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/MCELFObjectWriter.h"
15 #include "llvm/ADT/STLExtras.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/ADT/SmallString.h"
18 #include "llvm/ADT/StringMap.h"
19 #include "llvm/MC/MCAsmBackend.h"
20 #include "llvm/MC/MCAsmInfo.h"
21 #include "llvm/MC/MCAsmLayout.h"
22 #include "llvm/MC/MCAssembler.h"
23 #include "llvm/MC/MCContext.h"
24 #include "llvm/MC/MCELF.h"
25 #include "llvm/MC/MCELFSymbolFlags.h"
26 #include "llvm/MC/MCExpr.h"
27 #include "llvm/MC/MCFixupKindInfo.h"
28 #include "llvm/MC/MCObjectWriter.h"
29 #include "llvm/MC/MCSectionELF.h"
30 #include "llvm/MC/MCValue.h"
31 #include "llvm/MC/StringTableBuilder.h"
32 #include "llvm/Support/Compression.h"
33 #include "llvm/Support/Debug.h"
34 #include "llvm/Support/ELF.h"
35 #include "llvm/Support/Endian.h"
36 #include "llvm/Support/ErrorHandling.h"
41 #define DEBUG_TYPE "reloc-info"
44 class FragmentWriter {
48 FragmentWriter(bool IsLittleEndian);
49 template <typename T> void write(MCDataFragment &F, T Val);
52 typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
54 class SymbolTableWriter {
56 FragmentWriter &FWriter;
58 SectionIndexMapTy &SectionIndexMap;
60 // The symbol .symtab fragment we are writting to.
61 MCDataFragment *SymtabF;
63 // .symtab_shndx fragment we are writting to.
64 MCDataFragment *ShndxF;
66 // The numbel of symbols written so far.
69 void createSymtabShndx();
71 template <typename T> void write(MCDataFragment &F, T Value);
74 SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
75 SectionIndexMapTy &SectionIndexMap,
76 MCDataFragment *SymtabF);
78 void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
79 uint8_t other, uint32_t shndx, bool Reserved);
82 struct ELFRelocationEntry {
83 uint64_t Offset; // Where is the relocation.
84 const MCSymbol *Symbol; // The symbol to relocate with.
85 unsigned Type; // The type of the relocation.
86 uint64_t Addend; // The addend to use.
88 ELFRelocationEntry(uint64_t Offset, const MCSymbol *Symbol, unsigned Type,
90 : Offset(Offset), Symbol(Symbol), Type(Type), Addend(Addend) {}
93 class ELFObjectWriter : public MCObjectWriter {
94 FragmentWriter FWriter;
98 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
99 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
100 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
101 static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data,
102 bool Used, bool Renamed);
103 static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
104 static bool IsELFMetaDataSection(const MCSectionData &SD);
105 static uint64_t DataSectionSize(const MCSectionData &SD);
106 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout,
107 const MCSectionData &SD);
108 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout,
109 const MCSectionData &SD);
111 void WriteDataSectionData(MCAssembler &Asm,
112 const MCAsmLayout &Layout,
113 const MCSectionELF &Section);
115 /*static bool isFixupKindX86RIPRel(unsigned Kind) {
116 return Kind == X86::reloc_riprel_4byte ||
117 Kind == X86::reloc_riprel_4byte_movq_load;
120 /// ELFSymbolData - Helper struct for containing some precomputed
121 /// information on symbols.
122 struct ELFSymbolData {
123 MCSymbolData *SymbolData;
124 uint64_t StringIndex;
125 uint32_t SectionIndex;
128 // Support lexicographic sorting.
129 bool operator<(const ELFSymbolData &RHS) const {
130 unsigned LHSType = MCELF::GetType(*SymbolData);
131 unsigned RHSType = MCELF::GetType(*RHS.SymbolData);
132 if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
134 if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
136 if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
137 return SectionIndex < RHS.SectionIndex;
138 return Name < RHS.Name;
142 /// The target specific ELF writer instance.
143 std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
145 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
146 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
147 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
149 llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
151 StringTableBuilder ShStrTabBuilder;
154 /// @name Symbol Table Data
157 StringTableBuilder StrTabBuilder;
158 std::vector<uint64_t> FileSymbolData;
159 std::vector<ELFSymbolData> LocalSymbolData;
160 std::vector<ELFSymbolData> ExternalSymbolData;
161 std::vector<ELFSymbolData> UndefinedSymbolData;
167 // This holds the symbol table index of the last local symbol.
168 unsigned LastLocalSymbolIndex;
169 // This holds the .strtab section index.
170 unsigned StringTableIndex;
171 // This holds the .symtab section index.
172 unsigned SymbolTableIndex;
174 unsigned ShstrtabIndex;
177 // TargetObjectWriter wrappers.
178 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
179 bool hasRelocationAddend() const {
180 return TargetObjectWriter->hasRelocationAddend();
182 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
183 bool IsPCRel) const {
184 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
188 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_ostream &_OS,
190 : MCObjectWriter(_OS, IsLittleEndian), FWriter(IsLittleEndian),
191 TargetObjectWriter(MOTW), NeedsGOT(false) {}
193 virtual ~ELFObjectWriter();
195 void WriteWord(uint64_t W) {
202 template <typename T> void write(MCDataFragment &F, T Value) {
203 FWriter.write(F, Value);
206 void WriteHeader(const MCAssembler &Asm,
207 uint64_t SectionDataSize,
208 unsigned NumberOfSections);
210 void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
211 const MCAsmLayout &Layout);
213 void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm,
214 const MCAsmLayout &Layout,
215 SectionIndexMapTy &SectionIndexMap);
217 bool shouldRelocateWithSymbol(const MCAssembler &Asm,
218 const MCSymbolRefExpr *RefA,
219 const MCSymbolData *SD, uint64_t C,
220 unsigned Type) const;
222 void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
223 const MCFragment *Fragment, const MCFixup &Fixup,
224 MCValue Target, bool &IsPCRel,
225 uint64_t &FixedValue) override;
227 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
230 // Map from a group section to the signature symbol
231 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
232 // Map from a signature symbol to the group section
233 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
234 // Map from a section to the section with the relocations
235 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy;
236 // Map from a section to its offset
237 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy;
239 /// Compute the symbol table data
241 /// \param Asm - The assembler.
242 /// \param SectionIndexMap - Maps a section to its index.
243 /// \param RevGroupMap - Maps a signature symbol to the group section.
