ELFObjectWriter.cpp revision 6cc53be24c894532b33a92069b092112ced7ad99 
1//===- lib/MC/ELFObjectWriter.cpp - ELF File Writer -------------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements ELF object file writer information.
11//
12//===----------------------------------------------------------------------===//
13
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"
31
32#include "../Target/X86/X86FixupKinds.h"
33
34#include <vector>
35using namespace llvm;
36
37namespace {
38
39  class ELFObjectWriterImpl {
40    static bool isFixupKindX86PCRel(unsigned Kind) {
41      switch (Kind) {
42      default:
43        return false;
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:
48        return true;
49      }
50    }
51
52    /*static bool isFixupKindX86RIPRel(unsigned Kind) {
53      return Kind == X86::reloc_riprel_4byte ||
54        Kind == X86::reloc_riprel_4byte_movq_load;
55    }*/
56
57
58    /// ELFSymbolData - Helper struct for containing some precomputed information
59    /// on symbols.
60    struct ELFSymbolData {
61      MCSymbolData *SymbolData;
62      uint64_t StringIndex;
63      uint32_t SectionIndex;
64
65      // Support lexicographic sorting.
66      bool operator<(const ELFSymbolData &RHS) const {
67        return SymbolData->getSymbol().getName() <
68               RHS.SymbolData->getSymbol().getName();
69      }
70    };
71
72    /// @name Relocation Data
73    /// @{
74
75    struct ELFRelocationEntry {
76      // Make these big enough for both 32-bit and 64-bit
77      uint64_t r_offset;
78      uint64_t r_info;
79      uint64_t r_addend;
80
81      // Support lexicographic sorting.
82      bool operator<(const ELFRelocationEntry &RE) const {
83        return RE.r_offset < r_offset;
84      }
85    };
86
87    llvm::DenseMap<const MCSectionData*,
88                   std::vector<ELFRelocationEntry> > Relocations;
89    DenseMap<const MCSection*, uint64_t> SectionStringTableIndex;
90
91    /// @}
92    /// @name Symbol Table Data
93    /// @{
94
95    SmallString<256> StringTable;
96    std::vector<ELFSymbolData> LocalSymbolData;
97    std::vector<ELFSymbolData> ExternalSymbolData;
98    std::vector<ELFSymbolData> UndefinedSymbolData;
99
100    /// @}
101
102    ELFObjectWriter *Writer;
103
104    raw_ostream &OS;
105
106    // This holds the current offset into the object file.
107    size_t FileOff;
108
109    unsigned Is64Bit : 1;
110
111    bool HasRelocationAddend;
112
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;
117
118    unsigned ShstrtabIndex;
119
120  public:
121    ELFObjectWriterImpl(ELFObjectWriter *_Writer, bool _Is64Bit,
122                        bool _HasRelAddend)
123      : Writer(_Writer), OS(Writer->getStream()), FileOff(0),
124        Is64Bit(_Is64Bit), HasRelocationAddend(_HasRelAddend) {
125    }
126
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);
134    //}
135
136    void WriteWord(uint64_t W) {
137      if (Is64Bit)
138        Writer->Write64(W);
139      else
140        Writer->Write32(W);
141    }
142
143    void String8(char *buf, uint8_t Value) {
144      buf[0] = Value;
145    }
146
147    void StringLE16(char *buf, uint16_t Value) {
148      buf[0] = char(Value >> 0);
149      buf[1] = char(Value >> 8);
150    }
151
152    void StringLE32(char *buf, uint32_t Value) {
153      StringLE16(buf, uint16_t(Value >> 0));
154      StringLE16(buf + 2, uint16_t(Value >> 16));
155    }
156
157    void StringLE64(char *buf, uint64_t Value) {
158      StringLE32(buf, uint32_t(Value >> 0));
159      StringLE32(buf + 4, uint32_t(Value >> 32));
160    }
161
162    void StringBE16(char *buf ,uint16_t Value) {
163      buf[0] = char(Value >> 8);
164      buf[1] = char(Value >> 0);
165    }
166
167    void StringBE32(char *buf, uint32_t Value) {
168      StringBE16(buf, uint16_t(Value >> 16));
169      StringBE16(buf + 2, uint16_t(Value >> 0));
170    }
171
172    void StringBE64(char *buf, uint64_t Value) {
173      StringBE32(buf, uint32_t(Value >> 32));
174      StringBE32(buf + 4, uint32_t(Value >> 0));
175    }
176
177    void String16(char *buf, uint16_t Value) {
178      if (Writer->isLittleEndian())
179        StringLE16(buf, Value);
180      else
