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/MCELFObjectWriter.h"
15 #include "llvm/ADT/OwningPtr.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/ADT/SmallPtrSet.h"
18 #include "llvm/ADT/SmallString.h"
19 #include "llvm/ADT/StringMap.h"
20 #include "llvm/MC/MCAsmBackend.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/Support/Debug.h"
32 #include "llvm/Support/ELF.h"
33 #include "llvm/Support/ErrorHandling.h"
34 #include <vector>
35 using namespace llvm;
36
37 #undef DEBUG_TYPE
38 #define DEBUG_TYPE "reloc-info"
39
40 namespace {
41 class ELFObjectWriter : public MCObjectWriter {
42 protected:
43
44 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
45 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
46 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
47 static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data,
48 bool Used, bool Renamed);
49 static bool isLocal(const MCSymbolData &Data, bool isSignature,
50 bool isUsedInReloc);
51 static bool IsELFMetaDataSection(const MCSectionData &SD);
52 static uint64_t DataSectionSize(const MCSectionData &SD);
53 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout,
54 const MCSectionData &SD);
55 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout,
56 const MCSectionData &SD);
57
58 void WriteDataSectionData(MCAssembler &Asm,
59 const MCAsmLayout &Layout,
60 const MCSectionELF &Section);
61
62 /*static bool isFixupKindX86RIPRel(unsigned Kind) {
63 return Kind == X86::reloc_riprel_4byte ||
64 Kind == X86::reloc_riprel_4byte_movq_load;
65 }*/
66
67 /// ELFSymbolData - Helper struct for containing some precomputed
68 /// information on symbols.
69 struct ELFSymbolData {
70 MCSymbolData *SymbolData;
71 uint64_t StringIndex;
72 uint32_t SectionIndex;
73
74 // Support lexicographic sorting.
operator <__anonce3554260111::ELFObjectWriter::ELFSymbolData75 bool operator<(const ELFSymbolData &RHS) const {
76 if (MCELF::GetType(*SymbolData) == ELF::STT_FILE)
77 return true;
78 if (MCELF::GetType(*RHS.SymbolData) == ELF::STT_FILE)
79 return false;
80 return SymbolData->getSymbol().getName() <
81 RHS.SymbolData->getSymbol().getName();
82 }
83 };
84
85 /// The target specific ELF writer instance.
86 llvm::OwningPtr<MCELFObjectTargetWriter> TargetObjectWriter;
87
88 SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
89 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
90 DenseMap<const MCSymbol *, const MCSymbol *> Renames;
91
92 llvm::DenseMap<const MCSectionData*,
93 std::vector<ELFRelocationEntry> > Relocations;
94 DenseMap<const MCSection*, uint64_t> SectionStringTableIndex;
95
96 /// @}
97 /// @name Symbol Table Data
98 /// @{
99
100 SmallString<256> StringTable;
101 std::vector<ELFSymbolData> LocalSymbolData;
102 std::vector<ELFSymbolData> ExternalSymbolData;
103 std::vector<ELFSymbolData> UndefinedSymbolData;
104
105 /// @}
106
107 bool NeedsGOT;
108
109 bool NeedsSymtabShndx;
110
111 // This holds the symbol table index of the last local symbol.
112 unsigned LastLocalSymbolIndex;
113 // This holds the .strtab section index.
114 unsigned StringTableIndex;
115 // This holds the .symtab section index.
116 unsigned SymbolTableIndex;
117
118 unsigned ShstrtabIndex;
119
120
121 const MCSymbol *SymbolToReloc(const MCAssembler &Asm,
122 const MCValue &Target,
123 const MCFragment &F,
124 const MCFixup &Fixup,
125 bool IsPCRel) const;
126
127 // TargetObjectWriter wrappers.
ExplicitRelSym(const MCAssembler & Asm,const MCValue & Target,const MCFragment & F,const MCFixup & Fixup,bool IsPCRel) const128 const MCSymbol *ExplicitRelSym(const MCAssembler &Asm,
129 const MCValue &Target,
130 const MCFragment &F,
131 const MCFixup &Fixup,
132 bool IsPCRel) const {
133 return TargetObjectWriter->ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel);
134 }
undefinedExplicitRelSym(const MCValue & Target,const MCFixup & Fixup,bool IsPCRel) const135 const MCSymbol *undefinedExplicitRelSym(const MCValue &Target,
136 const MCFixup &Fixup,
137 bool IsPCRel) const {
138 return TargetObjectWriter->undefinedExplicitRelSym(Target, Fixup,
139 IsPCRel);
140 }
141
is64Bit() const142 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
hasRelocationAddend() const143 bool hasRelocationAddend() const {
144 return TargetObjectWriter->hasRelocationAddend();
145 }
GetRelocType(const MCValue & Target,const MCFixup & Fixup,bool IsPCRel,bool IsRelocWithSymbol,int64_t Addend) const146 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
147 bool IsPCRel, bool IsRelocWithSymbol,
148 int64_t Addend) const {
149 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel,
150 IsRelocWithSymbol, Addend);
151 }
152
153 public:
ELFObjectWriter(MCELFObjectTargetWriter * MOTW,raw_ostream & _OS,bool IsLittleEndian)154 ELFObjectWriter(MCELFObjectTargetWriter *MOTW,
155 raw_ostream &_OS, bool IsLittleEndian)
156 : MCObjectWriter(_OS, IsLittleEndian),
157 TargetObjectWriter(MOTW),
158 NeedsGOT(false), NeedsSymtabShndx(false) {
159 }
160
161 virtual ~ELFObjectWriter();
162
WriteWord(uint64_t W)163 void WriteWord(uint64_t W) {
164 if (is64Bit())
165 Write64(W);
166 else
167 Write32(W);
168 }
169
StringLE16(char * buf,uint16_t Value)170 void StringLE16(char *buf, uint16_t Value) {
171 buf[0] = char(Value >> 0);
172 buf[1] = char(Value >> 8);
173 }
174
StringLE32(char * buf,uint32_t Value)175 void StringLE32(char *buf, uint32_t Value) {
176 StringLE16(buf, uint16_t(Value >> 0));
177 StringLE16(buf + 2, uint16_t(Value >> 16));
178 }
179
StringLE64(char * buf,uint64_t Value)180 void StringLE64(char *buf, uint64_t Value) {
181 StringLE32(buf, uint32_t(Value >> 0));
182 StringLE32(buf + 4, uint32_t(Value >> 32));
183 }
184
StringBE16(char * buf,uint16_t Value)185 void StringBE16(char *buf ,uint16_t Value) {
186 buf[0] = char(Value >> 8);
187 buf[1] = char(Value >> 0);
188 }
189
StringBE32(char * buf,uint32_t Value)190 void StringBE32(char *buf, uint32_t Value) {
191 StringBE16(buf, uint16_t(Value >> 16));
192 StringBE16(buf + 2, uint16_t(Value >> 0));
193 }
194
StringBE64(char * buf,uint64_t Value)195 void StringBE64(char *buf, uint64_t Value) {
196 StringBE32(buf, uint32_t(Value >> 32));
197 StringBE32(buf + 4, uint32_t(Value >> 0));
198 }
199
