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 void createRelocationSection(MCAssembler &Asm, const MCSectionData &SD);
244 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
246 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout);
248 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
249 std::vector<const MCSectionELF *> &Sections);
251 // Create the sections that show up in the symbol table. Currently
252 // those are the .note.GNU-stack section and the group sections.
253 void createIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
254 RevGroupMapTy &RevGroupMap,
255 std::vector<const MCSectionELF *> &Sections,
256 SectionIndexMapTy &SectionIndexMap);
258 void ExecutePostLayoutBinding(MCAssembler &Asm,
259 const MCAsmLayout &Layout) override;
261 void writeSectionHeader(ArrayRef<const MCSectionELF *> Sections,
262 MCAssembler &Asm, const MCAsmLayout &Layout,
263 const SectionIndexMapTy &SectionIndexMap,
264 const SectionOffsetsTy &SectionOffsets);
266 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
267 uint64_t Address, uint64_t Offset,
268 uint64_t Size, uint32_t Link, uint32_t Info,
269 uint64_t Alignment, uint64_t EntrySize);
271 void WriteRelocationsFragment(const MCAssembler &Asm,
273 const MCSectionData *SD);
276 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
277 const MCSymbolData &DataA,
278 const MCFragment &FB,
280 bool IsPCRel) const override;
282 bool isWeak(const MCSymbolData &SD) const override;
284 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
285 void writeSection(MCAssembler &Asm,
286 const SectionIndexMapTy &SectionIndexMap,
287 uint32_t GroupSymbolIndex,
288 uint64_t Offset, uint64_t Size, uint64_t Alignment,
289 const MCSectionELF &Section);
293 FragmentWriter::FragmentWriter(bool IsLittleEndian)
294 : IsLittleEndian(IsLittleEndian) {}
296 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
298 Val = support::endian::byte_swap<T, support::little>(Val);
300 Val = support::endian::byte_swap<T, support::big>(Val);
301 const char *Start = (const char *)&Val;
302 F.getContents().append(Start, Start + sizeof(T));
305 void SymbolTableWriter::createSymtabShndx() {
309 MCContext &Ctx = Asm.getContext();
310 const MCSectionELF *SymtabShndxSection =
311 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
312 MCSectionData *SymtabShndxSD =
313 &Asm.getOrCreateSectionData(*SymtabShndxSection);
314 SymtabShndxSD->setAlignment(4);
315 ShndxF = new MCDataFragment(SymtabShndxSD);
316 Sections.push_back(SymtabShndxSection);
318 for (unsigned I = 0; I < NumWritten; ++I)
319 write(*ShndxF, uint32_t(0));
322 template <typename T>
323 void SymbolTableWriter::write(MCDataFragment &F, T Value) {
324 FWriter.write(F, Value);
327 SymbolTableWriter::SymbolTableWriter(
328 MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
329 std::vector<const MCSectionELF *> &Sections, MCDataFragment *SymtabF)
330 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit), Sections(Sections),
331 SymtabF(SymtabF), ShndxF(nullptr), NumWritten(0) {}
333 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
334 uint64_t size, uint8_t other,
335 uint32_t shndx, bool Reserved) {
336 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
343 write(*ShndxF, shndx);
345 write(*ShndxF, uint32_t(0));
348 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
351 write(*SymtabF, name); // st_name
352 write(*SymtabF, info); // st_info
353 write(*SymtabF, other); // st_other
354 write(*SymtabF, Index); // st_shndx
355 write(*SymtabF, value); // st_value
356 write(*SymtabF, size); // st_size
358 write(*SymtabF, name); // st_name
359 write(*SymtabF, uint32_t(value)); // st_value
360 write(*SymtabF, uint32_t(size)); // st_size
361 write(*SymtabF, info); // st_info
362 write(*SymtabF, other); // st_other
363 write(*SymtabF, Index); // st_shndx
369 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
370 const MCFixupKindInfo &FKI =
371 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
373 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
376 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
380 case MCSymbolRefExpr::VK_GOT:
381 case MCSymbolRefExpr::VK_PLT:
382 case MCSymbolRefExpr::VK_GOTPCREL:
383 case MCSymbolRefExpr::VK_GOTOFF:
384 case MCSymbolRefExpr::VK_TPOFF:
385 case MCSymbolRefExpr::VK_TLSGD:
386 case MCSymbolRefExpr::VK_GOTTPOFF:
387 case MCSymbolRefExpr::VK_INDNTPOFF:
388 case MCSymbolRefExpr::VK_NTPOFF:
389 case MCSymbolRefExpr::VK_GOTNTPOFF:
390 case MCSymbolRefExpr::VK_TLSLDM:
391 case MCSymbolRefExpr::VK_DTPOFF:
392 case MCSymbolRefExpr::VK_TLSLD:
397 ELFObjectWriter::~ELFObjectWriter()
400 // Emit the ELF header.
