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;
169 // This holds the symbol table index of the last local symbol.
170 unsigned LastLocalSymbolIndex;
171 // This holds the .strtab section index.
172 unsigned StringTableIndex;
174 unsigned ShstrtabIndex;
177 ELFObjectWriterImpl(ELFObjectWriter *_Writer, bool _Is64Bit,
178 uint16_t _EMachine, bool _HasRelAddend,
179 Triple::OSType _OSType)
180 : NeedsGOT(false), Writer(_Writer), OS(Writer->getStream()),
181 Is64Bit(_Is64Bit), HasRelocationAddend(_HasRelAddend),
182 OSType(_OSType), EMachine(_EMachine) {
185 void Write8(uint8_t Value) { Writer->Write8(Value); }
186 void Write16(uint16_t Value) { Writer->Write16(Value); }
187 void Write32(uint32_t Value) { Writer->Write32(Value); }
188 //void Write64(uint64_t Value) { Writer->Write64(Value); }
189 void WriteZeros(unsigned N) { Writer->WriteZeros(N); }
190 //void WriteBytes(StringRef Str, unsigned ZeroFillSize = 0) {
191 // Writer->WriteBytes(Str, ZeroFillSize);
194 void WriteWord(uint64_t W) {
201 void String8(char *buf, uint8_t Value) {
205 void StringLE16(char *buf, uint16_t Value) {
206 buf[0] = char(Value >> 0);
207 buf[1] = char(Value >> 8);
210 void StringLE32(char *buf, uint32_t Value) {
211 StringLE16(buf, uint16_t(Value >> 0));
212 StringLE16(buf + 2, uint16_t(Value >> 16));
215 void StringLE64(char *buf, uint64_t Value) {
216 StringLE32(buf, uint32_t(Value >> 0));
217 StringLE32(buf + 4, uint32_t(Value >> 32));
220 void StringBE16(char *buf ,uint16_t Value) {
221 buf[0] = char(Value >> 8);
222 buf[1] = char(Value >> 0);
225 void StringBE32(char *buf, uint32_t Value) {
226 StringBE16(buf, uint16_t(Value >> 16));
227 StringBE16(buf + 2, uint16_t(Value >> 0));
230 void StringBE64(char *buf, uint64_t Value) {
231 StringBE32(buf, uint32_t(Value >> 32));
232 StringBE32(buf + 4, uint32_t(Value >> 0));
235 void String16(char *buf, uint16_t Value) {
236 if (Writer->isLittleEndian())
237 StringLE16(buf, Value);
239 StringBE16(buf, Value);
242 void String32(char *buf, uint32_t Value) {
243 if (Writer->isLittleEndian())
244 StringLE32(buf, Value);
246 StringBE32(buf, Value);
249 void String64(char *buf, uint64_t Value) {
250 if (Writer->isLittleEndian())
251 StringLE64(buf, Value);
253 StringBE64(buf, Value);
256 void WriteHeader(uint64_t SectionDataSize, unsigned NumberOfSections);
258 void WriteSymbolEntry(MCDataFragment *F, uint64_t name, uint8_t info,
259 uint64_t value, uint64_t size,
260 uint8_t other, uint16_t shndx);
262 void WriteSymbol(MCDataFragment *F, ELFSymbolData &MSD,
263 const MCAsmLayout &Layout);
265 void WriteSymbolTable(MCDataFragment *F, const MCAssembler &Asm,
266 const MCAsmLayout &Layout,
267 unsigned NumRegularSections);
269 void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
270 const MCFragment *Fragment, const MCFixup &Fixup,
271 MCValue Target, uint64_t &FixedValue);
273 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
276 /// ComputeSymbolTable - Compute the symbol table data
278 /// \param StringTable [out] - The string table data.
