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"
45 typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
47 class ELFObjectWriter;
49 class SymbolTableWriter {
50 ELFObjectWriter &EWriter;
53 // indexes we are going to write to .symtab_shndx.
54 std::vector<uint32_t> ShndxIndexes;
56 // The numbel of symbols written so far.
59 void createSymtabShndx();
61 template <typename T> void write(T Value);
64 SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit);
66 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
67 uint8_t other, uint32_t shndx, bool Reserved);
69 ArrayRef<uint32_t> getShndxIndexes() const { return ShndxIndexes; }
72 class ELFObjectWriter : public MCObjectWriter {
75 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
76 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
77 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
78 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data,
79 bool Used, bool Renamed);
80 static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
81 static bool IsELFMetaDataSection(const MCSectionData &SD);
83 void writeDataSectionData(MCAssembler &Asm, const MCAsmLayout &Layout,
84 const MCSectionData &SD);
86 /// Helper struct for containing some precomputed information on symbols.
87 struct ELFSymbolData {
88 MCSymbolData *SymbolData;
90 uint32_t SectionIndex;
93 // Support lexicographic sorting.
94 bool operator<(const ELFSymbolData &RHS) const {
95 unsigned LHSType = MCELF::GetType(*SymbolData);
96 unsigned RHSType = MCELF::GetType(*RHS.SymbolData);
97 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
99 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
101 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
102 return SectionIndex < RHS.SectionIndex;
103 return Name < RHS.Name;
107 /// The target specific ELF writer instance.
108 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
110 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
111 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
112 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
114 llvm::DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>>
116 StringTableBuilder ShStrTabBuilder;
119 /// @name Symbol Table Data
122 StringTableBuilder StrTabBuilder;
123 std::vector<uint64_t> FileSymbolData;
124 std::vector<ELFSymbolData> LocalSymbolData;
125 std::vector<ELFSymbolData> ExternalSymbolData;
126 std::vector<ELFSymbolData> UndefinedSymbolData;
132 // This holds the symbol table index of the last local symbol.
133 unsigned LastLocalSymbolIndex;
134 // This holds the .strtab section index.
135 unsigned StringTableIndex;
136 // This holds the .symtab section index.
137 unsigned SymbolTableIndex;
139 unsigned ShstrtabIndex;
142 // TargetObjectWriter wrappers.
143 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
144 bool hasRelocationAddend() const {
145 return TargetObjectWriter->hasRelocationAddend();
147 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
148 bool IsPCRel) const {
149 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
153 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
155 : MCObjectWriter(OS, IsLittleEndian), TargetObjectWriter(MOTW),
158 void reset() override {
160 WeakrefUsedInReloc.clear();
163 ShStrTabBuilder.clear();
164 StrTabBuilder.clear();
165 FileSymbolData.clear();
166 LocalSymbolData.clear();
167 ExternalSymbolData.clear();
168 UndefinedSymbolData.clear();
169 MCObjectWriter::reset();
172 ~ELFObjectWriter() override;
174 void WriteWord(uint64_t W) {
181 template <typename T> void write(T Val) {
183 support::endian::Writer<support::little>(OS).write(Val);
185 support::endian::Writer<support::big>(OS).write(Val);
188 template <typename T> void write(MCDataFragment &F, T Value);
190 void writeHeader(const MCAssembler &Asm);
192 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
193 const MCAsmLayout &Layout);
195 // Start and end offset of each section
196 typedef std::vector<std::pair<uint64_t, uint64_t>> SectionOffsetsTy;
198 void WriteSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
199 std::vector<const MCSectionELF *> &Sections,
200 SectionOffsetsTy &SectionOffsets);
202 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
203 const MCSymbolRefExpr *RefA,
204 const MCSymbolData *SD, uint64_t C,
205 unsigned Type) const;
207 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
208 const MCFragment *Fragment, const MCFixup &Fixup,
209 MCValue Target, bool &IsPCRel,
210 uint64_t &FixedValue) override;
212 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
215 // Map from a signature symbol to the group section index
216 typedef DenseMap<const MCSymbol *, unsigned> RevGroupMapTy;
218 /// Compute the symbol table data
220 /// \param Asm - The assembler.
221 /// \param SectionIndexMap - Maps a section to its index.
222 /// \param RevGroupMap - Maps a signature symbol to the group section.
223 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
224 const SectionIndexMapTy &SectionIndexMap,
225 const RevGroupMapTy &RevGroupMap);
227 void maybeAddToGroup(MCAssembler &Asm,
228 ArrayRef<const MCSectionELF *> Sections,
229 const RevGroupMapTy &RevGroupMap,
230 const MCSectionELF &Section, unsigned Index);
232 void computeIndexMap(MCAssembler &Asm,
233 std::vector<const MCSectionELF *> &Sections,
234 SectionIndexMapTy &SectionIndexMap,
235 const RevGroupMapTy &RevGroupMap);
237 void createRelocationSection(MCAssembler &Asm, const MCSectionELF &Sec);
239 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
242 createSectionHeaderStringTable(MCAssembler &Asm,
243 std::vector<const MCSectionELF *> &Sections);
244 void createStringTable(MCAssembler &Asm,
245 std::vector<const MCSectionELF *> &Sections);
247 // Create the sections that show up in the symbol table. Currently
248 // those are the .note.GNU-stack section and the group sections.
