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 SectionIndexMapTy &SectionIndexMap;
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 SectionIndexMapTy &SectionIndexMap,
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 struct ELFRelocationEntry {
83 uint64_t Offset; // Where is the relocation.
84 const MCSymbol *Symbol; // The symbol to relocate with.
85 unsigned Type; // The type of the relocation.
86 uint64_t Addend; // The addend to use.
88 ELFRelocationEntry(uint64_t Offset, const MCSymbol *Symbol, unsigned Type,
90 : Offset(Offset), Symbol(Symbol), Type(Type), Addend(Addend) {}
93 class ELFObjectWriter : public MCObjectWriter {
94 FragmentWriter FWriter;
98 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
99 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
100 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
101 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data,
102 bool Used, bool Renamed);
103 static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
104 static bool IsELFMetaDataSection(const MCSectionData &SD);
105 static uint64_t DataSectionSize(const MCSectionData &SD);
106 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout,
107 const MCSectionData &SD);
108 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout,
109 const MCSectionData &SD);
111 void WriteDataSectionData(MCAssembler &Asm,
112 const MCAsmLayout &Layout,
113 const MCSectionELF &Section);
115 /// Helper struct for containing some precomputed information on symbols.
116 struct ELFSymbolData {
117 MCSymbolData *SymbolData;
118 uint64_t StringIndex;
119 uint32_t SectionIndex;
122 // Support lexicographic sorting.
123 bool operator<(const ELFSymbolData &RHS) const {
124 unsigned LHSType = MCELF::GetType(*SymbolData);
125 unsigned RHSType = MCELF::GetType(*RHS.SymbolData);
126 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
128 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
130 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
131 return SectionIndex < RHS.SectionIndex;
132 return Name < RHS.Name;
136 /// The target specific ELF writer instance.
137 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
139 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
140 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
141 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
143 llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
145 StringTableBuilder ShStrTabBuilder;
148 /// @name Symbol Table Data
151 StringTableBuilder StrTabBuilder;
152 std::vector<uint64_t> FileSymbolData;
153 std::vector<ELFSymbolData> LocalSymbolData;
154 std::vector<ELFSymbolData> ExternalSymbolData;
155 std::vector<ELFSymbolData> UndefinedSymbolData;
161 // This holds the symbol table index of the last local symbol.
162 unsigned LastLocalSymbolIndex;
163 // This holds the .strtab section index.
164 unsigned StringTableIndex;
165 // This holds the .symtab section index.
166 unsigned SymbolTableIndex;
168 unsigned ShstrtabIndex;
171 // TargetObjectWriter wrappers.
172 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
173 bool hasRelocationAddend() const {
174 return TargetObjectWriter->hasRelocationAddend();
176 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
177 bool IsPCRel) const {
178 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
182 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_ostream &OS,
184 : MCObjectWriter(OS, IsLittleEndian), FWriter(IsLittleEndian),
185 TargetObjectWriter(MOTW), NeedsGOT(false) {}
187 void reset() override {
189 WeakrefUsedInReloc.clear();
192 ShStrTabBuilder.clear();
193 StrTabBuilder.clear();
194 FileSymbolData.clear();
195 LocalSymbolData.clear();
196 ExternalSymbolData.clear();
197 UndefinedSymbolData.clear();
198 MCObjectWriter::reset();
201 ~ELFObjectWriter() override;
203 void WriteWord(uint64_t W) {
210 template <typename T> void write(MCDataFragment &F, T Value) {
211 FWriter.write(F, Value);
214 void WriteHeader(const MCAssembler &Asm,
215 uint64_t SectionHeaderOffset,
216 unsigned NumberOfSections);
218 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
219 const MCAsmLayout &Layout);
221 void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm,
222 const MCAsmLayout &Layout,
223 SectionIndexMapTy &SectionIndexMap);
225 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
226 const MCSymbolRefExpr *RefA,
227 const MCSymbolData *SD, uint64_t C,
228 unsigned Type) const;
230 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
231 const MCFragment *Fragment, const MCFixup &Fixup,
232 MCValue Target, bool &IsPCRel,
233 uint64_t &FixedValue) override;
235 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
238 // Map from a group section to the signature symbol
239 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
240 // Map from a signature symbol to the group section
241 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
242 // Map from a section to its offset
243 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy;
245 /// Compute the symbol table data
247 /// \param Asm - The assembler.
248 /// \param SectionIndexMap - Maps a section to its index.
249 /// \param RevGroupMap - Maps a signature symbol to the group section.
250 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
251 const SectionIndexMapTy &SectionIndexMap,
252 const RevGroupMapTy &RevGroupMap);
254 void computeIndexMap(MCAssembler &Asm, SectionIndexMapTy &SectionIndexMap);
256 MCSectionData *createRelocationSection(MCAssembler &Asm,
257 const MCSectionData &SD);
259 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
261 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout);
263 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
264 SectionIndexMapTy &SectionIndexMap);
266 // Create the sections that show up in the symbol table. Currently
267 // those are the .note.GNU-stack section and the group sections.
