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/ELFObjectWriter.h"
15 #include "llvm/ADT/SmallPtrSet.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/ADT/StringMap.h"
18 #include "llvm/ADT/Twine.h"
19 #include "llvm/MC/MCAssembler.h"
20 #include "llvm/MC/MCAsmLayout.h"
21 #include "llvm/MC/MCContext.h"
22 #include "llvm/MC/MCELFSymbolFlags.h"
23 #include "llvm/MC/MCExpr.h"
24 #include "llvm/MC/MCObjectWriter.h"
25 #include "llvm/MC/MCSectionELF.h"
26 #include "llvm/MC/MCSymbol.h"
27 #include "llvm/MC/MCValue.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/ErrorHandling.h"
30 #include "llvm/Support/ELF.h"
31 #include "llvm/Target/TargetAsmBackend.h"
33 #include "../Target/X86/X86FixupKinds.h"
38 static unsigned GetType(const MCSymbolData &SD) {
39 uint32_t Type = (SD.getFlags() & (0xf << ELF_STT_Shift)) >> ELF_STT_Shift;
40 assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT ||
41 Type == ELF::STT_FUNC || Type == ELF::STT_SECTION ||
42 Type == ELF::STT_FILE || Type == ELF::STT_COMMON ||
43 Type == ELF::STT_TLS);
47 static unsigned GetBinding(const MCSymbolData &SD) {
48 uint32_t Binding = (SD.getFlags() & (0xf << ELF_STB_Shift)) >> ELF_STB_Shift;
49 assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
50 Binding == ELF::STB_WEAK);
54 static void SetBinding(MCSymbolData &SD, unsigned Binding) {
55 assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
56 Binding == ELF::STB_WEAK);
57 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift);
58 SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift));
61 static unsigned GetVisibility(MCSymbolData &SD) {
63 (SD.getFlags() & (0xf << ELF_STV_Shift)) >> ELF_STV_Shift;
64 assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL ||
65 Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED);
69 static bool isFixupKindX86PCRel(unsigned Kind) {
73 case X86::reloc_pcrel_1byte:
74 case X86::reloc_pcrel_4byte:
75 case X86::reloc_riprel_4byte:
76 case X86::reloc_riprel_4byte_movq_load:
81 static bool RelocNeedsGOT(unsigned Type) {
85 case ELF::R_X86_64_GOT32:
86 case ELF::R_X86_64_PLT32:
87 case ELF::R_X86_64_GOTPCREL:
94 class ELFObjectWriterImpl {
95 /*static bool isFixupKindX86RIPRel(unsigned Kind) {
96 return Kind == X86::reloc_riprel_4byte ||
97 Kind == X86::reloc_riprel_4byte_movq_load;
101 /// ELFSymbolData - Helper struct for containing some precomputed information
103 struct ELFSymbolData {
104 MCSymbolData *SymbolData;
105 uint64_t StringIndex;
106 uint32_t SectionIndex;
108 // Support lexicographic sorting.
109 bool operator<(const ELFSymbolData &RHS) const {
110 if (GetType(*SymbolData) == ELF::STT_FILE)
112 if (GetType(*RHS.SymbolData) == ELF::STT_FILE)
114 return SymbolData->getSymbol().getName() <
115 RHS.SymbolData->getSymbol().getName();
119 /// @name Relocation Data
122 struct ELFRelocationEntry {
123 // Make these big enough for both 32-bit and 64-bit
127 const MCSymbol *Symbol;
130 // Support lexicographic sorting.
131 bool operator<(const ELFRelocationEntry &RE) const {
132 return RE.r_offset < r_offset;
136 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
138 llvm::DenseMap<const MCSectionData*,
139 std::vector<ELFRelocationEntry> > Relocations;
140 DenseMap<const MCSection*, uint64_t> SectionStringTableIndex;
143 /// @name Symbol Table Data
146 SmallString<256> StringTable;
147 std::vector<ELFSymbolData> LocalSymbolData;
148 std::vector<ELFSymbolData> ExternalSymbolData;
149 std::vector<ELFSymbolData> UndefinedSymbolData;
153 int NumRegularSections;
157 ELFObjectWriter *Writer;
161 unsigned Is64Bit : 1;
163 bool HasRelocationAddend;
165 Triple::OSType OSType;
167 // This holds the symbol table index of the last local symbol.
168 unsigned LastLocalSymbolIndex;
169 // This holds the .strtab section index.
