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);
82 /// Helper struct for containing some precomputed information on symbols.
83 struct ELFSymbolData {
84 MCSymbolData *SymbolData;
86 uint32_t SectionIndex;
89 // Support lexicographic sorting.
90 bool operator<(const ELFSymbolData &RHS) const {
91 unsigned LHSType = MCELF::GetType(*SymbolData);
92 unsigned RHSType = MCELF::GetType(*RHS.SymbolData);
93 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
95 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
97 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
98 return SectionIndex < RHS.SectionIndex;
99 return Name < RHS.Name;
103 /// The target specific ELF writer instance.
104 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
106 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
107 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
108 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
110 llvm::DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>>
112 StringTableBuilder ShStrTabBuilder;
115 /// @name Symbol Table Data
118 StringTableBuilder StrTabBuilder;
119 std::vector<uint64_t> FileSymbolData;
120 std::vector<ELFSymbolData> LocalSymbolData;
121 std::vector<ELFSymbolData> ExternalSymbolData;
122 std::vector<ELFSymbolData> UndefinedSymbolData;
128 // This holds the symbol table index of the last local symbol.
129 unsigned LastLocalSymbolIndex;
130 // This holds the .strtab section index.
131 unsigned StringTableIndex;
132 // This holds the .symtab section index.
133 unsigned SymbolTableIndex;
135 unsigned ShstrtabIndex;
138 // TargetObjectWriter wrappers.
139 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
140 bool hasRelocationAddend() const {
141 return TargetObjectWriter->hasRelocationAddend();
143 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
144 bool IsPCRel) const {
145 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
149 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
151 : MCObjectWriter(OS, IsLittleEndian), TargetObjectWriter(MOTW),
154 void reset() override {
156 WeakrefUsedInReloc.clear();
159 ShStrTabBuilder.clear();
160 StrTabBuilder.clear();
161 FileSymbolData.clear();
162 LocalSymbolData.clear();
163 ExternalSymbolData.clear();
164 UndefinedSymbolData.clear();
165 MCObjectWriter::reset();
168 ~ELFObjectWriter() override;
170 void WriteWord(uint64_t W) {
177 template <typename T> void write(T Val) {
179 support::endian::Writer<support::little>(OS).write(Val);
181 support::endian::Writer<support::big>(OS).write(Val);
184 template <typename T> void write(MCDataFragment &F, T Value);
186 void writeHeader(const MCAssembler &Asm);
188 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
189 const MCAsmLayout &Layout);
191 // Start and end offset of each section
192 typedef std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>
195 void WriteSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
196 std::vector<const MCSectionELF *> &Sections,
197 SectionOffsetsTy &SectionOffsets);
199 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
200 const MCSymbolRefExpr *RefA,
201 const MCSymbolData *SD, uint64_t C,
202 unsigned Type) const;
204 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
205 const MCFragment *Fragment, const MCFixup &Fixup,
206 MCValue Target, bool &IsPCRel,
207 uint64_t &FixedValue) override;
209 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
212 // Map from a signature symbol to the group section index
213 typedef DenseMap<const MCSymbol *, unsigned> RevGroupMapTy;
215 /// Compute the symbol table data
217 /// \param Asm - The assembler.
218 /// \param SectionIndexMap - Maps a section to its index.
219 /// \param RevGroupMap - Maps a signature symbol to the group section.
220 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
221 const SectionIndexMapTy &SectionIndexMap,
222 const RevGroupMapTy &RevGroupMap);
224 const MCSectionELF *createRelocationSection(MCAssembler &Asm,
225 const MCSectionELF &Sec);
227 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
230 createSectionHeaderStringTable(MCAssembler &Asm,
231 std::vector<const MCSectionELF *> &Sections);
233 createStringTable(MCAssembler &Asm,
234 std::vector<const MCSectionELF *> &Sections);
236 void ExecutePostLayoutBinding(MCAssembler &Asm,
237 const MCAsmLayout &Layout) override;
239 void writeSectionHeader(ArrayRef<const MCSectionELF *> Sections,
240 MCAssembler &Asm, const MCAsmLayout &Layout,
241 const SectionIndexMapTy &SectionIndexMap,
242 const SectionOffsetsTy &SectionOffsets);
244 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
245 uint64_t Address, uint64_t Offset,
246 uint64_t Size, uint32_t Link, uint32_t Info,
247 uint64_t Alignment, uint64_t EntrySize);
249 void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
252 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
253 const MCSymbolData &DataA,
254 const MCFragment &FB,
256 bool IsPCRel) const override;
258 bool isWeak(const MCSymbolData &SD) const override;
260 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
