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 computeIndexMap(MCAssembler &Asm, SectionIndexMapTy &SectionIndexMap);
236 MCSectionData *createRelocationSection(MCAssembler &Asm,
237 const MCSectionData &SD);
239 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
241 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout);
243 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
244 std::vector<const MCSectionELF *> &Sections);
246 // Create the sections that show up in the symbol table. Currently
247 // those are the .note.GNU-stack section and the group sections.
248 void createIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
249 RevGroupMapTy &RevGroupMap,
250 SectionIndexMapTy &SectionIndexMap);
252 void ExecutePostLayoutBinding(MCAssembler &Asm,
253 const MCAsmLayout &Layout) override;
255 void writeSectionHeader(ArrayRef<const MCSectionELF *> Sections,
256 MCAssembler &Asm, const MCAsmLayout &Layout,
257 const SectionIndexMapTy &SectionIndexMap,
258 const SectionOffsetsTy &SectionOffsets);
260 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
261 uint64_t Address, uint64_t Offset,
262 uint64_t Size, uint32_t Link, uint32_t Info,
263 uint64_t Alignment, uint64_t EntrySize);
265 void WriteRelocationsFragment(const MCAssembler &Asm,
267 const MCSectionData *SD);
270 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
271 const MCSymbolData &DataA,
272 const MCFragment &FB,
274 bool IsPCRel) const override;
276 bool isWeak(const MCSymbolData &SD) const override;
278 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
279 void writeSection(MCAssembler &Asm,
280 const SectionIndexMapTy &SectionIndexMap,
281 uint32_t GroupSymbolIndex,
282 uint64_t Offset, uint64_t Size, uint64_t Alignment,
283 const MCSectionELF &Section);
287 FragmentWriter::FragmentWriter(bool IsLittleEndian)
288 : IsLittleEndian(IsLittleEndian) {}
290 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
292 Val = support::endian::byte_swap<T, support::little>(Val);
294 Val = support::endian::byte_swap<T, support::big>(Val);
295 const char *Start = (const char *)&Val;
296 F.getContents().append(Start, Start + sizeof(T));
299 void SymbolTableWriter::createSymtabShndx() {
303 MCContext &Ctx = Asm.getContext();
304 const MCSectionELF *SymtabShndxSection =
305 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
306 MCSectionData *SymtabShndxSD =
307 &Asm.getOrCreateSectionData(*SymtabShndxSection);
308 SymtabShndxSD->setAlignment(4);
309 ShndxF = new MCDataFragment(SymtabShndxSD);
310 Sections.push_back(SymtabShndxSection);
312 for (unsigned I = 0; I < NumWritten; ++I)
313 write(*ShndxF, uint32_t(0));
316 template <typename T>
317 void SymbolTableWriter::write(MCDataFragment &F, T Value) {
318 FWriter.write(F, Value);
321 SymbolTableWriter::SymbolTableWriter(
322 MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
323 std::vector<const MCSectionELF *> &Sections, MCDataFragment *SymtabF)
324 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit), Sections(Sections),
325 SymtabF(SymtabF), ShndxF(nullptr), NumWritten(0) {}
327 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
328 uint64_t size, uint8_t other,
329 uint32_t shndx, bool Reserved) {
330 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
337 write(*ShndxF, shndx);
339 write(*ShndxF, uint32_t(0));
342 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
345 write(*SymtabF, name); // st_name
346 write(*SymtabF, info); // st_info
347 write(*SymtabF, other); // st_other
348 write(*SymtabF, Index); // st_shndx
349 write(*SymtabF, value); // st_value
350 write(*SymtabF, size); // st_size
352 write(*SymtabF, name); // st_name
353 write(*SymtabF, uint32_t(value)); // st_value
354 write(*SymtabF, uint32_t(size)); // st_size
355 write(*SymtabF, info); // st_info
356 write(*SymtabF, other); // st_other
357 write(*SymtabF, Index); // st_shndx
363 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
364 const MCFixupKindInfo &FKI =
365 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
367 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
370 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
374 case MCSymbolRefExpr::VK_GOT:
375 case MCSymbolRefExpr::VK_PLT:
376 case MCSymbolRefExpr::VK_GOTPCREL:
377 case MCSymbolRefExpr::VK_GOTOFF:
378 case MCSymbolRefExpr::VK_TPOFF:
379 case MCSymbolRefExpr::VK_TLSGD:
380 case MCSymbolRefExpr::VK_GOTTPOFF:
381 case MCSymbolRefExpr::VK_INDNTPOFF:
382 case MCSymbolRefExpr::VK_NTPOFF:
383 case MCSymbolRefExpr::VK_GOTNTPOFF:
384 case MCSymbolRefExpr::VK_TLSLDM:
385 case MCSymbolRefExpr::VK_DTPOFF:
386 case MCSymbolRefExpr::VK_TLSLD:
391 ELFObjectWriter::~ELFObjectWriter()
394 // Emit the ELF header.