String8(MCDataFragment & F,uint8_t Value)200 void String8(MCDataFragment &F, uint8_t Value) {
201 char buf[1];
202 buf[0] = Value;
203 F.getContents().append(&buf[0], &buf[1]);
204 }
205
String16(MCDataFragment & F,uint16_t Value)206 void String16(MCDataFragment &F, uint16_t Value) {
207 char buf[2];
208 if (isLittleEndian())
209 StringLE16(buf, Value);
210 else
211 StringBE16(buf, Value);
212 F.getContents().append(&buf[0], &buf[2]);
213 }
214
String32(MCDataFragment & F,uint32_t Value)215 void String32(MCDataFragment &F, uint32_t Value) {
216 char buf[4];
217 if (isLittleEndian())
218 StringLE32(buf, Value);
219 else
220 StringBE32(buf, Value);
221 F.getContents().append(&buf[0], &buf[4]);
222 }
223
String64(MCDataFragment & F,uint64_t Value)224 void String64(MCDataFragment &F, uint64_t Value) {
225 char buf[8];
226 if (isLittleEndian())
227 StringLE64(buf, Value);
228 else
229 StringBE64(buf, Value);
230 F.getContents().append(&buf[0], &buf[8]);
231 }
232
233 void WriteHeader(const MCAssembler &Asm,
234 uint64_t SectionDataSize,
235 unsigned NumberOfSections);
236
237 void WriteSymbolEntry(MCDataFragment *SymtabF,
238 MCDataFragment *ShndxF,
239 uint64_t name, uint8_t info,
240 uint64_t value, uint64_t size,
241 uint8_t other, uint32_t shndx,
242 bool Reserved);
243
244 void WriteSymbol(MCDataFragment *SymtabF, MCDataFragment *ShndxF,
245 ELFSymbolData &MSD,
246 const MCAsmLayout &Layout);
247
248 typedef DenseMap<const MCSectionELF*, uint32_t> SectionIndexMapTy;
249 void WriteSymbolTable(MCDataFragment *SymtabF,
250 MCDataFragment *ShndxF,
251 const MCAssembler &Asm,
252 const MCAsmLayout &Layout,
253 const SectionIndexMapTy &SectionIndexMap);
254
255 virtual void RecordRelocation(const MCAssembler &Asm,
256 const MCAsmLayout &Layout,
257 const MCFragment *Fragment,
258 const MCFixup &Fixup,
259 MCValue Target, uint64_t &FixedValue);
260
261 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
262 const MCSymbol *S);
263
264 // Map from a group section to the signature symbol
265 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
266 // Map from a signature symbol to the group section
267 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
268 // Map from a section to the section with the relocations
269 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy;
270 // Map from a section to its offset
271 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy;
272
273 /// ComputeSymbolTable - Compute the symbol table data
274 ///
275 /// \param Asm - The assembler.
276 /// \param SectionIndexMap - Maps a section to its index.
277 /// \param RevGroupMap - Maps a signature symbol to the group section.
278 /// \param NumRegularSections - Number of non-relocation sections.
279 void ComputeSymbolTable(MCAssembler &Asm,
280 const SectionIndexMapTy &SectionIndexMap,
281 RevGroupMapTy RevGroupMap,
282 unsigned NumRegularSections);
283
284 void ComputeIndexMap(MCAssembler &Asm,
285 SectionIndexMapTy &SectionIndexMap,
286 const RelMapTy &RelMap);
287
288 void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout,
289 RelMapTy &RelMap);
290
291 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
292 const RelMapTy &RelMap);
293
294 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
295 SectionIndexMapTy &SectionIndexMap,
296 const RelMapTy &RelMap);
297
298 // Create the sections that show up in the symbol table. Currently
299 // those are the .note.GNU-stack section and the group sections.
300 void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
301 GroupMapTy &GroupMap,
302 RevGroupMapTy &RevGroupMap,
303 SectionIndexMapTy &SectionIndexMap,
304 const RelMapTy &RelMap);
305
306 virtual void ExecutePostLayoutBinding(MCAssembler &Asm,
307 const MCAsmLayout &Layout);
308
309 void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap,
310 const MCAsmLayout &Layout,
311 const SectionIndexMapTy &SectionIndexMap,
312 const SectionOffsetMapTy &SectionOffsetMap);
313
314 void ComputeSectionOrder(MCAssembler &Asm,
315 std::vector<const MCSectionELF*> &Sections);
316
317 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
318 uint64_t Address, uint64_t Offset,
319 uint64_t Size, uint32_t Link, uint32_t Info,
320 uint64_t Alignment, uint64_t EntrySize);
321
322 void WriteRelocationsFragment(const MCAssembler &Asm,
323 MCDataFragment *F,
324 const MCSectionData *SD);
325
326 virtual bool
327 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
328 const MCSymbolData &DataA,
329 const MCFragment &FB,
330 bool InSet,
331 bool IsPCRel) const;
332
333 virtual void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout);
334 void WriteSection(MCAssembler &Asm,
335 const SectionIndexMapTy &SectionIndexMap,
336 uint32_t GroupSymbolIndex,
337 uint64_t Offset, uint64_t Size, uint64_t Alignment,
338 const MCSectionELF &Section);
339 };
340 }
341
isFixupKindPCRel(const MCAssembler & Asm,unsigned Kind)342 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
343 const MCFixupKindInfo &FKI =
344 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
345
346 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
347 }
348
RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant)349 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
350 switch (Variant) {
351 default:
352 return false;
353 case MCSymbolRefExpr::VK_GOT:
354 case MCSymbolRefExpr::VK_PLT:
355 case MCSymbolRefExpr::VK_GOTPCREL:
356 case MCSymbolRefExpr::VK_GOTOFF:
357 case MCSymbolRefExpr::VK_TPOFF:
358 case MCSymbolRefExpr::VK_TLSGD:
359 case MCSymbolRefExpr::VK_GOTTPOFF:
360 case MCSymbolRefExpr::VK_INDNTPOFF:
361 case MCSymbolRefExpr::VK_NTPOFF:
362 case MCSymbolRefExpr::VK_GOTNTPOFF:
363 case MCSymbolRefExpr::VK_TLSLDM:
364 case MCSymbolRefExpr::VK_DTPOFF:
365 case MCSymbolRefExpr::VK_TLSLD:
366 return true;
367 }
368 }
369
~ELFObjectWriter()370 ELFObjectWriter::~ELFObjectWriter()
371 {}
372
373 // Emit the ELF header.
WriteHeader(const MCAssembler & Asm,uint64_t SectionDataSize,unsigned NumberOfSections)374 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
375 uint64_t SectionDataSize,
376 unsigned NumberOfSections) {
377 // ELF Header
378 // ----------
379 //
380 // Note
381 // ----
382 // emitWord method behaves differently for ELF32 and ELF64, writing
383 // 4 bytes in the former and 8 in the latter.
