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 group section to the signature symbol
221 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
222 // Map from a signature symbol to the group section
223 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
224 // Start and end offset of each section
225 typedef std::vector<std::pair<uint64_t, uint64_t>> SectionOffsetsTy;
227 /// Compute the symbol table data
229 /// \param Asm - The assembler.
230 /// \param SectionIndexMap - Maps a section to its index.
231 /// \param RevGroupMap - Maps a signature symbol to the group section.
232 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
233 const SectionIndexMapTy &SectionIndexMap,
234 const RevGroupMapTy &RevGroupMap);
236 void computeIndexMap(MCAssembler &Asm, SectionIndexMapTy &SectionIndexMap);
238 MCSectionData *createRelocationSection(MCAssembler &Asm,
239 const MCSectionData &SD);
241 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
243 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout);
245 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
246 std::vector<const MCSectionELF *> &Sections);
248 // Create the sections that show up in the symbol table. Currently
249 // those are the .note.GNU-stack section and the group sections.
250 void createIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
251 GroupMapTy &GroupMap, RevGroupMapTy &RevGroupMap,
252 SectionIndexMapTy &SectionIndexMap);
254 void ExecutePostLayoutBinding(MCAssembler &Asm,
255 const MCAsmLayout &Layout) override;
257 void writeSectionHeader(ArrayRef<const MCSectionELF *> Sections,
258 MCAssembler &Asm, const GroupMapTy &GroupMap,
259 const MCAsmLayout &Layout,
260 const SectionIndexMapTy &SectionIndexMap,
261 const SectionOffsetsTy &SectionOffsets);
263 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
264 uint64_t Address, uint64_t Offset,
265 uint64_t Size, uint32_t Link, uint32_t Info,
266 uint64_t Alignment, uint64_t EntrySize);
268 void WriteRelocationsFragment(const MCAssembler &Asm,
270 const MCSectionData *SD);
273 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
274 const MCSymbolData &DataA,
275 const MCFragment &FB,
277 bool IsPCRel) const override;
279 bool isWeak(const MCSymbolData &SD) const override;
281 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
282 void writeSection(MCAssembler &Asm,
283 const SectionIndexMapTy &SectionIndexMap,
284 uint32_t GroupSymbolIndex,
285 uint64_t Offset, uint64_t Size, uint64_t Alignment,
286 const MCSectionELF &Section);
290 FragmentWriter::FragmentWriter(bool IsLittleEndian)
291 : IsLittleEndian(IsLittleEndian) {}
293 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
295 Val = support::endian::byte_swap<T, support::little>(Val);
297 Val = support::endian::byte_swap<T, support::big>(Val);
298 const char *Start = (const char *)&Val;
299 F.getContents().append(Start, Start + sizeof(T));
302 void SymbolTableWriter::createSymtabShndx() {
306 MCContext &Ctx = Asm.getContext();
307 const MCSectionELF *SymtabShndxSection =
308 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
309 MCSectionData *SymtabShndxSD =
310 &Asm.getOrCreateSectionData(*SymtabShndxSection);
311 SymtabShndxSD->setAlignment(4);
312 ShndxF = new MCDataFragment(SymtabShndxSD);
313 Sections.push_back(SymtabShndxSection);
315 for (unsigned I = 0; I < NumWritten; ++I)
316 write(*ShndxF, uint32_t(0));
319 template <typename T>
320 void SymbolTableWriter::write(MCDataFragment &F, T Value) {
321 FWriter.write(F, Value);
324 SymbolTableWriter::SymbolTableWriter(
325 MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
326 std::vector<const MCSectionELF *> &Sections, MCDataFragment *SymtabF)
327 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit), Sections(Sections),
328 SymtabF(SymtabF), ShndxF(nullptr), NumWritten(0) {}
330 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
331 uint64_t size, uint8_t other,
332 uint32_t shndx, bool Reserved) {
333 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
340 write(*ShndxF, shndx);
342 write(*ShndxF, uint32_t(0));
345 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
348 write(*SymtabF, name); // st_name
349 write(*SymtabF, info); // st_info
350 write(*SymtabF, other); // st_other
351 write(*SymtabF, Index); // st_shndx
352 write(*SymtabF, value); // st_value
353 write(*SymtabF, size); // st_size
355 write(*SymtabF, name); // st_name
356 write(*SymtabF, uint32_t(value)); // st_value
357 write(*SymtabF, uint32_t(size)); // st_size
358 write(*SymtabF, info); // st_info
359 write(*SymtabF, other); // st_other
360 write(*SymtabF, Index); // st_shndx
366 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
367 const MCFixupKindInfo &FKI =
368 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
370 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
373 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
377 case MCSymbolRefExpr::VK_GOT:
378 case MCSymbolRefExpr::VK_PLT:
379 case MCSymbolRefExpr::VK_GOTPCREL:
380 case MCSymbolRefExpr::VK_GOTOFF:
381 case MCSymbolRefExpr::VK_TPOFF:
382 case MCSymbolRefExpr::VK_TLSGD:
383 case MCSymbolRefExpr::VK_GOTTPOFF:
384 case MCSymbolRefExpr::VK_INDNTPOFF:
385 case MCSymbolRefExpr::VK_NTPOFF:
386 case MCSymbolRefExpr::VK_GOTNTPOFF:
387 case MCSymbolRefExpr::VK_TLSLDM:
388 case MCSymbolRefExpr::VK_DTPOFF:
389 case MCSymbolRefExpr::VK_TLSLD:
394 ELFObjectWriter::~ELFObjectWriter()
397 // Emit the ELF header.
