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"
44 class FragmentWriter {
48 FragmentWriter(bool IsLittleEndian);
49 template <typename T> void write(MCDataFragment &F, T Val);
52 typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
54 class SymbolTableWriter {
56 FragmentWriter &FWriter;
58 std::vector<const MCSectionELF *> &Sections;
60 // The symbol .symtab fragment we are writting to.
61 MCDataFragment *SymtabF;
63 // .symtab_shndx fragment we are writting to.
64 MCDataFragment *ShndxF;
66 // The numbel of symbols written so far.
69 void createSymtabShndx();
71 template <typename T> void write(MCDataFragment &F, T Value);
74 SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
75 std::vector<const MCSectionELF *> &Sections,
76 MCDataFragment *SymtabF);
78 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
79 uint8_t other, uint32_t shndx, bool Reserved);
82 class ELFObjectWriter : public MCObjectWriter {
83 FragmentWriter FWriter;
87 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
88 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
89 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
90 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data,
91 bool Used, bool Renamed);
92 static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
93 static bool IsELFMetaDataSection(const MCSectionData &SD);
95 void writeDataSectionData(MCAssembler &Asm, const MCAsmLayout &Layout,
96 const MCSectionData &SD);
98 /// Helper struct for containing some precomputed information on symbols.
99 struct ELFSymbolData {
100 MCSymbolData *SymbolData;
101 uint64_t StringIndex;
102 uint32_t SectionIndex;
105 // Support lexicographic sorting.
106 bool operator<(const ELFSymbolData &RHS) const {
107 unsigned LHSType = MCELF::GetType(*SymbolData);
108 unsigned RHSType = MCELF::GetType(*RHS.SymbolData);
109 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
111 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
113 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
114 return SectionIndex < RHS.SectionIndex;
115 return Name < RHS.Name;
119 /// The target specific ELF writer instance.
120 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
122 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
123 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
124 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
126 llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
128 StringTableBuilder ShStrTabBuilder;
131 /// @name Symbol Table Data
134 StringTableBuilder StrTabBuilder;
135 std::vector<uint64_t> FileSymbolData;
136 std::vector<ELFSymbolData> LocalSymbolData;
137 std::vector<ELFSymbolData> ExternalSymbolData;
138 std::vector<ELFSymbolData> UndefinedSymbolData;
144 // This holds the symbol table index of the last local symbol.
145 unsigned LastLocalSymbolIndex;
146 // This holds the .strtab section index.
147 unsigned StringTableIndex;
148 // This holds the .symtab section index.
149 unsigned SymbolTableIndex;
151 unsigned ShstrtabIndex;
154 // TargetObjectWriter wrappers.
155 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
156 bool hasRelocationAddend() const {
157 return TargetObjectWriter->hasRelocationAddend();
159 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
160 bool IsPCRel) const {
161 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
165 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
167 : MCObjectWriter(OS, IsLittleEndian), FWriter(IsLittleEndian),
168 TargetObjectWriter(MOTW), NeedsGOT(false) {}
170 void reset() override {
172 WeakrefUsedInReloc.clear();
175 ShStrTabBuilder.clear();
176 StrTabBuilder.clear();
177 FileSymbolData.clear();
178 LocalSymbolData.clear();
179 ExternalSymbolData.clear();
180 UndefinedSymbolData.clear();
181 MCObjectWriter::reset();
184 ~ELFObjectWriter() override;
186 void WriteWord(uint64_t W) {
193 template <typename T> void write(MCDataFragment &F, T Value) {
194 FWriter.write(F, Value);
197 void WriteHeader(const MCAssembler &Asm,
198 unsigned NumberOfSections);
200 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
201 const MCAsmLayout &Layout);
203 void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm,
204 const MCAsmLayout &Layout,
205 std::vector<const MCSectionELF *> &Sections);
207 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
208 const MCSymbolRefExpr *RefA,
209 const MCSymbolData *SD, uint64_t C,
210 unsigned Type) const;
212 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
213 const MCFragment *Fragment, const MCFixup &Fixup,
214 MCValue Target, bool &IsPCRel,
215 uint64_t &FixedValue) override;
217 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
220 // Map from a signature symbol to the group section
221 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
222 // Start and end offset of each section
223 typedef std::vector<std::pair<uint64_t, uint64_t>> SectionOffsetsTy;
225 /// Compute the symbol table data
227 /// \param Asm - The assembler.
228 /// \param SectionIndexMap - Maps a section to its index.
229 /// \param RevGroupMap - Maps a signature symbol to the group section.
230 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
231 const SectionIndexMapTy &SectionIndexMap,
232 const RevGroupMapTy &RevGroupMap);
234 void maybeAddToGroup(MCAssembler &Asm, const RevGroupMapTy &RevGroupMap,
235 const MCSectionELF &Section, unsigned Index);
237 void computeIndexMap(MCAssembler &Asm,
238 std::vector<const MCSectionELF *> &Sections,
239 SectionIndexMapTy &SectionIndexMap,
240 const RevGroupMapTy &RevGroupMap);
242 MCSectionData *createRelocationSection(MCAssembler &Asm,
243 const MCSectionData &SD);
245 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
247 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout);
249 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
250 std::vector<const MCSectionELF *> &Sections);
252 // Create the sections that show up in the symbol table. Currently
253 // those are the .note.GNU-stack section and the group sections.