181        StringBE16(buf, Value);
182    }
183
184    void String32(char *buf, uint32_t Value) {
185      if (Writer->isLittleEndian())
186        StringLE32(buf, Value);
187      else
188        StringBE32(buf, Value);
189    }
190
191    void String64(char *buf, uint64_t Value) {
192      if (Writer->isLittleEndian())
193        StringLE64(buf, Value);
194      else
195        StringBE64(buf, Value);
196    }
197
198    void WriteHeader(uint64_t SectionDataSize, unsigned NumberOfSections);
199
200    void WriteSymbolEntry(MCDataFragment *F, uint64_t name, uint8_t info,
201                          uint64_t value, uint64_t size,
202                          uint8_t other, uint16_t shndx);
203
204    void WriteSymbol(MCDataFragment *F, ELFSymbolData &MSD,
205                     const MCAsmLayout &Layout);
206
207    void WriteSymbolTable(MCDataFragment *F, const MCAssembler &Asm,
208                          const MCAsmLayout &Layout);
209
210    void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
211                          const MCFragment *Fragment, const MCFixup &Fixup,
212                          MCValue Target, uint64_t &FixedValue);
213
214    uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
215                                         const MCSymbol *S);
216
217    /// ComputeSymbolTable - Compute the symbol table data
218    ///
219    /// \param StringTable [out] - The string table data.
220    /// \param StringIndexMap [out] - Map from symbol names to offsets in the
221    /// string table.
222    void ComputeSymbolTable(MCAssembler &Asm);
223
224    void WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
225                         const MCSectionData &SD);
226
227    void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) {
228      for (MCAssembler::const_iterator it = Asm.begin(),
229             ie = Asm.end(); it != ie; ++it) {
230        WriteRelocation(Asm, Layout, *it);
231      }
232    }
233
234    void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout);
235
236    void ExecutePostLayoutBinding(MCAssembler &Asm) {
237      // Compute symbol table information.
238      ComputeSymbolTable(Asm);
239    }
240
241    void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
242                          uint64_t Address, uint64_t Offset,
243                          uint64_t Size, uint32_t Link, uint32_t Info,
244                          uint64_t Alignment, uint64_t EntrySize);
245
246    void WriteRelocationsFragment(const MCAssembler &Asm, MCDataFragment *F,
247                                  const MCSectionData *SD);
248
249    void WriteObject(const MCAssembler &Asm, const MCAsmLayout &Layout);
250  };
251
252}
253
254// Emit the ELF header.
255void ELFObjectWriterImpl::WriteHeader(uint64_t SectionDataSize,
256                                      unsigned NumberOfSections) {
257  // ELF Header
258  // ----------
259  //
260  // Note
261  // ----
262  // emitWord method behaves differently for ELF32 and ELF64, writing
263  // 4 bytes in the former and 8 in the latter.
264
265  Write8(0x7f); // e_ident[EI_MAG0]
266  Write8('E');  // e_ident[EI_MAG1]
267  Write8('L');  // e_ident[EI_MAG2]
268  Write8('F');  // e_ident[EI_MAG3]
269
270  Write8(Is64Bit ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
271
272  // e_ident[EI_DATA]
273  Write8(Writer->isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
274
275  Write8(ELF::EV_CURRENT);        // e_ident[EI_VERSION]
276  Write8(ELF::ELFOSABI_LINUX);    // e_ident[EI_OSABI]
277  Write8(0);                  // e_ident[EI_ABIVERSION]
278
279  WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
280
281  Write16(ELF::ET_REL);             // e_type
282
283  // FIXME: Make this configurable
284  Write16(Is64Bit ? ELF::EM_X86_64 : ELF::EM_386); // e_machine = target
285
286  Write32(ELF::EV_CURRENT);         // e_version
287  WriteWord(0);                    // e_entry, no entry point in .o file
288  WriteWord(0);                    // e_phoff, no program header for .o
289  WriteWord(SectionDataSize + (Is64Bit ? sizeof(ELF::Elf64_Ehdr) :
290            sizeof(ELF::Elf32_Ehdr)));  // e_shoff = sec hdr table off in bytes
291
292  // FIXME: Make this configurable.
