1 //===- lib/MC/ELFObjectWriter.cpp - ELF File Writer -----------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements ELF object file writer information.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/MC/MCELFObjectWriter.h"
15 #include "llvm/ADT/STLExtras.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/ADT/SmallString.h"
18 #include "llvm/ADT/StringMap.h"
19 #include "llvm/MC/MCAsmBackend.h"
20 #include "llvm/MC/MCAsmInfo.h"
21 #include "llvm/MC/MCAsmLayout.h"
22 #include "llvm/MC/MCAssembler.h"
23 #include "llvm/MC/MCContext.h"
24 #include "llvm/MC/MCELF.h"
25 #include "llvm/MC/MCELFSymbolFlags.h"
26 #include "llvm/MC/MCExpr.h"
27 #include "llvm/MC/MCFixupKindInfo.h"
28 #include "llvm/MC/MCObjectWriter.h"
29 #include "llvm/MC/MCSectionELF.h"
30 #include "llvm/MC/MCValue.h"
31 #include "llvm/MC/StringTableBuilder.h"
32 #include "llvm/Support/Compression.h"
33 #include "llvm/Support/Debug.h"
34 #include "llvm/Support/ELF.h"
35 #include "llvm/Support/Endian.h"
36 #include "llvm/Support/ErrorHandling.h"
41 #define DEBUG_TYPE "reloc-info"
44 class FragmentWriter {
48 FragmentWriter(bool IsLittleEndian);
49 template <typename T> void write(MCDataFragment &F, T Val);
52 typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
54 class SymbolTableWriter {
56 FragmentWriter &FWriter;
58 std::vector<const MCSectionELF *> &Sections;
60 // The symbol .symtab fragment we are writting to.
61 MCDataFragment *SymtabF;
63 // .symtab_shndx fragment we are writting to.
64 MCDataFragment *ShndxF;
66 // The numbel of symbols written so far.
69 void createSymtabShndx();
71 template <typename T> void write(MCDataFragment &F, T Value);
74 SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
75 std::vector<const MCSectionELF *> &Sections,
76 MCDataFragment *SymtabF);
78 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
79 uint8_t other, uint32_t shndx, bool Reserved);
82 class ELFObjectWriter : public MCObjectWriter {
83 FragmentWriter FWriter;
87 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
88 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
89 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
90 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data,
91 bool Used, bool Renamed);
92 static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
93 static bool IsELFMetaDataSection(const MCSectionData &SD);
95 void writeDataSectionData(MCAssembler &Asm, const MCAsmLayout &Layout,
96 const MCSectionData &SD);
98 /// Helper struct for containing some precomputed information on symbols.
99 struct ELFSymbolData {
100 MCSymbolData *SymbolData;
101 uint64_t StringIndex;
102 uint32_t SectionIndex;
105 // Support lexicographic sorting.
106 bool operator<(const ELFSymbolData &RHS) const {
107 unsigned LHSType = MCELF::GetType(*SymbolData);
108 unsigned RHSType = MCELF::GetType(*RHS.SymbolData);
109 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
111 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
113 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
114 return SectionIndex < RHS.SectionIndex;
115 return Name < RHS.Name;
119 /// The target specific ELF writer instance.
120 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
122 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
123 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
124 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
126 llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
128 StringTableBuilder ShStrTabBuilder;
131 /// @name Symbol Table Data
134 StringTableBuilder StrTabBuilder;
135 std::vector<uint64_t> FileSymbolData;
136 std::vector<ELFSymbolData> LocalSymbolData;
137 std::vector<ELFSymbolData> ExternalSymbolData;
138 std::vector<ELFSymbolData> UndefinedSymbolData;
144 // This holds the symbol table index of the last local symbol.
145 unsigned LastLocalSymbolIndex;
146 // This holds the .strtab section index.
147 unsigned StringTableIndex;
148 // This holds the .symtab section index.
149 unsigned SymbolTableIndex;
151 unsigned ShstrtabIndex;
154 // TargetObjectWriter wrappers.
155 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
156 bool hasRelocationAddend() const {
157 return TargetObjectWriter->hasRelocationAddend();
159 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
160 bool IsPCRel) const {
161 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
165 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
167 : MCObjectWriter(OS, IsLittleEndian), FWriter(IsLittleEndian),
168 TargetObjectWriter(MOTW), NeedsGOT(false) {}
170 void reset() override {
172 WeakrefUsedInReloc.clear();
175 ShStrTabBuilder.clear();
176 StrTabBuilder.clear();
177 FileSymbolData.clear();
178 LocalSymbolData.clear();
179 ExternalSymbolData.clear();
180 UndefinedSymbolData.clear();
181 MCObjectWriter::reset();
184 ~ELFObjectWriter() override;
186 void WriteWord(uint64_t W) {
193 template <typename T> void write(MCDataFragment &F, T Value) {
194 FWriter.write(F, Value);
197 void WriteHeader(const MCAssembler &Asm,
198 unsigned NumberOfSections);
200 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
201 const MCAsmLayout &Layout);
203 void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm,
204 const MCAsmLayout &Layout,
205 std::vector<const MCSectionELF *> &Sections);
207 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
208 const MCSymbolRefExpr *RefA,
209 const MCSymbolData *SD, uint64_t C,
210 unsigned Type) const;
212 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
213 const MCFragment *Fragment, const MCFixup &Fixup,
214 MCValue Target, bool &IsPCRel,
215 uint64_t &FixedValue) override;
217 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
220 // Map from a signature symbol to the group section index
221 typedef DenseMap<const MCSymbol *, unsigned> RevGroupMapTy;
222 // Start and end offset of each section
223 typedef std::vector<std::pair<uint64_t, uint64_t>> SectionOffsetsTy;
225 /// Compute the symbol table data
227 /// \param Asm - The assembler.