384
385 Write8(0x7f); // e_ident[EI_MAG0]
386 Write8('E'); // e_ident[EI_MAG1]
387 Write8('L'); // e_ident[EI_MAG2]
388 Write8('F'); // e_ident[EI_MAG3]
389
390 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
391
392 // e_ident[EI_DATA]
393 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
394
395 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
396 // e_ident[EI_OSABI]
397 Write8(TargetObjectWriter->getOSABI());
398 Write8(0); // e_ident[EI_ABIVERSION]
399
400 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
401
402 Write16(ELF::ET_REL); // e_type
403
404 Write16(TargetObjectWriter->getEMachine()); // e_machine = target
405
406 Write32(ELF::EV_CURRENT); // e_version
407 WriteWord(0); // e_entry, no entry point in .o file
408 WriteWord(0); // e_phoff, no program header for .o
409 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
410 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes
411
412 // e_flags = whatever the target wants
413 Write32(Asm.getELFHeaderEFlags());
414
415 // e_ehsize = ELF header size
416 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
417
418 Write16(0); // e_phentsize = prog header entry size
419 Write16(0); // e_phnum = # prog header entries = 0
420
421 // e_shentsize = Section header entry size
422 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
423
424 // e_shnum = # of section header ents
425 if (NumberOfSections >= ELF::SHN_LORESERVE)
426 Write16(ELF::SHN_UNDEF);
427 else
428 Write16(NumberOfSections);
429
430 // e_shstrndx = Section # of '.shstrtab'
431 if (ShstrtabIndex >= ELF::SHN_LORESERVE)
432 Write16(ELF::SHN_XINDEX);
433 else
434 Write16(ShstrtabIndex);
435 }
436
WriteSymbolEntry(MCDataFragment * SymtabF,MCDataFragment * ShndxF,uint64_t name,uint8_t info,uint64_t value,uint64_t size,uint8_t other,uint32_t shndx,bool Reserved)437 void ELFObjectWriter::WriteSymbolEntry(MCDataFragment *SymtabF,
438 MCDataFragment *ShndxF,
439 uint64_t name,
440 uint8_t info, uint64_t value,
441 uint64_t size, uint8_t other,
442 uint32_t shndx,
443 bool Reserved) {
444 if (ShndxF) {
445 if (shndx >= ELF::SHN_LORESERVE && !Reserved)
446 String32(*ShndxF, shndx);
447 else
448 String32(*ShndxF, 0);
449 }
450
451 uint16_t Index = (shndx >= ELF::SHN_LORESERVE && !Reserved) ?
452 uint16_t(ELF::SHN_XINDEX) : shndx;
453
454 if (is64Bit()) {
455 String32(*SymtabF, name); // st_name
456 String8(*SymtabF, info); // st_info
457 String8(*SymtabF, other); // st_other
458 String16(*SymtabF, Index); // st_shndx
459 String64(*SymtabF, value); // st_value
460 String64(*SymtabF, size); // st_size
461 } else {
462 String32(*SymtabF, name); // st_name
463 String32(*SymtabF, value); // st_value
464 String32(*SymtabF, size); // st_size
465 String8(*SymtabF, info); // st_info
466 String8(*SymtabF, other); // st_other
467 String16(*SymtabF, Index); // st_shndx
468 }
469 }
470
SymbolValue(MCSymbolData & Data,const MCAsmLayout & Layout)471 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
472 const MCAsmLayout &Layout) {
473 if (Data.isCommon() && Data.isExternal())
474 return Data.getCommonAlignment();
475
476 const MCSymbol &Symbol = Data.getSymbol();
477
478 if (Symbol.isAbsolute() && Symbol.isVariable()) {
479 if (const MCExpr *Value = Symbol.getVariableValue()) {
480 int64_t IntValue;
481 if (Value->EvaluateAsAbsolute(IntValue, Layout))
482 return (uint64_t)IntValue;
483 }
484 }
485
486 if (!Symbol.isInSection())
487 return 0;
488
489
490 if (Data.getFragment()) {
491 if (Data.getFlags() & ELF_Other_ThumbFunc)
492 return Layout.getSymbolOffset(&Data)+1;
493 else
494 return Layout.getSymbolOffset(&Data);
495 }
496
497 return 0;
498 }
499
ExecutePostLayoutBinding(MCAssembler & Asm,const MCAsmLayout & Layout)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.
504
505 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
506 ie = Asm.symbol_end(); it != ie; ++it) {
507 const MCSymbol &Alias = it->getSymbol();
508 const MCSymbol &Symbol = Alias.AliasedSymbol();
509 MCSymbolData &SD = Asm.getSymbolData(Symbol);
510
511 // Not an alias.
512 if (&Symbol == &Alias)
513 continue;
514
515 StringRef AliasName = Alias.getName();
516 size_t Pos = AliasName.find('@');
517 if (Pos == StringRef::npos)
518 continue;
519
520 // Aliases defined with .symvar copy the binding from the symbol they alias.
521 // This is the first place we are able to copy this information.
522 it->setExternal(SD.isExternal());
523 MCELF::SetBinding(*it, MCELF::GetBinding(SD));
524
525 StringRef Rest = AliasName.substr(Pos);
526 if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
527 continue;
528
529 // FIXME: produce a better error message.
530 if (Symbol.isUndefined() && Rest.startswith("@@") &&
531 !Rest.startswith("@@@"))
532 report_fatal_error("A @@ version cannot be undefined");
533
534 Renames.insert(std::make_pair(&Symbol, &Alias));
535 }
536 }
537
WriteSymbol(MCDataFragment * SymtabF,MCDataFragment * ShndxF,ELFSymbolData & MSD,const MCAsmLayout & Layout)538 void ELFObjectWriter::WriteSymbol(MCDataFragment *SymtabF,
539 MCDataFragment *ShndxF,
540 ELFSymbolData &MSD,
541 const MCAsmLayout &Layout) {
542 MCSymbolData &OrigData = *MSD.SymbolData;
543 MCSymbolData &Data =
544 Layout.getAssembler().getSymbolData(OrigData.getSymbol().AliasedSymbol());
545
546 bool IsReserved = Data.isCommon() || Data.getSymbol().isAbsolute() ||
547 Data.getSymbol().isVariable();
548
549 // Binding and Type share the same byte as upper and lower nibbles
550 uint8_t Binding = MCELF::GetBinding(OrigData);
551 uint8_t Type = MCELF::GetType(Data);
552 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
553
554 // Other and Visibility share the same byte with Visability using the lower
555 // 2 bits
556 uint8_t Visibility = MCELF::GetVisibility(OrigData);
557 uint8_t Other = MCELF::getOther(OrigData) <<
558 (ELF_Other_Shift - ELF_STV_Shift);
559 Other |= Visibility;
560
561 uint64_t Value = SymbolValue(Data, Layout);
562 uint64_t Size = 0;
563
564 assert(!(Data.isCommon() && !Data.isExternal()));
565
566 const MCExpr *ESize = Data.getSize();
567 if (ESize) {
568 int64_t Res;
569 if (!ESize->EvaluateAsAbsolute(Res, Layout))
570 report_fatal_error("Size expression must be absolute.");
571 Size = Res;
572 }
573
574 // Write out the symbol table entry
575 WriteSymbolEntry(SymtabF, ShndxF, MSD.StringIndex, Info, Value,
576 Size, Other, MSD.SectionIndex, IsReserved);
577 }
578
WriteSymbolTable(MCDataFragment * SymtabF,MCDataFragment * ShndxF,const MCAssembler & Asm,const MCAsmLayout & Layout,const SectionIndexMapTy & SectionIndexMap)579 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
580 MCDataFragment *ShndxF,
581 const MCAssembler &Asm,
582 const MCAsmLayout &Layout,
583 const SectionIndexMapTy &SectionIndexMap) {
584 // The string table must be emitted first because we need the index
585 // into the string table for all the symbol names.
586 assert(StringTable.size() && "Missing string table");
587
588 // FIXME: Make sure the start of the symbol table is aligned.
589
590 // The first entry is the undefined symbol entry.
591 WriteSymbolEntry(SymtabF, ShndxF, 0, 0, 0, 0, 0, 0, false);
592
593 // Write the symbol table entries.
594 LastLocalSymbolIndex = LocalSymbolData.size() + 1;
595 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
596 ELFSymbolData &MSD = LocalSymbolData[i];
597 WriteSymbol(SymtabF, ShndxF, MSD, Layout);
598 }
599
600 // Write out a symbol table entry for each regular section.
