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)) {
448 uint64_t AddressA = 0;
449 uint64_t AddressB = 0;
450 const MCSymbol &SymA = Res.getSymA()->getSymbol();
451 const MCSymbol &SymB = Res.getSymB()->getSymbol();
453 if (SymA.isDefined()) {
454 MCSymbolData &A = Layout.getAssembler().getSymbolData(SymA);
455 AddressA = Layout.getSymbolAddress(&A);
458 if (SymB.isDefined()) {
459 MCSymbolData &B = Layout.getAssembler().getSymbolData(SymB);
460 AddressB = Layout.getSymbolAddress(&B);
463 Size = AddressA - AddressB;
465 } else if (ESize->getKind() == MCExpr::Constant) {
466 Size = static_cast<const MCConstantExpr *>(ESize)->getValue();
468 assert(0 && "Unsupported size expression");
472 // Write out the symbol table entry
473 WriteSymbolEntry(F, MSD.StringIndex, Info, Value,
474 Size, Other, MSD.SectionIndex);
477 void ELFObjectWriterImpl::WriteSymbolTable(MCDataFragment *F,
478 const MCAssembler &Asm,
479 const MCAsmLayout &Layout,
480 unsigned NumRegularSections) {
481 // The string table must be emitted first because we need the index
482 // into the string table for all the symbol names.
483 assert(StringTable.size() && "Missing string table");
485 // FIXME: Make sure the start of the symbol table is aligned.
487 // The first entry is the undefined symbol entry.
488 unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
489 F->getContents().append(EntrySize, '\x00');
491 // Write the symbol table entries.
492 LastLocalSymbolIndex = LocalSymbolData.size() + 1;
493 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
494 ELFSymbolData &MSD = LocalSymbolData[i];
495 WriteSymbol(F, MSD, Layout);
498 // Write out a symbol table entry for each regular section.
500 for (MCAssembler::const_iterator it = Asm.begin();
501 Index <= NumRegularSections; ++it, ++Index) {
502 const MCSectionELF &Section =
503 static_cast<const MCSectionELF&>(it->getSection());
504 // Leave out relocations so we don't have indexes within
505 // the relocations messed up
506 if (Section.getType() == ELF::SHT_RELA || Section.getType() == ELF::SHT_REL)
508 WriteSymbolEntry(F, 0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT, Index);
509 LastLocalSymbolIndex++;
512 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
513 ELFSymbolData &MSD = ExternalSymbolData[i];
514 MCSymbolData &Data = *MSD.SymbolData;
515 assert((Data.getFlags() & ELF_STB_Global) &&
516 "External symbol requires STB_GLOBAL flag");
517 WriteSymbol(F, MSD, Layout);
518 if (GetBinding(Data) == ELF::STB_LOCAL)
519 LastLocalSymbolIndex++;
522 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
523 ELFSymbolData &MSD = UndefinedSymbolData[i];
524 MCSymbolData &Data = *MSD.SymbolData;
525 WriteSymbol(F, MSD, Layout);
526 if (GetBinding(Data) == ELF::STB_LOCAL)
527 LastLocalSymbolIndex++;
531 static bool ShouldRelocOnSymbol(const MCSymbolData &SD,
532 const MCValue &Target,
533 const MCFragment &F) {
534 const MCSymbol &Symbol = SD.getSymbol();
535 if (Symbol.isUndefined())
538 const MCSectionELF &Section =
539 static_cast<const MCSectionELF&>(Symbol.getSection());
541 if (Section.getFlags() & MCSectionELF::SHF_MERGE)
542 return Target.getConstant() != 0;
547 MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind();
548 const MCSectionELF &Sec2 =
549 static_cast<const MCSectionELF&>(F.getParent()->getSection());
551 if (&Sec2 != &Section &&
552 (Kind == MCSymbolRefExpr::VK_PLT || Kind == MCSymbolRefExpr::VK_GOTPCREL))
558 // FIXME: this is currently X86/X86_64 only
559 void ELFObjectWriterImpl::RecordRelocation(const MCAssembler &Asm,