268 void createIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
269 GroupMapTy &GroupMap, RevGroupMapTy &RevGroupMap,
270 SectionIndexMapTy &SectionIndexMap);
272 void ExecutePostLayoutBinding(MCAssembler &Asm,
273 const MCAsmLayout &Layout) override;
275 void writeSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap,
276 const MCAsmLayout &Layout,
277 const SectionIndexMapTy &SectionIndexMap,
278 const SectionOffsetMapTy &SectionOffsetMap);
280 void ComputeSectionOrder(MCAssembler &Asm,
281 std::vector<const MCSectionELF*> &Sections);
283 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
284 uint64_t Address, uint64_t Offset,
285 uint64_t Size, uint32_t Link, uint32_t Info,
286 uint64_t Alignment, uint64_t EntrySize);
288 void WriteRelocationsFragment(const MCAssembler &Asm,
290 const MCSectionData *SD);
293 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
294 const MCSymbolData &DataA,
295 const MCSymbolData *DataB,
296 const MCFragment &FB,
298 bool IsPCRel) const override;
300 bool isWeak(const MCSymbolData &SD) const override;
302 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
303 void writeSection(MCAssembler &Asm,
304 const SectionIndexMapTy &SectionIndexMap,
305 uint32_t GroupSymbolIndex,
306 uint64_t Offset, uint64_t Size, uint64_t Alignment,
307 const MCSectionELF &Section);
311 FragmentWriter::FragmentWriter(bool IsLittleEndian)
312 : IsLittleEndian(IsLittleEndian) {}
314 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
316 Val = support::endian::byte_swap<T, support::little>(Val);
318 Val = support::endian::byte_swap<T, support::big>(Val);
319 const char *Start = (const char *)&Val;
320 F.getContents().append(Start, Start + sizeof(T));
323 void SymbolTableWriter::createSymtabShndx() {
327 MCContext &Ctx = Asm.getContext();
328 const MCSectionELF *SymtabShndxSection =
329 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
330 MCSectionData *SymtabShndxSD =
331 &Asm.getOrCreateSectionData(*SymtabShndxSection);
332 SymtabShndxSD->setAlignment(4);
333 ShndxF = new MCDataFragment(SymtabShndxSD);
334 unsigned Index = SectionIndexMap.size() + 1;
335 SectionIndexMap[SymtabShndxSection] = Index;
337 for (unsigned I = 0; I < NumWritten; ++I)
338 write(*ShndxF, uint32_t(0));
341 template <typename T>
342 void SymbolTableWriter::write(MCDataFragment &F, T Value) {
343 FWriter.write(F, Value);
346 SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter,
348 SectionIndexMapTy &SectionIndexMap,
349 MCDataFragment *SymtabF)
350 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit),
351 SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr),
354 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
355 uint64_t size, uint8_t other,
356 uint32_t shndx, bool Reserved) {
357 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
364 write(*ShndxF, shndx);
366 write(*ShndxF, uint32_t(0));
369 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
372 write(*SymtabF, name); // st_name
373 write(*SymtabF, info); // st_info
374 write(*SymtabF, other); // st_other
375 write(*SymtabF, Index); // st_shndx
376 write(*SymtabF, value); // st_value
377 write(*SymtabF, size); // st_size
379 write(*SymtabF, name); // st_name
380 write(*SymtabF, uint32_t(value)); // st_value
381 write(*SymtabF, uint32_t(size)); // st_size
382 write(*SymtabF, info); // st_info
383 write(*SymtabF, other); // st_other
384 write(*SymtabF, Index); // st_shndx
390 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
391 const MCFixupKindInfo &FKI =
392 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
394 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
397 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
401 case MCSymbolRefExpr::VK_GOT:
402 case MCSymbolRefExpr::VK_PLT:
403 case MCSymbolRefExpr::VK_GOTPCREL:
404 case MCSymbolRefExpr::VK_GOTOFF:
405 case MCSymbolRefExpr::VK_TPOFF:
406 case MCSymbolRefExpr::VK_TLSGD:
407 case MCSymbolRefExpr::VK_GOTTPOFF:
408 case MCSymbolRefExpr::VK_INDNTPOFF:
409 case MCSymbolRefExpr::VK_NTPOFF:
410 case MCSymbolRefExpr::VK_GOTNTPOFF:
411 case MCSymbolRefExpr::VK_TLSLDM:
412 case MCSymbolRefExpr::VK_DTPOFF:
413 case MCSymbolRefExpr::VK_TLSLD:
418 ELFObjectWriter::~ELFObjectWriter()
421 // Emit the ELF header.
422 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
423 uint64_t SectionHeaderOffset,
424 unsigned NumberOfSections) {
430 // emitWord method behaves differently for ELF32 and ELF64, writing
431 // 4 bytes in the former and 8 in the latter.
433 Write8(0x7f); // e_ident[EI_MAG0]
434 Write8('E'); // e_ident[EI_MAG1]
435 Write8('L'); // e_ident[EI_MAG2]
436 Write8('F'); // e_ident[EI_MAG3]
438 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
441 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
443 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
445 Write8(TargetObjectWriter->getOSABI());
446 Write8(0); // e_ident[EI_ABIVERSION]
448 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
450 Write16(ELF::ET_REL); // e_type
452 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
454 Write32(ELF::EV_CURRENT); // e_version
455 WriteWord(0); // e_entry, no entry point in .o file
456 WriteWord(0); // e_phoff, no program header for .o
457 WriteWord(SectionHeaderOffset); // e_shoff = sec hdr table off in bytes
459 // e_flags = whatever the target wants
460 Write32(Asm.getELFHeaderEFlags());
462 // e_ehsize = ELF header size
463 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
465 Write16(0); // e_phentsize = prog header entry size
466 Write16(0); // e_phnum = # prog header entries = 0
468 // e_shentsize = Section header entry size
469 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
471 // e_shnum = # of section header ents
472 if (NumberOfSections >= ELF::SHN_LORESERVE)
473 Write16(ELF::SHN_UNDEF);
475 Write16(NumberOfSections);
477 // e_shstrndx = Section # of '.shstrtab'
478 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
479 Write16(ELF::SHN_XINDEX);
481 Write16(ShstrtabIndex);
484 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
485 const MCAsmLayout &Layout) {
486 if (Data.isCommon() && Data.isExternal())
487 return Data.getCommonAlignment();
490 if (!Layout.getSymbolOffset(&Data, Res))
493 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
499 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
500 const MCAsmLayout &Layout) {
501 // The presence of symbol versions causes undefined symbols and
502 // versions declared with @@@ to be renamed.
