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,
254 MCSectionData *createRelocationSection(MCAssembler &Asm,
255 const MCSectionData &SD);
257 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
259 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
260 const RelMapTy &RelMap);
262 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
263 SectionIndexMapTy &SectionIndexMap);
265 // Create the sections that show up in the symbol table. Currently
266 // those are the .note.GNU-stack section and the group sections.
267 void createIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
268 GroupMapTy &GroupMap,
269 RevGroupMapTy &RevGroupMap,
270 SectionIndexMapTy &SectionIndexMap,
273 void ExecutePostLayoutBinding(MCAssembler &Asm,
274 const MCAsmLayout &Layout) override;
276 void writeSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap,
277 const MCAsmLayout &Layout,
278 const SectionIndexMapTy &SectionIndexMap,
279 const RelMapTy &RelMap,
280 const SectionOffsetMapTy &SectionOffsetMap);
282 void ComputeSectionOrder(MCAssembler &Asm,
283 std::vector<const MCSectionELF*> &Sections);
285 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
286 uint64_t Address, uint64_t Offset,
287 uint64_t Size, uint32_t Link, uint32_t Info,
288 uint64_t Alignment, uint64_t EntrySize);
290 void WriteRelocationsFragment(const MCAssembler &Asm,
292 const MCSectionData *SD);
295 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
296 const MCSymbolData &DataA,
297 const MCFragment &FB,
299 bool IsPCRel) const override;
301 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
302 void writeSection(MCAssembler &Asm,
303 const SectionIndexMapTy &SectionIndexMap,
304 const RelMapTy &RelMap,
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;
371 raw_svector_ostream OS(SymtabF->getContents());
374 write(*SymtabF, name); // st_name
375 write(*SymtabF, info); // st_info
376 write(*SymtabF, other); // st_other
377 write(*SymtabF, Index); // st_shndx
378 write(*SymtabF, value); // st_value
379 write(*SymtabF, size); // st_size
381 write(*SymtabF, name); // st_name
382 write(*SymtabF, uint32_t(value)); // st_value
383 write(*SymtabF, uint32_t(size)); // st_size
384 write(*SymtabF, info); // st_info
385 write(*SymtabF, other); // st_other
386 write(*SymtabF, Index); // st_shndx
392 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
393 const MCFixupKindInfo &FKI =
394 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
396 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
399 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
403 case MCSymbolRefExpr::VK_GOT:
404 case MCSymbolRefExpr::VK_PLT:
405 case MCSymbolRefExpr::VK_GOTPCREL:
406 case MCSymbolRefExpr::VK_GOTOFF:
407 case MCSymbolRefExpr::VK_TPOFF:
408 case MCSymbolRefExpr::VK_TLSGD:
409 case MCSymbolRefExpr::VK_GOTTPOFF:
410 case MCSymbolRefExpr::VK_INDNTPOFF:
411 case MCSymbolRefExpr::VK_NTPOFF:
412 case MCSymbolRefExpr::VK_GOTNTPOFF:
413 case MCSymbolRefExpr::VK_TLSLDM:
414 case MCSymbolRefExpr::VK_DTPOFF:
415 case MCSymbolRefExpr::VK_TLSLD:
420 ELFObjectWriter::~ELFObjectWriter()
423 // Emit the ELF header.
424 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
425 uint64_t SectionDataSize,
426 unsigned NumberOfSections) {
432 // emitWord method behaves differently for ELF32 and ELF64, writing
433 // 4 bytes in the former and 8 in the latter.
435 Write8(0x7f); // e_ident[EI_MAG0]
436 Write8('E'); // e_ident[EI_MAG1]
437 Write8('L'); // e_ident[EI_MAG2]
438 Write8('F'); // e_ident[EI_MAG3]
440 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
443 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
445 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
447 Write8(TargetObjectWriter->getOSABI());
448 Write8(0); // e_ident[EI_ABIVERSION]
450 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
452 Write16(ELF::ET_REL); // e_type
454 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
456 Write32(ELF::EV_CURRENT); // e_version
457 WriteWord(0); // e_entry, no entry point in .o file
458 WriteWord(0); // e_phoff, no program header for .o
459 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
460 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes
462 // e_flags = whatever the target wants
463 Write32(Asm.getELFHeaderEFlags());
465 // e_ehsize = ELF header size
466 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
468 Write16(0); // e_phentsize = prog header entry size
469 Write16(0); // e_phnum = # prog header entries = 0
471 // e_shentsize = Section header entry size
472 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
474 // e_shnum = # of section header ents
475 if (NumberOfSections >= ELF::SHN_LORESERVE)
476 Write16(ELF::SHN_UNDEF);
478 Write16(NumberOfSections);
480 // e_shstrndx = Section # of '.shstrtab'
481 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
482 Write16(ELF::SHN_XINDEX);
484 Write16(ShstrtabIndex);
487 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
488 const MCAsmLayout &Layout) {
489 if (Data.isCommon() && Data.isExternal())
490 return Data.getCommonAlignment();
493 if (!Layout.getSymbolOffset(&Data, Res))
496 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
502 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
503 const MCAsmLayout &Layout) {
504 // The presence of symbol versions causes undefined symbols and
505 // versions declared with @@@ to be renamed.
