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 bool isFixupKindX86PCRel(unsigned Kind) {
65 case X86::reloc_pcrel_1byte:
66 case X86::reloc_pcrel_4byte:
67 case X86::reloc_riprel_4byte:
68 case X86::reloc_riprel_4byte_movq_load:
73 static bool RelocNeedsGOT(unsigned Type) {
77 case ELF::R_X86_64_GOT32:
78 case ELF::R_X86_64_PLT32:
79 case ELF::R_X86_64_GOTPCREL:
86 class ELFObjectWriterImpl {
87 /*static bool isFixupKindX86RIPRel(unsigned Kind) {
88 return Kind == X86::reloc_riprel_4byte ||
89 Kind == X86::reloc_riprel_4byte_movq_load;
93 /// ELFSymbolData - Helper struct for containing some precomputed information
95 struct ELFSymbolData {
96 MCSymbolData *SymbolData;
98 uint32_t SectionIndex;
100 // Support lexicographic sorting.
101 bool operator<(const ELFSymbolData &RHS) const {
102 if (GetType(*SymbolData) == ELF::STT_FILE)
104 if (GetType(*RHS.SymbolData) == ELF::STT_FILE)
106 return SymbolData->getSymbol().getName() <
107 RHS.SymbolData->getSymbol().getName();
111 /// @name Relocation Data
114 struct ELFRelocationEntry {
115 // Make these big enough for both 32-bit and 64-bit
119 const MCSymbol *Symbol;
122 // Support lexicographic sorting.
123 bool operator<(const ELFRelocationEntry &RE) const {
124 return RE.r_offset < r_offset;
128 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
130 llvm::DenseMap<const MCSectionData*,
131 std::vector<ELFRelocationEntry> > Relocations;
132 DenseMap<const MCSection*, uint64_t> SectionStringTableIndex;
135 /// @name Symbol Table Data
138 SmallString<256> StringTable;
139 std::vector<ELFSymbolData> LocalSymbolData;
140 std::vector<ELFSymbolData> ExternalSymbolData;
141 std::vector<ELFSymbolData> UndefinedSymbolData;
145 int NumRegularSections;
149 ELFObjectWriter *Writer;
153 unsigned Is64Bit : 1;
155 bool HasRelocationAddend;
157 Triple::OSType OSType;
159 // This holds the symbol table index of the last local symbol.
160 unsigned LastLocalSymbolIndex;
161 // This holds the .strtab section index.
162 unsigned StringTableIndex;
164 unsigned ShstrtabIndex;
167 ELFObjectWriterImpl(ELFObjectWriter *_Writer, bool _Is64Bit,
168 bool _HasRelAddend, Triple::OSType _OSType)
169 : NeedsGOT(false), Writer(_Writer), OS(Writer->getStream()),
170 Is64Bit(_Is64Bit), HasRelocationAddend(_HasRelAddend),
174 void Write8(uint8_t Value) { Writer->Write8(Value); }
175 void Write16(uint16_t Value) { Writer->Write16(Value); }
176 void Write32(uint32_t Value) { Writer->Write32(Value); }
177 //void Write64(uint64_t Value) { Writer->Write64(Value); }
178 void WriteZeros(unsigned N) { Writer->WriteZeros(N); }
179 //void WriteBytes(StringRef Str, unsigned ZeroFillSize = 0) {
180 // Writer->WriteBytes(Str, ZeroFillSize);
183 void WriteWord(uint64_t W) {
190 void String8(char *buf, uint8_t Value) {
194 void StringLE16(char *buf, uint16_t Value) {
195 buf[0] = char(Value >> 0);
196 buf[1] = char(Value >> 8);
199 void StringLE32(char *buf, uint32_t Value) {
200 StringLE16(buf, uint16_t(Value >> 0));
201 StringLE16(buf + 2, uint16_t(Value >> 16));
204 void StringLE64(char *buf, uint64_t Value) {
205 StringLE32(buf, uint32_t(Value >> 0));
206 StringLE32(buf + 4, uint32_t(Value >> 32));
209 void StringBE16(char *buf ,uint16_t Value) {
210 buf[0] = char(Value >> 8);
211 buf[1] = char(Value >> 0);
214 void StringBE32(char *buf, uint32_t Value) {
215 StringBE16(buf, uint16_t(Value >> 16));
216 StringBE16(buf + 2, uint16_t(Value >> 0));
219 void StringBE64(char *buf, uint64_t Value) {
220 StringBE32(buf, uint32_t(Value >> 32));
221 StringBE32(buf + 4, uint32_t(Value >> 0));