249 void createIndexedSections(MCAssembler &Asm, const MCAsmLayout &Layout,
250 RevGroupMapTy &RevGroupMap,
251 std::vector<const MCSectionELF *> &Sections,
252 SectionIndexMapTy &SectionIndexMap);
254 void ExecutePostLayoutBinding(MCAssembler &Asm,
255 const MCAsmLayout &Layout) override;
257 void writeSectionHeader(ArrayRef<const MCSectionELF *> Sections,
258 MCAssembler &Asm, const MCAsmLayout &Layout,
259 const SectionIndexMapTy &SectionIndexMap,
260 const SectionOffsetsTy &SectionOffsets);
262 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
263 uint64_t Address, uint64_t Offset,
264 uint64_t Size, uint32_t Link, uint32_t Info,
265 uint64_t Alignment, uint64_t EntrySize);
267 void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
270 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
271 const MCSymbolData &DataA,
272 const MCFragment &FB,
274 bool IsPCRel) const override;
276 bool isWeak(const MCSymbolData &SD) const override;
278 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
279 void writeSection(MCAssembler &Asm,
280 const SectionIndexMapTy &SectionIndexMap,
281 uint32_t GroupSymbolIndex,
282 uint64_t Offset, uint64_t Size, uint64_t Alignment,
283 const MCSectionELF &Section);
287 template <typename T> void ELFObjectWriter::write(MCDataFragment &F, T Val) {
289 Val = support::endian::byte_swap<T, support::little>(Val);
291 Val = support::endian::byte_swap<T, support::big>(Val);
292 const char *Start = (const char *)&Val;
293 F.getContents().append(Start, Start + sizeof(T));
296 void SymbolTableWriter::createSymtabShndx() {
297 if (!ShndxIndexes.empty())
300 ShndxIndexes.resize(NumWritten);
303 template <typename T> void SymbolTableWriter::write(T Value) {
304 EWriter.write(Value);
307 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
308 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
310 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
311 uint64_t size, uint8_t other,
312 uint32_t shndx, bool Reserved) {
313 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
318 if (!ShndxIndexes.empty()) {
320 ShndxIndexes.push_back(shndx);
322 ShndxIndexes.push_back(0);
325 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
328 write(name); // st_name
329 write(info); // st_info
330 write(other); // st_other
331 write(Index); // st_shndx
332 write(value); // st_value
333 write(size); // st_size
335 write(name); // st_name
336 write(uint32_t(value)); // st_value
337 write(uint32_t(size)); // st_size
338 write(info); // st_info
339 write(other); // st_other
340 write(Index); // st_shndx
346 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
347 const MCFixupKindInfo &FKI =
348 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
350 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
353 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
357 case MCSymbolRefExpr::VK_GOT:
358 case MCSymbolRefExpr::VK_PLT:
359 case MCSymbolRefExpr::VK_GOTPCREL:
360 case MCSymbolRefExpr::VK_GOTOFF:
361 case MCSymbolRefExpr::VK_TPOFF:
362 case MCSymbolRefExpr::VK_TLSGD:
363 case MCSymbolRefExpr::VK_GOTTPOFF:
364 case MCSymbolRefExpr::VK_INDNTPOFF:
365 case MCSymbolRefExpr::VK_NTPOFF:
366 case MCSymbolRefExpr::VK_GOTNTPOFF:
367 case MCSymbolRefExpr::VK_TLSLDM:
368 case MCSymbolRefExpr::VK_DTPOFF:
369 case MCSymbolRefExpr::VK_TLSLD:
374 ELFObjectWriter::~ELFObjectWriter()
377 // Emit the ELF header.
378 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
384 // emitWord method behaves differently for ELF32 and ELF64, writing
385 // 4 bytes in the former and 8 in the latter.
387 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
389 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
392 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
394 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
396 Write8(TargetObjectWriter->getOSABI());
397 Write8(0); // e_ident[EI_ABIVERSION]
399 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
401 Write16(ELF::ET_REL); // e_type
403 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
405 Write32(ELF::EV_CURRENT); // e_version
406 WriteWord(0); // e_entry, no entry point in .o file
407 WriteWord(0); // e_phoff, no program header for .o
408 WriteWord(0); // e_shoff = sec hdr table off in bytes
410 // e_flags = whatever the target wants
411 Write32(Asm.getELFHeaderEFlags());
413 // e_ehsize = ELF header size
414 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
416 Write16(0); // e_phentsize = prog header entry size
417 Write16(0); // e_phnum = # prog header entries = 0
419 // e_shentsize = Section header entry size
420 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
422 // e_shnum = # of section header ents
425 // e_shstrndx = Section # of '.shstrtab'
426 assert(ShstrtabIndex < ELF::SHN_LORESERVE);
427 Write16(ShstrtabIndex);
430 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
431 const MCAsmLayout &Layout) {
432 if (Data.isCommon() && Data.isExternal())
433 return Data.getCommonAlignment();
436 if (!Layout.getSymbolOffset(&Data, Res))
439 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
445 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
446 const MCAsmLayout &Layout) {
447 // The presence of symbol versions causes undefined symbols and
448 // versions declared with @@@ to be renamed.
450 for (MCSymbolData &OriginalData : Asm.symbols()) {
451 const MCSymbol &Alias = OriginalData.getSymbol();
454 if (!Alias.isVariable())
456 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
459 const MCSymbol &Symbol = Ref->getSymbol();
460 MCSymbolData &SD = Asm.getSymbolData(Symbol);
462 StringRef AliasName = Alias.getName();
463 size_t Pos = AliasName.find('@');
464 if (Pos == StringRef::npos)
467 // Aliases defined with .symvar copy the binding from the symbol they alias.
468 // This is the first place we are able to copy this information.