293  Write32(0);   // e_flags = whatever the target wants
294
295  // e_ehsize = ELF header size
296  Write16(Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
297
298  Write16(0);                  // e_phentsize = prog header entry size
299  Write16(0);                  // e_phnum = # prog header entries = 0
300
301  // e_shentsize = Section header entry size
302  Write16(Is64Bit ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
303
304  // e_shnum     = # of section header ents
305  Write16(NumberOfSections);
306
307  // e_shstrndx  = Section # of '.shstrtab'
308  Write16(ShstrtabIndex);
309}
310
311void ELFObjectWriterImpl::WriteSymbolEntry(MCDataFragment *F, uint64_t name,
312                                           uint8_t info, uint64_t value,
313                                           uint64_t size, uint8_t other,
314                                           uint16_t shndx) {
315  if (Is64Bit) {
316    char buf[8];
317
318    String32(buf, name);
319    F->getContents() += StringRef(buf, 4); // st_name
320
321    String8(buf, info);
322    F->getContents() += StringRef(buf, 1);  // st_info
323
324    String8(buf, other);
325    F->getContents() += StringRef(buf, 1); // st_other
326
327    String16(buf, shndx);
328    F->getContents() += StringRef(buf, 2); // st_shndx
329
330    String64(buf, value);
331    F->getContents() += StringRef(buf, 8); // st_value
332
333    String64(buf, size);
334    F->getContents() += StringRef(buf, 8);  // st_size
335  } else {
336    char buf[4];
337
338    String32(buf, name);
339    F->getContents() += StringRef(buf, 4);  // st_name
340
341    String32(buf, value);
342    F->getContents() += StringRef(buf, 4); // st_value
343
344    String32(buf, size);
345    F->getContents() += StringRef(buf, 4);  // st_size
346
347    String8(buf, info);
348    F->getContents() += StringRef(buf, 1);  // st_info
349
350    String8(buf, other);
351    F->getContents() += StringRef(buf, 1); // st_other
352
353    String16(buf, shndx);
354    F->getContents() += StringRef(buf, 2); // st_shndx
355  }
356}
357
358void ELFObjectWriterImpl::WriteSymbol(MCDataFragment *F, ELFSymbolData &MSD,
359                                      const MCAsmLayout &Layout) {
360  MCSymbolData &Data = *MSD.SymbolData;
361  uint8_t Info = (Data.getFlags() & 0xff);
362  uint8_t Other = ((Data.getFlags() & 0xf00) >> ELF_STV_Shift);
363  uint64_t Value = 0;
364  uint64_t Size = 0;
365  const MCExpr *ESize;
366
367  if (Data.isCommon() && Data.isExternal())
368    Value = Data.getCommonAlignment();
369
370  if (!Data.isCommon())
371    if (MCFragment *FF = Data.getFragment())
372      Value = Layout.getSymbolAddress(&Data) -
373              Layout.getSectionAddress(FF->getParent());
374
375  ESize = Data.getSize();
376  if (Data.getSize()) {
377    MCValue Res;
378    if (ESize->getKind() == MCExpr::Binary) {
379      const MCBinaryExpr *BE = static_cast<const MCBinaryExpr *>(ESize);
380
381      if (BE->EvaluateAsRelocatable(Res, &Layout)) {
382        MCSymbolData &A =
383          Layout.getAssembler().getSymbolData(Res.getSymA()->getSymbol());
384        MCSymbolData &B =
385          Layout.getAssembler().getSymbolData(Res.getSymB()->getSymbol());
386
387        Size = Layout.getSymbolAddress(&A) - Layout.getSymbolAddress(&B);
388      }
389    } else if (ESize->getKind() == MCExpr::Constant) {
390      Size = static_cast<const MCConstantExpr *>(ESize)->getValue();
391    } else {
392      assert(0 && "Unsupported size expression");
393    }
394  }
395
396  // Write out the symbol table entry
397  WriteSymbolEntry(F, MSD.StringIndex, Info, Value,
398                   Size, Other, MSD.SectionIndex);
399}
400
401void ELFObjectWriterImpl::WriteSymbolTable(MCDataFragment *F,
402                                           const MCAssembler &Asm,
403                                           const MCAsmLayout &Layout) {
404  // The string table must be emitted first because we need the index
405  // into the string table for all the symbol names.