244 /// \param NumRegularSections - Number of non-relocation sections.
245 void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
246 const SectionIndexMapTy &SectionIndexMap,
247 const RevGroupMapTy &RevGroupMap,
248 unsigned NumRegularSections);
250 void ComputeIndexMap(MCAssembler &Asm,
251 SectionIndexMapTy &SectionIndexMap,
252 const RelMapTy &RelMap);
254 void CreateRelocationSections(MCAssembler &Asm, RelMapTy &RelMap);
256 void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
258 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
259 const RelMapTy &RelMap);
261 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
262 SectionIndexMapTy &SectionIndexMap,
263 const RelMapTy &RelMap);
265 // Create the sections that show up in the symbol table. Currently
266 // those are the .note.GNU-stack section and the group sections.
267 void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
268 GroupMapTy &GroupMap,
269 RevGroupMapTy &RevGroupMap,
270 SectionIndexMapTy &SectionIndexMap,
271 const RelMapTy &RelMap);
273 void ExecutePostLayoutBinding(MCAssembler &Asm,
274 const MCAsmLayout &Layout) override;
276 void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap,
277 const MCAsmLayout &Layout,
278 const SectionIndexMapTy &SectionIndexMap,
279 const SectionOffsetMapTy &SectionOffsetMap);
281 void ComputeSectionOrder(MCAssembler &Asm,
282 std::vector<const MCSectionELF*> &Sections);
284 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
285 uint64_t Address, uint64_t Offset,
286 uint64_t Size, uint32_t Link, uint32_t Info,
287 uint64_t Alignment, uint64_t EntrySize);
289 void WriteRelocationsFragment(const MCAssembler &Asm,
291 const MCSectionData *SD);
294 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
295 const MCSymbolData &DataA,
296 const MCFragment &FB,
298 bool IsPCRel) const override;
300 void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
301 void WriteSection(MCAssembler &Asm,
302 const SectionIndexMapTy &SectionIndexMap,
303 uint32_t GroupSymbolIndex,
304 uint64_t Offset, uint64_t Size, uint64_t Alignment,
305 const MCSectionELF &Section);
309 FragmentWriter::FragmentWriter(bool IsLittleEndian)
310 : IsLittleEndian(IsLittleEndian) {}
312 template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
314 Val = support::endian::byte_swap<T, support::little>(Val);
316 Val = support::endian::byte_swap<T, support::big>(Val);
317 const char *Start = (const char *)&Val;
318 F.getContents().append(Start, Start + sizeof(T));
321 void SymbolTableWriter::createSymtabShndx() {
325 MCContext &Ctx = Asm.getContext();
326 const MCSectionELF *SymtabShndxSection =
327 Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
328 MCSectionData *SymtabShndxSD =
329 &Asm.getOrCreateSectionData(*SymtabShndxSection);
330 SymtabShndxSD->setAlignment(4);
331 ShndxF = new MCDataFragment(SymtabShndxSD);
332 unsigned Index = SectionIndexMap.size() + 1;
333 SectionIndexMap[SymtabShndxSection] = Index;
335 for (unsigned I = 0; I < NumWritten; ++I)
336 write(*ShndxF, uint32_t(0));
339 template <typename T>
340 void SymbolTableWriter::write(MCDataFragment &F, T Value) {
341 FWriter.write(F, Value);
344 SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter,
346 SectionIndexMapTy &SectionIndexMap,
347 MCDataFragment *SymtabF)
348 : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit),
349 SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr),
352 void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
353 uint64_t size, uint8_t other,
354 uint32_t shndx, bool Reserved) {
355 bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
362 write(*ShndxF, shndx);
364 write(*ShndxF, uint32_t(0));
367 uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
369 raw_svector_ostream OS(SymtabF->getContents());
372 write(*SymtabF, name); // st_name
373 write(*SymtabF, info); // st_info
374 write(*SymtabF, other); // st_other
375 write(*SymtabF, Index); // st_shndx
376 write(*SymtabF, value); // st_value
377 write(*SymtabF, size); // st_size
379 write(*SymtabF, name); // st_name
380 write(*SymtabF, uint32_t(value)); // st_value
381 write(*SymtabF, uint32_t(size)); // st_size
382 write(*SymtabF, info); // st_info
383 write(*SymtabF, other); // st_other
384 write(*SymtabF, Index); // st_shndx
390 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
391 const MCFixupKindInfo &FKI =
392 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
394 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
397 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
401 case MCSymbolRefExpr::VK_GOT:
402 case MCSymbolRefExpr::VK_PLT:
403 case MCSymbolRefExpr::VK_GOTPCREL:
404 case MCSymbolRefExpr::VK_GOTOFF:
405 case MCSymbolRefExpr::VK_TPOFF:
406 case MCSymbolRefExpr::VK_TLSGD:
407 case MCSymbolRefExpr::VK_GOTTPOFF:
408 case MCSymbolRefExpr::VK_INDNTPOFF:
409 case MCSymbolRefExpr::VK_NTPOFF:
410 case MCSymbolRefExpr::VK_GOTNTPOFF:
411 case MCSymbolRefExpr::VK_TLSLDM:
412 case MCSymbolRefExpr::VK_DTPOFF:
413 case MCSymbolRefExpr::VK_TLSLD:
418 ELFObjectWriter::~ELFObjectWriter()
421 // Emit the ELF header.
422 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
423 uint64_t SectionDataSize,
424 unsigned NumberOfSections) {
430 // emitWord method behaves differently for ELF32 and ELF64, writing
431 // 4 bytes in the former and 8 in the latter.