469 OriginalData.setExternal(SD.isExternal());
470 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
472 StringRef Rest = AliasName.substr(Pos);
473 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
476 // FIXME: produce a better error message.
477 if (Symbol.isUndefined() && Rest.startswith("@@") &&
478 !Rest.startswith("@@@"))
479 report_fatal_error("A @@ version cannot be undefined");
481 Renames.insert(std::make_pair(&Symbol, &Alias));
485 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
486 uint8_t Type = newType;
488 // Propagation rules:
489 // IFUNC > FUNC > OBJECT > NOTYPE
490 // TLS_OBJECT > OBJECT > NOTYPE
492 // dont let the new type degrade the old type
496 case ELF::STT_GNU_IFUNC:
497 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
498 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
499 Type = ELF::STT_GNU_IFUNC;
502 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
503 Type == ELF::STT_TLS)
504 Type = ELF::STT_FUNC;
506 case ELF::STT_OBJECT:
507 if (Type == ELF::STT_NOTYPE)
508 Type = ELF::STT_OBJECT;
511 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
512 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
520 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
521 const MCAsmLayout &Layout) {
522 MCSymbolData &OrigData = *MSD.SymbolData;
523 assert((!OrigData.getFragment() ||
524 (&OrigData.getFragment()->getParent()->getSection() ==
525 &OrigData.getSymbol().getSection())) &&
526 "The symbol's section doesn't match the fragment's symbol");
527 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
529 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
531 bool IsReserved = !Base || OrigData.isCommon();
533 // Binding and Type share the same byte as upper and lower nibbles
534 uint8_t Binding = MCELF::GetBinding(OrigData);
535 uint8_t Type = MCELF::GetType(OrigData);
536 MCSymbolData *BaseSD = nullptr;
538 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
539 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
541 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
543 // Other and Visibility share the same byte with Visibility using the lower
545 uint8_t Visibility = MCELF::GetVisibility(OrigData);
546 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
549 uint64_t Value = SymbolValue(OrigData, Layout);
552 const MCExpr *ESize = OrigData.getSize();
554 ESize = BaseSD->getSize();
558 if (!ESize->evaluateKnownAbsolute(Res, Layout))
559 report_fatal_error("Size expression must be absolute.");
563 // Write out the symbol table entry
564 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
565 MSD.SectionIndex, IsReserved);
568 void ELFObjectWriter::WriteSymbolTable(
569 MCAssembler &Asm, const MCAsmLayout &Layout,
570 std::vector<const MCSectionELF *> &Sections,
571 SectionOffsetsTy &SectionOffsets) {
573 MCContext &Ctx = Asm.getContext();
575 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
578 const MCSectionELF *SymtabSection =
579 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
580 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
581 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
582 SymbolTableIndex = Sections.size() + 1;
583 Sections.push_back(SymtabSection);
585 // The string table must be emitted first because we need the index
586 // into the string table for all the symbol names.
588 SymbolTableWriter Writer(*this, is64Bit());
590 uint64_t Padding = OffsetToAlignment(OS.tell(), SymtabSD.getAlignment());
593 uint64_t SecStart = OS.tell();
595 // The first entry is the undefined symbol entry.
596 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
598 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
599 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
600 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
603 // Write the symbol table entries.
604 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
606 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
607 ELFSymbolData &MSD = LocalSymbolData[i];
608 WriteSymbol(Writer, MSD, Layout);
611 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
612 ELFSymbolData &MSD = ExternalSymbolData[i];
613 MCSymbolData &Data = *MSD.SymbolData;
614 assert(((Data.getFlags() & ELF_STB_Global) ||
615 (Data.getFlags() & ELF_STB_Weak)) &&
616 "External symbol requires STB_GLOBAL or STB_WEAK flag");
617 WriteSymbol(Writer, MSD, Layout);
618 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
619 LastLocalSymbolIndex++;
622 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
623 ELFSymbolData &MSD = UndefinedSymbolData[i];
624 MCSymbolData &Data = *MSD.SymbolData;
625 WriteSymbol(Writer, MSD, Layout);
626 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
627 LastLocalSymbolIndex++;
630 uint64_t SecEnd = OS.tell();
631 SectionOffsets.push_back(std::make_pair(SecStart, SecEnd));
633 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
634 if (ShndxIndexes.empty())
637 SecStart = OS.tell();
638 const MCSectionELF *SymtabShndxSection =
639 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
640 Sections.push_back(SymtabShndxSection);
641 MCSectionData *SymtabShndxSD =
642 &Asm.getOrCreateSectionData(*SymtabShndxSection);
643 SymtabShndxSD->setAlignment(4);
644 for (uint32_t Index : ShndxIndexes)
647 SectionOffsets.push_back(std::make_pair(SecStart, SecEnd));
650 // It is always valid to create a relocation with a symbol. It is preferable
651 // to use a relocation with a section if that is possible. Using the section
652 // allows us to omit some local symbols from the symbol table.
653 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
654 const MCSymbolRefExpr *RefA,
655 const MCSymbolData *SD,
657 unsigned Type) const {
658 // A PCRel relocation to an absolute value has no symbol (or section). We
659 // represent that with a relocation to a null section.
663 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
667 // The .odp creation emits a relocation against the symbol ".TOC." which
668 // create a R_PPC64_TOC relocation. However the relocation symbol name
669 // in final object creation should be NULL, since the symbol does not
670 // really exist, it is just the reference to TOC base for the current
671 // object file. Since the symbol is undefined, returning false results
672 // in a relocation with a null section which is the desired result.