224 void String16(char *buf, uint16_t Value) {
225 if (Writer->isLittleEndian())
226 StringLE16(buf, Value);
228 StringBE16(buf, Value);
231 void String32(char *buf, uint32_t Value) {
232 if (Writer->isLittleEndian())
233 StringLE32(buf, Value);
235 StringBE32(buf, Value);
238 void String64(char *buf, uint64_t Value) {
239 if (Writer->isLittleEndian())
240 StringLE64(buf, Value);
242 StringBE64(buf, Value);
245 void WriteHeader(uint64_t SectionDataSize, unsigned NumberOfSections);
247 void WriteSymbolEntry(MCDataFragment *F, uint64_t name, uint8_t info,
248 uint64_t value, uint64_t size,
249 uint8_t other, uint16_t shndx);
251 void WriteSymbol(MCDataFragment *F, ELFSymbolData &MSD,
252 const MCAsmLayout &Layout);
254 void WriteSymbolTable(MCDataFragment *F, const MCAssembler &Asm,
255 const MCAsmLayout &Layout,
256 unsigned NumRegularSections);
258 void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
259 const MCFragment *Fragment, const MCFixup &Fixup,
260 MCValue Target, uint64_t &FixedValue);
262 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
265 /// ComputeSymbolTable - Compute the symbol table data
267 /// \param StringTable [out] - The string table data.
268 /// \param StringIndexMap [out] - Map from symbol names to offsets in the
270 void ComputeSymbolTable(MCAssembler &Asm);
272 void WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
273 const MCSectionData &SD);
275 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) {
276 for (MCAssembler::const_iterator it = Asm.begin(),
277 ie = Asm.end(); it != ie; ++it) {
278 WriteRelocation(Asm, Layout, *it);
282 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout);
284 void ExecutePostLayoutBinding(MCAssembler &Asm) {
287 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
288 uint64_t Address, uint64_t Offset,
289 uint64_t Size, uint32_t Link, uint32_t Info,
290 uint64_t Alignment, uint64_t EntrySize);
292 void WriteRelocationsFragment(const MCAssembler &Asm, MCDataFragment *F,
293 const MCSectionData *SD);
295 bool IsFixupFullyResolved(const MCAssembler &Asm,
296 const MCValue Target,
298 const MCFragment *DF) const;
300 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout);
305 // Emit the ELF header.
306 void ELFObjectWriterImpl::WriteHeader(uint64_t SectionDataSize,
307 unsigned NumberOfSections) {
313 // emitWord method behaves differently for ELF32 and ELF64, writing
314 // 4 bytes in the former and 8 in the latter.
316 Write8(0x7f); // e_ident[EI_MAG0]
317 Write8('E'); // e_ident[EI_MAG1]
318 Write8('L'); // e_ident[EI_MAG2]
319 Write8('F'); // e_ident[EI_MAG3]
321 Write8(Is64Bit ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
324 Write8(Writer->isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
326 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
329 case Triple::FreeBSD: Write8(ELF::ELFOSABI_FREEBSD); break;
330 case Triple::Linux: Write8(ELF::ELFOSABI_LINUX); break;
331 default: Write8(ELF::ELFOSABI_NONE); break;
333 Write8(0); // e_ident[EI_ABIVERSION]
335 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
337 Write16(ELF::ET_REL); // e_type
339 // FIXME: Make this configurable
340 Write16(Is64Bit ? ELF::EM_X86_64 : ELF::EM_386); // e_machine = target
342 Write32(ELF::EV_CURRENT); // e_version
343 WriteWord(0); // e_entry, no entry point in .o file
344 WriteWord(0); // e_phoff, no program header for .o
345 WriteWord(SectionDataSize + (Is64Bit ? sizeof(ELF::Elf64_Ehdr) :
346 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes
348 // FIXME: Make this configurable.