406  assert(StringTable.size() && "Missing string table");
407
408  // FIXME: Make sure the start of the symbol table is aligned.
409
410  // The first entry is the undefined symbol entry.
411  unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
412  F->getContents().append(EntrySize, '\x00');
413
414  // Write the symbol table entries.
415  LastLocalSymbolIndex = LocalSymbolData.size() + 1;
416  for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
417    ELFSymbolData &MSD = LocalSymbolData[i];
418    WriteSymbol(F, MSD, Layout);
419  }
420
421  // Write out a symbol table entry for each section.
422  // leaving out the just added .symtab which is at
423  // the very end
424  unsigned Index = 1;
425  for (MCAssembler::const_iterator it = Asm.begin(),
426       ie = Asm.end(); it != ie; ++it, ++Index) {
427    const MCSectionELF &Section =
428      static_cast<const MCSectionELF&>(it->getSection());
429    // Leave out relocations so we don't have indexes within
430    // the relocations messed up
431    if (Section.getType() == ELF::SHT_RELA || Section.getType() == ELF::SHT_REL)
432      continue;
433    if (Index == Asm.size())
434      continue;
435    WriteSymbolEntry(F, 0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT, Index);
436    LastLocalSymbolIndex++;
437  }
438
439  for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
440    ELFSymbolData &MSD = ExternalSymbolData[i];
441    MCSymbolData &Data = *MSD.SymbolData;
442    assert((Data.getFlags() & ELF_STB_Global) &&
443           "External symbol requires STB_GLOBAL flag");
444    WriteSymbol(F, MSD, Layout);
445    if (Data.getFlags() & ELF_STB_Local)
446      LastLocalSymbolIndex++;
447  }
448
449  for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
450    ELFSymbolData &MSD = UndefinedSymbolData[i];
451    MCSymbolData &Data = *MSD.SymbolData;
452    Data.setFlags(Data.getFlags() | ELF_STB_Global);
453    WriteSymbol(F, MSD, Layout);
454    if (Data.getFlags() & ELF_STB_Local)
455      LastLocalSymbolIndex++;
456  }
457}
458
459// FIXME: this is currently X86/X86_64 only
460void ELFObjectWriterImpl::RecordRelocation(const MCAssembler &Asm,
461                                           const MCAsmLayout &Layout,
462                                           const MCFragment *Fragment,
463                                           const MCFixup &Fixup,
464                                           MCValue Target,
465                                           uint64_t &FixedValue) {
466  int64_t Addend = 0;
467  unsigned Index = 0;
468  int64_t Value = Target.getConstant();
469
470  if (!Target.isAbsolute()) {
471    const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
472    MCSymbolData &SD = Asm.getSymbolData(*Symbol);
473    const MCSymbolData *Base = Asm.getAtom(Layout, &SD);
474    MCFragment *F = SD.getFragment();
475
476    if (Base) {
477      if (F && (!Symbol->isInSection() || SD.isCommon()) && !SD.isExternal()) {
478        Index = F->getParent()->getOrdinal() + LocalSymbolData.size() + 1;
479        Value += Layout.getSymbolAddress(&SD);
480      } else
481        Index = getSymbolIndexInSymbolTable(Asm, Symbol);
482      if (Base != &SD)
483        Value += Layout.getSymbolAddress(&SD) - Layout.getSymbolAddress(Base);
484      Addend = Value;
485      // Compensate for the addend on i386.
486      if (Is64Bit)
487        Value = 0;
488    } else {
489      if (F) {
490        // Index of the section in .symtab against this symbol
491        // is being relocated + 2 (empty section + abs. symbols).