673 case MCSymbolRefExpr::VK_PPC_TOCBASE:
676 // These VariantKind cause the relocation to refer to something other than
677 // the symbol itself, like a linker generated table. Since the address of
678 // symbol is not relevant, we cannot replace the symbol with the
679 // section and patch the difference in the addend.
680 case MCSymbolRefExpr::VK_GOT:
681 case MCSymbolRefExpr::VK_PLT:
682 case MCSymbolRefExpr::VK_GOTPCREL:
683 case MCSymbolRefExpr::VK_Mips_GOT:
684 case MCSymbolRefExpr::VK_PPC_GOT_LO:
685 case MCSymbolRefExpr::VK_PPC_GOT_HI:
686 case MCSymbolRefExpr::VK_PPC_GOT_HA:
690 // An undefined symbol is not in any section, so the relocation has to point
691 // to the symbol itself.
692 const MCSymbol &Sym = SD->getSymbol();
693 if (Sym.isUndefined())
696 unsigned Binding = MCELF::GetBinding(*SD);
699 llvm_unreachable("Invalid Binding");
703 // If the symbol is weak, it might be overridden by a symbol in another
704 // file. The relocation has to point to the symbol so that the linker
707 case ELF::STB_GLOBAL:
708 // Global ELF symbols can be preempted by the dynamic linker. The relocation
709 // has to point to the symbol for a reason analogous to the STB_WEAK case.
713 // If a relocation points to a mergeable section, we have to be careful.
714 // If the offset is zero, a relocation with the section will encode the
715 // same information. With a non-zero offset, the situation is different.
716 // For example, a relocation can point 42 bytes past the end of a string.
717 // If we change such a relocation to use the section, the linker would think
718 // that it pointed to another string and subtracting 42 at runtime will
719 // produce the wrong value.
720 auto &Sec = cast<MCSectionELF>(Sym.getSection());
721 unsigned Flags = Sec.getFlags();
722 if (Flags & ELF::SHF_MERGE) {
726 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
727 // only handle section relocations to mergeable sections if using RELA.
728 if (!hasRelocationAddend())
732 // Most TLS relocations use a got, so they need the symbol. Even those that
733 // are just an offset (@tpoff), require a symbol in gold versions before
734 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
735 // http://sourceware.org/PR16773.
736 if (Flags & ELF::SHF_TLS)
739 // If the symbol is a thumb function the final relocation must set the lowest
740 // bit. With a symbol that is done by just having the symbol have that bit
741 // set, so we would lose the bit if we relocated with the section.
742 // FIXME: We could use the section but add the bit to the relocation value.
743 if (Asm.isThumbFunc(&Sym))
746 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
751 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
752 const MCSymbol &Sym = Ref.getSymbol();
754 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
757 if (!Sym.isVariable())
760 const MCExpr *Expr = Sym.getVariableValue();
761 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
765 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
766 return &Inner->getSymbol();
770 // True if the assembler knows nothing about the final value of the symbol.
771 // This doesn't cover the comdat issues, since in those cases the assembler
772 // can at least know that all symbols in the section will move together.
773 static bool isWeak(const MCSymbolData &D) {
774 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
777 switch (MCELF::GetBinding(D)) {
779 llvm_unreachable("Unknown binding");
782 case ELF::STB_GLOBAL:
785 case ELF::STB_GNU_UNIQUE:
790 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
791 const MCAsmLayout &Layout,
792 const MCFragment *Fragment,
793 const MCFixup &Fixup, MCValue Target,
794 bool &IsPCRel, uint64_t &FixedValue) {
795 const MCSectionData *FixupSectionD = Fragment->getParent();
796 const MCSectionELF &FixupSection =
797 cast<MCSectionELF>(FixupSectionD->getSection());
798 uint64_t C = Target.getConstant();
799 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
801 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
802 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
803 "Should not have constructed this");
805 // Let A, B and C being the components of Target and R be the location of
806 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
807 // If it is pcrel, we want to compute (A - B + C - R).
809 // In general, ELF has no relocations for -B. It can only represent (A + C)
810 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
811 // replace B to implement it: (A - R - K + C)
813 Asm.getContext().FatalError(
815 "No relocation available to represent this relative expression");
817 const MCSymbol &SymB = RefB->getSymbol();
819 if (SymB.isUndefined())
820 Asm.getContext().FatalError(
822 Twine("symbol '") + SymB.getName() +
823 "' can not be undefined in a subtraction expression");
825 assert(!SymB.isAbsolute() && "Should have been folded");
826 const MCSection &SecB = SymB.getSection();
827 if (&SecB != &FixupSection)
828 Asm.getContext().FatalError(
829 Fixup.getLoc(), "Cannot represent a difference across sections");
831 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
833 Asm.getContext().FatalError(
834 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
836 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
837 uint64_t K = SymBOffset - FixupOffset;
842 // We either rejected the fixup or folded B into C at this point.
843 const MCSymbolRefExpr *RefA = Target.getSymA();
844 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
845 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
847 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
848 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
849 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
850 C += Layout.getSymbolOffset(SymAD);
853 if (hasRelocationAddend()) {
860 // FIXME: What is this!?!?
