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 {
73 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
74 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
75 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
76 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data,
77 bool Used, bool Renamed);
78 static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
80 /// Helper struct for containing some precomputed information on symbols.
81 struct ELFSymbolData {
82 MCSymbolData *SymbolData;
84 uint32_t SectionIndex;
87 // Support lexicographic sorting.
88 bool operator<(const ELFSymbolData &RHS) const {
89 unsigned LHSType = MCELF::GetType(*SymbolData);
90 unsigned RHSType = MCELF::GetType(*RHS.SymbolData);
91 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
93 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
95 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
96 return SectionIndex < RHS.SectionIndex;
97 return Name < RHS.Name;
101 /// The target specific ELF writer instance.
102 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
104 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
105 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
106 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
108 llvm::DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>>
110 StringTableBuilder ShStrTabBuilder;
113 /// @name Symbol Table Data
116 StringTableBuilder StrTabBuilder;
117 std::vector<uint64_t> FileSymbolData;
118 std::vector<ELFSymbolData> LocalSymbolData;
119 std::vector<ELFSymbolData> ExternalSymbolData;
120 std::vector<ELFSymbolData> UndefinedSymbolData;
126 // This holds the symbol table index of the last local symbol.
127 unsigned LastLocalSymbolIndex;
128 // This holds the .strtab section index.
129 unsigned StringTableIndex;
130 // This holds the .symtab section index.
131 unsigned SymbolTableIndex;
133 unsigned ShstrtabIndex;
135 // Sections in the order they are to be output in the section table.
136 std::vector<const MCSectionELF *> SectionTable;
137 unsigned addToSectionTable(const MCSectionELF *Sec);
139 // TargetObjectWriter wrappers.
140 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
141 bool hasRelocationAddend() const {
142 return TargetObjectWriter->hasRelocationAddend();
144 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
145 bool IsPCRel) const {
146 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
150 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
152 : MCObjectWriter(OS, IsLittleEndian), TargetObjectWriter(MOTW),
155 void reset() override {
157 WeakrefUsedInReloc.clear();
160 ShStrTabBuilder.clear();
161 StrTabBuilder.clear();
162 FileSymbolData.clear();
163 LocalSymbolData.clear();
164 ExternalSymbolData.clear();
165 UndefinedSymbolData.clear();
166 MCObjectWriter::reset();
169 ~ELFObjectWriter() override;
171 void WriteWord(uint64_t W) {
178 template <typename T> void write(T Val) {
180 support::endian::Writer<support::little>(OS).write(Val);
182 support::endian::Writer<support::big>(OS).write(Val);
185 template <typename T> void write(MCDataFragment &F, T Value);
187 void writeHeader(const MCAssembler &Asm);
189 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
190 const MCAsmLayout &Layout);
192 // Start and end offset of each section
193 typedef std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>
196 void WriteSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
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);
229 const MCSectionELF *createSectionHeaderStringTable();
230 const MCSectionELF *createStringTable(MCContext &Ctx);
232 void ExecutePostLayoutBinding(MCAssembler &Asm,
233 const MCAsmLayout &Layout) override;
235 void writeSectionHeader(MCAssembler &Asm, const MCAsmLayout &Layout,
236 const SectionIndexMapTy &SectionIndexMap,
237 const SectionOffsetsTy &SectionOffsets);
239 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
240 uint64_t Address, uint64_t Offset,
241 uint64_t Size, uint32_t Link, uint32_t Info,
242 uint64_t Alignment, uint64_t EntrySize);
244 void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
247 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
248 const MCSymbolData &DataA,
249 const MCFragment &FB,
251 bool IsPCRel) const override;
253 bool isWeak(const MCSymbolData &SD) const override;
255 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
256 void writeSection(MCAssembler &Asm,
257 const SectionIndexMapTy &SectionIndexMap,
258 uint32_t GroupSymbolIndex,
259 uint64_t Offset, uint64_t Size, uint64_t Alignment,
260 const MCSectionELF &Section);
264 unsigned ELFObjectWriter::addToSectionTable(const MCSectionELF *Sec) {
265 SectionTable.push_back(Sec);
266 ShStrTabBuilder.add(Sec->getSectionName());
267 return SectionTable.size();
270 template <typename T> void ELFObjectWriter::write(MCDataFragment &F, T Val) {
