 support::endian::Writer<support::little>(OS).write(Val);
179 support::endian::Writer<support::big>(OS).write(Val);
182 template <typename T> void write(MCDataFragment &F, T Value);
184 void writeHeader(const MCAssembler &Asm);
186 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
187 const MCAsmLayout &Layout);
189 // Start and end offset of each section
190 typedef std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>
193 void WriteSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
194 std::vector<const MCSectionELF *> &Sections,
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 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
228 createSectionHeaderStringTable(MCAssembler &Asm,
229 std::vector<const MCSectionELF *> &Sections);
231 createStringTable(MCAssembler &Asm,
232 std::vector<const MCSectionELF *> &Sections);
234 void ExecutePostLayoutBinding(MCAssembler &Asm,
235 const MCAsmLayout &Layout) override;
237 void writeSectionHeader(ArrayRef<const MCSectionELF *> Sections,
238 MCAssembler &Asm, const MCAsmLayout &Layout,
239 const SectionIndexMapTy &SectionIndexMap,
240 const SectionOffsetsTy &SectionOffsets);
242 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
243 uint64_t Address, uint64_t Offset,
244 uint64_t Size, uint32_t Link, uint32_t Info,
245 uint64_t Alignment, uint64_t EntrySize);
247 void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
250 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
251 const MCSymbolData &DataA,
252 const MCFragment &FB,
254 bool IsPCRel) const override;
256 bool isWeak(const MCSymbolData &SD) const override;
258 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
259 void writeSection(MCAssembler &Asm,
260 const SectionIndexMapTy &SectionIndexMap,
261 uint32_t GroupSymbolIndex,
262 uint64_t Offset, uint64_t Size, uint64_t Alignment,
263 const MCSectionELF &Section);
267 template <typename T> void ELFObjectWriter::write(MCDataFragment &F, T Val) {
269 Val = support::endian::byte_swap<T, support::little>(Val);
271 Val = support::endian::byte_swap<T, support::big>(Val);
272 const char *Start = (const char *)&Val;
273 F.getContents().append(Start, Start + sizeof(T));
276 void SymbolTableWriter::createSymtabShndx() {
277 if (!ShndxIndexes.empty())
280 ShndxIndexes.resize(NumWritten);
283 template <typename T> void SymbolTableWriter::write(T Value) {
284 EWriter.write(Value);
287 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
288 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
290 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
291 uint64_t size, uint8_t other,
292 uint32_t shndx, bool Reserved) {
293 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
298 if (!ShndxIndexes.empty()) {
300 ShndxIndexes.push_back(shndx);
302 ShndxIndexes.push_back(0);
305 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
308 write(name); // st_name
309 write(info); // st_info
310 write(other); // st_other
311 write(Index); // st_shndx
312 write(value); // st_value
313 write(size); // st_size
315 write(name); // st_name
316 write(uint32_t(value)); // st_value
317 write(uint32_t(size)); // st_size
318 write(info); // st_info
319 write(other); // st_other
320 write(Index); // st_shndx
326 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
327 const MCFixupKindInfo &FKI =
328 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
330 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
333 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
337 case MCSymbolRefExpr::VK_GOT:
338 case MCSymbolRefExpr::VK_PLT:
339 case MCSymbolRefExpr::VK_GOTPCREL:
340 case MCSymbolRefExpr::VK_GOTOFF:
341 case MCSymbolRefExpr::VK_TPOFF:
342 case MCSymbolRefExpr::VK_TLSGD:
343 case MCSymbolRefExpr::VK_GOTTPOFF:
344 case MCSymbolRefExpr::VK_INDNTPOFF:
345 case MCSymbolRefExpr::VK_NTPOFF:
346 case MCSymbolRefExpr::VK_GOTNTPOFF:
347 case MCSymbolRefExpr::VK_TLSLDM:
348 case MCSymbolRefExpr::VK_DTPOFF:
349 case MCSymbolRefExpr::VK_TLSLD:
354 ELFObjectWriter::~ELFObjectWriter()
357 // Emit the ELF header.
358 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
364 // emitWord method behaves differently for ELF32 and ELF64, writing
365 // 4 bytes in the former and 8 in the latter.