861 MCSymbolRefExpr::VariantKind Modifier =
862 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
863 if (RelocNeedsGOT(Modifier))
866 if (!RelocateWithSymbol) {
867 const MCSection *SecA =
868 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
869 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
870 MCSymbol *SectionSymbol =
871 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
873 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
874 Relocations[&FixupSection].push_back(Rec);
879 if (const MCSymbol *R = Renames.lookup(SymA))
882 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
883 WeakrefUsedInReloc.insert(WeakRef);
885 UsedInReloc.insert(SymA);
887 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
888 Relocations[&FixupSection].push_back(Rec);
894 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
896 const MCSymbolData &SD = Asm.getSymbolData(*S);
897 return SD.getIndex();
900 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
901 const MCSymbolData &Data, bool Used,
903 const MCSymbol &Symbol = Data.getSymbol();
904 if (Symbol.isVariable()) {
905 const MCExpr *Expr = Symbol.getVariableValue();
906 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
907 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
918 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
921 if (Symbol.isVariable()) {
922 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
923 if (Base && Base->isUndefined())
927 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
928 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
931 if (Symbol.isTemporary())
937 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
938 if (Data.isExternal())
941 const MCSymbol &Symbol = Data.getSymbol();
942 if (Symbol.isDefined())
951 void ELFObjectWriter::maybeAddToGroup(MCAssembler &Asm,
952 ArrayRef<const MCSectionELF *> Sections,
953 const RevGroupMapTy &RevGroupMap,
954 const MCSectionELF &Section,
956 const MCSymbol *Sym = Section.getGroup();
959 const MCSectionELF *Group = Sections[RevGroupMap.lookup(Sym) - 1];
960 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
961 // FIXME: we could use the previous fragment
962 MCDataFragment *F = new MCDataFragment(&Data);
966 void ELFObjectWriter::computeIndexMap(
967 MCAssembler &Asm, std::vector<const MCSectionELF *> &Sections,
968 SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap) {
969 for (const MCSectionData &SD : Asm) {
970 const MCSectionELF &Section =
971 static_cast<const MCSectionELF &>(SD.getSection());
972 if (Section.getType() == ELF::SHT_GROUP)
974 Sections.push_back(&Section);
975 unsigned Index = Sections.size();
976 SectionIndexMap[&Section] = Index;
977 maybeAddToGroup(Asm, Sections, RevGroupMap, Section, Index);
978 createRelocationSection(Asm, Section);
982 void ELFObjectWriter::computeSymbolTable(
983 MCAssembler &Asm, const MCAsmLayout &Layout,
984 const SectionIndexMapTy &SectionIndexMap,
985 const RevGroupMapTy &RevGroupMap) {
986 // FIXME: Is this the correct place to do this?
987 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
989 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
990 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
991 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
992 Data.setExternal(true);
993 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
996 // Add the data for the symbols.
997 for (MCSymbolData &SD : Asm.symbols()) {
998 const MCSymbol &Symbol = SD.getSymbol();
1000 bool Used = UsedInReloc.count(&Symbol);
1001 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
1002 bool isSignature = RevGroupMap.count(&Symbol);
1004 if (!isInSymtab(Layout, SD,
1005 Used || WeakrefUsed || isSignature,
1006 Renames.count(&Symbol)))
1010 MSD.SymbolData = &SD;
1011 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
1013 // Undefined symbols are global, but this is the first place we
1014 // are able to set it.
1015 bool Local = isLocal(SD, Used);
1016 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1018 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1019 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1020 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1024 MSD.SectionIndex = ELF::SHN_ABS;
1025 } else if (SD.isCommon()) {
1027 MSD.SectionIndex = ELF::SHN_COMMON;
1028 } else if (BaseSymbol->isUndefined()) {
1029 if (isSignature && !Used)
1030 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
1032 MSD.SectionIndex = ELF::SHN_UNDEF;
1033 if (!Used && WeakrefUsed)
1034 MCELF::SetBinding(SD, ELF::STB_WEAK);
1036 const MCSectionELF &Section =
1037 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1038 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1039 assert(MSD.SectionIndex && "Invalid section index!");
1042 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
1045 // FIXME: All name handling should be done before we get to the writer,
1046 // including dealing with GNU-style version suffixes. Fixing this isn't
1049 // We thus have to be careful to not perform the symbol version replacement
1052 // The ELF format is used on Windows by the MCJIT engine. Thus, on
1053 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
1054 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
1055 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
1056 // the EFLObjectWriter should not interpret the "@@@" sub-string as
1057 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1058 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1059 // "__imp_?" or "__imp_@?".
1061 // It would have been interesting to perform the MS mangling prefix check
1062 // only when the target triple is of the form *-pc-windows-elf. But, it
1063 // seems that this information is not easily accessible from the
1065 StringRef Name = Symbol.getName();
1066 if (!Name.startswith("?") && !Name.startswith("@?") &&
1067 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1068 // This symbol isn't following the MSVC C++ name mangling convention. We
1069 // can thus safely interpret the @@@ in symbol names as specifying symbol
1071 SmallString<32> Buf;
1072 size_t Pos = Name.find("@@@");
1073 if (Pos != StringRef::npos) {
1074 Buf += Name.substr(0, Pos);
1075 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1076 Buf += Name.substr(Pos + Skip);
1081 // Sections have their own string table
1082 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1083 MSD.Name = StrTabBuilder.add(Name);
1085 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1086 UndefinedSymbolData.push_back(MSD);
1088 LocalSymbolData.push_back(MSD);
1090 ExternalSymbolData.push_back(MSD);
1093 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1094 StrTabBuilder.add(*i);
1096 StrTabBuilder.finalize(StringTableBuilder::ELF);
1098 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1099 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1101 for (ELFSymbolData &MSD : LocalSymbolData)
1102 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1104 : StrTabBuilder.getOffset(MSD.Name);
1105 for (ELFSymbolData &MSD : ExternalSymbolData)
1106 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1107 for (ELFSymbolData& MSD : UndefinedSymbolData)
1108 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1110 // Symbols are required to be in lexicographic order.