272 Val = support::endian::byte_swap<T, support::little>(Val);
274 Val = support::endian::byte_swap<T, support::big>(Val);
275 const char *Start = (const char *)&Val;
276 F.getContents().append(Start, Start + sizeof(T));
279 void SymbolTableWriter::createSymtabShndx() {
280 if (!ShndxIndexes.empty())
283 ShndxIndexes.resize(NumWritten);
286 template <typename T> void SymbolTableWriter::write(T Value) {
287 EWriter.write(Value);
290 SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
291 : EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
293 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
294 uint64_t size, uint8_t other,
295 uint32_t shndx, bool Reserved) {
296 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
301 if (!ShndxIndexes.empty()) {
303 ShndxIndexes.push_back(shndx);
305 ShndxIndexes.push_back(0);
308 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
311 write(name); // st_name
312 write(info); // st_info
313 write(other); // st_other
314 write(Index); // st_shndx
315 write(value); // st_value
316 write(size); // st_size
318 write(name); // st_name
319 write(uint32_t(value)); // st_value
320 write(uint32_t(size)); // st_size
321 write(info); // st_info
322 write(other); // st_other
323 write(Index); // st_shndx
329 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
330 const MCFixupKindInfo &FKI =
331 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
333 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
336 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
340 case MCSymbolRefExpr::VK_GOT:
341 case MCSymbolRefExpr::VK_PLT:
342 case MCSymbolRefExpr::VK_GOTPCREL:
343 case MCSymbolRefExpr::VK_GOTOFF:
344 case MCSymbolRefExpr::VK_TPOFF:
345 case MCSymbolRefExpr::VK_TLSGD:
346 case MCSymbolRefExpr::VK_GOTTPOFF:
347 case MCSymbolRefExpr::VK_INDNTPOFF:
348 case MCSymbolRefExpr::VK_NTPOFF:
349 case MCSymbolRefExpr::VK_GOTNTPOFF:
350 case MCSymbolRefExpr::VK_TLSLDM:
351 case MCSymbolRefExpr::VK_DTPOFF:
352 case MCSymbolRefExpr::VK_TLSLD:
357 ELFObjectWriter::~ELFObjectWriter()
360 // Emit the ELF header.
361 void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
367 // emitWord method behaves differently for ELF32 and ELF64, writing
368 // 4 bytes in the former and 8 in the latter.
370 WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
372 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
375 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
377 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
379 Write8(TargetObjectWriter->getOSABI());
380 Write8(0); // e_ident[EI_ABIVERSION]
382 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
384 Write16(ELF::ET_REL); // e_type
386 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
388 Write32(ELF::EV_CURRENT); // e_version
389 WriteWord(0); // e_entry, no entry point in .o file
390 WriteWord(0); // e_phoff, no program header for .o
391 WriteWord(0); // e_shoff = sec hdr table off in bytes
393 // e_flags = whatever the target wants
394 Write32(Asm.getELFHeaderEFlags());
396 // e_ehsize = ELF header size
397 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
399 Write16(0); // e_phentsize = prog header entry size
400 Write16(0); // e_phnum = # prog header entries = 0
402 // e_shentsize = Section header entry size
403 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
405 // e_shnum = # of section header ents
408 // e_shstrndx = Section # of '.shstrtab'
409 assert(ShstrtabIndex < ELF::SHN_LORESERVE);
410 Write16(ShstrtabIndex);
413 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
414 const MCAsmLayout &Layout) {
415 if (Data.isCommon() && Data.isExternal())
416 return Data.getCommonAlignment();
419 if (!Layout.getSymbolOffset(&Data, Res))
422 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
428 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
429 const MCAsmLayout &Layout) {
430 // The presence of symbol versions causes undefined symbols and
431 // versions declared with @@@ to be renamed.
433 for (MCSymbolData &OriginalData : Asm.symbols()) {
434 const MCSymbol &Alias = OriginalData.getSymbol();
437 if (!Alias.isVariable())
439 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
442 const MCSymbol &Symbol = Ref->getSymbol();
443 MCSymbolData &SD = Asm.getSymbolData(Symbol);
445 StringRef AliasName = Alias.getName();
446 size_t Pos = AliasName.find('@');
447 if (Pos == StringRef::npos)
450 // Aliases defined with .symvar copy the binding from the symbol they alias.
451 // This is the first place we are able to copy this information.
452 OriginalData.setExternal(SD.isExternal());
453 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
455 StringRef Rest = AliasName.substr(Pos);
456 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
459 // FIXME: produce a better error message.
