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 class ELFObjectWriter : public MCObjectWriter {
83 FragmentWriter FWriter;
87 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
88 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
89 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
90 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data,
91 bool Used, bool Renamed);
92 static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
93 static bool IsELFMetaDataSection(const MCSectionData &SD);
94 static uint64_t DataSectionSize(const MCSectionData &SD);
95 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout,
96 const MCSectionData &SD);
98 void writeDataSectionData(MCAssembler &Asm, const MCAsmLayout &Layout,
99 const MCSectionData &SD);
101 /// Helper struct for containing some precomputed information on symbols.
102 struct ELFSymbolData {
103 MCSymbolData *SymbolData;
104 uint64_t StringIndex;
105 uint32_t SectionIndex;
108 // Support lexicographic sorting.
109 bool operator<(const ELFSymbolData &RHS) const {
110 unsigned LHSType = MCELF::GetType(*SymbolData);
111 unsigned RHSType = MCELF::GetType(*RHS.SymbolData);
112 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
114 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
116 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
117 return SectionIndex < RHS.SectionIndex;
118 return Name < RHS.Name;
122 /// The target specific ELF writer instance.
123 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
125 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
126 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
127 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
129 llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
131 StringTableBuilder ShStrTabBuilder;
134 /// @name Symbol Table Data
137 StringTableBuilder StrTabBuilder;
138 std::vector<uint64_t> FileSymbolData;
139 std::vector<ELFSymbolData> LocalSymbolData;
140 std::vector<ELFSymbolData> ExternalSymbolData;
141 std::vector<ELFSymbolData> UndefinedSymbolData;
147 // This holds the symbol table index of the last local symbol.
148 unsigned LastLocalSymbolIndex;
149 // This holds the .strtab section index.
150 unsigned StringTableIndex;
151 // This holds the .symtab section index.
152 unsigned SymbolTableIndex;
154 unsigned ShstrtabIndex;
157 // TargetObjectWriter wrappers.
158 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
159 bool hasRelocationAddend() const {
160 return TargetObjectWriter->hasRelocationAddend();
162 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
163 bool IsPCRel) const {
164 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
168 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
170 : MCObjectWriter(OS, IsLittleEndian), FWriter(IsLittleEndian),
171 TargetObjectWriter(MOTW), NeedsGOT(false) {}
173 void reset() override {
175 WeakrefUsedInReloc.clear();
178 ShStrTabBuilder.clear();
179 StrTabBuilder.clear();
180 FileSymbolData.clear();
181 LocalSymbolData.clear();
182 ExternalSymbolData.clear();
183 UndefinedSymbolData.clear();
184 MCObjectWriter::reset();
187 ~ELFObjectWriter() override;
189 void WriteWord(uint64_t W) {
196 template <typename T> void write(MCDataFragment &F, T Value) {
197 FWriter.write(F, Value);
200 void WriteHeader(const MCAssembler &Asm,
201 unsigned NumberOfSections);
203 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
204 const MCAsmLayout &Layout);
206 void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm,
207 const MCAsmLayout &Layout,
208 SectionIndexMapTy &SectionIndexMap);
210 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
211 const MCSymbolRefExpr *RefA,
212 const MCSymbolData *SD, uint64_t C,
213 unsigned Type) const;
215 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
216 const MCFragment *Fragment, const MCFixup &Fixup,
217 MCValue Target, bool &IsPCRel,
218 uint64_t &FixedValue) override;
220 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
223 // Map from a group section to the signature symbol
224 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
225 // Map from a signature symbol to the group section
226 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
227 // Map from a section to its offset
228 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy;
230 /// Compute the symbol table data
232 /// \param Asm - The assembler.
233 /// \param SectionIndexMap - Maps a section to its index.
234 /// \param RevGroupMap - Maps a signature symbol to the group section.
235 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
236 const SectionIndexMapTy &SectionIndexMap,
237 const RevGroupMapTy &RevGroupMap);
239 void computeIndexMap(MCAssembler &Asm, SectionIndexMapTy &SectionIndexMap);
241 MCSectionData *createRelocationSection(MCAssembler &Asm,
242 const MCSectionData &SD);
244 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
246 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout);
248 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
249 SectionIndexMapTy &SectionIndexMap);
251 // Create the sections that show up in the symbol table. Currently
252 // those are the .note.GNU-stack section and the group sections.
