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/STLExtras.h"
16 #include "llvm/ADT/StringMap.h"
17 #include "llvm/ADT/Twine.h"
18 #include "llvm/MC/MCAssembler.h"
19 #include "llvm/MC/MCAsmLayout.h"
20 #include "llvm/MC/MCContext.h"
21 #include "llvm/MC/MCELFSymbolFlags.h"
22 #include "llvm/MC/MCExpr.h"
23 #include "llvm/MC/MCObjectWriter.h"
24 #include "llvm/MC/MCSectionELF.h"
25 #include "llvm/MC/MCSymbol.h"
26 #include "llvm/MC/MCValue.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/ErrorHandling.h"
29 #include "llvm/Support/ELF.h"
30 #include "llvm/Target/TargetAsmBackend.h"
32 #include "../Target/X86/X86FixupKinds.h"
39 class ELFObjectWriterImpl {
40 static bool isFixupKindX86PCRel(unsigned Kind) {
44 case X86::reloc_pcrel_1byte:
45 case X86::reloc_pcrel_4byte:
46 case X86::reloc_riprel_4byte:
47 case X86::reloc_riprel_4byte_movq_load:
52 static bool isFixupKindX86RIPRel(unsigned Kind) {
53 return Kind == X86::reloc_riprel_4byte ||
54 Kind == X86::reloc_riprel_4byte_movq_load;
58 /// ELFSymbolData - Helper struct for containing some precomputed information
60 struct ELFSymbolData {
61 MCSymbolData *SymbolData;
63 uint32_t SectionIndex;
65 // Support lexicographic sorting.
66 bool operator<(const ELFSymbolData &RHS) const {
67 const std::string &Name = SymbolData->getSymbol().getName();
68 return Name < RHS.SymbolData->getSymbol().getName();
72 /// @name Relocation Data
75 struct ELFRelocationEntry {
76 // Make these big enough for both 32-bit and 64-bit
81 // Support lexicographic sorting.
82 bool operator<(const ELFRelocationEntry &RE) const {
83 return RE.r_offset < r_offset;
87 llvm::DenseMap<const MCSectionData*,
88 std::vector<ELFRelocationEntry> > Relocations;
89 DenseMap<const MCSection*, uint64_t> SectionStringTableIndex;
92 /// @name Symbol Table Data
95 SmallString<256> StringTable;
96 std::vector<ELFSymbolData> LocalSymbolData;
97 std::vector<ELFSymbolData> ExternalSymbolData;
98 std::vector<ELFSymbolData> UndefinedSymbolData;
102 ELFObjectWriter *Writer;
106 // This holds the current offset into the object file.
109 unsigned Is64Bit : 1;
111 bool HasRelocationAddend;
113 // This holds the symbol table index of the last local symbol.
114 unsigned LastLocalSymbolIndex;
115 // This holds the .strtab section index.