228 /// \param SectionIndexMap - Maps a section to its index.
229 /// \param RevGroupMap - Maps a signature symbol to the group section.
230 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
231 const SectionIndexMapTy &SectionIndexMap,
232 const RevGroupMapTy &RevGroupMap);
234 void maybeAddToGroup(MCAssembler &Asm,
235 ArrayRef<const MCSectionELF *> Sections,
236 const RevGroupMapTy &RevGroupMap,
237 const MCSectionELF &Section, unsigned Index);
239 void computeIndexMap(MCAssembler &Asm,
240 std::vector<const MCSectionELF *> &Sections,
241 SectionIndexMapTy &SectionIndexMap,
242 const RevGroupMapTy &RevGroupMap);
244 void createRelocationSection(MCAssembler &Asm, const MCSectionData &SD);
246 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
248 void WriteRelocations(MCAssembler &Asm, const MCAsmLayout &Layout);
250 void CreateMetadataSections(MCAssembler &Asm, const MCAsmLayout &Layout,
251 std::vector<const MCSectionELF *> &Sections);
253 // Create the sections that show up in the symbol table. Currently
254 // those are the .note.GNU-stack section and the group sections.
255 void createIndexedSections(MCAssembler &Asm, const MCAsmLayout &Layout,
256 RevGroupMapTy &RevGroupMap,
257 std::vector<const MCSectionELF *> &Sections,
258 SectionIndexMapTy &SectionIndexMap);
260 void ExecutePostLayoutBinding(MCAssembler &Asm,
261 const MCAsmLayout &Layout) override;
263 void writeSectionHeader(ArrayRef<const MCSectionELF *> Sections,
264 MCAssembler &Asm, const MCAsmLayout &Layout,
265 const SectionIndexMapTy &SectionIndexMap,
266 const SectionOffsetsTy &SectionOffsets);
268 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
269 uint64_t Address, uint64_t Offset,
270 uint64_t Size, uint32_t Link, uint32_t Info,
271 uint64_t Alignment, uint64_t EntrySize);
273 void WriteRelocationsFragment(const MCAssembler &Asm,
275 const MCSectionData *SD);
278 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
279 const MCSymbolData &DataA,
280 const MCFragment &FB,
282 bool IsPCRel) const override;
284 bool isWeak(const MCSymbolData &SD) const override;
286 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
287 void writeSection(MCAssembler &Asm,
288 const SectionIndexMapTy &SectionIndexMap,
289 uint32_t GroupSymbolIndex,
290 uint64_t Offset, uint64_t Size, uint64_t Alignment,
291 const MCSectionELF &Section);
295 FragmentWriter::FragmentWriter(bool IsLittleEndian)
296 : IsLittleEndian(IsLittleEndian) {}
298 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
300 Val = support::endian::byte_swap<T, support::little>(Val);
302 Val = support::endian::byte_swap<T, support::big>(Val);
303 const char *Start = (const char *)&Val;
304 F.getContents().append(Start, Start + sizeof(T));
307 void SymbolTableWriter::createSymtabShndx() {
311 MCContext &Ctx = Asm.getContext();
312 const MCSectionELF *SymtabShndxSection =
313 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
314 MCSectionData *SymtabShndxSD =
315 &Asm.getOrCreateSectionData(*SymtabShndxSection);
316 SymtabShndxSD->setAlignment(4);
317 ShndxF = new MCDataFragment(SymtabShndxSD);
318 Sections.push_back(SymtabShndxSection);
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(
330 MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
331 std::vector<const MCSectionELF *> &Sections, MCDataFragment *SymtabF)
332 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit), Sections(Sections),
333 SymtabF(SymtabF), ShndxF(nullptr), NumWritten(0) {}
335 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
336 uint64_t size, uint8_t other,
337 uint32_t shndx, bool Reserved) {
338 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
345 write(*ShndxF, shndx);
347 write(*ShndxF, uint32_t(0));
350 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
353 write(*SymtabF, name); // st_name
354 write(*SymtabF, info); // st_info
355 write(*SymtabF, other); // st_other
356 write(*SymtabF, Index); // st_shndx
357 write(*SymtabF, value); // st_value
358 write(*SymtabF, size); // st_size
360 write(*SymtabF, name); // st_name
361 write(*SymtabF, uint32_t(value)); // st_value
362 write(*SymtabF, uint32_t(size)); // st_size
363 write(*SymtabF, info); // st_info
364 write(*SymtabF, other); // st_other
365 write(*SymtabF, Index); // st_shndx
371 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
372 const MCFixupKindInfo &FKI =
373 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
375 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
378 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
382 case MCSymbolRefExpr::VK_GOT:
383 case MCSymbolRefExpr::VK_PLT:
384 case MCSymbolRefExpr::VK_GOTPCREL:
385 case MCSymbolRefExpr::VK_GOTOFF:
386 case MCSymbolRefExpr::VK_TPOFF:
387 case MCSymbolRefExpr::VK_TLSGD:
388 case MCSymbolRefExpr::VK_GOTTPOFF:
389 case MCSymbolRefExpr::VK_INDNTPOFF:
390 case MCSymbolRefExpr::VK_NTPOFF:
391 case MCSymbolRefExpr::VK_GOTNTPOFF:
392 case MCSymbolRefExpr::VK_TLSLDM:
393 case MCSymbolRefExpr::VK_DTPOFF:
394 case MCSymbolRefExpr::VK_TLSLD:
399 ELFObjectWriter::~ELFObjectWriter()
402 // Emit the ELF header.
403 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
404 unsigned NumberOfSections) {
410 // emitWord method behaves differently for ELF32 and ELF64, writing
411 // 4 bytes in the former and 8 in the latter.