254 void createIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
255 RevGroupMapTy &RevGroupMap,
256 std::vector<const MCSectionELF *> &Sections,
257 SectionIndexMapTy &SectionIndexMap);
259 void ExecutePostLayoutBinding(MCAssembler &Asm,
260 const MCAsmLayout &Layout) override;
262 void writeSectionHeader(ArrayRef<const MCSectionELF *> Sections,
263 MCAssembler &Asm, const MCAsmLayout &Layout,
264 const SectionIndexMapTy &SectionIndexMap,
265 const SectionOffsetsTy &SectionOffsets);
267 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
268 uint64_t Address, uint64_t Offset,
269 uint64_t Size, uint32_t Link, uint32_t Info,
270 uint64_t Alignment, uint64_t EntrySize);
272 void WriteRelocationsFragment(const MCAssembler &Asm,
274 const MCSectionData *SD);
277 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
278 const MCSymbolData &DataA,
279 const MCFragment &FB,
281 bool IsPCRel) const override;
283 bool isWeak(const MCSymbolData &SD) const override;
285 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
286 void writeSection(MCAssembler &Asm,
287 const SectionIndexMapTy &SectionIndexMap,
288 uint32_t GroupSymbolIndex,
289 uint64_t Offset, uint64_t Size, uint64_t Alignment,
290 const MCSectionELF &Section);
294 FragmentWriter::FragmentWriter(bool IsLittleEndian)
295 : IsLittleEndian(IsLittleEndian) {}
297 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
299 Val = support::endian::byte_swap<T, support::little>(Val);
301 Val = support::endian::byte_swap<T, support::big>(Val);
302 const char *Start = (const char *)&Val;
303 F.getContents().append(Start, Start + sizeof(T));
306 void SymbolTableWriter::createSymtabShndx() {
310 MCContext &Ctx = Asm.getContext();
311 const MCSectionELF *SymtabShndxSection =
312 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
313 MCSectionData *SymtabShndxSD =
314 &Asm.getOrCreateSectionData(*SymtabShndxSection);
315 SymtabShndxSD->setAlignment(4);
316 ShndxF = new MCDataFragment(SymtabShndxSD);
317 Sections.push_back(SymtabShndxSection);
319 for (unsigned I = 0; I < NumWritten; ++I)
320 write(*ShndxF, uint32_t(0));
323 template <typename T>
324 void SymbolTableWriter::write(MCDataFragment &F, T Value) {
325 FWriter.write(F, Value);
328 SymbolTableWriter::SymbolTableWriter(
329 MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
330 std::vector<const MCSectionELF *> &Sections, MCDataFragment *SymtabF)
331 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit), Sections(Sections),
332 SymtabF(SymtabF), ShndxF(nullptr), NumWritten(0) {}
334 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
335 uint64_t size, uint8_t other,
336 uint32_t shndx, bool Reserved) {
337 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
344 write(*ShndxF, shndx);
346 write(*ShndxF, uint32_t(0));
349 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
352 write(*SymtabF, name); // st_name
353 write(*SymtabF, info); // st_info
354 write(*SymtabF, other); // st_other
355 write(*SymtabF, Index); // st_shndx
356 write(*SymtabF, value); // st_value
357 write(*SymtabF, size); // st_size
359 write(*SymtabF, name); // st_name
360 write(*SymtabF, uint32_t(value)); // st_value
361 write(*SymtabF, uint32_t(size)); // st_size
362 write(*SymtabF, info); // st_info
363 write(*SymtabF, other); // st_other
364 write(*SymtabF, Index); // st_shndx
370 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
371 const MCFixupKindInfo &FKI =
372 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
374 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
377 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
381 case MCSymbolRefExpr::VK_GOT:
382 case MCSymbolRefExpr::VK_PLT:
383 case MCSymbolRefExpr::VK_GOTPCREL:
384 case MCSymbolRefExpr::VK_GOTOFF:
385 case MCSymbolRefExpr::VK_TPOFF:
386 case MCSymbolRefExpr::VK_TLSGD:
387 case MCSymbolRefExpr::VK_GOTTPOFF:
388 case MCSymbolRefExpr::VK_INDNTPOFF:
389 case MCSymbolRefExpr::VK_NTPOFF:
390 case MCSymbolRefExpr::VK_GOTNTPOFF:
391 case MCSymbolRefExpr::VK_TLSLDM:
392 case MCSymbolRefExpr::VK_DTPOFF:
393 case MCSymbolRefExpr::VK_TLSLD:
398 ELFObjectWriter::~ELFObjectWriter()
401 // Emit the ELF header.
402 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
403 unsigned NumberOfSections) {
409 // emitWord method behaves differently for ELF32 and ELF64, writing
410 // 4 bytes in the former and 8 in the latter.
412 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
414 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
417 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
419 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
421 Write8(TargetObjectWriter->getOSABI());
422 Write8(0); // e_ident[EI_ABIVERSION]
424 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
426 Write16(ELF::ET_REL); // e_type
428 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
430 Write32(ELF::EV_CURRENT); // e_version
431 WriteWord(0); // e_entry, no entry point in .o file
432 WriteWord(0); // e_phoff, no program header for .o
433 WriteWord(0); // e_shoff = sec hdr table off in bytes
435 // e_flags = whatever the target wants
436 Write32(Asm.getELFHeaderEFlags());
438 // e_ehsize = ELF header size
439 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
441 Write16(0); // e_phentsize = prog header entry size
442 Write16(0); // e_phnum = # prog header entries = 0
444 // e_shentsize = Section header entry size
445 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
447 // e_shnum = # of section header ents
448 if (NumberOfSections >= ELF::SHN_LORESERVE)
449 Write16(ELF::SHN_UNDEF);
451 Write16(NumberOfSections);
453 // e_shstrndx = Section # of '.shstrtab'
454 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
455 Write16(ELF::SHN_XINDEX);
457 Write16(ShstrtabIndex);
460 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
461 const MCAsmLayout &Layout) {
462 if (Data.isCommon() && Data.isExternal())
463 return Data.getCommonAlignment();
466 if (!Layout.getSymbolOffset(&Data, Res))
469 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
475 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
476 const MCAsmLayout &Layout) {
477 // The presence of symbol versions causes undefined symbols and
478 // versions declared with @@@ to be renamed.