433 Write8(0x7f); // e_ident[EI_MAG0]
434 Write8('E'); // e_ident[EI_MAG1]
435 Write8('L'); // e_ident[EI_MAG2]
436 Write8('F'); // e_ident[EI_MAG3]
438 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
441 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
443 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
445 Write8(TargetObjectWriter->getOSABI());
446 Write8(0); // e_ident[EI_ABIVERSION]
448 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
450 Write16(ELF::ET_REL); // e_type
452 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
454 Write32(ELF::EV_CURRENT); // e_version
455 WriteWord(0); // e_entry, no entry point in .o file
456 WriteWord(0); // e_phoff, no program header for .o
457 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
458 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes
460 // e_flags = whatever the target wants
461 Write32(Asm.getELFHeaderEFlags());
463 // e_ehsize = ELF header size
464 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
466 Write16(0); // e_phentsize = prog header entry size
467 Write16(0); // e_phnum = # prog header entries = 0
469 // e_shentsize = Section header entry size
470 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
472 // e_shnum = # of section header ents
473 if (NumberOfSections >= ELF::SHN_LORESERVE)
474 Write16(ELF::SHN_UNDEF);
476 Write16(NumberOfSections);
478 // e_shstrndx = Section # of '.shstrtab'
479 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
480 Write16(ELF::SHN_XINDEX);
482 Write16(ShstrtabIndex);
485 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
486 const MCAsmLayout &Layout) {
487 if (Data.isCommon() && Data.isExternal())
488 return Data.getCommonAlignment();
491 if (!Layout.getSymbolOffset(&Data, Res))
494 if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
500 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
501 const MCAsmLayout &Layout) {
502 // The presence of symbol versions causes undefined symbols and
503 // versions declared with @@@ to be renamed.
505 for (MCSymbolData &OriginalData : Asm.symbols()) {
506 const MCSymbol &Alias = OriginalData.getSymbol();
509 if (!Alias.isVariable())
511 auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
514 const MCSymbol &Symbol = Ref->getSymbol();
515 MCSymbolData &SD = Asm.getSymbolData(Symbol);
517 StringRef AliasName = Alias.getName();
518 size_t Pos = AliasName.find('@');
519 if (Pos == StringRef::npos)
522 // Aliases defined with .symvar copy the binding from the symbol they alias.
523 // This is the first place we are able to copy this information.
524 OriginalData.setExternal(SD.isExternal());
525 MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
527 StringRef Rest = AliasName.substr(Pos);
528 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
531 // FIXME: produce a better error message.
532 if (Symbol.isUndefined() && Rest.startswith("@@") &&
533 !Rest.startswith("@@@"))
534 report_fatal_error("A @@ version cannot be undefined");
536 Renames.insert(std::make_pair(&Symbol, &Alias));
540 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
541 uint8_t Type = newType;
543 // Propagation rules:
544 // IFUNC > FUNC > OBJECT > NOTYPE
545 // TLS_OBJECT > OBJECT > NOTYPE
547 // dont let the new type degrade the old type
551 case ELF::STT_GNU_IFUNC:
552 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
553 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
554 Type = ELF::STT_GNU_IFUNC;
557 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
558 Type == ELF::STT_TLS)
559 Type = ELF::STT_FUNC;
561 case ELF::STT_OBJECT:
562 if (Type == ELF::STT_NOTYPE)
563 Type = ELF::STT_OBJECT;
566 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
567 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
575 void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
576 const MCAsmLayout &Layout) {
577 MCSymbolData &OrigData = *MSD.SymbolData;
578 assert((!OrigData.getFragment() ||
579 (&OrigData.getFragment()->getParent()->getSection() ==
580 &OrigData.getSymbol().getSection())) &&
581 "The symbol's section doesn't match the fragment's symbol");
582 const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
584 // This has to be in sync with when computeSymbolTable uses SHN_ABS or
586 bool IsReserved = !Base || OrigData.isCommon();
588 // Binding and Type share the same byte as upper and lower nibbles
589 uint8_t Binding = MCELF::GetBinding(OrigData);
590 uint8_t Type = MCELF::GetType(OrigData);
591 MCSymbolData *BaseSD = nullptr;
593 BaseSD = &Layout.getAssembler().getSymbolData(*Base);
594 Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
596 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
598 // Other and Visibility share the same byte with Visibility using the lower
600 uint8_t Visibility = MCELF::GetVisibility(OrigData);
601 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
604 uint64_t Value = SymbolValue(OrigData, Layout);
607 const MCExpr *ESize = OrigData.getSize();
609 ESize = BaseSD->getSize();
613 if (!ESize->EvaluateAsAbsolute(Res, Layout))
614 report_fatal_error("Size expression must be absolute.");
618 // Write out the symbol table entry
619 Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
620 MSD.SectionIndex, IsReserved);
623 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
625 const MCAsmLayout &Layout,
626 SectionIndexMapTy &SectionIndexMap) {
627 // The string table must be emitted first because we need the index
628 // into the string table for all the symbol names.
630 // FIXME: Make sure the start of the symbol table is aligned.
632 SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF);
634 // The first entry is the undefined symbol entry.
635 Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
637 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
638 Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
639 ELF::STV_DEFAULT, ELF::SHN_ABS, true);
642 // Write the symbol table entries.
643 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
645 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
646 ELFSymbolData &MSD = LocalSymbolData[i];
647 WriteSymbol(Writer, MSD, Layout);
650 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
651 ELFSymbolData &MSD = ExternalSymbolData[i];
652 MCSymbolData &Data = *MSD.SymbolData;
653 assert(((Data.getFlags() & ELF_STB_Global) ||
654 (Data.getFlags() & ELF_STB_Weak)) &&
655 "External symbol requires STB_GLOBAL or STB_WEAK flag");
656 WriteSymbol(Writer, MSD, Layout);
657 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
658 LastLocalSymbolIndex++;
661 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
662 ELFSymbolData &MSD = UndefinedSymbolData[i];
663 MCSymbolData &Data = *MSD.SymbolData;
664 WriteSymbol(Writer, MSD, Layout);
665 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
666 LastLocalSymbolIndex++;
670 // It is always valid to create a relocation with a symbol. It is preferable
671 // to use a relocation with a section if that is possible. Using the section
672 // allows us to omit some local symbols from the symbol table.
673 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
674 const MCSymbolRefExpr *RefA,
675 const MCSymbolData *SD,
677 unsigned Type) const {
678 // A PCRel relocation to an absolute value has no symbol (or section). We
679 // represent that with a relocation to a null section.
683 MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
687 // The .odp creation emits a relocation against the symbol ".TOC." which
688 // create a R_PPC64_TOC relocation. However the relocation symbol name
689 // in final object creation should be NULL, since the symbol does not
690 // really exist, it is just the reference to TOC base for the current
691 // object file. Since the symbol is undefined, returning false results
692 // in a relocation with a null section which is the desired result.
693 case MCSymbolRefExpr::VK_PPC_TOCBASE:
696 // These VariantKind cause the relocation to refer to something other than
697 // the symbol itself, like a linker generated table. Since the address of
698 // symbol is not relevant, we cannot replace the symbol with the
699 // section and patch the difference in the addend.