349 Write32(0); // e_flags = whatever the target wants
351 // e_ehsize = ELF header size
352 Write16(Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
354 Write16(0); // e_phentsize = prog header entry size
355 Write16(0); // e_phnum = # prog header entries = 0
357 // e_shentsize = Section header entry size
358 Write16(Is64Bit ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
360 // e_shnum = # of section header ents
361 Write16(NumberOfSections);
363 // e_shstrndx = Section # of '.shstrtab'
364 Write16(ShstrtabIndex);
367 void ELFObjectWriterImpl::WriteSymbolEntry(MCDataFragment *F, uint64_t name,
368 uint8_t info, uint64_t value,
369 uint64_t size, uint8_t other,
375 F->getContents() += StringRef(buf, 4); // st_name
378 F->getContents() += StringRef(buf, 1); // st_info
381 F->getContents() += StringRef(buf, 1); // st_other
383 String16(buf, shndx);
384 F->getContents() += StringRef(buf, 2); // st_shndx
386 String64(buf, value);
387 F->getContents() += StringRef(buf, 8); // st_value
390 F->getContents() += StringRef(buf, 8); // st_size
395 F->getContents() += StringRef(buf, 4); // st_name
397 String32(buf, value);
398 F->getContents() += StringRef(buf, 4); // st_value
401 F->getContents() += StringRef(buf, 4); // st_size
404 F->getContents() += StringRef(buf, 1); // st_info
407 F->getContents() += StringRef(buf, 1); // st_other
409 String16(buf, shndx);
410 F->getContents() += StringRef(buf, 2); // st_shndx
414 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout) {
415 if (Data.isCommon() && Data.isExternal())
416 return Data.getCommonAlignment();
418 const MCSymbol &Symbol = Data.getSymbol();
419 if (!Symbol.isInSection())
422 if (!Data.isCommon() && !(Data.getFlags() & ELF_STB_Weak))
423 if (MCFragment *FF = Data.getFragment())
424 return Layout.getSymbolAddress(&Data) -
425 Layout.getSectionAddress(FF->getParent());
430 void ELFObjectWriterImpl::WriteSymbol(MCDataFragment *F, ELFSymbolData &MSD,
431 const MCAsmLayout &Layout) {
432 MCSymbolData &Data = *MSD.SymbolData;
433 uint8_t Info = (Data.getFlags() & 0xff);
434 uint8_t Other = ((Data.getFlags() & 0xf00) >> ELF_STV_Shift);
435 uint64_t Value = SymbolValue(Data, Layout);
439 assert(!(Data.isCommon() && !Data.isExternal()));
441 ESize = Data.getSize();
442 if (Data.getSize()) {
444 if (ESize->getKind() == MCExpr::Binary) {
445 const MCBinaryExpr *BE = static_cast<const MCBinaryExpr *>(ESize);
447 if (BE->EvaluateAsRelocatable(Res, &Layout)) {
449 Layout.getAssembler().getSymbolData(Res.getSymA()->getSymbol());
451 Layout.getAssembler().getSymbolData(Res.getSymB()->getSymbol());
453 Size = Layout.getSymbolAddress(&A) - Layout.getSymbolAddress(&B);
455 } else if (ESize->getKind() == MCExpr::Constant) {
456 Size = static_cast<const MCConstantExpr *>(ESize)->getValue();
458 assert(0 && "Unsupported size expression");
462 // Write out the symbol table entry
463 WriteSymbolEntry(F, MSD.StringIndex, Info, Value,
464 Size, Other, MSD.SectionIndex);
467 void ELFObjectWriterImpl::WriteSymbolTable(MCDataFragment *F,
468 const MCAssembler &Asm,
469 const MCAsmLayout &Layout,
470 unsigned NumRegularSections) {
471 // The string table must be emitted first because we need the index
472 // into the string table for all the symbol names.
473 assert(StringTable.size() && "Missing string table");
475 // FIXME: Make sure the start of the symbol table is aligned.
477 // The first entry is the undefined symbol entry.
478 unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
479 F->getContents().append(EntrySize, '\x00');
481 // Write the symbol table entries.
482 LastLocalSymbolIndex = LocalSymbolData.size() + 1;
483 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
484 ELFSymbolData &MSD = LocalSymbolData[i];
485 WriteSymbol(F, MSD, Layout);
488 // Write out a symbol table entry for each regular section.