395 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
396 unsigned NumberOfSections) {
402 // emitWord method behaves differently for ELF32 and ELF64, writing
403 // 4 bytes in the former and 8 in the latter.
405 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
407 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
410 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
412 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
414 Write8(TargetObjectWriter->getOSABI());
415 Write8(0); // e_ident[EI_ABIVERSION]
417 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
419 Write16(ELF::ET_REL); // e_type
421 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
423 Write32(ELF::EV_CURRENT); // e_version
424 WriteWord(0); // e_entry, no entry point in .o file
425 WriteWord(0); // e_phoff, no program header for .o
426 WriteWord(0); // e_shoff = sec hdr table off in bytes
428 // e_flags = whatever the target wants
429 Write32(Asm.getELFHeaderEFlags());
431 // e_ehsize = ELF header size
432 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
434 Write16(0); // e_phentsize = prog header entry size
435 Write16(0); // e_phnum = # prog header entries = 0
437 // e_shentsize = Section header entry size
438 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
440 // e_shnum = # of section header ents
441 if (NumberOfSections >= ELF::SHN_LORESERVE)
442 Write16(ELF::SHN_UNDEF);
444 Write16(NumberOfSections);
446 // e_shstrndx = Section # of '.shstrtab'
447 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
448 Write16(ELF::SHN_XINDEX);
450 Write16(ShstrtabIndex);
453 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
454 const MCAsmLayout &Layout) {
455 if (Data.isCommon() && Data.isExternal())
456 return Data.getCommonAlignment();
459 if (!Layout.getSymbolOffset(&Data, Res))
462 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
468 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
469 const MCAsmLayout &Layout) {
470 // The presence of symbol versions causes undefined symbols and
471 // versions declared with @@@ to be renamed.
473 for (MCSymbolData &OriginalData : Asm.symbols()) {
474 const MCSymbol &Alias = OriginalData.getSymbol();
477 if (!Alias.isVariable())
479 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
482 const MCSymbol &Symbol = Ref->getSymbol();
483 MCSymbolData &SD = Asm.getSymbolData(Symbol);
485 StringRef AliasName = Alias.getName();
486 size_t Pos = AliasName.find('@');
487 if (Pos == StringRef::npos)
490 // Aliases defined with .symvar copy the binding from the symbol they alias.
491 // This is the first place we are able to copy this information.
492 OriginalData.setExternal(SD.isExternal());
493 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
495 StringRef Rest = AliasName.substr(Pos);
496 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
499 // FIXME: produce a better error message.
500 if (Symbol.isUndefined() && Rest.startswith("@@") &&
501 !Rest.startswith("@@@"))
502 report_fatal_error("A @@ version cannot be undefined");
504 Renames.insert(std::make_pair(&Symbol, &Alias));
508 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
509 uint8_t Type = newType;
511 // Propagation rules:
512 // IFUNC > FUNC > OBJECT > NOTYPE
513 // TLS_OBJECT > OBJECT > NOTYPE
515 // dont let the new type degrade the old type
519 case ELF::STT_GNU_IFUNC:
520 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
521 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
522 Type = ELF::STT_GNU_IFUNC;
525 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
526 Type == ELF::STT_TLS)
527 Type = ELF::STT_FUNC;
529 case ELF::STT_OBJECT:
530 if (Type == ELF::STT_NOTYPE)
531 Type = ELF::STT_OBJECT;
534 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
535 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
543 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
544 const MCAsmLayout &Layout) {
545 MCSymbolData &OrigData = *MSD.SymbolData;
546 assert((!OrigData.getFragment() ||
547 (&OrigData.getFragment()->getParent()->getSection() ==
548 &OrigData.getSymbol().getSection())) &&
549 "The symbol's section doesn't match the fragment's symbol");
550 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
552 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
554 bool IsReserved = !Base || OrigData.isCommon();
556 // Binding and Type share the same byte as upper and lower nibbles
557 uint8_t Binding = MCELF::GetBinding(OrigData);
558 uint8_t Type = MCELF::GetType(OrigData);
559 MCSymbolData *BaseSD = nullptr;
561 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
562 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
564 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
566 // Other and Visibility share the same byte with Visibility using the lower
568 uint8_t Visibility = MCELF::GetVisibility(OrigData);
569 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
572 uint64_t Value = SymbolValue(OrigData, Layout);
575 const MCExpr *ESize = OrigData.getSize();
577 ESize = BaseSD->getSize();
581 if (!ESize->evaluateKnownAbsolute(Res, Layout))
582 report_fatal_error("Size expression must be absolute.");
586 // Write out the symbol table entry
587 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
588 MSD.SectionIndex, IsReserved);
591 void ELFObjectWriter::WriteSymbolTable(
592 MCDataFragment *SymtabF, MCAssembler &Asm, const MCAsmLayout &Layout,
593 std::vector<const MCSectionELF *> &Sections) {
594 // The string table must be emitted first because we need the index
595 // into the string table for all the symbol names.
597 // FIXME: Make sure the start of the symbol table is aligned.
599 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), Sections, SymtabF);
601 // The first entry is the undefined symbol entry.