504 for (MCSymbolData &OriginalData : Asm.symbols()) {
505 const MCSymbol &Alias = OriginalData.getSymbol();
508 if (!Alias.isVariable())
510 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
513 const MCSymbol &Symbol = Ref->getSymbol();
514 MCSymbolData &SD = Asm.getSymbolData(Symbol);
516 StringRef AliasName = Alias.getName();
517 size_t Pos = AliasName.find('@');
518 if (Pos == StringRef::npos)
521 // Aliases defined with .symvar copy the binding from the symbol they alias.
522 // This is the first place we are able to copy this information.
523 OriginalData.setExternal(SD.isExternal());
524 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
526 StringRef Rest = AliasName.substr(Pos);
527 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
530 // FIXME: produce a better error message.
531 if (Symbol.isUndefined() && Rest.startswith("@@") &&
532 !Rest.startswith("@@@"))
533 report_fatal_error("A @@ version cannot be undefined");
535 Renames.insert(std::make_pair(&Symbol, &Alias));
539 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
540 uint8_t Type = newType;
542 // Propagation rules:
543 // IFUNC > FUNC > OBJECT > NOTYPE
544 // TLS_OBJECT > OBJECT > NOTYPE
546 // dont let the new type degrade the old type
550 case ELF::STT_GNU_IFUNC:
551 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
552 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
553 Type = ELF::STT_GNU_IFUNC;
556 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
557 Type == ELF::STT_TLS)
558 Type = ELF::STT_FUNC;
560 case ELF::STT_OBJECT:
561 if (Type == ELF::STT_NOTYPE)
562 Type = ELF::STT_OBJECT;
565 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
566 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
574 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
575 const MCAsmLayout &Layout) {
576 MCSymbolData &OrigData = *MSD.SymbolData;
577 assert((!OrigData.getFragment() ||
578 (&OrigData.getFragment()->getParent()->getSection() ==
579 &OrigData.getSymbol().getSection())) &&
580 "The symbol's section doesn't match the fragment's symbol");
581 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
583 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
585 bool IsReserved = !Base || OrigData.isCommon();
587 // Binding and Type share the same byte as upper and lower nibbles
588 uint8_t Binding = MCELF::GetBinding(OrigData);
589 uint8_t Type = MCELF::GetType(OrigData);
590 MCSymbolData *BaseSD = nullptr;
592 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
593 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
595 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
597 // Other and Visibility share the same byte with Visibility using the lower
599 uint8_t Visibility = MCELF::GetVisibility(OrigData);
600 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
603 uint64_t Value = SymbolValue(OrigData, Layout);
606 const MCExpr *ESize = OrigData.getSize();
608 ESize = BaseSD->getSize();
612 if (!ESize->evaluateKnownAbsolute(Res, Layout))
613 report_fatal_error("Size expression must be absolute.");
617 // Write out the symbol table entry
618 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
619 MSD.SectionIndex, IsReserved);
622 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
624 const MCAsmLayout &Layout,
625 SectionIndexMapTy &SectionIndexMap) {
626 // The string table must be emitted first because we need the index
627 // into the string table for all the symbol names.
629 // FIXME: Make sure the start of the symbol table is aligned.
631 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF);
633 // The first entry is the undefined symbol entry.
634 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
636 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
637 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
638 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
641 // Write the symbol table entries.
642 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
644 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
645 ELFSymbolData &MSD = LocalSymbolData[i];
646 WriteSymbol(Writer, MSD, Layout);
649 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
650 ELFSymbolData &MSD = ExternalSymbolData[i];
651 MCSymbolData &Data = *MSD.SymbolData;
652 assert(((Data.getFlags() & ELF_STB_Global) ||
653 (Data.getFlags() & ELF_STB_Weak)) &&
654 "External symbol requires STB_GLOBAL or STB_WEAK flag");
655 WriteSymbol(Writer, MSD, Layout);
656 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
657 LastLocalSymbolIndex++;
660 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
661 ELFSymbolData &MSD = UndefinedSymbolData[i];
662 MCSymbolData &Data = *MSD.SymbolData;
663 WriteSymbol(Writer, MSD, Layout);
664 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
665 LastLocalSymbolIndex++;
669 // It is always valid to create a relocation with a symbol. It is preferable
670 // to use a relocation with a section if that is possible. Using the section
671 // allows us to omit some local symbols from the symbol table.
672 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
673 const MCSymbolRefExpr *RefA,
674 const MCSymbolData *SD,
676 unsigned Type) const {
677 // A PCRel relocation to an absolute value has no symbol (or section). We
678 // represent that with a relocation to a null section.
682 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
686 // The .odp creation emits a relocation against the symbol ".TOC." which
687 // create a R_PPC64_TOC relocation. However the relocation symbol name
688 // in final object creation should be NULL, since the symbol does not
689 // really exist, it is just the reference to TOC base for the current
690 // object file. Since the symbol is undefined, returning false results
691 // in a relocation with a null section which is the desired result.
692 case MCSymbolRefExpr::VK_PPC_TOCBASE:
695 // These VariantKind cause the relocation to refer to something other than
696 // the symbol itself, like a linker generated table. Since the address of
697 // symbol is not relevant, we cannot replace the symbol with the
698 // section and patch the difference in the addend.
699 case MCSymbolRefExpr::VK_GOT:
700 case MCSymbolRefExpr::VK_PLT:
701 case MCSymbolRefExpr::VK_GOTPCREL:
702 case MCSymbolRefExpr::VK_Mips_GOT:
703 case MCSymbolRefExpr::VK_PPC_GOT_LO:
704 case MCSymbolRefExpr::VK_PPC_GOT_HI:
705 case MCSymbolRefExpr::VK_PPC_GOT_HA:
709 // An undefined symbol is not in any section, so the relocation has to point
710 // to the symbol itself.