367 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
369 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
372 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
374 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
376 Write8(TargetObjectWriter->getOSABI());
377 Write8(0); // e_ident[EI_ABIVERSION]
379 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
381 Write16(ELF::ET_REL); // e_type
383 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
385 Write32(ELF::EV_CURRENT); // e_version
386 WriteWord(0); // e_entry, no entry point in .o file
387 WriteWord(0); // e_phoff, no program header for .o
388 WriteWord(0); // e_shoff = sec hdr table off in bytes
390 // e_flags = whatever the target wants
391 Write32(Asm.getELFHeaderEFlags());
393 // e_ehsize = ELF header size
394 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
396 Write16(0); // e_phentsize = prog header entry size
397 Write16(0); // e_phnum = # prog header entries = 0
399 // e_shentsize = Section header entry size
400 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
402 // e_shnum = # of section header ents
405 // e_shstrndx = Section # of '.shstrtab'
406 assert(ShstrtabIndex < ELF::SHN_LORESERVE);
407 Write16(ShstrtabIndex);
410 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
411 const MCAsmLayout &Layout) {
412 if (Data.isCommon() && Data.isExternal())
413 return Data.getCommonAlignment();
416 if (!Layout.getSymbolOffset(&Data, Res))
419 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
425 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
426 const MCAsmLayout &Layout) {
427 // The presence of symbol versions causes undefined symbols and
428 // versions declared with @@@ to be renamed.
430 for (MCSymbolData &OriginalData : Asm.symbols()) {
431 const MCSymbol &Alias = OriginalData.getSymbol();
434 if (!Alias.isVariable())
436 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
439 const MCSymbol &Symbol = Ref->getSymbol();
440 MCSymbolData &SD = Asm.getSymbolData(Symbol);
442 StringRef AliasName = Alias.getName();
443 size_t Pos = AliasName.find('@');
444 if (Pos == StringRef::npos)
447 // Aliases defined with .symvar copy the binding from the symbol they alias.
448 // This is the first place we are able to copy this information.
449 OriginalData.setExternal(SD.isExternal());
450 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
452 StringRef Rest = AliasName.substr(Pos);
453 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
456 // FIXME: produce a better error message.
457 if (Symbol.isUndefined() && Rest.startswith("@@") &&
458 !Rest.startswith("@@@"))
459 report_fatal_error("A @@ version cannot be undefined");
461 Renames.insert(std::make_pair(&Symbol, &Alias));
465 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
466 uint8_t Type = newType;
468 // Propagation rules:
469 // IFUNC > FUNC > OBJECT > NOTYPE
470 // TLS_OBJECT > OBJECT > NOTYPE
472 // dont let the new type degrade the old type
476 case ELF::STT_GNU_IFUNC:
477 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
478 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
479 Type = ELF::STT_GNU_IFUNC;
482 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
483 Type == ELF::STT_TLS)
484 Type = ELF::STT_FUNC;
486 case ELF::STT_OBJECT:
487 if (Type == ELF::STT_NOTYPE)
488 Type = ELF::STT_OBJECT;
491 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
492 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
500 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
501 const MCAsmLayout &Layout) {
502 MCSymbolData &OrigData = *MSD.SymbolData;
503 assert((!OrigData.getFragment() ||
504 (&OrigData.getFragment()->getParent()->getSection() ==
505 &OrigData.getSymbol().getSection())) &&
506 "The symbol's section doesn't match the fragment's symbol");
507 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
509 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
511 bool IsReserved = !Base || OrigData.isCommon();
513 // Binding and Type share the same byte as upper and lower nibbles
514 uint8_t Binding = MCELF::GetBinding(OrigData);
515 uint8_t Type = MCELF::GetType(OrigData);
516 MCSymbolData *BaseSD = nullptr;
518 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
519 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
521 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
523 // Other and Visibility share the same byte with Visibility using the lower
525 uint8_t Visibility = MCELF::GetVisibility(OrigData);
526 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
529 uint64_t Value = SymbolValue(OrigData, Layout);
532 const MCExpr *ESize = OrigData.getSize();
534 ESize = BaseSD->getSize();
538 if (!ESize->evaluateKnownAbsolute(Res, Layout))
539 report_fatal_error("Size expression must be absolute.");
543 // Write out the symbol table entry
544 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
545 MSD.SectionIndex, IsReserved);
548 void ELFObjectWriter::WriteSymbolTable(
549 MCAssembler &Asm, const MCAsmLayout &Layout,
550 std::vector<const MCSectionELF *> &Sections,
551 SectionOffsetsTy &SectionOffsets) {
553 MCContext &Ctx = Asm.getContext();
555 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
558 const MCSectionELF *SymtabSection =
559 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
560 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
561 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
562 SymbolTableIndex = Sections.size() + 1;
563 Sections.push_back(SymtabSection);
565 // The string table must be emitted first because we need the index
566 // into the string table for all the symbol names.
568 SymbolTableWriter Writer(*this, is64Bit());
570 uint64_t Padding = OffsetToAlignment(OS.tell(), SymtabSD.getAlignment());
573 uint64_t SecStart = OS.tell();
575 // The first entry is the undefined symbol entry.
576 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
578 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
579 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
580 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
583 // Write the symbol table entries.