279 /// \param StringIndexMap [out] - Map from symbol names to offsets in the
281 void ComputeSymbolTable(MCAssembler &Asm);
283 void WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
284 const MCSectionData &SD);
286 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) {
287 for (MCAssembler::const_iterator it = Asm.begin(),
288 ie = Asm.end(); it != ie; ++it) {
289 WriteRelocation(Asm, Layout, *it);
293 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout);
295 void ExecutePostLayoutBinding(MCAssembler &Asm) {
298 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
299 uint64_t Address, uint64_t Offset,
300 uint64_t Size, uint32_t Link, uint32_t Info,
301 uint64_t Alignment, uint64_t EntrySize);
303 void WriteRelocationsFragment(const MCAssembler &Asm, MCDataFragment *F,
304 const MCSectionData *SD);
306 bool IsFixupFullyResolved(const MCAssembler &Asm,
307 const MCValue Target,
309 const MCFragment *DF) const;
311 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout);
316 // Emit the ELF header.
317 void ELFObjectWriterImpl::WriteHeader(uint64_t SectionDataSize,
318 unsigned NumberOfSections) {
324 // emitWord method behaves differently for ELF32 and ELF64, writing
325 // 4 bytes in the former and 8 in the latter.
327 Write8(0x7f); // e_ident[EI_MAG0]
328 Write8('E'); // e_ident[EI_MAG1]
329 Write8('L'); // e_ident[EI_MAG2]
330 Write8('F'); // e_ident[EI_MAG3]
332 Write8(Is64Bit ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
335 Write8(Writer->isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
337 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
340 case Triple::FreeBSD: Write8(ELF::ELFOSABI_FREEBSD); break;
341 case Triple::Linux: Write8(ELF::ELFOSABI_LINUX); break;
342 default: Write8(ELF::ELFOSABI_NONE); break;
344 Write8(0); // e_ident[EI_ABIVERSION]
346 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
348 Write16(ELF::ET_REL); // e_type
350 Write16(EMachine); // e_machine = target
352 Write32(ELF::EV_CURRENT); // e_version
353 WriteWord(0); // e_entry, no entry point in .o file
354 WriteWord(0); // e_phoff, no program header for .o
355 WriteWord(SectionDataSize + (Is64Bit ? sizeof(ELF::Elf64_Ehdr) :
356 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes
358 // FIXME: Make this configurable.
359 Write32(0); // e_flags = whatever the target wants
361 // e_ehsize = ELF header size
362 Write16(Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
364 Write16(0); // e_phentsize = prog header entry size
365 Write16(0); // e_phnum = # prog header entries = 0
367 // e_shentsize = Section header entry size
368 Write16(Is64Bit ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
370 // e_shnum = # of section header ents
371 Write16(NumberOfSections);
373 // e_shstrndx = Section # of '.shstrtab'
374 Write16(ShstrtabIndex);
377 void ELFObjectWriterImpl::WriteSymbolEntry(MCDataFragment *F, uint64_t name,
378 uint8_t info, uint64_t value,
379 uint64_t size, uint8_t other,
385 F->getContents() += StringRef(buf, 4); // st_name
388 F->getContents() += StringRef(buf, 1); // st_info
391 F->getContents() += StringRef(buf, 1); // st_other
393 String16(buf, shndx);
394 F->getContents() += StringRef(buf, 2); // st_shndx
396 String64(buf, value);
397 F->getContents() += StringRef(buf, 8); // st_value
400 F->getContents() += StringRef(buf, 8); // st_size
405 F->getContents() += StringRef(buf, 4); // st_name
407 String32(buf, value);
408 F->getContents() += StringRef(buf, 4); // st_value
411 F->getContents() += StringRef(buf, 4); // st_size
414 F->getContents() += StringRef(buf, 1); // st_info
417 F->getContents() += StringRef(buf, 1); // st_other
419 String16(buf, shndx);
420 F->getContents() += StringRef(buf, 2); // st_shndx
424 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout) {
425 if (Data.isCommon() && Data.isExternal())
426 return Data.getCommonAlignment();
428 const MCSymbol &Symbol = Data.getSymbol();
429 if (!Symbol.isInSection())
432 if (!Data.isCommon() && !(Data.getFlags() & ELF_STB_Weak))
433 if (MCFragment *FF = Data.getFragment())