401 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
402 unsigned NumberOfSections) {
408 // emitWord method behaves differently for ELF32 and ELF64, writing
409 // 4 bytes in the former and 8 in the latter.
411 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
413 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
416 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
418 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
420 Write8(TargetObjectWriter->getOSABI());
421 Write8(0); // e_ident[EI_ABIVERSION]
423 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
425 Write16(ELF::ET_REL); // e_type
427 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
429 Write32(ELF::EV_CURRENT); // e_version
430 WriteWord(0); // e_entry, no entry point in .o file
431 WriteWord(0); // e_phoff, no program header for .o
432 WriteWord(0); // e_shoff = sec hdr table off in bytes
434 // e_flags = whatever the target wants
435 Write32(Asm.getELFHeaderEFlags());
437 // e_ehsize = ELF header size
438 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
440 Write16(0); // e_phentsize = prog header entry size
441 Write16(0); // e_phnum = # prog header entries = 0
443 // e_shentsize = Section header entry size
444 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
446 // e_shnum = # of section header ents
447 if (NumberOfSections >= ELF::SHN_LORESERVE)
448 Write16(ELF::SHN_UNDEF);
450 Write16(NumberOfSections);
452 // e_shstrndx = Section # of '.shstrtab'
453 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
454 Write16(ELF::SHN_XINDEX);
456 Write16(ShstrtabIndex);
459 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
460 const MCAsmLayout &Layout) {
461 if (Data.isCommon() && Data.isExternal())
462 return Data.getCommonAlignment();
465 if (!Layout.getSymbolOffset(&Data, Res))
468 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
474 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
475 const MCAsmLayout &Layout) {
476 // The presence of symbol versions causes undefined symbols and
477 // versions declared with @@@ to be renamed.
479 for (MCSymbolData &OriginalData : Asm.symbols()) {
480 const MCSymbol &Alias = OriginalData.getSymbol();
483 if (!Alias.isVariable())
485 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
488 const MCSymbol &Symbol = Ref->getSymbol();
489 MCSymbolData &SD = Asm.getSymbolData(Symbol);
491 StringRef AliasName = Alias.getName();
492 size_t Pos = AliasName.find('@');
493 if (Pos == StringRef::npos)
496 // Aliases defined with .symvar copy the binding from the symbol they alias.
497 // This is the first place we are able to copy this information.
498 OriginalData.setExternal(SD.isExternal());
499 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
501 StringRef Rest = AliasName.substr(Pos);
502 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
505 // FIXME: produce a better error message.
506 if (Symbol.isUndefined() && Rest.startswith("@@") &&
507 !Rest.startswith("@@@"))
508 report_fatal_error("A @@ version cannot be undefined");
510 Renames.insert(std::make_pair(&Symbol, &Alias));
514 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
515 uint8_t Type = newType;
517 // Propagation rules:
518 // IFUNC > FUNC > OBJECT > NOTYPE
519 // TLS_OBJECT > OBJECT > NOTYPE
521 // dont let the new type degrade the old type
525 case ELF::STT_GNU_IFUNC:
526 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
527 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
528 Type = ELF::STT_GNU_IFUNC;
531 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
532 Type == ELF::STT_TLS)
533 Type = ELF::STT_FUNC;
535 case ELF::STT_OBJECT:
536 if (Type == ELF::STT_NOTYPE)
537 Type = ELF::STT_OBJECT;
540 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
541 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
549 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
550 const MCAsmLayout &Layout) {
551 MCSymbolData &OrigData = *MSD.SymbolData;
552 assert((!OrigData.getFragment() ||
553 (&OrigData.getFragment()->getParent()->getSection() ==
554 &OrigData.getSymbol().getSection())) &&
555 "The symbol's section doesn't match the fragment's symbol");
556 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
558 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
560 bool IsReserved = !Base || OrigData.isCommon();
562 // Binding and Type share the same byte as upper and lower nibbles
563 uint8_t Binding = MCELF::GetBinding(OrigData);
564 uint8_t Type = MCELF::GetType(OrigData);
565 MCSymbolData *BaseSD = nullptr;
567 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
568 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
570 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
572 // Other and Visibility share the same byte with Visibility using the lower
574 uint8_t Visibility = MCELF::GetVisibility(OrigData);
575 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
578 uint64_t Value = SymbolValue(OrigData, Layout);
581 const MCExpr *ESize = OrigData.getSize();
583 ESize = BaseSD->getSize();
587 if (!ESize->evaluateKnownAbsolute(Res, Layout))
588 report_fatal_error("Size expression must be absolute.");
592 // Write out the symbol table entry
593 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
594 MSD.SectionIndex, IsReserved);
597 void ELFObjectWriter::WriteSymbolTable(
598 MCDataFragment *SymtabF, MCAssembler &Asm, const MCAsmLayout &Layout,
599 std::vector<const MCSectionELF *> &Sections) {
600 // The string table must be emitted first because we need the index
601 // into the string table for all the symbol names.
603 // FIXME: Make sure the start of the symbol table is aligned.