398 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
399 unsigned NumberOfSections) {
405 // emitWord method behaves differently for ELF32 and ELF64, writing
406 // 4 bytes in the former and 8 in the latter.
408 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
410 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
413 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
415 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
417 Write8(TargetObjectWriter->getOSABI());
418 Write8(0); // e_ident[EI_ABIVERSION]
420 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
422 Write16(ELF::ET_REL); // e_type
424 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
426 Write32(ELF::EV_CURRENT); // e_version
427 WriteWord(0); // e_entry, no entry point in .o file
428 WriteWord(0); // e_phoff, no program header for .o
429 WriteWord(0); // e_shoff = sec hdr table off in bytes
431 // e_flags = whatever the target wants
432 Write32(Asm.getELFHeaderEFlags());
434 // e_ehsize = ELF header size
435 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
437 Write16(0); // e_phentsize = prog header entry size
438 Write16(0); // e_phnum = # prog header entries = 0
440 // e_shentsize = Section header entry size
441 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
443 // e_shnum = # of section header ents
444 if (NumberOfSections >= ELF::SHN_LORESERVE)
445 Write16(ELF::SHN_UNDEF);
447 Write16(NumberOfSections);
449 // e_shstrndx = Section # of '.shstrtab'
450 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
451 Write16(ELF::SHN_XINDEX);
453 Write16(ShstrtabIndex);
456 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
457 const MCAsmLayout &Layout) {
458 if (Data.isCommon() && Data.isExternal())
459 return Data.getCommonAlignment();
462 if (!Layout.getSymbolOffset(&Data, Res))
465 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
471 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
472 const MCAsmLayout &Layout) {
473 // The presence of symbol versions causes undefined symbols and
474 // versions declared with @@@ to be renamed.
476 for (MCSymbolData &OriginalData : Asm.symbols()) {
477 const MCSymbol &Alias = OriginalData.getSymbol();
480 if (!Alias.isVariable())
482 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
485 const MCSymbol &Symbol = Ref->getSymbol();
486 MCSymbolData &SD = Asm.getSymbolData(Symbol);
488 StringRef AliasName = Alias.getName();
489 size_t Pos = AliasName.find('@');
490 if (Pos == StringRef::npos)
493 // Aliases defined with .symvar copy the binding from the symbol they alias.
494 // This is the first place we are able to copy this information.
495 OriginalData.setExternal(SD.isExternal());
496 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
498 StringRef Rest = AliasName.substr(Pos);
499 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
502 // FIXME: produce a better error message.