700 case MCSymbolRefExpr::VK_GOT:
701 case MCSymbolRefExpr::VK_PLT:
702 case MCSymbolRefExpr::VK_GOTPCREL:
703 case MCSymbolRefExpr::VK_Mips_GOT:
704 case MCSymbolRefExpr::VK_PPC_GOT_LO:
705 case MCSymbolRefExpr::VK_PPC_GOT_HI:
706 case MCSymbolRefExpr::VK_PPC_GOT_HA:
710 // An undefined symbol is not in any section, so the relocation has to point
711 // to the symbol itself.
712 const MCSymbol &Sym = SD->getSymbol();
713 if (Sym.isUndefined())
716 unsigned Binding = MCELF::GetBinding(*SD);
719 llvm_unreachable("Invalid Binding");
723 // If the symbol is weak, it might be overridden by a symbol in another
724 // file. The relocation has to point to the symbol so that the linker
727 case ELF::STB_GLOBAL:
728 // Global ELF symbols can be preempted by the dynamic linker. The relocation
729 // has to point to the symbol for a reason analogous to the STB_WEAK case.
733 // If a relocation points to a mergeable section, we have to be careful.
734 // If the offset is zero, a relocation with the section will encode the
735 // same information. With a non-zero offset, the situation is different.
736 // For example, a relocation can point 42 bytes past the end of a string.
737 // If we change such a relocation to use the section, the linker would think
738 // that it pointed to another string and subtracting 42 at runtime will
739 // produce the wrong value.
740 auto &Sec = cast<MCSectionELF>(Sym.getSection());
741 unsigned Flags = Sec.getFlags();
742 if (Flags & ELF::SHF_MERGE) {
746 // It looks like gold has a bug (http://sourceware.org/PR16794) and can
747 // only handle section relocations to mergeable sections if using RELA.
748 if (!hasRelocationAddend())
752 // Most TLS relocations use a got, so they need the symbol. Even those that
753 // are just an offset (@tpoff), require a symbol in gold versions before
754 // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
755 // http://sourceware.org/PR16773.
756 if (Flags & ELF::SHF_TLS)
759 // If the symbol is a thumb function the final relocation must set the lowest
760 // bit. With a symbol that is done by just having the symbol have that bit
761 // set, so we would lose the bit if we relocated with the section.
762 // FIXME: We could use the section but add the bit to the relocation value.
763 if (Asm.isThumbFunc(&Sym))
766 if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
771 static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
772 const MCSymbol &Sym = Ref.getSymbol();
774 if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
777 if (!Sym.isVariable())
780 const MCExpr *Expr = Sym.getVariableValue();
781 const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
785 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
786 return &Inner->getSymbol();
790 void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
791 const MCAsmLayout &Layout,
792 const MCFragment *Fragment,
793 const MCFixup &Fixup, MCValue Target,
794 bool &IsPCRel, uint64_t &FixedValue) {
795 const MCSectionData *FixupSection = Fragment->getParent();
796 uint64_t C = Target.getConstant();
797 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
799 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
800 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
801 "Should not have constructed this");
803 // Let A, B and C being the components of Target and R be the location of
804 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
805 // If it is pcrel, we want to compute (A - B + C - R).
807 // In general, ELF has no relocations for -B. It can only represent (A + C)
808 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
809 // replace B to implement it: (A - R - K + C)
811 Asm.getContext().FatalError(
813 "No relocation available to represent this relative expression");
815 const MCSymbol &SymB = RefB->getSymbol();
817 if (SymB.isUndefined())
818 Asm.getContext().FatalError(
820 Twine("symbol '") + SymB.getName() +
821 "' can not be undefined in a subtraction expression");
823 assert(!SymB.isAbsolute() && "Should have been folded");
824 const MCSection &SecB = SymB.getSection();
825 if (&SecB != &FixupSection->getSection())
826 Asm.getContext().FatalError(
827 Fixup.getLoc(), "Cannot represent a difference across sections");
829 const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
830 uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
831 uint64_t K = SymBOffset - FixupOffset;
836 // We either rejected the fixup or folded B into C at this point.
837 const MCSymbolRefExpr *RefA = Target.getSymA();
838 const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
839 const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
841 unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
842 bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
843 if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
844 C += Layout.getSymbolOffset(SymAD);
847 if (hasRelocationAddend()) {
854 // FIXME: What is this!?!?
855 MCSymbolRefExpr::VariantKind Modifier =
856 RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
857 if (RelocNeedsGOT(Modifier))
860 if (!RelocateWithSymbol) {
861 const MCSection *SecA =
862 (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
863 auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
864 MCSymbol *SectionSymbol =
865 ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
867 ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
868 Relocations[FixupSection].push_back(Rec);
873 if (const MCSymbol *R = Renames.lookup(SymA))
876 if (const MCSymbol *WeakRef = getWeakRef(*RefA))
877 WeakrefUsedInReloc.insert(WeakRef);
879 UsedInReloc.insert(SymA);
881 ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
882 Relocations[FixupSection].push_back(Rec);
888 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
890 const MCSymbolData &SD = Asm.getSymbolData(*S);
891 return SD.getIndex();
894 bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
895 const MCSymbolData &Data, bool Used,
897 const MCSymbol &Symbol = Data.getSymbol();
898 if (Symbol.isVariable()) {
899 const MCExpr *Expr = Symbol.getVariableValue();
900 if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
901 if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
912 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
915 if (Symbol.isVariable()) {
916 const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
917 if (Base && Base->isUndefined())
921 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
922 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
925 if (Symbol.isTemporary())
931 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
932 if (Data.isExternal())
935 const MCSymbol &Symbol = Data.getSymbol();
936 if (Symbol.isDefined())
945 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
946 SectionIndexMapTy &SectionIndexMap,
947 const RelMapTy &RelMap) {
949 for (MCAssembler::iterator it = Asm.begin(),
950 ie = Asm.end(); it != ie; ++it) {
951 const MCSectionELF &Section =
952 static_cast<const MCSectionELF &>(it->getSection());
953 if (Section.getType() != ELF::SHT_GROUP)
955 SectionIndexMap[&Section] = Index++;
958 for (MCAssembler::iterator it = Asm.begin(),
959 ie = Asm.end(); it != ie; ++it) {
960 const MCSectionELF &Section =
961 static_cast<const MCSectionELF &>(it->getSection());
962 if (Section.getType() == ELF::SHT_GROUP ||
963 Section.getType() == ELF::SHT_REL ||
964 Section.getType() == ELF::SHT_RELA)
966 SectionIndexMap[&Section] = Index++;
967 const MCSectionELF *RelSection = RelMap.lookup(&Section);
969 SectionIndexMap[RelSection] = Index++;
974 ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
975 const SectionIndexMapTy &SectionIndexMap,
976 const RevGroupMapTy &RevGroupMap,
977 unsigned NumRegularSections) {
978 // FIXME: Is this the correct place to do this?