492        Index = F->getParent()->getOrdinal() + LocalSymbolData.size() + 1;
493
494        MCSectionData *FSD = F->getParent();
495        // Offset of the symbol in the section
496        Addend = Layout.getSymbolAddress(&SD) - Layout.getSectionAddress(FSD);
497      } else {
498        FixedValue = Value;
499        return;
500      }
501    }
502  }
503
504  FixedValue = Value;
505
506  // determine the type of the relocation
507  bool IsPCRel = isFixupKindX86PCRel(Fixup.getKind());
508  unsigned Type;
509  if (Is64Bit) {
510    if (IsPCRel) {
511      Type = ELF::R_X86_64_PC32;
512    } else {
513      switch ((unsigned)Fixup.getKind()) {
514      default: llvm_unreachable("invalid fixup kind!");
515      case FK_Data_8: Type = ELF::R_X86_64_64; break;
516      case X86::reloc_pcrel_4byte:
517      case FK_Data_4:
518        // check that the offset fits within a signed long
519        if (isInt<32>(Target.getConstant()))
520          Type = ELF::R_X86_64_32S;
521        else
522          Type = ELF::R_X86_64_32;
523        break;
524      case FK_Data_2: Type = ELF::R_X86_64_16; break;
525      case X86::reloc_pcrel_1byte:
526      case FK_Data_1: Type = ELF::R_X86_64_8; break;
527      }
528    }
529  } else {
530    if (IsPCRel) {
531      Type = ELF::R_386_PC32;
532    } else {
533      switch ((unsigned)Fixup.getKind()) {
534      default: llvm_unreachable("invalid fixup kind!");
535      case X86::reloc_pcrel_4byte:
536      case FK_Data_4: Type = ELF::R_386_32; break;
537      case FK_Data_2: Type = ELF::R_386_16; break;
538      case X86::reloc_pcrel_1byte:
539      case FK_Data_1: Type = ELF::R_386_8; break;
540      }
541    }
542  }
543
544  ELFRelocationEntry ERE;
545
546  if (Is64Bit) {
547    struct ELF::Elf64_Rela ERE64;
548    ERE64.setSymbolAndType(Index, Type);
549    ERE.r_info = ERE64.r_info;
550  } else {
551    struct ELF::Elf32_Rela ERE32;
552    ERE32.setSymbolAndType(Index, Type);
553    ERE.r_info = ERE32.r_info;
554  }
555
556  ERE.r_offset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
557
558  if (HasRelocationAddend)
559    ERE.r_addend = Addend;
560  else
561    ERE.r_addend = 0; // Silence compiler warning.
562
563  Relocations[Fragment->getParent()].push_back(ERE);
564}
565
566uint64_t
567ELFObjectWriterImpl::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
568                                                 const MCSymbol *S) {
569  MCSymbolData &SD = Asm.getSymbolData(*S);
570
571  // Local symbol.
572  if (!SD.isExternal() && !S->isUndefined())
573    return SD.getIndex() + /* empty symbol */ 1;
574
575  // External or undefined symbol.
576  return SD.getIndex() + Asm.size() + /* empty symbol */ 1;
577}
578
579void ELFObjectWriterImpl::ComputeSymbolTable(MCAssembler &Asm) {
580  // Build section lookup table.
581  DenseMap<const MCSection*, uint8_t> SectionIndexMap;
582  unsigned Index = 1;
583  for (MCAssembler::iterator it = Asm.begin(),
584         ie = Asm.end(); it != ie; ++it, ++Index)
585    SectionIndexMap[&it->getSection()] = Index;
586
587  // Index 0 is always the empty string.
588  StringMap<uint64_t> StringIndexMap;
589  StringTable += '\x00';
590
591  // Add the data for local symbols.
592  for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
593         ie = Asm.symbol_end(); it != ie; ++it) {
594    const MCSymbol &Symbol = it->getSymbol();
595
596    // Ignore non-linker visible symbols.
597    if (!Asm.isSymbolLinkerVisible(Symbol))
598      continue;
599
600    if (it->isExternal() || Symbol.isUndefined())
601      continue;
602
603    uint64_t &Entry = StringIndexMap[Symbol.getName()];
604    if (!Entry) {
605      Entry = StringTable.size();
606      StringTable += Symbol.getName();
607      StringTable += '\x00';
608    }
609
610    ELFSymbolData MSD;
611    MSD.SymbolData = it;
612    MSD.StringIndex = Entry;
613
614    if (Symbol.isAbsolute()) {
615      MSD.SectionIndex = ELF::SHN_ABS;
616      LocalSymbolData.push_back(MSD);
617    } else {
618      MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
619      assert(MSD.SectionIndex && "Invalid section index!");
620      LocalSymbolData.push_back(MSD);
621    }
622  }
623
624  // Now add non-local symbols.