413 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
415 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
418 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
420 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
422 Write8(TargetObjectWriter->getOSABI());
423 Write8(0); // e_ident[EI_ABIVERSION]
425 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
427 Write16(ELF::ET_REL); // e_type
429 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
431 Write32(ELF::EV_CURRENT); // e_version
432 WriteWord(0); // e_entry, no entry point in .o file
433 WriteWord(0); // e_phoff, no program header for .o
434 WriteWord(0); // e_shoff = sec hdr table off in bytes
436 // e_flags = whatever the target wants
437 Write32(Asm.getELFHeaderEFlags());
439 // e_ehsize = ELF header size
440 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
442 Write16(0); // e_phentsize = prog header entry size
443 Write16(0); // e_phnum = # prog header entries = 0
445 // e_shentsize = Section header entry size
446 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
448 // e_shnum = # of section header ents
449 if (NumberOfSections >= ELF::SHN_LORESERVE)
450 Write16(ELF::SHN_UNDEF);
452 Write16(NumberOfSections);
454 // e_shstrndx = Section # of '.shstrtab'
455 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
456 Write16(ELF::SHN_XINDEX);
458 Write16(ShstrtabIndex);
461 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
462 const MCAsmLayout &Layout) {
463 if (Data.isCommon() && Data.isExternal())
464 return Data.getCommonAlignment();
467 if (!Layout.getSymbolOffset(&Data, Res))
470 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
476 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
477 const MCAsmLayout &Layout) {
478 // The presence of symbol versions causes undefined symbols and
479 // versions declared with @@@ to be renamed.
481 for (MCSymbolData &OriginalData : Asm.symbols()) {
482 const MCSymbol &Alias = OriginalData.getSymbol();
485 if (!Alias.isVariable())
487 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
490 const MCSymbol &Symbol = Ref->getSymbol();
491 MCSymbolData &SD = Asm.getSymbolData(Symbol);
493 StringRef AliasName = Alias.getName();
494 size_t Pos = AliasName.find('@');
495 if (Pos == StringRef::npos)
498 // Aliases defined with .symvar copy the binding from the symbol they alias.
499 // This is the first place we are able to copy this information.
500 OriginalData.setExternal(SD.isExternal());
501 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
503 StringRef Rest = AliasName.substr(Pos);
504 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
507 // FIXME: produce a better error message.
508 if (Symbol.isUndefined() && Rest.startswith("@@") &&
509 !Rest.startswith("@@@"))
510 report_fatal_error("A @@ version cannot be undefined");
512 Renames.insert(std::make_pair(&Symbol, &Alias));
516 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
517 uint8_t Type = newType;
519 // Propagation rules:
520 // IFUNC > FUNC > OBJECT > NOTYPE
521 // TLS_OBJECT > OBJECT > NOTYPE
523 // dont let the new type degrade the old type
527 case ELF::STT_GNU_IFUNC:
528 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
529 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
530 Type = ELF::STT_GNU_IFUNC;
533 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
534 Type == ELF::STT_TLS)
535 Type = ELF::STT_FUNC;
537 case ELF::STT_OBJECT:
538 if (Type == ELF::STT_NOTYPE)
539 Type = ELF::STT_OBJECT;
542 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
543 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
551 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
552 const MCAsmLayout &Layout) {
553 MCSymbolData &OrigData = *MSD.SymbolData;
554 assert((!OrigData.getFragment() ||
555 (&OrigData.getFragment()->getParent()->getSection() ==
556 &OrigData.getSymbol().getSection())) &&
557 "The symbol's section doesn't match the fragment's symbol");
558 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
560 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
562 bool IsReserved = !Base || OrigData.isCommon();
564 // Binding and Type share the same byte as upper and lower nibbles
565 uint8_t Binding = MCELF::GetBinding(OrigData);
566 uint8_t Type = MCELF::GetType(OrigData);
567 MCSymbolData *BaseSD = nullptr;
569 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
570 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
572 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
574 // Other and Visibility share the same byte with Visibility using the lower
576 uint8_t Visibility = MCELF::GetVisibility(OrigData);
577 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
580 uint64_t Value = SymbolValue(OrigData, Layout);
583 const MCExpr *ESize = OrigData.getSize();
585 ESize = BaseSD->getSize();
589 if (!ESize->evaluateKnownAbsolute(Res, Layout))
590 report_fatal_error("Size expression must be absolute.");
594 // Write out the symbol table entry
595 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
596 MSD.SectionIndex, IsReserved);
599 void ELFObjectWriter::WriteSymbolTable(
600 MCDataFragment *SymtabF, MCAssembler &Asm, const MCAsmLayout &Layout,
601 std::vector<const MCSectionELF *> &Sections) {
602 // The string table must be emitted first because we need the index
603 // into the string table for all the symbol names.
605 // FIXME: Make sure the start of the symbol table is aligned.
607 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), Sections, SymtabF);
609 // The first entry is the undefined symbol entry.
610 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
612 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
613 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
614 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
617 // Write the symbol table entries.
618 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
620 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
621 ELFSymbolData &MSD = LocalSymbolData[i];
622 WriteSymbol(Writer, MSD, Layout);
625 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
626 ELFSymbolData &MSD = ExternalSymbolData[i];
627 MCSymbolData &Data = *MSD.SymbolData;
628 assert(((Data.getFlags() & ELF_STB_Global) ||
629 (Data.getFlags() & ELF_STB_Weak)) &&
630 "External symbol requires STB_GLOBAL or STB_WEAK flag");
631 WriteSymbol(Writer, MSD, Layout);
632 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
633 LastLocalSymbolIndex++;
636 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
637 ELFSymbolData &MSD = UndefinedSymbolData[i];
638 MCSymbolData &Data = *MSD.SymbolData;
639 WriteSymbol(Writer, MSD, Layout);
640 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
641 LastLocalSymbolIndex++;
645 // It is always valid to create a relocation with a symbol. It is preferable
646 // to use a relocation with a section if that is possible. Using the section
647 // allows us to omit some local symbols from the symbol table.
