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 /*static bool isFixupKindX86RIPRel(unsigned Kind) {
116 return Kind == X86::reloc_riprel_4byte ||
117 Kind == X86::reloc_riprel_4byte_movq_load;
120 /// ELFSymbolData - Helper struct for containing some precomputed
121 /// information on symbols.
122 struct ELFSymbolData {
123 MCSymbolData *SymbolData;
124 uint64_t StringIndex;
125 uint32_t SectionIndex;
128 // Support lexicographic sorting.
129 bool operator<(const ELFSymbolData &RHS) const {
130 unsigned LHSType = MCELF::GetType(*SymbolData);
131 unsigned RHSType = MCELF::GetType(*RHS.SymbolData);
132 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
134 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
136 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
137 return SectionIndex < RHS.SectionIndex;
138 return Name < RHS.Name;
142 /// The target specific ELF writer instance.
143 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
145 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
146 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
147 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
149 llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
151 StringTableBuilder ShStrTabBuilder;
154 /// @name Symbol Table Data
157 StringTableBuilder StrTabBuilder;
158 std::vector<uint64_t> FileSymbolData;
159 std::vector<ELFSymbolData> LocalSymbolData;
160 std::vector<ELFSymbolData> ExternalSymbolData;
161 std::vector<ELFSymbolData> UndefinedSymbolData;
167 // This holds the symbol table index of the last local symbol.
168 unsigned LastLocalSymbolIndex;
169 // This holds the .strtab section index.
170 unsigned StringTableIndex;
171 // This holds the .symtab section index.
172 unsigned SymbolTableIndex;
174 unsigned ShstrtabIndex;
177 // TargetObjectWriter wrappers.
178 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
179 bool hasRelocationAddend() const {
180 return TargetObjectWriter->hasRelocationAddend();
182 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
183 bool IsPCRel) const {
184 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
188 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_ostream &_OS,
190 : MCObjectWriter(_OS, IsLittleEndian), FWriter(IsLittleEndian),
191 TargetObjectWriter(MOTW), NeedsGOT(false) {}
193 virtual ~ELFObjectWriter();
195 void WriteWord(uint64_t W) {
202 template <typename T> void write(MCDataFragment &F, T Value) {
203 FWriter.write(F, Value);
206 void WriteHeader(const MCAssembler &Asm,
207 uint64_t SectionDataSize,
208 unsigned NumberOfSections);
210 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
211 const MCAsmLayout &Layout);
213 void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm,
214 const MCAsmLayout &Layout,
215 SectionIndexMapTy &SectionIndexMap);
217 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
218 const MCSymbolRefExpr *RefA,
219 const MCSymbolData *SD, uint64_t C,
220 unsigned Type) const;
222 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
223 const MCFragment *Fragment, const MCFixup &Fixup,
224 MCValue Target, bool &IsPCRel,
225 uint64_t &FixedValue) override;
227 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
230 // Map from a group section to the signature symbol
231 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
232 // Map from a signature symbol to the group section
233 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
234 // Map from a section to the section with the relocations
235 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy;
236 // Map from a section to its offset
237 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy;
239 /// Compute the symbol table data
241 /// \param Asm - The assembler.
242 /// \param SectionIndexMap - Maps a section to its index.
243 /// \param RevGroupMap - Maps a signature symbol to the group section.
244 /// \param NumRegularSections - Number of non-relocation sections.
245 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
246 const SectionIndexMapTy &SectionIndexMap,
247 const RevGroupMapTy &RevGroupMap,
248 unsigned NumRegularSections);
250 void ComputeIndexMap(MCAssembler &Asm,
251 SectionIndexMapTy &SectionIndexMap,
252 const RelMapTy &RelMap);
254 void CreateRelocationSections(MCAssembler &Asm, RelMapTy &RelMap);
256 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
258 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
259 const RelMapTy &RelMap);
261 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
262 SectionIndexMapTy &SectionIndexMap);
264 // Create the sections that show up in the symbol table. Currently
265 // those are the .note.GNU-stack section and the group sections.