170 unsigned StringTableIndex;
172 unsigned ShstrtabIndex;
175 ELFObjectWriterImpl(ELFObjectWriter *_Writer, bool _Is64Bit,
176 bool _HasRelAddend, Triple::OSType _OSType)
177 : NeedsGOT(false), Writer(_Writer), OS(Writer->getStream()),
178 Is64Bit(_Is64Bit), HasRelocationAddend(_HasRelAddend),
182 void Write8(uint8_t Value) { Writer->Write8(Value); }
183 void Write16(uint16_t Value) { Writer->Write16(Value); }
184 void Write32(uint32_t Value) { Writer->Write32(Value); }
185 //void Write64(uint64_t Value) { Writer->Write64(Value); }
186 void WriteZeros(unsigned N) { Writer->WriteZeros(N); }
187 //void WriteBytes(StringRef Str, unsigned ZeroFillSize = 0) {
188 // Writer->WriteBytes(Str, ZeroFillSize);
191 void WriteWord(uint64_t W) {
198 void String8(char *buf, uint8_t Value) {
202 void StringLE16(char *buf, uint16_t Value) {
203 buf[0] = char(Value >> 0);
204 buf[1] = char(Value >> 8);
207 void StringLE32(char *buf, uint32_t Value) {
208 StringLE16(buf, uint16_t(Value >> 0));
209 StringLE16(buf + 2, uint16_t(Value >> 16));
212 void StringLE64(char *buf, uint64_t Value) {
213 StringLE32(buf, uint32_t(Value >> 0));
214 StringLE32(buf + 4, uint32_t(Value >> 32));
217 void StringBE16(char *buf ,uint16_t Value) {
218 buf[0] = char(Value >> 8);
219 buf[1] = char(Value >> 0);
222 void StringBE32(char *buf, uint32_t Value) {
223 StringBE16(buf, uint16_t(Value >> 16));
224 StringBE16(buf + 2, uint16_t(Value >> 0));
227 void StringBE64(char *buf, uint64_t Value) {
228 StringBE32(buf, uint32_t(Value >> 32));
229 StringBE32(buf + 4, uint32_t(Value >> 0));
232 void String16(char *buf, uint16_t Value) {
233 if (Writer->isLittleEndian())
234 StringLE16(buf, Value);
236 StringBE16(buf, Value);
239 void String32(char *buf, uint32_t Value) {
240 if (Writer->isLittleEndian())
241 StringLE32(buf, Value);
243 StringBE32(buf, Value);
246 void String64(char *buf, uint64_t Value) {
247 if (Writer->isLittleEndian())
248 StringLE64(buf, Value);
250 StringBE64(buf, Value);
253 void WriteHeader(uint64_t SectionDataSize, unsigned NumberOfSections);
255 void WriteSymbolEntry(MCDataFragment *F, uint64_t name, uint8_t info,
256 uint64_t value, uint64_t size,
257 uint8_t other, uint16_t shndx);
259 void WriteSymbol(MCDataFragment *F, ELFSymbolData &MSD,
260 const MCAsmLayout &Layout);
262 void WriteSymbolTable(MCDataFragment *F, const MCAssembler &Asm,
263 const MCAsmLayout &Layout,
264 unsigned NumRegularSections);
266 void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
267 const MCFragment *Fragment, const MCFixup &Fixup,
268 MCValue Target, uint64_t &FixedValue);
270 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
273 /// ComputeSymbolTable - Compute the symbol table data
275 /// \param StringTable [out] - The string table data.
276 /// \param StringIndexMap [out] - Map from symbol names to offsets in the
278 void ComputeSymbolTable(MCAssembler &Asm);
280 void WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
281 const MCSectionData &SD);
283 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) {
284 for (MCAssembler::const_iterator it = Asm.begin(),
285 ie = Asm.end(); it != ie; ++it) {
286 WriteRelocation(Asm, Layout, *it);
290 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout);
292 void ExecutePostLayoutBinding(MCAssembler &Asm) {
295 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
296 uint64_t Address, uint64_t Offset,
297 uint64_t Size, uint32_t Link, uint32_t Info,
298 uint64_t Alignment, uint64_t EntrySize);
300 void WriteRelocationsFragment(const MCAssembler &Asm, MCDataFragment *F,
301 const MCSectionData *SD);
303 bool IsFixupFullyResolved(const MCAssembler &Asm,
304 const MCValue Target,
306 const MCFragment *DF) const;
308 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout);
313 // Emit the ELF header.
314 void ELFObjectWriterImpl::WriteHeader(uint64_t SectionDataSize,
315 unsigned NumberOfSections) {
321 // emitWord method behaves differently for ELF32 and ELF64, writing
322 // 4 bytes in the former and 8 in the latter.