605 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), Sections, SymtabF);
607 // The first entry is the undefined symbol entry.
608 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
610 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
611 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
612 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
615 // Write the symbol table entries.
616 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
618 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
619 ELFSymbolData &MSD = LocalSymbolData[i];
620 WriteSymbol(Writer, MSD, Layout);
623 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
624 ELFSymbolData &MSD = ExternalSymbolData[i];
625 MCSymbolData &Data = *MSD.SymbolData;
626 assert(((Data.getFlags() & ELF_STB_Global) ||
627 (Data.getFlags() & ELF_STB_Weak)) &&
628 "External symbol requires STB_GLOBAL or STB_WEAK flag");
629 WriteSymbol(Writer, MSD, Layout);
630 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
631 LastLocalSymbolIndex++;
634 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
635 ELFSymbolData &MSD = UndefinedSymbolData[i];
636 MCSymbolData &Data = *MSD.SymbolData;
637 WriteSymbol(Writer, MSD, Layout);
638 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
639 LastLocalSymbolIndex++;
643 // It is always valid to create a relocation with a symbol. It is preferable
644 // to use a relocation with a section if that is possible. Using the section
645 // allows us to omit some local symbols from the symbol table.
646 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
647 const MCSymbolRefExpr *RefA,
648 const MCSymbolData *SD,
650 unsigned Type) const {
651 // A PCRel relocation to an absolute value has no symbol (or section). We
652 // represent that with a relocation to a null section.
656 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
660 // The .odp creation emits a relocation against the symbol ".TOC." which
661 // create a R_PPC64_TOC relocation. However the relocation symbol name
662 // in final object creation should be NULL, since the symbol does not
663 // really exist, it is just the reference to TOC base for the current
664 // object file. Since the symbol is undefined, returning false results
665 // in a relocation with a null section which is the desired result.
666 case MCSymbolRefExpr::VK_PPC_TOCBASE:
669 // These VariantKind cause the relocation to refer to something other than
670 // the symbol itself, like a linker generated table. Since the address of
671 // symbol is not relevant, we cannot replace the symbol with the
672 // section and patch the difference in the addend.
673 case MCSymbolRefExpr::VK_GOT:
674 case MCSymbolRefExpr::VK_PLT:
675 case MCSymbolRefExpr::VK_GOTPCREL:
676 case MCSymbolRefExpr::VK_Mips_GOT:
677 case MCSymbolRefExpr::VK_PPC_GOT_LO:
678 case MCSymbolRefExpr::VK_PPC_GOT_HI:
679 case MCSymbolRefExpr::VK_PPC_GOT_HA:
683 // An undefined symbol is not in any section, so the relocation has to point
684 // to the symbol itself.
685 const MCSymbol &Sym = SD->getSymbol();
686 if (Sym.isUndefined())
689 unsigned Binding = MCELF::GetBinding(*SD);
692 llvm_unreachable("Invalid Binding");
696 // If the symbol is weak, it might be overridden by a symbol in another
697 // file. The relocation has to point to the symbol so that the linker
700 case ELF::STB_GLOBAL:
701 // Global ELF symbols can be preempted by the dynamic linker. The relocation
702 // has to point to the symbol for a reason analogous to the STB_WEAK case.
706 // If a relocation points to a mergeable section, we have to be careful.
707 // If the offset is zero, a relocation with the section will encode the
708 // same information. With a non-zero offset, the situation is different.
709 // For example, a relocation can point 42 bytes past the end of a string.
710 // If we change such a relocation to use the section, the linker would think
711 // that it pointed to another string and subtracting 42 at runtime will
712 // produce the wrong value.
713 auto &Sec = cast<MCSectionELF>(Sym.getSection());
714 unsigned Flags = Sec.getFlags();
715 if (Flags & ELF::SHF_MERGE) {
719 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
720 // only handle section relocations to mergeable sections if using RELA.
721 if (!hasRelocationAddend())
725 // Most TLS relocations use a got, so they need the symbol. Even those that
726 // are just an offset (@tpoff), require a symbol in gold versions before
727 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
728 // http://sourceware.org/PR16773.
729 if (Flags & ELF::SHF_TLS)
732 // If the symbol is a thumb function the final relocation must set the lowest
733 // bit. With a symbol that is done by just having the symbol have that bit
734 // set, so we would lose the bit if we relocated with the section.
735 // FIXME: We could use the section but add the bit to the relocation value.
736 if (Asm.isThumbFunc(&Sym))
739 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
744 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
745 const MCSymbol &Sym = Ref.getSymbol();
747 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
750 if (!Sym.isVariable())
753 const MCExpr *Expr = Sym.getVariableValue();
754 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
758 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
759 return &Inner->getSymbol();
763 // True if the assembler knows nothing about the final value of the symbol.
764 // This doesn't cover the comdat issues, since in those cases the assembler
765 // can at least know that all symbols in the section will move together.