507 for (MCSymbolData &OriginalData : Asm.symbols()) {
508 const MCSymbol &Alias = OriginalData.getSymbol();
511 if (!Alias.isVariable())
513 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
516 const MCSymbol &Symbol = Ref->getSymbol();
517 MCSymbolData &SD = Asm.getSymbolData(Symbol);
519 StringRef AliasName = Alias.getName();
520 size_t Pos = AliasName.find('@');
521 if (Pos == StringRef::npos)
524 // Aliases defined with .symvar copy the binding from the symbol they alias.
525 // This is the first place we are able to copy this information.
526 OriginalData.setExternal(SD.isExternal());
527 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
529 StringRef Rest = AliasName.substr(Pos);
530 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
533 // FIXME: produce a better error message.
534 if (Symbol.isUndefined() && Rest.startswith("@@") &&
535 !Rest.startswith("@@@"))
536 report_fatal_error("A @@ version cannot be undefined");
538 Renames.insert(std::make_pair(&Symbol, &Alias));
542 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
543 uint8_t Type = newType;
545 // Propagation rules:
546 // IFUNC > FUNC > OBJECT > NOTYPE
547 // TLS_OBJECT > OBJECT > NOTYPE
549 // dont let the new type degrade the old type
553 case ELF::STT_GNU_IFUNC:
554 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
555 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
556 Type = ELF::STT_GNU_IFUNC;
559 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
560 Type == ELF::STT_TLS)
561 Type = ELF::STT_FUNC;
563 case ELF::STT_OBJECT:
564 if (Type == ELF::STT_NOTYPE)
565 Type = ELF::STT_OBJECT;
568 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
569 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
577 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
578 const MCAsmLayout &Layout) {
579 MCSymbolData &OrigData = *MSD.SymbolData;
580 assert((!OrigData.getFragment() ||
581 (&OrigData.getFragment()->getParent()->getSection() ==
582 &OrigData.getSymbol().getSection())) &&
583 "The symbol's section doesn't match the fragment's symbol");
584 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
586 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
588 bool IsReserved = !Base || OrigData.isCommon();
590 // Binding and Type share the same byte as upper and lower nibbles
591 uint8_t Binding = MCELF::GetBinding(OrigData);
592 uint8_t Type = MCELF::GetType(OrigData);
593 MCSymbolData *BaseSD = nullptr;
595 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
596 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
598 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
600 // Other and Visibility share the same byte with Visibility using the lower
602 uint8_t Visibility = MCELF::GetVisibility(OrigData);
603 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
606 uint64_t Value = SymbolValue(OrigData, Layout);
609 const MCExpr *ESize = OrigData.getSize();
611 ESize = BaseSD->getSize();
615 if (!ESize->EvaluateAsAbsolute(Res, Layout))
616 report_fatal_error("Size expression must be absolute.");
620 // Write out the symbol table entry
621 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
622 MSD.SectionIndex, IsReserved);
625 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
627 const MCAsmLayout &Layout,
628 SectionIndexMapTy &SectionIndexMap) {
629 // The string table must be emitted first because we need the index
630 // into the string table for all the symbol names.
632 // FIXME: Make sure the start of the symbol table is aligned.
634 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF);
636 // The first entry is the undefined symbol entry.
637 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
639 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
640 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
641 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
644 // Write the symbol table entries.
645 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
647 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
648 ELFSymbolData &MSD = LocalSymbolData[i];
649 WriteSymbol(Writer, MSD, Layout);
652 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
653 ELFSymbolData &MSD = ExternalSymbolData[i];
654 MCSymbolData &Data = *MSD.SymbolData;
655 assert(((Data.getFlags() & ELF_STB_Global) ||
656 (Data.getFlags() & ELF_STB_Weak)) &&
657 "External symbol requires STB_GLOBAL or STB_WEAK flag");
658 WriteSymbol(Writer, MSD, Layout);
659 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
660 LastLocalSymbolIndex++;
663 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
664 ELFSymbolData &MSD = UndefinedSymbolData[i];
665 MCSymbolData &Data = *MSD.SymbolData;
666 WriteSymbol(Writer, MSD, Layout);
667 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
668 LastLocalSymbolIndex++;
672 // It is always valid to create a relocation with a symbol. It is preferable
673 // to use a relocation with a section if that is possible. Using the section
674 // allows us to omit some local symbols from the symbol table.
675 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
676 const MCSymbolRefExpr *RefA,
677 const MCSymbolData *SD,
679 unsigned Type) const {
680 // A PCRel relocation to an absolute value has no symbol (or section). We
681 // represent that with a relocation to a null section.
685 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
689 // The .odp creation emits a relocation against the symbol ".TOC." which
690 // create a R_PPC64_TOC relocation. However the relocation symbol name
691 // in final object creation should be NULL, since the symbol does not
692 // really exist, it is just the reference to TOC base for the current
693 // object file. Since the symbol is undefined, returning false results
694 // in a relocation with a null section which is the desired result.
695 case MCSymbolRefExpr::VK_PPC_TOCBASE:
698 // These VariantKind cause the relocation to refer to something other than
699 // the symbol itself, like a linker generated table. Since the address of
700 // symbol is not relevant, we cannot replace the symbol with the
701 // section and patch the difference in the addend.