560 const MCAsmLayout &Layout,
561 const MCFragment *Fragment,
562 const MCFixup &Fixup,
564 uint64_t &FixedValue) {
567 int64_t Value = Target.getConstant();
568 const MCSymbol *Symbol = 0;
570 bool IsPCRel = isFixupKindX86PCRel(Fixup.getKind());
571 if (!Target.isAbsolute()) {
572 Symbol = &Target.getSymA()->getSymbol();
573 MCSymbolData &SD = Asm.getSymbolData(*Symbol);
574 MCFragment *F = SD.getFragment();
576 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
577 const MCSymbol &SymbolB = RefB->getSymbol();
578 MCSymbolData &SDB = Asm.getSymbolData(SymbolB);
580 MCSectionData *Sec = Fragment->getParent();
582 // Offset of the symbol in the section
583 int64_t a = Layout.getSymbolAddress(&SDB) - Layout.getSectionAddress(Sec);
585 // Ofeset of the relocation in the section
586 int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
590 // Check that this case has already been fully resolved before we get
592 if (Symbol->isDefined() && !SD.isExternal() &&
594 &Fragment->getParent()->getSection() == &Symbol->getSection()) {
595 llvm_unreachable("We don't need a relocation in this case.");
599 bool RelocOnSymbol = ShouldRelocOnSymbol(SD, Target, *Fragment);
600 if (!RelocOnSymbol) {
601 Index = F->getParent()->getOrdinal();
603 MCSectionData *FSD = F->getParent();
604 // Offset of the symbol in the section
605 Value += Layout.getSymbolAddress(&SD) - Layout.getSectionAddress(FSD);
607 UsedInReloc.insert(Symbol);
611 // Compensate for the addend on i386.
618 // determine the type of the relocation
620 MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
625 case MCSymbolRefExpr::VK_None:
626 Type = ELF::R_X86_64_PC32;
628 case MCSymbolRefExpr::VK_PLT:
629 Type = ELF::R_X86_64_PLT32;
631 case llvm::MCSymbolRefExpr::VK_GOTPCREL:
632 Type = ELF::R_X86_64_GOTPCREL;
635 llvm_unreachable("Unimplemented");
638 switch ((unsigned)Fixup.getKind()) {
639 default: llvm_unreachable("invalid fixup kind!");
640 case FK_Data_8: Type = ELF::R_X86_64_64; break;
641 case X86::reloc_signed_4byte:
642 case X86::reloc_pcrel_4byte:
643 assert(isInt<32>(Target.getConstant()));
645 case MCSymbolRefExpr::VK_None:
646 Type = ELF::R_X86_64_32S;
648 case MCSymbolRefExpr::VK_GOT:
649 Type = ELF::R_X86_64_GOT32;
651 case llvm::MCSymbolRefExpr::VK_GOTPCREL:
652 Type = ELF::R_X86_64_GOTPCREL;
655 llvm_unreachable("Unimplemented");
659 Type = ELF::R_X86_64_32;
661 case FK_Data_2: Type = ELF::R_X86_64_16; break;
662 case X86::reloc_pcrel_1byte:
663 case FK_Data_1: Type = ELF::R_X86_64_8; break;
668 Type = ELF::R_386_PC32;
670 switch ((unsigned)Fixup.getKind()) {
671 default: llvm_unreachable("invalid fixup kind!");
673 // FIXME: Should we avoid selecting reloc_signed_4byte in 32 bit mode
675 case X86::reloc_signed_4byte:
676 case X86::reloc_pcrel_4byte:
677 case FK_Data_4: Type = ELF::R_386_32; break;
678 case FK_Data_2: Type = ELF::R_386_16; break;
679 case X86::reloc_pcrel_1byte:
680 case FK_Data_1: Type = ELF::R_386_8; break;
685 if (RelocNeedsGOT(Type))
688 ELFRelocationEntry ERE;
694 ERE.r_offset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
696 if (HasRelocationAddend)
697 ERE.r_addend = Addend;
699 ERE.r_addend = 0; // Silence compiler warning.
701 Relocations[Fragment->getParent()].push_back(ERE);
705 ELFObjectWriterImpl::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
707 MCSymbolData &SD = Asm.getSymbolData(*S);
710 if (!SD.isExternal() && !S->isUndefined())
711 return SD.getIndex() + /* empty symbol */ 1;
713 // External or undefined symbol.