1111 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1112 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1113 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1115 // Set the symbol indices. Local symbols must come before all other
1116 // symbols with non-local bindings.
1117 unsigned Index = FileSymbolData.size() + 1;
1118 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1119 LocalSymbolData[i].SymbolData->setIndex(Index++);
1121 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1122 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1123 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1124 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1127 void ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1128 const MCSectionELF &Sec) {
1129 if (Relocations[&Sec].empty())
1132 MCContext &Ctx = Asm.getContext();
1133 const StringRef SectionName = Sec.getSectionName();
1134 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1135 RelaSectionName += SectionName;
1138 if (hasRelocationAddend())
1139 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1141 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1144 if (Sec.getFlags() & ELF::SHF_GROUP)
1145 Flags = ELF::SHF_GROUP;
1147 const MCSectionELF *RelaSection = Ctx.createELFRelSection(
1148 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1149 Flags, EntrySize, Sec.getGroup(), &Sec);
1150 MCSectionData &RelSD = Asm.getOrCreateSectionData(*RelaSection);
1151 RelSD.setAlignment(is64Bit() ? 8 : 4);
1154 static SmallVector<char, 128>
1155 getUncompressedData(const MCAsmLayout &Layout,
1156 MCSectionData::FragmentListType &Fragments) {
1157 SmallVector<char, 128> UncompressedData;
1158 for (const MCFragment &F : Fragments) {
1159 const SmallVectorImpl<char> *Contents;
1160 switch (F.getKind()) {
1161 case MCFragment::FT_Data:
1162 Contents = &cast<MCDataFragment>(F).getContents();
1164 case MCFragment::FT_Dwarf:
1165 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1167 case MCFragment::FT_DwarfFrame:
1168 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1172 "Not expecting any other fragment types in a debug_* section");
1174 UncompressedData.append(Contents->begin(), Contents->end());
1176 return UncompressedData;
1179 // Include the debug info compression header:
1180 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1181 // useful for consumers to preallocate a buffer to decompress into.
1183 prependCompressionHeader(uint64_t Size,
1184 SmallVectorImpl<char> &CompressedContents) {
1185 const StringRef Magic = "ZLIB";
1186 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1188 if (sys::IsLittleEndianHost)
1189 sys::swapByteOrder(Size);
1190 CompressedContents.insert(CompressedContents.begin(),
1191 Magic.size() + sizeof(Size), 0);
1192 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1193 std::copy(reinterpret_cast<char *>(&Size),
1194 reinterpret_cast<char *>(&Size + 1),
1195 CompressedContents.begin() + Magic.size());
1199 // Return a single fragment containing the compressed contents of the whole
1200 // section. Null if the section was not compressed for any reason.
1201 static std::unique_ptr<MCDataFragment>
1202 getCompressedFragment(const MCAsmLayout &Layout,
1203 MCSectionData::FragmentListType &Fragments) {
1204 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1206 // Gather the uncompressed data from all the fragments, recording the
1207 // alignment fragment, if seen, and any fixups.
1208 SmallVector<char, 128> UncompressedData =
1209 getUncompressedData(Layout, Fragments);
1211 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1213 zlib::Status Success = zlib::compress(
1214 StringRef(UncompressedData.data(), UncompressedData.size()),
1215 CompressedContents);
1216 if (Success != zlib::StatusOK)
1219 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1222 return CompressedFragment;
1225 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1228 static void UpdateSymbols(const MCAsmLayout &Layout,
1229 const std::vector<MCSymbolData *> &Symbols,
1230 MCFragment &NewFragment) {
1231 for (MCSymbolData *Sym : Symbols) {
1232 Sym->setOffset(Sym->getOffset() +
1233 Layout.getFragmentOffset(Sym->getFragment()));
1234 Sym->setFragment(&NewFragment);
1238 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1239 const DefiningSymbolMap &DefiningSymbols,
1240 const MCSectionELF &Section,
1241 MCSectionData &SD) {
1242 StringRef SectionName = Section.getSectionName();
1243 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1245 std::unique_ptr<MCDataFragment> CompressedFragment =
1246 getCompressedFragment(Layout, Fragments);
1248 // Leave the section as-is if the fragments could not be compressed.
1249 if (!CompressedFragment)
1252 // Update the fragment+offsets of any symbols referring to fragments in this
1253 // section to refer to the new fragment.
1254 auto I = DefiningSymbols.find(&SD);
1255 if (I != DefiningSymbols.end())
1256 UpdateSymbols(Layout, I->second, *CompressedFragment);
1258 // Invalidate the layout for the whole section since it will have new and
1259 // different fragments now.
1260 Layout.invalidateFragmentsFrom(&Fragments.front());
1263 // Complete the initialization of the new fragment
1264 CompressedFragment->setParent(&SD);
1265 CompressedFragment->setLayoutOrder(0);
1266 Fragments.push_back(CompressedFragment.release());
1268 // Rename from .debug_* to .zdebug_*
1269 Asm.getContext().renameELFSection(&Section,
1270 (".z" + SectionName.drop_front(1)).str());
1273 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1274 MCAsmLayout &Layout) {
1275 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1278 DefiningSymbolMap DefiningSymbols;
1280 for (MCSymbolData &SD : Asm.symbols())
1281 if (MCFragment *F = SD.getFragment())
1282 DefiningSymbols[F->getParent()].push_back(&SD);
1284 for (MCSectionData &SD : Asm) {
1285 const MCSectionELF &Section =
1286 static_cast<const MCSectionELF &>(SD.getSection());
1287 StringRef SectionName = Section.getSectionName();
1289 // Compressing debug_frame requires handling alignment fragments which is
1290 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1291 // for writing to arbitrary buffers) for little benefit.