480 for (MCSymbolData &OriginalData : Asm.symbols()) {
481 const MCSymbol &Alias = OriginalData.getSymbol();
484 if (!Alias.isVariable())
486 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
489 const MCSymbol &Symbol = Ref->getSymbol();
490 MCSymbolData &SD = Asm.getSymbolData(Symbol);
492 StringRef AliasName = Alias.getName();
493 size_t Pos = AliasName.find('@');
494 if (Pos == StringRef::npos)
497 // Aliases defined with .symvar copy the binding from the symbol they alias.
498 // This is the first place we are able to copy this information.
499 OriginalData.setExternal(SD.isExternal());
500 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
502 StringRef Rest = AliasName.substr(Pos);
503 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
506 // FIXME: produce a better error message.
507 if (Symbol.isUndefined() && Rest.startswith("@@") &&
508 !Rest.startswith("@@@"))
509 report_fatal_error("A @@ version cannot be undefined");
511 Renames.insert(std::make_pair(&Symbol, &Alias));
515 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
516 uint8_t Type = newType;
518 // Propagation rules:
519 // IFUNC > FUNC > OBJECT > NOTYPE
520 // TLS_OBJECT > OBJECT > NOTYPE
522 // dont let the new type degrade the old type
526 case ELF::STT_GNU_IFUNC:
527 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
528 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
529 Type = ELF::STT_GNU_IFUNC;
532 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
533 Type == ELF::STT_TLS)
534 Type = ELF::STT_FUNC;
536 case ELF::STT_OBJECT:
537 if (Type == ELF::STT_NOTYPE)
538 Type = ELF::STT_OBJECT;
541 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
542 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
550 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
551 const MCAsmLayout &Layout) {
552 MCSymbolData &OrigData = *MSD.SymbolData;
553 assert((!OrigData.getFragment() ||
554 (&OrigData.getFragment()->getParent()->getSection() ==
555 &OrigData.getSymbol().getSection())) &&
556 "The symbol's section doesn't match the fragment's symbol");
557 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
559 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
561 bool IsReserved = !Base || OrigData.isCommon();
563 // Binding and Type share the same byte as upper and lower nibbles
564 uint8_t Binding = MCELF::GetBinding(OrigData);
565 uint8_t Type = MCELF::GetType(OrigData);
566 MCSymbolData *BaseSD = nullptr;
568 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
569 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
571 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
573 // Other and Visibility share the same byte with Visibility using the lower
575 uint8_t Visibility = MCELF::GetVisibility(OrigData);
576 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
579 uint64_t Value = SymbolValue(OrigData, Layout);
582 const MCExpr *ESize = OrigData.getSize();
584 ESize = BaseSD->getSize();
588 if (!ESize->evaluateKnownAbsolute(Res, Layout))
589 report_fatal_error("Size expression must be absolute.");
593 // Write out the symbol table entry
594 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
595 MSD.SectionIndex, IsReserved);
598 void ELFObjectWriter::WriteSymbolTable(
599 MCDataFragment *SymtabF, MCAssembler &Asm, const MCAsmLayout &Layout,
600 std::vector<const MCSectionELF *> &Sections) {
601 // The string table must be emitted first because we need the index
602 // into the string table for all the symbol names.
604 // FIXME: Make sure the start of the symbol table is aligned.
606 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), Sections, SymtabF);
608 // The first entry is the undefined symbol entry.
609 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
611 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
612 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
613 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
616 // Write the symbol table entries.
617 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
619 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
620 ELFSymbolData &MSD = LocalSymbolData[i];
621 WriteSymbol(Writer, MSD, Layout);
624 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
625 ELFSymbolData &MSD = ExternalSymbolData[i];
626 MCSymbolData &Data = *MSD.SymbolData;
627 assert(((Data.getFlags() & ELF_STB_Global) ||
628 (Data.getFlags() & ELF_STB_Weak)) &&
629 "External symbol requires STB_GLOBAL or STB_WEAK flag");
630 WriteSymbol(Writer, MSD, Layout);
631 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
632 LastLocalSymbolIndex++;
635 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
636 ELFSymbolData &MSD = UndefinedSymbolData[i];
637 MCSymbolData &Data = *MSD.SymbolData;
638 WriteSymbol(Writer, MSD, Layout);
639 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
640 LastLocalSymbolIndex++;
644 // It is always valid to create a relocation with a symbol. It is preferable
645 // to use a relocation with a section if that is possible. Using the section
646 // allows us to omit some local symbols from the symbol table.
647 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
648 const MCSymbolRefExpr *RefA,
649 const MCSymbolData *SD,
651 unsigned Type) const {
652 // A PCRel relocation to an absolute value has no symbol (or section). We
653 // represent that with a relocation to a null section.
657 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
661 // The .odp creation emits a relocation against the symbol ".TOC." which
662 // create a R_PPC64_TOC relocation. However the relocation symbol name
663 // in final object creation should be NULL, since the symbol does not
664 // really exist, it is just the reference to TOC base for the current
665 // object file. Since the symbol is undefined, returning false results
666 // in a relocation with a null section which is the desired result.
667 case MCSymbolRefExpr::VK_PPC_TOCBASE:
670 // These VariantKind cause the relocation to refer to something other than
671 // the symbol itself, like a linker generated table. Since the address of
672 // symbol is not relevant, we cannot replace the symbol with the
673 // section and patch the difference in the addend.