714 return SD.getIndex() + NumRegularSections + /* empty symbol */ 1;
717 static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data,
719 const MCSymbol &Symbol = Data.getSymbol();
720 if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined())
723 if (!Used && Symbol.isTemporary())
729 static bool isLocal(const MCSymbolData &Data) {
730 if (Data.isExternal())
733 const MCSymbol &Symbol = Data.getSymbol();
734 if (Symbol.isUndefined() && !Symbol.isVariable())
740 void ELFObjectWriterImpl::ComputeSymbolTable(MCAssembler &Asm) {
741 // FIXME: Is this the correct place to do this?
743 llvm::StringRef Name = "_GLOBAL_OFFSET_TABLE_";
744 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
745 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
746 Data.setExternal(true);
749 // Build section lookup table.
750 NumRegularSections = Asm.size();
751 DenseMap<const MCSection*, uint32_t> SectionIndexMap;
753 for (MCAssembler::iterator it = Asm.begin(),
754 ie = Asm.end(); it != ie; ++it, ++Index)
755 SectionIndexMap[&it->getSection()] = Index;
757 // Index 0 is always the empty string.
758 StringMap<uint64_t> StringIndexMap;
759 StringTable += '\x00';
761 // Add the data for local symbols.
762 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
763 ie = Asm.symbol_end(); it != ie; ++it) {
764 const MCSymbol &Symbol = it->getSymbol();
766 if (!isInSymtab(Asm, *it, UsedInReloc.count(&Symbol)))
772 uint64_t &Entry = StringIndexMap[Symbol.getName()];
774 Entry = StringTable.size();
775 StringTable += Symbol.getName();
776 StringTable += '\x00';
781 MSD.StringIndex = Entry;
783 if (Symbol.isAbsolute()) {
784 MSD.SectionIndex = ELF::SHN_ABS;
785 LocalSymbolData.push_back(MSD);
787 const MCSymbol *SymbolP = &Symbol;
788 if (Symbol.isVariable()) {
789 const MCExpr *Value = Symbol.getVariableValue();
790 assert (Value->getKind() == MCExpr::SymbolRef && "Unimplemented");
791 const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Value);
792 SymbolP = &Ref->getSymbol();
794 MSD.SectionIndex = SectionIndexMap.lookup(&SymbolP->getSection());
795 assert(MSD.SectionIndex && "Invalid section index!");
796 LocalSymbolData.push_back(MSD);
800 // Now add non-local symbols.
801 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
802 ie = Asm.symbol_end(); it != ie; ++it) {
803 const MCSymbol &Symbol = it->getSymbol();
805 if (!isInSymtab(Asm, *it, UsedInReloc.count(&Symbol)))
811 uint64_t &Entry = StringIndexMap[Symbol.getName()];
813 Entry = StringTable.size();
814 StringTable += Symbol.getName();
815 StringTable += '\x00';
820 MSD.StringIndex = Entry;
822 // FIXME: There is duplicated code with the local case.
823 if (it->isCommon()) {
824 MSD.SectionIndex = ELF::SHN_COMMON;
825 ExternalSymbolData.push_back(MSD);
826 } else if (Symbol.isVariable()) {
827 const MCExpr *Value = Symbol.getVariableValue();
828 assert (Value->getKind() == MCExpr::SymbolRef && "Unimplemented");
829 const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Value);
830 const MCSymbol &RefSymbol = Ref->getSymbol();
831 if (RefSymbol.isDefined()) {
832 MSD.SectionIndex = SectionIndexMap.lookup(&RefSymbol.getSection());
833 assert(MSD.SectionIndex && "Invalid section index!");
834 ExternalSymbolData.push_back(MSD);
836 } else if (Symbol.isUndefined()) {
837 MSD.SectionIndex = ELF::SHN_UNDEF;
838 // FIXME: Undefined symbols are global, but this is the first place we
839 // are able to set it.