702 case MCSymbolRefExpr::VK_GOT:
703 case MCSymbolRefExpr::VK_PLT:
704 case MCSymbolRefExpr::VK_GOTPCREL:
705 case MCSymbolRefExpr::VK_Mips_GOT:
706 case MCSymbolRefExpr::VK_PPC_GOT_LO:
707 case MCSymbolRefExpr::VK_PPC_GOT_HI:
708 case MCSymbolRefExpr::VK_PPC_GOT_HA:
712 // An undefined symbol is not in any section, so the relocation has to point
713 // to the symbol itself.
714 const MCSymbol &Sym = SD->getSymbol();
715 if (Sym.isUndefined())
718 unsigned Binding = MCELF::GetBinding(*SD);
721 llvm_unreachable("Invalid Binding");
725 // If the symbol is weak, it might be overridden by a symbol in another
726 // file. The relocation has to point to the symbol so that the linker
729 case ELF::STB_GLOBAL:
730 // Global ELF symbols can be preempted by the dynamic linker. The relocation
731 // has to point to the symbol for a reason analogous to the STB_WEAK case.
735 // If a relocation points to a mergeable section, we have to be careful.
736 // If the offset is zero, a relocation with the section will encode the
737 // same information. With a non-zero offset, the situation is different.
738 // For example, a relocation can point 42 bytes past the end of a string.
739 // If we change such a relocation to use the section, the linker would think
740 // that it pointed to another string and subtracting 42 at runtime will
741 // produce the wrong value.
742 auto &Sec = cast<MCSectionELF>(Sym.getSection());
743 unsigned Flags = Sec.getFlags();
744 if (Flags & ELF::SHF_MERGE) {
748 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
749 // only handle section relocations to mergeable sections if using RELA.
750 if (!hasRelocationAddend())
754 // Most TLS relocations use a got, so they need the symbol. Even those that
755 // are just an offset (@tpoff), require a symbol in gold versions before
756 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
757 // http://sourceware.org/PR16773.
758 if (Flags & ELF::SHF_TLS)
761 // If the symbol is a thumb function the final relocation must set the lowest
762 // bit. With a symbol that is done by just having the symbol have that bit
763 // set, so we would lose the bit if we relocated with the section.
764 // FIXME: We could use the section but add the bit to the relocation value.
765 if (Asm.isThumbFunc(&Sym))
768 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
773 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
774 const MCSymbol &Sym = Ref.getSymbol();
776 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
779 if (!Sym.isVariable())
782 const MCExpr *Expr = Sym.getVariableValue();
783 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
787 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
788 return &Inner->getSymbol();
792 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
793 const MCAsmLayout &Layout,
794 const MCFragment *Fragment,
795 const MCFixup &Fixup, MCValue Target,
796 bool &IsPCRel, uint64_t &FixedValue) {
797 const MCSectionData *FixupSection = Fragment->getParent();
798 uint64_t C = Target.getConstant();
799 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
801 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
802 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
803 "Should not have constructed this");
805 // Let A, B and C being the components of Target and R be the location of
806 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
807 // If it is pcrel, we want to compute (A - B + C - R).
809 // In general, ELF has no relocations for -B. It can only represent (A + C)
810 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
811 // replace B to implement it: (A - R - K + C)
813 Asm.getContext().FatalError(
815 "No relocation available to represent this relative expression");
817 const MCSymbol &SymB = RefB->getSymbol();
819 if (SymB.isUndefined())
820 Asm.getContext().FatalError(
822 Twine("symbol '") + SymB.getName() +
823 "' can not be undefined in a subtraction expression");
825 assert(!SymB.isAbsolute() && "Should have been folded");
826 const MCSection &SecB = SymB.getSection();
827 if (&SecB != &FixupSection->getSection())
828 Asm.getContext().FatalError(
829 Fixup.getLoc(), "Cannot represent a difference across sections");
831 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
832 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
833 uint64_t K = SymBOffset - FixupOffset;
838 // We either rejected the fixup or folded B into C at this point.
839 const MCSymbolRefExpr *RefA = Target.getSymA();
840 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
841 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
843 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
844 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
845 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
846 C += Layout.getSymbolOffset(SymAD);
849 if (hasRelocationAddend()) {
856 // FIXME: What is this!?!?