116 unsigned StringTableIndex;
118 unsigned ShstrtabIndex;
121 ELFObjectWriterImpl(ELFObjectWriter *_Writer, bool _Is64Bit,
123 : Writer(_Writer), OS(Writer->getStream()), FileOff(0),
124 Is64Bit(_Is64Bit), HasRelocationAddend(_HasRelAddend) {
127 void Write8(uint8_t Value) { Writer->Write8(Value); }
128 void Write16(uint16_t Value) { Writer->Write16(Value); }
129 void Write32(uint32_t Value) { Writer->Write32(Value); }
130 void Write64(uint64_t Value) { Writer->Write64(Value); }
131 void WriteZeros(unsigned N) { Writer->WriteZeros(N); }
132 void WriteBytes(StringRef Str, unsigned ZeroFillSize = 0) {
133 Writer->WriteBytes(Str, ZeroFillSize);
136 void WriteWord(uint64_t W) {
144 void String8(char *buf, uint8_t Value) {
148 void StringLE16(char *buf, uint16_t Value) {
149 buf[0] = char(Value >> 0);
150 buf[1] = char(Value >> 8);
153 void StringLE32(char *buf, uint32_t Value) {
154 buf[0] = char(Value >> 0);
155 buf[1] = char(Value >> 8);
156 buf[2] = char(Value >> 16);
157 buf[3] = char(Value >> 24);
160 void StringLE64(char *buf, uint64_t Value) {
161 buf[0] = char(Value >> 0);
162 buf[1] = char(Value >> 8);
163 buf[2] = char(Value >> 16);
164 buf[3] = char(Value >> 24);
165 buf[4] = char(Value >> 32);
166 buf[5] = char(Value >> 40);
167 buf[6] = char(Value >> 48);
168 buf[7] = char(Value >> 56);
171 void StringBE16(char *buf ,uint16_t Value) {
172 buf[0] = char(Value >> 8);
173 buf[1] = char(Value >> 0);
176 void StringBE32(char *buf, uint32_t Value) {
177 buf[0] = char(Value >> 24);
178 buf[1] = char(Value >> 16);
179 buf[2] = char(Value >> 8);
180 buf[3] = char(Value >> 0);
183 void StringBE64(char *buf, uint64_t Value) {
184 buf[0] = char(Value >> 56);
185 buf[1] = char(Value >> 48);
186 buf[2] = char(Value >> 40);
187 buf[3] = char(Value >> 32);
188 buf[4] = char(Value >> 24);
189 buf[5] = char(Value >> 16);
190 buf[6] = char(Value >> 8);
191 buf[7] = char(Value >> 0);
194 void String16(char *buf, uint16_t Value) {
195 if (Writer->isLittleEndian())
196 StringLE16(buf, Value);
198 StringBE16(buf, Value);
201 void String32(char *buf, uint32_t Value) {
202 if (Writer->isLittleEndian())
203 StringLE32(buf, Value);
205 StringBE32(buf, Value);
208 void String64(char *buf, uint64_t Value) {
209 if (Writer->isLittleEndian())
210 StringLE64(buf, Value);
212 StringBE64(buf, Value);
215 void WriteHeader(uint64_t SectionDataSize, unsigned NumberOfSections);
217 void WriteSymbolEntry(MCDataFragment *F, uint64_t name, uint8_t info,
218 uint64_t value, uint64_t size,
219 uint8_t other, uint16_t shndx);
221 void WriteSymbol(MCDataFragment *F, ELFSymbolData &MSD,
222 const MCAsmLayout &Layout);
224 void WriteSymbolTable(MCDataFragment *F, const MCAssembler &Asm,
225 const MCAsmLayout &Layout);
227 void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
228 const MCFragment *Fragment, const MCFixup &Fixup,
229 MCValue Target, uint64_t &FixedValue);
231 // XXX-PERF: this should be cached
232 uint64_t getNumOfLocalSymbols(const MCAssembler &Asm) {
233 std::vector<const MCSymbol*> Local;
236 for (MCAssembler::const_symbol_iterator it = Asm.symbol_begin(),
237 ie = Asm.symbol_end(); it != ie; ++it) {
238 const MCSymbol &Symbol = it->getSymbol();
240 // Ignore non-linker visible symbols.
241 if (!Asm.isSymbolLinkerVisible(Symbol))
244 if (it->isExternal() || Symbol.isUndefined())
253 uint64_t getSymbolIndexInSymbolTable(MCAssembler &Asm, const MCSymbol *S);
255 /// ComputeSymbolTable - Compute the symbol table data
257 /// \param StringTable [out] - The string table data.
258 /// \param StringIndexMap [out] - Map from symbol names to offsets in the
260 void ComputeSymbolTable(MCAssembler &Asm);
262 void WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
263 const MCSectionData &SD);
265 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) {
266 for (MCAssembler::const_iterator it = Asm.begin(),
267 ie = Asm.end(); it != ie; ++it) {
268 WriteRelocation(Asm, Layout, *it);
272 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout);
274 void ExecutePostLayoutBinding(MCAssembler &Asm) {}
276 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
277 uint64_t Address, uint64_t Offset,
278 uint64_t Size, uint32_t Link, uint32_t Info,
279 uint64_t Alignment, uint64_t EntrySize);
281 void WriteRelocationsFragment(const MCAssembler &Asm, MCDataFragment *F,
282 const MCSectionData *SD);
284 void WriteObject(const MCAssembler &Asm, const MCAsmLayout &Layout);
289 // Emit the ELF header.