584 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
586 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
587 ELFSymbolData &MSD = LocalSymbolData[i];
588 WriteSymbol(Writer, MSD, Layout);
591 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
592 ELFSymbolData &MSD = ExternalSymbolData[i];
593 MCSymbolData &Data = *MSD.SymbolData;
594 assert(((Data.getFlags() & ELF_STB_Global) ||
595 (Data.getFlags() & ELF_STB_Weak)) &&
596 "External symbol requires STB_GLOBAL or STB_WEAK flag");
597 WriteSymbol(Writer, MSD, Layout);
598 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
599 LastLocalSymbolIndex++;
602 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
603 ELFSymbolData &MSD = UndefinedSymbolData[i];
604 MCSymbolData &Data = *MSD.SymbolData;
605 WriteSymbol(Writer, MSD, Layout);
606 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
607 LastLocalSymbolIndex++;
610 uint64_t SecEnd = OS.tell();
611 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
613 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
614 if (ShndxIndexes.empty())
617 SecStart = OS.tell();
618 const MCSectionELF *SymtabShndxSection =
619 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
620 Sections.push_back(SymtabShndxSection);
621 MCSectionData *SymtabShndxSD =
622 &Asm.getOrCreateSectionData(*SymtabShndxSection);
623 SymtabShndxSD->setAlignment(4);
624 for (uint32_t Index : ShndxIndexes)
627 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
630 // It is always valid to create a relocation with a symbol. It is preferable
631 // to use a relocation with a section if that is possible. Using the section
632 // allows us to omit some local symbols from the symbol table.
633 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
634 const MCSymbolRefExpr *RefA,
635 const MCSymbolData *SD,
637 unsigned Type) const {
638 // A PCRel relocation to an absolute value has no symbol (or section). We
639 // represent that with a relocation to a null section.
643 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
647 // The .odp creation emits a relocation against the symbol ".TOC." which
648 // create a R_PPC64_TOC relocation. However the relocation symbol name
649 // in final object creation should be NULL, since the symbol does not
650 // really exist, it is just the reference to TOC base for the current
651 // object file. Since the symbol is undefined, returning false results
652 // in a relocation with a null section which is the desired result.
653 case MCSymbolRefExpr::VK_PPC_TOCBASE:
656 // These VariantKind cause the relocation to refer to something other than
657 // the symbol itself, like a linker generated table. Since the address of
658 // symbol is not relevant, we cannot replace the symbol with the
659 // section and patch the difference in the addend.
660 case MCSymbolRefExpr::VK_GOT:
661 case MCSymbolRefExpr::VK_PLT:
662 case MCSymbolRefExpr::VK_GOTPCREL:
663 case MCSymbolRefExpr::VK_Mips_GOT:
664 case MCSymbolRefExpr::VK_PPC_GOT_LO:
665 case MCSymbolRefExpr::VK_PPC_GOT_HI:
666 case MCSymbolRefExpr::VK_PPC_GOT_HA:
670 // An undefined symbol is not in any section, so the relocation has to point
671 // to the symbol itself.
672 const MCSymbol &Sym = SD->getSymbol();
673 if (Sym.isUndefined())
676 unsigned Binding = MCELF::GetBinding(*SD);
679 llvm_unreachable("Invalid Binding");
683 // If the symbol is weak, it might be overridden by a symbol in another
684 // file. The relocation has to point to the symbol so that the linker
687 case ELF::STB_GLOBAL:
688 // Global ELF symbols can be preempted by the dynamic linker. The relocation
689 // has to point to the symbol for a reason analogous to the STB_WEAK case.
693 // If a relocation points to a mergeable section, we have to be careful.
694 // If the offset is zero, a relocation with the section will encode the
695 // same information. With a non-zero offset, the situation is different.
696 // For example, a relocation can point 42 bytes past the end of a string.
697 // If we change such a relocation to use the section, the linker would think
698 // that it pointed to another string and subtracting 42 at runtime will
699 // produce the wrong value.
700 auto &Sec = cast<MCSectionELF>(Sym.getSection());
701 unsigned Flags = Sec.getFlags();
702 if (Flags & ELF::SHF_MERGE) {
706 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
707 // only handle section relocations to mergeable sections if using RELA.
708 if (!hasRelocationAddend())
712 // Most TLS relocations use a got, so they need the symbol. Even those that
713 // are just an offset (@tpoff), require a symbol in gold versions before
714 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
715 // http://sourceware.org/PR16773.
716 if (Flags & ELF::SHF_TLS)
719 // If the symbol is a thumb function the final relocation must set the lowest
720 // bit. With a symbol that is done by just having the symbol have that bit
721 // set, so we would lose the bit if we relocated with the section.
722 // FIXME: We could use the section but add the bit to the relocation value.