503 if (Symbol.isUndefined() && Rest.startswith("@@") &&
504 !Rest.startswith("@@@"))
505 report_fatal_error("A @@ version cannot be undefined");
507 Renames.insert(std::make_pair(&Symbol, &Alias));
511 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
512 uint8_t Type = newType;
514 // Propagation rules:
515 // IFUNC > FUNC > OBJECT > NOTYPE
516 // TLS_OBJECT > OBJECT > NOTYPE
518 // dont let the new type degrade the old type
522 case ELF::STT_GNU_IFUNC:
523 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
524 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
525 Type = ELF::STT_GNU_IFUNC;
528 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
529 Type == ELF::STT_TLS)
530 Type = ELF::STT_FUNC;
532 case ELF::STT_OBJECT:
533 if (Type == ELF::STT_NOTYPE)
534 Type = ELF::STT_OBJECT;
537 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
538 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
546 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
547 const MCAsmLayout &Layout) {
548 MCSymbolData &OrigData = *MSD.SymbolData;
549 assert((!OrigData.getFragment() ||
550 (&OrigData.getFragment()->getParent()->getSection() ==
551 &OrigData.getSymbol().getSection())) &&
552 "The symbol's section doesn't match the fragment's symbol");
553 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
555 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
557 bool IsReserved = !Base || OrigData.isCommon();
559 // Binding and Type share the same byte as upper and lower nibbles
560 uint8_t Binding = MCELF::GetBinding(OrigData);
561 uint8_t Type = MCELF::GetType(OrigData);
562 MCSymbolData *BaseSD = nullptr;
564 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
565 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
567 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
569 // Other and Visibility share the same byte with Visibility using the lower
571 uint8_t Visibility = MCELF::GetVisibility(OrigData);
572 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
575 uint64_t Value = SymbolValue(OrigData, Layout);
578 const MCExpr *ESize = OrigData.getSize();
580 ESize = BaseSD->getSize();
584 if (!ESize->evaluateKnownAbsolute(Res, Layout))
585 report_fatal_error("Size expression must be absolute.");
589 // Write out the symbol table entry
590 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
591 MSD.SectionIndex, IsReserved);
594 void ELFObjectWriter::WriteSymbolTable(
595 MCDataFragment *SymtabF, MCAssembler &Asm, const MCAsmLayout &Layout,
596 std::vector<const MCSectionELF *> &Sections) {
597 // The string table must be emitted first because we need the index
598 // into the string table for all the symbol names.
600 // FIXME: Make sure the start of the symbol table is aligned.
602 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), Sections, SymtabF);
604 // The first entry is the undefined symbol entry.
605 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
607 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
608 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
609 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
612 // Write the symbol table entries.
613 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
615 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
616 ELFSymbolData &MSD = LocalSymbolData[i];
617 WriteSymbol(Writer, MSD, Layout);
620 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
621 ELFSymbolData &MSD = ExternalSymbolData[i];
622 MCSymbolData &Data = *MSD.SymbolData;
623 assert(((Data.getFlags() & ELF_STB_Global) ||
624 (Data.getFlags() & ELF_STB_Weak)) &&
625 "External symbol requires STB_GLOBAL or STB_WEAK flag");
626 WriteSymbol(Writer, MSD, Layout);
627 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
628 LastLocalSymbolIndex++;
631 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
632 ELFSymbolData &MSD = UndefinedSymbolData[i];
633 MCSymbolData &Data = *MSD.SymbolData;
634 WriteSymbol(Writer, MSD, Layout);
635 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
636 LastLocalSymbolIndex++;
640 // It is always valid to create a relocation with a symbol. It is preferable
641 // to use a relocation with a section if that is possible. Using the section
642 // allows us to omit some local symbols from the symbol table.
643 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
644 const MCSymbolRefExpr *RefA,
645 const MCSymbolData *SD,
647 unsigned Type) const {
648 // A PCRel relocation to an absolute value has no symbol (or section). We
649 // represent that with a relocation to a null section.
653 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
657 // The .odp creation emits a relocation against the symbol ".TOC." which
658 // create a R_PPC64_TOC relocation. However the relocation symbol name
659 // in final object creation should be NULL, since the symbol does not
660 // really exist, it is just the reference to TOC base for the current
661 // object file. Since the symbol is undefined, returning false results
662 // in a relocation with a null section which is the desired result.
663 case MCSymbolRefExpr::VK_PPC_TOCBASE:
666 // These VariantKind cause the relocation to refer to something other than
667 // the symbol itself, like a linker generated table. Since the address of
668 // symbol is not relevant, we cannot replace the symbol with the
669 // section and patch the difference in the addend.
670 case MCSymbolRefExpr::VK_GOT:
671 case MCSymbolRefExpr::VK_PLT:
672 case MCSymbolRefExpr::VK_GOTPCREL:
673 case MCSymbolRefExpr::VK_Mips_GOT:
674 case MCSymbolRefExpr::VK_PPC_GOT_LO:
675 case MCSymbolRefExpr::VK_PPC_GOT_HI:
676 case MCSymbolRefExpr::VK_PPC_GOT_HA:
680 // An undefined symbol is not in any section, so the relocation has to point
681 // to the symbol itself.
682 const MCSymbol &Sym = SD->getSymbol();
683 if (Sym.isUndefined())
686 unsigned Binding = MCELF::GetBinding(*SD);
689 llvm_unreachable("Invalid Binding");
693 // If the symbol is weak, it might be overridden by a symbol in another
694 // file. The relocation has to point to the symbol so that the linker
697 case ELF::STB_GLOBAL:
698 // Global ELF symbols can be preempted by the dynamic linker. The relocation
699 // has to point to the symbol for a reason analogous to the STB_WEAK case.
703 // If a relocation points to a mergeable section, we have to be careful.