625  for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
626         ie = Asm.symbol_end(); it != ie; ++it) {
627    const MCSymbol &Symbol = it->getSymbol();
628
629    // Ignore non-linker visible symbols.
630    if (!Asm.isSymbolLinkerVisible(Symbol))
631      continue;
632
633    if (!it->isExternal() && !Symbol.isUndefined())
634      continue;
635
636    uint64_t &Entry = StringIndexMap[Symbol.getName()];
637    if (!Entry) {
638      Entry = StringTable.size();
639      StringTable += Symbol.getName();
640      StringTable += '\x00';
641    }
642
643    ELFSymbolData MSD;
644    MSD.SymbolData = it;
645    MSD.StringIndex = Entry;
646
647    if (Symbol.isUndefined()) {
648      MSD.SectionIndex = ELF::SHN_UNDEF;
649      // XXX: for some reason we dont Emit* this
650      it->setFlags(it->getFlags() | ELF_STB_Global);
651      UndefinedSymbolData.push_back(MSD);
652    } else if (Symbol.isAbsolute()) {
653      MSD.SectionIndex = ELF::SHN_ABS;
654      ExternalSymbolData.push_back(MSD);
655    } else if (it->isCommon()) {
656      MSD.SectionIndex = ELF::SHN_COMMON;
657      ExternalSymbolData.push_back(MSD);
658    } else {
659      MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
660      assert(MSD.SectionIndex && "Invalid section index!");
661      ExternalSymbolData.push_back(MSD);
662    }
663  }
664
665  // Symbols are required to be in lexicographic order.
666  array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
667  array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
668  array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
669
670  // Set the symbol indices. Local symbols must come before all other
671  // symbols with non-local bindings.
672  Index = 0;
673  for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
674    LocalSymbolData[i].SymbolData->setIndex(Index++);
675  for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
676    ExternalSymbolData[i].SymbolData->setIndex(Index++);
677  for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
678    UndefinedSymbolData[i].SymbolData->setIndex(Index++);
679}
680
681void ELFObjectWriterImpl::WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
682                                          const MCSectionData &SD) {
683  if (!Relocations[&SD].empty()) {
684    MCContext &Ctx = Asm.getContext();
685    const MCSection *RelaSection;
686    const MCSectionELF &Section =
687      static_cast<const MCSectionELF&>(SD.getSection());
688
689    const StringRef SectionName = Section.getSectionName();
690    std::string RelaSectionName = HasRelocationAddend ? ".rela" : ".rel";
691    RelaSectionName += SectionName;
692
693    unsigned EntrySize;
694    if (HasRelocationAddend)
695      EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
696    else
697      EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
698
699    RelaSection = Ctx.getELFSection(RelaSectionName, HasRelocationAddend ?
700                                    ELF::SHT_RELA : ELF::SHT_REL, 0,
701                                    SectionKind::getReadOnly(),
702                                    false, EntrySize);
703
704    MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
705    RelaSD.setAlignment(1);
706
707    MCDataFragment *F = new MCDataFragment(&RelaSD);
708
709    WriteRelocationsFragment(Asm, F, &SD);
710
711    Asm.AddSectionToTheEnd(RelaSD, Layout);
712  }
713}
714
715void ELFObjectWriterImpl::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
716                                           uint64_t Flags, uint64_t Address,
717                                           uint64_t Offset, uint64_t Size,
718                                           uint32_t Link, uint32_t Info,
719                                           uint64_t Alignment,
720                                           uint64_t EntrySize) {
721  Write32(Name);        // sh_name: index into string table
722  Write32(Type);        // sh_type
723  WriteWord(Flags);     // sh_flags
724  WriteWord(Address);   // sh_addr
725  WriteWord(Offset);    // sh_offset
726  WriteWord(Size);      // sh_size
727  Write32(Link);        // sh_link
728  Write32(Info);        // sh_info
729  WriteWord(Alignment); // sh_addralign
730  WriteWord(EntrySize); // sh_entsize
731}
732
733void ELFObjectWriterImpl::WriteRelocationsFragment(const MCAssembler &Asm,