723 if (Asm.isThumbFunc(&Sym))
726 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
731 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
732 const MCSymbol &Sym = Ref.getSymbol();
734 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
737 if (!Sym.isVariable())
740 const MCExpr *Expr = Sym.getVariableValue();
741 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
745 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
746 return &Inner->getSymbol();
750 // True if the assembler knows nothing about the final value of the symbol.
751 // This doesn't cover the comdat issues, since in those cases the assembler
752 // can at least know that all symbols in the section will move together.
753 static bool isWeak(const MCSymbolData &D) {
754 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
757 switch (MCELF::GetBinding(D)) {
759 llvm_unreachable("Unknown binding");
762 case ELF::STB_GLOBAL:
765 case ELF::STB_GNU_UNIQUE:
770 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
771 const MCAsmLayout &Layout,
772 const MCFragment *Fragment,
773 const MCFixup &Fixup, MCValue Target,
774 bool &IsPCRel, uint64_t &FixedValue) {
775 const MCSectionData *FixupSectionD = Fragment->getParent();
776 const MCSectionELF &FixupSection =
777 cast<MCSectionELF>(FixupSectionD->getSection());
778 uint64_t C = Target.getConstant();
779 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
781 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
782 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
783 "Should not have constructed this");
785 // Let A, B and C being the components of Target and R be the location of
786 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
787 // If it is pcrel, we want to compute (A - B + C - R).
789 // In general, ELF has no relocations for -B. It can only represent (A + C)
790 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
791 // replace B to implement it: (A - R - K + C)
793 Asm.getContext().FatalError(
795 "No relocation available to represent this relative expression");
797 const MCSymbol &SymB = RefB->getSymbol();
799 if (SymB.isUndefined())
800 Asm.getContext().FatalError(
802 Twine("symbol '") + SymB.getName() +
803 "' can not be undefined in a subtraction expression");
805 assert(!SymB.isAbsolute() && "Should have been folded");
806 const MCSection &SecB = SymB.getSection();
807 if (&SecB != &FixupSection)
808 Asm.getContext().FatalError(
809 Fixup.getLoc(), "Cannot represent a difference across sections");
811 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
813 Asm.getContext().FatalError(
814 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
816 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
817 uint64_t K = SymBOffset - FixupOffset;
822 // We either rejected the fixup or folded B into C at this point.
823 const MCSymbolRefExpr *RefA = Target.getSymA();
824 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
825 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
827 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
828 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
829 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
830 C += Layout.getSymbolOffset(SymAD);
833 if (hasRelocationAddend()) {
840 // FIXME: What is this!?!?
841 MCSymbolRefExpr::VariantKind Modifier =
842 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
843 if (RelocNeedsGOT(Modifier))
846 if (!RelocateWithSymbol) {
847 const MCSection *SecA =
848 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
849 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
850 MCSymbol *SectionSymbol =
851 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
853 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
854 Relocations[&FixupSection].push_back(Rec);
859 if (const MCSymbol *R = Renames.lookup(SymA))
862 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
863 WeakrefUsedInReloc.insert(WeakRef);
865 UsedInReloc.insert(SymA);
867 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
868 Relocations[&FixupSection].push_back(Rec);
874 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
876 const MCSymbolData &SD = Asm.getSymbolData(*S);
877 return SD.getIndex();
880 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
881 const MCSymbolData &Data, bool Used,
883 const MCSymbol &Symbol = Data.getSymbol();
884 if (Symbol.isVariable()) {
885 const MCExpr *Expr = Symbol.getVariableValue();
886 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
887 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
898 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
901 if (Symbol.isVariable()) {
902 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
903 if (Base && Base->isUndefined())
907 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
908 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
911 if (Symbol.isTemporary())
917 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
918 if (Data.isExternal())
921 const MCSymbol &Symbol = Data.getSymbol();
922 if (Symbol.isDefined())
931 void ELFObjectWriter::computeSymbolTable(
932 MCAssembler &Asm, const MCAsmLayout &Layout,
933 const SectionIndexMapTy &SectionIndexMap,
934 const RevGroupMapTy &RevGroupMap) {
935 // FIXME: Is this the correct place to do this?
936 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
938 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
939 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
940 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
941 Data.setExternal(true);
942 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
945 // Add the data for the symbols.
946 for (MCSymbolData &SD : Asm.symbols()) {
947 const MCSymbol &Symbol = SD.getSymbol();
949 bool Used = UsedInReloc.count(&Symbol);
950 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
951 bool isSignature = RevGroupMap.count(&Symbol);
953 if (!isInSymtab(Layout, SD,
954 Used || WeakrefUsed || isSignature,
955 Renames.count(&Symbol)))
959 MSD.SymbolData = &SD;
960 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
962 // Undefined symbols are global, but this is the first place we
963 // are able to set it.