704 // If the offset is zero, a relocation with the section will encode the
705 // same information. With a non-zero offset, the situation is different.
706 // For example, a relocation can point 42 bytes past the end of a string.
707 // If we change such a relocation to use the section, the linker would think
708 // that it pointed to another string and subtracting 42 at runtime will
709 // produce the wrong value.
710 auto &Sec = cast<MCSectionELF>(Sym.getSection());
711 unsigned Flags = Sec.getFlags();
712 if (Flags & ELF::SHF_MERGE) {
716 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
717 // only handle section relocations to mergeable sections if using RELA.
718 if (!hasRelocationAddend())
722 // Most TLS relocations use a got, so they need the symbol. Even those that
723 // are just an offset (@tpoff), require a symbol in gold versions before
724 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
725 // http://sourceware.org/PR16773.
726 if (Flags & ELF::SHF_TLS)
729 // If the symbol is a thumb function the final relocation must set the lowest
730 // bit. With a symbol that is done by just having the symbol have that bit
731 // set, so we would lose the bit if we relocated with the section.
732 // FIXME: We could use the section but add the bit to the relocation value.
733 if (Asm.isThumbFunc(&Sym))
736 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
741 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
742 const MCSymbol &Sym = Ref.getSymbol();
744 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
747 if (!Sym.isVariable())
750 const MCExpr *Expr = Sym.getVariableValue();
751 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
755 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
756 return &Inner->getSymbol();
760 // True if the assembler knows nothing about the final value of the symbol.
761 // This doesn't cover the comdat issues, since in those cases the assembler
762 // can at least know that all symbols in the section will move together.
763 static bool isWeak(const MCSymbolData &D) {
764 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
767 switch (MCELF::GetBinding(D)) {
769 llvm_unreachable("Unknown binding");
772 case ELF::STB_GLOBAL:
775 case ELF::STB_GNU_UNIQUE:
780 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
781 const MCAsmLayout &Layout,
782 const MCFragment *Fragment,
783 const MCFixup &Fixup, MCValue Target,
784 bool &IsPCRel, uint64_t &FixedValue) {
785 const MCSectionData *FixupSection = Fragment->getParent();
786 uint64_t C = Target.getConstant();
787 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
789 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
790 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
791 "Should not have constructed this");
793 // Let A, B and C being the components of Target and R be the location of
794 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
795 // If it is pcrel, we want to compute (A - B + C - R).
797 // In general, ELF has no relocations for -B. It can only represent (A + C)
798 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
799 // replace B to implement it: (A - R - K + C)
801 Asm.getContext().FatalError(
803 "No relocation available to represent this relative expression");
805 const MCSymbol &SymB = RefB->getSymbol();
807 if (SymB.isUndefined())
808 Asm.getContext().FatalError(
810 Twine("symbol '") + SymB.getName() +
811 "' can not be undefined in a subtraction expression");
813 assert(!SymB.isAbsolute() && "Should have been folded");
814 const MCSection &SecB = SymB.getSection();
815 if (&SecB != &FixupSection->getSection())
816 Asm.getContext().FatalError(
817 Fixup.getLoc(), "Cannot represent a difference across sections");
819 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
821 Asm.getContext().FatalError(
822 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
824 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
825 uint64_t K = SymBOffset - FixupOffset;
830 // We either rejected the fixup or folded B into C at this point.
831 const MCSymbolRefExpr *RefA = Target.getSymA();
832 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
833 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
835 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
836 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
837 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
838 C += Layout.getSymbolOffset(SymAD);
841 if (hasRelocationAddend()) {
848 // FIXME: What is this!?!?