602 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
604 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
605 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
606 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
609 // Write the symbol table entries.
610 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
612 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
613 ELFSymbolData &MSD = LocalSymbolData[i];
614 WriteSymbol(Writer, MSD, Layout);
617 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
618 ELFSymbolData &MSD = ExternalSymbolData[i];
619 MCSymbolData &Data = *MSD.SymbolData;
620 assert(((Data.getFlags() & ELF_STB_Global) ||
621 (Data.getFlags() & ELF_STB_Weak)) &&
622 "External symbol requires STB_GLOBAL or STB_WEAK flag");
623 WriteSymbol(Writer, MSD, Layout);
624 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
625 LastLocalSymbolIndex++;
628 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
629 ELFSymbolData &MSD = UndefinedSymbolData[i];
630 MCSymbolData &Data = *MSD.SymbolData;
631 WriteSymbol(Writer, MSD, Layout);
632 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
633 LastLocalSymbolIndex++;
637 // It is always valid to create a relocation with a symbol. It is preferable
638 // to use a relocation with a section if that is possible. Using the section
639 // allows us to omit some local symbols from the symbol table.
640 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
641 const MCSymbolRefExpr *RefA,
642 const MCSymbolData *SD,
644 unsigned Type) const {
645 // A PCRel relocation to an absolute value has no symbol (or section). We
646 // represent that with a relocation to a null section.
650 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
654 // The .odp creation emits a relocation against the symbol ".TOC." which
655 // create a R_PPC64_TOC relocation. However the relocation symbol name
656 // in final object creation should be NULL, since the symbol does not
657 // really exist, it is just the reference to TOC base for the current
658 // object file. Since the symbol is undefined, returning false results
659 // in a relocation with a null section which is the desired result.
660 case MCSymbolRefExpr::VK_PPC_TOCBASE:
663 // These VariantKind cause the relocation to refer to something other than
664 // the symbol itself, like a linker generated table. Since the address of
665 // symbol is not relevant, we cannot replace the symbol with the
666 // section and patch the difference in the addend.
667 case MCSymbolRefExpr::VK_GOT:
668 case MCSymbolRefExpr::VK_PLT:
669 case MCSymbolRefExpr::VK_GOTPCREL:
670 case MCSymbolRefExpr::VK_Mips_GOT:
671 case MCSymbolRefExpr::VK_PPC_GOT_LO:
672 case MCSymbolRefExpr::VK_PPC_GOT_HI:
673 case MCSymbolRefExpr::VK_PPC_GOT_HA:
677 // An undefined symbol is not in any section, so the relocation has to point
678 // to the symbol itself.
679 const MCSymbol &Sym = SD->getSymbol();
680 if (Sym.isUndefined())
683 unsigned Binding = MCELF::GetBinding(*SD);
686 llvm_unreachable("Invalid Binding");
690 // If the symbol is weak, it might be overridden by a symbol in another
691 // file. The relocation has to point to the symbol so that the linker
694 case ELF::STB_GLOBAL:
695 // Global ELF symbols can be preempted by the dynamic linker. The relocation
696 // has to point to the symbol for a reason analogous to the STB_WEAK case.
700 // If a relocation points to a mergeable section, we have to be careful.
701 // If the offset is zero, a relocation with the section will encode the
702 // same information. With a non-zero offset, the situation is different.
703 // For example, a relocation can point 42 bytes past the end of a string.
704 // If we change such a relocation to use the section, the linker would think
705 // that it pointed to another string and subtracting 42 at runtime will
706 // produce the wrong value.
707 auto &Sec = cast<MCSectionELF>(Sym.getSection());
708 unsigned Flags = Sec.getFlags();
709 if (Flags & ELF::SHF_MERGE) {
713 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
714 // only handle section relocations to mergeable sections if using RELA.
715 if (!hasRelocationAddend())
719 // Most TLS relocations use a got, so they need the symbol. Even those that
720 // are just an offset (@tpoff), require a symbol in gold versions before
721 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
722 // http://sourceware.org/PR16773.
723 if (Flags & ELF::SHF_TLS)
726 // If the symbol is a thumb function the final relocation must set the lowest
727 // bit. With a symbol that is done by just having the symbol have that bit
728 // set, so we would lose the bit if we relocated with the section.
729 // FIXME: We could use the section but add the bit to the relocation value.
730 if (Asm.isThumbFunc(&Sym))
733 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
738 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
739 const MCSymbol &Sym = Ref.getSymbol();
741 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
744 if (!Sym.isVariable())
747 const MCExpr *Expr = Sym.getVariableValue();
748 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
752 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
753 return &Inner->getSymbol();
757 // True if the assembler knows nothing about the final value of the symbol.
758 // This doesn't cover the comdat issues, since in those cases the assembler
759 // can at least know that all symbols in the section will move together.