964 bool Local = isLocal(SD, Used);
965 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
967 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
968 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
969 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
973 MSD.SectionIndex = ELF::SHN_ABS;
974 } else if (SD.isCommon()) {
976 MSD.SectionIndex = ELF::SHN_COMMON;
977 } else if (BaseSymbol->isUndefined()) {
978 if (isSignature && !Used)
979 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
981 MSD.SectionIndex = ELF::SHN_UNDEF;
982 if (!Used && WeakrefUsed)
983 MCELF::SetBinding(SD, ELF::STB_WEAK);
985 const MCSectionELF &Section =
986 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
987 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
988 assert(MSD.SectionIndex && "Invalid section index!");
991 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
994 // FIXME: All name handling should be done before we get to the writer,
995 // including dealing with GNU-style version suffixes. Fixing this isn't
998 // We thus have to be careful to not perform the symbol version replacement
1001 // The ELF format is used on Windows by the MCJIT engine. Thus, on
1002 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
1003 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
1004 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
1005 // the EFLObjectWriter should not interpret the "@@@" sub-string as
1006 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1007 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1008 // "__imp_?" or "__imp_@?".
1010 // It would have been interesting to perform the MS mangling prefix check
1011 // only when the target triple is of the form *-pc-windows-elf. But, it
1012 // seems that this information is not easily accessible from the
1014 StringRef Name = Symbol.getName();
1015 if (!Name.startswith("?") && !Name.startswith("@?") &&
1016 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1017 // This symbol isn't following the MSVC C++ name mangling convention. We
1018 // can thus safely interpret the @@@ in symbol names as specifying symbol
1020 SmallString<32> Buf;
1021 size_t Pos = Name.find("@@@");
1022 if (Pos != StringRef::npos) {
1023 Buf += Name.substr(0, Pos);
1024 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1025 Buf += Name.substr(Pos + Skip);
1030 // Sections have their own string table
1031 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1032 MSD.Name = StrTabBuilder.add(Name);
1034 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1035 UndefinedSymbolData.push_back(MSD);
1037 LocalSymbolData.push_back(MSD);
1039 ExternalSymbolData.push_back(MSD);
1042 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1043 StrTabBuilder.add(*i);
1045 StrTabBuilder.finalize(StringTableBuilder::ELF);
1047 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1048 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1050 for (ELFSymbolData &MSD : LocalSymbolData)
1051 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1053 : StrTabBuilder.getOffset(MSD.Name);
1054 for (ELFSymbolData &MSD : ExternalSymbolData)
1055 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1056 for (ELFSymbolData& MSD : UndefinedSymbolData)
1057 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1059 // Symbols are required to be in lexicographic order.
1060 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1061 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1062 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1064 // Set the symbol indices. Local symbols must come before all other
1065 // symbols with non-local bindings.
1066 unsigned Index = FileSymbolData.size() + 1;
1067 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1068 LocalSymbolData[i].SymbolData->setIndex(Index++);
1070 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1071 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1072 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1073 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1076 const MCSectionELF *
1077 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1078 const MCSectionELF &Sec) {
1079 if (Relocations[&Sec].empty())
1082 MCContext &Ctx = Asm.getContext();
1083 const StringRef SectionName = Sec.getSectionName();
1084 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1085 RelaSectionName += SectionName;
1088 if (hasRelocationAddend())
1089 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1091 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1094 if (Sec.getFlags() & ELF::SHF_GROUP)
1095 Flags = ELF::SHF_GROUP;
1097 const MCSectionELF *RelaSection = Ctx.createELFRelSection(
1098 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1099 Flags, EntrySize, Sec.getGroup(), &Sec);
1100 MCSectionData &RelSD = Asm.getOrCreateSectionData(*RelaSection);
1101 RelSD.setAlignment(is64Bit() ? 8 : 4);
1105 static SmallVector<char, 128>
1106 getUncompressedData(const MCAsmLayout &Layout,
1107 MCSectionData::FragmentListType &Fragments) {
1108 SmallVector<char, 128> UncompressedData;
1109 for (const MCFragment &F : Fragments) {
1110 const SmallVectorImpl<char> *Contents;
1111 switch (F.getKind()) {
1112 case MCFragment::FT_Data:
1113 Contents = &cast<MCDataFragment>(F).getContents();
1115 case MCFragment::FT_Dwarf:
1116 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1118 case MCFragment::FT_DwarfFrame:
1119 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1123 "Not expecting any other fragment types in a debug_* section");
1125 UncompressedData.append(Contents->begin(), Contents->end());
1127 return UncompressedData;
1130 // Include the debug info compression header:
1131 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1132 // useful for consumers to preallocate a buffer to decompress into.