1292 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1295 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1299 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1300 uint64_t Flags, uint64_t Address,
1301 uint64_t Offset, uint64_t Size,
1302 uint32_t Link, uint32_t Info,
1304 uint64_t EntrySize) {
1305 Write32(Name); // sh_name: index into string table
1306 Write32(Type); // sh_type
1307 WriteWord(Flags); // sh_flags
1308 WriteWord(Address); // sh_addr
1309 WriteWord(Offset); // sh_offset
1310 WriteWord(Size); // sh_size
1311 Write32(Link); // sh_link
1312 Write32(Info); // sh_info
1313 WriteWord(Alignment); // sh_addralign
1314 WriteWord(EntrySize); // sh_entsize
1317 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1318 const MCSectionELF &Sec) {
1319 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1321 // Sort the relocation entries. Most targets just sort by Offset, but some
1322 // (e.g., MIPS) have additional constraints.
1323 TargetObjectWriter->sortRelocs(Asm, Relocs);
1325 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1326 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1328 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1331 write(Entry.Offset);
1332 if (TargetObjectWriter->isN64()) {
1333 write(uint32_t(Index));
1335 write(TargetObjectWriter->getRSsym(Entry.Type));
1336 write(TargetObjectWriter->getRType3(Entry.Type));
1337 write(TargetObjectWriter->getRType2(Entry.Type));
1338 write(TargetObjectWriter->getRType(Entry.Type));
1340 struct ELF::Elf64_Rela ERE64;
1341 ERE64.setSymbolAndType(Index, Entry.Type);
1342 write(ERE64.r_info);
1344 if (hasRelocationAddend())
1345 write(Entry.Addend);
1347 write(uint32_t(Entry.Offset));
1349 struct ELF::Elf32_Rela ERE32;
1350 ERE32.setSymbolAndType(Index, Entry.Type);
1351 write(ERE32.r_info);
1353 if (hasRelocationAddend())
1354 write(uint32_t(Entry.Addend));
1359 void ELFObjectWriter::createSectionHeaderStringTable(
1360 MCAssembler &Asm, std::vector<const MCSectionELF *> &Sections) {
1361 const MCSectionELF *ShstrtabSection = Sections[ShstrtabIndex - 1];
1363 Asm.getOrCreateSectionData(*ShstrtabSection);
1365 for (MCSectionData &SD : Asm) {
1366 const MCSectionELF &Section =
1367 static_cast<const MCSectionELF &>(SD.getSection());
1368 ShStrTabBuilder.add(Section.getSectionName());
1370 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1371 OS << ShStrTabBuilder.data();
1374 void ELFObjectWriter::createStringTable(
1375 MCAssembler &Asm, std::vector<const MCSectionELF *> &Sections) {
1376 MCContext &Ctx = Asm.getContext();
1377 const MCSectionELF *StrtabSection =
1378 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1379 Asm.getOrCreateSectionData(*StrtabSection);
1380 Sections.push_back(StrtabSection);
1381 StringTableIndex = Sections.size();
1382 OS << StrTabBuilder.data();
1385 void ELFObjectWriter::createIndexedSections(
1386 MCAssembler &Asm, const MCAsmLayout &Layout, RevGroupMapTy &RevGroupMap,
1387 std::vector<const MCSectionELF *> &Sections,
1388 SectionIndexMapTy &SectionIndexMap) {
1389 MCContext &Ctx = Asm.getContext();
1391 const MCSectionELF *ShstrtabSection =
1392 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1393 Sections.push_back(ShstrtabSection);
1394 ShstrtabIndex = Sections.size();
1395 assert(ShstrtabIndex == 1);
1398 for (const MCSectionData &SD : Asm) {
1399 const MCSectionELF &Section =
1400 static_cast<const MCSectionELF &>(SD.getSection());
1401 if (!(Section.getFlags() & ELF::SHF_GROUP))
1404 const MCSymbol *SignatureSymbol = Section.getGroup();
1405 Asm.getOrCreateSymbolData(*SignatureSymbol);
1406 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1408 const MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1409 Sections.push_back(Group);
1410 GroupIdx = Sections.size();
1412 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1413 Data.setAlignment(4);
1414 MCDataFragment *F = new MCDataFragment(&Data);
1415 write(*F, uint32_t(ELF::GRP_COMDAT));
1419 computeIndexMap(Asm, Sections, SectionIndexMap, RevGroupMap);
1422 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1423 const SectionIndexMapTy &SectionIndexMap,
1424 uint32_t GroupSymbolIndex,
1425 uint64_t Offset, uint64_t Size,
1427 const MCSectionELF &Section) {
1428 uint64_t sh_link = 0;
1429 uint64_t sh_info = 0;
1431 switch(Section.getType()) {
1436 case ELF::SHT_DYNAMIC:
1437 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1441 case ELF::SHT_RELA: {
1442 sh_link = SymbolTableIndex;
1443 assert(sh_link && ".symtab not found");
1444 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1445 sh_info = SectionIndexMap.lookup(InfoSection);
1449 case ELF::SHT_SYMTAB:
1450 case ELF::SHT_DYNSYM:
1451 sh_link = StringTableIndex;
1452 sh_info = LastLocalSymbolIndex;
1455 case ELF::SHT_SYMTAB_SHNDX:
1456 sh_link = SymbolTableIndex;
1459 case ELF::SHT_GROUP:
1460 sh_link = SymbolTableIndex;
1461 sh_info = GroupSymbolIndex;
1465 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1466 Section.getType() == ELF::SHT_ARM_EXIDX)
1467 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1469 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1471 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1472 Alignment, Section.getEntrySize());
1475 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1476 return SD.getOrdinal() == ~UINT32_C(0) &&
1477 !SD.getSection().isVirtualSection();
1480 void ELFObjectWriter::writeDataSectionData(MCAssembler &Asm,
1481 const MCAsmLayout &Layout,
1482 const MCSectionData &SD) {
1483 if (IsELFMetaDataSection(SD)) {
1484 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1486 const MCFragment &F = *i;
1487 assert(F.getKind() == MCFragment::FT_Data);
1488 WriteBytes(cast<MCDataFragment>(F).getContents());
1491 Asm.writeSectionData(&SD, Layout);
1495 void ELFObjectWriter::writeSectionHeader(
1496 ArrayRef<const MCSectionELF *> Sections, MCAssembler &Asm,
1497 const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap,
1498 const SectionOffsetsTy &SectionOffsets) {
1499 const unsigned NumSections = Asm.size();
1501 // Null section first.