849 MCSymbolRefExpr::VariantKind Modifier =
850 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
851 if (RelocNeedsGOT(Modifier))
854 if (!RelocateWithSymbol) {
855 const MCSection *SecA =
856 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
857 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
858 MCSymbol *SectionSymbol =
859 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
861 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
862 Relocations[FixupSection].push_back(Rec);
867 if (const MCSymbol *R = Renames.lookup(SymA))
870 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
871 WeakrefUsedInReloc.insert(WeakRef);
873 UsedInReloc.insert(SymA);
875 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
876 Relocations[FixupSection].push_back(Rec);
882 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
884 const MCSymbolData &SD = Asm.getSymbolData(*S);
885 return SD.getIndex();
888 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
889 const MCSymbolData &Data, bool Used,
891 const MCSymbol &Symbol = Data.getSymbol();
892 if (Symbol.isVariable()) {
893 const MCExpr *Expr = Symbol.getVariableValue();
894 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
895 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
906 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
909 if (Symbol.isVariable()) {
910 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
911 if (Base && Base->isUndefined())
915 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
916 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
919 if (Symbol.isTemporary())
925 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
926 if (Data.isExternal())
929 const MCSymbol &Symbol = Data.getSymbol();
930 if (Symbol.isDefined())
939 void ELFObjectWriter::computeIndexMap(MCAssembler &Asm,
940 SectionIndexMapTy &SectionIndexMap) {
942 for (const MCSectionData &SD : Asm) {
943 const MCSectionELF &Section =
944 static_cast<const MCSectionELF &>(SD.getSection());
945 if (Section.getType() != ELF::SHT_GROUP)
947 SectionIndexMap[&Section] = Index++;
950 std::vector<const MCSectionELF *> RelSections;
951 for (const MCSectionData &SD : Asm) {
952 const MCSectionELF &Section =
953 static_cast<const MCSectionELF &>(SD.getSection());
954 if (Section.getType() == ELF::SHT_GROUP ||
955 Section.getType() == ELF::SHT_REL ||
956 Section.getType() == ELF::SHT_RELA)
958 SectionIndexMap[&Section] = Index++;
959 if (MCSectionData *RelSD = createRelocationSection(Asm, SD)) {
960 const MCSectionELF *RelSection =
961 static_cast<const MCSectionELF *>(&RelSD->getSection());
962 RelSections.push_back(RelSection);
966 // Put relocation sections close together. The linker reads them
967 // first, so this improves cache locality.
968 for (const MCSectionELF * Sec: RelSections)
969 SectionIndexMap[Sec] = Index++;
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++);
1118 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1119 const MCSectionData &SD) {
1120 if (Relocations[&SD].empty())
1123 MCContext &Ctx = Asm.getContext();
1124 const MCSectionELF &Section =
1125 static_cast<const MCSectionELF &>(SD.getSection());
1127 const StringRef SectionName = Section.getSectionName();
1128 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1129 RelaSectionName += SectionName;
1132 if (hasRelocationAddend())
1133 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1135 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1138 if (Section.getFlags() & ELF::SHF_GROUP)
1139 Flags = ELF::SHF_GROUP;
1141 const MCSectionELF *RelaSection = Ctx.createELFRelSection(
1142 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1143 Flags, EntrySize, Section.getGroup(), &Section);
1144 return &Asm.getOrCreateSectionData(*RelaSection);
1147 static SmallVector<char, 128>
1148 getUncompressedData(MCAsmLayout &Layout,
1149 MCSectionData::FragmentListType &Fragments) {
1150 SmallVector<char, 128> UncompressedData;
1151 for (const MCFragment &F : Fragments) {
1152 const SmallVectorImpl<char> *Contents;
1153 switch (F.getKind()) {
1154 case MCFragment::FT_Data:
1155 Contents = &cast<MCDataFragment>(F).getContents();
1157 case MCFragment::FT_Dwarf:
1158 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1160 case MCFragment::FT_DwarfFrame:
1161 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1165 "Not expecting any other fragment types in a debug_* section");
1167 UncompressedData.append(Contents->begin(), Contents->end());
1169 return UncompressedData;
1172 // Include the debug info compression header:
1173 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1174 // useful for consumers to preallocate a buffer to decompress into.
1176 prependCompressionHeader(uint64_t Size,
1177 SmallVectorImpl<char> &CompressedContents) {
1178 const StringRef Magic = "ZLIB";
1179 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1181 if (sys::IsLittleEndianHost)
1182 sys::swapByteOrder(Size);
1183 CompressedContents.insert(CompressedContents.begin(),
1184 Magic.size() + sizeof(Size), 0);
1185 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1186 std::copy(reinterpret_cast<char *>(&Size),
1187 reinterpret_cast<char *>(&Size + 1),
1188 CompressedContents.begin() + Magic.size());
1192 // Return a single fragment containing the compressed contents of the whole
1193 // section. Null if the section was not compressed for any reason.
1194 static std::unique_ptr<MCDataFragment>
1195 getCompressedFragment(MCAsmLayout &Layout,
1196 MCSectionData::FragmentListType &Fragments) {
1197 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1199 // Gather the uncompressed data from all the fragments, recording the
1200 // alignment fragment, if seen, and any fixups.