648 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
649 const MCSymbolRefExpr *RefA,
650 const MCSymbolData *SD,
652 unsigned Type) const {
653 // A PCRel relocation to an absolute value has no symbol (or section). We
654 // represent that with a relocation to a null section.
658 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
662 // The .odp creation emits a relocation against the symbol ".TOC." which
663 // create a R_PPC64_TOC relocation. However the relocation symbol name
664 // in final object creation should be NULL, since the symbol does not
665 // really exist, it is just the reference to TOC base for the current
666 // object file. Since the symbol is undefined, returning false results
667 // in a relocation with a null section which is the desired result.
668 case MCSymbolRefExpr::VK_PPC_TOCBASE:
671 // These VariantKind cause the relocation to refer to something other than
672 // the symbol itself, like a linker generated table. Since the address of
673 // symbol is not relevant, we cannot replace the symbol with the
674 // section and patch the difference in the addend.
675 case MCSymbolRefExpr::VK_GOT:
676 case MCSymbolRefExpr::VK_PLT:
677 case MCSymbolRefExpr::VK_GOTPCREL:
678 case MCSymbolRefExpr::VK_Mips_GOT:
679 case MCSymbolRefExpr::VK_PPC_GOT_LO:
680 case MCSymbolRefExpr::VK_PPC_GOT_HI:
681 case MCSymbolRefExpr::VK_PPC_GOT_HA:
685 // An undefined symbol is not in any section, so the relocation has to point
686 // to the symbol itself.
687 const MCSymbol &Sym = SD->getSymbol();
688 if (Sym.isUndefined())
691 unsigned Binding = MCELF::GetBinding(*SD);
694 llvm_unreachable("Invalid Binding");
698 // If the symbol is weak, it might be overridden by a symbol in another
699 // file. The relocation has to point to the symbol so that the linker
702 case ELF::STB_GLOBAL:
703 // Global ELF symbols can be preempted by the dynamic linker. The relocation
704 // has to point to the symbol for a reason analogous to the STB_WEAK case.
708 // If a relocation points to a mergeable section, we have to be careful.
709 // If the offset is zero, a relocation with the section will encode the
710 // same information. With a non-zero offset, the situation is different.
711 // For example, a relocation can point 42 bytes past the end of a string.
712 // If we change such a relocation to use the section, the linker would think
713 // that it pointed to another string and subtracting 42 at runtime will
714 // produce the wrong value.
715 auto &Sec = cast<MCSectionELF>(Sym.getSection());
716 unsigned Flags = Sec.getFlags();
717 if (Flags & ELF::SHF_MERGE) {
721 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
722 // only handle section relocations to mergeable sections if using RELA.
723 if (!hasRelocationAddend())
727 // Most TLS relocations use a got, so they need the symbol. Even those that
728 // are just an offset (@tpoff), require a symbol in gold versions before
729 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
730 // http://sourceware.org/PR16773.
731 if (Flags & ELF::SHF_TLS)
734 // If the symbol is a thumb function the final relocation must set the lowest
735 // bit. With a symbol that is done by just having the symbol have that bit
736 // set, so we would lose the bit if we relocated with the section.
737 // FIXME: We could use the section but add the bit to the relocation value.
738 if (Asm.isThumbFunc(&Sym))
741 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
746 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
747 const MCSymbol &Sym = Ref.getSymbol();
749 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
752 if (!Sym.isVariable())
755 const MCExpr *Expr = Sym.getVariableValue();
756 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
760 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
761 return &Inner->getSymbol();
765 // True if the assembler knows nothing about the final value of the symbol.
766 // This doesn't cover the comdat issues, since in those cases the assembler
767 // can at least know that all symbols in the section will move together.
768 static bool isWeak(const MCSymbolData &D) {
769 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
772 switch (MCELF::GetBinding(D)) {
774 llvm_unreachable("Unknown binding");
777 case ELF::STB_GLOBAL:
780 case ELF::STB_GNU_UNIQUE:
785 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
786 const MCAsmLayout &Layout,
787 const MCFragment *Fragment,
788 const MCFixup &Fixup, MCValue Target,
789 bool &IsPCRel, uint64_t &FixedValue) {
790 const MCSectionData *FixupSection = Fragment->getParent();
791 uint64_t C = Target.getConstant();
792 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
794 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
795 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
796 "Should not have constructed this");
798 // Let A, B and C being the components of Target and R be the location of
799 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
800 // If it is pcrel, we want to compute (A - B + C - R).
802 // In general, ELF has no relocations for -B. It can only represent (A + C)
803 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
804 // replace B to implement it: (A - R - K + C)
806 Asm.getContext().FatalError(
808 "No relocation available to represent this relative expression");
810 const MCSymbol &SymB = RefB->getSymbol();
812 if (SymB.isUndefined())
813 Asm.getContext().FatalError(
815 Twine("symbol '") + SymB.getName() +
816 "' can not be undefined in a subtraction expression");
818 assert(!SymB.isAbsolute() && "Should have been folded");
819 const MCSection &SecB = SymB.getSection();
820 if (&SecB != &FixupSection->getSection())
821 Asm.getContext().FatalError(
822 Fixup.getLoc(), "Cannot represent a difference across sections");
824 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
826 Asm.getContext().FatalError(
827 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
829 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
830 uint64_t K = SymBOffset - FixupOffset;
835 // We either rejected the fixup or folded B into C at this point.