434 return Layout.getSymbolAddress(&Data) -
435 Layout.getSectionAddress(FF->getParent());
440 static const MCSymbol &AliasedSymbol(const MCSymbol &Symbol) {
441 const MCSymbol *S = &Symbol;
442 while (S->isVariable()) {
443 const MCExpr *Value = S->getVariableValue();
444 assert (Value->getKind() == MCExpr::SymbolRef && "Unimplemented");
445 const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Value);
446 S = &Ref->getSymbol();
451 void ELFObjectWriterImpl::WriteSymbol(MCDataFragment *F, ELFSymbolData &MSD,
452 const MCAsmLayout &Layout) {
453 MCSymbolData &OrigData = *MSD.SymbolData;
455 Layout.getAssembler().getSymbolData(AliasedSymbol(OrigData.getSymbol()));
457 uint8_t Binding = GetBinding(OrigData);
458 uint8_t Visibility = GetVisibility(OrigData);
459 uint8_t Type = GetType(Data);
461 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
462 uint8_t Other = Visibility;
464 uint64_t Value = SymbolValue(Data, Layout);
468 assert(!(Data.isCommon() && !Data.isExternal()));
470 ESize = Data.getSize();
471 if (Data.getSize()) {
473 if (ESize->getKind() == MCExpr::Binary) {
474 const MCBinaryExpr *BE = static_cast<const MCBinaryExpr *>(ESize);
476 if (BE->EvaluateAsRelocatable(Res, &Layout)) {
477 assert(!Res.getSymA() || !Res.getSymA()->getSymbol().isDefined());
478 assert(!Res.getSymB() || !Res.getSymB()->getSymbol().isDefined());
479 Size = Res.getConstant();
481 } else if (ESize->getKind() == MCExpr::Constant) {
482 Size = static_cast<const MCConstantExpr *>(ESize)->getValue();
484 assert(0 && "Unsupported size expression");
488 // Write out the symbol table entry
489 WriteSymbolEntry(F, MSD.StringIndex, Info, Value,
490 Size, Other, MSD.SectionIndex);
493 void ELFObjectWriterImpl::WriteSymbolTable(MCDataFragment *F,
494 const MCAssembler &Asm,
495 const MCAsmLayout &Layout,
496 unsigned NumRegularSections) {
497 // The string table must be emitted first because we need the index
498 // into the string table for all the symbol names.
499 assert(StringTable.size() && "Missing string table");
501 // FIXME: Make sure the start of the symbol table is aligned.
503 // The first entry is the undefined symbol entry.
504 unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
505 F->getContents().append(EntrySize, '\x00');
507 // Write the symbol table entries.
508 LastLocalSymbolIndex = LocalSymbolData.size() + 1;
509 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
510 ELFSymbolData &MSD = LocalSymbolData[i];
511 WriteSymbol(F, MSD, Layout);
514 // Write out a symbol table entry for each regular section.
516 for (MCAssembler::const_iterator it = Asm.begin();
517 Index <= NumRegularSections; ++it, ++Index) {
518 const MCSectionELF &Section =
519 static_cast<const MCSectionELF&>(it->getSection());
520 // Leave out relocations so we don't have indexes within
521 // the relocations messed up
522 if (Section.getType() == ELF::SHT_RELA || Section.getType() == ELF::SHT_REL)
524 WriteSymbolEntry(F, 0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT, Index);
525 LastLocalSymbolIndex++;
528 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
529 ELFSymbolData &MSD = ExternalSymbolData[i];
530 MCSymbolData &Data = *MSD.SymbolData;
531 assert(((Data.getFlags() & ELF_STB_Global) ||
532 (Data.getFlags() & ELF_STB_Weak)) &&
533 "External symbol requires STB_GLOBAL or STB_WEAK flag");
534 WriteSymbol(F, MSD, Layout);
535 if (GetBinding(Data) == ELF::STB_LOCAL)
536 LastLocalSymbolIndex++;
539 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
540 ELFSymbolData &MSD = UndefinedSymbolData[i];
541 MCSymbolData &Data = *MSD.SymbolData;
542 WriteSymbol(F, MSD, Layout);
543 if (GetBinding(Data) == ELF::STB_LOCAL)
544 LastLocalSymbolIndex++;
548 static bool ShouldRelocOnSymbol(const MCSymbolData &SD,
549 const MCValue &Target,
550 const MCFragment &F) {
551 const MCSymbol &Symbol = SD.getSymbol();
552 if (Symbol.isUndefined())
555 const MCSectionELF &Section =
556 static_cast<const MCSectionELF&>(Symbol.getSection());