857 MCSymbolRefExpr::VariantKind Modifier =
858 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
859 if (RelocNeedsGOT(Modifier))
862 if (!RelocateWithSymbol) {
863 const MCSection *SecA =
864 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
865 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
866 MCSymbol *SectionSymbol =
867 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
869 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
870 Relocations[FixupSection].push_back(Rec);
875 if (const MCSymbol *R = Renames.lookup(SymA))
878 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
879 WeakrefUsedInReloc.insert(WeakRef);
881 UsedInReloc.insert(SymA);
883 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
884 Relocations[FixupSection].push_back(Rec);
890 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
892 const MCSymbolData &SD = Asm.getSymbolData(*S);
893 return SD.getIndex();
896 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
897 const MCSymbolData &Data, bool Used,
899 const MCSymbol &Symbol = Data.getSymbol();
900 if (Symbol.isVariable()) {
901 const MCExpr *Expr = Symbol.getVariableValue();
902 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
903 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
914 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
917 if (Symbol.isVariable()) {
918 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
919 if (Base && Base->isUndefined())
923 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
924 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
927 if (Symbol.isTemporary())
933 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
934 if (Data.isExternal())
937 const MCSymbol &Symbol = Data.getSymbol();
938 if (Symbol.isDefined())
947 void ELFObjectWriter::computeIndexMap(MCAssembler &Asm,
948 SectionIndexMapTy &SectionIndexMap,
951 for (MCAssembler::iterator it = Asm.begin(),
952 ie = Asm.end(); it != ie; ++it) {
953 const MCSectionELF &Section =
954 static_cast<const MCSectionELF &>(it->getSection());
955 if (Section.getType() != ELF::SHT_GROUP)
957 SectionIndexMap[&Section] = Index++;
960 for (MCAssembler::iterator it = Asm.begin(),
961 ie = Asm.end(); it != ie; ++it) {
962 const MCSectionData &SD = *it;
963 const MCSectionELF &Section =
964 static_cast<const MCSectionELF &>(SD.getSection());
965 if (Section.getType() == ELF::SHT_GROUP ||
966 Section.getType() == ELF::SHT_REL ||
967 Section.getType() == ELF::SHT_RELA)
969 SectionIndexMap[&Section] = Index++;
970 if (MCSectionData *RelSD = createRelocationSection(Asm, SD)) {
971 const MCSectionELF *RelSection =
972 static_cast<const MCSectionELF *>(&RelSD->getSection());
973 RelMap[RelSection] = &Section;
974 SectionIndexMap[RelSection] = Index++;
980 ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
981 const SectionIndexMapTy &SectionIndexMap,
982 const RevGroupMapTy &RevGroupMap,
983 unsigned NumRegularSections) {
984 // FIXME: Is this the correct place to do this?
985 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
987 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
988 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
989 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
990 Data.setExternal(true);
991 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
994 // Add the data for the symbols.
995 for (MCSymbolData &SD : Asm.symbols()) {
996 const MCSymbol &Symbol = SD.getSymbol();
998 bool Used = UsedInReloc.count(&Symbol);
999 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
1000 bool isSignature = RevGroupMap.count(&Symbol);
1002 if (!isInSymtab(Layout, SD,
1003 Used || WeakrefUsed || isSignature,
1004 Renames.count(&Symbol)))
1008 MSD.SymbolData = &SD;
1009 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
1011 // Undefined symbols are global, but this is the first place we
1012 // are able to set it.
1013 bool Local = isLocal(SD, Used);
1014 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1016 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1017 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1018 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1022 MSD.SectionIndex = ELF::SHN_ABS;
1023 } else if (SD.isCommon()) {
1025 MSD.SectionIndex = ELF::SHN_COMMON;
1026 } else if (BaseSymbol->isUndefined()) {
1027 if (isSignature && !Used)
1028 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap.lookup(&Symbol));
1030 MSD.SectionIndex = ELF::SHN_UNDEF;
1031 if (!Used && WeakrefUsed)
1032 MCELF::SetBinding(SD, ELF::STB_WEAK);
1034 const MCSectionELF &Section =
1035 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1036 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1037 assert(MSD.SectionIndex && "Invalid section index!");
1040 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
1043 // FIXME: All name handling should be done before we get to the writer,
1044 // including dealing with GNU-style version suffixes. Fixing this isn't
1047 // We thus have to be careful to not perform the symbol version replacement
1050 // The ELF format is used on Windows by the MCJIT engine. Thus, on
1051 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
1052 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
1053 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
1054 // the EFLObjectWriter should not interpret the "@@@" sub-string as
1055 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1056 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1057 // "__imp_?" or "__imp_@?".
1059 // It would have been interesting to perform the MS mangling prefix check
1060 // only when the target triple is of the form *-pc-windows-elf. But, it
1061 // seems that this information is not easily accessible from the
1063 StringRef Name = Symbol.getName();
1064 if (!Name.startswith("?") && !Name.startswith("@?") &&
1065 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1066 // This symbol isn't following the MSVC C++ name mangling convention. We
1067 // can thus safely interpret the @@@ in symbol names as specifying symbol
1069 SmallString<32> Buf;
1070 size_t Pos = Name.find("@@@");
1071 if (Pos != StringRef::npos) {
1072 Buf += Name.substr(0, Pos);
1073 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1074 Buf += Name.substr(Pos + Skip);
1079 // Sections have their own string table
1080 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1081 MSD.Name = StrTabBuilder.add(Name);
1083 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1084 UndefinedSymbolData.push_back(MSD);
1086 LocalSymbolData.push_back(MSD);
1088 ExternalSymbolData.push_back(MSD);
1091 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1092 StrTabBuilder.add(*i);
1094 StrTabBuilder.finalize(StringTableBuilder::ELF);
1096 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1097 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1099 for (ELFSymbolData &MSD : LocalSymbolData)
1100 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1102 : StrTabBuilder.getOffset(MSD.Name);
1103 for (ELFSymbolData &MSD : ExternalSymbolData)
1104 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1105 for (ELFSymbolData& MSD : UndefinedSymbolData)
1106 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1108 // Symbols are required to be in lexicographic order.