460 if (Symbol.isUndefined() && Rest.startswith("@@") &&
461 !Rest.startswith("@@@"))
462 report_fatal_error("A @@ version cannot be undefined");
464 Renames.insert(std::make_pair(&Symbol, &Alias));
468 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
469 uint8_t Type = newType;
471 // Propagation rules:
472 // IFUNC > FUNC > OBJECT > NOTYPE
473 // TLS_OBJECT > OBJECT > NOTYPE
475 // dont let the new type degrade the old type
479 case ELF::STT_GNU_IFUNC:
480 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
481 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
482 Type = ELF::STT_GNU_IFUNC;
485 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
486 Type == ELF::STT_TLS)
487 Type = ELF::STT_FUNC;
489 case ELF::STT_OBJECT:
490 if (Type == ELF::STT_NOTYPE)
491 Type = ELF::STT_OBJECT;
494 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
495 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
503 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
504 const MCAsmLayout &Layout) {
505 MCSymbolData &OrigData = *MSD.SymbolData;
506 assert((!OrigData.getFragment() ||
507 (&OrigData.getFragment()->getParent()->getSection() ==
508 &OrigData.getSymbol().getSection())) &&
509 "The symbol's section doesn't match the fragment's symbol");
510 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
512 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
514 bool IsReserved = !Base || OrigData.isCommon();
516 // Binding and Type share the same byte as upper and lower nibbles
517 uint8_t Binding = MCELF::GetBinding(OrigData);
518 uint8_t Type = MCELF::GetType(OrigData);
519 MCSymbolData *BaseSD = nullptr;
521 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
522 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
524 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
526 // Other and Visibility share the same byte with Visibility using the lower
528 uint8_t Visibility = MCELF::GetVisibility(OrigData);
529 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
532 uint64_t Value = SymbolValue(OrigData, Layout);
535 const MCExpr *ESize = OrigData.getSize();
537 ESize = BaseSD->getSize();
541 if (!ESize->evaluateKnownAbsolute(Res, Layout))
542 report_fatal_error("Size expression must be absolute.");
546 // Write out the symbol table entry
547 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
548 MSD.SectionIndex, IsReserved);
551 void ELFObjectWriter::WriteSymbolTable(MCAssembler &Asm,
552 const MCAsmLayout &Layout,
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 = addToSectionTable(SymtabSection);
566 // The string table must be emitted first because we need the index
567 // into the string table for all the symbol names.
569 SymbolTableWriter Writer(*this, is64Bit());
571 uint64_t Padding = OffsetToAlignment(OS.tell(), SymtabSD.getAlignment());
574 uint64_t SecStart = OS.tell();
576 // The first entry is the undefined symbol entry.
577 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
579 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
580 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
581 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
584 // Write the symbol table entries.
585 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
587 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
588 ELFSymbolData &MSD = LocalSymbolData[i];
589 WriteSymbol(Writer, MSD, Layout);
592 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
593 ELFSymbolData &MSD = ExternalSymbolData[i];
594 MCSymbolData &Data = *MSD.SymbolData;
595 assert(((Data.getFlags() & ELF_STB_Global) ||
596 (Data.getFlags() & ELF_STB_Weak)) &&
597 "External symbol requires STB_GLOBAL or STB_WEAK flag");
598 WriteSymbol(Writer, MSD, Layout);
599 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
600 LastLocalSymbolIndex++;
603 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
604 ELFSymbolData &MSD = UndefinedSymbolData[i];
605 MCSymbolData &Data = *MSD.SymbolData;
606 WriteSymbol(Writer, MSD, Layout);
607 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
608 LastLocalSymbolIndex++;
611 uint64_t SecEnd = OS.tell();
612 SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
614 ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
615 if (ShndxIndexes.empty())
618 SecStart = OS.tell();
619 const MCSectionELF *SymtabShndxSection =
620 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
621 addToSectionTable(SymtabShndxSection);
622 MCSectionData *SymtabShndxSD =
623 &Asm.getOrCreateSectionData(*SymtabShndxSection);
624 SymtabShndxSD->setAlignment(4);
625 for (uint32_t Index : ShndxIndexes)
628 SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
631 // It is always valid to create a relocation with a symbol. It is preferable
632 // to use a relocation with a section if that is possible. Using the section
633 // allows us to omit some local symbols from the symbol table.
634 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
635 const MCSymbolRefExpr *RefA,
636 const MCSymbolData *SD,
638 unsigned Type) const {
639 // A PCRel relocation to an absolute value has no symbol (or section). We
640 // represent that with a relocation to a null section.
644 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
648 // The .odp creation emits a relocation against the symbol ".TOC." which
649 // create a R_PPC64_TOC relocation. However the relocation symbol name
650 // in final object creation should be NULL, since the symbol does not
651 // really exist, it is just the reference to TOC base for the current
652 // object file. Since the symbol is undefined, returning false results
653 // in a relocation with a null section which is the desired result.
654 case MCSymbolRefExpr::VK_PPC_TOCBASE:
657 // These VariantKind cause the relocation to refer to something other than
658 // the symbol itself, like a linker generated table. Since the address of
659 // symbol is not relevant, we cannot replace the symbol with the
660 // section and patch the difference in the addend.
661 case MCSymbolRefExpr::VK_GOT:
662 case MCSymbolRefExpr::VK_PLT:
663 case MCSymbolRefExpr::VK_GOTPCREL:
664 case MCSymbolRefExpr::VK_Mips_GOT:
665 case MCSymbolRefExpr::VK_PPC_GOT_LO:
666 case MCSymbolRefExpr::VK_PPC_GOT_HI:
667 case MCSymbolRefExpr::VK_PPC_GOT_HA:
671 // An undefined symbol is not in any section, so the relocation has to point
672 // to the symbol itself.