601 for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e;
602 ++i) {
603 const MCSectionELF &Section =
604 static_cast<const MCSectionELF&>(i->getSection());
605 if (Section.getType() == ELF::SHT_RELA ||
606 Section.getType() == ELF::SHT_REL ||
607 Section.getType() == ELF::SHT_STRTAB ||
608 Section.getType() == ELF::SHT_SYMTAB ||
609 Section.getType() == ELF::SHT_SYMTAB_SHNDX)
610 continue;
611 WriteSymbolEntry(SymtabF, ShndxF, 0, ELF::STT_SECTION, 0, 0,
612 ELF::STV_DEFAULT, SectionIndexMap.lookup(&Section),
613 false);
614 LastLocalSymbolIndex++;
615 }
616
617 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
618 ELFSymbolData &MSD = ExternalSymbolData[i];
619 MCSymbolData &Data = *MSD.SymbolData;
620 assert(((Data.getFlags() & ELF_STB_Global) ||
621 (Data.getFlags() & ELF_STB_Weak)) &&
622 "External symbol requires STB_GLOBAL or STB_WEAK flag");
623 WriteSymbol(SymtabF, ShndxF, MSD, Layout);
624 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
625 LastLocalSymbolIndex++;
626 }
627
628 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
629 ELFSymbolData &MSD = UndefinedSymbolData[i];
630 MCSymbolData &Data = *MSD.SymbolData;
631 WriteSymbol(SymtabF, ShndxF, MSD, Layout);
632 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
633 LastLocalSymbolIndex++;
634 }
635 }
636
SymbolToReloc(const MCAssembler & Asm,const MCValue & Target,const MCFragment & F,const MCFixup & Fixup,bool IsPCRel) const637 const MCSymbol *ELFObjectWriter::SymbolToReloc(const MCAssembler &Asm,
638 const MCValue &Target,
639 const MCFragment &F,
640 const MCFixup &Fixup,
641 bool IsPCRel) const {
642 const MCSymbol &Symbol = Target.getSymA()->getSymbol();
643 const MCSymbol &ASymbol = Symbol.AliasedSymbol();
644 const MCSymbol *Renamed = Renames.lookup(&Symbol);
645 const MCSymbolData &SD = Asm.getSymbolData(Symbol);
646
647 if (ASymbol.isUndefined()) {
648 if (Renamed)
649 return Renamed;
650 return undefinedExplicitRelSym(Target, Fixup, IsPCRel);
651 }
652
653 if (SD.isExternal()) {
654 if (Renamed)
655 return Renamed;
656 return &Symbol;
657 }
658
659 const MCSectionELF &Section =
660 static_cast<const MCSectionELF&>(ASymbol.getSection());
661 const SectionKind secKind = Section.getKind();
662
663 if (secKind.isBSS())
664 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel);
665
666 if (secKind.isThreadLocal()) {
667 if (Renamed)
668 return Renamed;
669 return &Symbol;
670 }
671
672 MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind();
673 const MCSectionELF &Sec2 =
674 static_cast<const MCSectionELF&>(F.getParent()->getSection());
675
676 if (&Sec2 != &Section &&
677 (Kind == MCSymbolRefExpr::VK_PLT ||
678 Kind == MCSymbolRefExpr::VK_GOTPCREL ||
679 Kind == MCSymbolRefExpr::VK_GOTOFF)) {
680 if (Renamed)
681 return Renamed;
682 return &Symbol;
683 }
684
685 if (Section.getFlags() & ELF::SHF_MERGE) {
686 if (Target.getConstant() == 0)
687 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel);
688 if (Renamed)
689 return Renamed;
690 return &Symbol;
691 }
692
693 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel);
694
695 }
696
697
RecordRelocation(const MCAssembler & Asm,const MCAsmLayout & Layout,const MCFragment * Fragment,const MCFixup & Fixup,MCValue Target,uint64_t & FixedValue)698 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
699 const MCAsmLayout &Layout,
700 const MCFragment *Fragment,
701 const MCFixup &Fixup,
702 MCValue Target,
703 uint64_t &FixedValue) {
704 int64_t Addend = 0;
705 int Index = 0;
706 int64_t Value = Target.getConstant();
707 const MCSymbol *RelocSymbol = NULL;
708
709 bool IsPCRel = isFixupKindPCRel(Asm, Fixup.getKind());
710 if (!Target.isAbsolute()) {
711 const MCSymbol &Symbol = Target.getSymA()->getSymbol();
712 const MCSymbol &ASymbol = Symbol.AliasedSymbol();
713 RelocSymbol = SymbolToReloc(Asm, Target, *Fragment, Fixup, IsPCRel);
714
715 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
716 const MCSymbol &SymbolB = RefB->getSymbol();
717 MCSymbolData &SDB = Asm.getSymbolData(SymbolB);
718 IsPCRel = true;
719
720 // Offset of the symbol in the section
721 int64_t a = Layout.getSymbolOffset(&SDB);
722
723 // Offset of the relocation in the section
724 int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
725 Value += b - a;
726 }
727
728 if (!RelocSymbol) {
729 MCSymbolData &SD = Asm.getSymbolData(ASymbol);
730 MCFragment *F = SD.getFragment();
731
732 if (F) {
733 Index = F->getParent()->getOrdinal() + 1;
734 // Offset of the symbol in the section
735 Value += Layout.getSymbolOffset(&SD);
736 } else {
737 Index = 0;
738 }
739 } else {
740 if (Asm.getSymbolData(Symbol).getFlags() & ELF_Other_Weakref)
741 WeakrefUsedInReloc.insert(RelocSymbol);
742 else
743 UsedInReloc.insert(RelocSymbol);
744 Index = -1;
745 }
746 Addend = Value;
747 if (hasRelocationAddend())
748 Value = 0;
749 }
750
751 FixedValue = Value;
752 unsigned Type = GetRelocType(Target, Fixup, IsPCRel,
753 (RelocSymbol != 0), Addend);