253 void createIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
254 GroupMapTy &GroupMap, RevGroupMapTy &RevGroupMap,
255 SectionIndexMapTy &SectionIndexMap);
257 void ExecutePostLayoutBinding(MCAssembler &Asm,
258 const MCAsmLayout &Layout) override;
260 void writeSectionHeader(ArrayRef<const MCSectionELF *> Sections,
261 MCAssembler &Asm, const GroupMapTy &GroupMap,
262 const MCAsmLayout &Layout,
263 const SectionIndexMapTy &SectionIndexMap,
264 const SectionOffsetMapTy &SectionOffsetMap);
266 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
267 uint64_t Address, uint64_t Offset,
268 uint64_t Size, uint32_t Link, uint32_t Info,
269 uint64_t Alignment, uint64_t EntrySize);
271 void WriteRelocationsFragment(const MCAssembler &Asm,
273 const MCSectionData *SD);
276 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
277 const MCSymbolData &DataA,
278 const MCSymbolData *DataB,
279 const MCFragment &FB,
281 bool IsPCRel) const override;
283 bool isWeak(const MCSymbolData &SD) const override;
285 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
286 void writeSection(MCAssembler &Asm,
287 const SectionIndexMapTy &SectionIndexMap,
288 uint32_t GroupSymbolIndex,
289 uint64_t Offset, uint64_t Size, uint64_t Alignment,
290 const MCSectionELF &Section);
294 FragmentWriter::FragmentWriter(bool IsLittleEndian)
295 : IsLittleEndian(IsLittleEndian) {}
297 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
299 Val = support::endian::byte_swap<T, support::little>(Val);
301 Val = support::endian::byte_swap<T, support::big>(Val);
302 const char *Start = (const char *)&Val;
303 F.getContents().append(Start, Start + sizeof(T));
306 void SymbolTableWriter::createSymtabShndx() {
310 MCContext &Ctx = Asm.getContext();
311 const MCSectionELF *SymtabShndxSection =
312 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
313 MCSectionData *SymtabShndxSD =
314 &Asm.getOrCreateSectionData(*SymtabShndxSection);
315 SymtabShndxSD->setAlignment(4);
316 ShndxF = new MCDataFragment(SymtabShndxSD);
317 unsigned Index = SectionIndexMap.size() + 1;
318 SectionIndexMap[SymtabShndxSection] = Index;
320 for (unsigned I = 0; I < NumWritten; ++I)
321 write(*ShndxF, uint32_t(0));
324 template <typename T>
325 void SymbolTableWriter::write(MCDataFragment &F, T Value) {
326 FWriter.write(F, Value);
329 SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter,
331 SectionIndexMapTy &SectionIndexMap,
332 MCDataFragment *SymtabF)
333 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit),
334 SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr),
337 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
338 uint64_t size, uint8_t other,
339 uint32_t shndx, bool Reserved) {
340 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
347 write(*ShndxF, shndx);
349 write(*ShndxF, uint32_t(0));
352 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
355 write(*SymtabF, name); // st_name
356 write(*SymtabF, info); // st_info
357 write(*SymtabF, other); // st_other
358 write(*SymtabF, Index); // st_shndx
359 write(*SymtabF, value); // st_value
360 write(*SymtabF, size); // st_size
362 write(*SymtabF, name); // st_name
363 write(*SymtabF, uint32_t(value)); // st_value
364 write(*SymtabF, uint32_t(size)); // st_size
365 write(*SymtabF, info); // st_info
366 write(*SymtabF, other); // st_other
367 write(*SymtabF, Index); // st_shndx
373 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
374 const MCFixupKindInfo &FKI =
375 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
377 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
380 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
384 case MCSymbolRefExpr::VK_GOT:
385 case MCSymbolRefExpr::VK_PLT:
386 case MCSymbolRefExpr::VK_GOTPCREL:
387 case MCSymbolRefExpr::VK_GOTOFF:
388 case MCSymbolRefExpr::VK_TPOFF:
389 case MCSymbolRefExpr::VK_TLSGD:
390 case MCSymbolRefExpr::VK_GOTTPOFF:
391 case MCSymbolRefExpr::VK_INDNTPOFF:
392 case MCSymbolRefExpr::VK_NTPOFF:
393 case MCSymbolRefExpr::VK_GOTNTPOFF:
394 case MCSymbolRefExpr::VK_TLSLDM:
395 case MCSymbolRefExpr::VK_DTPOFF:
396 case MCSymbolRefExpr::VK_TLSLD:
401 ELFObjectWriter::~ELFObjectWriter()
404 // Emit the ELF header.
405 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
406 unsigned NumberOfSections) {
412 // emitWord method behaves differently for ELF32 and ELF64, writing
413 // 4 bytes in the former and 8 in the latter.
415 Write8(0x7f); // e_ident[EI_MAG0]
416 Write8('E'); // e_ident[EI_MAG1]
417 Write8('L'); // e_ident[EI_MAG2]
418 Write8('F'); // e_ident[EI_MAG3]
420 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
423 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
425 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
427 Write8(TargetObjectWriter->getOSABI());
428 Write8(0); // e_ident[EI_ABIVERSION]
430 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
432 Write16(ELF::ET_REL); // e_type
434 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
436 Write32(ELF::EV_CURRENT); // e_version
437 WriteWord(0); // e_entry, no entry point in .o file
438 WriteWord(0); // e_phoff, no program header for .o
439 WriteWord(0); // e_shoff = sec hdr table off in bytes
441 // e_flags = whatever the target wants
442 Write32(Asm.getELFHeaderEFlags());
444 // e_ehsize = ELF header size
445 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
447 Write16(0); // e_phentsize = prog header entry size
448 Write16(0); // e_phnum = # prog header entries = 0
450 // e_shentsize = Section header entry size
451 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
453 // e_shnum = # of section header ents
454 if (NumberOfSections >= ELF::SHN_LORESERVE)
455 Write16(ELF::SHN_UNDEF);
457 Write16(NumberOfSections);
459 // e_shstrndx = Section # of '.shstrtab'
460 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
461 Write16(ELF::SHN_XINDEX);
463 Write16(ShstrtabIndex);
466 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
467 const MCAsmLayout &Layout) {
468 if (Data.isCommon() && Data.isExternal())
469 return Data.getCommonAlignment();
472 if (!Layout.getSymbolOffset(&Data, Res))
475 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
481 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
482 const MCAsmLayout &Layout) {
483 // The presence of symbol versions causes undefined symbols and
484 // versions declared with @@@ to be renamed.