561 MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind();
562 const MCSectionELF &Sec2 =
563 static_cast<const MCSectionELF&>(F.getParent()->getSection());
565 if (Section.getKind().isBSS())
568 if (&Sec2 != &Section &&
569 (Kind == MCSymbolRefExpr::VK_PLT ||
570 Kind == MCSymbolRefExpr::VK_GOTPCREL ||
571 Kind == MCSymbolRefExpr::VK_GOTOFF))
574 if (Section.getFlags() & MCSectionELF::SHF_MERGE)
575 return Target.getConstant() != 0;
580 // FIXME: this is currently X86/X86_64 only
581 void ELFObjectWriterImpl::RecordRelocation(const MCAssembler &Asm,
582 const MCAsmLayout &Layout,
583 const MCFragment *Fragment,
584 const MCFixup &Fixup,
586 uint64_t &FixedValue) {
589 int64_t Value = Target.getConstant();
590 const MCSymbol *Symbol = 0;
592 bool IsPCRel = isFixupKindX86PCRel(Fixup.getKind());
593 if (!Target.isAbsolute()) {
594 Symbol = &AliasedSymbol(Target.getSymA()->getSymbol());
595 MCSymbolData &SD = Asm.getSymbolData(*Symbol);
596 MCFragment *F = SD.getFragment();
598 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
599 const MCSymbol &SymbolB = RefB->getSymbol();
600 MCSymbolData &SDB = Asm.getSymbolData(SymbolB);
602 MCSectionData *Sec = Fragment->getParent();
604 // Offset of the symbol in the section
605 int64_t a = Layout.getSymbolAddress(&SDB) - Layout.getSectionAddress(Sec);
607 // Ofeset of the relocation in the section
608 int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
612 // Check that this case has already been fully resolved before we get
614 if (Symbol->isDefined() && !SD.isExternal() &&
616 &Fragment->getParent()->getSection() == &Symbol->getSection()) {
617 llvm_unreachable("We don't need a relocation in this case.");
621 bool RelocOnSymbol = ShouldRelocOnSymbol(SD, Target, *Fragment);
622 if (!RelocOnSymbol) {
623 Index = F->getParent()->getOrdinal();
625 MCSectionData *FSD = F->getParent();
626 // Offset of the symbol in the section
627 Value += Layout.getSymbolAddress(&SD) - Layout.getSectionAddress(FSD);
629 UsedInReloc.insert(Symbol);
633 // Compensate for the addend on i386.
640 // determine the type of the relocation
642 MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
648 llvm_unreachable("Unimplemented");
649 case MCSymbolRefExpr::VK_None:
650 Type = ELF::R_X86_64_PC32;
652 case MCSymbolRefExpr::VK_PLT:
653 Type = ELF::R_X86_64_PLT32;
655 case llvm::MCSymbolRefExpr::VK_GOTPCREL:
656 Type = ELF::R_X86_64_GOTPCREL;
660 switch ((unsigned)Fixup.getKind()) {
661 default: llvm_unreachable("invalid fixup kind!");
662 case FK_Data_8: Type = ELF::R_X86_64_64; break;
663 case X86::reloc_signed_4byte:
664 case X86::reloc_pcrel_4byte:
665 assert(isInt<32>(Target.getConstant()));
668 llvm_unreachable("Unimplemented");
669 case MCSymbolRefExpr::VK_None:
670 Type = ELF::R_X86_64_32S;
672 case MCSymbolRefExpr::VK_GOT:
673 Type = ELF::R_X86_64_GOT32;
675 case MCSymbolRefExpr::VK_GOTPCREL:
676 Type = ELF::R_X86_64_GOTPCREL;
681 Type = ELF::R_X86_64_32;
683 case FK_Data_2: Type = ELF::R_X86_64_16; break;
684 case X86::reloc_pcrel_1byte:
685 case FK_Data_1: Type = ELF::R_X86_64_8; break;
692 llvm_unreachable("Unimplemented");
693 case MCSymbolRefExpr::VK_None:
694 Type = ELF::R_386_PC32;
696 case MCSymbolRefExpr::VK_PLT:
697 Type = ELF::R_386_PLT32;
701 switch ((unsigned)Fixup.getKind()) {
702 default: llvm_unreachable("invalid fixup kind!");
704 case X86::reloc_global_offset_table:
705 Type = ELF::R_386_GOTPC;
708 // FIXME: Should we avoid selecting reloc_signed_4byte in 32 bit mode
710 case X86::reloc_signed_4byte:
711 case X86::reloc_pcrel_4byte:
715 llvm_unreachable("Unimplemented");
716 case MCSymbolRefExpr::VK_None:
717 Type = ELF::R_386_32;
719 case MCSymbolRefExpr::VK_GOT:
720 Type = ELF::R_386_GOT32;
722 case MCSymbolRefExpr::VK_GOTOFF:
723 Type = ELF::R_386_GOTOFF;
727 case FK_Data_2: Type = ELF::R_386_16; break;
728 case X86::reloc_pcrel_1byte:
729 case FK_Data_1: Type = ELF::R_386_8; break;
734 if (RelocNeedsGOT(Type))
737 ELFRelocationEntry ERE;
743 ERE.r_offset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
745 if (HasRelocationAddend)