673 const MCSymbol &Sym = SD->getSymbol();
674 if (Sym.isUndefined())
677 unsigned Binding = MCELF::GetBinding(*SD);
680 llvm_unreachable("Invalid Binding");
684 // If the symbol is weak, it might be overridden by a symbol in another
685 // file. The relocation has to point to the symbol so that the linker
688 case ELF::STB_GLOBAL:
689 // Global ELF symbols can be preempted by the dynamic linker. The relocation
690 // has to point to the symbol for a reason analogous to the STB_WEAK case.
694 // If a relocation points to a mergeable section, we have to be careful.
695 // If the offset is zero, a relocation with the section will encode the
696 // same information. With a non-zero offset, the situation is different.
697 // For example, a relocation can point 42 bytes past the end of a string.
698 // If we change such a relocation to use the section, the linker would think
699 // that it pointed to another string and subtracting 42 at runtime will
700 // produce the wrong value.
701 auto &Sec = cast<MCSectionELF>(Sym.getSection());
702 unsigned Flags = Sec.getFlags();
703 if (Flags & ELF::SHF_MERGE) {
707 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
708 // only handle section relocations to mergeable sections if using RELA.
709 if (!hasRelocationAddend())
713 // Most TLS relocations use a got, so they need the symbol. Even those that
714 // are just an offset (@tpoff), require a symbol in gold versions before
715 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
716 // http://sourceware.org/PR16773.
717 if (Flags & ELF::SHF_TLS)
720 // If the symbol is a thumb function the final relocation must set the lowest
721 // bit. With a symbol that is done by just having the symbol have that bit
722 // set, so we would lose the bit if we relocated with the section.
723 // FIXME: We could use the section but add the bit to the relocation value.
724 if (Asm.isThumbFunc(&Sym))
727 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
732 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
733 const MCSymbol &Sym = Ref.getSymbol();
735 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
738 if (!Sym.isVariable())
741 const MCExpr *Expr = Sym.getVariableValue();
742 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
746 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
747 return &Inner->getSymbol();
751 // True if the assembler knows nothing about the final value of the symbol.
752 // This doesn't cover the comdat issues, since in those cases the assembler
753 // can at least know that all symbols in the section will move together.
754 static bool isWeak(const MCSymbolData &D) {
755 if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
758 switch (MCELF::GetBinding(D)) {
760 llvm_unreachable("Unknown binding");
763 case ELF::STB_GLOBAL:
766 case ELF::STB_GNU_UNIQUE:
771 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
772 const MCAsmLayout &Layout,
773 const MCFragment *Fragment,
774 const MCFixup &Fixup, MCValue Target,
775 bool &IsPCRel, uint64_t &FixedValue) {
776 const MCSectionData *FixupSectionD = Fragment->getParent();
777 const MCSectionELF &FixupSection =
778 cast<MCSectionELF>(FixupSectionD->getSection());
779 uint64_t C = Target.getConstant();
780 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
782 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
783 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
784 "Should not have constructed this");
786 // Let A, B and C being the components of Target and R be the location of
787 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
788 // If it is pcrel, we want to compute (A - B + C - R).
790 // In general, ELF has no relocations for -B. It can only represent (A + C)
791 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
792 // replace B to implement it: (A - R - K + C)
794 Asm.getContext().FatalError(
796 "No relocation available to represent this relative expression");
798 const MCSymbol &SymB = RefB->getSymbol();
800 if (SymB.isUndefined())
801 Asm.getContext().FatalError(
803 Twine("symbol '") + SymB.getName() +
804 "' can not be undefined in a subtraction expression");
806 assert(!SymB.isAbsolute() && "Should have been folded");
807 const MCSection &SecB = SymB.getSection();
808 if (&SecB != &FixupSection)
809 Asm.getContext().FatalError(
810 Fixup.getLoc(), "Cannot represent a difference across sections");
812 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
814 Asm.getContext().FatalError(
815 Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
817 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
818 uint64_t K = SymBOffset - FixupOffset;
823 // We either rejected the fixup or folded B into C at this point.
824 const MCSymbolRefExpr *RefA = Target.getSymA();
825 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
826 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
828 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
829 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
830 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
831 C += Layout.getSymbolOffset(SymAD);
834 if (hasRelocationAddend()) {
841 // FIXME: What is this!?!?
842 MCSymbolRefExpr::VariantKind Modifier =
843 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
844 if (RelocNeedsGOT(Modifier))
847 if (!RelocateWithSymbol) {
848 const MCSection *SecA =
849 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
850 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
851 MCSymbol *SectionSymbol =
852 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
854 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
855 Relocations[&FixupSection].push_back(Rec);
860 if (const MCSymbol *R = Renames.lookup(SymA))
863 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
864 WeakrefUsedInReloc.insert(WeakRef);
866 UsedInReloc.insert(SymA);
868 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
869 Relocations[&FixupSection].push_back(Rec);
875 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
877 const MCSymbolData &SD = Asm.getSymbolData(*S);
878 return SD.getIndex();
881 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
882 const MCSymbolData &Data, bool Used,
884 const MCSymbol &Symbol = Data.getSymbol();
885 if (Symbol.isVariable()) {
886 const MCExpr *Expr = Symbol.getVariableValue();
887 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
888 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
899 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
902 if (Symbol.isVariable()) {
903 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
904 if (Base && Base->isUndefined())
908 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
909 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
912 if (Symbol.isTemporary())
918 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
919 if (Data.isExternal())
922 const MCSymbol &Symbol = Data.getSymbol();
923 if (Symbol.isDefined())
932 void ELFObjectWriter::computeSymbolTable(
933 MCAssembler &Asm, const MCAsmLayout &Layout,
934 const SectionIndexMapTy &SectionIndexMap,
935 const RevGroupMapTy &RevGroupMap) {
936 // FIXME: Is this the correct place to do this?