490 for (MCAssembler::const_iterator it = Asm.begin();
491 Index <= NumRegularSections; ++it, ++Index) {
492 const MCSectionELF &Section =
493 static_cast<const MCSectionELF&>(it->getSection());
494 // Leave out relocations so we don't have indexes within
495 // the relocations messed up
496 if (Section.getType() == ELF::SHT_RELA || Section.getType() == ELF::SHT_REL)
498 WriteSymbolEntry(F, 0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT, Index);
499 LastLocalSymbolIndex++;
502 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
503 ELFSymbolData &MSD = ExternalSymbolData[i];
504 MCSymbolData &Data = *MSD.SymbolData;
505 assert((Data.getFlags() & ELF_STB_Global) &&
506 "External symbol requires STB_GLOBAL flag");
507 WriteSymbol(F, MSD, Layout);
508 if (GetBinding(Data) == ELF::STB_LOCAL)
509 LastLocalSymbolIndex++;
512 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
513 ELFSymbolData &MSD = UndefinedSymbolData[i];
514 MCSymbolData &Data = *MSD.SymbolData;
515 WriteSymbol(F, MSD, Layout);
516 if (GetBinding(Data) == ELF::STB_LOCAL)
517 LastLocalSymbolIndex++;
521 static bool ShouldRelocOnSymbol(const MCSymbolData &SD,
522 const MCValue &Target) {
523 const MCSymbol &Symbol = SD.getSymbol();
524 if (Symbol.isUndefined())
527 const MCSectionELF &Section =
528 static_cast<const MCSectionELF&>(Symbol.getSection());
530 if (Section.getFlags() & MCSectionELF::SHF_MERGE)
531 return Target.getConstant() != 0;
539 // FIXME: this is currently X86/X86_64 only
540 void ELFObjectWriterImpl::RecordRelocation(const MCAssembler &Asm,
541 const MCAsmLayout &Layout,
542 const MCFragment *Fragment,
543 const MCFixup &Fixup,
545 uint64_t &FixedValue) {
548 int64_t Value = Target.getConstant();
549 const MCSymbol *Symbol = 0;
551 bool IsPCRel = isFixupKindX86PCRel(Fixup.getKind());
552 if (!Target.isAbsolute()) {
553 Symbol = &Target.getSymA()->getSymbol();
554 MCSymbolData &SD = Asm.getSymbolData(*Symbol);
555 MCFragment *F = SD.getFragment();
557 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
558 const MCSymbol &SymbolB = RefB->getSymbol();
559 MCSymbolData &SDB = Asm.getSymbolData(SymbolB);
561 MCSectionData *Sec = Fragment->getParent();
563 // Offset of the symbol in the section
564 int64_t a = Layout.getSymbolAddress(&SDB) - Layout.getSectionAddress(Sec);
566 // Ofeset of the relocation in the section
567 int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
571 // Check that this case has already been fully resolved before we get
573 if (Symbol->isDefined() && !SD.isExternal() &&
575 &Fragment->getParent()->getSection() == &Symbol->getSection()) {
576 llvm_unreachable("We don't need a relocation in this case.");
580 bool RelocOnSymbol = ShouldRelocOnSymbol(SD, Target);
581 if (!RelocOnSymbol) {
582 Index = F->getParent()->getOrdinal();
584 MCSectionData *FSD = F->getParent();
585 // Offset of the symbol in the section
586 Value += Layout.getSymbolAddress(&SD) - Layout.getSectionAddress(FSD);
588 UsedInReloc.insert(Symbol);
592 // Compensate for the addend on i386.
599 // determine the type of the relocation
601 MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
606 case MCSymbolRefExpr::VK_None:
607 Type = ELF::R_X86_64_PC32;
609 case MCSymbolRefExpr::VK_PLT:
610 Type = ELF::R_X86_64_PLT32;
612 case llvm::MCSymbolRefExpr::VK_GOTPCREL:
613 Type = ELF::R_X86_64_GOTPCREL;
616 llvm_unreachable("Unimplemented");
619 switch ((unsigned)Fixup.getKind()) {
620 default: llvm_unreachable("invalid fixup kind!");
621 case FK_Data_8: Type = ELF::R_X86_64_64; break;
622 case X86::reloc_signed_4byte:
623 case X86::reloc_pcrel_4byte:
624 assert(isInt<32>(Target.getConstant()));
626 case MCSymbolRefExpr::VK_None:
627 Type = ELF::R_X86_64_32S;
629 case MCSymbolRefExpr::VK_GOT:
630 Type = ELF::R_X86_64_GOT32;
633 llvm_unreachable("Unimplemented");
637 Type = ELF::R_X86_64_32;
639 case FK_Data_2: Type = ELF::R_X86_64_16; break;
640 case X86::reloc_pcrel_1byte:
641 case FK_Data_1: Type = ELF::R_X86_64_8; break;
646 Type = ELF::R_386_PC32;
648 switch ((unsigned)Fixup.getKind()) {
649 default: llvm_unreachable("invalid fixup kind!");
651 // FIXME: Should we avoid selecting reloc_signed_4byte in 32 bit mode
653 case X86::reloc_signed_4byte:
654 case X86::reloc_pcrel_4byte:
655 case FK_Data_4: Type = ELF::R_386_32; break;
656 case FK_Data_2: Type = ELF::R_386_16; break;
657 case X86::reloc_pcrel_1byte:
658 case FK_Data_1: Type = ELF::R_386_8; break;
663 if (RelocNeedsGOT(Type))
666 ELFRelocationEntry ERE;
672 ERE.r_offset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
674 if (HasRelocationAddend)