1201 SmallVector<char, 128> UncompressedData =
1202 getUncompressedData(Layout, Fragments);
1204 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1206 zlib::Status Success = zlib::compress(
1207 StringRef(UncompressedData.data(), UncompressedData.size()),
1208 CompressedContents);
1209 if (Success != zlib::StatusOK)
1212 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1215 return CompressedFragment;
1218 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1221 static void UpdateSymbols(const MCAsmLayout &Layout,
1222 const std::vector<MCSymbolData *> &Symbols,
1223 MCFragment &NewFragment) {
1224 for (MCSymbolData *Sym : Symbols) {
1225 Sym->setOffset(Sym->getOffset() +
1226 Layout.getFragmentOffset(Sym->getFragment()));
1227 Sym->setFragment(&NewFragment);
1231 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1232 const DefiningSymbolMap &DefiningSymbols,
1233 const MCSectionELF &Section,
1234 MCSectionData &SD) {
1235 StringRef SectionName = Section.getSectionName();
1236 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1238 std::unique_ptr<MCDataFragment> CompressedFragment =
1239 getCompressedFragment(Layout, Fragments);
1241 // Leave the section as-is if the fragments could not be compressed.
1242 if (!CompressedFragment)
1245 // Update the fragment+offsets of any symbols referring to fragments in this
1246 // section to refer to the new fragment.
1247 auto I = DefiningSymbols.find(&SD);
1248 if (I != DefiningSymbols.end())
1249 UpdateSymbols(Layout, I->second, *CompressedFragment);
1251 // Invalidate the layout for the whole section since it will have new and
1252 // different fragments now.
1253 Layout.invalidateFragmentsFrom(&Fragments.front());
1256 // Complete the initialization of the new fragment
1257 CompressedFragment->setParent(&SD);
1258 CompressedFragment->setLayoutOrder(0);
1259 Fragments.push_back(CompressedFragment.release());
1261 // Rename from .debug_* to .zdebug_*
1262 Asm.getContext().renameELFSection(&Section,
1263 (".z" + SectionName.drop_front(1)).str());
1266 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1267 MCAsmLayout &Layout) {
1268 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1271 DefiningSymbolMap DefiningSymbols;
1273 for (MCSymbolData &SD : Asm.symbols())
1274 if (MCFragment *F = SD.getFragment())
1275 DefiningSymbols[F->getParent()].push_back(&SD);
1277 for (MCSectionData &SD : Asm) {
1278 const MCSectionELF &Section =
1279 static_cast<const MCSectionELF &>(SD.getSection());
1280 StringRef SectionName = Section.getSectionName();
1282 // Compressing debug_frame requires handling alignment fragments which is
1283 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1284 // for writing to arbitrary buffers) for little benefit.
1285 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1288 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1292 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) {
1293 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1294 MCSectionData &RelSD = *it;
1295 const MCSectionELF &RelSection =
1296 static_cast<const MCSectionELF &>(RelSD.getSection());
1298 unsigned Type = RelSection.getType();
1299 if (Type != ELF::SHT_REL && Type != ELF::SHT_RELA)
1302 const MCSectionELF *Section = RelSection.getAssociatedSection();
1303 MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1304 RelSD.setAlignment(is64Bit() ? 8 : 4);
1306 MCDataFragment *F = new MCDataFragment(&RelSD);
1307 WriteRelocationsFragment(Asm, F, &SD);
1311 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1312 uint64_t Flags, uint64_t Address,
1313 uint64_t Offset, uint64_t Size,
1314 uint32_t Link, uint32_t Info,
1316 uint64_t EntrySize) {
1317 Write32(Name); // sh_name: index into string table
1318 Write32(Type); // sh_type
1319 WriteWord(Flags); // sh_flags
1320 WriteWord(Address); // sh_addr
1321 WriteWord(Offset); // sh_offset
1322 WriteWord(Size); // sh_size
1323 Write32(Link); // sh_link
1324 Write32(Info); // sh_info
1325 WriteWord(Alignment); // sh_addralign
1326 WriteWord(EntrySize); // sh_entsize
1329 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1331 const MCSectionData *SD) {
1332 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1334 // Sort the relocation entries. Most targets just sort by Offset, but some
1335 // (e.g., MIPS) have additional constraints.