766 static bool isWeak(const MCSymbolData &D) {
767 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
770 switch (MCELF::GetBinding(D)) {
772 llvm_unreachable("Unknown binding");
775 case ELF::STB_GLOBAL:
778 case ELF::STB_GNU_UNIQUE:
783 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
784 const MCAsmLayout &Layout,
785 const MCFragment *Fragment,
786 const MCFixup &Fixup, MCValue Target,
787 bool &IsPCRel, uint64_t &FixedValue) {
788 const MCSectionData *FixupSection = Fragment->getParent();
789 uint64_t C = Target.getConstant();
790 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
792 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
793 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
794 "Should not have constructed this");
796 // Let A, B and C being the components of Target and R be the location of
797 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
798 // If it is pcrel, we want to compute (A - B + C - R).
800 // In general, ELF has no relocations for -B. It can only represent (A + C)
801 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
802 // replace B to implement it: (A - R - K + C)
804 Asm.getContext().FatalError(
806 "No relocation available to represent this relative expression");
808 const MCSymbol &SymB = RefB->getSymbol();
810 if (SymB.isUndefined())
811 Asm.getContext().FatalError(
813 Twine("symbol '") + SymB.getName() +
814 "' can not be undefined in a subtraction expression");
816 assert(!SymB.isAbsolute() && "Should have been folded");
817 const MCSection &SecB = SymB.getSection();
818 if (&SecB != &FixupSection->getSection())
819 Asm.getContext().FatalError(
820 Fixup.getLoc(), "Cannot represent a difference across sections");
822 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
824 Asm.getContext().FatalError(
825 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
827 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
828 uint64_t K = SymBOffset - FixupOffset;
833 // We either rejected the fixup or folded B into C at this point.
834 const MCSymbolRefExpr *RefA = Target.getSymA();
835 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
836 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
838 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
839 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
840 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
841 C += Layout.getSymbolOffset(SymAD);
844 if (hasRelocationAddend()) {
851 // FIXME: What is this!?!?
852 MCSymbolRefExpr::VariantKind Modifier =
853 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
854 if (RelocNeedsGOT(Modifier))
857 if (!RelocateWithSymbol) {
858 const MCSection *SecA =
859 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
860 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
861 MCSymbol *SectionSymbol =
862 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
864 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
865 Relocations[FixupSection].push_back(Rec);
870 if (const MCSymbol *R = Renames.lookup(SymA))
873 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
874 WeakrefUsedInReloc.insert(WeakRef);
876 UsedInReloc.insert(SymA);
878 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
879 Relocations[FixupSection].push_back(Rec);
885 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
887 const MCSymbolData &SD = Asm.getSymbolData(*S);
888 return SD.getIndex();
891 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
892 const MCSymbolData &Data, bool Used,
894 const MCSymbol &Symbol = Data.getSymbol();
895 if (Symbol.isVariable()) {
896 const MCExpr *Expr = Symbol.getVariableValue();
897 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
898 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
909 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
912 if (Symbol.isVariable()) {
913 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
914 if (Base && Base->isUndefined())
918 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
919 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
922 if (Symbol.isTemporary())
928 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
929 if (Data.isExternal())
932 const MCSymbol &Symbol = Data.getSymbol();
933 if (Symbol.isDefined())
942 void ELFObjectWriter::maybeAddToGroup(MCAssembler &Asm,
943 const RevGroupMapTy &RevGroupMap,
944 const MCSectionELF &Section,
946 const MCSymbol *Sym = Section.getGroup();
949 const MCSectionELF *Group = RevGroupMap.lookup(Sym);
950 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
951 // FIXME: we could use the previous fragment
952 MCDataFragment *F = new MCDataFragment(&Data);
956 void ELFObjectWriter::computeIndexMap(
957 MCAssembler &Asm, std::vector<const MCSectionELF *> &Sections,
958 SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap) {
959 for (const MCSectionData &SD : Asm) {
960 const MCSectionELF &Section =
961 static_cast<const MCSectionELF &>(SD.getSection());
962 if (Section.getType() == ELF::SHT_GROUP)
964 Sections.push_back(&Section);
965 unsigned Index = Sections.size();
966 SectionIndexMap[&Section] = Index;
967 maybeAddToGroup(Asm, RevGroupMap, Section, Index);
968 createRelocationSection(Asm, SD);
972 void ELFObjectWriter::computeSymbolTable(
973 MCAssembler &Asm, const MCAsmLayout &Layout,
974 const SectionIndexMapTy &SectionIndexMap,
975 const RevGroupMapTy &RevGroupMap) {
976 // FIXME: Is this the correct place to do this?
977 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
979 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
980 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
981 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
982 Data.setExternal(true);
983 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
986 // Add the data for the symbols.