1134 prependCompressionHeader(uint64_t Size,
1135 SmallVectorImpl<char> &CompressedContents) {
1136 const StringRef Magic = "ZLIB";
1137 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1139 if (sys::IsLittleEndianHost)
1140 sys::swapByteOrder(Size);
1141 CompressedContents.insert(CompressedContents.begin(),
1142 Magic.size() + sizeof(Size), 0);
1143 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1144 std::copy(reinterpret_cast<char *>(&Size),
1145 reinterpret_cast<char *>(&Size + 1),
1146 CompressedContents.begin() + Magic.size());
1150 // Return a single fragment containing the compressed contents of the whole
1151 // section. Null if the section was not compressed for any reason.
1152 static std::unique_ptr<MCDataFragment>
1153 getCompressedFragment(const MCAsmLayout &Layout,
1154 MCSectionData::FragmentListType &Fragments) {
1155 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1157 // Gather the uncompressed data from all the fragments, recording the
1158 // alignment fragment, if seen, and any fixups.
1159 SmallVector<char, 128> UncompressedData =
1160 getUncompressedData(Layout, Fragments);
1162 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1164 zlib::Status Success = zlib::compress(
1165 StringRef(UncompressedData.data(), UncompressedData.size()),
1166 CompressedContents);
1167 if (Success != zlib::StatusOK)
1170 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1173 return CompressedFragment;
1176 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1179 static void UpdateSymbols(const MCAsmLayout &Layout,
1180 const std::vector<MCSymbolData *> &Symbols,
1181 MCFragment &NewFragment) {
1182 for (MCSymbolData *Sym : Symbols) {
1183 Sym->setOffset(Sym->getOffset() +
1184 Layout.getFragmentOffset(Sym->getFragment()));
1185 Sym->setFragment(&NewFragment);
1189 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1190 const DefiningSymbolMap &DefiningSymbols,
1191 const MCSectionELF &Section,
1192 MCSectionData &SD) {
1193 StringRef SectionName = Section.getSectionName();
1194 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1196 std::unique_ptr<MCDataFragment> CompressedFragment =
1197 getCompressedFragment(Layout, Fragments);
1199 // Leave the section as-is if the fragments could not be compressed.
1200 if (!CompressedFragment)
1203 // Update the fragment+offsets of any symbols referring to fragments in this
1204 // section to refer to the new fragment.
1205 auto I = DefiningSymbols.find(&SD);
1206 if (I != DefiningSymbols.end())
1207 UpdateSymbols(Layout, I->second, *CompressedFragment);
1209 // Invalidate the layout for the whole section since it will have new and
1210 // different fragments now.
1211 Layout.invalidateFragmentsFrom(&Fragments.front());
1214 // Complete the initialization of the new fragment
1215 CompressedFragment->setParent(&SD);
1216 CompressedFragment->setLayoutOrder(0);
1217 Fragments.push_back(CompressedFragment.release());
1219 // Rename from .debug_* to .zdebug_*
1220 Asm.getContext().renameELFSection(&Section,
1221 (".z" + SectionName.drop_front(1)).str());
1224 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1225 MCAsmLayout &Layout) {
1226 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1229 DefiningSymbolMap DefiningSymbols;
1231 for (MCSymbolData &SD : Asm.symbols())
1232 if (MCFragment *F = SD.getFragment())
1233 DefiningSymbols[F->getParent()].push_back(&SD);
1235 for (MCSectionData &SD : Asm) {
1236 const MCSectionELF &Section =
1237 static_cast<const MCSectionELF &>(SD.getSection());
1238 StringRef SectionName = Section.getSectionName();
1240 // Compressing debug_frame requires handling alignment fragments which is
1241 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1242 // for writing to arbitrary buffers) for little benefit.
1243 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1246 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1250 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1251 uint64_t Flags, uint64_t Address,
1252 uint64_t Offset, uint64_t Size,
1253 uint32_t Link, uint32_t Info,
1255 uint64_t EntrySize) {
1256 Write32(Name); // sh_name: index into string table
1257 Write32(Type); // sh_type
1258 WriteWord(Flags); // sh_flags
1259 WriteWord(Address); // sh_addr
1260 WriteWord(Offset); // sh_offset
1261 WriteWord(Size); // sh_size
1262 Write32(Link); // sh_link
1263 Write32(Info); // sh_info
1264 WriteWord(Alignment); // sh_addralign
1265 WriteWord(EntrySize); // sh_entsize
1268 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1269 const MCSectionELF &Sec) {
1270 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1272 // Sort the relocation entries. Most targets just sort by Offset, but some
1273 // (e.g., MIPS) have additional constraints.