290 void ELFObjectWriterImpl::WriteHeader(uint64_t SectionDataSize,
291 unsigned NumberOfSections) {
297 // emitWord method behaves differently for ELF32 and ELF64, writing
298 // 4 bytes in the former and 8 in the latter.
300 Write8(0x7f); // e_ident[EI_MAG0]
301 Write8('E'); // e_ident[EI_MAG1]
302 Write8('L'); // e_ident[EI_MAG2]
303 Write8('F'); // e_ident[EI_MAG3]
305 Write8(Is64Bit ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
308 Write8(Writer->isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
310 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
311 Write8(ELF::ELFOSABI_LINUX); // e_ident[EI_OSABI]
312 Write8(0); // e_ident[EI_ABIVERSION]
314 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
316 Write16(ELF::ET_REL); // e_type
318 // FIXME: Make this configurable
319 Write16(ELF::EM_X86_64); // e_machine = target
321 Write32(ELF::EV_CURRENT); // e_version
322 WriteWord(0); // e_entry, no entry point in .o file
323 WriteWord(0); // e_phoff, no program header for .o
324 WriteWord(SectionDataSize + 64); // e_shoff = sec hdr table off in bytes
326 // FIXME: Make this configurable.
327 Write32(0); // e_flags = whatever the target wants
329 // e_ehsize = ELF header size
330 Write16(Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
332 Write16(0); // e_phentsize = prog header entry size
333 Write16(0); // e_phnum = # prog header entries = 0
335 // e_shentsize = Section header entry size
336 Write16(Is64Bit ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
338 // e_shnum = # of section header ents
339 Write16(NumberOfSections);
341 // e_shstrndx = Section # of '.shstrtab'
342 Write16(ShstrtabIndex);
345 void ELFObjectWriterImpl::WriteSymbolEntry(MCDataFragment *F, uint64_t name,
346 uint8_t info, uint64_t value,
347 uint64_t size, uint8_t other,
353 F->getContents() += StringRef(buf, 4); // st_name
356 F->getContents() += StringRef(buf, 1); // st_info
358 F->getContents() += StringRef(buf, 1); // st_other
360 String16(buf, shndx);
361 F->getContents() += StringRef(buf, 2); // st_shndx
363 String64(buf, value);
364 F->getContents() += StringRef(buf, 8); // st_value
367 F->getContents() += StringRef(buf, 8); // st_size
372 F->getContents() += StringRef(buf, 4); // st_name
374 String32(buf, value);
375 F->getContents() += StringRef(buf, 4); // st_value
378 F->getContents() += StringRef(buf, 4); // st_size
381 F->getContents() += StringRef(buf, 1); // st_info
384 F->getContents() += StringRef(buf, 1); // st_other
386 String16(buf, shndx);
387 F->getContents() += StringRef(buf, 2); // st_shndx
391 void ELFObjectWriterImpl::WriteSymbol(MCDataFragment *F, ELFSymbolData &MSD,
392 const MCAsmLayout &Layout) {
393 MCSymbolData &Data = *MSD.SymbolData;
394 uint8_t Info = (Data.getFlags() & 0xff);
395 uint8_t Other = ((Data.getFlags() & 0xf00) >> ELF_STV_Shift);
400 if (Data.isCommon() && Data.isExternal())
401 Value = Data.getCommonAlignment();
403 ESize = Data.getSize();
404 if (Data.getSize()) {
406 if (ESize->getKind() == MCExpr::Binary) {
407 const MCBinaryExpr *BE = static_cast<const MCBinaryExpr *>(ESize);
409 if (BE->EvaluateAsRelocatable(Res, &Layout)) {
411 Layout.getAssembler().getSymbolData(Res.getSymA()->getSymbol());
413 Layout.getAssembler().getSymbolData(Res.getSymB()->getSymbol());
415 Size = Layout.getSymbolAddress(&A) - Layout.getSymbolAddress(&B);
416 Value = Layout.getSymbolAddress(&Data);
418 } else if (ESize->getKind() == MCExpr::Constant) {
419 const MCConstantExpr *CE;
420 CE = static_cast<const MCConstantExpr *>(ESize);
421 Size = CE->getValue();
423 assert(0 && "Unsupported size expression");
427 // Write out the symbol table entry
428 WriteSymbolEntry(F, MSD.StringIndex, Info, Value,
429 Size, Other, MSD.SectionIndex);
432 void ELFObjectWriterImpl::WriteSymbolTable(MCDataFragment *F,
433 const MCAssembler &Asm,
434 const MCAsmLayout &Layout) {
435 // The string table must be emitted first because we need the index
436 // into the string table for all the symbol names.