937 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
939 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
940 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
941 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
942 Data.setExternal(true);
943 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
946 // Add the data for the symbols.
947 for (MCSymbolData &SD : Asm.symbols()) {
948 const MCSymbol &Symbol = SD.getSymbol();
950 bool Used = UsedInReloc.count(&Symbol);
951 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
952 bool isSignature = RevGroupMap.count(&Symbol);
954 if (!isInSymtab(Layout, SD,
955 Used || WeakrefUsed || isSignature,
956 Renames.count(&Symbol)))
960 MSD.SymbolData = &SD;
961 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
963 // Undefined symbols are global, but this is the first place we
964 // are able to set it.
965 bool Local = isLocal(SD, Used);
966 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
968 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
969 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
970 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
974 MSD.SectionIndex = ELF::SHN_ABS;
975 } else if (SD.isCommon()) {
977 MSD.SectionIndex = ELF::SHN_COMMON;
978 } else if (BaseSymbol->isUndefined()) {
979 if (isSignature && !Used)
980 MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
982 MSD.SectionIndex = ELF::SHN_UNDEF;
983 if (!Used && WeakrefUsed)
984 MCELF::SetBinding(SD, ELF::STB_WEAK);
986 const MCSectionELF &Section =
987 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
988 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
989 assert(MSD.SectionIndex && "Invalid section index!");
992 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
995 // FIXME: All name handling should be done before we get to the writer,
996 // including dealing with GNU-style version suffixes. Fixing this isn't
999 // We thus have to be careful to not perform the symbol version replacement
1002 // The ELF format is used on Windows by the MCJIT engine. Thus, on
1003 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
1004 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
1005 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
1006 // the EFLObjectWriter should not interpret the "@@@" sub-string as
1007 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1008 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1009 // "__imp_?" or "__imp_@?".
1011 // It would have been interesting to perform the MS mangling prefix check
1012 // only when the target triple is of the form *-pc-windows-elf. But, it
1013 // seems that this information is not easily accessible from the
1015 StringRef Name = Symbol.getName();
1016 if (!Name.startswith("?") && !Name.startswith("@?") &&
1017 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1018 // This symbol isn't following the MSVC C++ name mangling convention. We
1019 // can thus safely interpret the @@@ in symbol names as specifying symbol
1021 SmallString<32> Buf;
1022 size_t Pos = Name.find("@@@");
1023 if (Pos != StringRef::npos) {
1024 Buf += Name.substr(0, Pos);
1025 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1026 Buf += Name.substr(Pos + Skip);
1031 // Sections have their own string table
1032 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1033 MSD.Name = StrTabBuilder.add(Name);
1035 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1036 UndefinedSymbolData.push_back(MSD);
1038 LocalSymbolData.push_back(MSD);
1040 ExternalSymbolData.push_back(MSD);
1043 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1044 StrTabBuilder.add(*i);
1046 StrTabBuilder.finalize(StringTableBuilder::ELF);
1048 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1049 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1051 for (ELFSymbolData &MSD : LocalSymbolData)
1052 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1054 : StrTabBuilder.getOffset(MSD.Name);
1055 for (ELFSymbolData &MSD : ExternalSymbolData)
1056 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1057 for (ELFSymbolData& MSD : UndefinedSymbolData)
1058 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1060 // Symbols are required to be in lexicographic order.
1061 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1062 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1063 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1065 // Set the symbol indices. Local symbols must come before all other
1066 // symbols with non-local bindings.