266 void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
267 GroupMapTy &GroupMap,
268 RevGroupMapTy &RevGroupMap,
269 SectionIndexMapTy &SectionIndexMap,
270 const RelMapTy &RelMap);
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 MCFragment &FB,
297 bool IsPCRel) const override;
299 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
300 void WriteSection(MCAssembler &Asm,
301 const SectionIndexMapTy &SectionIndexMap,
302 uint32_t GroupSymbolIndex,
303 uint64_t Offset, uint64_t Size, uint64_t Alignment,
304 const MCSectionELF &Section);
308 FragmentWriter::FragmentWriter(bool IsLittleEndian)
309 : IsLittleEndian(IsLittleEndian) {}
311 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
313 Val = support::endian::byte_swap<T, support::little>(Val);
315 Val = support::endian::byte_swap<T, support::big>(Val);
316 const char *Start = (const char *)&Val;
317 F.getContents().append(Start, Start + sizeof(T));
320 void SymbolTableWriter::createSymtabShndx() {
324 MCContext &Ctx = Asm.getContext();
325 const MCSectionELF *SymtabShndxSection =
326 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
327 MCSectionData *SymtabShndxSD =
328 &Asm.getOrCreateSectionData(*SymtabShndxSection);
329 SymtabShndxSD->setAlignment(4);
330 ShndxF = new MCDataFragment(SymtabShndxSD);
331 unsigned Index = SectionIndexMap.size() + 1;
332 SectionIndexMap[SymtabShndxSection] = Index;
334 for (unsigned I = 0; I < NumWritten; ++I)
335 write(*ShndxF, uint32_t(0));
338 template <typename T>
339 void SymbolTableWriter::write(MCDataFragment &F, T Value) {
340 FWriter.write(F, Value);
343 SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter,
345 SectionIndexMapTy &SectionIndexMap,
346 MCDataFragment *SymtabF)
347 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit),
348 SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr),
351 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
352 uint64_t size, uint8_t other,
353 uint32_t shndx, bool Reserved) {
354 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
361 write(*ShndxF, shndx);
363 write(*ShndxF, uint32_t(0));
366 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
368 raw_svector_ostream OS(SymtabF->getContents());
371 write(*SymtabF, name); // st_name
372 write(*SymtabF, info); // st_info
373 write(*SymtabF, other); // st_other
374 write(*SymtabF, Index); // st_shndx
375 write(*SymtabF, value); // st_value
376 write(*SymtabF, size); // st_size
378 write(*SymtabF, name); // st_name
379 write(*SymtabF, uint32_t(value)); // st_value
380 write(*SymtabF, uint32_t(size)); // st_size
381 write(*SymtabF, info); // st_info
382 write(*SymtabF, other); // st_other
383 write(*SymtabF, Index); // st_shndx
389 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
390 const MCFixupKindInfo &FKI =
391 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
393 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
396 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
400 case MCSymbolRefExpr::VK_GOT:
401 case MCSymbolRefExpr::VK_PLT:
402 case MCSymbolRefExpr::VK_GOTPCREL:
403 case MCSymbolRefExpr::VK_GOTOFF:
404 case MCSymbolRefExpr::VK_TPOFF:
405 case MCSymbolRefExpr::VK_TLSGD:
406 case MCSymbolRefExpr::VK_GOTTPOFF:
407 case MCSymbolRefExpr::VK_INDNTPOFF:
408 case MCSymbolRefExpr::VK_NTPOFF:
409 case MCSymbolRefExpr::VK_GOTNTPOFF:
410 case MCSymbolRefExpr::VK_TLSLDM:
411 case MCSymbolRefExpr::VK_DTPOFF:
412 case MCSymbolRefExpr::VK_TLSLD:
417 ELFObjectWriter::~ELFObjectWriter()
420 // Emit the ELF header.
421 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
422 uint64_t SectionDataSize,
423 unsigned NumberOfSections) {
429 // emitWord method behaves differently for ELF32 and ELF64, writing
430 // 4 bytes in the former and 8 in the latter.
432 Write8(0x7f); // e_ident[EI_MAG0]
433 Write8('E'); // e_ident[EI_MAG1]
434 Write8('L'); // e_ident[EI_MAG2]
435 Write8('F'); // e_ident[EI_MAG3]
437 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
440 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
442 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
444 Write8(TargetObjectWriter->getOSABI());
445 Write8(0); // e_ident[EI_ABIVERSION]
447 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
449 Write16(ELF::ET_REL); // e_type
451 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
453 Write32(ELF::EV_CURRENT); // e_version
454 WriteWord(0); // e_entry, no entry point in .o file
455 WriteWord(0); // e_phoff, no program header for .o
456 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
457 sizeof(ELF::Elf32_Ehdr))); // 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->EvaluateAsAbsolute(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 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
790 const MCAsmLayout &Layout,
791 const MCFragment *Fragment,
792 const MCFixup &Fixup, MCValue Target,
793 bool &IsPCRel, uint64_t &FixedValue) {
794 const MCSectionData *FixupSection = Fragment->getParent();
795 uint64_t C = Target.getConstant();
796 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
798 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
799 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
800 "Should not have constructed this");
802 // Let A, B and C being the components of Target and R be the location of
803 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
804 // If it is pcrel, we want to compute (A - B + C - R).