486 for (MCSymbolData &OriginalData : Asm.symbols()) {
487 const MCSymbol &Alias = OriginalData.getSymbol();
490 if (!Alias.isVariable())
492 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
495 const MCSymbol &Symbol = Ref->getSymbol();
496 MCSymbolData &SD = Asm.getSymbolData(Symbol);
498 StringRef AliasName = Alias.getName();
499 size_t Pos = AliasName.find('@');
500 if (Pos == StringRef::npos)
503 // Aliases defined with .symvar copy the binding from the symbol they alias.
504 // This is the first place we are able to copy this information.
505 OriginalData.setExternal(SD.isExternal());
506 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
508 StringRef Rest = AliasName.substr(Pos);
509 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
512 // FIXME: produce a better error message.
513 if (Symbol.isUndefined() && Rest.startswith("@@") &&
514 !Rest.startswith("@@@"))
515 report_fatal_error("A @@ version cannot be undefined");
517 Renames.insert(std::make_pair(&Symbol, &Alias));
521 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
522 uint8_t Type = newType;
524 // Propagation rules:
525 // IFUNC > FUNC > OBJECT > NOTYPE
526 // TLS_OBJECT > OBJECT > NOTYPE
528 // dont let the new type degrade the old type
532 case ELF::STT_GNU_IFUNC:
533 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
534 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
535 Type = ELF::STT_GNU_IFUNC;
538 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
539 Type == ELF::STT_TLS)
540 Type = ELF::STT_FUNC;
542 case ELF::STT_OBJECT:
543 if (Type == ELF::STT_NOTYPE)
544 Type = ELF::STT_OBJECT;
547 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
548 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
556 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
557 const MCAsmLayout &Layout) {
558 MCSymbolData &OrigData = *MSD.SymbolData;
559 assert((!OrigData.getFragment() ||
560 (&OrigData.getFragment()->getParent()->getSection() ==
561 &OrigData.getSymbol().getSection())) &&
562 "The symbol's section doesn't match the fragment's symbol");
563 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
565 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
567 bool IsReserved = !Base || OrigData.isCommon();
569 // Binding and Type share the same byte as upper and lower nibbles
570 uint8_t Binding = MCELF::GetBinding(OrigData);
571 uint8_t Type = MCELF::GetType(OrigData);
572 MCSymbolData *BaseSD = nullptr;
574 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
575 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
577 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
579 // Other and Visibility share the same byte with Visibility using the lower
581 uint8_t Visibility = MCELF::GetVisibility(OrigData);
582 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
585 uint64_t Value = SymbolValue(OrigData, Layout);
588 const MCExpr *ESize = OrigData.getSize();
590 ESize = BaseSD->getSize();
594 if (!ESize->evaluateKnownAbsolute(Res, Layout))
595 report_fatal_error("Size expression must be absolute.");
599 // Write out the symbol table entry
600 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
601 MSD.SectionIndex, IsReserved);
604 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
606 const MCAsmLayout &Layout,
607 SectionIndexMapTy &SectionIndexMap) {
608 // The string table must be emitted first because we need the index
609 // into the string table for all the symbol names.
611 // FIXME: Make sure the start of the symbol table is aligned.
613 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF);
615 // The first entry is the undefined symbol entry.
616 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
618 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
619 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
620 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
623 // Write the symbol table entries.
624 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
626 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
627 ELFSymbolData &MSD = LocalSymbolData[i];
628 WriteSymbol(Writer, MSD, Layout);
631 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
632 ELFSymbolData &MSD = ExternalSymbolData[i];
633 MCSymbolData &Data = *MSD.SymbolData;
634 assert(((Data.getFlags() & ELF_STB_Global) ||
635 (Data.getFlags() & ELF_STB_Weak)) &&
636 "External symbol requires STB_GLOBAL or STB_WEAK flag");
637 WriteSymbol(Writer, MSD, Layout);
638 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
639 LastLocalSymbolIndex++;
642 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
643 ELFSymbolData &MSD = UndefinedSymbolData[i];
644 MCSymbolData &Data = *MSD.SymbolData;
645 WriteSymbol(Writer, MSD, Layout);
646 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
647 LastLocalSymbolIndex++;
651 // It is always valid to create a relocation with a symbol. It is preferable
652 // to use a relocation with a section if that is possible. Using the section
653 // allows us to omit some local symbols from the symbol table.
654 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
655 const MCSymbolRefExpr *RefA,
656 const MCSymbolData *SD,
658 unsigned Type) const {
659 // A PCRel relocation to an absolute value has no symbol (or section). We
660 // represent that with a relocation to a null section.
664 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
668 // The .odp creation emits a relocation against the symbol ".TOC." which
669 // create a R_PPC64_TOC relocation. However the relocation symbol name
670 // in final object creation should be NULL, since the symbol does not
671 // really exist, it is just the reference to TOC base for the current
672 // object file. Since the symbol is undefined, returning false results
673 // in a relocation with a null section which is the desired result.
674 case MCSymbolRefExpr::VK_PPC_TOCBASE:
677 // These VariantKind cause the relocation to refer to something other than
678 // the symbol itself, like a linker generated table. Since the address of
679 // symbol is not relevant, we cannot replace the symbol with the
680 // section and patch the difference in the addend.