1067 unsigned Index = FileSymbolData.size() + 1;
1068 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1069 LocalSymbolData[i].SymbolData->setIndex(Index++);
1071 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1072 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1073 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1074 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1077 const MCSectionELF *
1078 ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
1079 const MCSectionELF &Sec) {
1080 if (Relocations[&Sec].empty())
1083 MCContext &Ctx = Asm.getContext();
1084 const StringRef SectionName = Sec.getSectionName();
1085 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1086 RelaSectionName += SectionName;
1089 if (hasRelocationAddend())
1090 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1092 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1095 if (Sec.getFlags() & ELF::SHF_GROUP)
1096 Flags = ELF::SHF_GROUP;
1098 const MCSectionELF *RelaSection = Ctx.createELFRelSection(
1099 RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
1100 Flags, EntrySize, Sec.getGroup(), &Sec);
1101 MCSectionData &RelSD = Asm.getOrCreateSectionData(*RelaSection);
1102 RelSD.setAlignment(is64Bit() ? 8 : 4);
1106 static SmallVector<char, 128>
1107 getUncompressedData(const MCAsmLayout &Layout,
1108 MCSectionData::FragmentListType &Fragments) {
1109 SmallVector<char, 128> UncompressedData;
1110 for (const MCFragment &F : Fragments) {
1111 const SmallVectorImpl<char> *Contents;
1112 switch (F.getKind()) {
1113 case MCFragment::FT_Data:
1114 Contents = &cast<MCDataFragment>(F).getContents();
1116 case MCFragment::FT_Dwarf:
1117 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1119 case MCFragment::FT_DwarfFrame:
1120 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1124 "Not expecting any other fragment types in a debug_* section");
1126 UncompressedData.append(Contents->begin(), Contents->end());
1128 return UncompressedData;
1131 // Include the debug info compression header:
1132 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1133 // useful for consumers to preallocate a buffer to decompress into.
1135 prependCompressionHeader(uint64_t Size,
1136 SmallVectorImpl<char> &CompressedContents) {
1137 const StringRef Magic = "ZLIB";
1138 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1140 if (sys::IsLittleEndianHost)
1141 sys::swapByteOrder(Size);
1142 CompressedContents.insert(CompressedContents.begin(),
1143 Magic.size() + sizeof(Size), 0);
1144 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1145 std::copy(reinterpret_cast<char *>(&Size),
1146 reinterpret_cast<char *>(&Size + 1),
1147 CompressedContents.begin() + Magic.size());
1151 // Return a single fragment containing the compressed contents of the whole
1152 // section. Null if the section was not compressed for any reason.
1153 static std::unique_ptr<MCDataFragment>
1154 getCompressedFragment(const MCAsmLayout &Layout,
1155 MCSectionData::FragmentListType &Fragments) {
1156 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1158 // Gather the uncompressed data from all the fragments, recording the
1159 // alignment fragment, if seen, and any fixups.
1160 SmallVector<char, 128> UncompressedData =
1161 getUncompressedData(Layout, Fragments);
1163 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1165 zlib::Status Success = zlib::compress(
1166 StringRef(UncompressedData.data(), UncompressedData.size()),
1167 CompressedContents);
1168 if (Success != zlib::StatusOK)
1171 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1174 return CompressedFragment;
1177 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1180 static void UpdateSymbols(const MCAsmLayout &Layout,
1181 const std::vector<MCSymbolData *> &Symbols,
1182 MCFragment &NewFragment) {
1183 for (MCSymbolData *Sym : Symbols) {
1184 Sym->setOffset(Sym->getOffset() +
1185 Layout.getFragmentOffset(Sym->getFragment()));
1186 Sym->setFragment(&NewFragment);
1190 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1191 const DefiningSymbolMap &DefiningSymbols,
1192 const MCSectionELF &Section,
1193 MCSectionData &SD) {
1194 StringRef SectionName = Section.getSectionName();
1195 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1197 std::unique_ptr<MCDataFragment> CompressedFragment =
1198 getCompressedFragment(Layout, Fragments);
1200 // Leave the section as-is if the fragments could not be compressed.
1201 if (!CompressedFragment)
1204 // Update the fragment+offsets of any symbols referring to fragments in this
1205 // section to refer to the new fragment.
1206 auto I = DefiningSymbols.find(&SD);
1207 if (I != DefiningSymbols.end())
1208 UpdateSymbols(Layout, I->second, *CompressedFragment);
1210 // Invalidate the layout for the whole section since it will have new and
1211 // different fragments now.
1212 Layout.invalidateFragmentsFrom(&Fragments.front());
1215 // Complete the initialization of the new fragment
1216 CompressedFragment->setParent(&SD);
1217 CompressedFragment->setLayoutOrder(0);
1218 Fragments.push_back(CompressedFragment.release());
1220 // Rename from .debug_* to .zdebug_*
1221 Asm.getContext().renameELFSection(&Section,
1222 (".z" + SectionName.drop_front(1)).str());
1225 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1226 MCAsmLayout &Layout) {
1227 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1230 DefiningSymbolMap DefiningSymbols;
1232 for (MCSymbolData &SD : Asm.symbols())
1233 if (MCFragment *F = SD.getFragment())
1234 DefiningSymbols[F->getParent()].push_back(&SD);
1236 for (MCSectionData &SD : Asm) {
1237 const MCSectionELF &Section =
1238 static_cast<const MCSectionELF &>(SD.getSection());
1239 StringRef SectionName = Section.getSectionName();
1241 // Compressing debug_frame requires handling alignment fragments which is
1242 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1243 // for writing to arbitrary buffers) for little benefit.