711 const MCSymbol &Sym = SD->getSymbol();
712 if (Sym.isUndefined())
715 unsigned Binding = MCELF::GetBinding(*SD);
718 llvm_unreachable("Invalid Binding");
722 // If the symbol is weak, it might be overridden by a symbol in another
723 // file. The relocation has to point to the symbol so that the linker
726 case ELF::STB_GLOBAL:
727 // Global ELF symbols can be preempted by the dynamic linker. The relocation
728 // has to point to the symbol for a reason analogous to the STB_WEAK case.
732 // If a relocation points to a mergeable section, we have to be careful.
733 // If the offset is zero, a relocation with the section will encode the
734 // same information. With a non-zero offset, the situation is different.
735 // For example, a relocation can point 42 bytes past the end of a string.
736 // If we change such a relocation to use the section, the linker would think
737 // that it pointed to another string and subtracting 42 at runtime will
738 // produce the wrong value.
739 auto &Sec = cast<MCSectionELF>(Sym.getSection());
740 unsigned Flags = Sec.getFlags();
741 if (Flags & ELF::SHF_MERGE) {
745 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
746 // only handle section relocations to mergeable sections if using RELA.
747 if (!hasRelocationAddend())
751 // Most TLS relocations use a got, so they need the symbol. Even those that
752 // are just an offset (@tpoff), require a symbol in gold versions before
753 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
754 // http://sourceware.org/PR16773.
755 if (Flags & ELF::SHF_TLS)
758 // If the symbol is a thumb function the final relocation must set the lowest
759 // bit. With a symbol that is done by just having the symbol have that bit
760 // set, so we would lose the bit if we relocated with the section.
761 // FIXME: We could use the section but add the bit to the relocation value.
762 if (Asm.isThumbFunc(&Sym))
765 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
770 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
771 const MCSymbol &Sym = Ref.getSymbol();
773 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
776 if (!Sym.isVariable())
779 const MCExpr *Expr = Sym.getVariableValue();
780 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
784 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
785 return &Inner->getSymbol();
789 static bool isWeak(const MCSymbolData &D) {
790 return D.getFlags() & ELF_STB_Weak || MCELF::GetType(D) == ELF::STT_GNU_IFUNC;
793 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
794 const MCAsmLayout &Layout,
795 const MCFragment *Fragment,
796 const MCFixup &Fixup, MCValue Target,
797 bool &IsPCRel, uint64_t &FixedValue) {
798 const MCSectionData *FixupSection = Fragment->getParent();
799 uint64_t C = Target.getConstant();
800 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
802 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
803 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
804 "Should not have constructed this");
806 // Let A, B and C being the components of Target and R be the location of
807 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
808 // If it is pcrel, we want to compute (A - B + C - R).
810 // In general, ELF has no relocations for -B. It can only represent (A + C)
811 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
812 // replace B to implement it: (A - R - K + C)
814 Asm.getContext().FatalError(
816 "No relocation available to represent this relative expression");
818 const MCSymbol &SymB = RefB->getSymbol();
820 if (SymB.isUndefined())
821 Asm.getContext().FatalError(
823 Twine("symbol '") + SymB.getName() +
824 "' can not be undefined in a subtraction expression");
826 assert(!SymB.isAbsolute() && "Should have been folded");
827 const MCSection &SecB = SymB.getSection();
828 if (&SecB != &FixupSection->getSection())
829 Asm.getContext().FatalError(
830 Fixup.getLoc(), "Cannot represent a difference across sections");
832 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
834 Asm.getContext().FatalError(
835 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
837 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
838 uint64_t K = SymBOffset - FixupOffset;
843 // We either rejected the fixup or folded B into C at this point.
844 const MCSymbolRefExpr *RefA = Target.getSymA();
845 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
846 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
848 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
849 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
850 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
851 C += Layout.getSymbolOffset(SymAD);
854 if (hasRelocationAddend()) {
861 // FIXME: What is this!?!?
862 MCSymbolRefExpr::VariantKind Modifier =
863 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
864 if (RelocNeedsGOT(Modifier))
867 if (!RelocateWithSymbol) {
868 const MCSection *SecA =
869 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
870 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
871 MCSymbol *SectionSymbol =
872 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
874 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
875 Relocations[FixupSection].push_back(Rec);
880 if (const MCSymbol *R = Renames.lookup(SymA))
883 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
884 WeakrefUsedInReloc.insert(WeakRef);
886 UsedInReloc.insert(SymA);
888 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
889 Relocations[FixupSection].push_back(Rec);
895 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
897 const MCSymbolData &SD = Asm.getSymbolData(*S);
898 return SD.getIndex();
901 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
902 const MCSymbolData &Data, bool Used,
904 const MCSymbol &Symbol = Data.getSymbol();
905 if (Symbol.isVariable()) {
906 const MCExpr *Expr = Symbol.getVariableValue();
907 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
908 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
919 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
922 if (Symbol.isVariable()) {
923 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
924 if (Base && Base->isUndefined())
928 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
929 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
932 if (Symbol.isTemporary())
938 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
939 if (Data.isExternal())
942 const MCSymbol &Symbol = Data.getSymbol();
943 if (Symbol.isDefined())
952 void ELFObjectWriter::computeIndexMap(MCAssembler &Asm,
953 SectionIndexMapTy &SectionIndexMap) {
955 for (MCAssembler::iterator it = Asm.begin(),
956 ie = Asm.end(); it != ie; ++it) {
957 const MCSectionELF &Section =
958 static_cast<const MCSectionELF &>(it->getSection());
959 if (Section.getType() != ELF::SHT_GROUP)
961 SectionIndexMap[&Section] = Index++;
964 for (MCAssembler::iterator it = Asm.begin(),
965 ie = Asm.end(); it != ie; ++it) {
966 const MCSectionData &SD = *it;
967 const MCSectionELF &Section =
968 static_cast<const MCSectionELF &>(SD.getSection());
969 if (Section.getType() == ELF::SHT_GROUP ||
970 Section.getType() == ELF::SHT_REL ||
971 Section.getType() == ELF::SHT_RELA)
973 SectionIndexMap[&Section] = Index++;
974 if (MCSectionData *RelSD = createRelocationSection(Asm, SD)) {
975 const MCSectionELF *RelSection =
976 static_cast<const MCSectionELF *>(&RelSD->getSection());
977 SectionIndexMap[RelSection] = Index++;
982 void ELFObjectWriter::computeSymbolTable(
983 MCAssembler &Asm, const MCAsmLayout &Layout,
984 const SectionIndexMapTy &SectionIndexMap,
985 const RevGroupMapTy &RevGroupMap) {
986 // FIXME: Is this the correct place to do this?