754 MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ?
755 MCSymbolRefExpr::VK_None : Target.getSymA()->getKind();
756 if (RelocNeedsGOT(Modifier))
757 NeedsGOT = true;
758
759 uint64_t RelocOffset = Layout.getFragmentOffset(Fragment) +
760 Fixup.getOffset();
761
762 if (!hasRelocationAddend())
763 Addend = 0;
764
765 if (is64Bit())
766 assert(isInt<64>(Addend));
767 else
768 assert(isInt<32>(Addend));
769
770 ELFRelocationEntry ERE(RelocOffset, Index, Type, RelocSymbol, Addend, Fixup);
771 Relocations[Fragment->getParent()].push_back(ERE);
772 }
773
774
775 uint64_t
getSymbolIndexInSymbolTable(const MCAssembler & Asm,const MCSymbol * S)776 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
777 const MCSymbol *S) {
778 MCSymbolData &SD = Asm.getSymbolData(*S);
779 return SD.getIndex();
780 }
781
isInSymtab(const MCAssembler & Asm,const MCSymbolData & Data,bool Used,bool Renamed)782 bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm,
783 const MCSymbolData &Data,
784 bool Used, bool Renamed) {
785 if (Data.getFlags() & ELF_Other_Weakref)
786 return false;
787
788 if (Used)
789 return true;
790
791 if (Renamed)
792 return false;
793
794 const MCSymbol &Symbol = Data.getSymbol();
795
796 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
797 return true;
798
799 const MCSymbol &A = Symbol.AliasedSymbol();
800 if (Symbol.isVariable() && !A.isVariable() && A.isUndefined())
801 return false;
802
803 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
804 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
805 return false;
806
807 if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined())
808 return false;
809
810 if (Symbol.isTemporary())
811 return false;
812
813 return true;
814 }
815
isLocal(const MCSymbolData & Data,bool isSignature,bool isUsedInReloc)816 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature,
817 bool isUsedInReloc) {
818 if (Data.isExternal())
819 return false;
820
821 const MCSymbol &Symbol = Data.getSymbol();
822 const MCSymbol &RefSymbol = Symbol.AliasedSymbol();
823
824 if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) {
825 if (isSignature && !isUsedInReloc)
826 return true;
827
828 return false;
829 }
830
831 return true;
832 }
833
ComputeIndexMap(MCAssembler & Asm,SectionIndexMapTy & SectionIndexMap,const RelMapTy & RelMap)834 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
835 SectionIndexMapTy &SectionIndexMap,
836 const RelMapTy &RelMap) {
837 unsigned Index = 1;
838 for (MCAssembler::iterator it = Asm.begin(),
839 ie = Asm.end(); it != ie; ++it) {
840 const MCSectionELF &Section =
841 static_cast<const MCSectionELF &>(it->getSection());
842 if (Section.getType() != ELF::SHT_GROUP)
843 continue;
844 SectionIndexMap[&Section] = Index++;
845 }
846
847 for (MCAssembler::iterator it = Asm.begin(),
848 ie = Asm.end(); it != ie; ++it) {
849 const MCSectionELF &Section =
850 static_cast<const MCSectionELF &>(it->getSection());
851 if (Section.getType() == ELF::SHT_GROUP ||
852 Section.getType() == ELF::SHT_REL ||
853 Section.getType() == ELF::SHT_RELA)
854 continue;
855 SectionIndexMap[&Section] = Index++;
856 const MCSectionELF *RelSection = RelMap.lookup(&Section);
857 if (RelSection)
858 SectionIndexMap[RelSection] = Index++;
859 }
860 }
861
ComputeSymbolTable(MCAssembler & Asm,const SectionIndexMapTy & SectionIndexMap,RevGroupMapTy RevGroupMap,unsigned NumRegularSections)862 void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm,
863 const SectionIndexMapTy &SectionIndexMap,
864 RevGroupMapTy RevGroupMap,
865 unsigned NumRegularSections) {
866 // FIXME: Is this the correct place to do this?
867 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
868 if (NeedsGOT) {
869 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
870 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
871 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
872 Data.setExternal(true);
873 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
874 }
875
876 // Index 0 is always the empty string.
877 StringMap<uint64_t> StringIndexMap;
878 StringTable += '\x00';
879
880 // FIXME: We could optimize suffixes in strtab in the same way we
881 // optimize them in shstrtab.
882
883 // Add the data for the symbols.
884 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
885 ie = Asm.symbol_end(); it != ie; ++it) {
886 const MCSymbol &Symbol = it->getSymbol();
887
888 bool Used = UsedInReloc.count(&Symbol);
889 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
890 bool isSignature = RevGroupMap.count(&Symbol);
891
892 if (!isInSymtab(Asm, *it,
893 Used || WeakrefUsed || isSignature,
894 Renames.count(&Symbol)))
895 continue;
896
897 ELFSymbolData MSD;
898 MSD.SymbolData = it;
899 const MCSymbol &RefSymbol = Symbol.AliasedSymbol();
900
901 // Undefined symbols are global, but this is the first place we
902 // are able to set it.
903 bool Local = isLocal(*it, isSignature, Used);
904 if (!Local && MCELF::GetBinding(*it) == ELF::STB_LOCAL) {
905 MCSymbolData &SD = Asm.getSymbolData(RefSymbol);
906 MCELF::SetBinding(*it, ELF::STB_GLOBAL);
907 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
908 }
909
910 if (RefSymbol.isUndefined() && !Used && WeakrefUsed)
911 MCELF::SetBinding(*it, ELF::STB_WEAK);
912
913 if (it->isCommon()) {
914 assert(!Local);
915 MSD.SectionIndex = ELF::SHN_COMMON;
916 } else if (Symbol.isAbsolute() || RefSymbol.isVariable()) {
917 MSD.SectionIndex = ELF::SHN_ABS;
918 } else if (RefSymbol.isUndefined()) {
919 if (isSignature && !Used)
920 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]);
921 else
922 MSD.SectionIndex = ELF::SHN_UNDEF;
923 } else {
924 const MCSectionELF &Section =
925 static_cast<const MCSectionELF&>(RefSymbol.getSection());
926 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
927 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
928 NeedsSymtabShndx = true;
929 assert(MSD.SectionIndex && "Invalid section index!");
930 }
931
932 // The @@@ in symbol version is replaced with @ in undefined symbols and
933 // @@ in defined ones.
934 StringRef Name = Symbol.getName();
935 SmallString<32> Buf;
936
937 size_t Pos = Name.find("@@@");
938 if (Pos != StringRef::npos) {
939 Buf += Name.substr(0, Pos);
940 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
941 Buf += Name.substr(Pos + Skip);
942 Name = Buf;
943 }
944
945 uint64_t &Entry = StringIndexMap[Name];
946 if (!Entry) {
947 Entry = StringTable.size();
948 StringTable += Name;
949 StringTable += '\x00';
950 }
951 MSD.StringIndex = Entry;
952 if (MSD.SectionIndex == ELF::SHN_UNDEF)
953 UndefinedSymbolData.push_back(MSD);
954 else if (Local)
955 LocalSymbolData.push_back(MSD);
956 else
957 ExternalSymbolData.push_back(MSD);
958 }
959
960 // Symbols are required to be in lexicographic order.
961 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
962 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
963 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
964
965 // Set the symbol indices. Local symbols must come before all other
966 // symbols with non-local bindings.
967 unsigned Index = 1;
968 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
969 LocalSymbolData[i].SymbolData->setIndex(Index++);
970
971 Index += NumRegularSections;
972
973 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
974 ExternalSymbolData[i].SymbolData->setIndex(Index++);
975 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
976 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
977
978 if (Index >= ELF::SHN_LORESERVE)
979 NeedsSymtabShndx = true;
980 }
981
CreateRelocationSections(MCAssembler & Asm,MCAsmLayout & Layout,RelMapTy & RelMap)982 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm,
983 MCAsmLayout &Layout,
984 RelMapTy &RelMap) {
985 for (MCAssembler::const_iterator it = Asm.begin(),
986 ie = Asm.end(); it != ie; ++it) {
987 const MCSectionData &SD = *it;
988 if (Relocations[&SD].empty())
989 continue;
990
991 MCContext &Ctx = Asm.getContext();
992 const MCSectionELF &Section =
993 static_cast<const MCSectionELF&>(SD.getSection());
994
995 const StringRef SectionName = Section.getSectionName();
996 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
997 RelaSectionName += SectionName;
998
999 unsigned EntrySize;
1000 if (hasRelocationAddend())
1001 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1002 else
1003 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1004
1005 unsigned Flags = 0;
1006 StringRef Group = "";
1007 if (Section.getFlags() & ELF::SHF_GROUP) {
1008 Flags = ELF::SHF_GROUP;
1009 Group = Section.getGroup()->getName();
1010 }
1011
1012 const MCSectionELF *RelaSection =
1013 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ?