1109 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1110 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1111 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1113 // Set the symbol indices. Local symbols must come before all other
1114 // symbols with non-local bindings.
1115 unsigned Index = FileSymbolData.size() + 1;
1116 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1117 LocalSymbolData[i].SymbolData->setIndex(Index++);
1119 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1120 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1121 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1122 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1126 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1127 const MCSectionData &SD) {
1128 if (Relocations[&SD].empty())
1131 MCContext &Ctx = Asm.getContext();
1132 const MCSectionELF &Section =
1133 static_cast<const MCSectionELF &>(SD.getSection());
1135 const StringRef SectionName = Section.getSectionName();
1136 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1137 RelaSectionName += SectionName;
1140 if (hasRelocationAddend())
1141 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1143 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1146 StringRef Group = "";
1147 if (Section.getFlags() & ELF::SHF_GROUP) {
1148 Flags = ELF::SHF_GROUP;
1149 Group = Section.getGroup()->getName();
1152 const MCSectionELF *RelaSection = Ctx.getELFSection(
1153 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1154 Flags, EntrySize, Group, true);
1155 return &Asm.getOrCreateSectionData(*RelaSection);
1158 static SmallVector<char, 128>
1159 getUncompressedData(MCAsmLayout &Layout,
1160 MCSectionData::FragmentListType &Fragments) {
1161 SmallVector<char, 128> UncompressedData;
1162 for (const MCFragment &F : Fragments) {
1163 const SmallVectorImpl<char> *Contents;
1164 switch (F.getKind()) {
1165 case MCFragment::FT_Data:
1166 Contents = &cast<MCDataFragment>(F).getContents();
1168 case MCFragment::FT_Dwarf:
1169 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1171 case MCFragment::FT_DwarfFrame:
1172 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1176 "Not expecting any other fragment types in a debug_* section");
1178 UncompressedData.append(Contents->begin(), Contents->end());
1180 return UncompressedData;
1183 // Include the debug info compression header:
1184 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1185 // useful for consumers to preallocate a buffer to decompress into.
1187 prependCompressionHeader(uint64_t Size,
1188 SmallVectorImpl<char> &CompressedContents) {
1189 const StringRef Magic = "ZLIB";
1190 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1192 if (sys::IsLittleEndianHost)
1193 sys::swapByteOrder(Size);
1194 CompressedContents.insert(CompressedContents.begin(),
1195 Magic.size() + sizeof(Size), 0);
1196 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1197 std::copy(reinterpret_cast<char *>(&Size),
1198 reinterpret_cast<char *>(&Size + 1),
1199 CompressedContents.begin() + Magic.size());
1203 // Return a single fragment containing the compressed contents of the whole
1204 // section. Null if the section was not compressed for any reason.
1205 static std::unique_ptr<MCDataFragment>
1206 getCompressedFragment(MCAsmLayout &Layout,
1207 MCSectionData::FragmentListType &Fragments) {
1208 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1210 // Gather the uncompressed data from all the fragments, recording the
1211 // alignment fragment, if seen, and any fixups.
1212 SmallVector<char, 128> UncompressedData =
1213 getUncompressedData(Layout, Fragments);
1215 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1217 zlib::Status Success = zlib::compress(
1218 StringRef(UncompressedData.data(), UncompressedData.size()),
1219 CompressedContents);
1220 if (Success != zlib::StatusOK)
1223 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1226 return CompressedFragment;
1229 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1232 static void UpdateSymbols(const MCAsmLayout &Layout,
1233 const std::vector<MCSymbolData *> &Symbols,
1234 MCFragment &NewFragment) {
1235 for (MCSymbolData *Sym : Symbols) {
1236 Sym->setOffset(Sym->getOffset() +
1237 Layout.getFragmentOffset(Sym->getFragment()));
1238 Sym->setFragment(&NewFragment);
1242 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1243 const DefiningSymbolMap &DefiningSymbols,
1244 const MCSectionELF &Section,
1245 MCSectionData &SD) {
1246 StringRef SectionName = Section.getSectionName();
1247 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1249 std::unique_ptr<MCDataFragment> CompressedFragment =
1250 getCompressedFragment(Layout, Fragments);
1252 // Leave the section as-is if the fragments could not be compressed.
1253 if (!CompressedFragment)
1256 // Update the fragment+offsets of any symbols referring to fragments in this
1257 // section to refer to the new fragment.
1258 auto I = DefiningSymbols.find(&SD);
1259 if (I != DefiningSymbols.end())
1260 UpdateSymbols(Layout, I->second, *CompressedFragment);
1262 // Invalidate the layout for the whole section since it will have new and
1263 // different fragments now.
1264 Layout.invalidateFragmentsFrom(&Fragments.front());
1267 // Complete the initialization of the new fragment
1268 CompressedFragment->setParent(&SD);
1269 CompressedFragment->setLayoutOrder(0);
1270 Fragments.push_back(CompressedFragment.release());
1272 // Rename from .debug_* to .zdebug_*
1273 Asm.getContext().renameELFSection(&Section,
1274 (".z" + SectionName.drop_front(1)).str());
1277 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1278 MCAsmLayout &Layout) {
1279 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1282 DefiningSymbolMap DefiningSymbols;
1284 for (MCSymbolData &SD : Asm.symbols())
1285 if (MCFragment *F = SD.getFragment())
1286 DefiningSymbols[F->getParent()].push_back(&SD);
1288 for (MCSectionData &SD : Asm) {
1289 const MCSectionELF &Section =
1290 static_cast<const MCSectionELF &>(SD.getSection());
1291 StringRef SectionName = Section.getSectionName();
1293 // Compressing debug_frame requires handling alignment fragments which is
1294 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1295 // for writing to arbitrary buffers) for little benefit.