987 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
989 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
990 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
991 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
992 Data.setExternal(true);
993 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
996 // Add the data for the symbols.
997 for (MCSymbolData &SD : Asm.symbols()) {
998 const MCSymbol &Symbol = SD.getSymbol();
1000 bool Used = UsedInReloc.count(&Symbol);
1001 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
1002 bool isSignature = RevGroupMap.count(&Symbol);
1004 if (!isInSymtab(Layout, SD,
1005 Used || WeakrefUsed || isSignature,
1006 Renames.count(&Symbol)))
1010 MSD.SymbolData = &SD;
1011 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
1013 // Undefined symbols are global, but this is the first place we
1014 // are able to set it.
1015 bool Local = isLocal(SD, Used);
1016 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1018 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1019 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1020 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1024 MSD.SectionIndex = ELF::SHN_ABS;
1025 } else if (SD.isCommon()) {
1027 MSD.SectionIndex = ELF::SHN_COMMON;
1028 } else if (BaseSymbol->isUndefined()) {
1029 if (isSignature && !Used)
1030 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap.lookup(&Symbol));
1032 MSD.SectionIndex = ELF::SHN_UNDEF;
1033 if (!Used && WeakrefUsed)
1034 MCELF::SetBinding(SD, ELF::STB_WEAK);
1036 const MCSectionELF &Section =
1037 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1038 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1039 assert(MSD.SectionIndex && "Invalid section index!");
1042 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
1045 // FIXME: All name handling should be done before we get to the writer,
1046 // including dealing with GNU-style version suffixes. Fixing this isn't
1049 // We thus have to be careful to not perform the symbol version replacement
1052 // The ELF format is used on Windows by the MCJIT engine. Thus, on
1053 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
1054 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
1055 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
1056 // the EFLObjectWriter should not interpret the "@@@" sub-string as
1057 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1058 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1059 // "__imp_?" or "__imp_@?".
1061 // It would have been interesting to perform the MS mangling prefix check
1062 // only when the target triple is of the form *-pc-windows-elf. But, it
1063 // seems that this information is not easily accessible from the
1065 StringRef Name = Symbol.getName();
1066 if (!Name.startswith("?") && !Name.startswith("@?") &&
1067 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1068 // This symbol isn't following the MSVC C++ name mangling convention. We
1069 // can thus safely interpret the @@@ in symbol names as specifying symbol
1071 SmallString<32> Buf;
1072 size_t Pos = Name.find("@@@");
1073 if (Pos != StringRef::npos) {
1074 Buf += Name.substr(0, Pos);
1075 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1076 Buf += Name.substr(Pos + Skip);
1081 // Sections have their own string table
1082 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1083 MSD.Name = StrTabBuilder.add(Name);
1085 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1086 UndefinedSymbolData.push_back(MSD);
1088 LocalSymbolData.push_back(MSD);
1090 ExternalSymbolData.push_back(MSD);
1093 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1094 StrTabBuilder.add(*i);
1096 StrTabBuilder.finalize(StringTableBuilder::ELF);
1098 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1099 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1101 for (ELFSymbolData &MSD : LocalSymbolData)
1102 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1104 : StrTabBuilder.getOffset(MSD.Name);
1105 for (ELFSymbolData &MSD : ExternalSymbolData)
1106 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1107 for (ELFSymbolData& MSD : UndefinedSymbolData)
1108 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1110 // Symbols are required to be in lexicographic order.
1111 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1112 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1113 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1115 // Set the symbol indices. Local symbols must come before all other
1116 // symbols with non-local bindings.
1117 unsigned Index = FileSymbolData.size() + 1;
1118 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1119 LocalSymbolData[i].SymbolData->setIndex(Index++);
1121 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1122 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1123 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1124 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1128 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1129 const MCSectionData &SD) {
1130 if (Relocations[&SD].empty())
1133 MCContext &Ctx = Asm.getContext();
1134 const MCSectionELF &Section =
1135 static_cast<const MCSectionELF &>(SD.getSection());
1137 const StringRef SectionName = Section.getSectionName();
1138 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1139 RelaSectionName += SectionName;
1142 if (hasRelocationAddend())
1143 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1145 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1148 if (Section.getFlags() & ELF::SHF_GROUP)
1149 Flags = ELF::SHF_GROUP;
1151 const MCSectionELF *RelaSection = Ctx.createELFRelSection(
1152 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1153 Flags, EntrySize, Section.getGroup(), &Section);
1154 return &Asm.getOrCreateSectionData(*RelaSection);
1157 static SmallVector<char, 128>
1158 getUncompressedData(MCAsmLayout &Layout,
1159 MCSectionData::FragmentListType &Fragments) {
1160 SmallVector<char, 128> UncompressedData;
1161 for (const MCFragment &F : Fragments) {
1162 const SmallVectorImpl<char> *Contents;
1163 switch (F.getKind()) {
1164 case MCFragment::FT_Data:
1165 Contents = &cast<MCDataFragment>(F).getContents();
1167 case MCFragment::FT_Dwarf:
1168 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1170 case MCFragment::FT_DwarfFrame:
1171 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1175 "Not expecting any other fragment types in a debug_* section");
1177 UncompressedData.append(Contents->begin(), Contents->end());
1179 return UncompressedData;
1182 // Include the debug info compression header:
1183 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1184 // useful for consumers to preallocate a buffer to decompress into.