806 // In general, ELF has no relocations for -B. It can only represent (A + C)
807 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
808 // replace B to implement it: (A - R - K + C)
810 Asm.getContext().FatalError(
812 "No relocation available to represent this relative expression");
814 const MCSymbol &SymB = RefB->getSymbol();
816 if (SymB.isUndefined())
817 Asm.getContext().FatalError(
819 Twine("symbol '") + SymB.getName() +
820 "' can not be undefined in a subtraction expression");
822 assert(!SymB.isAbsolute() && "Should have been folded");
823 const MCSection &SecB = SymB.getSection();
824 if (&SecB != &FixupSection->getSection())
825 Asm.getContext().FatalError(
826 Fixup.getLoc(), "Cannot represent a difference across sections");
828 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
829 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
830 uint64_t K = SymBOffset - FixupOffset;
835 // We either rejected the fixup or folded B into C at this point.
836 const MCSymbolRefExpr *RefA = Target.getSymA();
837 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
838 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
840 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
841 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
842 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
843 C += Layout.getSymbolOffset(SymAD);
846 if (hasRelocationAddend()) {
853 // FIXME: What is this!?!?
854 MCSymbolRefExpr::VariantKind Modifier =
855 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
856 if (RelocNeedsGOT(Modifier))
859 if (!RelocateWithSymbol) {
860 const MCSection *SecA =
861 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
862 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
863 MCSymbol *SectionSymbol =
864 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
866 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
867 Relocations[FixupSection].push_back(Rec);
872 if (const MCSymbol *R = Renames.lookup(SymA))
875 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
876 WeakrefUsedInReloc.insert(WeakRef);
878 UsedInReloc.insert(SymA);
880 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
881 Relocations[FixupSection].push_back(Rec);
887 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
889 const MCSymbolData &SD = Asm.getSymbolData(*S);
890 return SD.getIndex();
893 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
894 const MCSymbolData &Data, bool Used,
896 const MCSymbol &Symbol = Data.getSymbol();
897 if (Symbol.isVariable()) {
898 const MCExpr *Expr = Symbol.getVariableValue();
899 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
900 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
911 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
914 if (Symbol.isVariable()) {
915 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
916 if (Base && Base->isUndefined())
920 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
921 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
924 if (Symbol.isTemporary())
930 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
931 if (Data.isExternal())
934 const MCSymbol &Symbol = Data.getSymbol();
935 if (Symbol.isDefined())
944 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
945 SectionIndexMapTy &SectionIndexMap,
946 const RelMapTy &RelMap) {
948 for (MCAssembler::iterator it = Asm.begin(),
949 ie = Asm.end(); it != ie; ++it) {
950 const MCSectionELF &Section =
951 static_cast<const MCSectionELF &>(it->getSection());
952 if (Section.getType() != ELF::SHT_GROUP)
954 SectionIndexMap[&Section] = Index++;
957 for (MCAssembler::iterator it = Asm.begin(),
958 ie = Asm.end(); it != ie; ++it) {
959 const MCSectionELF &Section =
960 static_cast<const MCSectionELF &>(it->getSection());
961 if (Section.getType() == ELF::SHT_GROUP ||
962 Section.getType() == ELF::SHT_REL ||
963 Section.getType() == ELF::SHT_RELA)
965 SectionIndexMap[&Section] = Index++;
966 const MCSectionELF *RelSection = RelMap.lookup(&Section);
968 SectionIndexMap[RelSection] = Index++;
973 ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
974 const SectionIndexMapTy &SectionIndexMap,
975 const RevGroupMapTy &RevGroupMap,
976 unsigned NumRegularSections) {
977 // FIXME: Is this the correct place to do this?
978 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
980 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
981 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
982 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
983 Data.setExternal(true);
984 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
987 // Add the data for the symbols.
988 for (MCSymbolData &SD : Asm.symbols()) {
989 const MCSymbol &Symbol = SD.getSymbol();
991 bool Used = UsedInReloc.count(&Symbol);
992 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
993 bool isSignature = RevGroupMap.count(&Symbol);
995 if (!isInSymtab(Layout, SD,
996 Used || WeakrefUsed || isSignature,
997 Renames.count(&Symbol)))
1001 MSD.SymbolData = &SD;
1002 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
1004 // Undefined symbols are global, but this is the first place we
1005 // are able to set it.