979 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
981 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
982 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
983 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
984 Data.setExternal(true);
985 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
988 // Add the data for the symbols.
989 for (MCSymbolData &SD : Asm.symbols()) {
990 const MCSymbol &Symbol = SD.getSymbol();
992 bool Used = UsedInReloc.count(&Symbol);
993 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
994 bool isSignature = RevGroupMap.count(&Symbol);
996 if (!isInSymtab(Layout, SD,
997 Used || WeakrefUsed || isSignature,
998 Renames.count(&Symbol)))
1002 MSD.SymbolData = &SD;
1003 const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
1005 // Undefined symbols are global, but this is the first place we
1006 // are able to set it.
1007 bool Local = isLocal(SD, Used);
1008 if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1010 MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1011 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1012 MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1016 MSD.SectionIndex = ELF::SHN_ABS;
1017 } else if (SD.isCommon()) {
1019 MSD.SectionIndex = ELF::SHN_COMMON;
1020 } else if (BaseSymbol->isUndefined()) {
1021 if (isSignature && !Used)
1022 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap.lookup(&Symbol));
1024 MSD.SectionIndex = ELF::SHN_UNDEF;
1025 if (!Used && WeakrefUsed)
1026 MCELF::SetBinding(SD, ELF::STB_WEAK);
1028 const MCSectionELF &Section =
1029 static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1030 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1031 assert(MSD.SectionIndex && "Invalid section index!");
1034 // The @@@ in symbol version is replaced with @ in undefined symbols and @@
1037 // FIXME: All name handling should be done before we get to the writer,
1038 // including dealing with GNU-style version suffixes. Fixing this isn’t
1041 // We thus have to be careful to not perform the symbol version replacement
1044 // The ELF format is used on Windows by the MCJIT engine. Thus, on
1045 // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
1046 // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
1047 // C++ name mangling can legally have "@@@" as a sub-string. In that case,
1048 // the EFLObjectWriter should not interpret the "@@@" sub-string as
1049 // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
1050 // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
1051 // "__imp_?" or "__imp_@?".
1053 // It would have been interesting to perform the MS mangling prefix check
1054 // only when the target triple is of the form *-pc-windows-elf. But, it
1055 // seems that this information is not easily accessible from the
1057 StringRef Name = Symbol.getName();
1058 if (!Name.startswith("?") && !Name.startswith("@?") &&
1059 !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
1060 // This symbol isn't following the MSVC C++ name mangling convention. We
1061 // can thus safely interpret the @@@ in symbol names as specifying symbol
1063 SmallString<32> Buf;
1064 size_t Pos = Name.find("@@@");
1065 if (Pos != StringRef::npos) {
1066 Buf += Name.substr(0, Pos);
1067 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1068 Buf += Name.substr(Pos + Skip);
1073 // Sections have their own string table
1074 if (MCELF::GetType(SD) != ELF::STT_SECTION)
1075 MSD.Name = StrTabBuilder.add(Name);
1077 if (MSD.SectionIndex == ELF::SHN_UNDEF)
1078 UndefinedSymbolData.push_back(MSD);
1080 LocalSymbolData.push_back(MSD);
1082 ExternalSymbolData.push_back(MSD);
1085 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1086 StrTabBuilder.add(*i);
1088 StrTabBuilder.finalize(StringTableBuilder::ELF);
1090 for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1091 FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1093 for (ELFSymbolData &MSD : LocalSymbolData)
1094 MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
1096 : StrTabBuilder.getOffset(MSD.Name);
1097 for (ELFSymbolData &MSD : ExternalSymbolData)
1098 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1099 for (ELFSymbolData& MSD : UndefinedSymbolData)
1100 MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1102 // Symbols are required to be in lexicographic order.
1103 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1104 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1105 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1107 // Set the symbol indices. Local symbols must come before all other
1108 // symbols with non-local bindings.
1109 unsigned Index = FileSymbolData.size() + 1;
1110 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1111 LocalSymbolData[i].SymbolData->setIndex(Index++);
1113 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1114 ExternalSymbolData[i].SymbolData->setIndex(Index++);
1115 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1116 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1119 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm,
1121 for (MCAssembler::const_iterator it = Asm.begin(),
1122 ie = Asm.end(); it != ie; ++it) {
1123 const MCSectionData &SD = *it;
1124 if (Relocations[&SD].empty())
1127 MCContext &Ctx = Asm.getContext();
1128 const MCSectionELF &Section =
1129 static_cast<const MCSectionELF&>(SD.getSection());
1131 const StringRef SectionName = Section.getSectionName();
1132 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1133 RelaSectionName += SectionName;
1136 if (hasRelocationAddend())
1137 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1139 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1142 StringRef Group = "";
1143 if (Section.getFlags() & ELF::SHF_GROUP) {
1144 Flags = ELF::SHF_GROUP;
1145 Group = Section.getGroup()->getName();
1148 const MCSectionELF *RelaSection =
1149 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ?
1150 ELF::SHT_RELA : ELF::SHT_REL, Flags,
1152 RelMap[&Section] = RelaSection;
1153 Asm.getOrCreateSectionData(*RelaSection);
1157 static SmallVector<char, 128>
1158 getUncompressedData(MCAsmLayout &Layout,
1159 MCSectionData::FragmentListType &Fragments) {
1160 SmallVector<char, 128> UncompressedData;
1161 for (const MCFragment &F : Fragments) {
1162 const SmallVectorImpl<char> *Contents;
1163 switch (F.getKind()) {
1164 case MCFragment::FT_Data:
1165 Contents = &cast<MCDataFragment>(F).getContents();
1167 case MCFragment::FT_Dwarf:
1168 Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1170 case MCFragment::FT_DwarfFrame:
1171 Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1175 "Not expecting any other fragment types in a debug_* section");
1177 UncompressedData.append(Contents->begin(), Contents->end());
1179 return UncompressedData;
1182 // Include the debug info compression header:
1183 // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1184 // useful for consumers to preallocate a buffer to decompress into.