1296 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1299 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1303 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
1304 const RelMapTy &RelMap) {
1305 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1306 MCSectionData &RelSD = *it;
1307 const MCSectionELF &RelSection =
1308 static_cast<const MCSectionELF &>(RelSD.getSection());
1310 unsigned Type = RelSection.getType();
1311 if (Type != ELF::SHT_REL && Type != ELF::SHT_RELA)
1314 const MCSectionELF *Section = RelMap.lookup(&RelSection);
1315 MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1316 RelSD.setAlignment(is64Bit() ? 8 : 4);
1318 MCDataFragment *F = new MCDataFragment(&RelSD);
1319 WriteRelocationsFragment(Asm, F, &SD);
1323 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1324 uint64_t Flags, uint64_t Address,
1325 uint64_t Offset, uint64_t Size,
1326 uint32_t Link, uint32_t Info,
1328 uint64_t EntrySize) {
1329 Write32(Name); // sh_name: index into string table
1330 Write32(Type); // sh_type
1331 WriteWord(Flags); // sh_flags
1332 WriteWord(Address); // sh_addr
1333 WriteWord(Offset); // sh_offset
1334 WriteWord(Size); // sh_size
1335 Write32(Link); // sh_link
1336 Write32(Info); // sh_info
1337 WriteWord(Alignment); // sh_addralign
1338 WriteWord(EntrySize); // sh_entsize
1341 // ELF doesn't require relocations to be in any order. We sort by the r_offset,
1342 // just to match gnu as for easier comparison. The use type is an arbitrary way
1343 // of making the sort deterministic.
1344 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
1345 const ELFRelocationEntry &A = *AP;
1346 const ELFRelocationEntry &B = *BP;
1347 if (A.Offset != B.Offset)
1348 return B.Offset - A.Offset;
1349 if (B.Type != A.Type)
1350 return A.Type - B.Type;
1351 //llvm_unreachable("ELFRelocs might be unstable!");
1355 static void sortRelocs(const MCAssembler &Asm,
1356 std::vector<ELFRelocationEntry> &Relocs) {
1357 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
1360 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1362 const MCSectionData *SD) {
1363 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1365 sortRelocs(Asm, Relocs);
1367 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1368 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1370 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1373 write(*F, Entry.Offset);
1374 if (TargetObjectWriter->isN64()) {
1375 write(*F, uint32_t(Index));
1377 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1378 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1379 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1380 write(*F, TargetObjectWriter->getRType(Entry.Type));
1382 struct ELF::Elf64_Rela ERE64;
1383 ERE64.setSymbolAndType(Index, Entry.Type);
1384 write(*F, ERE64.r_info);
1386 if (hasRelocationAddend())
1387 write(*F, Entry.Addend);
1389 write(*F, uint32_t(Entry.Offset));
1391 struct ELF::Elf32_Rela ERE32;
1392 ERE32.setSymbolAndType(Index, Entry.Type);
1393 write(*F, ERE32.r_info);
1395 if (hasRelocationAddend())
1396 write(*F, uint32_t(Entry.Addend));
1401 void ELFObjectWriter::CreateMetadataSections(
1402 MCAssembler &Asm, MCAsmLayout &Layout, SectionIndexMapTy &SectionIndexMap) {
1403 MCContext &Ctx = Asm.getContext();
1406 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1408 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1409 const MCSectionELF *ShstrtabSection =
1410 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1411 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1412 ShstrtabSD.setAlignment(1);
1413 ShstrtabIndex = SectionIndexMap.size() + 1;
1414 SectionIndexMap[ShstrtabSection] = ShstrtabIndex;
1416 const MCSectionELF *SymtabSection =
1417 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1419 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1420 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1421 SymbolTableIndex = SectionIndexMap.size() + 1;
1422 SectionIndexMap[SymtabSection] = SymbolTableIndex;
1424 const MCSectionELF *StrtabSection;
1425 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1426 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1427 StrtabSD.setAlignment(1);
1428 StringTableIndex = SectionIndexMap.size() + 1;
1429 SectionIndexMap[StrtabSection] = StringTableIndex;
1432 F = new MCDataFragment(&SymtabSD);
1433 WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
1435 F = new MCDataFragment(&StrtabSD);
1436 F->getContents().append(StrTabBuilder.data().begin(),
1437 StrTabBuilder.data().end());
1439 F = new MCDataFragment(&ShstrtabSD);
1441 // Section header string table.