987 for (MCSymbolData &SD : Asm.symbols()) {
988 const MCSymbol &Symbol = SD.getSymbol();
990 bool Used = UsedInReloc.count(&Symbol);
991 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
992 bool isSignature = RevGroupMap.count(&Symbol);
994 if (!isInSymtab(Layout, SD,
995 Used || WeakrefUsed || isSignature,
996 Renames.count(&Symbol)))
1000 MSD.SymbolData = &SD;
1001 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
1003 // Undefined symbols are global, but this is the first place we
1004 // are able to set it.
1005 bool Local = isLocal(SD, Used);
1006 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1008 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1009 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1010 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1014 MSD.SectionIndex = ELF::SHN_ABS;
1015 } else if (SD.isCommon()) {
1017 MSD.SectionIndex = ELF::SHN_COMMON;
1018 } else if (BaseSymbol->isUndefined()) {
1019 if (isSignature && !Used)
1020 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap.lookup(&Symbol));
1022 MSD.SectionIndex = ELF::SHN_UNDEF;
1023 if (!Used && WeakrefUsed)
1024 MCELF::SetBinding(SD, ELF::STB_WEAK);
1026 const MCSectionELF &Section =
1027 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1028 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1029 assert(MSD.SectionIndex && "Invalid section index!");
1032 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
1035 // FIXME: All name handling should be done before we get to the writer,
1036 // including dealing with GNU-style version suffixes. Fixing this isn't
1039 // We thus have to be careful to not perform the symbol version replacement
1042 // The ELF format is used on Windows by the MCJIT engine. Thus, on
1043 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
1044 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
1045 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
1046 // the EFLObjectWriter should not interpret the "@@@" sub-string as
1047 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1048 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1049 // "__imp_?" or "__imp_@?".
1051 // It would have been interesting to perform the MS mangling prefix check
1052 // only when the target triple is of the form *-pc-windows-elf. But, it
1053 // seems that this information is not easily accessible from the
1055 StringRef Name = Symbol.getName();
1056 if (!Name.startswith("?") && !Name.startswith("@?") &&
1057 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1058 // This symbol isn't following the MSVC C++ name mangling convention. We
1059 // can thus safely interpret the @@@ in symbol names as specifying symbol
1061 SmallString<32> Buf;
1062 size_t Pos = Name.find("@@@");
1063 if (Pos != StringRef::npos) {
1064 Buf += Name.substr(0, Pos);
1065 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1066 Buf += Name.substr(Pos + Skip);
1071 // Sections have their own string table
1072 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1073 MSD.Name = StrTabBuilder.add(Name);
1075 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1076 UndefinedSymbolData.push_back(MSD);
1078 LocalSymbolData.push_back(MSD);
1080 ExternalSymbolData.push_back(MSD);
1083 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1084 StrTabBuilder.add(*i);
1086 StrTabBuilder.finalize(StringTableBuilder::ELF);
1088 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1089 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1091 for (ELFSymbolData &MSD : LocalSymbolData)
1092 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1094 : StrTabBuilder.getOffset(MSD.Name);
1095 for (ELFSymbolData &MSD : ExternalSymbolData)
1096 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1097 for (ELFSymbolData& MSD : UndefinedSymbolData)
1098 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1100 // Symbols are required to be in lexicographic order.
1101 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1102 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1103 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1105 // Set the symbol indices. Local symbols must come before all other
1106 // symbols with non-local bindings.
1107 unsigned Index = FileSymbolData.size() + 1;
1108 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1109 LocalSymbolData[i].SymbolData->setIndex(Index++);
1111 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1112 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1113 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1114 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1117 void ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1118 const MCSectionData &SD) {
1119 if (Relocations[&SD].empty())
1122 MCContext &Ctx = Asm.getContext();
1123 const MCSectionELF &Section =
1124 static_cast<const MCSectionELF &>(SD.getSection());
1126 const StringRef SectionName = Section.getSectionName();
1127 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1128 RelaSectionName += SectionName;
1131 if (hasRelocationAddend())
1132 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1134 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1137 if (Section.getFlags() & ELF::SHF_GROUP)
1138 Flags = ELF::SHF_GROUP;
1140 const MCSectionELF *RelaSection = Ctx.createELFRelSection(
1141 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1142 Flags, EntrySize, Section.getGroup(), &Section);
1143 Asm.getOrCreateSectionData(*RelaSection);
1146 static SmallVector<char, 128>
1147 getUncompressedData(MCAsmLayout &Layout,
1148 MCSectionData::FragmentListType &Fragments) {
1149 SmallVector<char, 128> UncompressedData;
1150 for (const MCFragment &F : Fragments) {
1151 const SmallVectorImpl<char> *Contents;
1152 switch (F.getKind()) {
1153 case MCFragment::FT_Data:
1154 Contents = &cast<MCDataFragment>(F).getContents();
1156 case MCFragment::FT_Dwarf:
1157 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1159 case MCFragment::FT_DwarfFrame:
1160 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1164 "Not expecting any other fragment types in a debug_* section");
1166 UncompressedData.append(Contents->begin(), Contents->end());
1168 return UncompressedData;
1171 // Include the debug info compression header:
1172 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1173 // useful for consumers to preallocate a buffer to decompress into.