760 static bool isWeak(const MCSymbolData &D) {
761 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
764 switch (MCELF::GetBinding(D)) {
766 llvm_unreachable("Unknown binding");
769 case ELF::STB_GLOBAL:
772 case ELF::STB_GNU_UNIQUE:
777 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
778 const MCAsmLayout &Layout,
779 const MCFragment *Fragment,
780 const MCFixup &Fixup, MCValue Target,
781 bool &IsPCRel, uint64_t &FixedValue) {
782 const MCSectionData *FixupSection = Fragment->getParent();
783 uint64_t C = Target.getConstant();
784 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
786 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
787 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
788 "Should not have constructed this");
790 // Let A, B and C being the components of Target and R be the location of
791 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
792 // If it is pcrel, we want to compute (A - B + C - R).
794 // In general, ELF has no relocations for -B. It can only represent (A + C)
795 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
796 // replace B to implement it: (A - R - K + C)
798 Asm.getContext().FatalError(
800 "No relocation available to represent this relative expression");
802 const MCSymbol &SymB = RefB->getSymbol();
804 if (SymB.isUndefined())
805 Asm.getContext().FatalError(
807 Twine("symbol '") + SymB.getName() +
808 "' can not be undefined in a subtraction expression");
810 assert(!SymB.isAbsolute() && "Should have been folded");
811 const MCSection &SecB = SymB.getSection();
812 if (&SecB != &FixupSection->getSection())
813 Asm.getContext().FatalError(
814 Fixup.getLoc(), "Cannot represent a difference across sections");
816 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
818 Asm.getContext().FatalError(
819 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
821 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
822 uint64_t K = SymBOffset - FixupOffset;
827 // We either rejected the fixup or folded B into C at this point.
828 const MCSymbolRefExpr *RefA = Target.getSymA();
829 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
830 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
832 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
833 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
834 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
835 C += Layout.getSymbolOffset(SymAD);
838 if (hasRelocationAddend()) {
845 // FIXME: What is this!?!?
846 MCSymbolRefExpr::VariantKind Modifier =
847 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
848 if (RelocNeedsGOT(Modifier))
851 if (!RelocateWithSymbol) {
852 const MCSection *SecA =
853 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
854 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
855 MCSymbol *SectionSymbol =
856 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
858 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
859 Relocations[FixupSection].push_back(Rec);
864 if (const MCSymbol *R = Renames.lookup(SymA))
867 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
868 WeakrefUsedInReloc.insert(WeakRef);
870 UsedInReloc.insert(SymA);
872 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
873 Relocations[FixupSection].push_back(Rec);
879 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
881 const MCSymbolData &SD = Asm.getSymbolData(*S);
882 return SD.getIndex();
885 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
886 const MCSymbolData &Data, bool Used,
888 const MCSymbol &Symbol = Data.getSymbol();
889 if (Symbol.isVariable()) {
890 const MCExpr *Expr = Symbol.getVariableValue();
891 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
892 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
903 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
906 if (Symbol.isVariable()) {
907 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
908 if (Base && Base->isUndefined())
912 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
913 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
916 if (Symbol.isTemporary())
922 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
923 if (Data.isExternal())
926 const MCSymbol &Symbol = Data.getSymbol();
927 if (Symbol.isDefined())
936 void ELFObjectWriter::computeIndexMap(MCAssembler &Asm,
937 SectionIndexMapTy &SectionIndexMap) {
939 for (const MCSectionData &SD : Asm) {
940 const MCSectionELF &Section =
941 static_cast<const MCSectionELF &>(SD.getSection());
942 if (Section.getType() != ELF::SHT_GROUP)
944 SectionIndexMap[&Section] = Index++;
947 std::vector<const MCSectionELF *> RelSections;
948 for (const MCSectionData &SD : Asm) {
949 const MCSectionELF &Section =
950 static_cast<const MCSectionELF &>(SD.getSection());
951 if (Section.getType() == ELF::SHT_GROUP ||
952 Section.getType() == ELF::SHT_REL ||
953 Section.getType() == ELF::SHT_RELA)
955 SectionIndexMap[&Section] = Index++;
956 if (MCSectionData *RelSD = createRelocationSection(Asm, SD)) {
957 const MCSectionELF *RelSection =
958 static_cast<const MCSectionELF *>(&RelSD->getSection());
959 RelSections.push_back(RelSection);
963 // Put relocation sections close together. The linker reads them
964 // first, so this improves cache locality.
965 for (const MCSectionELF * Sec: RelSections)
966 SectionIndexMap[Sec] = Index++;
969 void ELFObjectWriter::computeSymbolTable(
970 MCAssembler &Asm, const MCAsmLayout &Layout,
971 const SectionIndexMapTy &SectionIndexMap,
972 const RevGroupMapTy &RevGroupMap) {
973 // FIXME: Is this the correct place to do this?
974 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
976 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
977 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
978 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
979 Data.setExternal(true);
980 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
983 // Add the data for the symbols.
984 for (MCSymbolData &SD : Asm.symbols()) {
985 const MCSymbol &Symbol = SD.getSymbol();
987 bool Used = UsedInReloc.count(&Symbol);
988 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
989 bool isSignature = RevGroupMap.count(&Symbol);
991 if (!isInSymtab(Layout, SD,
992 Used || WeakrefUsed || isSignature,
993 Renames.count(&Symbol)))
997 MSD.SymbolData = &SD;
998 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
1000 // Undefined symbols are global, but this is the first place we
1001 // are able to set it.