1336 TargetObjectWriter->sortRelocs(Asm, Relocs);
1338 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1339 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1341 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1344 write(*F, Entry.Offset);
1345 if (TargetObjectWriter->isN64()) {
1346 write(*F, uint32_t(Index));
1348 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1349 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1350 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1351 write(*F, TargetObjectWriter->getRType(Entry.Type));
1353 struct ELF::Elf64_Rela ERE64;
1354 ERE64.setSymbolAndType(Index, Entry.Type);
1355 write(*F, ERE64.r_info);
1357 if (hasRelocationAddend())
1358 write(*F, Entry.Addend);
1360 write(*F, uint32_t(Entry.Offset));
1362 struct ELF::Elf32_Rela ERE32;
1363 ERE32.setSymbolAndType(Index, Entry.Type);
1364 write(*F, ERE32.r_info);
1366 if (hasRelocationAddend())
1367 write(*F, uint32_t(Entry.Addend));
1372 void ELFObjectWriter::CreateMetadataSections(
1373 MCAssembler &Asm, MCAsmLayout &Layout,
1374 std::vector<const MCSectionELF *> &Sections) {
1375 MCContext &Ctx = Asm.getContext();
1378 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1380 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1381 const MCSectionELF *ShstrtabSection =
1382 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1383 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1384 ShstrtabSD.setAlignment(1);
1385 ShstrtabIndex = Sections.size() + 1;
1386 Sections.push_back(ShstrtabSection);
1388 const MCSectionELF *SymtabSection =
1389 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1391 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1392 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1393 SymbolTableIndex = Sections.size() + 1;
1394 Sections.push_back(SymtabSection);
1396 const MCSectionELF *StrtabSection;
1397 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1398 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1399 StrtabSD.setAlignment(1);
1400 StringTableIndex = Sections.size() + 1;
1401 Sections.push_back(StrtabSection);
1404 F = new MCDataFragment(&SymtabSD);
1405 WriteSymbolTable(F, Asm, Layout, Sections);
1407 F = new MCDataFragment(&StrtabSD);
1408 F->getContents().append(StrTabBuilder.data().begin(),
1409 StrTabBuilder.data().end());
1411 F = new MCDataFragment(&ShstrtabSD);
1413 // Section header string table.
1414 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1415 const MCSectionELF &Section =
1416 static_cast<const MCSectionELF&>(it->getSection());
1417 ShStrTabBuilder.add(Section.getSectionName());
1419 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1420 F->getContents().append(ShStrTabBuilder.data().begin(),
1421 ShStrTabBuilder.data().end());
1424 void ELFObjectWriter::createIndexedSections(
1425 MCAssembler &Asm, MCAsmLayout &Layout, GroupMapTy &GroupMap,
1426 RevGroupMapTy &RevGroupMap, SectionIndexMapTy &SectionIndexMap) {
1427 MCContext &Ctx = Asm.getContext();
1430 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1432 const MCSectionELF &Section =
1433 static_cast<const MCSectionELF&>(it->getSection());
1434 if (!(Section.getFlags() & ELF::SHF_GROUP))
1437 const MCSymbol *SignatureSymbol = Section.getGroup();
1438 Asm.getOrCreateSymbolData(*SignatureSymbol);
1439 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1441 Group = Ctx.CreateELFGroupSection();
1442 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1443 Data.setAlignment(4);
1444 MCDataFragment *F = new MCDataFragment(&Data);
1445 write(*F, uint32_t(ELF::GRP_COMDAT));
1447 GroupMap[Group] = SignatureSymbol;
1450 computeIndexMap(Asm, SectionIndexMap);
1452 // Add sections to the groups
1453 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1455 const MCSectionELF &Section =
1456 static_cast<const MCSectionELF&>(it->getSection());
1457 if (!(Section.getFlags() & ELF::SHF_GROUP))
1459 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1460 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1461 // FIXME: we could use the previous fragment
1462 MCDataFragment *F = new MCDataFragment(&Data);
1463 uint32_t Index = SectionIndexMap.lookup(&Section);
1468 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1469 const SectionIndexMapTy &SectionIndexMap,
1470 uint32_t GroupSymbolIndex,
1471 uint64_t Offset, uint64_t Size,
1473 const MCSectionELF &Section) {
1474 uint64_t sh_link = 0;
1475 uint64_t sh_info = 0;
1477 switch(Section.getType()) {
1482 case ELF::SHT_DYNAMIC:
1483 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1487 case ELF::SHT_RELA: {
1488 sh_link = SymbolTableIndex;
1489 assert(sh_link && ".symtab not found");
1490 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1491 sh_info = SectionIndexMap.lookup(InfoSection);
1495 case ELF::SHT_SYMTAB:
1496 case ELF::SHT_DYNSYM:
1497 sh_link = StringTableIndex;
1498 sh_info = LastLocalSymbolIndex;
1501 case ELF::SHT_SYMTAB_SHNDX:
1502 sh_link = SymbolTableIndex;
1505 case ELF::SHT_GROUP:
1506 sh_link = SymbolTableIndex;
1507 sh_info = GroupSymbolIndex;
1511 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1512 Section.getType() == ELF::SHT_ARM_EXIDX)
1513 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1515 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1517 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1518 Alignment, Section.getEntrySize());
1521 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1522 return SD.getOrdinal() == ~UINT32_C(0) &&
1523 !SD.getSection().isVirtualSection();
1526 void ELFObjectWriter::writeDataSectionData(MCAssembler &Asm,
1527 const MCAsmLayout &Layout,
1528 const MCSectionData &SD) {
1529 if (IsELFMetaDataSection(SD)) {
1530 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1532 const MCFragment &F = *i;
1533 assert(F.getKind() == MCFragment::FT_Data);
1534 WriteBytes(cast<MCDataFragment>(F).getContents());
1537 Asm.writeSectionData(&SD, Layout);
1541 void ELFObjectWriter::writeSectionHeader(
1542 ArrayRef<const MCSectionELF *> Sections, MCAssembler &Asm,
1543 const GroupMapTy &GroupMap, const MCAsmLayout &Layout,
1544 const SectionIndexMapTy &SectionIndexMap,
1545 const SectionOffsetsTy &SectionOffsets) {
1546 const unsigned NumSections = Asm.size();
1548 // Null section first.