836 const MCSymbolRefExpr *RefA = Target.getSymA();
837 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
838 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
840 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
841 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
842 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
843 C += Layout.getSymbolOffset(SymAD);
846 if (hasRelocationAddend()) {
853 // FIXME: What is this!?!?
854 MCSymbolRefExpr::VariantKind Modifier =
855 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
856 if (RelocNeedsGOT(Modifier))
859 if (!RelocateWithSymbol) {
860 const MCSection *SecA =
861 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
862 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
863 MCSymbol *SectionSymbol =
864 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
866 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
867 Relocations[FixupSection].push_back(Rec);
872 if (const MCSymbol *R = Renames.lookup(SymA))
875 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
876 WeakrefUsedInReloc.insert(WeakRef);
878 UsedInReloc.insert(SymA);
880 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
881 Relocations[FixupSection].push_back(Rec);
887 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
889 const MCSymbolData &SD = Asm.getSymbolData(*S);
890 return SD.getIndex();
893 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
894 const MCSymbolData &Data, bool Used,
896 const MCSymbol &Symbol = Data.getSymbol();
897 if (Symbol.isVariable()) {
898 const MCExpr *Expr = Symbol.getVariableValue();
899 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
900 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
911 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
914 if (Symbol.isVariable()) {
915 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
916 if (Base && Base->isUndefined())
920 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
921 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
924 if (Symbol.isTemporary())
930 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
931 if (Data.isExternal())
934 const MCSymbol &Symbol = Data.getSymbol();
935 if (Symbol.isDefined())
944 void ELFObjectWriter::maybeAddToGroup(MCAssembler &Asm,
945 ArrayRef<const MCSectionELF *> Sections,
946 const RevGroupMapTy &RevGroupMap,
947 const MCSectionELF &Section,
949 const MCSymbol *Sym = Section.getGroup();
952 const MCSectionELF *Group = Sections[RevGroupMap.lookup(Sym) - 1];
953 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
954 // FIXME: we could use the previous fragment
955 MCDataFragment *F = new MCDataFragment(&Data);
959 void ELFObjectWriter::computeIndexMap(
960 MCAssembler &Asm, std::vector<const MCSectionELF *> &Sections,
961 SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap) {
962 for (const MCSectionData &SD : Asm) {
963 const MCSectionELF &Section =
964 static_cast<const MCSectionELF &>(SD.getSection());
965 if (Section.getType() == ELF::SHT_GROUP)
967 Sections.push_back(&Section);
968 unsigned Index = Sections.size();
969 SectionIndexMap[&Section] = Index;
970 maybeAddToGroup(Asm, Sections, RevGroupMap, Section, Index);
971 createRelocationSection(Asm, SD);
975 void ELFObjectWriter::computeSymbolTable(
976 MCAssembler &Asm, const MCAsmLayout &Layout,
977 const SectionIndexMapTy &SectionIndexMap,
978 const RevGroupMapTy &RevGroupMap) {
979 // FIXME: Is this the correct place to do this?
980 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
982 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
983 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
984 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
985 Data.setExternal(true);
986 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
989 // Add the data for the symbols.
990 for (MCSymbolData &SD : Asm.symbols()) {
991 const MCSymbol &Symbol = SD.getSymbol();
993 bool Used = UsedInReloc.count(&Symbol);
994 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
995 bool isSignature = RevGroupMap.count(&Symbol);
997 if (!isInSymtab(Layout, SD,
998 Used || WeakrefUsed || isSignature,
999 Renames.count(&Symbol)))
1003 MSD.SymbolData = &SD;
1004 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
1006 // Undefined symbols are global, but this is the first place we
1007 // are able to set it.
1008 bool Local = isLocal(SD, Used);
1009 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1011 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1012 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1013 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1017 MSD.SectionIndex = ELF::SHN_ABS;
1018 } else if (SD.isCommon()) {
1020 MSD.SectionIndex = ELF::SHN_COMMON;
1021 } else if (BaseSymbol->isUndefined()) {
1022 if (isSignature && !Used)
1023 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
1025 MSD.SectionIndex = ELF::SHN_UNDEF;
1026 if (!Used && WeakrefUsed)
1027 MCELF::SetBinding(SD, ELF::STB_WEAK);
1029 const MCSectionELF &Section =
1030 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1031 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1032 assert(MSD.SectionIndex && "Invalid section index!");
1035 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
1038 // FIXME: All name handling should be done before we get to the writer,
1039 // including dealing with GNU-style version suffixes. Fixing this isn't
1042 // We thus have to be careful to not perform the symbol version replacement
1045 // The ELF format is used on Windows by the MCJIT engine. Thus, on
1046 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
1047 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
1048 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
1049 // the EFLObjectWriter should not interpret the "@@@" sub-string as
1050 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1051 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1052 // "__imp_?" or "__imp_@?".
1054 // It would have been interesting to perform the MS mangling prefix check
1055 // only when the target triple is of the form *-pc-windows-elf. But, it
1056 // seems that this information is not easily accessible from the
1058 StringRef Name = Symbol.getName();
1059 if (!Name.startswith("?") && !Name.startswith("@?") &&
1060 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1061 // This symbol isn't following the MSVC C++ name mangling convention. We
1062 // can thus safely interpret the @@@ in symbol names as specifying symbol
1064 SmallString<32> Buf;
1065 size_t Pos = Name.find("@@@");
1066 if (Pos != StringRef::npos) {
1067 Buf += Name.substr(0, Pos);
1068 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1069 Buf += Name.substr(Pos + Skip);
1074 // Sections have their own string table
1075 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1076 MSD.Name = StrTabBuilder.add(Name);
1078 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1079 UndefinedSymbolData.push_back(MSD);
1081 LocalSymbolData.push_back(MSD);
1083 ExternalSymbolData.push_back(MSD);
1086 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1087 StrTabBuilder.add(*i);
1089 StrTabBuilder.finalize(StringTableBuilder::ELF);
1091 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1092 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1094 for (ELFSymbolData &MSD : LocalSymbolData)
1095 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1097 : StrTabBuilder.getOffset(MSD.Name);
1098 for (ELFSymbolData &MSD : ExternalSymbolData)
1099 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1100 for (ELFSymbolData& MSD : UndefinedSymbolData)
1101 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1103 // Symbols are required to be in lexicographic order.