674 case MCSymbolRefExpr::VK_GOT:
675 case MCSymbolRefExpr::VK_PLT:
676 case MCSymbolRefExpr::VK_GOTPCREL:
677 case MCSymbolRefExpr::VK_Mips_GOT:
678 case MCSymbolRefExpr::VK_PPC_GOT_LO:
679 case MCSymbolRefExpr::VK_PPC_GOT_HI:
680 case MCSymbolRefExpr::VK_PPC_GOT_HA:
684 // An undefined symbol is not in any section, so the relocation has to point
685 // to the symbol itself.
686 const MCSymbol &Sym = SD->getSymbol();
687 if (Sym.isUndefined())
690 unsigned Binding = MCELF::GetBinding(*SD);
693 llvm_unreachable("Invalid Binding");
697 // If the symbol is weak, it might be overridden by a symbol in another
698 // file. The relocation has to point to the symbol so that the linker
701 case ELF::STB_GLOBAL:
702 // Global ELF symbols can be preempted by the dynamic linker. The relocation
703 // has to point to the symbol for a reason analogous to the STB_WEAK case.
707 // If a relocation points to a mergeable section, we have to be careful.
708 // If the offset is zero, a relocation with the section will encode the
709 // same information. With a non-zero offset, the situation is different.
710 // For example, a relocation can point 42 bytes past the end of a string.
711 // If we change such a relocation to use the section, the linker would think
712 // that it pointed to another string and subtracting 42 at runtime will
713 // produce the wrong value.
714 auto &Sec = cast<MCSectionELF>(Sym.getSection());
715 unsigned Flags = Sec.getFlags();
716 if (Flags & ELF::SHF_MERGE) {
720 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
721 // only handle section relocations to mergeable sections if using RELA.
722 if (!hasRelocationAddend())
726 // Most TLS relocations use a got, so they need the symbol. Even those that
727 // are just an offset (@tpoff), require a symbol in gold versions before
728 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
729 // http://sourceware.org/PR16773.
730 if (Flags & ELF::SHF_TLS)
733 // If the symbol is a thumb function the final relocation must set the lowest
734 // bit. With a symbol that is done by just having the symbol have that bit
735 // set, so we would lose the bit if we relocated with the section.
736 // FIXME: We could use the section but add the bit to the relocation value.
737 if (Asm.isThumbFunc(&Sym))
740 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
745 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
746 const MCSymbol &Sym = Ref.getSymbol();
748 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
751 if (!Sym.isVariable())
754 const MCExpr *Expr = Sym.getVariableValue();
755 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
759 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
760 return &Inner->getSymbol();
764 // True if the assembler knows nothing about the final value of the symbol.
765 // This doesn't cover the comdat issues, since in those cases the assembler
766 // can at least know that all symbols in the section will move together.
767 static bool isWeak(const MCSymbolData &D) {
768 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
771 switch (MCELF::GetBinding(D)) {
773 llvm_unreachable("Unknown binding");
776 case ELF::STB_GLOBAL:
779 case ELF::STB_GNU_UNIQUE:
784 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
785 const MCAsmLayout &Layout,
786 const MCFragment *Fragment,
787 const MCFixup &Fixup, MCValue Target,
788 bool &IsPCRel, uint64_t &FixedValue) {
789 const MCSectionData *FixupSection = Fragment->getParent();
790 uint64_t C = Target.getConstant();
791 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
793 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
794 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
795 "Should not have constructed this");
797 // Let A, B and C being the components of Target and R be the location of
798 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
799 // If it is pcrel, we want to compute (A - B + C - R).
801 // In general, ELF has no relocations for -B. It can only represent (A + C)
802 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
803 // replace B to implement it: (A - R - K + C)
805 Asm.getContext().FatalError(
807 "No relocation available to represent this relative expression");
809 const MCSymbol &SymB = RefB->getSymbol();
811 if (SymB.isUndefined())
812 Asm.getContext().FatalError(
814 Twine("symbol '") + SymB.getName() +
815 "' can not be undefined in a subtraction expression");
817 assert(!SymB.isAbsolute() && "Should have been folded");
818 const MCSection &SecB = SymB.getSection();
819 if (&SecB != &FixupSection->getSection())
820 Asm.getContext().FatalError(
821 Fixup.getLoc(), "Cannot represent a difference across sections");
823 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
825 Asm.getContext().FatalError(
826 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
828 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
829 uint64_t K = SymBOffset - FixupOffset;
834 // We either rejected the fixup or folded B into C at this point.
835 const MCSymbolRefExpr *RefA = Target.getSymA();
836 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
837 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
839 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
840 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
841 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
842 C += Layout.getSymbolOffset(SymAD);
845 if (hasRelocationAddend()) {
852 // FIXME: What is this!?!?