840 if (GetBinding(*it) == ELF::STB_LOCAL)
841 SetBinding(*it, ELF::STB_GLOBAL);
842 UndefinedSymbolData.push_back(MSD);
843 } else if (Symbol.isAbsolute()) {
844 MSD.SectionIndex = ELF::SHN_ABS;
845 ExternalSymbolData.push_back(MSD);
847 MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
848 assert(MSD.SectionIndex && "Invalid section index!");
849 ExternalSymbolData.push_back(MSD);
853 // Symbols are required to be in lexicographic order.
854 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
855 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
856 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
858 // Set the symbol indices. Local symbols must come before all other
859 // symbols with non-local bindings.
861 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
862 LocalSymbolData[i].SymbolData->setIndex(Index++);
863 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
864 ExternalSymbolData[i].SymbolData->setIndex(Index++);
865 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
866 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
869 void ELFObjectWriterImpl::WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
870 const MCSectionData &SD) {
871 if (!Relocations[&SD].empty()) {
872 MCContext &Ctx = Asm.getContext();
873 const MCSection *RelaSection;
874 const MCSectionELF &Section =
875 static_cast<const MCSectionELF&>(SD.getSection());
877 const StringRef SectionName = Section.getSectionName();
878 std::string RelaSectionName = HasRelocationAddend ? ".rela" : ".rel";
879 RelaSectionName += SectionName;
882 if (HasRelocationAddend)
883 EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
885 EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
887 RelaSection = Ctx.getELFSection(RelaSectionName, HasRelocationAddend ?
888 ELF::SHT_RELA : ELF::SHT_REL, 0,
889 SectionKind::getReadOnly(),
892 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
893 RelaSD.setAlignment(Is64Bit ? 8 : 4);
895 MCDataFragment *F = new MCDataFragment(&RelaSD);
897 WriteRelocationsFragment(Asm, F, &SD);
899 Asm.AddSectionToTheEnd(*Writer, RelaSD, Layout);
903 void ELFObjectWriterImpl::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
904 uint64_t Flags, uint64_t Address,
905 uint64_t Offset, uint64_t Size,
906 uint32_t Link, uint32_t Info,
908 uint64_t EntrySize) {
909 Write32(Name); // sh_name: index into string table
910 Write32(Type); // sh_type
911 WriteWord(Flags); // sh_flags
912 WriteWord(Address); // sh_addr
913 WriteWord(Offset); // sh_offset
914 WriteWord(Size); // sh_size
915 Write32(Link); // sh_link
916 Write32(Info); // sh_info
917 WriteWord(Alignment); // sh_addralign
918 WriteWord(EntrySize); // sh_entsize
921 void ELFObjectWriterImpl::WriteRelocationsFragment(const MCAssembler &Asm,
923 const MCSectionData *SD) {
924 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
925 // sort by the r_offset just like gnu as does
926 array_pod_sort(Relocs.begin(), Relocs.end());
928 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
929 ELFRelocationEntry entry = Relocs[e - i - 1];
932 entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol);
934 entry.Index += LocalSymbolData.size() + 1;
938 String64(buf, entry.r_offset);
939 F->getContents() += StringRef(buf, 8);
941 struct ELF::Elf64_Rela ERE64;
942 ERE64.setSymbolAndType(entry.Index, entry.Type);
943 String64(buf, ERE64.r_info);
944 F->getContents() += StringRef(buf, 8);
946 if (HasRelocationAddend) {
947 String64(buf, entry.r_addend);
948 F->getContents() += StringRef(buf, 8);
953 String32(buf, entry.r_offset);
954 F->getContents() += StringRef(buf, 4);
956 struct ELF::Elf32_Rela ERE32;
957 ERE32.setSymbolAndType(entry.Index, entry.Type);
958 String32(buf, ERE32.r_info);
959 F->getContents() += StringRef(buf, 4);
961 if (HasRelocationAddend) {
962 String32(buf, entry.r_addend);
963 F->getContents() += StringRef(buf, 4);
969 void ELFObjectWriterImpl::CreateMetadataSections(MCAssembler &Asm,
970 MCAsmLayout &Layout) {
971 MCContext &Ctx = Asm.getContext();
974 const MCSection *SymtabSection;
975 unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
977 unsigned NumRegularSections = Asm.size();
979 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
980 const MCSection *ShstrtabSection;
981 ShstrtabSection = Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
982 SectionKind::getReadOnly(), false);
983 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
984 ShstrtabSD.setAlignment(1);
985 ShstrtabIndex = Asm.size();
987 SymtabSection = Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
988 SectionKind::getReadOnly(),
990 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
991 SymtabSD.setAlignment(Is64Bit ? 8 : 4);
993 const MCSection *StrtabSection;
994 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
995 SectionKind::getReadOnly(), false);
996 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
997 StrtabSD.setAlignment(1);
998 StringTableIndex = Asm.size();
1000 WriteRelocations(Asm, Layout);
1003 F = new MCDataFragment(&SymtabSD);
1004 WriteSymbolTable(F, Asm, Layout, NumRegularSections);
1005 Asm.AddSectionToTheEnd(*Writer, SymtabSD, Layout);
1007 F = new MCDataFragment(&StrtabSD);
1008 F->getContents().append(StringTable.begin(), StringTable.end());
1009 Asm.AddSectionToTheEnd(*Writer, StrtabSD, Layout);
1011 F = new MCDataFragment(&ShstrtabSD);
1013 // Section header string table.