324 Write8(0x7f); // e_ident[EI_MAG0]
325 Write8('E'); // e_ident[EI_MAG1]
326 Write8('L'); // e_ident[EI_MAG2]
327 Write8('F'); // e_ident[EI_MAG3]
329 Write8(Is64Bit ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
332 Write8(Writer->isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
334 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
337 case Triple::FreeBSD: Write8(ELF::ELFOSABI_FREEBSD); break;
338 case Triple::Linux: Write8(ELF::ELFOSABI_LINUX); break;
339 default: Write8(ELF::ELFOSABI_NONE); break;
341 Write8(0); // e_ident[EI_ABIVERSION]
343 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
345 Write16(ELF::ET_REL); // e_type
347 // FIXME: Make this configurable
348 Write16(Is64Bit ? ELF::EM_X86_64 : ELF::EM_386); // e_machine = target
350 Write32(ELF::EV_CURRENT); // e_version
351 WriteWord(0); // e_entry, no entry point in .o file
352 WriteWord(0); // e_phoff, no program header for .o
353 WriteWord(SectionDataSize + (Is64Bit ? sizeof(ELF::Elf64_Ehdr) :
354 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes
356 // FIXME: Make this configurable.
357 Write32(0); // e_flags = whatever the target wants
359 // e_ehsize = ELF header size
360 Write16(Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
362 Write16(0); // e_phentsize = prog header entry size
363 Write16(0); // e_phnum = # prog header entries = 0
365 // e_shentsize = Section header entry size
366 Write16(Is64Bit ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
368 // e_shnum = # of section header ents
369 Write16(NumberOfSections);
371 // e_shstrndx = Section # of '.shstrtab'
372 Write16(ShstrtabIndex);
375 void ELFObjectWriterImpl::WriteSymbolEntry(MCDataFragment *F, uint64_t name,
376 uint8_t info, uint64_t value,
377 uint64_t size, uint8_t other,
383 F->getContents() += StringRef(buf, 4); // st_name
386 F->getContents() += StringRef(buf, 1); // st_info
389 F->getContents() += StringRef(buf, 1); // st_other
391 String16(buf, shndx);
392 F->getContents() += StringRef(buf, 2); // st_shndx
394 String64(buf, value);
395 F->getContents() += StringRef(buf, 8); // st_value
398 F->getContents() += StringRef(buf, 8); // st_size
403 F->getContents() += StringRef(buf, 4); // st_name
405 String32(buf, value);
406 F->getContents() += StringRef(buf, 4); // st_value
409 F->getContents() += StringRef(buf, 4); // st_size
412 F->getContents() += StringRef(buf, 1); // st_info
415 F->getContents() += StringRef(buf, 1); // st_other
417 String16(buf, shndx);
418 F->getContents() += StringRef(buf, 2); // st_shndx
422 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout) {
423 if (Data.isCommon() && Data.isExternal())
424 return Data.getCommonAlignment();
426 const MCSymbol &Symbol = Data.getSymbol();
427 if (!Symbol.isInSection())
430 if (!Data.isCommon() && !(Data.getFlags() & ELF_STB_Weak))
431 if (MCFragment *FF = Data.getFragment())
432 return Layout.getSymbolAddress(&Data) -
433 Layout.getSectionAddress(FF->getParent());
438 void ELFObjectWriterImpl::WriteSymbol(MCDataFragment *F, ELFSymbolData &MSD,
439 const MCAsmLayout &Layout) {
440 MCSymbolData &OrigData = *MSD.SymbolData;
441 MCSymbolData *AliasData = NULL;
442 if (OrigData.Symbol->isVariable()) {
443 const MCExpr *Value = OrigData.getSymbol().getVariableValue();
444 assert (Value->getKind() == MCExpr::SymbolRef && "Unimplemented");
445 const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Value);
446 AliasData = &Layout.getAssembler().getSymbolData(Ref->getSymbol());
448 MCSymbolData &Data = AliasData ? *AliasData : OrigData;
450 uint8_t Binding = GetBinding(OrigData);
451 uint8_t Visibility = GetVisibility(OrigData);
452 uint8_t Type = GetType(Data);
454 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
455 uint8_t Other = Visibility;
457 uint64_t Value = SymbolValue(Data, Layout);
461 assert(!(Data.isCommon() && !Data.isExternal()));
463 ESize = Data.getSize();
464 if (Data.getSize()) {
466 if (ESize->getKind() == MCExpr::Binary) {
467 const MCBinaryExpr *BE = static_cast<const MCBinaryExpr *>(ESize);
469 if (BE->EvaluateAsRelocatable(Res, &Layout)) {
470 uint64_t AddressA = 0;
471 uint64_t AddressB = 0;
472 const MCSymbol &SymA = Res.getSymA()->getSymbol();
473 const MCSymbol &SymB = Res.getSymB()->getSymbol();
475 if (SymA.isDefined()) {
476 MCSymbolData &A = Layout.getAssembler().getSymbolData(SymA);
477 AddressA = Layout.getSymbolAddress(&A);
480 if (SymB.isDefined()) {
481 MCSymbolData &B = Layout.getAssembler().getSymbolData(SymB);
482 AddressB = Layout.getSymbolAddress(&B);
485 Size = AddressA - AddressB;
487 } else if (ESize->getKind() == MCExpr::Constant) {
488 Size = static_cast<const MCConstantExpr *>(ESize)->getValue();
490 assert(0 && "Unsupported size expression");
494 // Write out the symbol table entry
495 WriteSymbolEntry(F, MSD.StringIndex, Info, Value,
496 Size, Other, MSD.SectionIndex);
499 void ELFObjectWriterImpl::WriteSymbolTable(MCDataFragment *F,
500 const MCAssembler &Asm,
501 const MCAsmLayout &Layout,
502 unsigned NumRegularSections) {
503 // The string table must be emitted first because we need the index
504 // into the string table for all the symbol names.