1006 bool Local = isLocal(SD, Used);
1007 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1009 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1010 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1011 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1015 MSD.SectionIndex = ELF::SHN_ABS;
1016 } else if (SD.isCommon()) {
1018 MSD.SectionIndex = ELF::SHN_COMMON;
1019 } else if (BaseSymbol->isUndefined()) {
1020 if (isSignature && !Used)
1021 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap.lookup(&Symbol));
1023 MSD.SectionIndex = ELF::SHN_UNDEF;
1024 if (!Used && WeakrefUsed)
1025 MCELF::SetBinding(SD, ELF::STB_WEAK);
1027 const MCSectionELF &Section =
1028 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1029 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1030 assert(MSD.SectionIndex && "Invalid section index!");
1033 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
1036 // FIXME: All name handling should be done before we get to the writer,
1037 // including dealing with GNU-style version suffixes. Fixing this isn’t
1040 // We thus have to be careful to not perform the symbol version replacement
1043 // The ELF format is used on Windows by the MCJIT engine. Thus, on
1044 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
1045 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
1046 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
1047 // the EFLObjectWriter should not interpret the "@@@" sub-string as
1048 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1049 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1050 // "__imp_?" or "__imp_@?".
1052 // It would have been interesting to perform the MS mangling prefix check
1053 // only when the target triple is of the form *-pc-windows-elf. But, it
1054 // seems that this information is not easily accessible from the
1056 StringRef Name = Symbol.getName();
1057 if (!Name.startswith("?") && !Name.startswith("@?") &&
1058 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1059 // This symbol isn't following the MSVC C++ name mangling convention. We
1060 // can thus safely interpret the @@@ in symbol names as specifying symbol
1062 SmallString<32> Buf;
1063 size_t Pos = Name.find("@@@");
1064 if (Pos != StringRef::npos) {
1065 Buf += Name.substr(0, Pos);
1066 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1067 Buf += Name.substr(Pos + Skip);
1072 // Sections have their own string table
1073 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1074 MSD.Name = StrTabBuilder.add(Name);
1076 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1077 UndefinedSymbolData.push_back(MSD);
1079 LocalSymbolData.push_back(MSD);
1081 ExternalSymbolData.push_back(MSD);
1084 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1085 StrTabBuilder.add(*i);
1087 StrTabBuilder.finalize(StringTableBuilder::ELF);
1089 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1090 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1092 for (ELFSymbolData &MSD : LocalSymbolData)
1093 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1095 : StrTabBuilder.getOffset(MSD.Name);
1096 for (ELFSymbolData &MSD : ExternalSymbolData)
1097 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1098 for (ELFSymbolData& MSD : UndefinedSymbolData)
1099 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1101 // Symbols are required to be in lexicographic order.
1102 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1103 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1104 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1106 // Set the symbol indices. Local symbols must come before all other
1107 // symbols with non-local bindings.
1108 unsigned Index = FileSymbolData.size() + 1;
1109 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1110 LocalSymbolData[i].SymbolData->setIndex(Index++);
1112 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1113 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1114 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1115 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1118 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm,
1120 for (MCAssembler::const_iterator it = Asm.begin(),
1121 ie = Asm.end(); it != ie; ++it) {
1122 const MCSectionData &SD = *it;
1123 if (Relocations[&SD].empty())
1126 MCContext &Ctx = Asm.getContext();
1127 const MCSectionELF &Section =
1128 static_cast<const MCSectionELF&>(SD.getSection());
1130 const StringRef SectionName = Section.getSectionName();
1131 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1132 RelaSectionName += SectionName;
1135 if (hasRelocationAddend())
1136 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1138 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1141 StringRef Group = "";
1142 if (Section.getFlags() & ELF::SHF_GROUP) {
1143 Flags = ELF::SHF_GROUP;
1144 Group = Section.getGroup()->getName();
1147 const MCSectionELF *RelaSection =
1148 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ?
1149 ELF::SHT_RELA : ELF::SHT_REL, Flags,
1151 RelMap[&Section] = RelaSection;
1152 Asm.getOrCreateSectionData(*RelaSection);
1156 static SmallVector<char, 128>
1157 getUncompressedData(MCAsmLayout &Layout,
1158 MCSectionData::FragmentListType &Fragments) {
1159 SmallVector<char, 128> UncompressedData;
1160 for (const MCFragment &F : Fragments) {
1161 const SmallVectorImpl<char> *Contents;
1162 switch (F.getKind()) {
1163 case MCFragment::FT_Data:
1164 Contents = &cast<MCDataFragment>(F).getContents();
1166 case MCFragment::FT_Dwarf:
1167 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1169 case MCFragment::FT_DwarfFrame:
1170 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1174 "Not expecting any other fragment types in a debug_* section");
1176 UncompressedData.append(Contents->begin(), Contents->end());
1178 return UncompressedData;
1181 // Include the debug info compression header:
1182 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1183 // useful for consumers to preallocate a buffer to decompress into.
1185 prependCompressionHeader(uint64_t Size,
1186 SmallVectorImpl<char> &CompressedContents) {
1187 static const StringRef Magic = "ZLIB";
1188 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1190 if (sys::IsLittleEndianHost)
1191 sys::swapByteOrder(Size);
1192 CompressedContents.insert(CompressedContents.begin(),
1193 Magic.size() + sizeof(Size), 0);
1194 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1195 std::copy(reinterpret_cast<char *>(&Size),
1196 reinterpret_cast<char *>(&Size + 1),
1197 CompressedContents.begin() + Magic.size());
1201 // Return a single fragment containing the compressed contents of the whole
1202 // section. Null if the section was not compressed for any reason.