261 void writeSection(MCAssembler &Asm,
262 const SectionIndexMapTy &SectionIndexMap,
263 uint32_t GroupSymbolIndex,
264 uint64_t Offset, uint64_t Size, uint64_t Alignment,
265 const MCSectionELF &Section);
269 template <typename T> void ELFObjectWriter::write(MCDataFragment &F, T Val) {
271 Val = support::endian::byte_swap<T, support::little>(Val);
273 Val = support::endian::byte_swap<T, support::big>(Val);
274 const char *Start = (const char *)&Val;
275 F.getContents().append(Start, Start + sizeof(T));
278 void SymbolTableWriter::createSymtabShndx() {
279 if (!ShndxIndexes.empty())
282 ShndxIndexes.resize(NumWritten);
285 template <typename T> void SymbolTableWriter::write(T Value) {
286 EWriter.write(Value);
289 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
290 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
292 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
293 uint64_t size, uint8_t other,
294 uint32_t shndx, bool Reserved) {
295 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
300 if (!ShndxIndexes.empty()) {
302 ShndxIndexes.push_back(shndx);
304 ShndxIndexes.push_back(0);
307 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
310 write(name); // st_name
311 write(info); // st_info
312 write(other); // st_other
313 write(Index); // st_shndx
314 write(value); // st_value
315 write(size); // st_size
317 write(name); // st_name
318 write(uint32_t(value)); // st_value
319 write(uint32_t(size)); // st_size
320 write(info); // st_info
321 write(other); // st_other
322 write(Index); // st_shndx
328 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
329 const MCFixupKindInfo &FKI =
330 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
332 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
335 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
339 case MCSymbolRefExpr::VK_GOT:
340 case MCSymbolRefExpr::VK_PLT:
341 case MCSymbolRefExpr::VK_GOTPCREL:
342 case MCSymbolRefExpr::VK_GOTOFF:
343 case MCSymbolRefExpr::VK_TPOFF:
344 case MCSymbolRefExpr::VK_TLSGD:
345 case MCSymbolRefExpr::VK_GOTTPOFF:
346 case MCSymbolRefExpr::VK_INDNTPOFF:
347 case MCSymbolRefExpr::VK_NTPOFF:
348 case MCSymbolRefExpr::VK_GOTNTPOFF:
349 case MCSymbolRefExpr::VK_TLSLDM:
350 case MCSymbolRefExpr::VK_DTPOFF:
351 case MCSymbolRefExpr::VK_TLSLD:
356 ELFObjectWriter::~ELFObjectWriter()
359 // Emit the ELF header.
360 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
366 // emitWord method behaves differently for ELF32 and ELF64, writing
367 // 4 bytes in the former and 8 in the latter.
369 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
371 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
374 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
376 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
378 Write8(TargetObjectWriter->getOSABI());
379 Write8(0); // e_ident[EI_ABIVERSION]
381 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
383 Write16(ELF::ET_REL); // e_type
385 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
387 Write32(ELF::EV_CURRENT); // e_version
388 WriteWord(0); // e_entry, no entry point in .o file
389 WriteWord(0); // e_phoff, no program header for .o
390 WriteWord(0); // e_shoff = sec hdr table off in bytes
392 // e_flags = whatever the target wants
393 Write32(Asm.getELFHeaderEFlags());
395 // e_ehsize = ELF header size
396 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
398 Write16(0); // e_phentsize = prog header entry size
399 Write16(0); // e_phnum = # prog header entries = 0
401 // e_shentsize = Section header entry size
402 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
404 // e_shnum = # of section header ents
407 // e_shstrndx = Section # of '.shstrtab'
408 assert(ShstrtabIndex < ELF::SHN_LORESERVE);
409 Write16(ShstrtabIndex);
412 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
413 const MCAsmLayout &Layout) {
414 if (Data.isCommon() && Data.isExternal())
415 return Data.getCommonAlignment();
418 if (!Layout.getSymbolOffset(&Data, Res))
421 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
427 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
428 const MCAsmLayout &Layout) {
429 // The presence of symbol versions causes undefined symbols and
430 // versions declared with @@@ to be renamed.
432 for (MCSymbolData &OriginalData : Asm.symbols()) {
433 const MCSymbol &Alias = OriginalData.getSymbol();
436 if (!Alias.isVariable())
438 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
441 const MCSymbol &Symbol = Ref->getSymbol();
442 MCSymbolData &SD = Asm.getSymbolData(Symbol);
444 StringRef AliasName = Alias.getName();
445 size_t Pos = AliasName.find('@');
446 if (Pos == StringRef::npos)
449 // Aliases defined with .symvar copy the binding from the symbol they alias.
450 // This is the first place we are able to copy this information.
451 OriginalData.setExternal(SD.isExternal());
452 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
454 StringRef Rest = AliasName.substr(Pos);
455 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
458 // FIXME: produce a better error message.