437 assert(StringTable.size() && "Missing string table");
439 // FIXME: Make sure the start of the symbol table is aligned.
441 // The first entry is the undefined symbol entry.
442 unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
443 for (unsigned i = 0; i < EntrySize; ++i)
444 F->getContents() += '\x00';
446 // Write the symbol table entries.
447 LastLocalSymbolIndex = LocalSymbolData.size() + 1;
448 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
449 ELFSymbolData &MSD = LocalSymbolData[i];
450 WriteSymbol(F, MSD, Layout);
453 // Write out a symbol table entry for each section.
454 for (unsigned Index = 1; Index < Asm.size(); ++Index)
455 WriteSymbolEntry(F, 0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT, Index);
456 LastLocalSymbolIndex += Asm.size() - 1;
458 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
459 ELFSymbolData &MSD = ExternalSymbolData[i];
460 MCSymbolData &Data = *MSD.SymbolData;
461 assert((Data.getFlags() & ELF_STB_Global) &&
462 "External symbol requires STB_GLOBAL flag");
463 WriteSymbol(F, MSD, Layout);
464 if (Data.getFlags() & ELF_STB_Local)
465 LastLocalSymbolIndex++;
468 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
469 ELFSymbolData &MSD = UndefinedSymbolData[i];
470 MCSymbolData &Data = *MSD.SymbolData;
471 Data.setFlags(Data.getFlags() | ELF_STB_Global);
472 WriteSymbol(F, MSD, Layout);
473 if (Data.getFlags() & ELF_STB_Local)
474 LastLocalSymbolIndex++;
478 // FIXME: this is currently X86_64 only
479 void ELFObjectWriterImpl::RecordRelocation(const MCAssembler &Asm,
480 const MCAsmLayout &Layout,
481 const MCFragment *Fragment,
482 const MCFixup &Fixup,
484 uint64_t &FixedValue) {
485 unsigned IsPCRel = isFixupKindX86PCRel(Fixup.getKind());
486 ELFRelocationEntry ERE;
487 struct ELF::Elf64_Rela ERE64;
489 uint64_t FixupOffset =
490 Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
496 Value = Target.getConstant();
498 if (Target.isAbsolute()) {
499 Type = ELF::R_X86_64_NONE;
502 const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
503 MCSymbolData &SD = Asm.getSymbolData(*Symbol);
504 const MCSymbolData *Base = Asm.getAtom(Layout, &SD);
507 Index = getSymbolIndexInSymbolTable(const_cast<MCAssembler &>(Asm), &Base->getSymbol());
509 Value += Layout.getSymbolAddress(&SD) - Layout.getSymbolAddress(Base);
513 MCFragment *F = SD.getFragment();
515 // Index of the section in .symtab against this symbol
516 // is being relocated + 2 (empty section + abs. symbols).