675 ERE.r_addend = Addend;
677 ERE.r_addend = 0; // Silence compiler warning.
679 Relocations[Fragment->getParent()].push_back(ERE);
683 ELFObjectWriterImpl::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
685 MCSymbolData &SD = Asm.getSymbolData(*S);
688 if (!SD.isExternal() && !S->isUndefined())
689 return SD.getIndex() + /* empty symbol */ 1;
691 // External or undefined symbol.
692 return SD.getIndex() + NumRegularSections + /* empty symbol */ 1;
695 static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data,
697 const MCSymbol &Symbol = Data.getSymbol();
698 if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined())
701 if (!Used && Symbol.isTemporary())
707 static bool isLocal(const MCSymbolData &Data) {
708 if (Data.isExternal())
711 const MCSymbol &Symbol = Data.getSymbol();
712 if (Symbol.isUndefined() && !Symbol.isVariable())
718 void ELFObjectWriterImpl::ComputeSymbolTable(MCAssembler &Asm) {
719 // FIXME: Is this the correct place to do this?
721 llvm::StringRef Name = "_GLOBAL_OFFSET_TABLE_";
722 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
723 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
724 Data.setExternal(true);
727 // Build section lookup table.
728 NumRegularSections = Asm.size();
729 DenseMap<const MCSection*, uint8_t> SectionIndexMap;
731 for (MCAssembler::iterator it = Asm.begin(),
732 ie = Asm.end(); it != ie; ++it, ++Index)
733 SectionIndexMap[&it->getSection()] = Index;
735 // Index 0 is always the empty string.
736 StringMap<uint64_t> StringIndexMap;
737 StringTable += '\x00';
739 // Add the data for local symbols.
740 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
741 ie = Asm.symbol_end(); it != ie; ++it) {
742 const MCSymbol &Symbol = it->getSymbol();
744 if (!isInSymtab(Asm, *it, UsedInReloc.count(&Symbol)))
750 uint64_t &Entry = StringIndexMap[Symbol.getName()];
752 Entry = StringTable.size();
753 StringTable += Symbol.getName();
754 StringTable += '\x00';
759 MSD.StringIndex = Entry;
761 if (Symbol.isAbsolute()) {
762 MSD.SectionIndex = ELF::SHN_ABS;
763 LocalSymbolData.push_back(MSD);
765 const MCSymbol *SymbolP = &Symbol;
766 if (Symbol.isVariable()) {
767 const MCExpr *Value = Symbol.getVariableValue();
768 assert (Value->getKind() == MCExpr::SymbolRef && "Unimplemented");
769 const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Value);
770 SymbolP = &Ref->getSymbol();
772 MSD.SectionIndex = SectionIndexMap.lookup(&SymbolP->getSection());
773 assert(MSD.SectionIndex && "Invalid section index!");
774 LocalSymbolData.push_back(MSD);
778 // Now add non-local symbols.
779 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
780 ie = Asm.symbol_end(); it != ie; ++it) {
781 const MCSymbol &Symbol = it->getSymbol();
783 if (!isInSymtab(Asm, *it, UsedInReloc.count(&Symbol)))
789 uint64_t &Entry = StringIndexMap[Symbol.getName()];
791 Entry = StringTable.size();
792 StringTable += Symbol.getName();
793 StringTable += '\x00';
798 MSD.StringIndex = Entry;
800 if (it->isCommon()) {
801 MSD.SectionIndex = ELF::SHN_COMMON;
802 ExternalSymbolData.push_back(MSD);
803 } else if (Symbol.isUndefined()) {
804 MSD.SectionIndex = ELF::SHN_UNDEF;
805 // FIXME: Undefined symbols are global, but this is the first place we
806 // are able to set it.