459 if (Symbol.isUndefined() && Rest.startswith("@@") &&
460 !Rest.startswith("@@@"))
461 report_fatal_error("A @@ version cannot be undefined");
463 Renames.insert(std::make_pair(&Symbol, &Alias));
467 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
468 uint8_t Type = newType;
470 // Propagation rules:
471 // IFUNC > FUNC > OBJECT > NOTYPE
472 // TLS_OBJECT > OBJECT > NOTYPE
474 // dont let the new type degrade the old type
478 case ELF::STT_GNU_IFUNC:
479 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
480 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
481 Type = ELF::STT_GNU_IFUNC;
484 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
485 Type == ELF::STT_TLS)
486 Type = ELF::STT_FUNC;
488 case ELF::STT_OBJECT:
489 if (Type == ELF::STT_NOTYPE)
490 Type = ELF::STT_OBJECT;
493 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
494 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
502 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
503 const MCAsmLayout &Layout) {
504 MCSymbolData &OrigData = *MSD.SymbolData;
505 assert((!OrigData.getFragment() ||
506 (&OrigData.getFragment()->getParent()->getSection() ==
507 &OrigData.getSymbol().getSection())) &&
508 "The symbol's section doesn't match the fragment's symbol");
509 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
511 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
513 bool IsReserved = !Base || OrigData.isCommon();
515 // Binding and Type share the same byte as upper and lower nibbles
516 uint8_t Binding = MCELF::GetBinding(OrigData);
517 uint8_t Type = MCELF::GetType(OrigData);
518 MCSymbolData *BaseSD = nullptr;
520 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
521 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
523 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
525 // Other and Visibility share the same byte with Visibility using the lower
527 uint8_t Visibility = MCELF::GetVisibility(OrigData);
528 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
531 uint64_t Value = SymbolValue(OrigData, Layout);
534 const MCExpr *ESize = OrigData.getSize();
536 ESize = BaseSD->getSize();
540 if (!ESize->evaluateKnownAbsolute(Res, Layout))
541 report_fatal_error("Size expression must be absolute.");
545 // Write out the symbol table entry
546 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
547 MSD.SectionIndex, IsReserved);
550 void ELFObjectWriter::WriteSymbolTable(
551 MCAssembler &Asm, const MCAsmLayout &Layout,
552 std::vector<const MCSectionELF *> &Sections,
553 SectionOffsetsTy &SectionOffsets) {
555 MCContext &Ctx = Asm.getContext();
557 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
560 const MCSectionELF *SymtabSection =
561 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
562 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
563 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
564 SymbolTableIndex = Sections.size() + 1;
565 Sections.push_back(SymtabSection);
567 // The string table must be emitted first because we need the index
568 // into the string table for all the symbol names.
570 SymbolTableWriter Writer(*this, is64Bit());
572 uint64_t Padding = OffsetToAlignment(OS.tell(), SymtabSD.getAlignment());
575 uint64_t SecStart = OS.tell();
577 // The first entry is the undefined symbol entry.
578 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
580 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
581 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
582 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
585 // Write the symbol table entries.
586 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
588 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
589 ELFSymbolData &MSD = LocalSymbolData[i];
590 WriteSymbol(Writer, MSD, Layout);
593 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
594 ELFSymbolData &MSD = ExternalSymbolData[i];
595 MCSymbolData &Data = *MSD.SymbolData;
596 assert(((Data.getFlags() & ELF_STB_Global) ||
597 (Data.getFlags() & ELF_STB_Weak)) &&
598 "External symbol requires STB_GLOBAL or STB_WEAK flag");
599 WriteSymbol(Writer, MSD, Layout);
600 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
601 LastLocalSymbolIndex++;
604 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
605 ELFSymbolData &MSD = UndefinedSymbolData[i];
606 MCSymbolData &Data = *MSD.SymbolData;
607 WriteSymbol(Writer, MSD, Layout);
608 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
609 LastLocalSymbolIndex++;
612 uint64_t SecEnd = OS.tell();
613 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
615 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
616 if (ShndxIndexes.empty())
619 SecStart = OS.tell();
620 const MCSectionELF *SymtabShndxSection =
621 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
622 Sections.push_back(SymtabShndxSection);
623 MCSectionData *SymtabShndxSD =
624 &Asm.getOrCreateSectionData(*SymtabShndxSection);
625 SymtabShndxSD->setAlignment(4);
626 for (uint32_t Index : ShndxIndexes)
629 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
632 // It is always valid to create a relocation with a symbol. It is preferable
633 // to use a relocation with a section if that is possible. Using the section
634 // allows us to omit some local symbols from the symbol table.
635 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
636 const MCSymbolRefExpr *RefA,
637 const MCSymbolData *SD,
639 unsigned Type) const {
640 // A PCRel relocation to an absolute value has no symbol (or section). We
641 // represent that with a relocation to a null section.
645 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
649 // The .odp creation emits a relocation against the symbol ".TOC." which
650 // create a R_PPC64_TOC relocation. However the relocation symbol name
651 // in final object creation should be NULL, since the symbol does not
652 // really exist, it is just the reference to TOC base for the current
653 // object file. Since the symbol is undefined, returning false results
654 // in a relocation with a null section which is the desired result.
655 case MCSymbolRefExpr::VK_PPC_TOCBASE:
658 // These VariantKind cause the relocation to refer to something other than
659 // the symbol itself, like a linker generated table. Since the address of
660 // symbol is not relevant, we cannot replace the symbol with the
661 // section and patch the difference in the addend.
662 case MCSymbolRefExpr::VK_GOT:
663 case MCSymbolRefExpr::VK_PLT:
664 case MCSymbolRefExpr::VK_GOTPCREL:
665 case MCSymbolRefExpr::VK_Mips_GOT:
666 case MCSymbolRefExpr::VK_PPC_GOT_LO:
667 case MCSymbolRefExpr::VK_PPC_GOT_HI:
668 case MCSymbolRefExpr::VK_PPC_GOT_HA:
672 // An undefined symbol is not in any section, so the relocation has to point
673 // to the symbol itself.