517 Index = SD.getFragment()->getParent()->getOrdinal() +
518 getNumOfLocalSymbols(Asm) + 1;
520 MCSectionData *FSD = F->getParent();
521 // Offset of the symbol in the section
522 Addend = Layout.getSymbolAddress(&SD) - Layout.getSectionAddress(FSD);
530 // determine the type of the relocation
532 Type = ELF::R_X86_64_PC32;
534 switch (Fixup.getKind()) {
535 case FK_Data_8: Type = ELF::R_X86_64_64; break;
536 case X86::reloc_pcrel_4byte:
539 Offset = Target.getConstant();
540 // check that the offset fits within a signed long
541 if (!(((long) -1 << 31) & Offset) || (((long) -1 << 31) & Offset) == ((long) -1 << 31))
542 Type = ELF::R_X86_64_32S;
544 Type = ELF::R_X86_64_32;
546 case FK_Data_2: Type = ELF::R_X86_64_16; break;
547 case X86::reloc_pcrel_1byte:
549 Type = ELF::R_X86_64_8;
556 ERE64.setSymbolAndType(Index, Type);
558 ERE.r_offset = FixupOffset;
559 ERE.r_info = ERE64.r_info;
560 if (HasRelocationAddend)
561 ERE.r_addend = Addend;
563 Relocations[Fragment->getParent()].push_back(ERE);
566 // XXX-PERF: this should be cached
567 uint64_t ELFObjectWriterImpl::getSymbolIndexInSymbolTable(MCAssembler &Asm,
569 std::vector<ELFSymbolData> Local;
570 std::vector<ELFSymbolData> External;
571 std::vector<ELFSymbolData> Undefined;
573 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
574 ie = Asm.symbol_end(); it != ie; ++it) {
575 const MCSymbol &Symbol = it->getSymbol();
577 // Ignore non-linker visible symbols.
578 if (!Asm.isSymbolLinkerVisible(Symbol))
581 if (it->isExternal() || Symbol.isUndefined())
587 Local.push_back(MSD);
589 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
590 ie = Asm.symbol_end(); it != ie; ++it) {
591 const MCSymbol &Symbol = it->getSymbol();
593 // Ignore non-linker visible symbols.
594 if (!Asm.isSymbolLinkerVisible(Symbol))
597 if (!it->isExternal() && !Symbol.isUndefined())
603 if (Symbol.isUndefined()) {
604 Undefined.push_back(MSD);
605 } else if (Symbol.isAbsolute()) {
606 External.push_back(MSD);
607 } else if (it->isCommon()) {
608 External.push_back(MSD);
610 External.push_back(MSD);
614 array_pod_sort(Local.begin(), Local.end());
615 array_pod_sort(External.begin(), External.end());
616 array_pod_sort(Undefined.begin(), Undefined.end());
618 for (unsigned i = 0, e = Local.size(); i != e; ++i)
619 if (&Local[i].SymbolData->getSymbol() == S)
620 return i + /* empty symbol */ 1;
621 for (unsigned i = 0, e = External.size(); i != e; ++i)
622 if (&External[i].SymbolData->getSymbol() == S)
623 return i + Local.size() + Asm.size() + /* empty symbol */ 1 +
624 /* .rela.text + .rela.eh_frame */ + 2;
625 for (unsigned i = 0, e = Undefined.size(); i != e; ++i)
626 if (&Undefined[i].SymbolData->getSymbol() == S)
627 return i + Local.size() + External.size() + Asm.size() + /* empty symbol */ 1 +
628 /* .rela.text + .rela.eh_frame */ + 2;
630 llvm_unreachable("Cannot find symbol which should exist!");
633 void ELFObjectWriterImpl::ComputeSymbolTable(MCAssembler &Asm) {
634 // Build section lookup table.
635 DenseMap<const MCSection*, uint8_t> SectionIndexMap;
637 for (MCAssembler::iterator it = Asm.begin(),
638 ie = Asm.end(); it != ie; ++it, ++Index)
639 SectionIndexMap[&it->getSection()] = Index;
641 // Index 0 is always the empty string.
642 StringMap<uint64_t> StringIndexMap;
643 StringTable += '\x00';
645 // Add the data for local symbols.
646 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
647 ie = Asm.symbol_end(); it != ie; ++it) {
648 const MCSymbol &Symbol = it->getSymbol();
650 // Ignore non-linker visible symbols.