505 assert(StringTable.size() && "Missing string table");
507 // FIXME: Make sure the start of the symbol table is aligned.
509 // The first entry is the undefined symbol entry.
510 unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
511 F->getContents().append(EntrySize, '\x00');
513 // Write the symbol table entries.
514 LastLocalSymbolIndex = LocalSymbolData.size() + 1;
515 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
516 ELFSymbolData &MSD = LocalSymbolData[i];
517 WriteSymbol(F, MSD, Layout);
520 // Write out a symbol table entry for each regular section.
522 for (MCAssembler::const_iterator it = Asm.begin();
523 Index <= NumRegularSections; ++it, ++Index) {
524 const MCSectionELF &Section =
525 static_cast<const MCSectionELF&>(it->getSection());
526 // Leave out relocations so we don't have indexes within
527 // the relocations messed up
528 if (Section.getType() == ELF::SHT_RELA || Section.getType() == ELF::SHT_REL)
530 WriteSymbolEntry(F, 0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT, Index);
531 LastLocalSymbolIndex++;
534 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
535 ELFSymbolData &MSD = ExternalSymbolData[i];
536 MCSymbolData &Data = *MSD.SymbolData;
537 assert(((Data.getFlags() & ELF_STB_Global) ||
538 (Data.getFlags() & ELF_STB_Weak)) &&
539 "External symbol requires STB_GLOBAL or STB_WEAK flag");
540 WriteSymbol(F, MSD, Layout);
541 if (GetBinding(Data) == ELF::STB_LOCAL)
542 LastLocalSymbolIndex++;
545 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
546 ELFSymbolData &MSD = UndefinedSymbolData[i];
547 MCSymbolData &Data = *MSD.SymbolData;
548 WriteSymbol(F, MSD, Layout);
549 if (GetBinding(Data) == ELF::STB_LOCAL)
550 LastLocalSymbolIndex++;
554 static bool ShouldRelocOnSymbol(const MCSymbolData &SD,
555 const MCValue &Target,
556 const MCFragment &F) {
557 const MCSymbol &Symbol = SD.getSymbol();
558 if (Symbol.isUndefined())
561 const MCSectionELF &Section =
562 static_cast<const MCSectionELF&>(Symbol.getSection());
567 if (Section.getFlags() & MCSectionELF::SHF_MERGE)
568 return Target.getConstant() != 0;
570 MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind();
571 const MCSectionELF &Sec2 =
572 static_cast<const MCSectionELF&>(F.getParent()->getSection());
574 if (&Sec2 != &Section &&
575 (Kind == MCSymbolRefExpr::VK_PLT || Kind == MCSymbolRefExpr::VK_GOTPCREL))
581 // FIXME: this is currently X86/X86_64 only
582 void ELFObjectWriterImpl::RecordRelocation(const MCAssembler &Asm,
583 const MCAsmLayout &Layout,
584 const MCFragment *Fragment,
585 const MCFixup &Fixup,
587 uint64_t &FixedValue) {
590 int64_t Value = Target.getConstant();
591 const MCSymbol *Symbol = 0;
593 bool IsPCRel = isFixupKindX86PCRel(Fixup.getKind());
594 if (!Target.isAbsolute()) {
595 Symbol = &Target.getSymA()->getSymbol();
596 MCSymbolData &SD = Asm.getSymbolData(*Symbol);
597 MCFragment *F = SD.getFragment();
599 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
600 const MCSymbol &SymbolB = RefB->getSymbol();
601 MCSymbolData &SDB = Asm.getSymbolData(SymbolB);
603 MCSectionData *Sec = Fragment->getParent();
605 // Offset of the symbol in the section
606 int64_t a = Layout.getSymbolAddress(&SDB) - Layout.getSectionAddress(Sec);
608 // Ofeset of the relocation in the section
609 int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
613 // Check that this case has already been fully resolved before we get
615 if (Symbol->isDefined() && !SD.isExternal() &&
617 &Fragment->getParent()->getSection() == &Symbol->getSection()) {
618 llvm_unreachable("We don't need a relocation in this case.");
622 bool RelocOnSymbol = ShouldRelocOnSymbol(SD, Target, *Fragment);
623 if (!RelocOnSymbol) {
624 Index = F->getParent()->getOrdinal();
626 MCSectionData *FSD = F->getParent();
627 // Offset of the symbol in the section
628 Value += Layout.getSymbolAddress(&SD) - Layout.getSectionAddress(FSD);
630 UsedInReloc.insert(Symbol);
634 // Compensate for the addend on i386.