674 const MCSymbol &Sym = SD->getSymbol();
675 if (Sym.isUndefined())
678 unsigned Binding = MCELF::GetBinding(*SD);
681 llvm_unreachable("Invalid Binding");
685 // If the symbol is weak, it might be overridden by a symbol in another
686 // file. The relocation has to point to the symbol so that the linker
689 case ELF::STB_GLOBAL:
690 // Global ELF symbols can be preempted by the dynamic linker. The relocation
691 // has to point to the symbol for a reason analogous to the STB_WEAK case.
695 // If a relocation points to a mergeable section, we have to be careful.
696 // If the offset is zero, a relocation with the section will encode the
697 // same information. With a non-zero offset, the situation is different.
698 // For example, a relocation can point 42 bytes past the end of a string.
699 // If we change such a relocation to use the section, the linker would think
700 // that it pointed to another string and subtracting 42 at runtime will
701 // produce the wrong value.
702 auto &Sec = cast<MCSectionELF>(Sym.getSection());
703 unsigned Flags = Sec.getFlags();
704 if (Flags & ELF::SHF_MERGE) {
708 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
709 // only handle section relocations to mergeable sections if using RELA.
710 if (!hasRelocationAddend())
714 // Most TLS relocations use a got, so they need the symbol. Even those that
715 // are just an offset (@tpoff), require a symbol in gold versions before
716 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
717 // http://sourceware.org/PR16773.
718 if (Flags & ELF::SHF_TLS)
721 // If the symbol is a thumb function the final relocation must set the lowest
722 // bit. With a symbol that is done by just having the symbol have that bit
723 // set, so we would lose the bit if we relocated with the section.
724 // FIXME: We could use the section but add the bit to the relocation value.
725 if (Asm.isThumbFunc(&Sym))
728 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
733 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
734 const MCSymbol &Sym = Ref.getSymbol();
736 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
739 if (!Sym.isVariable())
742 const MCExpr *Expr = Sym.getVariableValue();
743 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
747 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
748 return &Inner->getSymbol();
752 // True if the assembler knows nothing about the final value of the symbol.
753 // This doesn't cover the comdat issues, since in those cases the assembler
754 // can at least know that all symbols in the section will move together.
755 static bool isWeak(const MCSymbolData &D) {
756 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
759 switch (MCELF::GetBinding(D)) {
761 llvm_unreachable("Unknown binding");
764 case ELF::STB_GLOBAL:
767 case ELF::STB_GNU_UNIQUE:
772 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
773 const MCAsmLayout &Layout,
774 const MCFragment *Fragment,
775 const MCFixup &Fixup, MCValue Target,
776 bool &IsPCRel, uint64_t &FixedValue) {
777 const MCSectionData *FixupSectionD = Fragment->getParent();
778 const MCSectionELF &FixupSection =
779 cast<MCSectionELF>(FixupSectionD->getSection());
780 uint64_t C = Target.getConstant();
781 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
783 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
784 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
785 "Should not have constructed this");
787 // Let A, B and C being the components of Target and R be the location of
788 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
789 // If it is pcrel, we want to compute (A - B + C - R).
791 // In general, ELF has no relocations for -B. It can only represent (A + C)
792 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
793 // replace B to implement it: (A - R - K + C)
795 Asm.getContext().FatalError(
797 "No relocation available to represent this relative expression");
799 const MCSymbol &SymB = RefB->getSymbol();
801 if (SymB.isUndefined())
802 Asm.getContext().FatalError(
804 Twine("symbol '") + SymB.getName() +
805 "' can not be undefined in a subtraction expression");
807 assert(!SymB.isAbsolute() && "Should have been folded");
808 const MCSection &SecB = SymB.getSection();
809 if (&SecB != &FixupSection)
810 Asm.getContext().FatalError(
811 Fixup.getLoc(), "Cannot represent a difference across sections");
813 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
815 Asm.getContext().FatalError(
816 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
818 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
819 uint64_t K = SymBOffset - FixupOffset;
824 // We either rejected the fixup or folded B into C at this point.
825 const MCSymbolRefExpr *RefA = Target.getSymA();
826 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
827 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
829 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
830 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
831 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
832 C += Layout.getSymbolOffset(SymAD);
835 if (hasRelocationAddend()) {
842 // FIXME: What is this!?!?