681 case MCSymbolRefExpr::VK_GOT:
682 case MCSymbolRefExpr::VK_PLT:
683 case MCSymbolRefExpr::VK_GOTPCREL:
684 case MCSymbolRefExpr::VK_Mips_GOT:
685 case MCSymbolRefExpr::VK_PPC_GOT_LO:
686 case MCSymbolRefExpr::VK_PPC_GOT_HI:
687 case MCSymbolRefExpr::VK_PPC_GOT_HA:
691 // An undefined symbol is not in any section, so the relocation has to point
692 // to the symbol itself.
693 const MCSymbol &Sym = SD->getSymbol();
694 if (Sym.isUndefined())
697 unsigned Binding = MCELF::GetBinding(*SD);
700 llvm_unreachable("Invalid Binding");
704 // If the symbol is weak, it might be overridden by a symbol in another
705 // file. The relocation has to point to the symbol so that the linker
708 case ELF::STB_GLOBAL:
709 // Global ELF symbols can be preempted by the dynamic linker. The relocation
710 // has to point to the symbol for a reason analogous to the STB_WEAK case.
714 // If a relocation points to a mergeable section, we have to be careful.
715 // If the offset is zero, a relocation with the section will encode the
716 // same information. With a non-zero offset, the situation is different.
717 // For example, a relocation can point 42 bytes past the end of a string.
718 // If we change such a relocation to use the section, the linker would think
719 // that it pointed to another string and subtracting 42 at runtime will
720 // produce the wrong value.
721 auto &Sec = cast<MCSectionELF>(Sym.getSection());
722 unsigned Flags = Sec.getFlags();
723 if (Flags & ELF::SHF_MERGE) {
727 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
728 // only handle section relocations to mergeable sections if using RELA.
729 if (!hasRelocationAddend())
733 // Most TLS relocations use a got, so they need the symbol. Even those that
734 // are just an offset (@tpoff), require a symbol in gold versions before
735 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
736 // http://sourceware.org/PR16773.
737 if (Flags & ELF::SHF_TLS)
740 // If the symbol is a thumb function the final relocation must set the lowest
741 // bit. With a symbol that is done by just having the symbol have that bit
742 // set, so we would lose the bit if we relocated with the section.
743 // FIXME: We could use the section but add the bit to the relocation value.
744 if (Asm.isThumbFunc(&Sym))
747 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
752 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
753 const MCSymbol &Sym = Ref.getSymbol();
755 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
758 if (!Sym.isVariable())
761 const MCExpr *Expr = Sym.getVariableValue();
762 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
766 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
767 return &Inner->getSymbol();
771 static bool isWeak(const MCSymbolData &D) {
772 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
775 switch (MCELF::GetBinding(D)) {
777 llvm_unreachable("Unknown binding");
780 case ELF::STB_GLOBAL:
783 case ELF::STB_GNU_UNIQUE:
787 const MCSymbol &Sym = D.getSymbol();
788 if (!Sym.isInSection())
791 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
795 // It is invalid to replace a reference to a global in a comdat
796 // with a reference to a local since out of comdat references
797 // to a local are forbidden.
798 // We could try to return false for more cases, like the reference
799 // being in the same comdat or Sym being an alias to another global,
800 // but it is not clear if it is worth the effort.
804 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
805 const MCAsmLayout &Layout,
806 const MCFragment *Fragment,
807 const MCFixup &Fixup, MCValue Target,
808 bool &IsPCRel, uint64_t &FixedValue) {
809 const MCSectionData *FixupSection = Fragment->getParent();
810 uint64_t C = Target.getConstant();
811 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
813 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
814 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
815 "Should not have constructed this");
817 // Let A, B and C being the components of Target and R be the location of
818 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
819 // If it is pcrel, we want to compute (A - B + C - R).
821 // In general, ELF has no relocations for -B. It can only represent (A + C)
822 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
823 // replace B to implement it: (A - R - K + C)
825 Asm.getContext().FatalError(
827 "No relocation available to represent this relative expression");
829 const MCSymbol &SymB = RefB->getSymbol();
831 if (SymB.isUndefined())
832 Asm.getContext().FatalError(
834 Twine("symbol '") + SymB.getName() +
835 "' can not be undefined in a subtraction expression");
837 assert(!SymB.isAbsolute() && "Should have been folded");
838 const MCSection &SecB = SymB.getSection();
839 if (&SecB != &FixupSection->getSection())
840 Asm.getContext().FatalError(
841 Fixup.getLoc(), "Cannot represent a difference across sections");
843 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
845 Asm.getContext().FatalError(
846 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
848 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
849 uint64_t K = SymBOffset - FixupOffset;
854 // We either rejected the fixup or folded B into C at this point.
855 const MCSymbolRefExpr *RefA = Target.getSymA();
856 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
857 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
859 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
860 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
861 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
862 C += Layout.getSymbolOffset(SymAD);
865 if (hasRelocationAddend()) {
872 // FIXME: What is this!?!?