807 if (GetBinding(*it) == ELF::STB_LOCAL)
808 SetBinding(*it, ELF::STB_GLOBAL);
809 UndefinedSymbolData.push_back(MSD);
810 } else if (Symbol.isAbsolute()) {
811 MSD.SectionIndex = ELF::SHN_ABS;
812 ExternalSymbolData.push_back(MSD);
814 MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
815 assert(MSD.SectionIndex && "Invalid section index!");
816 ExternalSymbolData.push_back(MSD);
820 // Symbols are required to be in lexicographic order.
821 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
822 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
823 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
825 // Set the symbol indices. Local symbols must come before all other
826 // symbols with non-local bindings.
828 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
829 LocalSymbolData[i].SymbolData->setIndex(Index++);
830 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
831 ExternalSymbolData[i].SymbolData->setIndex(Index++);
832 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
833 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
836 void ELFObjectWriterImpl::WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
837 const MCSectionData &SD) {
838 if (!Relocations[&SD].empty()) {
839 MCContext &Ctx = Asm.getContext();
840 const MCSection *RelaSection;
841 const MCSectionELF &Section =
842 static_cast<const MCSectionELF&>(SD.getSection());
844 const StringRef SectionName = Section.getSectionName();
845 std::string RelaSectionName = HasRelocationAddend ? ".rela" : ".rel";
846 RelaSectionName += SectionName;
849 if (HasRelocationAddend)
850 EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
852 EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
854 RelaSection = Ctx.getELFSection(RelaSectionName, HasRelocationAddend ?
855 ELF::SHT_RELA : ELF::SHT_REL, 0,
856 SectionKind::getReadOnly(),
859 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
860 RelaSD.setAlignment(Is64Bit ? 8 : 4);
862 MCDataFragment *F = new MCDataFragment(&RelaSD);
864 WriteRelocationsFragment(Asm, F, &SD);
866 Asm.AddSectionToTheEnd(*Writer, RelaSD, Layout);
870 void ELFObjectWriterImpl::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
871 uint64_t Flags, uint64_t Address,
872 uint64_t Offset, uint64_t Size,
873 uint32_t Link, uint32_t Info,
875 uint64_t EntrySize) {
876 Write32(Name); // sh_name: index into string table
877 Write32(Type); // sh_type
878 WriteWord(Flags); // sh_flags
879 WriteWord(Address); // sh_addr
880 WriteWord(Offset); // sh_offset
881 WriteWord(Size); // sh_size
882 Write32(Link); // sh_link
883 Write32(Info); // sh_info
884 WriteWord(Alignment); // sh_addralign
885 WriteWord(EntrySize); // sh_entsize
888 void ELFObjectWriterImpl::WriteRelocationsFragment(const MCAssembler &Asm,
890 const MCSectionData *SD) {
891 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
892 // sort by the r_offset just like gnu as does
893 array_pod_sort(Relocs.begin(), Relocs.end());
895 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
896 ELFRelocationEntry entry = Relocs[e - i - 1];
899 entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol);
901 entry.Index += LocalSymbolData.size() + 1;
905 String64(buf, entry.r_offset);
906 F->getContents() += StringRef(buf, 8);
908 struct ELF::Elf64_Rela ERE64;
909 ERE64.setSymbolAndType(entry.Index, entry.Type);
910 String64(buf, ERE64.r_info);
911 F->getContents() += StringRef(buf, 8);
913 if (HasRelocationAddend) {
914 String64(buf, entry.r_addend);
915 F->getContents() += StringRef(buf, 8);
920 String32(buf, entry.r_offset);
921 F->getContents() += StringRef(buf, 4);
923 struct ELF::Elf32_Rela ERE32;
924 ERE32.setSymbolAndType(entry.Index, entry.Type);
925 String32(buf, ERE32.r_info);
926 F->getContents() += StringRef(buf, 4);
928 if (HasRelocationAddend) {
929 String32(buf, entry.r_addend);
930 F->getContents() += StringRef(buf, 4);
936 void ELFObjectWriterImpl::CreateMetadataSections(MCAssembler &Asm,
937 MCAsmLayout &Layout) {
938 MCContext &Ctx = Asm.getContext();