843 MCSymbolRefExpr::VariantKind Modifier =
844 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
845 if (RelocNeedsGOT(Modifier))
848 if (!RelocateWithSymbol) {
849 const MCSection *SecA =
850 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
851 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
852 MCSymbol *SectionSymbol =
853 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
855 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
856 Relocations[&FixupSection].push_back(Rec);
861 if (const MCSymbol *R = Renames.lookup(SymA))
864 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
865 WeakrefUsedInReloc.insert(WeakRef);
867 UsedInReloc.insert(SymA);
869 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
870 Relocations[&FixupSection].push_back(Rec);
876 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
878 const MCSymbolData &SD = Asm.getSymbolData(*S);
879 return SD.getIndex();
882 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
883 const MCSymbolData &Data, bool Used,
885 const MCSymbol &Symbol = Data.getSymbol();
886 if (Symbol.isVariable()) {
887 const MCExpr *Expr = Symbol.getVariableValue();
888 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
889 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
900 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
903 if (Symbol.isVariable()) {
904 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
905 if (Base && Base->isUndefined())
909 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
910 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
913 if (Symbol.isTemporary())
919 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
920 if (Data.isExternal())
923 const MCSymbol &Symbol = Data.getSymbol();
924 if (Symbol.isDefined())
933 void ELFObjectWriter::computeSymbolTable(
934 MCAssembler &Asm, const MCAsmLayout &Layout,
935 const SectionIndexMapTy &SectionIndexMap,
936 const RevGroupMapTy &RevGroupMap) {
937 // FIXME: Is this the correct place to do this?
938 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
940 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
941 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
942 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
943 Data.setExternal(true);
944 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
947 // Add the data for the symbols.
948 for (MCSymbolData &SD : Asm.symbols()) {
949 const MCSymbol &Symbol = SD.getSymbol();
951 bool Used = UsedInReloc.count(&Symbol);
952 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
953 bool isSignature = RevGroupMap.count(&Symbol);
955 if (!isInSymtab(Layout, SD,
956 Used || WeakrefUsed || isSignature,
957 Renames.count(&Symbol)))
961 MSD.SymbolData = &SD;
962 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
964 // Undefined symbols are global, but this is the first place we
965 // are able to set it.
966 bool Local = isLocal(SD, Used);
967 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
969 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
970 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
971 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
975 MSD.SectionIndex = ELF::SHN_ABS;
976 } else if (SD.isCommon()) {
978 MSD.SectionIndex = ELF::SHN_COMMON;
979 } else if (BaseSymbol->isUndefined()) {
980 if (isSignature && !Used)
981 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
983 MSD.SectionIndex = ELF::SHN_UNDEF;
984 if (!Used && WeakrefUsed)
985 MCELF::SetBinding(SD, ELF::STB_WEAK);
987 const MCSectionELF &Section =
988 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
989 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
990 assert(MSD.SectionIndex && "Invalid section index!");
993 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
996 // FIXME: All name handling should be done before we get to the writer,
997 // including dealing with GNU-style version suffixes. Fixing this isn't
1000 // We thus have to be careful to not perform the symbol version replacement
1003 // The ELF format is used on Windows by the MCJIT engine. Thus, on
1004 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
1005 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
1006 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
1007 // the EFLObjectWriter should not interpret the "@@@" sub-string as
1008 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1009 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1010 // "__imp_?" or "__imp_@?".
1012 // It would have been interesting to perform the MS mangling prefix check
1013 // only when the target triple is of the form *-pc-windows-elf. But, it
1014 // seems that this information is not easily accessible from the
1016 StringRef Name = Symbol.getName();
1017 if (!Name.startswith("?") && !Name.startswith("@?") &&
1018 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1019 // This symbol isn't following the MSVC C++ name mangling convention. We
1020 // can thus safely interpret the @@@ in symbol names as specifying symbol
1022 SmallString<32> Buf;
1023 size_t Pos = Name.find("@@@");
1024 if (Pos != StringRef::npos) {
1025 Buf += Name.substr(0, Pos);
1026 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1027 Buf += Name.substr(Pos + Skip);
1032 // Sections have their own string table
1033 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1034 MSD.Name = StrTabBuilder.add(Name);
1036 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1037 UndefinedSymbolData.push_back(MSD);
1039 LocalSymbolData.push_back(MSD);
1041 ExternalSymbolData.push_back(MSD);
1044 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1045 StrTabBuilder.add(*i);
1047 StrTabBuilder.finalize(StringTableBuilder::ELF);
1049 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1050 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1052 for (ELFSymbolData &MSD : LocalSymbolData)
1053 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1055 : StrTabBuilder.getOffset(MSD.Name);
1056 for (ELFSymbolData &MSD : ExternalSymbolData)
1057 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1058 for (ELFSymbolData& MSD : UndefinedSymbolData)
1059 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1061 // Symbols are required to be in lexicographic order.
1062 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1063 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1064 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1066 // Set the symbol indices. Local symbols must come before all other
1067 // symbols with non-local bindings.