1104 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1105 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1106 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1108 // Set the symbol indices. Local symbols must come before all other
1109 // symbols with non-local bindings.
1110 unsigned Index = FileSymbolData.size() + 1;
1111 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1112 LocalSymbolData[i].SymbolData->setIndex(Index++);
1114 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1115 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1116 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1117 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1120 void ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1121 const MCSectionData &SD) {
1122 if (Relocations[&SD].empty())
1125 MCContext &Ctx = Asm.getContext();
1126 const MCSectionELF &Section =
1127 static_cast<const MCSectionELF &>(SD.getSection());
1129 const StringRef SectionName = Section.getSectionName();
1130 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1131 RelaSectionName += SectionName;
1134 if (hasRelocationAddend())
1135 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1137 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1140 if (Section.getFlags() & ELF::SHF_GROUP)
1141 Flags = ELF::SHF_GROUP;
1143 const MCSectionELF *RelaSection = Ctx.createELFRelSection(
1144 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1145 Flags, EntrySize, Section.getGroup(), &Section);
1146 Asm.getOrCreateSectionData(*RelaSection);
1149 static SmallVector<char, 128>
1150 getUncompressedData(const MCAsmLayout &Layout,
1151 MCSectionData::FragmentListType &Fragments) {
1152 SmallVector<char, 128> UncompressedData;
1153 for (const MCFragment &F : Fragments) {
1154 const SmallVectorImpl<char> *Contents;
1155 switch (F.getKind()) {
1156 case MCFragment::FT_Data:
1157 Contents = &cast<MCDataFragment>(F).getContents();
1159 case MCFragment::FT_Dwarf:
1160 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1162 case MCFragment::FT_DwarfFrame:
1163 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1167 "Not expecting any other fragment types in a debug_* section");
1169 UncompressedData.append(Contents->begin(), Contents->end());
1171 return UncompressedData;
1174 // Include the debug info compression header:
1175 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1176 // useful for consumers to preallocate a buffer to decompress into.
1178 prependCompressionHeader(uint64_t Size,
1179 SmallVectorImpl<char> &CompressedContents) {
1180 const StringRef Magic = "ZLIB";
1181 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1183 if (sys::IsLittleEndianHost)
1184 sys::swapByteOrder(Size);
1185 CompressedContents.insert(CompressedContents.begin(),
1186 Magic.size() + sizeof(Size), 0);
1187 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1188 std::copy(reinterpret_cast<char *>(&Size),
1189 reinterpret_cast<char *>(&Size + 1),
1190 CompressedContents.begin() + Magic.size());
1194 // Return a single fragment containing the compressed contents of the whole
1195 // section. Null if the section was not compressed for any reason.
1196 static std::unique_ptr<MCDataFragment>
1197 getCompressedFragment(const MCAsmLayout &Layout,
1198 MCSectionData::FragmentListType &Fragments) {
1199 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1201 // Gather the uncompressed data from all the fragments, recording the
1202 // alignment fragment, if seen, and any fixups.
1203 SmallVector<char, 128> UncompressedData =
1204 getUncompressedData(Layout, Fragments);
1206 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1208 zlib::Status Success = zlib::compress(
1209 StringRef(UncompressedData.data(), UncompressedData.size()),
1210 CompressedContents);
1211 if (Success != zlib::StatusOK)
1214 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1217 return CompressedFragment;
1220 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1223 static void UpdateSymbols(const MCAsmLayout &Layout,
1224 const std::vector<MCSymbolData *> &Symbols,
1225 MCFragment &NewFragment) {
1226 for (MCSymbolData *Sym : Symbols) {
1227 Sym->setOffset(Sym->getOffset() +
1228 Layout.getFragmentOffset(Sym->getFragment()));
1229 Sym->setFragment(&NewFragment);
1233 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1234 const DefiningSymbolMap &DefiningSymbols,
1235 const MCSectionELF &Section,
1236 MCSectionData &SD) {
1237 StringRef SectionName = Section.getSectionName();
1238 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1240 std::unique_ptr<MCDataFragment> CompressedFragment =
1241 getCompressedFragment(Layout, Fragments);
1243 // Leave the section as-is if the fragments could not be compressed.
1244 if (!CompressedFragment)
1247 // Update the fragment+offsets of any symbols referring to fragments in this
1248 // section to refer to the new fragment.
1249 auto I = DefiningSymbols.find(&SD);
1250 if (I != DefiningSymbols.end())
1251 UpdateSymbols(Layout, I->second, *CompressedFragment);
1253 // Invalidate the layout for the whole section since it will have new and
1254 // different fragments now.