746 ERE.r_addend = Addend;
748 ERE.r_addend = 0; // Silence compiler warning.
750 Relocations[Fragment->getParent()].push_back(ERE);
754 ELFObjectWriterImpl::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
756 MCSymbolData &SD = Asm.getSymbolData(*S);
759 if (!SD.isExternal() && !S->isUndefined())
760 return SD.getIndex() + /* empty symbol */ 1;
762 // External or undefined symbol.
763 return SD.getIndex() + NumRegularSections + /* empty symbol */ 1;
766 static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data,
771 const MCSymbol &Symbol = Data.getSymbol();
772 if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined())
775 if (Symbol.isTemporary())
781 static bool isLocal(const MCSymbolData &Data) {
782 if (Data.isExternal())
785 const MCSymbol &Symbol = Data.getSymbol();
786 if (Symbol.isUndefined() && !Symbol.isVariable())
792 void ELFObjectWriterImpl::ComputeSymbolTable(MCAssembler &Asm) {
793 // FIXME: Is this the correct place to do this?
795 llvm::StringRef Name = "_GLOBAL_OFFSET_TABLE_";
796 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
797 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
798 Data.setExternal(true);
801 // Build section lookup table.
802 NumRegularSections = Asm.size();
803 DenseMap<const MCSection*, uint32_t> SectionIndexMap;
805 for (MCAssembler::iterator it = Asm.begin(),
806 ie = Asm.end(); it != ie; ++it, ++Index)
807 SectionIndexMap[&it->getSection()] = Index;
809 // Index 0 is always the empty string.
810 StringMap<uint64_t> StringIndexMap;
811 StringTable += '\x00';
813 // Add the data for the symbols.
814 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
815 ie = Asm.symbol_end(); it != ie; ++it) {
816 const MCSymbol &Symbol = it->getSymbol();
818 if (!isInSymtab(Asm, *it, UsedInReloc.count(&Symbol)))
823 bool Local = isLocal(*it);
826 if (it->isCommon()) {
828 MSD.SectionIndex = ELF::SHN_COMMON;
830 } else if (Symbol.isAbsolute()) {
831 MSD.SectionIndex = ELF::SHN_ABS;
833 } else if (Symbol.isVariable()) {
834 const MCSymbol &RefSymbol = AliasedSymbol(Symbol);
835 if (RefSymbol.isDefined()) {
836 MSD.SectionIndex = SectionIndexMap.lookup(&RefSymbol.getSection());
837 assert(MSD.SectionIndex && "Invalid section index!");
840 } else if (Symbol.isUndefined()) {
842 MSD.SectionIndex = ELF::SHN_UNDEF;
843 // FIXME: Undefined symbols are global, but this is the first place we
844 // are able to set it.
845 if (GetBinding(*it) == ELF::STB_LOCAL)
846 SetBinding(*it, ELF::STB_GLOBAL);
849 MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
850 assert(MSD.SectionIndex && "Invalid section index!");
855 uint64_t &Entry = StringIndexMap[Symbol.getName()];
857 Entry = StringTable.size();
858 StringTable += Symbol.getName();
859 StringTable += '\x00';
861 MSD.StringIndex = Entry;
862 if (MSD.SectionIndex == ELF::SHN_UNDEF)
863 UndefinedSymbolData.push_back(MSD);
865 LocalSymbolData.push_back(MSD);
867 ExternalSymbolData.push_back(MSD);
871 // Symbols are required to be in lexicographic order.