1203 static std::unique_ptr<MCDataFragment>
1204 getCompressedFragment(MCAsmLayout &Layout,
1205 MCSectionData::FragmentListType &Fragments) {
1206 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1208 // Gather the uncompressed data from all the fragments, recording the
1209 // alignment fragment, if seen, and any fixups.
1210 SmallVector<char, 128> UncompressedData =
1211 getUncompressedData(Layout, Fragments);
1213 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1215 zlib::Status Success = zlib::compress(
1216 StringRef(UncompressedData.data(), UncompressedData.size()),
1217 CompressedContents);
1218 if (Success != zlib::StatusOK)
1221 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1224 return CompressedFragment;
1227 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1230 static void UpdateSymbols(const MCAsmLayout &Layout,
1231 const std::vector<MCSymbolData *> &Symbols,
1232 MCFragment &NewFragment) {
1233 for (MCSymbolData *Sym : Symbols) {
1234 Sym->setOffset(Sym->getOffset() +
1235 Layout.getFragmentOffset(Sym->getFragment()));
1236 Sym->setFragment(&NewFragment);
1240 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1241 const DefiningSymbolMap &DefiningSymbols,
1242 const MCSectionELF &Section,
1243 MCSectionData &SD) {
1244 StringRef SectionName = Section.getSectionName();
1245 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1247 std::unique_ptr<MCDataFragment> CompressedFragment =
1248 getCompressedFragment(Layout, Fragments);
1250 // Leave the section as-is if the fragments could not be compressed.
1251 if (!CompressedFragment)
1254 // Update the fragment+offsets of any symbols referring to fragments in this
1255 // section to refer to the new fragment.
1256 auto I = DefiningSymbols.find(&SD);
1257 if (I != DefiningSymbols.end())
1258 UpdateSymbols(Layout, I->second, *CompressedFragment);
1260 // Invalidate the layout for the whole section since it will have new and
1261 // different fragments now.
1262 Layout.invalidateFragmentsFrom(&Fragments.front());
1265 // Complete the initialization of the new fragment
1266 CompressedFragment->setParent(&SD);
1267 CompressedFragment->setLayoutOrder(0);
1268 Fragments.push_back(CompressedFragment.release());
1270 // Rename from .debug_* to .zdebug_*
1271 Asm.getContext().renameELFSection(&Section,
1272 (".z" + SectionName.drop_front(1)).str());
1275 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1276 MCAsmLayout &Layout) {
1277 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1280 DefiningSymbolMap DefiningSymbols;
1282 for (MCSymbolData &SD : Asm.symbols())
1283 if (MCFragment *F = SD.getFragment())
1284 DefiningSymbols[F->getParent()].push_back(&SD);
1286 for (MCSectionData &SD : Asm) {
1287 const MCSectionELF &Section =
1288 static_cast<const MCSectionELF &>(SD.getSection());
1289 StringRef SectionName = Section.getSectionName();
1291 // Compressing debug_frame requires handling alignment fragments which is
1292 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1293 // for writing to arbitrary buffers) for little benefit.
1294 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1297 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1301 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
1302 const RelMapTy &RelMap) {
1303 for (MCAssembler::const_iterator it = Asm.begin(),
1304 ie = Asm.end(); it != ie; ++it) {
1305 const MCSectionData &SD = *it;
1306 const MCSectionELF &Section =
1307 static_cast<const MCSectionELF&>(SD.getSection());
1309 const MCSectionELF *RelaSection = RelMap.lookup(&Section);
1312 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
1313 RelaSD.setAlignment(is64Bit() ? 8 : 4);
1315 MCDataFragment *F = new MCDataFragment(&RelaSD);
1316 WriteRelocationsFragment(Asm, F, &*it);
1320 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1321 uint64_t Flags, uint64_t Address,
1322 uint64_t Offset, uint64_t Size,
1323 uint32_t Link, uint32_t Info,
1325 uint64_t EntrySize) {
1326 Write32(Name); // sh_name: index into string table
1327 Write32(Type); // sh_type
1328 WriteWord(Flags); // sh_flags
1329 WriteWord(Address); // sh_addr
1330 WriteWord(Offset); // sh_offset
1331 WriteWord(Size); // sh_size
1332 Write32(Link); // sh_link
1333 Write32(Info); // sh_info
1334 WriteWord(Alignment); // sh_addralign
1335 WriteWord(EntrySize); // sh_entsize
1338 // ELF doesn't require relocations to be in any order. We sort by the r_offset,
1339 // just to match gnu as for easier comparison. The use type is an arbitrary way
1340 // of making the sort deterministic.