1255 Layout.invalidateFragmentsFrom(&Fragments.front());
1258 // Complete the initialization of the new fragment
1259 CompressedFragment->setParent(&SD);
1260 CompressedFragment->setLayoutOrder(0);
1261 Fragments.push_back(CompressedFragment.release());
1263 // Rename from .debug_* to .zdebug_*
1264 Asm.getContext().renameELFSection(&Section,
1265 (".z" + SectionName.drop_front(1)).str());
1268 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1269 MCAsmLayout &Layout) {
1270 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1273 DefiningSymbolMap DefiningSymbols;
1275 for (MCSymbolData &SD : Asm.symbols())
1276 if (MCFragment *F = SD.getFragment())
1277 DefiningSymbols[F->getParent()].push_back(&SD);
1279 for (MCSectionData &SD : Asm) {
1280 const MCSectionELF &Section =
1281 static_cast<const MCSectionELF &>(SD.getSection());
1282 StringRef SectionName = Section.getSectionName();
1284 // Compressing debug_frame requires handling alignment fragments which is
1285 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1286 // for writing to arbitrary buffers) for little benefit.
1287 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1290 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1294 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm,
1295 const MCAsmLayout &Layout) {
1296 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1297 MCSectionData &RelSD = *it;
1298 const MCSectionELF &RelSection =
1299 static_cast<const MCSectionELF &>(RelSD.getSection());
1301 unsigned Type = RelSection.getType();
1302 if (Type != ELF::SHT_REL && Type != ELF::SHT_RELA)
1305 const MCSectionELF *Section = RelSection.getAssociatedSection();
1306 MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1307 RelSD.setAlignment(is64Bit() ? 8 : 4);
1309 MCDataFragment *F = new MCDataFragment(&RelSD);
1310 WriteRelocationsFragment(Asm, F, &SD);
1314 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1315 uint64_t Flags, uint64_t Address,
1316 uint64_t Offset, uint64_t Size,
1317 uint32_t Link, uint32_t Info,
1319 uint64_t EntrySize) {
1320 Write32(Name); // sh_name: index into string table
1321 Write32(Type); // sh_type
1322 WriteWord(Flags); // sh_flags
1323 WriteWord(Address); // sh_addr
1324 WriteWord(Offset); // sh_offset
1325 WriteWord(Size); // sh_size
1326 Write32(Link); // sh_link
1327 Write32(Info); // sh_info
1328 WriteWord(Alignment); // sh_addralign
1329 WriteWord(EntrySize); // sh_entsize
1332 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1334 const MCSectionData *SD) {
1335 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1337 // Sort the relocation entries. Most targets just sort by Offset, but some
1338 // (e.g., MIPS) have additional constraints.
1339 TargetObjectWriter->sortRelocs(Asm, Relocs);
1341 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1342 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1344 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1347 write(*F, Entry.Offset);
1348 if (TargetObjectWriter->isN64()) {
1349 write(*F, uint32_t(Index));
1351 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1352 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1353 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1354 write(*F, TargetObjectWriter->getRType(Entry.Type));
1356 struct ELF::Elf64_Rela ERE64;
1357 ERE64.setSymbolAndType(Index, Entry.Type);
1358 write(*F, ERE64.r_info);
1360 if (hasRelocationAddend())
1361 write(*F, Entry.Addend);
1363 write(*F, uint32_t(Entry.Offset));
1365 struct ELF::Elf32_Rela ERE32;
1366 ERE32.setSymbolAndType(Index, Entry.Type);
1367 write(*F, ERE32.r_info);
1369 if (hasRelocationAddend())
1370 write(*F, uint32_t(Entry.Addend));
1375 void ELFObjectWriter::CreateMetadataSections(
1376 MCAssembler &Asm, const MCAsmLayout &Layout,
1377 std::vector<const MCSectionELF *> &Sections) {
1378 MCContext &Ctx = Asm.getContext();
1381 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1383 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1384 const MCSectionELF *ShstrtabSection =
1385 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1386 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1387 ShstrtabSD.setAlignment(1);
1388 ShstrtabIndex = Sections.size() + 1;
1389 Sections.push_back(ShstrtabSection);
1391 const MCSectionELF *SymtabSection =
1392 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1394 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1395 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1396 SymbolTableIndex = Sections.size() + 1;
1397 Sections.push_back(SymtabSection);
1399 const MCSectionELF *StrtabSection;
1400 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1401 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1402 StrtabSD.setAlignment(1);
1403 StringTableIndex = Sections.size() + 1;
1404 Sections.push_back(StrtabSection);
1407 F = new MCDataFragment(&SymtabSD);
1408 WriteSymbolTable(F, Asm, Layout, Sections);
1410 F = new MCDataFragment(&StrtabSD);
1411 F->getContents().append(StrTabBuilder.data().begin(),
1412 StrTabBuilder.data().end());
1414 F = new MCDataFragment(&ShstrtabSD);
1416 // Section header string table.