1068 unsigned Index = FileSymbolData.size() + 1;
1069 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1070 LocalSymbolData[i].SymbolData->setIndex(Index++);
1072 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1073 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1074 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1075 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1078 const MCSectionELF *
1079 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1080 const MCSectionELF &Sec) {
1081 if (Relocations[&Sec].empty())
1084 MCContext &Ctx = Asm.getContext();
1085 const StringRef SectionName = Sec.getSectionName();
1086 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1087 RelaSectionName += SectionName;
1090 if (hasRelocationAddend())
1091 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1093 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1096 if (Sec.getFlags() & ELF::SHF_GROUP)
1097 Flags = ELF::SHF_GROUP;
1099 const MCSectionELF *RelaSection = Ctx.createELFRelSection(
1100 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1101 Flags, EntrySize, Sec.getGroup(), &Sec);
1102 MCSectionData &RelSD = Asm.getOrCreateSectionData(*RelaSection);
1103 RelSD.setAlignment(is64Bit() ? 8 : 4);
1107 static SmallVector<char, 128>
1108 getUncompressedData(const MCAsmLayout &Layout,
1109 MCSectionData::FragmentListType &Fragments) {
1110 SmallVector<char, 128> UncompressedData;
1111 for (const MCFragment &F : Fragments) {
1112 const SmallVectorImpl<char> *Contents;
1113 switch (F.getKind()) {
1114 case MCFragment::FT_Data:
1115 Contents = &cast<MCDataFragment>(F).getContents();
1117 case MCFragment::FT_Dwarf:
1118 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1120 case MCFragment::FT_DwarfFrame:
1121 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1125 "Not expecting any other fragment types in a debug_* section");
1127 UncompressedData.append(Contents->begin(), Contents->end());
1129 return UncompressedData;
1132 // Include the debug info compression header:
1133 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1134 // useful for consumers to preallocate a buffer to decompress into.
1136 prependCompressionHeader(uint64_t Size,
1137 SmallVectorImpl<char> &CompressedContents) {
1138 const StringRef Magic = "ZLIB";
1139 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1141 if (sys::IsLittleEndianHost)
1142 sys::swapByteOrder(Size);
1143 CompressedContents.insert(CompressedContents.begin(),
1144 Magic.size() + sizeof(Size), 0);
1145 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1146 std::copy(reinterpret_cast<char *>(&Size),
1147 reinterpret_cast<char *>(&Size + 1),
1148 CompressedContents.begin() + Magic.size());
1152 // Return a single fragment containing the compressed contents of the whole
1153 // section. Null if the section was not compressed for any reason.
1154 static std::unique_ptr<MCDataFragment>
1155 getCompressedFragment(const MCAsmLayout &Layout,
1156 MCSectionData::FragmentListType &Fragments) {
1157 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1159 // Gather the uncompressed data from all the fragments, recording the
1160 // alignment fragment, if seen, and any fixups.
1161 SmallVector<char, 128> UncompressedData =
1162 getUncompressedData(Layout, Fragments);
1164 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1166 zlib::Status Success = zlib::compress(
1167 StringRef(UncompressedData.data(), UncompressedData.size()),
1168 CompressedContents);
1169 if (Success != zlib::StatusOK)
1172 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1175 return CompressedFragment;
1178 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1181 static void UpdateSymbols(const MCAsmLayout &Layout,
1182 const std::vector<MCSymbolData *> &Symbols,
1183 MCFragment &NewFragment) {
1184 for (MCSymbolData *Sym : Symbols) {
1185 Sym->setOffset(Sym->getOffset() +
1186 Layout.getFragmentOffset(Sym->getFragment()));
1187 Sym->setFragment(&NewFragment);
1191 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1192 const DefiningSymbolMap &DefiningSymbols,
1193 const MCSectionELF &Section,
1194 MCSectionData &SD) {
1195 StringRef SectionName = Section.getSectionName();
1196 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1198 std::unique_ptr<MCDataFragment> CompressedFragment =
1199 getCompressedFragment(Layout, Fragments);
1201 // Leave the section as-is if the fragments could not be compressed.
1202 if (!CompressedFragment)
1205 // Update the fragment+offsets of any symbols referring to fragments in this
1206 // section to refer to the new fragment.
1207 auto I = DefiningSymbols.find(&SD);
1208 if (I != DefiningSymbols.end())
1209 UpdateSymbols(Layout, I->second, *CompressedFragment);
1211 // Invalidate the layout for the whole section since it will have new and
1212 // different fragments now.
1213 Layout.invalidateFragmentsFrom(&Fragments.front());
1216 // Complete the initialization of the new fragment
1217 CompressedFragment->setParent(&SD);
1218 CompressedFragment->setLayoutOrder(0);
1219 Fragments.push_back(CompressedFragment.release());
1221 // Rename from .debug_* to .zdebug_*
1222 Asm.getContext().renameELFSection(&Section,
1223 (".z" + SectionName.drop_front(1)).str());
1226 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1227 MCAsmLayout &Layout) {
1228 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1231 DefiningSymbolMap DefiningSymbols;
1233 for (MCSymbolData &SD : Asm.symbols())
1234 if (MCFragment *F = SD.getFragment())
1235 DefiningSymbols[F->getParent()].push_back(&SD);
1237 for (MCSectionData &SD : Asm) {
1238 const MCSectionELF &Section =
1239 static_cast<const MCSectionELF &>(SD.getSection());
1240 StringRef SectionName = Section.getSectionName();
1242 // Compressing debug_frame requires handling alignment fragments which is
1243 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1244 // for writing to arbitrary buffers) for little benefit.