1341 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
1342 const ELFRelocationEntry &A = *AP;
1343 const ELFRelocationEntry &B = *BP;
1344 if (A.Offset != B.Offset)
1345 return B.Offset - A.Offset;
1346 if (B.Type != A.Type)
1347 return A.Type - B.Type;
1348 llvm_unreachable("ELFRelocs might be unstable!");
1351 static void sortRelocs(const MCAssembler &Asm,
1352 std::vector<ELFRelocationEntry> &Relocs) {
1353 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
1356 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1358 const MCSectionData *SD) {
1359 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1361 sortRelocs(Asm, Relocs);
1363 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1364 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1366 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1369 write(*F, Entry.Offset);
1370 if (TargetObjectWriter->isN64()) {
1371 write(*F, uint32_t(Index));
1373 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1374 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1375 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1376 write(*F, TargetObjectWriter->getRType(Entry.Type));
1378 struct ELF::Elf64_Rela ERE64;
1379 ERE64.setSymbolAndType(Index, Entry.Type);
1380 write(*F, ERE64.r_info);
1382 if (hasRelocationAddend())
1383 write(*F, Entry.Addend);
1385 write(*F, uint32_t(Entry.Offset));
1387 struct ELF::Elf32_Rela ERE32;
1388 ERE32.setSymbolAndType(Index, Entry.Type);
1389 write(*F, ERE32.r_info);
1391 if (hasRelocationAddend())
1392 write(*F, uint32_t(Entry.Addend));
1397 void ELFObjectWriter::CreateMetadataSections(
1398 MCAssembler &Asm, MCAsmLayout &Layout, SectionIndexMapTy &SectionIndexMap) {
1399 MCContext &Ctx = Asm.getContext();
1402 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1404 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1405 const MCSectionELF *ShstrtabSection =
1406 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1407 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1408 ShstrtabSD.setAlignment(1);
1409 ShstrtabIndex = SectionIndexMap.size() + 1;
1410 SectionIndexMap[ShstrtabSection] = ShstrtabIndex;
1412 const MCSectionELF *SymtabSection =
1413 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1415 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1416 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1417 SymbolTableIndex = SectionIndexMap.size() + 1;
1418 SectionIndexMap[SymtabSection] = SymbolTableIndex;
1420 const MCSectionELF *StrtabSection;
1421 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1422 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1423 StrtabSD.setAlignment(1);
1424 StringTableIndex = SectionIndexMap.size() + 1;
1425 SectionIndexMap[StrtabSection] = StringTableIndex;
1428 F = new MCDataFragment(&SymtabSD);
1429 WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
1431 F = new MCDataFragment(&StrtabSD);
1432 F->getContents().append(StrTabBuilder.data().begin(),
1433 StrTabBuilder.data().end());
1435 F = new MCDataFragment(&ShstrtabSD);
1437 // Section header string table.
1438 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1439 const MCSectionELF &Section =
1440 static_cast<const MCSectionELF&>(it->getSection());
1441 ShStrTabBuilder.add(Section.getSectionName());
1443 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1444 F->getContents().append(ShStrTabBuilder.data().begin(),
1445 ShStrTabBuilder.data().end());
1448 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
1449 MCAsmLayout &Layout,
1450 GroupMapTy &GroupMap,
1451 RevGroupMapTy &RevGroupMap,
1452 SectionIndexMapTy &SectionIndexMap,
1453 const RelMapTy &RelMap) {
1454 MCContext &Ctx = Asm.getContext();
1457 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1459 const MCSectionELF &Section =
1460 static_cast<const MCSectionELF&>(it->getSection());
1461 if (!(Section.getFlags() & ELF::SHF_GROUP))
1464 const MCSymbol *SignatureSymbol = Section.getGroup();
1465 Asm.getOrCreateSymbolData(*SignatureSymbol);
1466 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1468 Group = Ctx.CreateELFGroupSection();
1469 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1470 Data.setAlignment(4);
1471 MCDataFragment *F = new MCDataFragment(&Data);
1472 write(*F, uint32_t(ELF::GRP_COMDAT));
1474 GroupMap[Group] = SignatureSymbol;
1477 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1479 // Add sections to the groups
1480 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1482 const MCSectionELF &Section =
1483 static_cast<const MCSectionELF&>(it->getSection());
1484 if (!(Section.getFlags() & ELF::SHF_GROUP))
1486 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1487 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1488 // FIXME: we could use the previous fragment
1489 MCDataFragment *F = new MCDataFragment(&Data);
1490 uint32_t Index = SectionIndexMap.lookup(&Section);
1495 void ELFObjectWriter::WriteSection(MCAssembler &Asm,
1496 const SectionIndexMapTy &SectionIndexMap,
1497 uint32_t GroupSymbolIndex,
1498 uint64_t Offset, uint64_t Size,
1500 const MCSectionELF &Section) {
1501 uint64_t sh_link = 0;
1502 uint64_t sh_info = 0;
1504 switch(Section.getType()) {
1505 case ELF::SHT_DYNAMIC:
1506 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1511 case ELF::SHT_RELA: {
1512 const MCSectionELF *SymtabSection;
1513 const MCSectionELF *InfoSection;
1515 Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 0);
1516 sh_link = SectionIndexMap.lookup(SymtabSection);
1517 assert(sh_link && ".symtab not found");
1519 // Remove ".rel" and ".rela" prefixes.