1186 prependCompressionHeader(uint64_t Size,
1187 SmallVectorImpl<char> &CompressedContents) {
1188 const StringRef Magic = "ZLIB";
1189 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1191 if (sys::IsLittleEndianHost)
1192 sys::swapByteOrder(Size);
1193 CompressedContents.insert(CompressedContents.begin(),
1194 Magic.size() + sizeof(Size), 0);
1195 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1196 std::copy(reinterpret_cast<char *>(&Size),
1197 reinterpret_cast<char *>(&Size + 1),
1198 CompressedContents.begin() + Magic.size());
1202 // Return a single fragment containing the compressed contents of the whole
1203 // section. Null if the section was not compressed for any reason.
1204 static std::unique_ptr<MCDataFragment>
1205 getCompressedFragment(MCAsmLayout &Layout,
1206 MCSectionData::FragmentListType &Fragments) {
1207 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1209 // Gather the uncompressed data from all the fragments, recording the
1210 // alignment fragment, if seen, and any fixups.
1211 SmallVector<char, 128> UncompressedData =
1212 getUncompressedData(Layout, Fragments);
1214 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1216 zlib::Status Success = zlib::compress(
1217 StringRef(UncompressedData.data(), UncompressedData.size()),
1218 CompressedContents);
1219 if (Success != zlib::StatusOK)
1222 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1225 return CompressedFragment;
1228 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1231 static void UpdateSymbols(const MCAsmLayout &Layout,
1232 const std::vector<MCSymbolData *> &Symbols,
1233 MCFragment &NewFragment) {
1234 for (MCSymbolData *Sym : Symbols) {
1235 Sym->setOffset(Sym->getOffset() +
1236 Layout.getFragmentOffset(Sym->getFragment()));
1237 Sym->setFragment(&NewFragment);
1241 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1242 const DefiningSymbolMap &DefiningSymbols,
1243 const MCSectionELF &Section,
1244 MCSectionData &SD) {
1245 StringRef SectionName = Section.getSectionName();
1246 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1248 std::unique_ptr<MCDataFragment> CompressedFragment =
1249 getCompressedFragment(Layout, Fragments);
1251 // Leave the section as-is if the fragments could not be compressed.
1252 if (!CompressedFragment)
1255 // Update the fragment+offsets of any symbols referring to fragments in this
1256 // section to refer to the new fragment.
1257 auto I = DefiningSymbols.find(&SD);
1258 if (I != DefiningSymbols.end())
1259 UpdateSymbols(Layout, I->second, *CompressedFragment);
1261 // Invalidate the layout for the whole section since it will have new and
1262 // different fragments now.
1263 Layout.invalidateFragmentsFrom(&Fragments.front());
1266 // Complete the initialization of the new fragment
1267 CompressedFragment->setParent(&SD);
1268 CompressedFragment->setLayoutOrder(0);
1269 Fragments.push_back(CompressedFragment.release());
1271 // Rename from .debug_* to .zdebug_*
1272 Asm.getContext().renameELFSection(&Section,
1273 (".z" + SectionName.drop_front(1)).str());
1276 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1277 MCAsmLayout &Layout) {
1278 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1281 DefiningSymbolMap DefiningSymbols;
1283 for (MCSymbolData &SD : Asm.symbols())
1284 if (MCFragment *F = SD.getFragment())
1285 DefiningSymbols[F->getParent()].push_back(&SD);
1287 for (MCSectionData &SD : Asm) {
1288 const MCSectionELF &Section =
1289 static_cast<const MCSectionELF &>(SD.getSection());
1290 StringRef SectionName = Section.getSectionName();
1292 // Compressing debug_frame requires handling alignment fragments which is
1293 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1294 // for writing to arbitrary buffers) for little benefit.
1295 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1298 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1302 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) {
1303 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1304 MCSectionData &RelSD = *it;
1305 const MCSectionELF &RelSection =
1306 static_cast<const MCSectionELF &>(RelSD.getSection());
1308 unsigned Type = RelSection.getType();
1309 if (Type != ELF::SHT_REL && Type != ELF::SHT_RELA)
1312 const MCSectionELF *Section = RelSection.getAssociatedSection();
1313 MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1314 RelSD.setAlignment(is64Bit() ? 8 : 4);
1316 MCDataFragment *F = new MCDataFragment(&RelSD);
1317 WriteRelocationsFragment(Asm, F, &SD);
1321 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1322 uint64_t Flags, uint64_t Address,
1323 uint64_t Offset, uint64_t Size,
1324 uint32_t Link, uint32_t Info,
1326 uint64_t EntrySize) {
1327 Write32(Name); // sh_name: index into string table
1328 Write32(Type); // sh_type
1329 WriteWord(Flags); // sh_flags
1330 WriteWord(Address); // sh_addr
1331 WriteWord(Offset); // sh_offset
1332 WriteWord(Size); // sh_size
1333 Write32(Link); // sh_link
1334 Write32(Info); // sh_info
1335 WriteWord(Alignment); // sh_addralign
1336 WriteWord(EntrySize); // sh_entsize
1339 // ELF doesn't require relocations to be in any order. We sort by the r_offset,
1340 // just to match gnu as for easier comparison. The use type is an arbitrary way
1341 // of making the sort deterministic.