1002 bool Local = isLocal(SD, Used);
1003 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1005 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1006 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1007 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1011 MSD.SectionIndex = ELF::SHN_ABS;
1012 } else if (SD.isCommon()) {
1014 MSD.SectionIndex = ELF::SHN_COMMON;
1015 } else if (BaseSymbol->isUndefined()) {
1016 if (isSignature && !Used)
1017 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap.lookup(&Symbol));
1019 MSD.SectionIndex = ELF::SHN_UNDEF;
1020 if (!Used && WeakrefUsed)
1021 MCELF::SetBinding(SD, ELF::STB_WEAK);
1023 const MCSectionELF &Section =
1024 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1025 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1026 assert(MSD.SectionIndex && "Invalid section index!");
1029 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
1032 // FIXME: All name handling should be done before we get to the writer,
1033 // including dealing with GNU-style version suffixes. Fixing this isn't
1036 // We thus have to be careful to not perform the symbol version replacement
1039 // The ELF format is used on Windows by the MCJIT engine. Thus, on
1040 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
1041 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
1042 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
1043 // the EFLObjectWriter should not interpret the "@@@" sub-string as
1044 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1045 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1046 // "__imp_?" or "__imp_@?".
1048 // It would have been interesting to perform the MS mangling prefix check
1049 // only when the target triple is of the form *-pc-windows-elf. But, it
1050 // seems that this information is not easily accessible from the
1052 StringRef Name = Symbol.getName();
1053 if (!Name.startswith("?") && !Name.startswith("@?") &&
1054 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1055 // This symbol isn't following the MSVC C++ name mangling convention. We
1056 // can thus safely interpret the @@@ in symbol names as specifying symbol
1058 SmallString<32> Buf;
1059 size_t Pos = Name.find("@@@");
1060 if (Pos != StringRef::npos) {
1061 Buf += Name.substr(0, Pos);
1062 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1063 Buf += Name.substr(Pos + Skip);
1068 // Sections have their own string table
1069 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1070 MSD.Name = StrTabBuilder.add(Name);
1072 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1073 UndefinedSymbolData.push_back(MSD);
1075 LocalSymbolData.push_back(MSD);
1077 ExternalSymbolData.push_back(MSD);
1080 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1081 StrTabBuilder.add(*i);
1083 StrTabBuilder.finalize(StringTableBuilder::ELF);
1085 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1086 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1088 for (ELFSymbolData &MSD : LocalSymbolData)
1089 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1091 : StrTabBuilder.getOffset(MSD.Name);
1092 for (ELFSymbolData &MSD : ExternalSymbolData)
1093 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1094 for (ELFSymbolData& MSD : UndefinedSymbolData)
1095 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1097 // Symbols are required to be in lexicographic order.
1098 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1099 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1100 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1102 // Set the symbol indices. Local symbols must come before all other
1103 // symbols with non-local bindings.
1104 unsigned Index = FileSymbolData.size() + 1;
1105 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1106 LocalSymbolData[i].SymbolData->setIndex(Index++);
1108 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1109 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1110 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1111 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1115 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1116 const MCSectionData &SD) {
1117 if (Relocations[&SD].empty())
1120 MCContext &Ctx = Asm.getContext();
1121 const MCSectionELF &Section =
1122 static_cast<const MCSectionELF &>(SD.getSection());
1124 const StringRef SectionName = Section.getSectionName();
1125 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1126 RelaSectionName += SectionName;
1129 if (hasRelocationAddend())
1130 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1132 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1135 if (Section.getFlags() & ELF::SHF_GROUP)
1136 Flags = ELF::SHF_GROUP;
1138 const MCSectionELF *RelaSection = Ctx.createELFRelSection(
1139 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1140 Flags, EntrySize, Section.getGroup(), &Section);
1141 return &Asm.getOrCreateSectionData(*RelaSection);
1144 static SmallVector<char, 128>
1145 getUncompressedData(MCAsmLayout &Layout,
1146 MCSectionData::FragmentListType &Fragments) {
1147 SmallVector<char, 128> UncompressedData;
1148 for (const MCFragment &F : Fragments) {
1149 const SmallVectorImpl<char> *Contents;
1150 switch (F.getKind()) {
1151 case MCFragment::FT_Data:
1152 Contents = &cast<MCDataFragment>(F).getContents();
1154 case MCFragment::FT_Dwarf:
1155 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1157 case MCFragment::FT_DwarfFrame:
1158 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1162 "Not expecting any other fragment types in a debug_* section");
1164 UncompressedData.append(Contents->begin(), Contents->end());
1166 return UncompressedData;
1169 // Include the debug info compression header:
1170 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1171 // useful for consumers to preallocate a buffer to decompress into.