1274 TargetObjectWriter->sortRelocs(Asm, Relocs);
1276 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1277 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1279 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1282 write(Entry.Offset);
1283 if (TargetObjectWriter->isN64()) {
1284 write(uint32_t(Index));
1286 write(TargetObjectWriter->getRSsym(Entry.Type));
1287 write(TargetObjectWriter->getRType3(Entry.Type));
1288 write(TargetObjectWriter->getRType2(Entry.Type));
1289 write(TargetObjectWriter->getRType(Entry.Type));
1291 struct ELF::Elf64_Rela ERE64;
1292 ERE64.setSymbolAndType(Index, Entry.Type);
1293 write(ERE64.r_info);
1295 if (hasRelocationAddend())
1296 write(Entry.Addend);
1298 write(uint32_t(Entry.Offset));
1300 struct ELF::Elf32_Rela ERE32;
1301 ERE32.setSymbolAndType(Index, Entry.Type);
1302 write(ERE32.r_info);
1304 if (hasRelocationAddend())
1305 write(uint32_t(Entry.Addend));
1310 const MCSectionELF *ELFObjectWriter::createSectionHeaderStringTable(
1311 MCAssembler &Asm, std::vector<const MCSectionELF *> &Sections) {
1312 const MCSectionELF *ShstrtabSection = Sections[ShstrtabIndex - 1];
1314 Asm.getOrCreateSectionData(*ShstrtabSection);
1316 for (MCSectionData &SD : Asm) {
1317 const MCSectionELF &Section =
1318 static_cast<const MCSectionELF &>(SD.getSection());
1319 ShStrTabBuilder.add(Section.getSectionName());
1321 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1322 OS << ShStrTabBuilder.data();
1323 return ShstrtabSection;
1326 const MCSectionELF *ELFObjectWriter::createStringTable(
1327 MCAssembler &Asm, std::vector<const MCSectionELF *> &Sections) {
1328 MCContext &Ctx = Asm.getContext();
1329 const MCSectionELF *StrtabSection =
1330 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1331 Asm.getOrCreateSectionData(*StrtabSection);
1332 Sections.push_back(StrtabSection);
1333 StringTableIndex = Sections.size();
1334 OS << StrTabBuilder.data();
1335 return StrtabSection;
1338 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1339 const SectionIndexMapTy &SectionIndexMap,
1340 uint32_t GroupSymbolIndex,
1341 uint64_t Offset, uint64_t Size,
1343 const MCSectionELF &Section) {
1344 uint64_t sh_link = 0;
1345 uint64_t sh_info = 0;
1347 switch(Section.getType()) {
1352 case ELF::SHT_DYNAMIC:
1353 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1357 case ELF::SHT_RELA: {
1358 sh_link = SymbolTableIndex;
1359 assert(sh_link && ".symtab not found");
1360 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1361 sh_info = SectionIndexMap.lookup(InfoSection);
1365 case ELF::SHT_SYMTAB:
1366 case ELF::SHT_DYNSYM:
1367 sh_link = StringTableIndex;
1368 sh_info = LastLocalSymbolIndex;
1371 case ELF::SHT_SYMTAB_SHNDX:
1372 sh_link = SymbolTableIndex;
1375 case ELF::SHT_GROUP:
1376 sh_link = SymbolTableIndex;
1377 sh_info = GroupSymbolIndex;
1381 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1382 Section.getType() == ELF::SHT_ARM_EXIDX)
1383 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1385 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1387 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1388 Alignment, Section.getEntrySize());
1391 void ELFObjectWriter::writeSectionHeader(
1392 ArrayRef<const MCSectionELF *> Sections, MCAssembler &Asm,
1393 const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap,
1394 const SectionOffsetsTy &SectionOffsets) {
1395 const unsigned NumSections = Asm.size();
1397 // Null section first.
1398 uint64_t FirstSectionSize =
1399 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1400 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1402 for (unsigned i = 0; i < NumSections; ++i) {
1403 const MCSectionELF &Section = *Sections[i];
1404 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1405 uint32_t GroupSymbolIndex;
1406 if (Section.getType() != ELF::SHT_GROUP)
1407 GroupSymbolIndex = 0;
1409 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section.getGroup());
1411 const std::pair<uint64_t, uint64_t> &Offsets =
1412 SectionOffsets.find(&Section)->second;
1413 uint64_t Size = Section.getType() == ELF::SHT_NOBITS
1414 ? Layout.getSectionAddressSize(&SD)
1415 : Offsets.second - Offsets.first;
1417 writeSection(Asm, SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1418 SD.getAlignment(), Section);
1422 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1423 const MCAsmLayout &Layout) {
1424 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1426 std::vector<const MCSectionELF *> Sections;
1427 MCContext &Ctx = Asm.getContext();
1428 const MCSectionELF *ShstrtabSection =
1429 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1430 Sections.push_back(ShstrtabSection);
1431 ShstrtabIndex = Sections.size();
1433 RevGroupMapTy RevGroupMap;
1434 SectionIndexMapTy SectionIndexMap;
1436 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1438 // Write out the ELF header ...