1342 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
1343 const ELFRelocationEntry &A = *AP;
1344 const ELFRelocationEntry &B = *BP;
1345 if (A.Offset != B.Offset)
1346 return B.Offset - A.Offset;
1347 if (B.Type != A.Type)
1348 return A.Type - B.Type;
1349 //llvm_unreachable("ELFRelocs might be unstable!");
1353 static void sortRelocs(const MCAssembler &Asm,
1354 std::vector<ELFRelocationEntry> &Relocs) {
1355 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
1358 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1360 const MCSectionData *SD) {
1361 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1363 sortRelocs(Asm, Relocs);
1365 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1366 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1368 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1371 write(*F, Entry.Offset);
1372 if (TargetObjectWriter->isN64()) {
1373 write(*F, uint32_t(Index));
1375 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1376 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1377 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1378 write(*F, TargetObjectWriter->getRType(Entry.Type));
1380 struct ELF::Elf64_Rela ERE64;
1381 ERE64.setSymbolAndType(Index, Entry.Type);
1382 write(*F, ERE64.r_info);
1384 if (hasRelocationAddend())
1385 write(*F, Entry.Addend);
1387 write(*F, uint32_t(Entry.Offset));
1389 struct ELF::Elf32_Rela ERE32;
1390 ERE32.setSymbolAndType(Index, Entry.Type);
1391 write(*F, ERE32.r_info);
1393 if (hasRelocationAddend())
1394 write(*F, uint32_t(Entry.Addend));
1399 void ELFObjectWriter::CreateMetadataSections(
1400 MCAssembler &Asm, MCAsmLayout &Layout, SectionIndexMapTy &SectionIndexMap) {
1401 MCContext &Ctx = Asm.getContext();
1404 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1406 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1407 const MCSectionELF *ShstrtabSection =
1408 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1409 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1410 ShstrtabSD.setAlignment(1);
1411 ShstrtabIndex = SectionIndexMap.size() + 1;
1412 SectionIndexMap[ShstrtabSection] = ShstrtabIndex;
1414 const MCSectionELF *SymtabSection =
1415 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1417 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1418 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1419 SymbolTableIndex = SectionIndexMap.size() + 1;
1420 SectionIndexMap[SymtabSection] = SymbolTableIndex;
1422 const MCSectionELF *StrtabSection;
1423 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1424 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1425 StrtabSD.setAlignment(1);
1426 StringTableIndex = SectionIndexMap.size() + 1;
1427 SectionIndexMap[StrtabSection] = StringTableIndex;
1430 F = new MCDataFragment(&SymtabSD);
1431 WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
1433 F = new MCDataFragment(&StrtabSD);
1434 F->getContents().append(StrTabBuilder.data().begin(),
1435 StrTabBuilder.data().end());
1437 F = new MCDataFragment(&ShstrtabSD);
1439 // Section header string table.
1440 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1441 const MCSectionELF &Section =
1442 static_cast<const MCSectionELF&>(it->getSection());
1443 ShStrTabBuilder.add(Section.getSectionName());
1445 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1446 F->getContents().append(ShStrTabBuilder.data().begin(),
1447 ShStrTabBuilder.data().end());
1450 void ELFObjectWriter::createIndexedSections(
1451 MCAssembler &Asm, MCAsmLayout &Layout, GroupMapTy &GroupMap,
1452 RevGroupMapTy &RevGroupMap, SectionIndexMapTy &SectionIndexMap) {
1453 MCContext &Ctx = Asm.getContext();
1456 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1458 const MCSectionELF &Section =
1459 static_cast<const MCSectionELF&>(it->getSection());
1460 if (!(Section.getFlags() & ELF::SHF_GROUP))
1463 const MCSymbol *SignatureSymbol = Section.getGroup();
1464 Asm.getOrCreateSymbolData(*SignatureSymbol);
1465 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1467 Group = Ctx.CreateELFGroupSection();
1468 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1469 Data.setAlignment(4);
1470 MCDataFragment *F = new MCDataFragment(&Data);
1471 write(*F, uint32_t(ELF::GRP_COMDAT));
1473 GroupMap[Group] = SignatureSymbol;
1476 computeIndexMap(Asm, SectionIndexMap);
1478 // Add sections to the groups
1479 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1481 const MCSectionELF &Section =
1482 static_cast<const MCSectionELF&>(it->getSection());
1483 if (!(Section.getFlags() & ELF::SHF_GROUP))
1485 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1486 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1487 // FIXME: we could use the previous fragment
1488 MCDataFragment *F = new MCDataFragment(&Data);
1489 uint32_t Index = SectionIndexMap.lookup(&Section);
1494 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1495 const SectionIndexMapTy &SectionIndexMap,
1496 uint32_t GroupSymbolIndex,
1497 uint64_t Offset, uint64_t Size,
1499 const MCSectionELF &Section) {
1500 uint64_t sh_link = 0;
1501 uint64_t sh_info = 0;
1503 switch(Section.getType()) {
1508 case ELF::SHT_DYNAMIC:
1509 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1513 case ELF::SHT_RELA: {
1514 sh_link = SymbolTableIndex;
1515 assert(sh_link && ".symtab not found");
1516 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1517 sh_info = SectionIndexMap.lookup(InfoSection);
1521 case ELF::SHT_SYMTAB:
1522 case ELF::SHT_DYNSYM:
1523 sh_link = StringTableIndex;
1524 sh_info = LastLocalSymbolIndex;
1527 case ELF::SHT_SYMTAB_SHNDX:
1528 sh_link = SymbolTableIndex;
1531 case ELF::SHT_GROUP:
1532 sh_link = SymbolTableIndex;
1533 sh_info = GroupSymbolIndex;
1537 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1538 Section.getType() == ELF::SHT_ARM_EXIDX)
1539 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1541 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1543 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1544 Alignment, Section.getEntrySize());
1547 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1548 return SD.getOrdinal() == ~UINT32_C(0) &&
1549 !SD.getSection().isVirtualSection();
1552 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1554 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1556 const MCFragment &F = *i;
1557 assert(F.getKind() == MCFragment::FT_Data);
1558 Ret += cast<MCDataFragment>(F).getContents().size();
1563 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
1564 const MCSectionData &SD) {
1565 if (IsELFMetaDataSection(SD))
1566 return DataSectionSize(SD);
1567 return Layout.getSectionFileSize(&SD);
1570 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1571 const MCSectionData &SD) {
1572 if (IsELFMetaDataSection(SD))
1573 return DataSectionSize(SD);
1574 return Layout.getSectionAddressSize(&SD);
1577 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
1578 const MCAsmLayout &Layout,
1579 const MCSectionELF &Section) {
1580 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1582 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1583 WriteZeros(Padding);
1585 if (IsELFMetaDataSection(SD)) {
1586 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1588 const MCFragment &F = *i;
1589 assert(F.getKind() == MCFragment::FT_Data);
1590 WriteBytes(cast<MCDataFragment>(F).getContents());
1593 Asm.writeSectionData(&SD, Layout);
1597 void ELFObjectWriter::writeSectionHeader(
1598 MCAssembler &Asm, const GroupMapTy &GroupMap, const MCAsmLayout &Layout,
1599 const SectionIndexMapTy &SectionIndexMap,
1600 const SectionOffsetMapTy &SectionOffsetMap) {
1601 const unsigned NumSections = Asm.size() + 1;
1603 std::vector<const MCSectionELF*> Sections;
1604 Sections.resize(NumSections - 1);
1606 for (SectionIndexMapTy::const_iterator i=
1607 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
1608 const std::pair<const MCSectionELF*, uint32_t> &p = *i;
1609 Sections[p.second - 1] = p.first;
1612 // Null section first.