873 MCSymbolRefExpr::VariantKind Modifier =
874 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
875 if (RelocNeedsGOT(Modifier))
878 if (!RelocateWithSymbol) {
879 const MCSection *SecA =
880 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
881 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
882 MCSymbol *SectionSymbol =
883 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
885 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
886 Relocations[FixupSection].push_back(Rec);
891 if (const MCSymbol *R = Renames.lookup(SymA))
894 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
895 WeakrefUsedInReloc.insert(WeakRef);
897 UsedInReloc.insert(SymA);
899 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
900 Relocations[FixupSection].push_back(Rec);
906 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
908 const MCSymbolData &SD = Asm.getSymbolData(*S);
909 return SD.getIndex();
912 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
913 const MCSymbolData &Data, bool Used,
915 const MCSymbol &Symbol = Data.getSymbol();
916 if (Symbol.isVariable()) {
917 const MCExpr *Expr = Symbol.getVariableValue();
918 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
919 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
930 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
933 if (Symbol.isVariable()) {
934 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
935 if (Base && Base->isUndefined())
939 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
940 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
943 if (Symbol.isTemporary())
949 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
950 if (Data.isExternal())
953 const MCSymbol &Symbol = Data.getSymbol();
954 if (Symbol.isDefined())
963 void ELFObjectWriter::computeIndexMap(MCAssembler &Asm,
964 SectionIndexMapTy &SectionIndexMap) {
966 for (MCAssembler::iterator it = Asm.begin(),
967 ie = Asm.end(); it != ie; ++it) {
968 const MCSectionELF &Section =
969 static_cast<const MCSectionELF &>(it->getSection());
970 if (Section.getType() != ELF::SHT_GROUP)
972 SectionIndexMap[&Section] = Index++;
975 std::vector<const MCSectionELF *> RelSections;
977 for (MCAssembler::iterator it = Asm.begin(),
978 ie = Asm.end(); it != ie; ++it) {
979 const MCSectionData &SD = *it;
980 const MCSectionELF &Section =
981 static_cast<const MCSectionELF &>(SD.getSection());
982 if (Section.getType() == ELF::SHT_GROUP ||
983 Section.getType() == ELF::SHT_REL ||
984 Section.getType() == ELF::SHT_RELA)
986 SectionIndexMap[&Section] = Index++;
987 if (MCSectionData *RelSD = createRelocationSection(Asm, SD)) {
988 const MCSectionELF *RelSection =
989 static_cast<const MCSectionELF *>(&RelSD->getSection());
990 RelSections.push_back(RelSection);
994 // Put relocation sections close together. The linker reads them
995 // first, so this improves cache locality.
996 for (const MCSectionELF * Sec: RelSections)
997 SectionIndexMap[Sec] = Index++;
1000 void ELFObjectWriter::computeSymbolTable(
1001 MCAssembler &Asm, const MCAsmLayout &Layout,
1002 const SectionIndexMapTy &SectionIndexMap,
1003 const RevGroupMapTy &RevGroupMap) {
1004 // FIXME: Is this the correct place to do this?
1005 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
1007 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
1008 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
1009 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
1010 Data.setExternal(true);
1011 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
1014 // Add the data for the symbols.
1015 for (MCSymbolData &SD : Asm.symbols()) {
1016 const MCSymbol &Symbol = SD.getSymbol();
1018 bool Used = UsedInReloc.count(&Symbol);
1019 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
1020 bool isSignature = RevGroupMap.count(&Symbol);
1022 if (!isInSymtab(Layout, SD,
1023 Used || WeakrefUsed || isSignature,
1024 Renames.count(&Symbol)))
1028 MSD.SymbolData = &SD;
1029 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
1031 // Undefined symbols are global, but this is the first place we
1032 // are able to set it.
1033 bool Local = isLocal(SD, Used);
1034 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1036 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1037 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1038 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1042 MSD.SectionIndex = ELF::SHN_ABS;
1043 } else if (SD.isCommon()) {
1045 MSD.SectionIndex = ELF::SHN_COMMON;
1046 } else if (BaseSymbol->isUndefined()) {
1047 if (isSignature && !Used)
1048 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap.lookup(&Symbol));
1050 MSD.SectionIndex = ELF::SHN_UNDEF;
1051 if (!Used && WeakrefUsed)
1052 MCELF::SetBinding(SD, ELF::STB_WEAK);
1054 const MCSectionELF &Section =
1055 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1056 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1057 assert(MSD.SectionIndex && "Invalid section index!");
1060 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
1063 // FIXME: All name handling should be done before we get to the writer,
1064 // including dealing with GNU-style version suffixes. Fixing this isn't
1067 // We thus have to be careful to not perform the symbol version replacement
1070 // The ELF format is used on Windows by the MCJIT engine. Thus, on
1071 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
1072 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
1073 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
1074 // the EFLObjectWriter should not interpret the "@@@" sub-string as
1075 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1076 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1077 // "__imp_?" or "__imp_@?".
1079 // It would have been interesting to perform the MS mangling prefix check
1080 // only when the target triple is of the form *-pc-windows-elf. But, it
1081 // seems that this information is not easily accessible from the
1083 StringRef Name = Symbol.getName();
1084 if (!Name.startswith("?") && !Name.startswith("@?") &&
1085 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1086 // This symbol isn't following the MSVC C++ name mangling convention. We
1087 // can thus safely interpret the @@@ in symbol names as specifying symbol
1089 SmallString<32> Buf;
1090 size_t Pos = Name.find("@@@");
1091 if (Pos != StringRef::npos) {
1092 Buf += Name.substr(0, Pos);
1093 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1094 Buf += Name.substr(Pos + Skip);
1099 // Sections have their own string table
1100 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1101 MSD.Name = StrTabBuilder.add(Name);
1103 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1104 UndefinedSymbolData.push_back(MSD);
1106 LocalSymbolData.push_back(MSD);
1108 ExternalSymbolData.push_back(MSD);
1111 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1112 StrTabBuilder.add(*i);
1114 StrTabBuilder.finalize(StringTableBuilder::ELF);
1116 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1117 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1119 for (ELFSymbolData &MSD : LocalSymbolData)
1120 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1122 : StrTabBuilder.getOffset(MSD.Name);
1123 for (ELFSymbolData &MSD : ExternalSymbolData)
1124 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1125 for (ELFSymbolData& MSD : UndefinedSymbolData)
1126 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1128 // Symbols are required to be in lexicographic order.