1417 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1418 const MCSectionELF &Section =
1419 static_cast<const MCSectionELF&>(it->getSection());
1420 ShStrTabBuilder.add(Section.getSectionName());
1422 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1423 F->getContents().append(ShStrTabBuilder.data().begin(),
1424 ShStrTabBuilder.data().end());
1427 void ELFObjectWriter::createIndexedSections(
1428 MCAssembler &Asm, const MCAsmLayout &Layout, RevGroupMapTy &RevGroupMap,
1429 std::vector<const MCSectionELF *> &Sections,
1430 SectionIndexMapTy &SectionIndexMap) {
1431 MCContext &Ctx = Asm.getContext();
1434 for (const MCSectionData &SD : Asm) {
1435 const MCSectionELF &Section =
1436 static_cast<const MCSectionELF &>(SD.getSection());
1437 if (!(Section.getFlags() & ELF::SHF_GROUP))
1440 const MCSymbol *SignatureSymbol = Section.getGroup();
1441 Asm.getOrCreateSymbolData(*SignatureSymbol);
1442 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1444 const MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1445 Sections.push_back(Group);
1446 GroupIdx = Sections.size();
1448 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1449 Data.setAlignment(4);
1450 MCDataFragment *F = new MCDataFragment(&Data);
1451 write(*F, uint32_t(ELF::GRP_COMDAT));
1455 computeIndexMap(Asm, Sections, SectionIndexMap, RevGroupMap);
1458 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1459 const SectionIndexMapTy &SectionIndexMap,
1460 uint32_t GroupSymbolIndex,
1461 uint64_t Offset, uint64_t Size,
1463 const MCSectionELF &Section) {
1464 uint64_t sh_link = 0;
1465 uint64_t sh_info = 0;
1467 switch(Section.getType()) {
1472 case ELF::SHT_DYNAMIC:
1473 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1477 case ELF::SHT_RELA: {
1478 sh_link = SymbolTableIndex;
1479 assert(sh_link && ".symtab not found");
1480 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1481 sh_info = SectionIndexMap.lookup(InfoSection);
1485 case ELF::SHT_SYMTAB:
1486 case ELF::SHT_DYNSYM:
1487 sh_link = StringTableIndex;
1488 sh_info = LastLocalSymbolIndex;
1491 case ELF::SHT_SYMTAB_SHNDX:
1492 sh_link = SymbolTableIndex;
1495 case ELF::SHT_GROUP:
1496 sh_link = SymbolTableIndex;
1497 sh_info = GroupSymbolIndex;
1501 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1502 Section.getType() == ELF::SHT_ARM_EXIDX)
1503 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1505 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1507 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1508 Alignment, Section.getEntrySize());
1511 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1512 return SD.getOrdinal() == ~UINT32_C(0) &&
1513 !SD.getSection().isVirtualSection();
1516 void ELFObjectWriter::writeDataSectionData(MCAssembler &Asm,
1517 const MCAsmLayout &Layout,
1518 const MCSectionData &SD) {
1519 if (IsELFMetaDataSection(SD)) {
1520 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1522 const MCFragment &F = *i;
1523 assert(F.getKind() == MCFragment::FT_Data);
1524 WriteBytes(cast<MCDataFragment>(F).getContents());
1527 Asm.writeSectionData(&SD, Layout);
1531 void ELFObjectWriter::writeSectionHeader(
1532 ArrayRef<const MCSectionELF *> Sections, MCAssembler &Asm,
1533 const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap,
1534 const SectionOffsetsTy &SectionOffsets) {
1535 const unsigned NumSections = Asm.size();
1537 // Null section first.
1538 uint64_t FirstSectionSize =
1539 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1540 uint32_t FirstSectionLink =
1541 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1542 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1544 for (unsigned i = 0; i < NumSections; ++i) {
1545 const MCSectionELF &Section = *Sections[i];
1546 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1547 uint32_t GroupSymbolIndex;
1548 if (Section.getType() != ELF::SHT_GROUP)
1549 GroupSymbolIndex = 0;
1551 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section.getGroup());
1553 const std::pair<uint64_t, uint64_t> &Offsets = SectionOffsets[i];
1554 uint64_t Size = Section.getType() == ELF::SHT_NOBITS
1555 ? Layout.getSectionAddressSize(&SD)
1556 : Offsets.second - Offsets.first;
1558 writeSection(Asm, SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1559 SD.getAlignment(), Section);
1563 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1564 const MCAsmLayout &Layout) {
1565 RevGroupMapTy RevGroupMap;
1566 SectionIndexMapTy SectionIndexMap;
1568 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1569 std::vector<const MCSectionELF *> Sections;
1570 createIndexedSections(Asm, Layout, RevGroupMap, Sections, SectionIndexMap);
1572 // Compute symbol table information.
1573 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1575 WriteRelocations(Asm, Layout);
1577 CreateMetadataSections(Asm, Layout, Sections);
1579 unsigned NumSections = Asm.size();
1580 SectionOffsetsTy SectionOffsets;
1582 // Write out the ELF header ...
1583 WriteHeader(Asm, NumSections + 1);
1585 // ... then the sections ...
1586 for (const MCSectionELF *Section : Sections) {
1587 const MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1588 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1589 WriteZeros(Padding);
1591 // Remember the offset into the file for this section.
1592 uint64_t SecStart = OS.tell();
1593 writeDataSectionData(Asm, Layout, SD);
1594 uint64_t SecEnd = OS.tell();
1595 SectionOffsets.push_back(std::make_pair(SecStart, SecEnd));
1598 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1599 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1600 WriteZeros(Padding);
1602 const unsigned SectionHeaderOffset = OS.tell();
1604 // ... then the section header table ...
1605 writeSectionHeader(Sections, Asm, Layout, SectionIndexMap, SectionOffsets);
1608 uint64_t Val = SectionHeaderOffset;
1609 if (sys::IsLittleEndianHost != IsLittleEndian)
1610 sys::swapByteOrder(Val);
1611 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1612 offsetof(ELF::Elf64_Ehdr, e_shoff));
1614 uint32_t Val = SectionHeaderOffset;
1615 if (sys::IsLittleEndianHost != IsLittleEndian)
1616 sys::swapByteOrder(Val);
1617 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1618 offsetof(ELF::Elf32_Ehdr, e_shoff));
1622 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1623 const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
1624 bool InSet, bool IsPCRel) const {
1627 if (::isWeak(DataA))
1630 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
1634 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
1638 // It is invalid to replace a reference to a global in a comdat
1639 // with a reference to a local since out of comdat references
1640 // to a local are forbidden.
1641 // We could try to return false for more cases, like the reference
1642 // being in the same comdat or Sym being an alias to another global,
1643 // but it is not clear if it is worth the effort.
1644 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1647 const MCSymbol &Sym = SD.getSymbol();
1648 if (!Sym.isInSection())
1651 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1652 return Sec.getGroup();
1655 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1656 raw_pwrite_stream &OS,
1657 bool IsLittleEndian) {
1658 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);