651 if (!Asm.isSymbolLinkerVisible(Symbol))
654 if (it->isExternal() || Symbol.isUndefined())
657 uint64_t &Entry = StringIndexMap[Symbol.getName()];
659 Entry = StringTable.size();
660 StringTable += Symbol.getName();
661 StringTable += '\x00';
666 MSD.StringIndex = Entry;
668 if (Symbol.isAbsolute()) {
669 MSD.SectionIndex = ELF::SHN_ABS;
670 LocalSymbolData.push_back(MSD);
672 MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
673 assert(MSD.SectionIndex && "Invalid section index!");
674 LocalSymbolData.push_back(MSD);
678 // Now add non-local symbols.
679 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
680 ie = Asm.symbol_end(); it != ie; ++it) {
681 const MCSymbol &Symbol = it->getSymbol();
683 // Ignore non-linker visible symbols.
684 if (!Asm.isSymbolLinkerVisible(Symbol))
687 if (!it->isExternal() && !Symbol.isUndefined())
690 uint64_t &Entry = StringIndexMap[Symbol.getName()];
692 Entry = StringTable.size();
693 StringTable += Symbol.getName();
694 StringTable += '\x00';
699 MSD.StringIndex = Entry;
701 if (Symbol.isUndefined()) {
702 MSD.SectionIndex = ELF::SHN_UNDEF;
703 // XXX: for some reason we dont Emit* this
704 it->setFlags(it->getFlags() | ELF_STB_Global);
705 UndefinedSymbolData.push_back(MSD);
706 } else if (Symbol.isAbsolute()) {
707 MSD.SectionIndex = ELF::SHN_ABS;
708 ExternalSymbolData.push_back(MSD);
709 } else if (it->isCommon()) {
710 MSD.SectionIndex = ELF::SHN_COMMON;
711 ExternalSymbolData.push_back(MSD);
713 MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
714 assert(MSD.SectionIndex && "Invalid section index!");
715 ExternalSymbolData.push_back(MSD);
719 // Symbols are required to be in lexicographic order.
720 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
721 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
722 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
724 // Set the symbol indices. Local symbols must come before all other
725 // symbols with non-local bindings.
727 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
728 LocalSymbolData[i].SymbolData->setIndex(Index++);
729 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
730 ExternalSymbolData[i].SymbolData->setIndex(Index++);
731 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
732 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
735 void ELFObjectWriterImpl::WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
736 const MCSectionData &SD) {
737 if (!Relocations[&SD].empty()) {
738 MCContext &Ctx = Asm.getContext();
739 const MCSection *RelaSection;
740 const MCSectionELF &Section =
741 static_cast<const MCSectionELF&>(SD.getSection());
743 const StringRef SectionName = Section.getSectionName();
744 std::string RelaSectionName = ".rela";
746 RelaSectionName += SectionName;
747 unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
749 RelaSection = Ctx.getELFSection(RelaSectionName, ELF::SHT_RELA, 0,
750 SectionKind::getReadOnly(),
753 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
754 RelaSD.setAlignment(1);
756 MCDataFragment *F = new MCDataFragment(&RelaSD);
758 WriteRelocationsFragment(Asm, F, &SD);
760 Asm.AddSectionToTheEnd(RelaSD, Layout);
764 void ELFObjectWriterImpl::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
765 uint64_t Flags, uint64_t Address,
766 uint64_t Offset, uint64_t Size,
767 uint32_t Link, uint32_t Info,
769 uint64_t EntrySize) {
770 Write32(Name); // sh_name: index into string table
771 Write32(Type); // sh_type
772 WriteWord(Flags); // sh_flags
773 WriteWord(Address); // sh_addr
774 WriteWord(Offset); // sh_offset
775 WriteWord(Size); // sh_size
776 Write32(Link); // sh_link
777 Write32(Info); // sh_info
778 WriteWord(Alignment); // sh_addralign
779 WriteWord(EntrySize); // sh_entsize
782 void ELFObjectWriterImpl::WriteRelocationsFragment(const MCAssembler &Asm,