853 MCSymbolRefExpr::VariantKind Modifier =
854 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
855 if (RelocNeedsGOT(Modifier))
858 if (!RelocateWithSymbol) {
859 const MCSection *SecA =
860 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
861 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
862 MCSymbol *SectionSymbol =
863 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
865 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
866 Relocations[FixupSection].push_back(Rec);
871 if (const MCSymbol *R = Renames.lookup(SymA))
874 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
875 WeakrefUsedInReloc.insert(WeakRef);
877 UsedInReloc.insert(SymA);
879 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
880 Relocations[FixupSection].push_back(Rec);
886 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
888 const MCSymbolData &SD = Asm.getSymbolData(*S);
889 return SD.getIndex();
892 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
893 const MCSymbolData &Data, bool Used,
895 const MCSymbol &Symbol = Data.getSymbol();
896 if (Symbol.isVariable()) {
897 const MCExpr *Expr = Symbol.getVariableValue();
898 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
899 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
910 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
913 if (Symbol.isVariable()) {
914 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
915 if (Base && Base->isUndefined())
919 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
920 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
923 if (Symbol.isTemporary())
929 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
930 if (Data.isExternal())
933 const MCSymbol &Symbol = Data.getSymbol();
934 if (Symbol.isDefined())
943 void ELFObjectWriter::maybeAddToGroup(MCAssembler &Asm,
944 const RevGroupMapTy &RevGroupMap,
945 const MCSectionELF &Section,
947 const MCSymbol *Sym = Section.getGroup();
950 const MCSectionELF *Group = RevGroupMap.lookup(Sym);
951 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
952 // FIXME: we could use the previous fragment
953 MCDataFragment *F = new MCDataFragment(&Data);
957 void ELFObjectWriter::computeIndexMap(
958 MCAssembler &Asm, std::vector<const MCSectionELF *> &Sections,
959 SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap) {
960 for (const MCSectionData &SD : Asm) {
961 const MCSectionELF &Section =
962 static_cast<const MCSectionELF &>(SD.getSection());
963 if (Section.getType() != ELF::SHT_GROUP)
965 Sections.push_back(&Section);
966 SectionIndexMap[&Section] = Sections.size();
969 std::vector<const MCSectionELF *> RelSections;
970 for (const MCSectionData &SD : Asm) {
971 const MCSectionELF &Section =
972 static_cast<const MCSectionELF &>(SD.getSection());
973 if (Section.getType() == ELF::SHT_GROUP ||
974 Section.getType() == ELF::SHT_REL ||
975 Section.getType() == ELF::SHT_RELA)
977 Sections.push_back(&Section);
978 unsigned Index = Sections.size();
979 SectionIndexMap[&Section] = Index;
980 maybeAddToGroup(Asm, RevGroupMap, Section, Index);
982 if (MCSectionData *RelSD = createRelocationSection(Asm, SD)) {
983 const MCSectionELF *RelSection =
984 static_cast<const MCSectionELF *>(&RelSD->getSection());
985 RelSections.push_back(RelSection);
989 // Put relocation sections close together. The linker reads them
990 // first, so this improves cache locality.
991 for (const MCSectionELF *Sec : RelSections) {
992 Sections.push_back(Sec);
993 unsigned Index = Sections.size();
994 maybeAddToGroup(Asm, RevGroupMap, *Sec, Index);
998 void ELFObjectWriter::computeSymbolTable(
999 MCAssembler &Asm, const MCAsmLayout &Layout,
1000 const SectionIndexMapTy &SectionIndexMap,
1001 const RevGroupMapTy &RevGroupMap) {
1002 // FIXME: Is this the correct place to do this?
1003 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
1005 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
1006 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
1007 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
1008 Data.setExternal(true);
1009 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
1012 // Add the data for the symbols.
1013 for (MCSymbolData &SD : Asm.symbols()) {
1014 const MCSymbol &Symbol = SD.getSymbol();
1016 bool Used = UsedInReloc.count(&Symbol);
1017 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
1018 bool isSignature = RevGroupMap.count(&Symbol);
1020 if (!isInSymtab(Layout, SD,
1021 Used || WeakrefUsed || isSignature,
1022 Renames.count(&Symbol)))
1026 MSD.SymbolData = &SD;
1027 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
1029 // Undefined symbols are global, but this is the first place we
1030 // are able to set it.
1031 bool Local = isLocal(SD, Used);
1032 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1034 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1035 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1036 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1040 MSD.SectionIndex = ELF::SHN_ABS;
1041 } else if (SD.isCommon()) {
1043 MSD.SectionIndex = ELF::SHN_COMMON;
1044 } else if (BaseSymbol->isUndefined()) {
1045 if (isSignature && !Used)
1046 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap.lookup(&Symbol));
1048 MSD.SectionIndex = ELF::SHN_UNDEF;
1049 if (!Used && WeakrefUsed)
1050 MCELF::SetBinding(SD, ELF::STB_WEAK);
1052 const MCSectionELF &Section =
1053 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1054 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1055 assert(MSD.SectionIndex && "Invalid section index!");
1058 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
1061 // FIXME: All name handling should be done before we get to the writer,
1062 // including dealing with GNU-style version suffixes. Fixing this isn't
1065 // We thus have to be careful to not perform the symbol version replacement
1068 // The ELF format is used on Windows by the MCJIT engine. Thus, on
1069 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
1070 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
1071 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
1072 // the EFLObjectWriter should not interpret the "@@@" sub-string as
1073 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1074 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1075 // "__imp_?" or "__imp_@?".
1077 // It would have been interesting to perform the MS mangling prefix check
1078 // only when the target triple is of the form *-pc-windows-elf. But, it
1079 // seems that this information is not easily accessible from the
1081 StringRef Name = Symbol.getName();
1082 if (!Name.startswith("?") && !Name.startswith("@?") &&
1083 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1084 // This symbol isn't following the MSVC C++ name mangling convention. We
1085 // can thus safely interpret the @@@ in symbol names as specifying symbol
1087 SmallString<32> Buf;
1088 size_t Pos = Name.find("@@@");
1089 if (Pos != StringRef::npos) {
1090 Buf += Name.substr(0, Pos);
1091 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1092 Buf += Name.substr(Pos + Skip);
1097 // Sections have their own string table
1098 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1099 MSD.Name = StrTabBuilder.add(Name);
1101 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1102 UndefinedSymbolData.push_back(MSD);
1104 LocalSymbolData.push_back(MSD);
1106 ExternalSymbolData.push_back(MSD);
1109 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1110 StrTabBuilder.add(*i);
1112 StrTabBuilder.finalize(StringTableBuilder::ELF);
1114 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1115 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1117 for (ELFSymbolData &MSD : LocalSymbolData)
1118 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1120 : StrTabBuilder.getOffset(MSD.Name);
1121 for (ELFSymbolData &MSD : ExternalSymbolData)
1122 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1123 for (ELFSymbolData& MSD : UndefinedSymbolData)
1124 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1126 // Symbols are required to be in lexicographic order.