1186 prependCompressionHeader(uint64_t Size,
1187 SmallVectorImpl<char> &CompressedContents) {
1188 static const StringRef Magic = "ZLIB";
1189 if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1191 if (sys::IsLittleEndianHost)
1192 sys::swapByteOrder(Size);
1193 CompressedContents.insert(CompressedContents.begin(),
1194 Magic.size() + sizeof(Size), 0);
1195 std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1196 std::copy(reinterpret_cast<char *>(&Size),
1197 reinterpret_cast<char *>(&Size + 1),
1198 CompressedContents.begin() + Magic.size());
1202 // Return a single fragment containing the compressed contents of the whole
1203 // section. Null if the section was not compressed for any reason.
1204 static std::unique_ptr<MCDataFragment>
1205 getCompressedFragment(MCAsmLayout &Layout,
1206 MCSectionData::FragmentListType &Fragments) {
1207 std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1209 // Gather the uncompressed data from all the fragments, recording the
1210 // alignment fragment, if seen, and any fixups.
1211 SmallVector<char, 128> UncompressedData =
1212 getUncompressedData(Layout, Fragments);
1214 SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1216 zlib::Status Success = zlib::compress(
1217 StringRef(UncompressedData.data(), UncompressedData.size()),
1218 CompressedContents);
1219 if (Success != zlib::StatusOK)
1222 if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1225 return CompressedFragment;
1228 typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1231 static void UpdateSymbols(const MCAsmLayout &Layout,
1232 const std::vector<MCSymbolData *> &Symbols,
1233 MCFragment &NewFragment) {
1234 for (MCSymbolData *Sym : Symbols) {
1235 Sym->setOffset(Sym->getOffset() +
1236 Layout.getFragmentOffset(Sym->getFragment()));
1237 Sym->setFragment(&NewFragment);
1241 static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1242 const DefiningSymbolMap &DefiningSymbols,
1243 const MCSectionELF &Section,
1244 MCSectionData &SD) {
1245 StringRef SectionName = Section.getSectionName();
1246 MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1248 std::unique_ptr<MCDataFragment> CompressedFragment =
1249 getCompressedFragment(Layout, Fragments);
1251 // Leave the section as-is if the fragments could not be compressed.
1252 if (!CompressedFragment)
1255 // Update the fragment+offsets of any symbols referring to fragments in this
1256 // section to refer to the new fragment.
1257 auto I = DefiningSymbols.find(&SD);
1258 if (I != DefiningSymbols.end())
1259 UpdateSymbols(Layout, I->second, *CompressedFragment);
1261 // Invalidate the layout for the whole section since it will have new and
1262 // different fragments now.
1263 Layout.invalidateFragmentsFrom(&Fragments.front());
1266 // Complete the initialization of the new fragment
1267 CompressedFragment->setParent(&SD);
1268 CompressedFragment->setLayoutOrder(0);
1269 Fragments.push_back(CompressedFragment.release());
1271 // Rename from .debug_* to .zdebug_*
1272 Asm.getContext().renameELFSection(&Section,
1273 (".z" + SectionName.drop_front(1)).str());
1276 void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1277 MCAsmLayout &Layout) {
1278 if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1281 DefiningSymbolMap DefiningSymbols;
1283 for (MCSymbolData &SD : Asm.symbols())
1284 if (MCFragment *F = SD.getFragment())
1285 DefiningSymbols[F->getParent()].push_back(&SD);
1287 for (MCSectionData &SD : Asm) {
1288 const MCSectionELF &Section =
1289 static_cast<const MCSectionELF &>(SD.getSection());
1290 StringRef SectionName = Section.getSectionName();
1292 // Compressing debug_frame requires handling alignment fragments which is
1293 // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1294 // for writing to arbitrary buffers) for little benefit.
1295 if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1298 CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1302 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
1303 const RelMapTy &RelMap) {
1304 for (MCAssembler::const_iterator it = Asm.begin(),
1305 ie = Asm.end(); it != ie; ++it) {
1306 const MCSectionData &SD = *it;
1307 const MCSectionELF &Section =
1308 static_cast<const MCSectionELF&>(SD.getSection());
1310 const MCSectionELF *RelaSection = RelMap.lookup(&Section);
1313 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
1314 RelaSD.setAlignment(is64Bit() ? 8 : 4);
1316 MCDataFragment *F = new MCDataFragment(&RelaSD);
1317 WriteRelocationsFragment(Asm, F, &*it);
1321 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1322 uint64_t Flags, uint64_t Address,
1323 uint64_t Offset, uint64_t Size,
1324 uint32_t Link, uint32_t Info,
1326 uint64_t EntrySize) {
1327 Write32(Name); // sh_name: index into string table
1328 Write32(Type); // sh_type
1329 WriteWord(Flags); // sh_flags
1330 WriteWord(Address); // sh_addr
1331 WriteWord(Offset); // sh_offset
1332 WriteWord(Size); // sh_size
1333 Write32(Link); // sh_link
1334 Write32(Info); // sh_info
1335 WriteWord(Alignment); // sh_addralign
1336 WriteWord(EntrySize); // sh_entsize
1339 // ELF doesn't require relocations to be in any order. We sort by the r_offset,
1340 // just to match gnu as for easier comparison. The use type is an arbitrary way
1341 // of making the sort deterministic.