1173 prependCompressionHeader(uint64_t Size,
1174 SmallVectorImpl<char> &CompressedContents) {
1175 const StringRef Magic = "ZLIB";
1176 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1178 if (sys::IsLittleEndianHost)
1179 sys::swapByteOrder(Size);
1180 CompressedContents.insert(CompressedContents.begin(),
1181 Magic.size() + sizeof(Size), 0);
1182 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1183 std::copy(reinterpret_cast<char *>(&Size),
1184 reinterpret_cast<char *>(&Size + 1),
1185 CompressedContents.begin() + Magic.size());
1189 // Return a single fragment containing the compressed contents of the whole
1190 // section. Null if the section was not compressed for any reason.
1191 static std::unique_ptr<MCDataFragment>
1192 getCompressedFragment(MCAsmLayout &Layout,
1193 MCSectionData::FragmentListType &Fragments) {
1194 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1196 // Gather the uncompressed data from all the fragments, recording the
1197 // alignment fragment, if seen, and any fixups.
1198 SmallVector<char, 128> UncompressedData =
1199 getUncompressedData(Layout, Fragments);
1201 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1203 zlib::Status Success = zlib::compress(
1204 StringRef(UncompressedData.data(), UncompressedData.size()),
1205 CompressedContents);
1206 if (Success != zlib::StatusOK)
1209 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1212 return CompressedFragment;
1215 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1218 static void UpdateSymbols(const MCAsmLayout &Layout,
1219 const std::vector<MCSymbolData *> &Symbols,
1220 MCFragment &NewFragment) {
1221 for (MCSymbolData *Sym : Symbols) {
1222 Sym->setOffset(Sym->getOffset() +
1223 Layout.getFragmentOffset(Sym->getFragment()));
1224 Sym->setFragment(&NewFragment);
1228 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1229 const DefiningSymbolMap &DefiningSymbols,
1230 const MCSectionELF &Section,
1231 MCSectionData &SD) {
1232 StringRef SectionName = Section.getSectionName();
1233 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1235 std::unique_ptr<MCDataFragment> CompressedFragment =
1236 getCompressedFragment(Layout, Fragments);
1238 // Leave the section as-is if the fragments could not be compressed.
1239 if (!CompressedFragment)
1242 // Update the fragment+offsets of any symbols referring to fragments in this
1243 // section to refer to the new fragment.
1244 auto I = DefiningSymbols.find(&SD);
1245 if (I != DefiningSymbols.end())
1246 UpdateSymbols(Layout, I->second, *CompressedFragment);
1248 // Invalidate the layout for the whole section since it will have new and
1249 // different fragments now.
1250 Layout.invalidateFragmentsFrom(&Fragments.front());
1253 // Complete the initialization of the new fragment
1254 CompressedFragment->setParent(&SD);
1255 CompressedFragment->setLayoutOrder(0);
1256 Fragments.push_back(CompressedFragment.release());
1258 // Rename from .debug_* to .zdebug_*
1259 Asm.getContext().renameELFSection(&Section,
1260 (".z" + SectionName.drop_front(1)).str());
1263 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1264 MCAsmLayout &Layout) {
1265 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1268 DefiningSymbolMap DefiningSymbols;
1270 for (MCSymbolData &SD : Asm.symbols())
1271 if (MCFragment *F = SD.getFragment())
1272 DefiningSymbols[F->getParent()].push_back(&SD);
1274 for (MCSectionData &SD : Asm) {
1275 const MCSectionELF &Section =
1276 static_cast<const MCSectionELF &>(SD.getSection());
1277 StringRef SectionName = Section.getSectionName();
1279 // Compressing debug_frame requires handling alignment fragments which is
1280 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1281 // for writing to arbitrary buffers) for little benefit.
1282 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1285 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1289 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) {
1290 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1291 MCSectionData &RelSD = *it;
1292 const MCSectionELF &RelSection =
1293 static_cast<const MCSectionELF &>(RelSD.getSection());
1295 unsigned Type = RelSection.getType();
1296 if (Type != ELF::SHT_REL && Type != ELF::SHT_RELA)
1299 const MCSectionELF *Section = RelSection.getAssociatedSection();
1300 MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1301 RelSD.setAlignment(is64Bit() ? 8 : 4);
1303 MCDataFragment *F = new MCDataFragment(&RelSD);
1304 WriteRelocationsFragment(Asm, F, &SD);
1308 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1309 uint64_t Flags, uint64_t Address,
1310 uint64_t Offset, uint64_t Size,
1311 uint32_t Link, uint32_t Info,
1313 uint64_t EntrySize) {
1314 Write32(Name); // sh_name: index into string table
1315 Write32(Type); // sh_type
1316 WriteWord(Flags); // sh_flags
1317 WriteWord(Address); // sh_addr
1318 WriteWord(Offset); // sh_offset
1319 WriteWord(Size); // sh_size
1320 Write32(Link); // sh_link
1321 Write32(Info); // sh_info
1322 WriteWord(Alignment); // sh_addralign
1323 WriteWord(EntrySize); // sh_entsize
1326 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1328 const MCSectionData *SD) {
1329 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1331 // Sort the relocation entries. Most targets just sort by Offset, but some
1332 // (e.g., MIPS) have additional constraints.