1127 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1128 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1129 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1131 // Set the symbol indices. Local symbols must come before all other
1132 // symbols with non-local bindings.
1133 unsigned Index = FileSymbolData.size() + 1;
1134 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1135 LocalSymbolData[i].SymbolData->setIndex(Index++);
1137 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1138 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1139 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1140 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1144 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1145 const MCSectionData &SD) {
1146 if (Relocations[&SD].empty())
1149 MCContext &Ctx = Asm.getContext();
1150 const MCSectionELF &Section =
1151 static_cast<const MCSectionELF &>(SD.getSection());
1153 const StringRef SectionName = Section.getSectionName();
1154 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1155 RelaSectionName += SectionName;
1158 if (hasRelocationAddend())
1159 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1161 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1164 if (Section.getFlags() & ELF::SHF_GROUP)
1165 Flags = ELF::SHF_GROUP;
1167 const MCSectionELF *RelaSection = Ctx.createELFRelSection(
1168 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1169 Flags, EntrySize, Section.getGroup(), &Section);
1170 return &Asm.getOrCreateSectionData(*RelaSection);
1173 static SmallVector<char, 128>
1174 getUncompressedData(MCAsmLayout &Layout,
1175 MCSectionData::FragmentListType &Fragments) {
1176 SmallVector<char, 128> UncompressedData;
1177 for (const MCFragment &F : Fragments) {
1178 const SmallVectorImpl<char> *Contents;
1179 switch (F.getKind()) {
1180 case MCFragment::FT_Data:
1181 Contents = &cast<MCDataFragment>(F).getContents();
1183 case MCFragment::FT_Dwarf:
1184 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1186 case MCFragment::FT_DwarfFrame:
1187 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1191 "Not expecting any other fragment types in a debug_* section");
1193 UncompressedData.append(Contents->begin(), Contents->end());
1195 return UncompressedData;
1198 // Include the debug info compression header:
1199 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1200 // useful for consumers to preallocate a buffer to decompress into.
1202 prependCompressionHeader(uint64_t Size,
1203 SmallVectorImpl<char> &CompressedContents) {
1204 const StringRef Magic = "ZLIB";
1205 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1207 if (sys::IsLittleEndianHost)
1208 sys::swapByteOrder(Size);
1209 CompressedContents.insert(CompressedContents.begin(),
1210 Magic.size() + sizeof(Size), 0);
1211 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1212 std::copy(reinterpret_cast<char *>(&Size),
1213 reinterpret_cast<char *>(&Size + 1),
1214 CompressedContents.begin() + Magic.size());
1218 // Return a single fragment containing the compressed contents of the whole
1219 // section. Null if the section was not compressed for any reason.
1220 static std::unique_ptr<MCDataFragment>
1221 getCompressedFragment(MCAsmLayout &Layout,
1222 MCSectionData::FragmentListType &Fragments) {
1223 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1225 // Gather the uncompressed data from all the fragments, recording the
1226 // alignment fragment, if seen, and any fixups.
1227 SmallVector<char, 128> UncompressedData =
1228 getUncompressedData(Layout, Fragments);
1230 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1232 zlib::Status Success = zlib::compress(
1233 StringRef(UncompressedData.data(), UncompressedData.size()),
1234 CompressedContents);
1235 if (Success != zlib::StatusOK)
1238 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1241 return CompressedFragment;
1244 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1247 static void UpdateSymbols(const MCAsmLayout &Layout,
1248 const std::vector<MCSymbolData *> &Symbols,
1249 MCFragment &NewFragment) {
1250 for (MCSymbolData *Sym : Symbols) {
1251 Sym->setOffset(Sym->getOffset() +
1252 Layout.getFragmentOffset(Sym->getFragment()));
1253 Sym->setFragment(&NewFragment);
1257 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1258 const DefiningSymbolMap &DefiningSymbols,
1259 const MCSectionELF &Section,
1260 MCSectionData &SD) {
1261 StringRef SectionName = Section.getSectionName();
1262 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1264 std::unique_ptr<MCDataFragment> CompressedFragment =
1265 getCompressedFragment(Layout, Fragments);
1267 // Leave the section as-is if the fragments could not be compressed.
1268 if (!CompressedFragment)
1271 // Update the fragment+offsets of any symbols referring to fragments in this
1272 // section to refer to the new fragment.
1273 auto I = DefiningSymbols.find(&SD);
1274 if (I != DefiningSymbols.end())
1275 UpdateSymbols(Layout, I->second, *CompressedFragment);
1277 // Invalidate the layout for the whole section since it will have new and
1278 // different fragments now.
1279 Layout.invalidateFragmentsFrom(&Fragments.front());
1282 // Complete the initialization of the new fragment
1283 CompressedFragment->setParent(&SD);
1284 CompressedFragment->setLayoutOrder(0);
1285 Fragments.push_back(CompressedFragment.release());
1287 // Rename from .debug_* to .zdebug_*
1288 Asm.getContext().renameELFSection(&Section,
1289 (".z" + SectionName.drop_front(1)).str());
1292 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1293 MCAsmLayout &Layout) {
1294 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1297 DefiningSymbolMap DefiningSymbols;
1299 for (MCSymbolData &SD : Asm.symbols())
1300 if (MCFragment *F = SD.getFragment())
1301 DefiningSymbols[F->getParent()].push_back(&SD);
1303 for (MCSectionData &SD : Asm) {
1304 const MCSectionELF &Section =
1305 static_cast<const MCSectionELF &>(SD.getSection());
1306 StringRef SectionName = Section.getSectionName();
1308 // Compressing debug_frame requires handling alignment fragments which is
1309 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1310 // for writing to arbitrary buffers) for little benefit.