1129 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1130 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1131 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1133 // Set the symbol indices. Local symbols must come before all other
1134 // symbols with non-local bindings.
1135 unsigned Index = FileSymbolData.size() + 1;
1136 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1137 LocalSymbolData[i].SymbolData->setIndex(Index++);
1139 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1140 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1141 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1142 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1146 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1147 const MCSectionData &SD) {
1148 if (Relocations[&SD].empty())
1151 MCContext &Ctx = Asm.getContext();
1152 const MCSectionELF &Section =
1153 static_cast<const MCSectionELF &>(SD.getSection());
1155 const StringRef SectionName = Section.getSectionName();
1156 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1157 RelaSectionName += SectionName;
1160 if (hasRelocationAddend())
1161 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1163 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1166 if (Section.getFlags() & ELF::SHF_GROUP)
1167 Flags = ELF::SHF_GROUP;
1169 const MCSectionELF *RelaSection = Ctx.createELFRelSection(
1170 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1171 Flags, EntrySize, Section.getGroup(), &Section);
1172 return &Asm.getOrCreateSectionData(*RelaSection);
1175 static SmallVector<char, 128>
1176 getUncompressedData(MCAsmLayout &Layout,
1177 MCSectionData::FragmentListType &Fragments) {
1178 SmallVector<char, 128> UncompressedData;
1179 for (const MCFragment &F : Fragments) {
1180 const SmallVectorImpl<char> *Contents;
1181 switch (F.getKind()) {
1182 case MCFragment::FT_Data:
1183 Contents = &cast<MCDataFragment>(F).getContents();
1185 case MCFragment::FT_Dwarf:
1186 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1188 case MCFragment::FT_DwarfFrame:
1189 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1193 "Not expecting any other fragment types in a debug_* section");
1195 UncompressedData.append(Contents->begin(), Contents->end());
1197 return UncompressedData;
1200 // Include the debug info compression header:
1201 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1202 // useful for consumers to preallocate a buffer to decompress into.
1204 prependCompressionHeader(uint64_t Size,
1205 SmallVectorImpl<char> &CompressedContents) {
1206 const StringRef Magic = "ZLIB";
1207 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1209 if (sys::IsLittleEndianHost)
1210 sys::swapByteOrder(Size);
1211 CompressedContents.insert(CompressedContents.begin(),
1212 Magic.size() + sizeof(Size), 0);
1213 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1214 std::copy(reinterpret_cast<char *>(&Size),
1215 reinterpret_cast<char *>(&Size + 1),
1216 CompressedContents.begin() + Magic.size());
1220 // Return a single fragment containing the compressed contents of the whole
1221 // section. Null if the section was not compressed for any reason.
1222 static std::unique_ptr<MCDataFragment>
1223 getCompressedFragment(MCAsmLayout &Layout,
1224 MCSectionData::FragmentListType &Fragments) {
1225 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1227 // Gather the uncompressed data from all the fragments, recording the
1228 // alignment fragment, if seen, and any fixups.
1229 SmallVector<char, 128> UncompressedData =
1230 getUncompressedData(Layout, Fragments);
1232 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1234 zlib::Status Success = zlib::compress(
1235 StringRef(UncompressedData.data(), UncompressedData.size()),
1236 CompressedContents);
1237 if (Success != zlib::StatusOK)
1240 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1243 return CompressedFragment;
1246 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1249 static void UpdateSymbols(const MCAsmLayout &Layout,
1250 const std::vector<MCSymbolData *> &Symbols,
1251 MCFragment &NewFragment) {
1252 for (MCSymbolData *Sym : Symbols) {
1253 Sym->setOffset(Sym->getOffset() +
1254 Layout.getFragmentOffset(Sym->getFragment()));
1255 Sym->setFragment(&NewFragment);
1259 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1260 const DefiningSymbolMap &DefiningSymbols,
1261 const MCSectionELF &Section,
1262 MCSectionData &SD) {
1263 StringRef SectionName = Section.getSectionName();
1264 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1266 std::unique_ptr<MCDataFragment> CompressedFragment =
1267 getCompressedFragment(Layout, Fragments);
1269 // Leave the section as-is if the fragments could not be compressed.
1270 if (!CompressedFragment)
1273 // Update the fragment+offsets of any symbols referring to fragments in this
1274 // section to refer to the new fragment.
1275 auto I = DefiningSymbols.find(&SD);
1276 if (I != DefiningSymbols.end())
1277 UpdateSymbols(Layout, I->second, *CompressedFragment);
1279 // Invalidate the layout for the whole section since it will have new and
1280 // different fragments now.