1442 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1443 const MCSectionELF &Section =
1444 static_cast<const MCSectionELF&>(it->getSection());
1445 ShStrTabBuilder.add(Section.getSectionName());
1447 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1448 F->getContents().append(ShStrTabBuilder.data().begin(),
1449 ShStrTabBuilder.data().end());
1452 void ELFObjectWriter::createIndexedSections(MCAssembler &Asm,
1453 MCAsmLayout &Layout,
1454 GroupMapTy &GroupMap,
1455 RevGroupMapTy &RevGroupMap,
1456 SectionIndexMapTy &SectionIndexMap,
1458 MCContext &Ctx = Asm.getContext();
1461 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1463 const MCSectionELF &Section =
1464 static_cast<const MCSectionELF&>(it->getSection());
1465 if (!(Section.getFlags() & ELF::SHF_GROUP))
1468 const MCSymbol *SignatureSymbol = Section.getGroup();
1469 Asm.getOrCreateSymbolData(*SignatureSymbol);
1470 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1472 Group = Ctx.CreateELFGroupSection();
1473 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1474 Data.setAlignment(4);
1475 MCDataFragment *F = new MCDataFragment(&Data);
1476 write(*F, uint32_t(ELF::GRP_COMDAT));
1478 GroupMap[Group] = SignatureSymbol;
1481 computeIndexMap(Asm, SectionIndexMap, RelMap);
1483 // Add sections to the groups
1484 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1486 const MCSectionELF &Section =
1487 static_cast<const MCSectionELF&>(it->getSection());
1488 if (!(Section.getFlags() & ELF::SHF_GROUP))
1490 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1491 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1492 // FIXME: we could use the previous fragment
1493 MCDataFragment *F = new MCDataFragment(&Data);
1494 uint32_t Index = SectionIndexMap.lookup(&Section);
1499 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1500 const SectionIndexMapTy &SectionIndexMap,
1501 const RelMapTy &RelMap,
1502 uint32_t GroupSymbolIndex,
1503 uint64_t Offset, uint64_t Size,
1505 const MCSectionELF &Section) {
1506 uint64_t sh_link = 0;
1507 uint64_t sh_info = 0;
1509 switch(Section.getType()) {
1510 case ELF::SHT_DYNAMIC:
1511 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1516 case ELF::SHT_RELA: {
1517 sh_link = SymbolTableIndex;
1518 assert(sh_link && ".symtab not found");
1519 const MCSectionELF *InfoSection = RelMap.find(&Section)->second;
1520 sh_info = SectionIndexMap.lookup(InfoSection);
1524 case ELF::SHT_SYMTAB:
1525 case ELF::SHT_DYNSYM:
1526 sh_link = StringTableIndex;
1527 sh_info = LastLocalSymbolIndex;
1530 case ELF::SHT_SYMTAB_SHNDX:
1531 sh_link = SymbolTableIndex;
1534 case ELF::SHT_PROGBITS:
1535 case ELF::SHT_STRTAB:
1536 case ELF::SHT_NOBITS:
1539 case ELF::SHT_ARM_ATTRIBUTES:
1540 case ELF::SHT_INIT_ARRAY:
1541 case ELF::SHT_FINI_ARRAY:
1542 case ELF::SHT_PREINIT_ARRAY:
1543 case ELF::SHT_X86_64_UNWIND:
1544 case ELF::SHT_MIPS_REGINFO:
1545 case ELF::SHT_MIPS_OPTIONS:
1546 case ELF::SHT_MIPS_ABIFLAGS:
1550 case ELF::SHT_GROUP:
1551 sh_link = SymbolTableIndex;
1552 sh_info = GroupSymbolIndex;
1556 llvm_unreachable("FIXME: sh_type value not supported!");
1559 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1560 Section.getType() == ELF::SHT_ARM_EXIDX) {
1561 StringRef SecName(Section.getSectionName());
1562 if (SecName == ".ARM.exidx") {
1563 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
1564 ".text", ELF::SHT_PROGBITS, ELF::SHF_EXECINSTR | ELF::SHF_ALLOC));
1565 } else if (SecName.startswith(".ARM.exidx")) {
1566 StringRef GroupName =
1567 Section.getGroup() ? Section.getGroup()->getName() : "";
1568 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
1569 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS,
1570 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, 0, GroupName));
1574 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1576 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1577 Alignment, Section.getEntrySize());
1580 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1581 return SD.getOrdinal() == ~UINT32_C(0) &&
1582 !SD.getSection().isVirtualSection();
1585 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1587 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1589 const MCFragment &F = *i;
1590 assert(F.getKind() == MCFragment::FT_Data);
1591 Ret += cast<MCDataFragment>(F).getContents().size();
1596 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
1597 const MCSectionData &SD) {
1598 if (IsELFMetaDataSection(SD))
1599 return DataSectionSize(SD);
1600 return Layout.getSectionFileSize(&SD);
1603 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1604 const MCSectionData &SD) {
1605 if (IsELFMetaDataSection(SD))
1606 return DataSectionSize(SD);
1607 return Layout.getSectionAddressSize(&SD);
1610 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
1611 const MCAsmLayout &Layout,
1612 const MCSectionELF &Section) {
1613 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1615 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1616 WriteZeros(Padding);
1618 if (IsELFMetaDataSection(SD)) {
1619 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1621 const MCFragment &F = *i;
1622 assert(F.getKind() == MCFragment::FT_Data);
1623 WriteBytes(cast<MCDataFragment>(F).getContents());
1626 Asm.writeSectionData(&SD, Layout);
1630 void ELFObjectWriter::writeSectionHeader(
1631 MCAssembler &Asm, const GroupMapTy &GroupMap, const MCAsmLayout &Layout,
1632 const SectionIndexMapTy &SectionIndexMap, const RelMapTy &RelMap,
1633 const SectionOffsetMapTy &SectionOffsetMap) {
1634 const unsigned NumSections = Asm.size() + 1;
1636 std::vector<const MCSectionELF*> Sections;
1637 Sections.resize(NumSections - 1);
1639 for (SectionIndexMapTy::const_iterator i=
1640 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
1641 const std::pair<const MCSectionELF*, uint32_t> &p = *i;
1642 Sections[p.second - 1] = p.first;
1645 // Null section first.