941 const MCSection *SymtabSection;
942 unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
944 unsigned NumRegularSections = Asm.size();
946 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
947 const MCSection *ShstrtabSection;
948 ShstrtabSection = Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
949 SectionKind::getReadOnly(), false);
950 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
951 ShstrtabSD.setAlignment(1);
952 ShstrtabIndex = Asm.size();
954 SymtabSection = Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
955 SectionKind::getReadOnly(),
957 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
958 SymtabSD.setAlignment(Is64Bit ? 8 : 4);
960 const MCSection *StrtabSection;
961 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
962 SectionKind::getReadOnly(), false);
963 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
964 StrtabSD.setAlignment(1);
965 StringTableIndex = Asm.size();
967 WriteRelocations(Asm, Layout);
970 F = new MCDataFragment(&SymtabSD);
971 WriteSymbolTable(F, Asm, Layout, NumRegularSections);
972 Asm.AddSectionToTheEnd(*Writer, SymtabSD, Layout);
974 F = new MCDataFragment(&StrtabSD);
975 F->getContents().append(StringTable.begin(), StringTable.end());
976 Asm.AddSectionToTheEnd(*Writer, StrtabSD, Layout);
978 F = new MCDataFragment(&ShstrtabSD);
980 // Section header string table.
982 // The first entry of a string table holds a null character so skip
985 F->getContents() += '\x00';
987 for (MCAssembler::const_iterator it = Asm.begin(),
988 ie = Asm.end(); it != ie; ++it) {
989 const MCSectionELF &Section =
990 static_cast<const MCSectionELF&>(it->getSection());
991 // FIXME: We could merge suffixes like in .text and .rela.text.
993 // Remember the index into the string table so we can write it
994 // into the sh_name field of the section header table.
995 SectionStringTableIndex[&it->getSection()] = Index;
997 Index += Section.getSectionName().size() + 1;
998 F->getContents() += Section.getSectionName();
999 F->getContents() += '\x00';
1002 Asm.AddSectionToTheEnd(*Writer, ShstrtabSD, Layout);
1005 bool ELFObjectWriterImpl::IsFixupFullyResolved(const MCAssembler &Asm,
1006 const MCValue Target,
1008 const MCFragment *DF) const {
1009 // If this is a PCrel relocation, find the section this fixup value is
1011 const MCSection *BaseSection = 0;
1013 BaseSection = &DF->getParent()->getSection();
1014 assert(BaseSection);
1017 const MCSection *SectionA = 0;
1018 const MCSymbol *SymbolA = 0;
1019 if (const MCSymbolRefExpr *A = Target.getSymA()) {
1020 SymbolA = &A->getSymbol();
1021 SectionA = &SymbolA->getSection();
1024 const MCSection *SectionB = 0;
1025 if (const MCSymbolRefExpr *B = Target.getSymB()) {
1026 SectionB = &B->getSymbol().getSection();
1030 return SectionA == SectionB;
1032 const MCSymbolData &DataA = Asm.getSymbolData(*SymbolA);
1033 if (DataA.isExternal())
1036 return !SectionB && BaseSection == SectionA;
1039 void ELFObjectWriterImpl::WriteObject(MCAssembler &Asm,
1040 const MCAsmLayout &Layout) {
1041 // Compute symbol table information.
1042 ComputeSymbolTable(Asm);
1044 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1045 const_cast<MCAsmLayout&>(Layout));
1047 // Add 1 for the null section.
1048 unsigned NumSections = Asm.size() + 1;
1049 uint64_t NaturalAlignment = Is64Bit ? 8 : 4;
1050 uint64_t HeaderSize = Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr);
1051 uint64_t FileOff = HeaderSize;
1053 for (MCAssembler::const_iterator it = Asm.begin(),
1054 ie = Asm.end(); it != ie; ++it) {
1055 const MCSectionData &SD = *it;
1057 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1059 // Get the size of the section in the output file (including padding).
1060 uint64_t Size = Layout.getSectionFileSize(&SD);
1065 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1067 // Write out the ELF header ...
1068 WriteHeader(FileOff - HeaderSize, NumSections);
1070 FileOff = HeaderSize;
1072 // ... then all of the sections ...