1311 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1314 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1318 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) {
1319 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1320 MCSectionData &RelSD = *it;
1321 const MCSectionELF &RelSection =
1322 static_cast<const MCSectionELF &>(RelSD.getSection());
1324 unsigned Type = RelSection.getType();
1325 if (Type != ELF::SHT_REL && Type != ELF::SHT_RELA)
1328 const MCSectionELF *Section = RelSection.getAssociatedSection();
1329 MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1330 RelSD.setAlignment(is64Bit() ? 8 : 4);
1332 MCDataFragment *F = new MCDataFragment(&RelSD);
1333 WriteRelocationsFragment(Asm, F, &SD);
1337 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1338 uint64_t Flags, uint64_t Address,
1339 uint64_t Offset, uint64_t Size,
1340 uint32_t Link, uint32_t Info,
1342 uint64_t EntrySize) {
1343 Write32(Name); // sh_name: index into string table
1344 Write32(Type); // sh_type
1345 WriteWord(Flags); // sh_flags
1346 WriteWord(Address); // sh_addr
1347 WriteWord(Offset); // sh_offset
1348 WriteWord(Size); // sh_size
1349 Write32(Link); // sh_link
1350 Write32(Info); // sh_info
1351 WriteWord(Alignment); // sh_addralign
1352 WriteWord(EntrySize); // sh_entsize
1355 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1357 const MCSectionData *SD) {
1358 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1360 // Sort the relocation entries. Most targets just sort by Offset, but some
1361 // (e.g., MIPS) have additional constraints.
1362 TargetObjectWriter->sortRelocs(Asm, Relocs);
1364 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1365 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1367 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1370 write(*F, Entry.Offset);
1371 if (TargetObjectWriter->isN64()) {
1372 write(*F, uint32_t(Index));
1374 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1375 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1376 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1377 write(*F, TargetObjectWriter->getRType(Entry.Type));
1379 struct ELF::Elf64_Rela ERE64;
1380 ERE64.setSymbolAndType(Index, Entry.Type);
1381 write(*F, ERE64.r_info);
1383 if (hasRelocationAddend())
1384 write(*F, Entry.Addend);
1386 write(*F, uint32_t(Entry.Offset));
1388 struct ELF::Elf32_Rela ERE32;
1389 ERE32.setSymbolAndType(Index, Entry.Type);
1390 write(*F, ERE32.r_info);
1392 if (hasRelocationAddend())
1393 write(*F, uint32_t(Entry.Addend));
1398 void ELFObjectWriter::CreateMetadataSections(
1399 MCAssembler &Asm, MCAsmLayout &Layout,
1400 std::vector<const MCSectionELF *> &Sections) {
1401 MCContext &Ctx = Asm.getContext();
1404 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1406 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1407 const MCSectionELF *ShstrtabSection =
1408 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1409 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1410 ShstrtabSD.setAlignment(1);
1411 ShstrtabIndex = Sections.size() + 1;
1412 Sections.push_back(ShstrtabSection);
1414 const MCSectionELF *SymtabSection =
1415 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1417 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1418 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1419 SymbolTableIndex = Sections.size() + 1;
1420 Sections.push_back(SymtabSection);
1422 const MCSectionELF *StrtabSection;
1423 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1424 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1425 StrtabSD.setAlignment(1);
1426 StringTableIndex = Sections.size() + 1;
1427 Sections.push_back(StrtabSection);
1430 F = new MCDataFragment(&SymtabSD);
1431 WriteSymbolTable(F, Asm, Layout, Sections);
1433 F = new MCDataFragment(&StrtabSD);
1434 F->getContents().append(StrTabBuilder.data().begin(),
1435 StrTabBuilder.data().end());
1437 F = new MCDataFragment(&ShstrtabSD);
1439 // Section header string table.