1520 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1521 StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1522 StringRef GroupName =
1523 Section.getGroup() ? Section.getGroup()->getName() : "";
1525 InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS,
1527 sh_info = SectionIndexMap.lookup(InfoSection);
1531 case ELF::SHT_SYMTAB:
1532 case ELF::SHT_DYNSYM:
1533 sh_link = StringTableIndex;
1534 sh_info = LastLocalSymbolIndex;
1537 case ELF::SHT_SYMTAB_SHNDX:
1538 sh_link = SymbolTableIndex;
1541 case ELF::SHT_PROGBITS:
1542 case ELF::SHT_STRTAB:
1543 case ELF::SHT_NOBITS:
1546 case ELF::SHT_ARM_ATTRIBUTES:
1547 case ELF::SHT_INIT_ARRAY:
1548 case ELF::SHT_FINI_ARRAY:
1549 case ELF::SHT_PREINIT_ARRAY:
1550 case ELF::SHT_X86_64_UNWIND:
1551 case ELF::SHT_MIPS_REGINFO:
1552 case ELF::SHT_MIPS_OPTIONS:
1553 case ELF::SHT_MIPS_ABIFLAGS:
1557 case ELF::SHT_GROUP:
1558 sh_link = SymbolTableIndex;
1559 sh_info = GroupSymbolIndex;
1563 llvm_unreachable("FIXME: sh_type value not supported!");
1566 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1567 Section.getType() == ELF::SHT_ARM_EXIDX) {
1568 StringRef SecName(Section.getSectionName());
1569 if (SecName == ".ARM.exidx") {
1570 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
1571 ".text", ELF::SHT_PROGBITS, ELF::SHF_EXECINSTR | ELF::SHF_ALLOC));
1572 } else if (SecName.startswith(".ARM.exidx")) {
1573 StringRef GroupName =
1574 Section.getGroup() ? Section.getGroup()->getName() : "";
1575 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
1576 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS,
1577 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, 0, GroupName));
1581 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1583 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1584 Alignment, Section.getEntrySize());
1587 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1588 return SD.getOrdinal() == ~UINT32_C(0) &&
1589 !SD.getSection().isVirtualSection();
1592 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1594 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1596 const MCFragment &F = *i;
1597 assert(F.getKind() == MCFragment::FT_Data);
1598 Ret += cast<MCDataFragment>(F).getContents().size();
1603 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
1604 const MCSectionData &SD) {
1605 if (IsELFMetaDataSection(SD))
1606 return DataSectionSize(SD);
1607 return Layout.getSectionFileSize(&SD);
1610 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1611 const MCSectionData &SD) {
1612 if (IsELFMetaDataSection(SD))
1613 return DataSectionSize(SD);
1614 return Layout.getSectionAddressSize(&SD);
1617 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
1618 const MCAsmLayout &Layout,
1619 const MCSectionELF &Section) {
1620 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1622 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1623 WriteZeros(Padding);
1625 if (IsELFMetaDataSection(SD)) {
1626 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1628 const MCFragment &F = *i;
1629 assert(F.getKind() == MCFragment::FT_Data);
1630 WriteBytes(cast<MCDataFragment>(F).getContents());
1633 Asm.writeSectionData(&SD, Layout);
1637 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm,
1638 const GroupMapTy &GroupMap,
1639 const MCAsmLayout &Layout,
1640 const SectionIndexMapTy &SectionIndexMap,
1641 const SectionOffsetMapTy &SectionOffsetMap) {
1642 const unsigned NumSections = Asm.size() + 1;
1644 std::vector<const MCSectionELF*> Sections;
1645 Sections.resize(NumSections - 1);
1647 for (SectionIndexMapTy::const_iterator i=
1648 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
1649 const std::pair<const MCSectionELF*, uint32_t> &p = *i;
1650 Sections[p.second - 1] = p.first;
1653 // Null section first.