1073 DenseMap<const MCSection*, uint64_t> SectionOffsetMap;
1075 DenseMap<const MCSection*, uint8_t> SectionIndexMap;
1078 for (MCAssembler::const_iterator it = Asm.begin(),
1079 ie = Asm.end(); it != ie; ++it) {
1080 const MCSectionData &SD = *it;
1082 uint64_t Padding = OffsetToAlignment(FileOff, SD.getAlignment());
1083 WriteZeros(Padding);
1086 // Remember the offset into the file for this section.
1087 SectionOffsetMap[&it->getSection()] = FileOff;
1088 SectionIndexMap[&it->getSection()] = Index++;
1090 FileOff += Layout.getSectionFileSize(&SD);
1092 Asm.WriteSectionData(it, Layout, Writer);
1095 uint64_t Padding = OffsetToAlignment(FileOff, NaturalAlignment);
1096 WriteZeros(Padding);
1099 // ... and then the section header table.
1100 // Should we align the section header table?
1102 // Null section first.
1103 WriteSecHdrEntry(0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
1105 for (MCAssembler::const_iterator it = Asm.begin(),
1106 ie = Asm.end(); it != ie; ++it) {
1107 const MCSectionData &SD = *it;
1108 const MCSectionELF &Section =
1109 static_cast<const MCSectionELF&>(SD.getSection());
1111 uint64_t sh_link = 0;
1112 uint64_t sh_info = 0;
1114 switch(Section.getType()) {
1115 case ELF::SHT_DYNAMIC:
1116 sh_link = SectionStringTableIndex[&it->getSection()];
1121 case ELF::SHT_RELA: {
1122 const MCSection *SymtabSection;
1123 const MCSection *InfoSection;
1125 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1126 SectionKind::getReadOnly(),
1128 sh_link = SectionIndexMap[SymtabSection];
1130 // Remove ".rel" and ".rela" prefixes.
1131 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1132 StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1134 InfoSection = Asm.getContext().getELFSection(SectionName,
1135 ELF::SHT_PROGBITS, 0,
1136 SectionKind::getReadOnly(),
1138 sh_info = SectionIndexMap[InfoSection];
1142 case ELF::SHT_SYMTAB:
1143 case ELF::SHT_DYNSYM:
1144 sh_link = StringTableIndex;
1145 sh_info = LastLocalSymbolIndex;
1148 case ELF::SHT_PROGBITS:
1149 case ELF::SHT_STRTAB:
1150 case ELF::SHT_NOBITS:
1156 case ELF::SHT_GROUP:
1157 case ELF::SHT_SYMTAB_SHNDX:
1159 assert(0 && "FIXME: sh_type value not supported!");
1163 WriteSecHdrEntry(SectionStringTableIndex[&it->getSection()],
1164 Section.getType(), Section.getFlags(),
1166 SectionOffsetMap.lookup(&SD.getSection()),
1167 Layout.getSectionSize(&SD), sh_link,
1168 sh_info, SD.getAlignment(),
1169 Section.getEntrySize());
1173 ELFObjectWriter::ELFObjectWriter(raw_ostream &OS,
1175 Triple::OSType OSType,
1176 bool IsLittleEndian,
1177 bool HasRelocationAddend)
1178 : MCObjectWriter(OS, IsLittleEndian)
1180 Impl = new ELFObjectWriterImpl(this, Is64Bit, HasRelocationAddend, OSType);
1183 ELFObjectWriter::~ELFObjectWriter() {
1184 delete (ELFObjectWriterImpl*) Impl;
1187 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
1188 ((ELFObjectWriterImpl*) Impl)->ExecutePostLayoutBinding(Asm);
1191 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
1192 const MCAsmLayout &Layout,
1193 const MCFragment *Fragment,
1194 const MCFixup &Fixup, MCValue Target,
1195 uint64_t &FixedValue) {
1196 ((ELFObjectWriterImpl*) Impl)->RecordRelocation(Asm, Layout, Fragment, Fixup,
1197 Target, FixedValue);
1200 bool ELFObjectWriter::IsFixupFullyResolved(const MCAssembler &Asm,
1201 const MCValue Target,
1203 const MCFragment *DF) const {
1204 return ((ELFObjectWriterImpl*) Impl)->IsFixupFullyResolved(Asm, Target,
1208 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1209 const MCAsmLayout &Layout) {
1210 ((ELFObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);