1440 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1441 const MCSectionELF &Section =
1442 static_cast<const MCSectionELF&>(it->getSection());
1443 ShStrTabBuilder.add(Section.getSectionName());
1445 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1446 F->getContents().append(ShStrTabBuilder.data().begin(),
1447 ShStrTabBuilder.data().end());
1450 void ELFObjectWriter::createIndexedSections(
1451 MCAssembler &Asm, MCAsmLayout &Layout, RevGroupMapTy &RevGroupMap,
1452 std::vector<const MCSectionELF *> &Sections,
1453 SectionIndexMapTy &SectionIndexMap) {
1454 MCContext &Ctx = Asm.getContext();
1457 for (const MCSectionData &SD : Asm) {
1458 const MCSectionELF &Section =
1459 static_cast<const MCSectionELF &>(SD.getSection());
1460 if (!(Section.getFlags() & ELF::SHF_GROUP))
1463 const MCSymbol *SignatureSymbol = Section.getGroup();
1464 Asm.getOrCreateSymbolData(*SignatureSymbol);
1465 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1467 Group = Ctx.createELFGroupSection(SignatureSymbol);
1468 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1469 Data.setAlignment(4);
1470 MCDataFragment *F = new MCDataFragment(&Data);
1471 write(*F, uint32_t(ELF::GRP_COMDAT));
1475 computeIndexMap(Asm, Sections, SectionIndexMap, RevGroupMap);
1478 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1479 const SectionIndexMapTy &SectionIndexMap,
1480 uint32_t GroupSymbolIndex,
1481 uint64_t Offset, uint64_t Size,
1483 const MCSectionELF &Section) {
1484 uint64_t sh_link = 0;
1485 uint64_t sh_info = 0;
1487 switch(Section.getType()) {
1492 case ELF::SHT_DYNAMIC:
1493 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1497 case ELF::SHT_RELA: {
1498 sh_link = SymbolTableIndex;
1499 assert(sh_link && ".symtab not found");
1500 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1501 sh_info = SectionIndexMap.lookup(InfoSection);
1505 case ELF::SHT_SYMTAB:
1506 case ELF::SHT_DYNSYM:
1507 sh_link = StringTableIndex;
1508 sh_info = LastLocalSymbolIndex;
1511 case ELF::SHT_SYMTAB_SHNDX:
1512 sh_link = SymbolTableIndex;
1515 case ELF::SHT_GROUP:
1516 sh_link = SymbolTableIndex;
1517 sh_info = GroupSymbolIndex;
1521 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1522 Section.getType() == ELF::SHT_ARM_EXIDX)
1523 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1525 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1527 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1528 Alignment, Section.getEntrySize());
1531 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1532 return SD.getOrdinal() == ~UINT32_C(0) &&
1533 !SD.getSection().isVirtualSection();
1536 void ELFObjectWriter::writeDataSectionData(MCAssembler &Asm,
1537 const MCAsmLayout &Layout,
1538 const MCSectionData &SD) {
1539 if (IsELFMetaDataSection(SD)) {
1540 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1542 const MCFragment &F = *i;
1543 assert(F.getKind() == MCFragment::FT_Data);
1544 WriteBytes(cast<MCDataFragment>(F).getContents());
1547 Asm.writeSectionData(&SD, Layout);
1551 void ELFObjectWriter::writeSectionHeader(
1552 ArrayRef<const MCSectionELF *> Sections, MCAssembler &Asm,
1553 const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap,
1554 const SectionOffsetsTy &SectionOffsets) {
1555 const unsigned NumSections = Asm.size();
1557 // Null section first.
1558 uint64_t FirstSectionSize =
1559 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1560 uint32_t FirstSectionLink =
1561 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1562 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1564 for (unsigned i = 0; i < NumSections; ++i) {
1565 const MCSectionELF &Section = *Sections[i];
1566 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1567 uint32_t GroupSymbolIndex;
1568 if (Section.getType() != ELF::SHT_GROUP)
1569 GroupSymbolIndex = 0;
1571 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section.getGroup());
1573 const std::pair<uint64_t, uint64_t> &Offsets = SectionOffsets[i];
1574 uint64_t Size = Section.getType() == ELF::SHT_NOBITS
1575 ? Layout.getSectionAddressSize(&SD)
1576 : Offsets.second - Offsets.first;
1578 writeSection(Asm, SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1579 SD.getAlignment(), Section);
1583 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1584 const MCAsmLayout &Layout) {
1585 RevGroupMapTy RevGroupMap;
1586 SectionIndexMapTy SectionIndexMap;
1588 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1589 std::vector<const MCSectionELF *> Sections;
1590 createIndexedSections(Asm, const_cast<MCAsmLayout &>(Layout), RevGroupMap,
1591 Sections, SectionIndexMap);
1593 // Compute symbol table information.
1594 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1596 WriteRelocations(Asm, const_cast<MCAsmLayout &>(Layout));
1598 CreateMetadataSections(const_cast<MCAssembler &>(Asm),
1599 const_cast<MCAsmLayout &>(Layout), Sections);
1601 unsigned NumSections = Asm.size();
1602 SectionOffsetsTy SectionOffsets;
1604 // Write out the ELF header ...
1605 WriteHeader(Asm, NumSections + 1);
1607 // ... then the sections ...
1608 for (const MCSectionELF *Section : Sections) {
1609 const MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1610 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1611 WriteZeros(Padding);
1613 // Remember the offset into the file for this section.
1614 uint64_t SecStart = OS.tell();
1615 writeDataSectionData(Asm, Layout, SD);
1616 uint64_t SecEnd = OS.tell();
1617 SectionOffsets.push_back(std::make_pair(SecStart, SecEnd));
1620 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1621 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1622 WriteZeros(Padding);
1624 const unsigned SectionHeaderOffset = OS.tell();
1626 // ... then the section header table ...
1627 writeSectionHeader(Sections, Asm, Layout, SectionIndexMap, SectionOffsets);
1630 uint64_t Val = SectionHeaderOffset;
1631 if (sys::IsLittleEndianHost != IsLittleEndian)
1632 sys::swapByteOrder(Val);
1633 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1634 offsetof(ELF::Elf64_Ehdr, e_shoff));
1636 uint32_t Val = SectionHeaderOffset;
1637 if (sys::IsLittleEndianHost != IsLittleEndian)
1638 sys::swapByteOrder(Val);
1639 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1640 offsetof(ELF::Elf32_Ehdr, e_shoff));
1644 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1645 const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
1646 bool InSet, bool IsPCRel) const {
1649 if (::isWeak(DataA))
1652 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
1656 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
1660 // It is invalid to replace a reference to a global in a comdat
1661 // with a reference to a local since out of comdat references
1662 // to a local are forbidden.
1663 // We could try to return false for more cases, like the reference
1664 // being in the same comdat or Sym being an alias to another global,
1665 // but it is not clear if it is worth the effort.
1666 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1669 const MCSymbol &Sym = SD.getSymbol();
1670 if (!Sym.isInSection())
1673 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1674 return Sec.getGroup();
1677 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1678 raw_pwrite_stream &OS,
1679 bool IsLittleEndian) {
1680 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);