1245 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1248 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1252 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1253 uint64_t Flags, uint64_t Address,
1254 uint64_t Offset, uint64_t Size,
1255 uint32_t Link, uint32_t Info,
1257 uint64_t EntrySize) {
1258 Write32(Name); // sh_name: index into string table
1259 Write32(Type); // sh_type
1260 WriteWord(Flags); // sh_flags
1261 WriteWord(Address); // sh_addr
1262 WriteWord(Offset); // sh_offset
1263 WriteWord(Size); // sh_size
1264 Write32(Link); // sh_link
1265 Write32(Info); // sh_info
1266 WriteWord(Alignment); // sh_addralign
1267 WriteWord(EntrySize); // sh_entsize
1270 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1271 const MCSectionELF &Sec) {
1272 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1274 // Sort the relocation entries. Most targets just sort by Offset, but some
1275 // (e.g., MIPS) have additional constraints.
1276 TargetObjectWriter->sortRelocs(Asm, Relocs);
1278 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1279 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1281 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1284 write(Entry.Offset);
1285 if (TargetObjectWriter->isN64()) {
1286 write(uint32_t(Index));
1288 write(TargetObjectWriter->getRSsym(Entry.Type));
1289 write(TargetObjectWriter->getRType3(Entry.Type));
1290 write(TargetObjectWriter->getRType2(Entry.Type));
1291 write(TargetObjectWriter->getRType(Entry.Type));
1293 struct ELF::Elf64_Rela ERE64;
1294 ERE64.setSymbolAndType(Index, Entry.Type);
1295 write(ERE64.r_info);
1297 if (hasRelocationAddend())
1298 write(Entry.Addend);
1300 write(uint32_t(Entry.Offset));
1302 struct ELF::Elf32_Rela ERE32;
1303 ERE32.setSymbolAndType(Index, Entry.Type);
1304 write(ERE32.r_info);
1306 if (hasRelocationAddend())
1307 write(uint32_t(Entry.Addend));
1312 const MCSectionELF *ELFObjectWriter::createSectionHeaderStringTable(
1313 MCAssembler &Asm, std::vector<const MCSectionELF *> &Sections) {
1314 const MCSectionELF *ShstrtabSection = Sections[ShstrtabIndex - 1];
1316 Asm.getOrCreateSectionData(*ShstrtabSection);
1318 for (MCSectionData &SD : Asm) {
1319 const MCSectionELF &Section =
1320 static_cast<const MCSectionELF &>(SD.getSection());
1321 ShStrTabBuilder.add(Section.getSectionName());
1323 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1324 OS << ShStrTabBuilder.data();
1325 return ShstrtabSection;
1328 const MCSectionELF *ELFObjectWriter::createStringTable(
1329 MCAssembler &Asm, std::vector<const MCSectionELF *> &Sections) {
1330 MCContext &Ctx = Asm.getContext();
1331 const MCSectionELF *StrtabSection =
1332 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1333 Asm.getOrCreateSectionData(*StrtabSection);
1334 Sections.push_back(StrtabSection);
1335 StringTableIndex = Sections.size();
1336 OS << StrTabBuilder.data();
1337 return StrtabSection;
1340 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1341 const SectionIndexMapTy &SectionIndexMap,
1342 uint32_t GroupSymbolIndex,
1343 uint64_t Offset, uint64_t Size,
1345 const MCSectionELF &Section) {
1346 uint64_t sh_link = 0;
1347 uint64_t sh_info = 0;
1349 switch(Section.getType()) {
1354 case ELF::SHT_DYNAMIC:
1355 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1359 case ELF::SHT_RELA: {
1360 sh_link = SymbolTableIndex;
1361 assert(sh_link && ".symtab not found");
1362 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1363 sh_info = SectionIndexMap.lookup(InfoSection);
1367 case ELF::SHT_SYMTAB:
1368 case ELF::SHT_DYNSYM:
1369 sh_link = StringTableIndex;
1370 sh_info = LastLocalSymbolIndex;
1373 case ELF::SHT_SYMTAB_SHNDX:
1374 sh_link = SymbolTableIndex;
1377 case ELF::SHT_GROUP:
1378 sh_link = SymbolTableIndex;
1379 sh_info = GroupSymbolIndex;
1383 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1384 Section.getType() == ELF::SHT_ARM_EXIDX)
1385 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1387 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1389 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1390 Alignment, Section.getEntrySize());
1393 void ELFObjectWriter::writeSectionHeader(
1394 ArrayRef<const MCSectionELF *> Sections, MCAssembler &Asm,
1395 const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap,
1396 const SectionOffsetsTy &SectionOffsets) {
1397 const unsigned NumSections = Asm.size();
1399 // Null section first.
1400 uint64_t FirstSectionSize =
1401 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1402 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1404 for (unsigned i = 0; i < NumSections; ++i) {
1405 const MCSectionELF &Section = *Sections[i];
1406 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1407 uint32_t GroupSymbolIndex;
1408 if (Section.getType() != ELF::SHT_GROUP)
1409 GroupSymbolIndex = 0;
1411 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section.getGroup());
1413 const std::pair<uint64_t, uint64_t> &Offsets =
1414 SectionOffsets.find(&Section)->second;
1415 uint64_t Size = Section.getType() == ELF::SHT_NOBITS
1416 ? Layout.getSectionAddressSize(&SD)
1417 : Offsets.second - Offsets.first;
1419 writeSection(Asm, SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1420 SD.getAlignment(), Section);
1424 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1425 const MCAsmLayout &Layout) {
1426 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1428 std::vector<const MCSectionELF *> Sections;
1429 MCContext &Ctx = Asm.getContext();
1430 const MCSectionELF *ShstrtabSection =
1431 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1432 Sections.push_back(ShstrtabSection);
1433 ShstrtabIndex = Sections.size();
1435 RevGroupMapTy RevGroupMap;
1436 SectionIndexMapTy SectionIndexMap;
1438 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1440 // Write out the ELF header ...