641 // determine the type of the relocation
643 MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
648 case MCSymbolRefExpr::VK_None:
649 Type = ELF::R_X86_64_PC32;
651 case MCSymbolRefExpr::VK_PLT:
652 Type = ELF::R_X86_64_PLT32;
654 case llvm::MCSymbolRefExpr::VK_GOTPCREL:
655 Type = ELF::R_X86_64_GOTPCREL;
658 llvm_unreachable("Unimplemented");
661 switch ((unsigned)Fixup.getKind()) {
662 default: llvm_unreachable("invalid fixup kind!");
663 case FK_Data_8: Type = ELF::R_X86_64_64; break;
664 case X86::reloc_signed_4byte:
665 case X86::reloc_pcrel_4byte:
666 assert(isInt<32>(Target.getConstant()));
668 case MCSymbolRefExpr::VK_None:
669 Type = ELF::R_X86_64_32S;
671 case MCSymbolRefExpr::VK_GOT:
672 Type = ELF::R_X86_64_GOT32;
674 case llvm::MCSymbolRefExpr::VK_GOTPCREL:
675 Type = ELF::R_X86_64_GOTPCREL;
678 llvm_unreachable("Unimplemented");
682 Type = ELF::R_X86_64_32;
684 case FK_Data_2: Type = ELF::R_X86_64_16; break;
685 case X86::reloc_pcrel_1byte:
686 case FK_Data_1: Type = ELF::R_X86_64_8; break;
691 Type = ELF::R_386_PC32;
693 switch ((unsigned)Fixup.getKind()) {
694 default: llvm_unreachable("invalid fixup kind!");
696 // FIXME: Should we avoid selecting reloc_signed_4byte in 32 bit mode
698 case X86::reloc_signed_4byte:
699 case X86::reloc_pcrel_4byte:
700 case FK_Data_4: Type = ELF::R_386_32; break;
701 case FK_Data_2: Type = ELF::R_386_16; break;
702 case X86::reloc_pcrel_1byte:
703 case FK_Data_1: Type = ELF::R_386_8; break;
708 if (RelocNeedsGOT(Type))
711 ELFRelocationEntry ERE;
717 ERE.r_offset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
719 if (HasRelocationAddend)
720 ERE.r_addend = Addend;
722 ERE.r_addend = 0; // Silence compiler warning.
724 Relocations[Fragment->getParent()].push_back(ERE);
728 ELFObjectWriterImpl::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
730 MCSymbolData &SD = Asm.getSymbolData(*S);
733 if (!SD.isExternal() && !S->isUndefined())
734 return SD.getIndex() + /* empty symbol */ 1;
736 // External or undefined symbol.
737 return SD.getIndex() + NumRegularSections + /* empty symbol */ 1;
740 static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data,
742 const MCSymbol &Symbol = Data.getSymbol();
743 if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined())
746 if (!Used && Symbol.isTemporary())
752 static bool isLocal(const MCSymbolData &Data) {
753 if (Data.isExternal())
756 const MCSymbol &Symbol = Data.getSymbol();
757 if (Symbol.isUndefined() && !Symbol.isVariable())
763 void ELFObjectWriterImpl::ComputeSymbolTable(MCAssembler &Asm) {
764 // FIXME: Is this the correct place to do this?
766 llvm::StringRef Name = "_GLOBAL_OFFSET_TABLE_";
767 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
768 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
769 Data.setExternal(true);
772 // Build section lookup table.
773 NumRegularSections = Asm.size();
774 DenseMap<const MCSection*, uint32_t> SectionIndexMap;
776 for (MCAssembler::iterator it = Asm.begin(),
777 ie = Asm.end(); it != ie; ++it, ++Index)
778 SectionIndexMap[&it->getSection()] = Index;
780 // Index 0 is always the empty string.
781 StringMap<uint64_t> StringIndexMap;
782 StringTable += '\x00';
784 // Add the data for local symbols.
785 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
786 ie = Asm.symbol_end(); it != ie; ++it) {
787 const MCSymbol &Symbol = it->getSymbol();
789 if (!isInSymtab(Asm, *it, UsedInReloc.count(&Symbol)))
795 uint64_t &Entry = StringIndexMap[Symbol.getName()];
797 Entry = StringTable.size();
798 StringTable += Symbol.getName();
799 StringTable += '\x00';
804 MSD.StringIndex = Entry;
806 if (Symbol.isAbsolute()) {
807 MSD.SectionIndex = ELF::SHN_ABS;
808 LocalSymbolData.push_back(MSD);
810 const MCSymbol *SymbolP = &Symbol;
811 if (Symbol.isVariable()) {
812 const MCExpr *Value = Symbol.getVariableValue();
813 assert (Value->getKind() == MCExpr::SymbolRef && "Unimplemented");
814 const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Value);
815 SymbolP = &Ref->getSymbol();
817 MSD.SectionIndex = SectionIndexMap.lookup(&SymbolP->getSection());
818 assert(MSD.SectionIndex && "Invalid section index!");
819 LocalSymbolData.push_back(MSD);
823 // Now add non-local symbols.