1333 TargetObjectWriter->sortRelocs(Asm, Relocs);
1335 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1336 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1338 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1341 write(*F, Entry.Offset);
1342 if (TargetObjectWriter->isN64()) {
1343 write(*F, uint32_t(Index));
1345 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1346 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1347 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1348 write(*F, TargetObjectWriter->getRType(Entry.Type));
1350 struct ELF::Elf64_Rela ERE64;
1351 ERE64.setSymbolAndType(Index, Entry.Type);
1352 write(*F, ERE64.r_info);
1354 if (hasRelocationAddend())
1355 write(*F, Entry.Addend);
1357 write(*F, uint32_t(Entry.Offset));
1359 struct ELF::Elf32_Rela ERE32;
1360 ERE32.setSymbolAndType(Index, Entry.Type);
1361 write(*F, ERE32.r_info);
1363 if (hasRelocationAddend())
1364 write(*F, uint32_t(Entry.Addend));
1369 void ELFObjectWriter::CreateMetadataSections(
1370 MCAssembler &Asm, MCAsmLayout &Layout,
1371 std::vector<const MCSectionELF *> &Sections) {
1372 MCContext &Ctx = Asm.getContext();
1375 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1377 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1378 const MCSectionELF *ShstrtabSection =
1379 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1380 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1381 ShstrtabSD.setAlignment(1);
1382 ShstrtabIndex = Sections.size() + 1;
1383 Sections.push_back(ShstrtabSection);
1385 const MCSectionELF *SymtabSection =
1386 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1388 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1389 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1390 SymbolTableIndex = Sections.size() + 1;
1391 Sections.push_back(SymtabSection);
1393 const MCSectionELF *StrtabSection;
1394 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1395 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1396 StrtabSD.setAlignment(1);
1397 StringTableIndex = Sections.size() + 1;
1398 Sections.push_back(StrtabSection);
1401 F = new MCDataFragment(&SymtabSD);
1402 WriteSymbolTable(F, Asm, Layout, Sections);
1404 F = new MCDataFragment(&StrtabSD);
1405 F->getContents().append(StrTabBuilder.data().begin(),
1406 StrTabBuilder.data().end());
1408 F = new MCDataFragment(&ShstrtabSD);
1410 // Section header string table.
1411 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1412 const MCSectionELF &Section =
1413 static_cast<const MCSectionELF&>(it->getSection());
1414 ShStrTabBuilder.add(Section.getSectionName());
1416 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1417 F->getContents().append(ShStrTabBuilder.data().begin(),
1418 ShStrTabBuilder.data().end());
1421 void ELFObjectWriter::createIndexedSections(
1422 MCAssembler &Asm, MCAsmLayout &Layout, RevGroupMapTy &RevGroupMap,
1423 SectionIndexMapTy &SectionIndexMap) {
1424 MCContext &Ctx = Asm.getContext();
1427 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1429 const MCSectionELF &Section =
1430 static_cast<const MCSectionELF&>(it->getSection());
1431 if (!(Section.getFlags() & ELF::SHF_GROUP))
1434 const MCSymbol *SignatureSymbol = Section.getGroup();
1435 Asm.getOrCreateSymbolData(*SignatureSymbol);
1436 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1438 Group = Ctx.createELFGroupSection(SignatureSymbol);
1439 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1440 Data.setAlignment(4);
1441 MCDataFragment *F = new MCDataFragment(&Data);
1442 write(*F, uint32_t(ELF::GRP_COMDAT));
1446 computeIndexMap(Asm, SectionIndexMap);
1448 // Add sections to the groups
1449 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1451 const MCSectionELF &Section =
1452 static_cast<const MCSectionELF&>(it->getSection());
1453 if (!(Section.getFlags() & ELF::SHF_GROUP))
1455 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1456 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1457 // FIXME: we could use the previous fragment
1458 MCDataFragment *F = new MCDataFragment(&Data);
1459 uint32_t Index = SectionIndexMap.lookup(&Section);
1464 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1465 const SectionIndexMapTy &SectionIndexMap,
1466 uint32_t GroupSymbolIndex,
1467 uint64_t Offset, uint64_t Size,
1469 const MCSectionELF &Section) {
1470 uint64_t sh_link = 0;
1471 uint64_t sh_info = 0;
1473 switch(Section.getType()) {
1478 case ELF::SHT_DYNAMIC:
1479 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1483 case ELF::SHT_RELA: {
1484 sh_link = SymbolTableIndex;
1485 assert(sh_link && ".symtab not found");
1486 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1487 sh_info = SectionIndexMap.lookup(InfoSection);
1491 case ELF::SHT_SYMTAB:
1492 case ELF::SHT_DYNSYM:
1493 sh_link = StringTableIndex;
1494 sh_info = LastLocalSymbolIndex;
1497 case ELF::SHT_SYMTAB_SHNDX:
1498 sh_link = SymbolTableIndex;
1501 case ELF::SHT_GROUP:
1502 sh_link = SymbolTableIndex;
1503 sh_info = GroupSymbolIndex;
1507 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1508 Section.getType() == ELF::SHT_ARM_EXIDX)
1509 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1511 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1513 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1514 Alignment, Section.getEntrySize());
1517 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1518 return SD.getOrdinal() == ~UINT32_C(0) &&
1519 !SD.getSection().isVirtualSection();
1522 void ELFObjectWriter::writeDataSectionData(MCAssembler &Asm,
1523 const MCAsmLayout &Layout,
1524 const MCSectionData &SD) {
1525 if (IsELFMetaDataSection(SD)) {
1526 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1528 const MCFragment &F = *i;
1529 assert(F.getKind() == MCFragment::FT_Data);
1530 WriteBytes(cast<MCDataFragment>(F).getContents());
1533 Asm.writeSectionData(&SD, Layout);
1537 void ELFObjectWriter::writeSectionHeader(
1538 ArrayRef<const MCSectionELF *> Sections, MCAssembler &Asm,
1539 const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap,
1540 const SectionOffsetsTy &SectionOffsets) {
1541 const unsigned NumSections = Asm.size();
1543 // Null section first.