1014 ELF::SHT_RELA : ELF::SHT_REL, Flags,
1015 SectionKind::getReadOnly(),
1016 EntrySize, Group);
1017 RelMap[&Section] = RelaSection;
1018 Asm.getOrCreateSectionData(*RelaSection);
1019 }
1020 }
1021
WriteRelocations(MCAssembler & Asm,MCAsmLayout & Layout,const RelMapTy & RelMap)1022 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
1023 const RelMapTy &RelMap) {
1024 for (MCAssembler::const_iterator it = Asm.begin(),
1025 ie = Asm.end(); it != ie; ++it) {
1026 const MCSectionData &SD = *it;
1027 const MCSectionELF &Section =
1028 static_cast<const MCSectionELF&>(SD.getSection());
1029
1030 const MCSectionELF *RelaSection = RelMap.lookup(&Section);
1031 if (!RelaSection)
1032 continue;
1033 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
1034 RelaSD.setAlignment(is64Bit() ? 8 : 4);
1035
1036 MCDataFragment *F = new MCDataFragment(&RelaSD);
1037 WriteRelocationsFragment(Asm, F, &*it);
1038 }
1039 }
1040
WriteSecHdrEntry(uint32_t Name,uint32_t Type,uint64_t Flags,uint64_t Address,uint64_t Offset,uint64_t Size,uint32_t Link,uint32_t Info,uint64_t Alignment,uint64_t EntrySize)1041 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1042 uint64_t Flags, uint64_t Address,
1043 uint64_t Offset, uint64_t Size,
1044 uint32_t Link, uint32_t Info,
1045 uint64_t Alignment,
1046 uint64_t EntrySize) {
1047 Write32(Name); // sh_name: index into string table
1048 Write32(Type); // sh_type
1049 WriteWord(Flags); // sh_flags
1050 WriteWord(Address); // sh_addr
1051 WriteWord(Offset); // sh_offset
1052 WriteWord(Size); // sh_size
1053 Write32(Link); // sh_link
1054 Write32(Info); // sh_info
1055 WriteWord(Alignment); // sh_addralign
1056 WriteWord(EntrySize); // sh_entsize
1057 }
1058
WriteRelocationsFragment(const MCAssembler & Asm,MCDataFragment * F,const MCSectionData * SD)1059 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1060 MCDataFragment *F,
1061 const MCSectionData *SD) {
1062 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1063
1064 // Sort the relocation entries. Most targets just sort by r_offset, but some
1065 // (e.g., MIPS) have additional constraints.
1066 TargetObjectWriter->sortRelocs(Asm, Relocs);
1067
1068 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1069 ELFRelocationEntry entry = Relocs[e - i - 1];
1070
1071 if (!entry.Index)
1072 ;
1073 else if (entry.Index < 0)
1074 entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol);
1075 else
1076 entry.Index += LocalSymbolData.size();
1077 if (is64Bit()) {
1078 String64(*F, entry.r_offset);
1079 if (TargetObjectWriter->isN64()) {
1080 String32(*F, entry.Index);
1081
1082 String8(*F, TargetObjectWriter->getRSsym(entry.Type));
1083 String8(*F, TargetObjectWriter->getRType3(entry.Type));
1084 String8(*F, TargetObjectWriter->getRType2(entry.Type));
1085 String8(*F, TargetObjectWriter->getRType(entry.Type));
1086 }
1087 else {
1088 struct ELF::Elf64_Rela ERE64;
1089 ERE64.setSymbolAndType(entry.Index, entry.Type);
1090 String64(*F, ERE64.r_info);
1091 }
1092 if (hasRelocationAddend())
1093 String64(*F, entry.r_addend);
1094 } else {
1095 String32(*F, entry.r_offset);
1096
1097 struct ELF::Elf32_Rela ERE32;
1098 ERE32.setSymbolAndType(entry.Index, entry.Type);
1099 String32(*F, ERE32.r_info);
1100
1101 if (hasRelocationAddend())
1102 String32(*F, entry.r_addend);
1103 }
1104 }
1105 }
1106
compareBySuffix(const void * a,const void * b)1107 static int compareBySuffix(const void *a, const void *b) {
1108 const MCSectionELF *secA = *static_cast<const MCSectionELF* const *>(a);
1109 const MCSectionELF *secB = *static_cast<const MCSectionELF* const *>(b);
1110 const StringRef &NameA = secA->getSectionName();
1111 const StringRef &NameB = secB->getSectionName();
1112 const unsigned sizeA = NameA.size();
1113 const unsigned sizeB = NameB.size();
1114 const unsigned len = std::min(sizeA, sizeB);
1115 for (unsigned int i = 0; i < len; ++i) {
1116 char ca = NameA[sizeA - i - 1];
1117 char cb = NameB[sizeB - i - 1];
1118 if (ca != cb)
1119 return cb - ca;
1120 }
1121
1122 return sizeB - sizeA;
1123 }
1124
CreateMetadataSections(MCAssembler & Asm,MCAsmLayout & Layout,SectionIndexMapTy & SectionIndexMap,const RelMapTy & RelMap)1125 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
1126 MCAsmLayout &Layout,
1127 SectionIndexMapTy &SectionIndexMap,
1128 const RelMapTy &RelMap) {
1129 MCContext &Ctx = Asm.getContext();
1130 MCDataFragment *F;
1131
1132 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1133
1134 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1135 const MCSectionELF *ShstrtabSection =
1136 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
1137 SectionKind::getReadOnly());
1138 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1139 ShstrtabSD.setAlignment(1);
1140
1141 const MCSectionELF *SymtabSection =
1142 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1143 SectionKind::getReadOnly(),
1144 EntrySize, "");
1145 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1146 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1147
1148 MCSectionData *SymtabShndxSD = NULL;
1149
1150 if (NeedsSymtabShndx) {
1151 const MCSectionELF *SymtabShndxSection =
1152 Ctx.getELFSection(".symtab_shndx", ELF::SHT_SYMTAB_SHNDX, 0,
1153 SectionKind::getReadOnly(), 4, "");
1154 SymtabShndxSD = &Asm.getOrCreateSectionData(*SymtabShndxSection);
1155 SymtabShndxSD->setAlignment(4);
1156 }
1157
1158 const MCSectionELF *StrtabSection;
1159 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
1160 SectionKind::getReadOnly());
1161 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1162 StrtabSD.setAlignment(1);
1163
1164 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1165
1166 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection);
1167 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection);
1168 StringTableIndex = SectionIndexMap.lookup(StrtabSection);
1169
1170 // Symbol table
1171 F = new MCDataFragment(&SymtabSD);
1172 MCDataFragment *ShndxF = NULL;
1173 if (NeedsSymtabShndx) {
1174 ShndxF = new MCDataFragment(SymtabShndxSD);
1175 }
1176 WriteSymbolTable(F, ShndxF, Asm, Layout, SectionIndexMap);
1177
1178 F = new MCDataFragment(&StrtabSD);
1179 F->getContents().append(StringTable.begin(), StringTable.end());
1180
1181 F = new MCDataFragment(&ShstrtabSD);
1182
1183 std::vector<const MCSectionELF*> Sections;
1184 for (MCAssembler::const_iterator it = Asm.begin(),
1185 ie = Asm.end(); it != ie; ++it) {
1186 const MCSectionELF &Section =
1187 static_cast<const MCSectionELF&>(it->getSection());
1188 Sections.push_back(&Section);
1189 }
1190 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix);
1191
1192 // Section header string table.
1193 //
1194 // The first entry of a string table holds a null character so skip
1195 // section 0.
1196 uint64_t Index = 1;
1197 F->getContents().push_back('\x00');
1198
1199 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) {
1200 const MCSectionELF &Section = *Sections[I];
1201
1202 StringRef Name = Section.getSectionName();
1203 if (I != 0) {
1204 StringRef PreviousName = Sections[I - 1]->getSectionName();
1205 if (PreviousName.endswith(Name)) {
1206 SectionStringTableIndex[&Section] = Index - Name.size() - 1;
1207 continue;
1208 }
1209 }
1210 // Remember the index into the string table so we can write it
1211 // into the sh_name field of the section header table.