1549 uint64_t FirstSectionSize =
1550 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1551 uint32_t FirstSectionLink =
1552 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1553 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1555 for (unsigned i = 0; i < NumSections; ++i) {
1556 const MCSectionELF &Section = *Sections[i];
1557 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1558 uint32_t GroupSymbolIndex;
1559 if (Section.getType() != ELF::SHT_GROUP)
1560 GroupSymbolIndex = 0;
1562 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1563 GroupMap.lookup(&Section));
1565 const std::pair<uint64_t, uint64_t> &Offsets = SectionOffsets[i];
1566 uint64_t Size = Section.getType() == ELF::SHT_NOBITS
1567 ? Layout.getSectionAddressSize(&SD)
1568 : Offsets.second - Offsets.first;
1570 writeSection(Asm, SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1571 SD.getAlignment(), Section);
1575 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1576 const MCAsmLayout &Layout) {
1577 GroupMapTy GroupMap;
1578 RevGroupMapTy RevGroupMap;
1579 SectionIndexMapTy SectionIndexMap;
1581 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1582 createIndexedSections(Asm, const_cast<MCAsmLayout &>(Layout), GroupMap,
1583 RevGroupMap, SectionIndexMap);
1585 // Compute symbol table information.
1586 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1588 WriteRelocations(Asm, const_cast<MCAsmLayout &>(Layout));
1590 std::vector<const MCSectionELF*> Sections;
1591 Sections.resize(SectionIndexMap.size());
1592 for (auto &Pair : SectionIndexMap)
1593 Sections[Pair.second - 1] = Pair.first;
1595 CreateMetadataSections(const_cast<MCAssembler &>(Asm),
1596 const_cast<MCAsmLayout &>(Layout), Sections);
1598 unsigned NumSections = Asm.size();
1599 SectionOffsetsTy SectionOffsets;
1601 // Write out the ELF header ...
1602 WriteHeader(Asm, NumSections + 1);
1604 // ... then the sections ...
1605 for (const MCSectionELF *Section : Sections) {
1606 const MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1607 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1608 WriteZeros(Padding);
1610 // Remember the offset into the file for this section.
1611 uint64_t SecStart = OS.tell();
1612 writeDataSectionData(Asm, Layout, SD);
1613 uint64_t SecEnd = OS.tell();
1614 SectionOffsets.push_back(std::make_pair(SecStart, SecEnd));
1617 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1618 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1619 WriteZeros(Padding);
1621 const unsigned SectionHeaderOffset = OS.tell();
1623 // ... then the section header table ...
1624 writeSectionHeader(Sections, Asm, GroupMap, Layout, SectionIndexMap,
1628 uint64_t Val = SectionHeaderOffset;
1629 if (sys::IsLittleEndianHost != IsLittleEndian)
1630 sys::swapByteOrder(Val);
1631 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1632 offsetof(ELF::Elf64_Ehdr, e_shoff));
1634 uint32_t Val = SectionHeaderOffset;
1635 if (sys::IsLittleEndianHost != IsLittleEndian)
1636 sys::swapByteOrder(Val);
1637 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1638 offsetof(ELF::Elf32_Ehdr, e_shoff));
1642 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1643 const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
1644 bool InSet, bool IsPCRel) const {
1647 if (::isWeak(DataA))
1650 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
1654 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
1658 // It is invalid to replace a reference to a global in a comdat
1659 // with a reference to a local since out of comdat references
1660 // to a local are forbidden.
1661 // We could try to return false for more cases, like the reference
1662 // being in the same comdat or Sym being an alias to another global,
1663 // but it is not clear if it is worth the effort.
1664 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1667 const MCSymbol &Sym = SD.getSymbol();
1668 if (!Sym.isInSection())
1671 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1672 return Sec.getGroup();
1675 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1676 raw_pwrite_stream &OS,
1677 bool IsLittleEndian) {
1678 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);