784 const MCSectionData *SD) {
785 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
786 // sort by the r_offset just like gnu as does
787 array_pod_sort(Relocs.begin(), Relocs.end());
789 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
790 ELFRelocationEntry entry = Relocs[e - i - 1];
793 F->getContents() += StringRef((const char *)&entry.r_offset, 8);
794 F->getContents() += StringRef((const char *)&entry.r_info, 8);
796 if (HasRelocationAddend)
797 F->getContents() += StringRef((const char *)&entry.r_addend, 8);
799 F->getContents() += StringRef((const char *)&entry.r_offset, 4);
800 F->getContents() += StringRef((const char *)&entry.r_info, 4);
802 if (HasRelocationAddend)
803 F->getContents() += StringRef((const char *)&entry.r_addend, 4);
808 void ELFObjectWriterImpl::CreateMetadataSections(MCAssembler &Asm,
809 MCAsmLayout &Layout) {
810 MCContext &Ctx = Asm.getContext();
813 WriteRelocations(Asm, Layout);
815 const MCSection *SymtabSection;
816 unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
818 SymtabSection = Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
819 SectionKind::getReadOnly(),
822 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
824 SymtabSD.setAlignment(Is64Bit ? 8 : 4);
826 F = new MCDataFragment(&SymtabSD);
829 WriteSymbolTable(F, Asm, Layout);
830 Asm.AddSectionToTheEnd(SymtabSD, Layout);
832 const MCSection *StrtabSection;
833 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
834 SectionKind::getReadOnly(), false);
836 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
837 StrtabSD.setAlignment(1);
839 // FIXME: This isn't right. If the sections get rearranged this will
840 // be wrong. We need a proper lookup.
841 StringTableIndex = Asm.size();
843 F = new MCDataFragment(&StrtabSD);
844 F->getContents().append(StringTable.begin(), StringTable.end());
845 Asm.AddSectionToTheEnd(StrtabSD, Layout);
847 const MCSection *ShstrtabSection;
848 ShstrtabSection = Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
849 SectionKind::getReadOnly(), false);
851 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
852 ShstrtabSD.setAlignment(1);
854 F = new MCDataFragment(&ShstrtabSD);
856 // FIXME: This isn't right. If the sections get rearranged this will
857 // be wrong. We need a proper lookup.
858 ShstrtabIndex = Asm.size();
860 // Section header string table.
862 // The first entry of a string table holds a null character so skip
865 F->getContents() += '\x00';
867 for (MCAssembler::const_iterator it = Asm.begin(),
868 ie = Asm.end(); it != ie; ++it) {
869 const MCSectionData &SD = *it;
870 const MCSectionELF &Section =
871 static_cast<const MCSectionELF&>(SD.getSection());
874 // Remember the index into the string table so we can write it
875 // into the sh_name field of the section header table.
876 SectionStringTableIndex[&it->getSection()] = Index;
878 Index += Section.getSectionName().size() + 1;
879 F->getContents() += Section.getSectionName();
880 F->getContents() += '\x00';
883 Asm.AddSectionToTheEnd(ShstrtabSD, Layout);
886 void ELFObjectWriterImpl::WriteObject(const MCAssembler &Asm,
887 const MCAsmLayout &Layout) {
888 // Compute symbol table information.
889 ComputeSymbolTable(const_cast<MCAssembler&>(Asm));
891 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
892 const_cast<MCAsmLayout&>(Layout));
894 // Add 1 for the null section.
895 unsigned NumSections = Asm.size() + 1;
897 uint64_t SectionDataSize = 0;
899 for (MCAssembler::const_iterator it = Asm.begin(),
900 ie = Asm.end(); it != ie; ++it) {
901 const MCSectionData &SD = *it;
903 // Get the size of the section in the output file (including padding).
904 uint64_t Size = Layout.getSectionFileSize(&SD);
905 SectionDataSize += Size;
908 // Write out the ELF header ...