1212 SectionStringTableIndex[&Section] = Index;
1213
1214 Index += Name.size() + 1;
1215 F->getContents().append(Name.begin(), Name.end());
1216 F->getContents().push_back('\x00');
1217 }
1218 }
1219
CreateIndexedSections(MCAssembler & Asm,MCAsmLayout & Layout,GroupMapTy & GroupMap,RevGroupMapTy & RevGroupMap,SectionIndexMapTy & SectionIndexMap,const RelMapTy & RelMap)1220 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
1221 MCAsmLayout &Layout,
1222 GroupMapTy &GroupMap,
1223 RevGroupMapTy &RevGroupMap,
1224 SectionIndexMapTy &SectionIndexMap,
1225 const RelMapTy &RelMap) {
1226 // Create the .note.GNU-stack section if needed.
1227 MCContext &Ctx = Asm.getContext();
1228 if (Asm.getNoExecStack()) {
1229 const MCSectionELF *GnuStackSection =
1230 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0,
1231 SectionKind::getReadOnly());
1232 Asm.getOrCreateSectionData(*GnuStackSection);
1233 }
1234
1235 // Build the groups
1236 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1237 it != ie; ++it) {
1238 const MCSectionELF &Section =
1239 static_cast<const MCSectionELF&>(it->getSection());
1240 if (!(Section.getFlags() & ELF::SHF_GROUP))
1241 continue;
1242
1243 const MCSymbol *SignatureSymbol = Section.getGroup();
1244 Asm.getOrCreateSymbolData(*SignatureSymbol);
1245 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1246 if (!Group) {
1247 Group = Ctx.CreateELFGroupSection();
1248 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1249 Data.setAlignment(4);
1250 MCDataFragment *F = new MCDataFragment(&Data);
1251 String32(*F, ELF::GRP_COMDAT);
1252 }
1253 GroupMap[Group] = SignatureSymbol;
1254 }
1255
1256 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1257
1258 // Add sections to the groups
1259 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1260 it != ie; ++it) {
1261 const MCSectionELF &Section =
1262 static_cast<const MCSectionELF&>(it->getSection());
1263 if (!(Section.getFlags() & ELF::SHF_GROUP))
1264 continue;
1265 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1266 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1267 // FIXME: we could use the previous fragment
1268 MCDataFragment *F = new MCDataFragment(&Data);
1269 unsigned Index = SectionIndexMap.lookup(&Section);
1270 String32(*F, Index);
1271 }
1272 }
1273
WriteSection(MCAssembler & Asm,const SectionIndexMapTy & SectionIndexMap,uint32_t GroupSymbolIndex,uint64_t Offset,uint64_t Size,uint64_t Alignment,const MCSectionELF & Section)1274 void ELFObjectWriter::WriteSection(MCAssembler &Asm,
1275 const SectionIndexMapTy &SectionIndexMap,
1276 uint32_t GroupSymbolIndex,
1277 uint64_t Offset, uint64_t Size,
1278 uint64_t Alignment,
1279 const MCSectionELF &Section) {
1280 uint64_t sh_link = 0;
1281 uint64_t sh_info = 0;
1282
1283 switch(Section.getType()) {
1284 case ELF::SHT_DYNAMIC:
1285 sh_link = SectionStringTableIndex[&Section];
1286 sh_info = 0;
1287 break;
1288
1289 case ELF::SHT_REL:
1290 case ELF::SHT_RELA: {
1291 const MCSectionELF *SymtabSection;
1292 const MCSectionELF *InfoSection;
1293 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB,
1294 0,
1295 SectionKind::getReadOnly());
1296 sh_link = SectionIndexMap.lookup(SymtabSection);
1297 assert(sh_link && ".symtab not found");
1298
1299 // Remove ".rel" and ".rela" prefixes.
1300 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1301 StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1302
1303 InfoSection = Asm.getContext().getELFSection(SectionName,
1304 ELF::SHT_PROGBITS, 0,
1305 SectionKind::getReadOnly());
1306 sh_info = SectionIndexMap.lookup(InfoSection);
1307 break;
1308 }
1309
1310 case ELF::SHT_SYMTAB:
1311 case ELF::SHT_DYNSYM:
1312 sh_link = StringTableIndex;
1313 sh_info = LastLocalSymbolIndex;
1314 break;
1315
1316 case ELF::SHT_SYMTAB_SHNDX:
1317 sh_link = SymbolTableIndex;
1318 break;
1319
1320 case ELF::SHT_PROGBITS:
1321 case ELF::SHT_STRTAB:
1322 case ELF::SHT_NOBITS:
1323 case ELF::SHT_NOTE:
1324 case ELF::SHT_NULL:
1325 case ELF::SHT_ARM_ATTRIBUTES:
1326 case ELF::SHT_INIT_ARRAY:
1327 case ELF::SHT_FINI_ARRAY:
1328 case ELF::SHT_PREINIT_ARRAY:
1329 case ELF::SHT_X86_64_UNWIND:
1330 case ELF::SHT_MIPS_REGINFO:
1331 case ELF::SHT_MIPS_OPTIONS:
1332 // Nothing to do.
1333 break;
1334
1335 case ELF::SHT_GROUP:
1336 sh_link = SymbolTableIndex;
1337 sh_info = GroupSymbolIndex;
1338 break;
1339
1340 default:
1341 assert(0 && "FIXME: sh_type value not supported!");
1342 break;
1343 }
1344
1345 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1346 Section.getType() == ELF::SHT_ARM_EXIDX) {
1347 StringRef SecName(Section.getSectionName());
1348 if (SecName == ".ARM.exidx") {
1349 sh_link = SectionIndexMap.lookup(
1350 Asm.getContext().getELFSection(".text",
1351 ELF::SHT_PROGBITS,
1352 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
1353 SectionKind::getText()));
1354 } else if (SecName.startswith(".ARM.exidx")) {
1355 sh_link = SectionIndexMap.lookup(
1356 Asm.getContext().getELFSection(SecName.substr(sizeof(".ARM.exidx") - 1),
1357 ELF::SHT_PROGBITS,
1358 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
1359 SectionKind::getText()));
1360 }
1361 }
1362
1363 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(),
1364 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1365 Alignment, Section.getEntrySize());
1366 }
1367
IsELFMetaDataSection(const MCSectionData & SD)1368 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1369 return SD.getOrdinal() == ~UINT32_C(0) &&
1370 !SD.getSection().isVirtualSection();
1371 }
1372
DataSectionSize(const MCSectionData & SD)1373 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1374 uint64_t Ret = 0;
1375 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1376 ++i) {
1377 const MCFragment &F = *i;
1378 assert(F.getKind() == MCFragment::FT_Data);
1379 Ret += cast<MCDataFragment>(F).getContents().size();
1380 }
1381 return Ret;
1382 }
1383
GetSectionFileSize(const MCAsmLayout & Layout,const MCSectionData & SD)1384 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
1385 const MCSectionData &SD) {
1386 if (IsELFMetaDataSection(SD))
1387 return DataSectionSize(SD);
1388 return Layout.getSectionFileSize(&SD);
1389 }
1390
GetSectionAddressSize(const MCAsmLayout & Layout,const MCSectionData & SD)1391 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1392 const MCSectionData &SD) {
1393 if (IsELFMetaDataSection(SD))
1394 return DataSectionSize(SD);
1395 return Layout.getSectionAddressSize(&SD);
1396 }
1397
WriteDataSectionData(MCAssembler & Asm,const MCAsmLayout & Layout,const MCSectionELF & Section)1398 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
1399 const MCAsmLayout &Layout,
1400 const MCSectionELF &Section) {
1401 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1402
1403 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1404 WriteZeros(Padding);
1405
1406 if (IsELFMetaDataSection(SD)) {
1407 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1408 ++i) {
1409 const MCFragment &F = *i;
1410 assert(F.getKind() == MCFragment::FT_Data);
1411 WriteBytes(cast<MCDataFragment>(F).getContents());
1412 }
1413 } else {
1414 Asm.writeSectionData(&SD, Layout);
1415 }
1416 }
1417
WriteSectionHeader(MCAssembler & Asm,const GroupMapTy & GroupMap,const MCAsmLayout & Layout,const SectionIndexMapTy & SectionIndexMap,const SectionOffsetMapTy & SectionOffsetMap)1418 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm,
1419 const GroupMapTy &GroupMap,
1420 const MCAsmLayout &Layout,
1421 const SectionIndexMapTy &SectionIndexMap,
1422 const SectionOffsetMapTy &SectionOffsetMap) {
1423 const unsigned NumSections = Asm.size() + 1;
1424
1425 std::vector<const MCSectionELF*> Sections;
1426 Sections.resize(NumSections - 1);
1427
1428 for (SectionIndexMapTy::const_iterator i=
1429 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
1430 const std::pair<const MCSectionELF*, uint32_t> &p = *i;
1431 Sections[p.second - 1] = p.first;
1432 }
1433
1434 // Null section first.