1015 // The first entry of a string table holds a null character so skip
1018 F->getContents() += '\x00';
1020 for (MCAssembler::const_iterator it = Asm.begin(),
1021 ie = Asm.end(); it != ie; ++it) {
1022 const MCSectionELF &Section =
1023 static_cast<const MCSectionELF&>(it->getSection());
1024 // FIXME: We could merge suffixes like in .text and .rela.text.
1026 // Remember the index into the string table so we can write it
1027 // into the sh_name field of the section header table.
1028 SectionStringTableIndex[&it->getSection()] = Index;
1030 Index += Section.getSectionName().size() + 1;
1031 F->getContents() += Section.getSectionName();
1032 F->getContents() += '\x00';
1035 Asm.AddSectionToTheEnd(*Writer, ShstrtabSD, Layout);
1038 bool ELFObjectWriterImpl::IsFixupFullyResolved(const MCAssembler &Asm,
1039 const MCValue Target,
1041 const MCFragment *DF) const {
1042 // If this is a PCrel relocation, find the section this fixup value is
1044 const MCSection *BaseSection = 0;
1046 BaseSection = &DF->getParent()->getSection();
1047 assert(BaseSection);
1050 const MCSection *SectionA = 0;
1051 const MCSymbol *SymbolA = 0;
1052 if (const MCSymbolRefExpr *A = Target.getSymA()) {
1053 SymbolA = &A->getSymbol();
1054 SectionA = &SymbolA->getSection();
1057 const MCSection *SectionB = 0;
1058 if (const MCSymbolRefExpr *B = Target.getSymB()) {
1059 SectionB = &B->getSymbol().getSection();
1063 return SectionA == SectionB;
1065 const MCSymbolData &DataA = Asm.getSymbolData(*SymbolA);
1066 if (DataA.isExternal())
1069 return !SectionB && BaseSection == SectionA;
1072 void ELFObjectWriterImpl::WriteObject(MCAssembler &Asm,
1073 const MCAsmLayout &Layout) {
1074 // Compute symbol table information.
1075 ComputeSymbolTable(Asm);
1077 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1078 const_cast<MCAsmLayout&>(Layout));
1080 // Add 1 for the null section.
1081 unsigned NumSections = Asm.size() + 1;
1082 uint64_t NaturalAlignment = Is64Bit ? 8 : 4;
1083 uint64_t HeaderSize = Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr);
1084 uint64_t FileOff = HeaderSize;
1086 for (MCAssembler::const_iterator it = Asm.begin(),
1087 ie = Asm.end(); it != ie; ++it) {
1088 const MCSectionData &SD = *it;
1090 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1092 // Get the size of the section in the output file (including padding).
1093 uint64_t Size = Layout.getSectionFileSize(&SD);
1098 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1100 // Write out the ELF header ...
1101 WriteHeader(FileOff - HeaderSize, NumSections);
1103 FileOff = HeaderSize;
1105 // ... then all of the sections ...