1281 Layout.invalidateFragmentsFrom(&Fragments.front());
1284 // Complete the initialization of the new fragment
1285 CompressedFragment->setParent(&SD);
1286 CompressedFragment->setLayoutOrder(0);
1287 Fragments.push_back(CompressedFragment.release());
1289 // Rename from .debug_* to .zdebug_*
1290 Asm.getContext().renameELFSection(&Section,
1291 (".z" + SectionName.drop_front(1)).str());
1294 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1295 MCAsmLayout &Layout) {
1296 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1299 DefiningSymbolMap DefiningSymbols;
1301 for (MCSymbolData &SD : Asm.symbols())
1302 if (MCFragment *F = SD.getFragment())
1303 DefiningSymbols[F->getParent()].push_back(&SD);
1305 for (MCSectionData &SD : Asm) {
1306 const MCSectionELF &Section =
1307 static_cast<const MCSectionELF &>(SD.getSection());
1308 StringRef SectionName = Section.getSectionName();
1310 // Compressing debug_frame requires handling alignment fragments which is
1311 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1312 // for writing to arbitrary buffers) for little benefit.
1313 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1316 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1320 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) {
1321 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1322 MCSectionData &RelSD = *it;
1323 const MCSectionELF &RelSection =
1324 static_cast<const MCSectionELF &>(RelSD.getSection());
1326 unsigned Type = RelSection.getType();
1327 if (Type != ELF::SHT_REL && Type != ELF::SHT_RELA)
1330 const MCSectionELF *Section = RelSection.getAssociatedSection();
1331 MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1332 RelSD.setAlignment(is64Bit() ? 8 : 4);
1334 MCDataFragment *F = new MCDataFragment(&RelSD);
1335 WriteRelocationsFragment(Asm, F, &SD);
1339 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1340 uint64_t Flags, uint64_t Address,
1341 uint64_t Offset, uint64_t Size,
1342 uint32_t Link, uint32_t Info,
1344 uint64_t EntrySize) {
1345 Write32(Name); // sh_name: index into string table
1346 Write32(Type); // sh_type
1347 WriteWord(Flags); // sh_flags
1348 WriteWord(Address); // sh_addr
1349 WriteWord(Offset); // sh_offset
1350 WriteWord(Size); // sh_size
1351 Write32(Link); // sh_link
1352 Write32(Info); // sh_info
1353 WriteWord(Alignment); // sh_addralign
1354 WriteWord(EntrySize); // sh_entsize
1357 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1359 const MCSectionData *SD) {
1360 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1362 // Sort the relocation entries. Most targets just sort by Offset, but some
1363 // (e.g., MIPS) have additional constraints.
1364 TargetObjectWriter->sortRelocs(Asm, Relocs);
1366 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1367 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1369 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1372 write(*F, Entry.Offset);
1373 if (TargetObjectWriter->isN64()) {
1374 write(*F, uint32_t(Index));
1376 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1377 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1378 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1379 write(*F, TargetObjectWriter->getRType(Entry.Type));
1381 struct ELF::Elf64_Rela ERE64;
1382 ERE64.setSymbolAndType(Index, Entry.Type);
1383 write(*F, ERE64.r_info);
1385 if (hasRelocationAddend())
1386 write(*F, Entry.Addend);
1388 write(*F, uint32_t(Entry.Offset));
1390 struct ELF::Elf32_Rela ERE32;
1391 ERE32.setSymbolAndType(Index, Entry.Type);
1392 write(*F, ERE32.r_info);
1394 if (hasRelocationAddend())
1395 write(*F, uint32_t(Entry.Addend));
1400 void ELFObjectWriter::CreateMetadataSections(
1401 MCAssembler &Asm, MCAsmLayout &Layout, SectionIndexMapTy &SectionIndexMap) {
1402 MCContext &Ctx = Asm.getContext();
1405 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1407 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1408 const MCSectionELF *ShstrtabSection =
1409 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1410 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1411 ShstrtabSD.setAlignment(1);
1412 ShstrtabIndex = SectionIndexMap.size() + 1;
1413 SectionIndexMap[ShstrtabSection] = ShstrtabIndex;
1415 const MCSectionELF *SymtabSection =
1416 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1418 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1419 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1420 SymbolTableIndex = SectionIndexMap.size() + 1;
1421 SectionIndexMap[SymtabSection] = SymbolTableIndex;
1423 const MCSectionELF *StrtabSection;
1424 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1425 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1426 StrtabSD.setAlignment(1);
1427 StringTableIndex = SectionIndexMap.size() + 1;
1428 SectionIndexMap[StrtabSection] = StringTableIndex;
1431 F = new MCDataFragment(&SymtabSD);
1432 WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
1434 F = new MCDataFragment(&StrtabSD);
1435 F->getContents().append(StrTabBuilder.data().begin(),
1436 StrTabBuilder.data().end());
1438 F = new MCDataFragment(&ShstrtabSD);
1440 // Section header string table.