1502 uint64_t FirstSectionSize =
1503 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1504 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1506 for (unsigned i = 0; i < NumSections; ++i) {
1507 const MCSectionELF &Section = *Sections[i];
1508 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1509 uint32_t GroupSymbolIndex;
1510 if (Section.getType() != ELF::SHT_GROUP)
1511 GroupSymbolIndex = 0;
1513 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section.getGroup());
1515 const std::pair<uint64_t, uint64_t> &Offsets = SectionOffsets[i];
1516 uint64_t Size = Section.getType() == ELF::SHT_NOBITS
1517 ? Layout.getSectionAddressSize(&SD)
1518 : Offsets.second - Offsets.first;
1520 writeSection(Asm, SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1521 SD.getAlignment(), Section);
1525 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1526 const MCAsmLayout &Layout) {
1527 RevGroupMapTy RevGroupMap;
1528 SectionIndexMapTy SectionIndexMap;
1530 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1531 std::vector<const MCSectionELF *> Sections;
1532 createIndexedSections(Asm, Layout, RevGroupMap, Sections, SectionIndexMap);
1534 // Compute symbol table information.
1535 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1537 SectionOffsetsTy SectionOffsets;
1539 // Write out the ELF header ...
1542 // ... then the sections ...
1543 SectionOffsets.push_back(std::make_pair(0, 0));
1544 for (auto I = ++Sections.begin(), E = Sections.end(); I != E; ++I) {
1545 const MCSectionELF &Sec = **I;
1546 const MCSectionData &SD = Asm.getOrCreateSectionData(Sec);
1547 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1548 WriteZeros(Padding);
1550 // Remember the offset into the file for this section.
1551 uint64_t SecStart = OS.tell();
1553 unsigned Type = Sec.getType();
1554 if (Type != ELF::SHT_REL && Type != ELF::SHT_RELA)
1555 writeDataSectionData(Asm, Layout, SD);
1557 writeRelocations(Asm, *Sec.getAssociatedSection());
1559 uint64_t SecEnd = OS.tell();
1560 SectionOffsets.push_back(std::make_pair(SecStart, SecEnd));
1563 WriteSymbolTable(Asm, Layout, Sections, SectionOffsets);
1566 uint64_t SecStart = OS.tell();
1567 createStringTable(Asm, Sections);
1568 uint64_t SecEnd = OS.tell();
1569 SectionOffsets.push_back(std::make_pair(SecStart, SecEnd));
1573 uint64_t SecStart = OS.tell();
1574 createSectionHeaderStringTable(Asm, Sections);
1575 uint64_t SecEnd = OS.tell();
1576 SectionOffsets[0] = std::make_pair(SecStart, SecEnd);
1579 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1580 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1581 WriteZeros(Padding);
1583 const unsigned SectionHeaderOffset = OS.tell();
1585 // ... then the section header table ...
1586 writeSectionHeader(Sections, Asm, Layout, SectionIndexMap, SectionOffsets);
1588 uint16_t NumSections = (Sections.size() + 1 >= ELF::SHN_LORESERVE)
1590 : Sections.size() + 1;
1591 if (sys::IsLittleEndianHost != IsLittleEndian)
1592 sys::swapByteOrder(NumSections);
1593 unsigned NumSectionsOffset;
1596 uint64_t Val = SectionHeaderOffset;
1597 if (sys::IsLittleEndianHost != IsLittleEndian)
1598 sys::swapByteOrder(Val);
1599 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1600 offsetof(ELF::Elf64_Ehdr, e_shoff));
1601 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1603 uint32_t Val = SectionHeaderOffset;
1604 if (sys::IsLittleEndianHost != IsLittleEndian)
1605 sys::swapByteOrder(Val);
1606 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1607 offsetof(ELF::Elf32_Ehdr, e_shoff));
1608 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1610 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1614 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1615 const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
1616 bool InSet, bool IsPCRel) const {
1619 if (::isWeak(DataA))
1622 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
1626 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
1630 // It is invalid to replace a reference to a global in a comdat
1631 // with a reference to a local since out of comdat references
1632 // to a local are forbidden.
1633 // We could try to return false for more cases, like the reference
1634 // being in the same comdat or Sym being an alias to another global,
1635 // but it is not clear if it is worth the effort.
1636 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1639 const MCSymbol &Sym = SD.getSymbol();
1640 if (!Sym.isInSection())
1643 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1644 return Sec.getGroup();
1647 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1648 raw_pwrite_stream &OS,
1649 bool IsLittleEndian) {
1650 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);