1342 static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
1343 const ELFRelocationEntry &A = *AP;
1344 const ELFRelocationEntry &B = *BP;
1345 if (A.Offset != B.Offset)
1346 return B.Offset - A.Offset;
1347 if (B.Type != A.Type)
1348 return A.Type - B.Type;
1349 llvm_unreachable("ELFRelocs might be unstable!");
1352 static void sortRelocs(const MCAssembler &Asm,
1353 std::vector<ELFRelocationEntry> &Relocs) {
1354 array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
1357 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1359 const MCSectionData *SD) {
1360 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1362 sortRelocs(Asm, Relocs);
1364 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1365 const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1367 Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
1370 write(*F, Entry.Offset);
1371 if (TargetObjectWriter->isN64()) {
1372 write(*F, uint32_t(Index));
1374 write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1375 write(*F, TargetObjectWriter->getRType3(Entry.Type));
1376 write(*F, TargetObjectWriter->getRType2(Entry.Type));
1377 write(*F, TargetObjectWriter->getRType(Entry.Type));
1379 struct ELF::Elf64_Rela ERE64;
1380 ERE64.setSymbolAndType(Index, Entry.Type);
1381 write(*F, ERE64.r_info);
1383 if (hasRelocationAddend())
1384 write(*F, Entry.Addend);
1386 write(*F, uint32_t(Entry.Offset));
1388 struct ELF::Elf32_Rela ERE32;
1389 ERE32.setSymbolAndType(Index, Entry.Type);
1390 write(*F, ERE32.r_info);
1392 if (hasRelocationAddend())
1393 write(*F, uint32_t(Entry.Addend));
1398 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
1399 MCAsmLayout &Layout,
1400 SectionIndexMapTy &SectionIndexMap,
1401 const RelMapTy &RelMap) {
1402 MCContext &Ctx = Asm.getContext();
1405 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1407 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1408 const MCSectionELF *ShstrtabSection =
1409 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
1410 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1411 ShstrtabSD.setAlignment(1);
1413 const MCSectionELF *SymtabSection =
1414 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1416 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1417 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1419 const MCSectionELF *StrtabSection;
1420 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
1421 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1422 StrtabSD.setAlignment(1);
1424 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1426 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection);
1427 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection);
1428 StringTableIndex = SectionIndexMap.lookup(StrtabSection);
1431 F = new MCDataFragment(&SymtabSD);
1432 WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
1434 F = new MCDataFragment(&StrtabSD);
1435 F->getContents().append(StrTabBuilder.data().begin(),
1436 StrTabBuilder.data().end());
1438 F = new MCDataFragment(&ShstrtabSD);
1440 // Section header string table.
1441 for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1442 const MCSectionELF &Section =
1443 static_cast<const MCSectionELF&>(it->getSection());
1444 ShStrTabBuilder.add(Section.getSectionName());
1446 ShStrTabBuilder.finalize(StringTableBuilder::ELF);
1447 F->getContents().append(ShStrTabBuilder.data().begin(),
1448 ShStrTabBuilder.data().end());
1451 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
1452 MCAsmLayout &Layout,
1453 GroupMapTy &GroupMap,
1454 RevGroupMapTy &RevGroupMap,
1455 SectionIndexMapTy &SectionIndexMap,
1456 const RelMapTy &RelMap) {
1457 MCContext &Ctx = Asm.getContext();
1460 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1462 const MCSectionELF &Section =
1463 static_cast<const MCSectionELF&>(it->getSection());
1464 if (!(Section.getFlags() & ELF::SHF_GROUP))
1467 const MCSymbol *SignatureSymbol = Section.getGroup();
1468 Asm.getOrCreateSymbolData(*SignatureSymbol);
1469 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1471 Group = Ctx.CreateELFGroupSection();
1472 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1473 Data.setAlignment(4);
1474 MCDataFragment *F = new MCDataFragment(&Data);
1475 write(*F, uint32_t(ELF::GRP_COMDAT));
1477 GroupMap[Group] = SignatureSymbol;
1480 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1482 // Add sections to the groups
1483 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1485 const MCSectionELF &Section =
1486 static_cast<const MCSectionELF&>(it->getSection());
1487 if (!(Section.getFlags() & ELF::SHF_GROUP))
1489 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1490 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1491 // FIXME: we could use the previous fragment
1492 MCDataFragment *F = new MCDataFragment(&Data);
1493 uint32_t Index = SectionIndexMap.lookup(&Section);
1498 void ELFObjectWriter::WriteSection(MCAssembler &Asm,
1499 const SectionIndexMapTy &SectionIndexMap,
1500 uint32_t GroupSymbolIndex,
1501 uint64_t Offset, uint64_t Size,
1503 const MCSectionELF &Section) {
1504 uint64_t sh_link = 0;
1505 uint64_t sh_info = 0;
1507 switch(Section.getType()) {
1508 case ELF::SHT_DYNAMIC:
1509 sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1514 case ELF::SHT_RELA: {
1515 const MCSectionELF *SymtabSection;
1516 const MCSectionELF *InfoSection;
1518 Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 0);
1519 sh_link = SectionIndexMap.lookup(SymtabSection);
1520 assert(sh_link && ".symtab not found");
1522 // Remove ".rel" and ".rela" prefixes.
1523 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1524 StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1525 StringRef GroupName =
1526 Section.getGroup() ? Section.getGroup()->getName() : "";
1528 InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS,
1530 sh_info = SectionIndexMap.lookup(InfoSection);
1534 case ELF::SHT_SYMTAB:
1535 case ELF::SHT_DYNSYM:
1536 sh_link = StringTableIndex;
1537 sh_info = LastLocalSymbolIndex;
1540 case ELF::SHT_SYMTAB_SHNDX:
1541 sh_link = SymbolTableIndex;
1544 case ELF::SHT_PROGBITS:
1545 case ELF::SHT_STRTAB:
1546 case ELF::SHT_NOBITS:
1549 case ELF::SHT_ARM_ATTRIBUTES:
1550 case ELF::SHT_INIT_ARRAY:
1551 case ELF::SHT_FINI_ARRAY:
1552 case ELF::SHT_PREINIT_ARRAY:
1553 case ELF::SHT_X86_64_UNWIND:
1554 case ELF::SHT_MIPS_REGINFO:
1555 case ELF::SHT_MIPS_OPTIONS:
1556 case ELF::SHT_MIPS_ABIFLAGS:
1560 case ELF::SHT_GROUP:
1561 sh_link = SymbolTableIndex;
1562 sh_info = GroupSymbolIndex;
1566 llvm_unreachable("FIXME: sh_type value not supported!");
1569 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1570 Section.getType() == ELF::SHT_ARM_EXIDX) {
1571 StringRef SecName(Section.getSectionName());
1572 if (SecName == ".ARM.exidx") {
1573 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
1574 ".text", ELF::SHT_PROGBITS, ELF::SHF_EXECINSTR | ELF::SHF_ALLOC));
1575 } else if (SecName.startswith(".ARM.exidx")) {
1576 StringRef GroupName =
1577 Section.getGroup() ? Section.getGroup()->getName() : "";
1578 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
1579 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS,
1580 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, 0, GroupName));
1584 WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1586 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1587 Alignment, Section.getEntrySize());
1590 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1591 return SD.getOrdinal() == ~UINT32_C(0) &&
1592 !SD.getSection().isVirtualSection();
1595 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1597 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1599 const MCFragment &F = *i;
1600 assert(F.getKind() == MCFragment::FT_Data);
1601 Ret += cast<MCDataFragment>(F).getContents().size();
1606 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
1607 const MCSectionData &SD) {
1608 if (IsELFMetaDataSection(SD))
1609 return DataSectionSize(SD);
1610 return Layout.getSectionFileSize(&SD);
1613 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1614 const MCSectionData &SD) {
1615 if (IsELFMetaDataSection(SD))
1616 return DataSectionSize(SD);
1617 return Layout.getSectionAddressSize(&SD);
1620 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
1621 const MCAsmLayout &Layout,
1622 const MCSectionELF &Section) {
1623 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1625 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1626 WriteZeros(Padding);
1628 if (IsELFMetaDataSection(SD)) {
1629 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1631 const MCFragment &F = *i;
1632 assert(F.getKind() == MCFragment::FT_Data);
1633 WriteBytes(cast<MCDataFragment>(F).getContents());
1636 Asm.writeSectionData(&SD, Layout);
1640 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm,
1641 const GroupMapTy &GroupMap,
1642 const MCAsmLayout &Layout,
1643 const SectionIndexMapTy &SectionIndexMap,
1644 const SectionOffsetMapTy &SectionOffsetMap) {
1645 const unsigned NumSections = Asm.size() + 1;
1647 std::vector<const MCSectionELF*> Sections;
1648 Sections.resize(NumSections - 1);
1650 for (SectionIndexMapTy::const_iterator i=
1651 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
1652 const std::pair<const MCSectionELF*, uint32_t> &p = *i;
1653 Sections[p.second - 1] = p.first;
1656 // Null section first.