1613 uint64_t FirstSectionSize =
1614 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1615 uint32_t FirstSectionLink =
1616 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1617 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1619 for (unsigned i = 0; i < NumSections - 1; ++i) {
1620 const MCSectionELF &Section = *Sections[i];
1621 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1622 uint32_t GroupSymbolIndex;
1623 if (Section.getType() != ELF::SHT_GROUP)
1624 GroupSymbolIndex = 0;
1626 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1627 GroupMap.lookup(&Section));
1629 uint64_t Size = GetSectionAddressSize(Layout, SD);
1631 writeSection(Asm, SectionIndexMap, GroupSymbolIndex,
1632 SectionOffsetMap.lookup(&Section), Size, SD.getAlignment(),
1637 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
1638 std::vector<const MCSectionELF*> &Sections) {
1639 for (MCAssembler::iterator it = Asm.begin(),
1640 ie = Asm.end(); it != ie; ++it) {
1641 const MCSectionELF &Section =
1642 static_cast<const MCSectionELF &>(it->getSection());
1643 if (Section.getType() == ELF::SHT_GROUP)
1644 Sections.push_back(&Section);
1647 for (MCAssembler::iterator it = Asm.begin(),
1648 ie = Asm.end(); it != ie; ++it) {
1649 const MCSectionELF &Section =
1650 static_cast<const MCSectionELF &>(it->getSection());
1651 if (Section.getType() != ELF::SHT_GROUP &&
1652 Section.getType() != ELF::SHT_REL &&
1653 Section.getType() != ELF::SHT_RELA)
1654 Sections.push_back(&Section);
1657 for (MCAssembler::iterator it = Asm.begin(),
1658 ie = Asm.end(); it != ie; ++it) {
1659 const MCSectionELF &Section =
1660 static_cast<const MCSectionELF &>(it->getSection());
1661 if (Section.getType() == ELF::SHT_REL ||
1662 Section.getType() == ELF::SHT_RELA)
1663 Sections.push_back(&Section);
1667 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1668 const MCAsmLayout &Layout) {
1669 GroupMapTy GroupMap;
1670 RevGroupMapTy RevGroupMap;
1671 SectionIndexMapTy SectionIndexMap;
1673 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1674 createIndexedSections(Asm, const_cast<MCAsmLayout &>(Layout), GroupMap,
1675 RevGroupMap, SectionIndexMap);
1677 // Compute symbol table information.
1678 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1680 WriteRelocations(Asm, const_cast<MCAsmLayout &>(Layout));
1682 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1683 const_cast<MCAsmLayout&>(Layout),
1686 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1687 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
1688 sizeof(ELF::Elf32_Ehdr);
1689 uint64_t FileOff = HeaderSize;
1691 std::vector<const MCSectionELF*> Sections;
1692 ComputeSectionOrder(Asm, Sections);
1693 unsigned NumSections = Sections.size();
1694 SectionOffsetMapTy SectionOffsetMap;
1695 for (unsigned i = 0; i < NumSections; ++i) {
1697 const MCSectionELF &Section = *Sections[i];
1698 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1700 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1702 // Remember the offset into the file for this section.
1703 SectionOffsetMap[&Section] = FileOff;
1705 // Get the size of the section in the output file (including padding).
1706 FileOff += GetSectionFileSize(Layout, SD);
1709 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1711 const unsigned SectionHeaderOffset = FileOff;
1713 // Write out the ELF header ...
1714 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
1716 // ... then the sections ...
1717 for (unsigned i = 0; i < NumSections; ++i)
1718 WriteDataSectionData(Asm, Layout, *Sections[i]);
1720 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1721 WriteZeros(Padding);
1723 // ... then the section header table ...
1724 writeSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, SectionOffsetMap);
1727 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1728 const MCAssembler &Asm, const MCSymbolData &DataA,
1729 const MCSymbolData *DataB, const MCFragment &FB, bool InSet,
1730 bool IsPCRel) const {
1731 if (!InSet && (::isWeak(DataA) || (DataB && ::isWeak(*DataB))))
1733 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1734 Asm, DataA, DataB, FB, InSet, IsPCRel);
1737 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
1738 return ::isWeak(SD);
1741 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1743 bool IsLittleEndian) {
1744 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);