1175 prependCompressionHeader(uint64_t Size,
1176 SmallVectorImpl<char> &CompressedContents) {
1177 const StringRef Magic = "ZLIB";
1178 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1180 if (sys::IsLittleEndianHost)
1181 sys::swapByteOrder(Size);
1182 CompressedContents.insert(CompressedContents.begin(),
1183 Magic.size() + sizeof(Size), 0);
1184 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1185 std::copy(reinterpret_cast<char *>(&Size),
1186 reinterpret_cast<char *>(&Size + 1),
1187 CompressedContents.begin() + Magic.size());
1191 // Return a single fragment containing the compressed contents of the whole
1192 // section. Null if the section was not compressed for any reason.
1193 static std::unique_ptr<MCDataFragment>
1194 getCompressedFragment(MCAsmLayout &Layout,
1195 MCSectionData::FragmentListType &Fragments) {
1196 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1198 // Gather the uncompressed data from all the fragments, recording the
1199 // alignment fragment, if seen, and any fixups.
1200 SmallVector<char, 128> UncompressedData =
1201 getUncompressedData(Layout, Fragments);
1203 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1205 zlib::Status Success = zlib::compress(
1206 StringRef(UncompressedData.data(), UncompressedData.size()),
1207 CompressedContents);
1208 if (Success != zlib::StatusOK)
1211 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1214 return CompressedFragment;
1217 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1220 static void UpdateSymbols(const MCAsmLayout &Layout,
1221 const std::vector<MCSymbolData *> &Symbols,
1222 MCFragment &NewFragment) {
1223 for (MCSymbolData *Sym : Symbols) {
1224 Sym->setOffset(Sym->getOffset() +
1225 Layout.getFragmentOffset(Sym->getFragment()));
1226 Sym->setFragment(&NewFragment);
1230 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1231 const DefiningSymbolMap &DefiningSymbols,
1232 const MCSectionELF &Section,
1233 MCSectionData &SD) {
1234 StringRef SectionName = Section.getSectionName();
1235 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1237 std::unique_ptr<MCDataFragment> CompressedFragment =
1238 getCompressedFragment(Layout, Fragments);
1240 // Leave the section as-is if the fragments could not be compressed.
1241 if (!CompressedFragment)
1244 // Update the fragment+offsets of any symbols referring to fragments in this
1245 // section to refer to the new fragment.
1246 auto I = DefiningSymbols.find(&SD);
1247 if (I != DefiningSymbols.end())
1248 UpdateSymbols(Layout, I->second, *CompressedFragment);
1250 // Invalidate the layout for the whole section since it will have new and
1251 // different fragments now.
1252 Layout.invalidateFragmentsFrom(&Fragments.front());
1255 // Complete the initialization of the new fragment
1256 CompressedFragment->setParent(&SD);
1257 CompressedFragment->setLayoutOrder(0);
1258 Fragments.push_back(CompressedFragment.release());
1260 // Rename from .debug_* to .zdebug_*
1261 Asm.getContext().renameELFSection(&Section,
1262 (".z" + SectionName.drop_front(1)).str());
1265 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1266 MCAsmLayout &Layout) {
1267 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1270 DefiningSymbolMap DefiningSymbols;
1272 for (MCSymbolData &SD : Asm.symbols())
1273 if (MCFragment *F = SD.getFragment())
1274 DefiningSymbols[F->getParent()].push_back(&SD);
1276 for (MCSectionData &SD : Asm) {
1277 const MCSectionELF &Section =
1278 static_cast<const MCSectionELF &>(SD.getSection());
1279 StringRef SectionName = Section.getSectionName();
1281 // Compressing debug_frame requires handling alignment fragments which is
1282 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1283 // for writing to arbitrary buffers) for little benefit.
1284 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1287 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1291 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) {
1292 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1293 MCSectionData &RelSD = *it;
1294 const MCSectionELF &RelSection =
1295 static_cast<const MCSectionELF &>(RelSD.getSection());
1297 unsigned Type = RelSection.getType();
1298 if (Type != ELF::SHT_REL && Type != ELF::SHT_RELA)
1301 const MCSectionELF *Section = RelSection.getAssociatedSection();
1302 MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1303 RelSD.setAlignment(is64Bit() ? 8 : 4);
1305 MCDataFragment *F = new MCDataFragment(&RelSD);
1306 WriteRelocationsFragment(Asm, F, &SD);
1310 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1311 uint64_t Flags, uint64_t Address,
1312 uint64_t Offset, uint64_t Size,
1313 uint32_t Link, uint32_t Info,
1315 uint64_t EntrySize) {
1316 Write32(Name); // sh_name: index into string table
1317 Write32(Type); // sh_type
1318 WriteWord(Flags); // sh_flags
1319 WriteWord(Address); // sh_addr
1320 WriteWord(Offset); // sh_offset
1321 WriteWord(Size); // sh_size
1322 Write32(Link); // sh_link
1323 Write32(Info); // sh_info
1324 WriteWord(Alignment); // sh_addralign
1325 WriteWord(EntrySize); // sh_entsize
1328 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1330 const MCSectionData *SD) {
1331 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1333 // Sort the relocation entries. Most targets just sort by Offset, but some
1334 // (e.g., MIPS) have additional constraints.