909 WriteHeader(SectionDataSize, NumSections);
910 FileOff = Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr);
912 // ... then all of the sections ...
913 DenseMap<const MCSection*, uint64_t> SectionOffsetMap;
915 for (MCAssembler::const_iterator it = Asm.begin(),
916 ie = Asm.end(); it != ie; ++it) {
917 // Remember the offset into the file for this section.
918 SectionOffsetMap[&it->getSection()] = FileOff;
920 const MCSectionData &SD = *it;
921 FileOff += Layout.getSectionFileSize(&SD);
923 Asm.WriteSectionData(it, Layout, Writer);
926 // ... and then the section header table.
927 // Should we align the section header table?
929 // Null section first.
930 WriteSecHdrEntry(0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
932 for (MCAssembler::const_iterator it = Asm.begin(),
933 ie = Asm.end(); it != ie; ++it) {
934 const MCSectionData &SD = *it;
935 const MCSectionELF &Section =
936 static_cast<const MCSectionELF&>(SD.getSection());
938 uint64_t sh_link = 0;
939 uint64_t sh_info = 0;
941 switch(Section.getType()) {
942 case ELF::SHT_DYNAMIC:
943 sh_link = SectionStringTableIndex[&it->getSection()];
948 case ELF::SHT_RELA: {
949 const MCSection *SymtabSection;
950 const MCSection *InfoSection;
951 StringRef SectionName;
952 const MCSectionData *SymtabSD;
953 const MCSectionData *InfoSD;
955 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
956 SectionKind::getReadOnly(),
958 SymtabSD = &Asm.getSectionData(*SymtabSection);
959 // we have to count the empty section in too
960 sh_link = SymtabSD->getLayoutOrder() + 1;
962 SectionName = Section.getSectionName();
963 SectionName = SectionName.slice(5, SectionName.size());
964 InfoSection = Asm.getContext().getELFSection(SectionName,
965 ELF::SHT_PROGBITS, 0,
966 SectionKind::getReadOnly(),
968 InfoSD = &Asm.getSectionData(*InfoSection);
969 sh_info = InfoSD->getLayoutOrder() + 1;
973 case ELF::SHT_SYMTAB:
974 case ELF::SHT_DYNSYM:
975 sh_link = StringTableIndex;
976 sh_info = LastLocalSymbolIndex;
979 case ELF::SHT_PROGBITS:
980 case ELF::SHT_STRTAB:
981 case ELF::SHT_NOBITS:
987 case ELF::SHT_SYMTAB_SHNDX:
989 assert(0 && "FIXME: sh_type value not supported!");
993 WriteSecHdrEntry(SectionStringTableIndex[&it->getSection()],
994 Section.getType(), Section.getFlags(),
995 Layout.getSectionAddress(&SD),
996 SectionOffsetMap.lookup(&SD.getSection()),
997 Layout.getSectionSize(&SD), sh_link,
998 sh_info, SD.getAlignment(),
999 Section.getEntrySize());
1003 ELFObjectWriter::ELFObjectWriter(raw_ostream &OS,
1005 bool IsLittleEndian,
1006 bool HasRelocationAddend)
1007 : MCObjectWriter(OS, IsLittleEndian)
1009 Impl = new ELFObjectWriterImpl(this, Is64Bit, HasRelocationAddend);
1012 ELFObjectWriter::~ELFObjectWriter() {
1013 delete (ELFObjectWriterImpl*) Impl;
1016 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
1017 ((ELFObjectWriterImpl*) Impl)->ExecutePostLayoutBinding(Asm);
1020 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
1021 const MCAsmLayout &Layout,
1022 const MCFragment *Fragment,
1023 const MCFixup &Fixup, MCValue Target,
1024 uint64_t &FixedValue) {
1025 ((ELFObjectWriterImpl*) Impl)->RecordRelocation(Asm, Layout, Fragment, Fixup,
1026 Target, FixedValue);
1029 void ELFObjectWriter::WriteObject(const MCAssembler &Asm,
1030 const MCAsmLayout &Layout) {
1031 ((ELFObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);