1244 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1247 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1251 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1252 uint64_t Flags, uint64_t Address,
1253 uint64_t Offset, uint64_t Size,
1254 uint32_t Link, uint32_t Info,
1256 uint64_t EntrySize) {
1257 Write32(Name); // sh_name: index into string table
1258 Write32(Type); // sh_type
1259 WriteWord(Flags); // sh_flags
1260 WriteWord(Address); // sh_addr
1261 WriteWord(Offset); // sh_offset
1262 WriteWord(Size); // sh_size
1263 Write32(Link); // sh_link
1264 Write32(Info); // sh_info
1265 WriteWord(Alignment); // sh_addralign
1266 WriteWord(EntrySize); // sh_entsize
1269 void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
1270 const MCSectionELF &Sec) {
1271 std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
1273 // Sort the relocation entries. Most targets just sort by Offset, but some
1274 // (e.g., MIPS) have additional constraints.
1275 TargetObjectWriter->sortRelocs(Asm, Relocs);
1277 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1278 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1280 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1283 write(Entry.Offset);
1284 if (TargetObjectWriter->isN64()) {
1285 write(uint32_t(Index));
1287 write(TargetObjectWriter->getRSsym(Entry.Type));
1288 write(TargetObjectWriter->getRType3(Entry.Type));
1289 write(TargetObjectWriter->getRType2(Entry.Type));
1290 write(TargetObjectWriter->getRType(Entry.Type));
1292 struct ELF::Elf64_Rela ERE64;
1293 ERE64.setSymbolAndType(Index, Entry.Type);
1294 write(ERE64.r_info);
1296 if (hasRelocationAddend())
1297 write(Entry.Addend);
1299 write(uint32_t(Entry.Offset));
1301 struct ELF::Elf32_Rela ERE32;
1302 ERE32.setSymbolAndType(Index, Entry.Type);
1303 write(ERE32.r_info);
1305 if (hasRelocationAddend())
1306 write(uint32_t(Entry.Addend));
1311 const MCSectionELF *ELFObjectWriter::createSectionHeaderStringTable() {
1312 const MCSectionELF *ShstrtabSection = SectionTable[ShstrtabIndex - 1];
1313 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1314 OS << ShStrTabBuilder.data();
1315 return ShstrtabSection;
1318 const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
1319 const MCSectionELF *StrtabSection =
1320 Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1321 StringTableIndex = addToSectionTable(StrtabSection);
1322 OS << StrTabBuilder.data();
1323 return StrtabSection;
1326 void ELFObjectWriter::writeSection(MCAssembler &Asm,
1327 const SectionIndexMapTy &SectionIndexMap,
1328 uint32_t GroupSymbolIndex,
1329 uint64_t Offset, uint64_t Size,
1331 const MCSectionELF &Section) {
1332 uint64_t sh_link = 0;
1333 uint64_t sh_info = 0;
1335 switch(Section.getType()) {
1340 case ELF::SHT_DYNAMIC:
1341 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1345 case ELF::SHT_RELA: {
1346 sh_link = SymbolTableIndex;
1347 assert(sh_link && ".symtab not found");
1348 const MCSectionELF *InfoSection = Section.getAssociatedSection();
1349 sh_info = SectionIndexMap.lookup(InfoSection);
1353 case ELF::SHT_SYMTAB:
1354 case ELF::SHT_DYNSYM:
1355 sh_link = StringTableIndex;
1356 sh_info = LastLocalSymbolIndex;
1359 case ELF::SHT_SYMTAB_SHNDX:
1360 sh_link = SymbolTableIndex;
1363 case ELF::SHT_GROUP:
1364 sh_link = SymbolTableIndex;
1365 sh_info = GroupSymbolIndex;
1369 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1370 Section.getType() == ELF::SHT_ARM_EXIDX)
1371 sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
1373 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1375 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1376 Alignment, Section.getEntrySize());
1379 void ELFObjectWriter::writeSectionHeader(
1380 MCAssembler &Asm, const MCAsmLayout &Layout,
1381 const SectionIndexMapTy &SectionIndexMap,
1382 const SectionOffsetsTy &SectionOffsets) {
1383 const unsigned NumSections = SectionTable.size();
1385 // Null section first.
1386 uint64_t FirstSectionSize =
1387 (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
1388 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
1390 for (const MCSectionELF *Section : SectionTable) {
1391 const MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
1392 uint32_t GroupSymbolIndex;
1393 unsigned Type = Section->getType();
1394 if (Type != ELF::SHT_GROUP)
1395 GroupSymbolIndex = 0;
1397 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section->getGroup());
1399 const std::pair<uint64_t, uint64_t> &Offsets =
1400 SectionOffsets.find(Section)->second;
1401 uint64_t Size = Type == ELF::SHT_NOBITS ? Layout.getSectionAddressSize(&SD)
1402 : Offsets.second - Offsets.first;
1404 writeSection(Asm, SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
1405 SD.getAlignment(), *Section);
1409 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1410 const MCAsmLayout &Layout) {
1411 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1413 MCContext &Ctx = Asm.getContext();
1414 const MCSectionELF *ShstrtabSection =
1415 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1416 ShstrtabIndex = addToSectionTable(ShstrtabSection);
1418 RevGroupMapTy RevGroupMap;
1419 SectionIndexMapTy SectionIndexMap;
1421 std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
1423 // Write out the ELF header ...