1335 TargetObjectWriter->sortRelocs(Asm, Relocs);
1337 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1338 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1340 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1343 write(*F, Entry.Offset);
1344 if (TargetObjectWriter->isN64()) {
1345 write(*F, uint32_t(Index));
1347 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1348 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1349 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1350 write(*F, TargetObjectWriter->getRType(Entry.Type));
1352 struct ELF::Elf64_Rela ERE64;
1353 ERE64.setSymbolAndType(Index, Entry.Type);
1354 write(*F, ERE64.r_info);
1356 if (hasRelocationAddend())
1357 write(*F, Entry.Addend);
1359 write(*F, uint32_t(Entry.Offset));
1361 struct ELF::Elf32_Rela ERE32;
1362 ERE32.setSymbolAndType(Index, Entry.Type);
1363 write(*F, ERE32.r_info);
1365 if (hasRelocationAddend())
1366 write(*F, uint32_t(Entry.Addend));
1371 void ELFObjectWriter::CreateMetadataSections(
1372 MCAssembler &Asm, MCAsmLayout &Layout,
1373 std::vector<const MCSectionELF *> &Sections) {
1374 MCContext &Ctx = Asm.getContext();
1377 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1379 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1380 const MCSectionELF *ShstrtabSection =
1381 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1382 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1383 ShstrtabSD.setAlignment(1);
1384 ShstrtabIndex = Sections.size() + 1;
1385 Sections.push_back(ShstrtabSection);
1387 const MCSectionELF *SymtabSection =
1388 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1390 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1391 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1392 SymbolTableIndex = Sections.size() + 1;
1393 Sections.push_back(SymtabSection);
1395 const MCSectionELF *StrtabSection;
1396 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1397 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1398 StrtabSD.setAlignment(1);
1399 StringTableIndex = Sections.size() + 1;
1400 Sections.push_back(StrtabSection);
1403 F = new MCDataFragment(&SymtabSD);
1404 WriteSymbolTable(F, Asm, Layout, Sections);
1406 F = new MCDataFragment(&StrtabSD);
1407 F->getContents().append(StrTabBuilder.data().begin(),
1408 StrTabBuilder.data().end());
1410 F = new MCDataFragment(&ShstrtabSD);
1412 // Section header string table.
1413 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1414 const MCSectionELF &Section =
1415 static_cast<const MCSectionELF&>(it->getSection());
1416 ShStrTabBuilder.add(Section.getSectionName());
1418 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1419 F->getContents().append(ShStrTabBuilder.data().begin(),
1420 ShStrTabBuilder.data().end());
1423 void ELFObjectWriter::createIndexedSections(
1424 MCAssembler &Asm, MCAsmLayout &Layout, RevGroupMapTy &RevGroupMap,
1425 std::vector<const MCSectionELF *> &Sections,
1426 SectionIndexMapTy &SectionIndexMap) {
1427 MCContext &Ctx = Asm.getContext();
1430 for (const MCSectionData &SD : Asm) {
1431 const MCSectionELF &Section =
1432 static_cast<const MCSectionELF &>(SD.getSection());
1433 if (!(Section.getFlags() & ELF::SHF_GROUP))
1436 const MCSymbol *SignatureSymbol = Section.getGroup();
1437 Asm.getOrCreateSymbolData(*SignatureSymbol);
1438 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1440 Group = Ctx.createELFGroupSection(SignatureSymbol);
1441 Sections.push_back(Group);
1442 SectionIndexMap[Group] = Sections.size();
1444 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1445 Data.setAlignment(4);
1446 MCDataFragment *F = new MCDataFragment(&Data);
1447 write(*F, uint32_t(ELF::GRP_COMDAT));
1451 computeIndexMap(Asm, Sections, SectionIndexMap, RevGroupMap);
1454 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1455 const SectionIndexMapTy &SectionIndexMap,
1456 uint32_t GroupSymbolIndex,
1457 uint64_t Offset, uint64_t Size,
1459 const MCSectionELF &Section) {
1460 uint64_t sh_link = 0;
1461 uint64_t sh_info = 0;
1463 switch(Section.getType()) {
1468 case ELF::SHT_DYNAMIC:
1469 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1473 case ELF::SHT_RELA: {
1474 sh_link = SymbolTableIndex;
1475 assert(sh_link && ".symtab not found");
1476 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1477 sh_info = SectionIndexMap.lookup(InfoSection);
1481 case ELF::SHT_SYMTAB:
1482 case ELF::SHT_DYNSYM:
1483 sh_link = StringTableIndex;
1484 sh_info = LastLocalSymbolIndex;
1487 case ELF::SHT_SYMTAB_SHNDX:
1488 sh_link = SymbolTableIndex;
1491 case ELF::SHT_GROUP:
1492 sh_link = SymbolTableIndex;
1493 sh_info = GroupSymbolIndex;
1497 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1498 Section.getType() == ELF::SHT_ARM_EXIDX)
1499 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1501 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1503 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1504 Alignment, Section.getEntrySize());
1507 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1508 return SD.getOrdinal() == ~UINT32_C(0) &&
1509 !SD.getSection().isVirtualSection();
1512 void ELFObjectWriter::writeDataSectionData(MCAssembler &Asm,
1513 const MCAsmLayout &Layout,
1514 const MCSectionData &SD) {
1515 if (IsELFMetaDataSection(SD)) {
1516 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1518 const MCFragment &F = *i;
1519 assert(F.getKind() == MCFragment::FT_Data);
1520 WriteBytes(cast<MCDataFragment>(F).getContents());
1523 Asm.writeSectionData(&SD, Layout);
1527 void ELFObjectWriter::writeSectionHeader(
1528 ArrayRef<const MCSectionELF *> Sections, MCAssembler &Asm,
1529 const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap,
1530 const SectionOffsetsTy &SectionOffsets) {
1531 const unsigned NumSections = Asm.size();
1533 // Null section first.