1441 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1442 const MCSectionELF &Section =
1443 static_cast<const MCSectionELF&>(it->getSection());
1444 ShStrTabBuilder.add(Section.getSectionName());
1446 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1447 F->getContents().append(ShStrTabBuilder.data().begin(),
1448 ShStrTabBuilder.data().end());
1451 void ELFObjectWriter::createIndexedSections(
1452 MCAssembler &Asm, MCAsmLayout &Layout, GroupMapTy &GroupMap,
1453 RevGroupMapTy &RevGroupMap, SectionIndexMapTy &SectionIndexMap) {
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);
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()) {
1509 case ELF::SHT_DYNAMIC:
1510 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1514 case ELF::SHT_RELA: {
1515 sh_link = SymbolTableIndex;
1516 assert(sh_link && ".symtab not found");
1517 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1518 sh_info = SectionIndexMap.lookup(InfoSection);
1522 case ELF::SHT_SYMTAB:
1523 case ELF::SHT_DYNSYM:
1524 sh_link = StringTableIndex;
1525 sh_info = LastLocalSymbolIndex;
1528 case ELF::SHT_SYMTAB_SHNDX:
1529 sh_link = SymbolTableIndex;
1532 case ELF::SHT_GROUP:
1533 sh_link = SymbolTableIndex;
1534 sh_info = GroupSymbolIndex;
1538 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1539 Section.getType() == ELF::SHT_ARM_EXIDX)
1540 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1542 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1544 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1545 Alignment, Section.getEntrySize());
1548 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1549 return SD.getOrdinal() == ~UINT32_C(0) &&
1550 !SD.getSection().isVirtualSection();
1553 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1555 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1557 const MCFragment &F = *i;
1558 assert(F.getKind() == MCFragment::FT_Data);
1559 Ret += cast<MCDataFragment>(F).getContents().size();
1564 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1565 const MCSectionData &SD) {
1566 if (IsELFMetaDataSection(SD))
1567 return DataSectionSize(SD);
1568 return Layout.getSectionAddressSize(&SD);
1571 void ELFObjectWriter::writeDataSectionData(MCAssembler &Asm,
1572 const MCAsmLayout &Layout,
1573 const MCSectionData &SD) {
1574 if (IsELFMetaDataSection(SD)) {
1575 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1577 const MCFragment &F = *i;
1578 assert(F.getKind() == MCFragment::FT_Data);
1579 WriteBytes(cast<MCDataFragment>(F).getContents());
1582 Asm.writeSectionData(&SD, Layout);
1586 void ELFObjectWriter::writeSectionHeader(
1587 ArrayRef<const MCSectionELF *> Sections, MCAssembler &Asm,
1588 const GroupMapTy &GroupMap, const MCAsmLayout &Layout,
1589 const SectionIndexMapTy &SectionIndexMap,
1590 const SectionOffsetMapTy &SectionOffsetMap) {
1591 const unsigned NumSections = Asm.size();
1593 // Null section first.
1594 uint64_t FirstSectionSize =
1595 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1596 uint32_t FirstSectionLink =
1597 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1598 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1600 for (unsigned i = 0; i < NumSections; ++i) {
1601 const MCSectionELF &Section = *Sections[i];
1602 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1603 uint32_t GroupSymbolIndex;
1604 if (Section.getType() != ELF::SHT_GROUP)
1605 GroupSymbolIndex = 0;
1607 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1608 GroupMap.lookup(&Section));
1610 uint64_t Size = GetSectionAddressSize(Layout, SD);
1612 writeSection(Asm, SectionIndexMap, GroupSymbolIndex,
1613 SectionOffsetMap.lookup(&Section), Size, SD.getAlignment(),
1618 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1619 const MCAsmLayout &Layout) {
1620 GroupMapTy GroupMap;
1621 RevGroupMapTy RevGroupMap;
1622 SectionIndexMapTy SectionIndexMap;
1624 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1625 createIndexedSections(Asm, const_cast<MCAsmLayout &>(Layout), GroupMap,
1626 RevGroupMap, SectionIndexMap);
1628 // Compute symbol table information.
1629 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1631 WriteRelocations(Asm, const_cast<MCAsmLayout &>(Layout));
1633 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1634 const_cast<MCAsmLayout&>(Layout),
1637 unsigned NumSections = Asm.size();
1638 std::vector<const MCSectionELF*> Sections;
1639 Sections.resize(NumSections);
1641 for (auto &Pair : SectionIndexMap)
1642 Sections[Pair.second - 1] = Pair.first;
1644 SectionOffsetMapTy SectionOffsetMap;
1646 // Write out the ELF header ...
1647 WriteHeader(Asm, NumSections + 1);
1649 // ... then the sections ...
1650 for (unsigned i = 0; i < NumSections; ++i) {
1651 const MCSectionELF &Section = *Sections[i];
1652 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1653 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1654 WriteZeros(Padding);
1656 // Remember the offset into the file for this section.
1657 SectionOffsetMap[&Section] = OS.tell();
1659 writeDataSectionData(Asm, Layout, SD);
1662 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1663 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1664 WriteZeros(Padding);
1666 const unsigned SectionHeaderOffset = OS.tell();
1668 // ... then the section header table ...
1669 writeSectionHeader(Sections, Asm, GroupMap, Layout, SectionIndexMap,
1673 uint64_t Val = SectionHeaderOffset;
1674 if (sys::IsLittleEndianHost != IsLittleEndian)
1675 sys::swapByteOrder(Val);
1676 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1677 offsetof(ELF::Elf64_Ehdr, e_shoff));
1679 uint32_t Val = SectionHeaderOffset;
1680 if (sys::IsLittleEndianHost != IsLittleEndian)
1681 sys::swapByteOrder(Val);
1682 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1683 offsetof(ELF::Elf32_Ehdr, e_shoff));
1687 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1688 const MCAssembler &Asm, const MCSymbolData &DataA,
1689 const MCSymbolData *DataB, const MCFragment &FB, bool InSet,
1690 bool IsPCRel) const {
1691 if (!InSet && (::isWeak(DataA) || (DataB && ::isWeak(*DataB))))
1693 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1694 Asm, DataA, DataB, FB, InSet, IsPCRel);
1697 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
1698 return ::isWeak(SD);
1701 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1702 raw_pwrite_stream &OS,
1703 bool IsLittleEndian) {
1704 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);