872 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
873 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
874 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
876 // Set the symbol indices. Local symbols must come before all other
877 // symbols with non-local bindings.
879 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
880 LocalSymbolData[i].SymbolData->setIndex(Index++);
881 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
882 ExternalSymbolData[i].SymbolData->setIndex(Index++);
883 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
884 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
887 void ELFObjectWriterImpl::WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
888 const MCSectionData &SD) {
889 if (!Relocations[&SD].empty()) {
890 MCContext &Ctx = Asm.getContext();
891 const MCSection *RelaSection;
892 const MCSectionELF &Section =
893 static_cast<const MCSectionELF&>(SD.getSection());
895 const StringRef SectionName = Section.getSectionName();
896 std::string RelaSectionName = HasRelocationAddend ? ".rela" : ".rel";
897 RelaSectionName += SectionName;
900 if (HasRelocationAddend)
901 EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
903 EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
905 RelaSection = Ctx.getELFSection(RelaSectionName, HasRelocationAddend ?
906 ELF::SHT_RELA : ELF::SHT_REL, 0,
907 SectionKind::getReadOnly(),
910 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
911 RelaSD.setAlignment(Is64Bit ? 8 : 4);
913 MCDataFragment *F = new MCDataFragment(&RelaSD);
915 WriteRelocationsFragment(Asm, F, &SD);
917 Asm.AddSectionToTheEnd(*Writer, RelaSD, Layout);
921 void ELFObjectWriterImpl::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
922 uint64_t Flags, uint64_t Address,
923 uint64_t Offset, uint64_t Size,
924 uint32_t Link, uint32_t Info,
926 uint64_t EntrySize) {
927 Write32(Name); // sh_name: index into string table
928 Write32(Type); // sh_type
929 WriteWord(Flags); // sh_flags
930 WriteWord(Address); // sh_addr
931 WriteWord(Offset); // sh_offset
932 WriteWord(Size); // sh_size
933 Write32(Link); // sh_link
934 Write32(Info); // sh_info
935 WriteWord(Alignment); // sh_addralign
936 WriteWord(EntrySize); // sh_entsize
939 void ELFObjectWriterImpl::WriteRelocationsFragment(const MCAssembler &Asm,
941 const MCSectionData *SD) {
942 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
943 // sort by the r_offset just like gnu as does
944 array_pod_sort(Relocs.begin(), Relocs.end());
946 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
947 ELFRelocationEntry entry = Relocs[e - i - 1];
950 entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol);
952 entry.Index += LocalSymbolData.size() + 1;
956 String64(buf, entry.r_offset);
957 F->getContents() += StringRef(buf, 8);
959 struct ELF::Elf64_Rela ERE64;
960 ERE64.setSymbolAndType(entry.Index, entry.Type);
961 String64(buf, ERE64.r_info);
962 F->getContents() += StringRef(buf, 8);
964 if (HasRelocationAddend) {
965 String64(buf, entry.r_addend);
966 F->getContents() += StringRef(buf, 8);
971 String32(buf, entry.r_offset);
972 F->getContents() += StringRef(buf, 4);
974 struct ELF::Elf32_Rela ERE32;
975 ERE32.setSymbolAndType(entry.Index, entry.Type);
976 String32(buf, ERE32.r_info);
977 F->getContents() += StringRef(buf, 4);
979 if (HasRelocationAddend) {
980 String32(buf, entry.r_addend);
981 F->getContents() += StringRef(buf, 4);
987 void ELFObjectWriterImpl::CreateMetadataSections(MCAssembler &Asm,
988 MCAsmLayout &Layout) {
989 MCContext &Ctx = Asm.getContext();
992 const MCSection *SymtabSection;
993 unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
995 unsigned NumRegularSections = Asm.size();
997 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
998 const MCSection *ShstrtabSection;
999 ShstrtabSection = Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
1000 SectionKind::getReadOnly(), false);
1001 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1002 ShstrtabSD.setAlignment(1);
1003 ShstrtabIndex = Asm.size();
1005 SymtabSection = Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1006 SectionKind::getReadOnly(),
1008 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1009 SymtabSD.setAlignment(Is64Bit ? 8 : 4);
1011 const MCSection *StrtabSection;
1012 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
1013 SectionKind::getReadOnly(), false);
1014 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1015 StrtabSD.setAlignment(1);
1016 StringTableIndex = Asm.size();
1018 WriteRelocations(Asm, Layout);
1021 F = new MCDataFragment(&SymtabSD);
1022 WriteSymbolTable(F, Asm, Layout, NumRegularSections);
1023 Asm.AddSectionToTheEnd(*Writer, SymtabSD, Layout);
1025 F = new MCDataFragment(&StrtabSD);
1026 F->getContents().append(StringTable.begin(), StringTable.end());
1027 Asm.AddSectionToTheEnd(*Writer, StrtabSD, Layout);
1029 F = new MCDataFragment(&ShstrtabSD);
1031 // Section header string table.