1534 uint64_t FirstSectionSize =
1535 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1536 uint32_t FirstSectionLink =
1537 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1538 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1540 for (unsigned i = 0; i < NumSections; ++i) {
1541 const MCSectionELF &Section = *Sections[i];
1542 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1543 uint32_t GroupSymbolIndex;
1544 if (Section.getType() != ELF::SHT_GROUP)
1545 GroupSymbolIndex = 0;
1547 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section.getGroup());
1549 const std::pair<uint64_t, uint64_t> &Offsets = SectionOffsets[i];
1550 uint64_t Size = Section.getType() == ELF::SHT_NOBITS
1551 ? Layout.getSectionAddressSize(&SD)
1552 : Offsets.second - Offsets.first;
1554 writeSection(Asm, SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1555 SD.getAlignment(), Section);
1559 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1560 const MCAsmLayout &Layout) {
1561 RevGroupMapTy RevGroupMap;
1562 SectionIndexMapTy SectionIndexMap;
1564 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1565 std::vector<const MCSectionELF *> Sections;
1566 createIndexedSections(Asm, const_cast<MCAsmLayout &>(Layout), RevGroupMap,
1567 Sections, SectionIndexMap);
1569 // Compute symbol table information.
1570 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1572 WriteRelocations(Asm, const_cast<MCAsmLayout &>(Layout));
1574 CreateMetadataSections(const_cast<MCAssembler &>(Asm),
1575 const_cast<MCAsmLayout &>(Layout), Sections);
1577 unsigned NumSections = Asm.size();
1578 SectionOffsetsTy SectionOffsets;
1580 // Write out the ELF header ...
1581 WriteHeader(Asm, NumSections + 1);
1583 // ... then the sections ...
1584 for (const MCSectionELF *Section : Sections) {
1585 const MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1586 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1587 WriteZeros(Padding);
1589 // Remember the offset into the file for this section.
1590 uint64_t SecStart = OS.tell();
1591 writeDataSectionData(Asm, Layout, SD);
1592 uint64_t SecEnd = OS.tell();
1593 SectionOffsets.push_back(std::make_pair(SecStart, SecEnd));
1596 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1597 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1598 WriteZeros(Padding);
1600 const unsigned SectionHeaderOffset = OS.tell();
1602 // ... then the section header table ...
1603 writeSectionHeader(Sections, Asm, Layout, SectionIndexMap, SectionOffsets);
1606 uint64_t Val = SectionHeaderOffset;
1607 if (sys::IsLittleEndianHost != IsLittleEndian)
1608 sys::swapByteOrder(Val);
1609 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1610 offsetof(ELF::Elf64_Ehdr, e_shoff));
1612 uint32_t Val = SectionHeaderOffset;
1613 if (sys::IsLittleEndianHost != IsLittleEndian)
1614 sys::swapByteOrder(Val);
1615 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1616 offsetof(ELF::Elf32_Ehdr, e_shoff));
1620 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1621 const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
1622 bool InSet, bool IsPCRel) const {
1625 if (::isWeak(DataA))
1628 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
1632 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
1636 // It is invalid to replace a reference to a global in a comdat
1637 // with a reference to a local since out of comdat references
1638 // to a local are forbidden.
1639 // We could try to return false for more cases, like the reference
1640 // being in the same comdat or Sym being an alias to another global,
1641 // but it is not clear if it is worth the effort.
1642 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1645 const MCSymbol &Sym = SD.getSymbol();
1646 if (!Sym.isInSection())
1649 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1650 return Sec.getGroup();
1653 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1654 raw_pwrite_stream &OS,
1655 bool IsLittleEndian) {
1656 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);