1441 // ... then the sections ...
1442 SectionOffsetsTy SectionOffsets;
1443 bool ComputedSymtab = false;
1444 for (const MCSectionData &SD : Asm) {
1445 const MCSectionELF &Section =
1446 static_cast<const MCSectionELF &>(SD.getSection());
1448 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1449 WriteZeros(Padding);
1451 // Remember the offset into the file for this section.
1452 uint64_t SecStart = OS.tell();
1454 const MCSymbol *SignatureSymbol = Section.getGroup();
1455 unsigned Type = Section.getType();
1456 if (Type == ELF::SHT_GROUP) {
1457 assert(SignatureSymbol);
1458 write(uint32_t(ELF::GRP_COMDAT));
1459 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1460 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1463 } else if (Type == ELF::SHT_REL || Type == ELF::SHT_RELA) {
1464 if (!ComputedSymtab) {
1465 // Compute symbol table information.
1466 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1467 ComputedSymtab = true;
1469 writeRelocations(Asm, *Section.getAssociatedSection());
1471 Asm.writeSectionData(&SD, Layout);
1474 uint64_t SecEnd = OS.tell();
1475 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1477 if (Type == ELF::SHT_GROUP || Type == ELF::SHT_REL || Type == ELF::SHT_RELA)
1480 const MCSectionELF *RelSection = createRelocationSection(Asm, Section);
1482 if (SignatureSymbol) {
1483 Asm.getOrCreateSymbolData(*SignatureSymbol);
1484 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1486 const MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1487 Sections.push_back(Group);
1488 GroupIdx = Sections.size();
1489 MCSectionData *GroupD = &Asm.getOrCreateSectionData(*Group);
1490 GroupD->setAlignment(4);
1492 GroupMembers[SignatureSymbol].push_back(&Section);
1494 GroupMembers[SignatureSymbol].push_back(RelSection);
1497 Sections.push_back(&Section);
1498 SectionIndexMap[&Section] = Sections.size();
1500 Sections.push_back(RelSection);
1501 SectionIndexMap[RelSection] = Sections.size();
1505 if (!ComputedSymtab) {
1506 // Compute symbol table information.
1507 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1508 ComputedSymtab = true;
1511 WriteSymbolTable(Asm, Layout, Sections, SectionOffsets);
1514 uint64_t SecStart = OS.tell();
1515 const MCSectionELF *Sec = createStringTable(Asm, Sections);
1516 uint64_t SecEnd = OS.tell();
1517 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1521 uint64_t SecStart = OS.tell();
1522 const MCSectionELF *Sec = createSectionHeaderStringTable(Asm, Sections);
1523 uint64_t SecEnd = OS.tell();
1524 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1527 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1528 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1529 WriteZeros(Padding);
1531 const unsigned SectionHeaderOffset = OS.tell();
1533 // ... then the section header table ...
1534 writeSectionHeader(Sections, Asm, Layout, SectionIndexMap, SectionOffsets);
1536 uint16_t NumSections = (Sections.size() + 1 >= ELF::SHN_LORESERVE)
1537 ? (uint16_t)ELF::SHN_UNDEF
1538 : Sections.size() + 1;
1539 if (sys::IsLittleEndianHost != IsLittleEndian)
1540 sys::swapByteOrder(NumSections);
1541 unsigned NumSectionsOffset;
1544 uint64_t Val = SectionHeaderOffset;
1545 if (sys::IsLittleEndianHost != IsLittleEndian)
1546 sys::swapByteOrder(Val);
1547 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1548 offsetof(ELF::Elf64_Ehdr, e_shoff));
1549 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1551 uint32_t Val = SectionHeaderOffset;
1552 if (sys::IsLittleEndianHost != IsLittleEndian)
1553 sys::swapByteOrder(Val);
1554 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1555 offsetof(ELF::Elf32_Ehdr, e_shoff));
1556 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1558 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1562 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1563 const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
1564 bool InSet, bool IsPCRel) const {
1567 if (::isWeak(DataA))
1570 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
1574 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
1578 // It is invalid to replace a reference to a global in a comdat
1579 // with a reference to a local since out of comdat references
1580 // to a local are forbidden.
1581 // We could try to return false for more cases, like the reference
1582 // being in the same comdat or Sym being an alias to another global,
1583 // but it is not clear if it is worth the effort.
1584 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1587 const MCSymbol &Sym = SD.getSymbol();
1588 if (!Sym.isInSection())
1591 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1592 return Sec.getGroup();
1595 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1596 raw_pwrite_stream &OS,
1597 bool IsLittleEndian) {
1598 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);