824 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
825 ie = Asm.symbol_end(); it != ie; ++it) {
826 const MCSymbol &Symbol = it->getSymbol();
828 if (!isInSymtab(Asm, *it, UsedInReloc.count(&Symbol)))
834 uint64_t &Entry = StringIndexMap[Symbol.getName()];
836 Entry = StringTable.size();
837 StringTable += Symbol.getName();
838 StringTable += '\x00';
843 MSD.StringIndex = Entry;
845 // FIXME: There is duplicated code with the local case.
846 if (it->isCommon()) {
847 MSD.SectionIndex = ELF::SHN_COMMON;
848 ExternalSymbolData.push_back(MSD);
849 } else if (Symbol.isVariable()) {
850 const MCExpr *Value = Symbol.getVariableValue();
851 assert (Value->getKind() == MCExpr::SymbolRef && "Unimplemented");
852 const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Value);
853 const MCSymbol &RefSymbol = Ref->getSymbol();
854 if (RefSymbol.isDefined()) {
855 MSD.SectionIndex = SectionIndexMap.lookup(&RefSymbol.getSection());
856 assert(MSD.SectionIndex && "Invalid section index!");
857 ExternalSymbolData.push_back(MSD);
859 } else if (Symbol.isUndefined()) {
860 MSD.SectionIndex = ELF::SHN_UNDEF;
861 // FIXME: Undefined symbols are global, but this is the first place we
862 // are able to set it.
863 if (GetBinding(*it) == ELF::STB_LOCAL)
864 SetBinding(*it, ELF::STB_GLOBAL);
865 UndefinedSymbolData.push_back(MSD);
866 } else if (Symbol.isAbsolute()) {
867 MSD.SectionIndex = ELF::SHN_ABS;
868 ExternalSymbolData.push_back(MSD);
870 MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
871 assert(MSD.SectionIndex && "Invalid section index!");
872 ExternalSymbolData.push_back(MSD);
876 // Symbols are required to be in lexicographic order.
877 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
878 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
879 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
881 // Set the symbol indices. Local symbols must come before all other
882 // symbols with non-local bindings.
884 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
885 LocalSymbolData[i].SymbolData->setIndex(Index++);
886 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
887 ExternalSymbolData[i].SymbolData->setIndex(Index++);
888 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
889 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
892 void ELFObjectWriterImpl::WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
893 const MCSectionData &SD) {
894 if (!Relocations[&SD].empty()) {
895 MCContext &Ctx = Asm.getContext();
896 const MCSection *RelaSection;
897 const MCSectionELF &Section =
898 static_cast<const MCSectionELF&>(SD.getSection());
900 const StringRef SectionName = Section.getSectionName();
901 std::string RelaSectionName = HasRelocationAddend ? ".rela" : ".rel";
902 RelaSectionName += SectionName;
905 if (HasRelocationAddend)
906 EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
908 EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
910 RelaSection = Ctx.getELFSection(RelaSectionName, HasRelocationAddend ?
911 ELF::SHT_RELA : ELF::SHT_REL, 0,
912 SectionKind::getReadOnly(),
915 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
916 RelaSD.setAlignment(Is64Bit ? 8 : 4);
918 MCDataFragment *F = new MCDataFragment(&RelaSD);
920 WriteRelocationsFragment(Asm, F, &SD);
922 Asm.AddSectionToTheEnd(*Writer, RelaSD, Layout);
926 void ELFObjectWriterImpl::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
927 uint64_t Flags, uint64_t Address,
928 uint64_t Offset, uint64_t Size,
929 uint32_t Link, uint32_t Info,
931 uint64_t EntrySize) {
932 Write32(Name); // sh_name: index into string table
933 Write32(Type); // sh_type
934 WriteWord(Flags); // sh_flags
935 WriteWord(Address); // sh_addr
936 WriteWord(Offset); // sh_offset
937 WriteWord(Size); // sh_size
938 Write32(Link); // sh_link
939 Write32(Info); // sh_info
940 WriteWord(Alignment); // sh_addralign
941 WriteWord(EntrySize); // sh_entsize
944 void ELFObjectWriterImpl::WriteRelocationsFragment(const MCAssembler &Asm,
946 const MCSectionData *SD) {
947 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
948 // sort by the r_offset just like gnu as does
949 array_pod_sort(Relocs.begin(), Relocs.end());
951 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
952 ELFRelocationEntry entry = Relocs[e - i - 1];
955 entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol);
957 entry.Index += LocalSymbolData.size() + 1;
961 String64(buf, entry.r_offset);
962 F->getContents() += StringRef(buf, 8);
964 struct ELF::Elf64_Rela ERE64;