1033 // The first entry of a string table holds a null character so skip
1036 F->getContents() += '\x00';
1038 for (MCAssembler::const_iterator it = Asm.begin(),
1039 ie = Asm.end(); it != ie; ++it) {
1040 const MCSectionELF &Section =
1041 static_cast<const MCSectionELF&>(it->getSection());
1042 // FIXME: We could merge suffixes like in .text and .rela.text.
1044 // Remember the index into the string table so we can write it
1045 // into the sh_name field of the section header table.
1046 SectionStringTableIndex[&it->getSection()] = Index;
1048 Index += Section.getSectionName().size() + 1;
1049 F->getContents() += Section.getSectionName();
1050 F->getContents() += '\x00';
1053 Asm.AddSectionToTheEnd(*Writer, ShstrtabSD, Layout);
1056 bool ELFObjectWriterImpl::IsFixupFullyResolved(const MCAssembler &Asm,
1057 const MCValue Target,
1059 const MCFragment *DF) const {
1060 // If this is a PCrel relocation, find the section this fixup value is
1062 const MCSection *BaseSection = 0;
1064 BaseSection = &DF->getParent()->getSection();
1065 assert(BaseSection);
1068 const MCSection *SectionA = 0;
1069 const MCSymbol *SymbolA = 0;
1070 if (const MCSymbolRefExpr *A = Target.getSymA()) {
1071 SymbolA = &A->getSymbol();
1072 SectionA = &SymbolA->getSection();
1075 const MCSection *SectionB = 0;
1076 if (const MCSymbolRefExpr *B = Target.getSymB()) {
1077 SectionB = &B->getSymbol().getSection();
1081 return SectionA == SectionB;
1083 const MCSymbolData &DataA = Asm.getSymbolData(*SymbolA);
1084 if (DataA.isExternal())
1087 return !SectionB && BaseSection == SectionA;
1090 void ELFObjectWriterImpl::WriteObject(MCAssembler &Asm,
1091 const MCAsmLayout &Layout) {
1092 // Compute symbol table information.
1093 ComputeSymbolTable(Asm);
1095 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1096 const_cast<MCAsmLayout&>(Layout));
1098 // Add 1 for the null section.
1099 unsigned NumSections = Asm.size() + 1;
1100 uint64_t NaturalAlignment = Is64Bit ? 8 : 4;
1101 uint64_t HeaderSize = Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr);
1102 uint64_t FileOff = HeaderSize;
1104 for (MCAssembler::const_iterator it = Asm.begin(),
1105 ie = Asm.end(); it != ie; ++it) {
1106 const MCSectionData &SD = *it;
1108 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1110 // Get the size of the section in the output file (including padding).
1111 uint64_t Size = Layout.getSectionFileSize(&SD);
1116 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1118 // Write out the ELF header ...
1119 WriteHeader(FileOff - HeaderSize, NumSections);
1121 FileOff = HeaderSize;
1123 // ... then all of the sections ...