1435 uint64_t FirstSectionSize =
1436 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1437 uint32_t FirstSectionLink =
1438 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1439 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1440
1441 for (unsigned i = 0; i < NumSections - 1; ++i) {
1442 const MCSectionELF &Section = *Sections[i];
1443 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1444 uint32_t GroupSymbolIndex;
1445 if (Section.getType() != ELF::SHT_GROUP)
1446 GroupSymbolIndex = 0;
1447 else
1448 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1449 GroupMap.lookup(&Section));
1450
1451 uint64_t Size = GetSectionAddressSize(Layout, SD);
1452
1453 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex,
1454 SectionOffsetMap.lookup(&Section), Size,
1455 SD.getAlignment(), Section);
1456 }
1457 }
1458
ComputeSectionOrder(MCAssembler & Asm,std::vector<const MCSectionELF * > & Sections)1459 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
1460 std::vector<const MCSectionELF*> &Sections) {
1461 for (MCAssembler::iterator it = Asm.begin(),
1462 ie = Asm.end(); it != ie; ++it) {
1463 const MCSectionELF &Section =
1464 static_cast<const MCSectionELF &>(it->getSection());
1465 if (Section.getType() == ELF::SHT_GROUP)
1466 Sections.push_back(&Section);
1467 }
1468
1469 for (MCAssembler::iterator it = Asm.begin(),
1470 ie = Asm.end(); it != ie; ++it) {
1471 const MCSectionELF &Section =
1472 static_cast<const MCSectionELF &>(it->getSection());
1473 if (Section.getType() != ELF::SHT_GROUP &&
1474 Section.getType() != ELF::SHT_REL &&
1475 Section.getType() != ELF::SHT_RELA)
1476 Sections.push_back(&Section);
1477 }
1478
1479 for (MCAssembler::iterator it = Asm.begin(),
1480 ie = Asm.end(); it != ie; ++it) {
1481 const MCSectionELF &Section =
1482 static_cast<const MCSectionELF &>(it->getSection());
1483 if (Section.getType() == ELF::SHT_REL ||
1484 Section.getType() == ELF::SHT_RELA)
1485 Sections.push_back(&Section);
1486 }
1487 }
1488
WriteObject(MCAssembler & Asm,const MCAsmLayout & Layout)1489 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1490 const MCAsmLayout &Layout) {
1491 GroupMapTy GroupMap;
1492 RevGroupMapTy RevGroupMap;
1493 SectionIndexMapTy SectionIndexMap;
1494
1495 unsigned NumUserSections = Asm.size();
1496
1497 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
1498 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1499
1500 const unsigned NumUserAndRelocSections = Asm.size();
1501 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
1502 RevGroupMap, SectionIndexMap, RelMap);
1503 const unsigned AllSections = Asm.size();
1504 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
1505
1506 unsigned NumRegularSections = NumUserSections + NumIndexedSections;
1507
1508 // Compute symbol table information.
1509 ComputeSymbolTable(Asm, SectionIndexMap, RevGroupMap, NumRegularSections);
1510
1511
1512 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1513
1514 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1515 const_cast<MCAsmLayout&>(Layout),
1516 SectionIndexMap,
1517 RelMap);
1518
1519 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1520 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
1521 sizeof(ELF::Elf32_Ehdr);
1522 uint64_t FileOff = HeaderSize;
1523
1524 std::vector<const MCSectionELF*> Sections;
1525 ComputeSectionOrder(Asm, Sections);
1526 unsigned NumSections = Sections.size();
1527 SectionOffsetMapTy SectionOffsetMap;
1528 for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
1529 const MCSectionELF &Section = *Sections[i];
1530 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1531
1532 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1533
1534 // Remember the offset into the file for this section.
1535 SectionOffsetMap[&Section] = FileOff;
1536
1537 // Get the size of the section in the output file (including padding).
1538 FileOff += GetSectionFileSize(Layout, SD);
1539 }
1540
1541 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1542
1543 const unsigned SectionHeaderOffset = FileOff - HeaderSize;
1544
1545 uint64_t SectionHeaderEntrySize = is64Bit() ?
1546 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
1547 FileOff += (NumSections + 1) * SectionHeaderEntrySize;
1548
1549 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
1550 const MCSectionELF &Section = *Sections[i];
1551 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1552
1553 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1554
1555 // Remember the offset into the file for this section.
1556 SectionOffsetMap[&Section] = FileOff;
1557
1558 // Get the size of the section in the output file (including padding).
1559 FileOff += GetSectionFileSize(Layout, SD);
1560 }
1561
1562 // Write out the ELF header ...
1563 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
1564
1565 // ... then the regular sections ...
1566 // + because of .shstrtab
1567 for (unsigned i = 0; i < NumRegularSections + 1; ++i)
1568 WriteDataSectionData(Asm, Layout, *Sections[i]);
1569
1570 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1571 WriteZeros(Padding);
1572
1573 // ... then the section header table ...
1574 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap,
1575 SectionOffsetMap);
1576
1577 // ... and then the remaining sections ...
1578 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
1579 WriteDataSectionData(Asm, Layout, *Sections[i]);
1580 }
1581
1582 bool
IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler & Asm,const MCSymbolData & DataA,const MCFragment & FB,bool InSet,bool IsPCRel) const1583 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
1584 const MCSymbolData &DataA,
1585 const MCFragment &FB,
1586 bool InSet,
1587 bool IsPCRel) const {
1588 if (DataA.getFlags() & ELF_STB_Weak)
1589 return false;
1590 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1591 Asm, DataA, FB,InSet, IsPCRel);
1592 }
1593
createELFObjectWriter(MCELFObjectTargetWriter * MOTW,raw_ostream & OS,bool IsLittleEndian)1594 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1595 raw_ostream &OS,
1596 bool IsLittleEndian) {
1597 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);
1598 }
1599