1544 uint64_t FirstSectionSize =
1545 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1546 uint32_t FirstSectionLink =
1547 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1548 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1550 for (unsigned i = 0; i < NumSections; ++i) {
1551 const MCSectionELF &Section = *Sections[i];
1552 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1553 uint32_t GroupSymbolIndex;
1554 if (Section.getType() != ELF::SHT_GROUP)
1555 GroupSymbolIndex = 0;
1557 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section.getGroup());
1559 const std::pair<uint64_t, uint64_t> &Offsets = SectionOffsets[i];
1560 uint64_t Size = Section.getType() == ELF::SHT_NOBITS
1561 ? Layout.getSectionAddressSize(&SD)
1562 : Offsets.second - Offsets.first;
1564 writeSection(Asm, SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1565 SD.getAlignment(), Section);
1569 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1570 const MCAsmLayout &Layout) {
1571 RevGroupMapTy RevGroupMap;
1572 SectionIndexMapTy SectionIndexMap;
1574 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1575 createIndexedSections(Asm, const_cast<MCAsmLayout &>(Layout), RevGroupMap,
1578 // Compute symbol table information.
1579 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1581 WriteRelocations(Asm, const_cast<MCAsmLayout &>(Layout));
1583 std::vector<const MCSectionELF*> Sections;
1584 Sections.resize(SectionIndexMap.size());
1585 for (auto &Pair : SectionIndexMap)
1586 Sections[Pair.second - 1] = Pair.first;
1588 CreateMetadataSections(const_cast<MCAssembler &>(Asm),
1589 const_cast<MCAsmLayout &>(Layout), Sections);
1591 unsigned NumSections = Asm.size();
1592 SectionOffsetsTy SectionOffsets;
1594 // Write out the ELF header ...
1595 WriteHeader(Asm, NumSections + 1);
1597 // ... then the sections ...
1598 for (const MCSectionELF *Section : Sections) {
1599 const MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1600 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1601 WriteZeros(Padding);
1603 // Remember the offset into the file for this section.
1604 uint64_t SecStart = OS.tell();
1605 writeDataSectionData(Asm, Layout, SD);
1606 uint64_t SecEnd = OS.tell();
1607 SectionOffsets.push_back(std::make_pair(SecStart, SecEnd));
1610 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1611 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1612 WriteZeros(Padding);
1614 const unsigned SectionHeaderOffset = OS.tell();
1616 // ... then the section header table ...
1617 writeSectionHeader(Sections, Asm, Layout, SectionIndexMap, SectionOffsets);
1620 uint64_t Val = SectionHeaderOffset;
1621 if (sys::IsLittleEndianHost != IsLittleEndian)
1622 sys::swapByteOrder(Val);
1623 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1624 offsetof(ELF::Elf64_Ehdr, e_shoff));
1626 uint32_t Val = SectionHeaderOffset;
1627 if (sys::IsLittleEndianHost != IsLittleEndian)
1628 sys::swapByteOrder(Val);
1629 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1630 offsetof(ELF::Elf32_Ehdr, e_shoff));
1634 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1635 const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
1636 bool InSet, bool IsPCRel) const {
1639 if (::isWeak(DataA))
1642 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
1646 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
1650 // It is invalid to replace a reference to a global in a comdat
1651 // with a reference to a local since out of comdat references
1652 // to a local are forbidden.
1653 // We could try to return false for more cases, like the reference
1654 // being in the same comdat or Sym being an alias to another global,
1655 // but it is not clear if it is worth the effort.
1656 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1659 const MCSymbol &Sym = SD.getSymbol();
1660 if (!Sym.isInSection())
1663 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1664 return Sec.getGroup();
1667 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1668 raw_pwrite_stream &OS,
1669 bool IsLittleEndian) {
1670 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);