734                                                   MCDataFragment *F,
735                                                   const MCSectionData *SD) {
736  std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
737  // sort by the r_offset just like gnu as does
738  array_pod_sort(Relocs.begin(), Relocs.end());
739
740  for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
741    ELFRelocationEntry entry = Relocs[e - i - 1];
742
743    unsigned WordSize = Is64Bit ? 8 : 4;
744    F->getContents() += StringRef((const char *)&entry.r_offset, WordSize);
745    F->getContents() += StringRef((const char *)&entry.r_info, WordSize);
746
747    if (HasRelocationAddend)
748      F->getContents() += StringRef((const char *)&entry.r_addend, WordSize);
749  }
750}
751
752void ELFObjectWriterImpl::CreateMetadataSections(MCAssembler &Asm,
753                                                 MCAsmLayout &Layout) {
754  MCContext &Ctx = Asm.getContext();
755  MCDataFragment *F;
756
757  WriteRelocations(Asm, Layout);
758
759  const MCSection *SymtabSection;
760  unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
761
762  SymtabSection = Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
763                                    SectionKind::getReadOnly(),
764                                    false, EntrySize);
765
766  MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
767
768  SymtabSD.setAlignment(Is64Bit ? 8 : 4);
769
770  F = new MCDataFragment(&SymtabSD);
771
772  // Symbol table
773  WriteSymbolTable(F, Asm, Layout);
774  Asm.AddSectionToTheEnd(SymtabSD, Layout);
775
776  const MCSection *StrtabSection;
777  StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
778                                    SectionKind::getReadOnly(), false);
779
780  MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
781  StrtabSD.setAlignment(1);
782
783  // FIXME: This isn't right. If the sections get rearranged this will
784  // be wrong. We need a proper lookup.
785  StringTableIndex = Asm.size();
786
787  F = new MCDataFragment(&StrtabSD);
788  F->getContents().append(StringTable.begin(), StringTable.end());
789  Asm.AddSectionToTheEnd(StrtabSD, Layout);
790
791  const MCSection *ShstrtabSection;
792  ShstrtabSection = Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
793                                      SectionKind::getReadOnly(), false);
794
795  MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
796  ShstrtabSD.setAlignment(1);
797
798  F = new MCDataFragment(&ShstrtabSD);
799
800  // FIXME: This isn't right. If the sections get rearranged this will
801  // be wrong. We need a proper lookup.
802  ShstrtabIndex = Asm.size();
803
804  // Section header string table.
805  //
806  // The first entry of a string table holds a null character so skip
807  // section 0.
808  uint64_t Index = 1;
809  F->getContents() += '\x00';
810
811  for (MCAssembler::const_iterator it = Asm.begin(),
812         ie = Asm.end(); it != ie; ++it) {
813    const MCSectionELF &Section =
814      static_cast<const MCSectionELF&>(it->getSection());
815
816    // Remember the index into the string table so we can write it
817    // into the sh_name field of the section header table.
818    SectionStringTableIndex[&it->getSection()] = Index;
819
820    Index += Section.getSectionName().size() + 1;
821    F->getContents() += Section.getSectionName();
822    F->getContents() += '\x00';
823  }
824
825  Asm.AddSectionToTheEnd(ShstrtabSD, Layout);
826}
827
828void ELFObjectWriterImpl::WriteObject(const MCAssembler &Asm,
829                                      const MCAsmLayout &Layout) {
830  CreateMetadataSections(const_cast<MCAssembler&>(Asm),
831                         const_cast<MCAsmLayout&>(Layout));
832
833  // Add 1 for the null section.
834  unsigned NumSections = Asm.size() + 1;
835
836  uint64_t SectionDataSize = 0;
837
838  for (MCAssembler::const_iterator it = Asm.begin(),
839         ie = Asm.end(); it != ie; ++it) {
840    const MCSectionData &SD = *it;
841
842    // Get the size of the section in the output file (including padding).
843    uint64_t Size = Layout.getSectionFileSize(&SD);
844    SectionDataSize += Size;
845  }
846
847  // Write out the ELF header ...
848  WriteHeader(SectionDataSize, NumSections);
849  FileOff = Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr);
850
851  // ... then all of the sections ...