965 ERE64.setSymbolAndType(entry.Index, entry.Type);
966 String64(buf, ERE64.r_info);
967 F->getContents() += StringRef(buf, 8);
969 if (HasRelocationAddend) {
970 String64(buf, entry.r_addend);
971 F->getContents() += StringRef(buf, 8);
976 String32(buf, entry.r_offset);
977 F->getContents() += StringRef(buf, 4);
979 struct ELF::Elf32_Rela ERE32;
980 ERE32.setSymbolAndType(entry.Index, entry.Type);
981 String32(buf, ERE32.r_info);
982 F->getContents() += StringRef(buf, 4);
984 if (HasRelocationAddend) {
985 String32(buf, entry.r_addend);
986 F->getContents() += StringRef(buf, 4);
992 void ELFObjectWriterImpl::CreateMetadataSections(MCAssembler &Asm,
993 MCAsmLayout &Layout) {
994 MCContext &Ctx = Asm.getContext();
997 const MCSection *SymtabSection;
998 unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1000 unsigned NumRegularSections = Asm.size();
1002 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1003 const MCSection *ShstrtabSection;
1004 ShstrtabSection = Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
1005 SectionKind::getReadOnly(), false);
1006 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1007 ShstrtabSD.setAlignment(1);
1008 ShstrtabIndex = Asm.size();
1010 SymtabSection = Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1011 SectionKind::getReadOnly(),
1013 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1014 SymtabSD.setAlignment(Is64Bit ? 8 : 4);
1016 const MCSection *StrtabSection;
1017 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
1018 SectionKind::getReadOnly(), false);
1019 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1020 StrtabSD.setAlignment(1);
1021 StringTableIndex = Asm.size();
1023 WriteRelocations(Asm, Layout);
1026 F = new MCDataFragment(&SymtabSD);
1027 WriteSymbolTable(F, Asm, Layout, NumRegularSections);
1028 Asm.AddSectionToTheEnd(*Writer, SymtabSD, Layout);
1030 F = new MCDataFragment(&StrtabSD);
1031 F->getContents().append(StringTable.begin(), StringTable.end());
1032 Asm.AddSectionToTheEnd(*Writer, StrtabSD, Layout);
1034 F = new MCDataFragment(&ShstrtabSD);
1036 // Section header string table.
1038 // The first entry of a string table holds a null character so skip
1041 F->getContents() += '\x00';
1043 for (MCAssembler::const_iterator it = Asm.begin(),
1044 ie = Asm.end(); it != ie; ++it) {
1045 const MCSectionELF &Section =
1046 static_cast<const MCSectionELF&>(it->getSection());
1047 // FIXME: We could merge suffixes like in .text and .rela.text.
1049 // Remember the index into the string table so we can write it
1050 // into the sh_name field of the section header table.
1051 SectionStringTableIndex[&it->getSection()] = Index;
1053 Index += Section.getSectionName().size() + 1;
1054 F->getContents() += Section.getSectionName();
1055 F->getContents() += '\x00';
1058 Asm.AddSectionToTheEnd(*Writer, ShstrtabSD, Layout);
1061 bool ELFObjectWriterImpl::IsFixupFullyResolved(const MCAssembler &Asm,
1062 const MCValue Target,
1064 const MCFragment *DF) const {
1065 // If this is a PCrel relocation, find the section this fixup value is
1067 const MCSection *BaseSection = 0;
1069 BaseSection = &DF->getParent()->getSection();
1070 assert(BaseSection);
1073 const MCSection *SectionA = 0;
1074 const MCSymbol *SymbolA = 0;
1075 if (const MCSymbolRefExpr *A = Target.getSymA()) {
1076 SymbolA = &A->getSymbol();
1077 SectionA = &SymbolA->getSection();
1080 const MCSection *SectionB = 0;
1081 if (const MCSymbolRefExpr *B = Target.getSymB()) {
1082 SectionB = &B->getSymbol().getSection();
1086 return SectionA == SectionB;
1088 const MCSymbolData &DataA = Asm.getSymbolData(*SymbolA);
1089 if (DataA.isExternal())
1092 return !SectionB && BaseSection == SectionA;
1095 void ELFObjectWriterImpl::WriteObject(MCAssembler &Asm,
1096 const MCAsmLayout &Layout) {
1097 // Compute symbol table information.
1098 ComputeSymbolTable(Asm);
1100 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1101 const_cast<MCAsmLayout&>(Layout));
1103 // Add 1 for the null section.
1104 unsigned NumSections = Asm.size() + 1;
1105 uint64_t NaturalAlignment = Is64Bit ? 8 : 4;
1106 uint64_t HeaderSize = Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr);
1107 uint64_t FileOff = HeaderSize;
1109 for (MCAssembler::const_iterator it = Asm.begin(),
1110 ie = Asm.end(); it != ie; ++it) {
1111 const MCSectionData &SD = *it;
1113 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1115 // Get the size of the section in the output file (including padding).