1654 uint64_t FirstSectionSize =
1655 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1656 uint32_t FirstSectionLink =
1657 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1658 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1660 for (unsigned i = 0; i < NumSections - 1; ++i) {
1661 const MCSectionELF &Section = *Sections[i];
1662 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1663 uint32_t GroupSymbolIndex;
1664 if (Section.getType() != ELF::SHT_GROUP)
1665 GroupSymbolIndex = 0;
1667 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1668 GroupMap.lookup(&Section));
1670 uint64_t Size = GetSectionAddressSize(Layout, SD);
1672 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex,
1673 SectionOffsetMap.lookup(&Section), Size,
1674 SD.getAlignment(), Section);
1678 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
1679 std::vector<const MCSectionELF*> &Sections) {
1680 for (MCAssembler::iterator it = Asm.begin(),
1681 ie = Asm.end(); it != ie; ++it) {
1682 const MCSectionELF &Section =
1683 static_cast<const MCSectionELF &>(it->getSection());
1684 if (Section.getType() == ELF::SHT_GROUP)
1685 Sections.push_back(&Section);
1688 for (MCAssembler::iterator it = Asm.begin(),
1689 ie = Asm.end(); it != ie; ++it) {
1690 const MCSectionELF &Section =
1691 static_cast<const MCSectionELF &>(it->getSection());
1692 if (Section.getType() != ELF::SHT_GROUP &&
1693 Section.getType() != ELF::SHT_REL &&
1694 Section.getType() != ELF::SHT_RELA)
1695 Sections.push_back(&Section);
1698 for (MCAssembler::iterator it = Asm.begin(),
1699 ie = Asm.end(); it != ie; ++it) {
1700 const MCSectionELF &Section =
1701 static_cast<const MCSectionELF &>(it->getSection());
1702 if (Section.getType() == ELF::SHT_REL ||
1703 Section.getType() == ELF::SHT_RELA)
1704 Sections.push_back(&Section);
1708 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1709 const MCAsmLayout &Layout) {
1710 GroupMapTy GroupMap;
1711 RevGroupMapTy RevGroupMap;
1712 SectionIndexMapTy SectionIndexMap;
1714 unsigned NumUserSections = Asm.size();
1716 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1718 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
1719 CreateRelocationSections(Asm, RelMap);
1721 const unsigned NumUserAndRelocSections = Asm.size();
1722 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
1723 RevGroupMap, SectionIndexMap, RelMap);
1724 const unsigned AllSections = Asm.size();
1725 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
1727 unsigned NumRegularSections = NumUserSections + NumIndexedSections;
1729 // Compute symbol table information.
1730 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
1731 NumRegularSections);
1733 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1735 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1736 const_cast<MCAsmLayout&>(Layout),
1739 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1740 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
1741 sizeof(ELF::Elf32_Ehdr);
1742 uint64_t FileOff = HeaderSize;
1744 std::vector<const MCSectionELF*> Sections;
1745 ComputeSectionOrder(Asm, Sections);
1746 unsigned NumSections = Sections.size();
1747 SectionOffsetMapTy SectionOffsetMap;
1748 for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
1749 const MCSectionELF &Section = *Sections[i];
1750 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1752 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1754 // Remember the offset into the file for this section.
1755 SectionOffsetMap[&Section] = FileOff;
1757 // Get the size of the section in the output file (including padding).
1758 FileOff += GetSectionFileSize(Layout, SD);
1761 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1763 const unsigned SectionHeaderOffset = FileOff - HeaderSize;
1765 uint64_t SectionHeaderEntrySize = is64Bit() ?
1766 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
1767 FileOff += (NumSections + 1) * SectionHeaderEntrySize;
1769 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
1770 const MCSectionELF &Section = *Sections[i];
1771 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1773 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1775 // Remember the offset into the file for this section.
1776 SectionOffsetMap[&Section] = FileOff;
1778 // Get the size of the section in the output file (including padding).
1779 FileOff += GetSectionFileSize(Layout, SD);
1782 // Write out the ELF header ...
1783 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
1785 // ... then the regular sections ...
1786 // + because of .shstrtab
1787 for (unsigned i = 0; i < NumRegularSections + 1; ++i)
1788 WriteDataSectionData(Asm, Layout, *Sections[i]);
1790 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1791 WriteZeros(Padding);
1793 // ... then the section header table ...
1794 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap,
1797 // ... and then the remaining sections ...
1798 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
1799 WriteDataSectionData(Asm, Layout, *Sections[i]);
1803 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
1804 const MCSymbolData &DataA,
1805 const MCFragment &FB,
1807 bool IsPCRel) const {
1808 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC)
1810 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1811 Asm, DataA, FB,InSet, IsPCRel);
1814 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1816 bool IsLittleEndian) {
1817 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);