1124 DenseMap<const MCSection*, uint64_t> SectionOffsetMap;
1126 DenseMap<const MCSection*, uint32_t> SectionIndexMap;
1129 for (MCAssembler::const_iterator it = Asm.begin(),
1130 ie = Asm.end(); it != ie; ++it) {
1131 const MCSectionData &SD = *it;
1133 uint64_t Padding = OffsetToAlignment(FileOff, SD.getAlignment());
1134 WriteZeros(Padding);
1137 // Remember the offset into the file for this section.
1138 SectionOffsetMap[&it->getSection()] = FileOff;
1139 SectionIndexMap[&it->getSection()] = Index++;
1141 FileOff += Layout.getSectionFileSize(&SD);
1143 Asm.WriteSectionData(it, Layout, Writer);
1146 uint64_t Padding = OffsetToAlignment(FileOff, NaturalAlignment);
1147 WriteZeros(Padding);
1150 // ... and then the section header table.
1151 // Should we align the section header table?
1153 // Null section first.
1154 WriteSecHdrEntry(0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
1156 for (MCAssembler::const_iterator it = Asm.begin(),
1157 ie = Asm.end(); it != ie; ++it) {
1158 const MCSectionData &SD = *it;
1159 const MCSectionELF &Section =
1160 static_cast<const MCSectionELF&>(SD.getSection());
1162 uint64_t sh_link = 0;
1163 uint64_t sh_info = 0;
1165 switch(Section.getType()) {
1166 case ELF::SHT_DYNAMIC:
1167 sh_link = SectionStringTableIndex[&it->getSection()];
1172 case ELF::SHT_RELA: {
1173 const MCSection *SymtabSection;
1174 const MCSection *InfoSection;
1176 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1177 SectionKind::getReadOnly(),
1179 sh_link = SectionIndexMap[SymtabSection];
1181 // Remove ".rel" and ".rela" prefixes.
1182 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1183 StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1185 InfoSection = Asm.getContext().getELFSection(SectionName,
1186 ELF::SHT_PROGBITS, 0,
1187 SectionKind::getReadOnly(),
1189 sh_info = SectionIndexMap[InfoSection];
1193 case ELF::SHT_SYMTAB:
1194 case ELF::SHT_DYNSYM:
1195 sh_link = StringTableIndex;
1196 sh_info = LastLocalSymbolIndex;
1199 case ELF::SHT_PROGBITS:
1200 case ELF::SHT_STRTAB:
1201 case ELF::SHT_NOBITS:
1203 case ELF::SHT_ARM_ATTRIBUTES:
1208 assert(0 && "FIXME: sh_type value not supported!");
1212 WriteSecHdrEntry(SectionStringTableIndex[&it->getSection()],
1213 Section.getType(), Section.getFlags(),
1215 SectionOffsetMap.lookup(&SD.getSection()),
1216 Layout.getSectionSize(&SD), sh_link,
1217 sh_info, SD.getAlignment(),
1218 Section.getEntrySize());
1222 ELFObjectWriter::ELFObjectWriter(raw_ostream &OS,
1224 Triple::OSType OSType,
1226 bool IsLittleEndian,
1227 bool HasRelocationAddend)
1228 : MCObjectWriter(OS, IsLittleEndian)
1230 Impl = new ELFObjectWriterImpl(this, Is64Bit, EMachine,
1231 HasRelocationAddend, OSType);
1234 ELFObjectWriter::~ELFObjectWriter() {
1235 delete (ELFObjectWriterImpl*) Impl;
1238 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
1239 ((ELFObjectWriterImpl*) Impl)->ExecutePostLayoutBinding(Asm);
1242 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
1243 const MCAsmLayout &Layout,
1244 const MCFragment *Fragment,
1245 const MCFixup &Fixup, MCValue Target,
1246 uint64_t &FixedValue) {
1247 ((ELFObjectWriterImpl*) Impl)->RecordRelocation(Asm, Layout, Fragment, Fixup,
1248 Target, FixedValue);
1251 bool ELFObjectWriter::IsFixupFullyResolved(const MCAssembler &Asm,
1252 const MCValue Target,
1254 const MCFragment *DF) const {
1255 return ((ELFObjectWriterImpl*) Impl)->IsFixupFullyResolved(Asm, Target,
1259 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1260 const MCAsmLayout &Layout) {
1261 ((ELFObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);