1443 // ... then the sections ...
1444 SectionOffsetsTy SectionOffsets;
1445 bool ComputedSymtab = false;
1446 for (const MCSectionData &SD : Asm) {
1447 const MCSectionELF &Section =
1448 static_cast<const MCSectionELF &>(SD.getSection());
1450 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1451 WriteZeros(Padding);
1453 // Remember the offset into the file for this section.
1454 uint64_t SecStart = OS.tell();
1456 const MCSymbol *SignatureSymbol = Section.getGroup();
1457 unsigned Type = Section.getType();
1458 if (Type == ELF::SHT_GROUP) {
1459 assert(SignatureSymbol);
1460 write(uint32_t(ELF::GRP_COMDAT));
1461 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1462 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1465 } else if (Type == ELF::SHT_REL || Type == ELF::SHT_RELA) {
1466 if (!ComputedSymtab) {
1467 // Compute symbol table information.
1468 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1469 ComputedSymtab = true;
1471 writeRelocations(Asm, *Section.getAssociatedSection());
1473 Asm.writeSectionData(&SD, Layout);
1476 uint64_t SecEnd = OS.tell();
1477 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1479 if (Type == ELF::SHT_GROUP || Type == ELF::SHT_REL || Type == ELF::SHT_RELA)
1482 const MCSectionELF *RelSection = createRelocationSection(Asm, Section);
1484 if (SignatureSymbol) {
1485 Asm.getOrCreateSymbolData(*SignatureSymbol);
1486 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1488 const MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1489 Sections.push_back(Group);
1490 GroupIdx = Sections.size();
1491 MCSectionData *GroupD = &Asm.getOrCreateSectionData(*Group);
1492 GroupD->setAlignment(4);
1494 GroupMembers[SignatureSymbol].push_back(&Section);
1496 GroupMembers[SignatureSymbol].push_back(RelSection);
1499 Sections.push_back(&Section);
1500 SectionIndexMap[&Section] = Sections.size();
1502 Sections.push_back(RelSection);
1503 SectionIndexMap[RelSection] = Sections.size();
1507 if (!ComputedSymtab) {
1508 // Compute symbol table information.
1509 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1510 ComputedSymtab = true;
1513 WriteSymbolTable(Asm, Layout, Sections, SectionOffsets);
1516 uint64_t SecStart = OS.tell();
1517 const MCSectionELF *Sec = createStringTable(Asm, Sections);
1518 uint64_t SecEnd = OS.tell();
1519 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1523 uint64_t SecStart = OS.tell();
1524 const MCSectionELF *Sec = createSectionHeaderStringTable(Asm, Sections);
1525 uint64_t SecEnd = OS.tell();
1526 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1529 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1530 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1531 WriteZeros(Padding);
1533 const unsigned SectionHeaderOffset = OS.tell();
1535 // ... then the section header table ...
1536 writeSectionHeader(Sections, Asm, Layout, SectionIndexMap, SectionOffsets);
1538 uint16_t NumSections = (Sections.size() + 1 >= ELF::SHN_LORESERVE)
1539 ? (uint16_t)ELF::SHN_UNDEF
1540 : Sections.size() + 1;
1541 if (sys::IsLittleEndianHost != IsLittleEndian)
1542 sys::swapByteOrder(NumSections);
1543 unsigned NumSectionsOffset;
1546 uint64_t Val = SectionHeaderOffset;
1547 if (sys::IsLittleEndianHost != IsLittleEndian)
1548 sys::swapByteOrder(Val);
1549 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1550 offsetof(ELF::Elf64_Ehdr, e_shoff));
1551 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1553 uint32_t Val = SectionHeaderOffset;
1554 if (sys::IsLittleEndianHost != IsLittleEndian)
1555 sys::swapByteOrder(Val);
1556 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1557 offsetof(ELF::Elf32_Ehdr, e_shoff));
1558 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1560 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1564 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1565 const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
1566 bool InSet, bool IsPCRel) const {
1569 if (::isWeak(DataA))
1572 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
1576 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
1580 // It is invalid to replace a reference to a global in a comdat
1581 // with a reference to a local since out of comdat references
1582 // to a local are forbidden.
1583 // We could try to return false for more cases, like the reference
1584 // being in the same comdat or Sym being an alias to another global,
1585 // but it is not clear if it is worth the effort.
1586 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1589 const MCSymbol &Sym = SD.getSymbol();
1590 if (!Sym.isInSection())
1593 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1594 return Sec.getGroup();
1597 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1598 raw_pwrite_stream &OS,
1599 bool IsLittleEndian) {
1600 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);