1646 uint64_t FirstSectionSize =
1647 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1648 uint32_t FirstSectionLink =
1649 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1650 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1652 for (unsigned i = 0; i < NumSections - 1; ++i) {
1653 const MCSectionELF &Section = *Sections[i];
1654 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1655 uint32_t GroupSymbolIndex;
1656 if (Section.getType() != ELF::SHT_GROUP)
1657 GroupSymbolIndex = 0;
1659 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1660 GroupMap.lookup(&Section));
1662 uint64_t Size = GetSectionAddressSize(Layout, SD);
1664 writeSection(Asm, SectionIndexMap, RelMap, GroupSymbolIndex,
1665 SectionOffsetMap.lookup(&Section), Size,
1666 SD.getAlignment(), Section);
1670 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
1671 std::vector<const MCSectionELF*> &Sections) {
1672 for (MCAssembler::iterator it = Asm.begin(),
1673 ie = Asm.end(); it != ie; ++it) {
1674 const MCSectionELF &Section =
1675 static_cast<const MCSectionELF &>(it->getSection());
1676 if (Section.getType() == ELF::SHT_GROUP)
1677 Sections.push_back(&Section);
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 Section.getType() != ELF::SHT_REL &&
1686 Section.getType() != ELF::SHT_RELA)
1687 Sections.push_back(&Section);
1690 for (MCAssembler::iterator it = Asm.begin(),
1691 ie = Asm.end(); it != ie; ++it) {
1692 const MCSectionELF &Section =
1693 static_cast<const MCSectionELF &>(it->getSection());
1694 if (Section.getType() == ELF::SHT_REL ||
1695 Section.getType() == ELF::SHT_RELA)
1696 Sections.push_back(&Section);
1700 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1701 const MCAsmLayout &Layout) {
1702 GroupMapTy GroupMap;
1703 RevGroupMapTy RevGroupMap;
1704 SectionIndexMapTy SectionIndexMap;
1706 unsigned NumUserSections = Asm.size();
1708 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1710 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
1711 const unsigned NumUserAndRelocSections = Asm.size();
1712 createIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
1713 RevGroupMap, SectionIndexMap, RelMap);
1714 const unsigned AllSections = Asm.size();
1715 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
1717 unsigned NumRegularSections = NumUserSections + NumIndexedSections;
1719 // Compute symbol table information.
1720 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
1721 NumRegularSections);
1723 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1725 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1726 const_cast<MCAsmLayout&>(Layout),
1729 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1730 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
1731 sizeof(ELF::Elf32_Ehdr);
1732 uint64_t FileOff = HeaderSize;
1734 std::vector<const MCSectionELF*> Sections;
1735 ComputeSectionOrder(Asm, Sections);
1736 unsigned NumSections = Sections.size();
1737 SectionOffsetMapTy SectionOffsetMap;
1738 for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
1739 const MCSectionELF &Section = *Sections[i];
1740 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1742 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1744 // Remember the offset into the file for this section.
1745 SectionOffsetMap[&Section] = FileOff;
1747 // Get the size of the section in the output file (including padding).
1748 FileOff += GetSectionFileSize(Layout, SD);
1751 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1753 const unsigned SectionHeaderOffset = FileOff - HeaderSize;
1755 uint64_t SectionHeaderEntrySize = is64Bit() ?
1756 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
1757 FileOff += (NumSections + 1) * SectionHeaderEntrySize;
1759 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
1760 const MCSectionELF &Section = *Sections[i];
1761 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1763 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1765 // Remember the offset into the file for this section.
1766 SectionOffsetMap[&Section] = FileOff;
1768 // Get the size of the section in the output file (including padding).
1769 FileOff += GetSectionFileSize(Layout, SD);
1772 // Write out the ELF header ...
1773 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
1775 // ... then the regular sections ...
1776 // + because of .shstrtab
1777 for (unsigned i = 0; i < NumRegularSections + 1; ++i)
1778 WriteDataSectionData(Asm, Layout, *Sections[i]);
1780 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1781 WriteZeros(Padding);
1783 // ... then the section header table ...
1784 writeSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, RelMap,
1787 // ... and then the remaining sections ...
1788 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
1789 WriteDataSectionData(Asm, Layout, *Sections[i]);
1793 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
1794 const MCSymbolData &DataA,
1795 const MCFragment &FB,
1797 bool IsPCRel) const {
1798 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC)
1800 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1801 Asm, DataA, FB,InSet, IsPCRel);
1804 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1806 bool IsLittleEndian) {
1807 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);