1106 DenseMap<const MCSection*, uint64_t> SectionOffsetMap;
1108 DenseMap<const MCSection*, uint8_t> SectionIndexMap;
1111 for (MCAssembler::const_iterator it = Asm.begin(),
1112 ie = Asm.end(); it != ie; ++it) {
1113 const MCSectionData &SD = *it;
1115 uint64_t Padding = OffsetToAlignment(FileOff, SD.getAlignment());
1116 WriteZeros(Padding);
1119 // Remember the offset into the file for this section.
1120 SectionOffsetMap[&it->getSection()] = FileOff;
1121 SectionIndexMap[&it->getSection()] = Index++;
1123 FileOff += Layout.getSectionFileSize(&SD);
1125 Asm.WriteSectionData(it, Layout, Writer);
1128 uint64_t Padding = OffsetToAlignment(FileOff, NaturalAlignment);
1129 WriteZeros(Padding);
1132 // ... and then the section header table.
1133 // Should we align the section header table?
1135 // Null section first.
1136 WriteSecHdrEntry(0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
1138 for (MCAssembler::const_iterator it = Asm.begin(),
1139 ie = Asm.end(); it != ie; ++it) {
1140 const MCSectionData &SD = *it;
1141 const MCSectionELF &Section =
1142 static_cast<const MCSectionELF&>(SD.getSection());
1144 uint64_t sh_link = 0;
1145 uint64_t sh_info = 0;
1147 switch(Section.getType()) {
1148 case ELF::SHT_DYNAMIC:
1149 sh_link = SectionStringTableIndex[&it->getSection()];
1154 case ELF::SHT_RELA: {
1155 const MCSection *SymtabSection;
1156 const MCSection *InfoSection;
1158 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1159 SectionKind::getReadOnly(),
1161 sh_link = SectionIndexMap[SymtabSection];
1163 // Remove ".rel" and ".rela" prefixes.
1164 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1165 StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1167 InfoSection = Asm.getContext().getELFSection(SectionName,
1168 ELF::SHT_PROGBITS, 0,
1169 SectionKind::getReadOnly(),
1171 sh_info = SectionIndexMap[InfoSection];
1175 case ELF::SHT_SYMTAB:
1176 case ELF::SHT_DYNSYM:
1177 sh_link = StringTableIndex;
1178 sh_info = LastLocalSymbolIndex;
1181 case ELF::SHT_PROGBITS:
1182 case ELF::SHT_STRTAB:
1183 case ELF::SHT_NOBITS:
1189 case ELF::SHT_GROUP:
1190 case ELF::SHT_SYMTAB_SHNDX:
1192 assert(0 && "FIXME: sh_type value not supported!");
1196 WriteSecHdrEntry(SectionStringTableIndex[&it->getSection()],
1197 Section.getType(), Section.getFlags(),
1199 SectionOffsetMap.lookup(&SD.getSection()),
1200 Layout.getSectionSize(&SD), sh_link,
1201 sh_info, SD.getAlignment(),
1202 Section.getEntrySize());
1206 ELFObjectWriter::ELFObjectWriter(raw_ostream &OS,
1208 Triple::OSType OSType,
1209 bool IsLittleEndian,
1210 bool HasRelocationAddend)
1211 : MCObjectWriter(OS, IsLittleEndian)
1213 Impl = new ELFObjectWriterImpl(this, Is64Bit, HasRelocationAddend, OSType);
1216 ELFObjectWriter::~ELFObjectWriter() {
1217 delete (ELFObjectWriterImpl*) Impl;
1220 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
1221 ((ELFObjectWriterImpl*) Impl)->ExecutePostLayoutBinding(Asm);
1224 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
1225 const MCAsmLayout &Layout,
1226 const MCFragment *Fragment,
1227 const MCFixup &Fixup, MCValue Target,
1228 uint64_t &FixedValue) {
1229 ((ELFObjectWriterImpl*) Impl)->RecordRelocation(Asm, Layout, Fragment, Fixup,
1230 Target, FixedValue);
1233 bool ELFObjectWriter::IsFixupFullyResolved(const MCAssembler &Asm,
1234 const MCValue Target,
1236 const MCFragment *DF) const {
1237 return ((ELFObjectWriterImpl*) Impl)->IsFixupFullyResolved(Asm, Target,
1241 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1242 const MCAsmLayout &Layout) {
1243 ((ELFObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);