1116 uint64_t Size = Layout.getSectionFileSize(&SD);
1121 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1123 // Write out the ELF header ...
1124 WriteHeader(FileOff - HeaderSize, NumSections);
1126 FileOff = HeaderSize;
1128 // ... then all of the sections ...
1129 DenseMap<const MCSection*, uint64_t> SectionOffsetMap;
1131 DenseMap<const MCSection*, uint32_t> SectionIndexMap;
1134 for (MCAssembler::const_iterator it = Asm.begin(),
1135 ie = Asm.end(); it != ie; ++it) {
1136 const MCSectionData &SD = *it;
1138 uint64_t Padding = OffsetToAlignment(FileOff, SD.getAlignment());
1139 WriteZeros(Padding);
1142 // Remember the offset into the file for this section.
1143 SectionOffsetMap[&it->getSection()] = FileOff;
1144 SectionIndexMap[&it->getSection()] = Index++;
1146 FileOff += Layout.getSectionFileSize(&SD);
1148 Asm.WriteSectionData(it, Layout, Writer);
1151 uint64_t Padding = OffsetToAlignment(FileOff, NaturalAlignment);
1152 WriteZeros(Padding);
1155 // ... and then the section header table.
1156 // Should we align the section header table?
1158 // Null section first.
1159 WriteSecHdrEntry(0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
1161 for (MCAssembler::const_iterator it = Asm.begin(),
1162 ie = Asm.end(); it != ie; ++it) {
1163 const MCSectionData &SD = *it;
1164 const MCSectionELF &Section =
1165 static_cast<const MCSectionELF&>(SD.getSection());
1167 uint64_t sh_link = 0;
1168 uint64_t sh_info = 0;
1170 switch(Section.getType()) {
1171 case ELF::SHT_DYNAMIC:
1172 sh_link = SectionStringTableIndex[&it->getSection()];
1177 case ELF::SHT_RELA: {
1178 const MCSection *SymtabSection;
1179 const MCSection *InfoSection;
1181 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1182 SectionKind::getReadOnly(),
1184 sh_link = SectionIndexMap[SymtabSection];
1186 // Remove ".rel" and ".rela" prefixes.
1187 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1188 StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1190 InfoSection = Asm.getContext().getELFSection(SectionName,
1191 ELF::SHT_PROGBITS, 0,
1192 SectionKind::getReadOnly(),
1194 sh_info = SectionIndexMap[InfoSection];
1198 case ELF::SHT_SYMTAB:
1199 case ELF::SHT_DYNSYM:
1200 sh_link = StringTableIndex;
1201 sh_info = LastLocalSymbolIndex;
1204 case ELF::SHT_PROGBITS:
1205 case ELF::SHT_STRTAB:
1206 case ELF::SHT_NOBITS:
1212 case ELF::SHT_GROUP:
1213 case ELF::SHT_SYMTAB_SHNDX:
1215 assert(0 && "FIXME: sh_type value not supported!");
1219 WriteSecHdrEntry(SectionStringTableIndex[&it->getSection()],
1220 Section.getType(), Section.getFlags(),
1222 SectionOffsetMap.lookup(&SD.getSection()),
1223 Layout.getSectionSize(&SD), sh_link,
1224 sh_info, SD.getAlignment(),
1225 Section.getEntrySize());
1229 ELFObjectWriter::ELFObjectWriter(raw_ostream &OS,
1231 Triple::OSType OSType,
1232 bool IsLittleEndian,
1233 bool HasRelocationAddend)
1234 : MCObjectWriter(OS, IsLittleEndian)
1236 Impl = new ELFObjectWriterImpl(this, Is64Bit, HasRelocationAddend, OSType);
1239 ELFObjectWriter::~ELFObjectWriter() {
1240 delete (ELFObjectWriterImpl*) Impl;
1243 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
1244 ((ELFObjectWriterImpl*) Impl)->ExecutePostLayoutBinding(Asm);
1247 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
1248 const MCAsmLayout &Layout,
1249 const MCFragment *Fragment,
1250 const MCFixup &Fixup, MCValue Target,
1251 uint64_t &FixedValue) {
1252 ((ELFObjectWriterImpl*) Impl)->RecordRelocation(Asm, Layout, Fragment, Fixup,
1253 Target, FixedValue);
1256 bool ELFObjectWriter::IsFixupFullyResolved(const MCAssembler &Asm,
1257 const MCValue Target,
1259 const MCFragment *DF) const {
1260 return ((ELFObjectWriterImpl*) Impl)->IsFixupFullyResolved(Asm, Target,
1264 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1265 const MCAsmLayout &Layout) {
1266 ((ELFObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);