1426 // ... then the sections ...
1427 SectionOffsetsTy SectionOffsets;
1428 bool ComputedSymtab = false;
1429 for (const MCSectionData &SD : Asm) {
1430 const MCSectionELF &Section =
1431 static_cast<const MCSectionELF &>(SD.getSection());
1433 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1434 WriteZeros(Padding);
1436 // Remember the offset into the file for this section.
1437 uint64_t SecStart = OS.tell();
1439 const MCSymbol *SignatureSymbol = Section.getGroup();
1440 unsigned Type = Section.getType();
1441 if (Type == ELF::SHT_GROUP) {
1442 assert(SignatureSymbol);
1443 write(uint32_t(ELF::GRP_COMDAT));
1444 for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
1445 uint32_t SecIndex = SectionIndexMap.lookup(Member);
1448 } else if (Type == ELF::SHT_REL || Type == ELF::SHT_RELA) {
1449 if (!ComputedSymtab) {
1450 // Compute symbol table information.
1451 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1452 ComputedSymtab = true;
1454 writeRelocations(Asm, *Section.getAssociatedSection());
1456 Asm.writeSectionData(&SD, Layout);
1459 uint64_t SecEnd = OS.tell();
1460 SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
1462 if (Type == ELF::SHT_GROUP || Type == ELF::SHT_REL || Type == ELF::SHT_RELA)
1465 const MCSectionELF *RelSection = createRelocationSection(Asm, Section);
1467 if (SignatureSymbol) {
1468 Asm.getOrCreateSymbolData(*SignatureSymbol);
1469 unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
1471 const MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
1472 GroupIdx = addToSectionTable(Group);
1473 MCSectionData *GroupD = &Asm.getOrCreateSectionData(*Group);
1474 GroupD->setAlignment(4);
1476 GroupMembers[SignatureSymbol].push_back(&Section);
1478 GroupMembers[SignatureSymbol].push_back(RelSection);
1481 SectionIndexMap[&Section] = addToSectionTable(&Section);
1483 SectionIndexMap[RelSection] = addToSectionTable(RelSection);
1486 if (!ComputedSymtab) {
1487 // Compute symbol table information.
1488 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
1489 ComputedSymtab = true;
1492 WriteSymbolTable(Asm, Layout, SectionOffsets);
1495 uint64_t SecStart = OS.tell();
1496 const MCSectionELF *Sec = createStringTable(Ctx);
1497 uint64_t SecEnd = OS.tell();
1498 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1502 uint64_t SecStart = OS.tell();
1503 const MCSectionELF *Sec = createSectionHeaderStringTable();
1504 uint64_t SecEnd = OS.tell();
1505 SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
1508 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1509 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1510 WriteZeros(Padding);
1512 const unsigned SectionHeaderOffset = OS.tell();
1514 // ... then the section header table ...
1515 writeSectionHeader(Asm, Layout, SectionIndexMap, SectionOffsets);
1517 uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
1518 ? (uint16_t)ELF::SHN_UNDEF
1519 : SectionTable.size() + 1;
1520 if (sys::IsLittleEndianHost != IsLittleEndian)
1521 sys::swapByteOrder(NumSections);
1522 unsigned NumSectionsOffset;
1525 uint64_t Val = SectionHeaderOffset;
1526 if (sys::IsLittleEndianHost != IsLittleEndian)
1527 sys::swapByteOrder(Val);
1528 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1529 offsetof(ELF::Elf64_Ehdr, e_shoff));
1530 NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
1532 uint32_t Val = SectionHeaderOffset;
1533 if (sys::IsLittleEndianHost != IsLittleEndian)
1534 sys::swapByteOrder(Val);
1535 OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
1536 offsetof(ELF::Elf32_Ehdr, e_shoff));
1537 NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
1539 OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
1543 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1544 const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
1545 bool InSet, bool IsPCRel) const {
1548 if (::isWeak(DataA))
1551 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
1555 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
1559 // It is invalid to replace a reference to a global in a comdat
1560 // with a reference to a local since out of comdat references
1561 // to a local are forbidden.
1562 // We could try to return false for more cases, like the reference
1563 // being in the same comdat or Sym being an alias to another global,
1564 // but it is not clear if it is worth the effort.
1565 if (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
1568 const MCSymbol &Sym = SD.getSymbol();
1569 if (!Sym.isInSection())
1572 const auto &Sec = cast<MCSectionELF>(Sym.getSection());
1573 return Sec.getGroup();
1576 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1577 raw_pwrite_stream &OS,
1578 bool IsLittleEndian) {
1579 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);