852  DenseMap<const MCSection*, uint64_t> SectionOffsetMap;
853
854  DenseMap<const MCSection*, uint8_t> SectionIndexMap;
855
856  unsigned Index = 1;
857  for (MCAssembler::const_iterator it = Asm.begin(),
858         ie = Asm.end(); it != ie; ++it) {
859    // Remember the offset into the file for this section.
860    SectionOffsetMap[&it->getSection()] = FileOff;
861
862    SectionIndexMap[&it->getSection()] = Index++;
863
864    const MCSectionData &SD = *it;
865    FileOff += Layout.getSectionFileSize(&SD);
866
867    Asm.WriteSectionData(it, Layout, Writer);
868  }
869
870  // ... and then the section header table.
871  // Should we align the section header table?
872  //
873  // Null section first.
874  WriteSecHdrEntry(0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
875
876  for (MCAssembler::const_iterator it = Asm.begin(),
877         ie = Asm.end(); it != ie; ++it) {
878    const MCSectionData &SD = *it;
879    const MCSectionELF &Section =
880      static_cast<const MCSectionELF&>(SD.getSection());
881
882    uint64_t sh_link = 0;
883    uint64_t sh_info = 0;
884
885    switch(Section.getType()) {
886    case ELF::SHT_DYNAMIC:
887      sh_link = SectionStringTableIndex[&it->getSection()];
888      sh_info = 0;
889      break;
890
891    case ELF::SHT_REL:
892    case ELF::SHT_RELA: {
893      const MCSection *SymtabSection;
894      const MCSection *InfoSection;
895
896      SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
897                                                     SectionKind::getReadOnly(),
898                                                     false);
899      sh_link = SectionIndexMap[SymtabSection];
900
901      // Remove ".rel" and ".rela" prefixes.
902      unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
903      StringRef SectionName = Section.getSectionName().substr(SecNameLen);
904
905      InfoSection = Asm.getContext().getELFSection(SectionName,
906                                                   ELF::SHT_PROGBITS, 0,
907                                                   SectionKind::getReadOnly(),
908                                                   false);
909      sh_info = SectionIndexMap[InfoSection];
910      break;
911    }
912
913    case ELF::SHT_SYMTAB:
914    case ELF::SHT_DYNSYM:
915      sh_link = StringTableIndex;
916      sh_info = LastLocalSymbolIndex;
917      break;
918
919    case ELF::SHT_PROGBITS:
920    case ELF::SHT_STRTAB:
921    case ELF::SHT_NOBITS:
922      // Nothing to do.
923      break;
924
925    case ELF::SHT_HASH:
926    case ELF::SHT_GROUP:
927    case ELF::SHT_SYMTAB_SHNDX:
928    default:
929      assert(0 && "FIXME: sh_type value not supported!");
930      break;
931    }
932
933    WriteSecHdrEntry(SectionStringTableIndex[&it->getSection()],
934                     Section.getType(), Section.getFlags(),
935                     Layout.getSectionAddress(&SD),
936                     SectionOffsetMap.lookup(&SD.getSection()),
937                     Layout.getSectionSize(&SD), sh_link,
938                     sh_info, SD.getAlignment(),
939                     Section.getEntrySize());
940  }
941}
942
943ELFObjectWriter::ELFObjectWriter(raw_ostream &OS,
944                                 bool Is64Bit,
945                                 bool IsLittleEndian,
946                                 bool HasRelocationAddend)
947  : MCObjectWriter(OS, IsLittleEndian)
948{
949  Impl = new ELFObjectWriterImpl(this, Is64Bit, HasRelocationAddend);
950}
951
952ELFObjectWriter::~ELFObjectWriter() {
953  delete (ELFObjectWriterImpl*) Impl;
954}
955
956void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
957  ((ELFObjectWriterImpl*) Impl)->ExecutePostLayoutBinding(Asm);
958}
959
960void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
961                                       const MCAsmLayout &Layout,
962                                       const MCFragment *Fragment,
963                                       const MCFixup &Fixup, MCValue Target,
964                                       uint64_t &FixedValue) {
965  ((ELFObjectWriterImpl*) Impl)->RecordRelocation(Asm, Layout, Fragment, Fixup,
966                                                  Target, FixedValue);
967}
968
969void ELFObjectWriter::WriteObject(const MCAssembler &Asm,
970                                  const MCAsmLayout &Layout) {
971  ((ELFObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);
972}
973