1657 uint64_t FirstSectionSize =
1658 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1659 uint32_t FirstSectionLink =
1660 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1661 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1663 for (unsigned i = 0; i < NumSections - 1; ++i) {
1664 const MCSectionELF &Section = *Sections[i];
1665 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1666 uint32_t GroupSymbolIndex;
1667 if (Section.getType() != ELF::SHT_GROUP)
1668 GroupSymbolIndex = 0;
1670 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1671 GroupMap.lookup(&Section));
1673 uint64_t Size = GetSectionAddressSize(Layout, SD);
1675 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex,
1676 SectionOffsetMap.lookup(&Section), Size,
1677 SD.getAlignment(), Section);
1681 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
1682 std::vector<const MCSectionELF*> &Sections) {
1683 for (MCAssembler::iterator it = Asm.begin(),
1684 ie = Asm.end(); it != ie; ++it) {
1685 const MCSectionELF &Section =
1686 static_cast<const MCSectionELF &>(it->getSection());
1687 if (Section.getType() == ELF::SHT_GROUP)
1688 Sections.push_back(&Section);
1691 for (MCAssembler::iterator it = Asm.begin(),
1692 ie = Asm.end(); it != ie; ++it) {
1693 const MCSectionELF &Section =
1694 static_cast<const MCSectionELF &>(it->getSection());
1695 if (Section.getType() != ELF::SHT_GROUP &&
1696 Section.getType() != ELF::SHT_REL &&
1697 Section.getType() != ELF::SHT_RELA)
1698 Sections.push_back(&Section);
1701 for (MCAssembler::iterator it = Asm.begin(),
1702 ie = Asm.end(); it != ie; ++it) {
1703 const MCSectionELF &Section =
1704 static_cast<const MCSectionELF &>(it->getSection());
1705 if (Section.getType() == ELF::SHT_REL ||
1706 Section.getType() == ELF::SHT_RELA)
1707 Sections.push_back(&Section);
1711 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1712 const MCAsmLayout &Layout) {
1713 GroupMapTy GroupMap;
1714 RevGroupMapTy RevGroupMap;
1715 SectionIndexMapTy SectionIndexMap;
1717 unsigned NumUserSections = Asm.size();
1719 CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1721 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
1722 CreateRelocationSections(Asm, RelMap);
1724 const unsigned NumUserAndRelocSections = Asm.size();
1725 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
1726 RevGroupMap, SectionIndexMap, RelMap);
1727 const unsigned AllSections = Asm.size();
1728 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
1730 unsigned NumRegularSections = NumUserSections + NumIndexedSections;
1732 // Compute symbol table information.
1733 computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
1734 NumRegularSections);
1736 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1738 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1739 const_cast<MCAsmLayout&>(Layout),
1743 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1744 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
1745 sizeof(ELF::Elf32_Ehdr);
1746 uint64_t FileOff = HeaderSize;
1748 std::vector<const MCSectionELF*> Sections;
1749 ComputeSectionOrder(Asm, Sections);
1750 unsigned NumSections = Sections.size();
1751 SectionOffsetMapTy SectionOffsetMap;
1752 for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
1753 const MCSectionELF &Section = *Sections[i];
1754 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1756 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1758 // Remember the offset into the file for this section.
1759 SectionOffsetMap[&Section] = FileOff;
1761 // Get the size of the section in the output file (including padding).
1762 FileOff += GetSectionFileSize(Layout, SD);
1765 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1767 const unsigned SectionHeaderOffset = FileOff - HeaderSize;
1769 uint64_t SectionHeaderEntrySize = is64Bit() ?
1770 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
1771 FileOff += (NumSections + 1) * SectionHeaderEntrySize;
1773 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
1774 const MCSectionELF &Section = *Sections[i];
1775 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1777 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1779 // Remember the offset into the file for this section.
1780 SectionOffsetMap[&Section] = FileOff;
1782 // Get the size of the section in the output file (including padding).
1783 FileOff += GetSectionFileSize(Layout, SD);
1786 // Write out the ELF header ...
1787 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
1789 // ... then the regular sections ...
1790 // + because of .shstrtab
1791 for (unsigned i = 0; i < NumRegularSections + 1; ++i)
1792 WriteDataSectionData(Asm, Layout, *Sections[i]);
1794 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1795 WriteZeros(Padding);
1797 // ... then the section header table ...
1798 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap,
1801 // ... and then the remaining sections ...
1802 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
1803 WriteDataSectionData(Asm, Layout, *Sections[i]);
1807 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
1808 const MCSymbolData &DataA,
1809 const MCFragment &FB,
1811 bool IsPCRel) const {
1812 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC)
1814 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1815 Asm, DataA, FB,InSet, IsPCRel);
1818 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1820 bool IsLittleEndian) {
1821 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);