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 <__anon2645bec20111::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 // FIXME: no tests cover this. Is adjustFixupOffset dead code?
763 TargetObjectWriter->adjustFixupOffset(Fixup, RelocOffset);
764
765 if (!hasRelocationAddend())
766 Addend = 0;
767
768 if (is64Bit())
769 assert(isInt<64>(Addend));
770 else
771 assert(isInt<32>(Addend));
772
773 ELFRelocationEntry ERE(RelocOffset, Index, Type, RelocSymbol, Addend, Fixup);
774 Relocations[Fragment->getParent()].push_back(ERE);
775 }
776
777
778 uint64_t
getSymbolIndexInSymbolTable(const MCAssembler & Asm,const MCSymbol * S)779 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
780 const MCSymbol *S) {
781 MCSymbolData &SD = Asm.getSymbolData(*S);
782 return SD.getIndex();
783 }
784
isInSymtab(const MCAssembler & Asm,const MCSymbolData & Data,bool Used,bool Renamed)785 bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm,
786 const MCSymbolData &Data,
787 bool Used, bool Renamed) {
788 if (Data.getFlags() & ELF_Other_Weakref)
789 return false;
790
791 if (Used)
792 return true;
793
794 if (Renamed)
795 return false;
796
797 const MCSymbol &Symbol = Data.getSymbol();
798
799 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
800 return true;
801
802 const MCSymbol &A = Symbol.AliasedSymbol();
803 if (Symbol.isVariable() && !A.isVariable() && A.isUndefined())
804 return false;
805
806 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
807 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
808 return false;
809
810 if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined())
811 return false;
812
813 if (Symbol.isTemporary())
814 return false;
815
816 return true;
817 }
818
isLocal(const MCSymbolData & Data,bool isSignature,bool isUsedInReloc)819 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature,
820 bool isUsedInReloc) {
821 if (Data.isExternal())
822 return false;
823
824 const MCSymbol &Symbol = Data.getSymbol();
825 const MCSymbol &RefSymbol = Symbol.AliasedSymbol();
826
827 if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) {
828 if (isSignature && !isUsedInReloc)
829 return true;
830
831 return false;
832 }
833
834 return true;
835 }
836
ComputeIndexMap(MCAssembler & Asm,SectionIndexMapTy & SectionIndexMap,const RelMapTy & RelMap)837 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
838 SectionIndexMapTy &SectionIndexMap,
839 const RelMapTy &RelMap) {
840 unsigned Index = 1;
841 for (MCAssembler::iterator it = Asm.begin(),
842 ie = Asm.end(); it != ie; ++it) {
843 const MCSectionELF &Section =
844 static_cast<const MCSectionELF &>(it->getSection());
845 if (Section.getType() != ELF::SHT_GROUP)
846 continue;
847 SectionIndexMap[&Section] = Index++;
848 }
849
850 for (MCAssembler::iterator it = Asm.begin(),
851 ie = Asm.end(); it != ie; ++it) {
852 const MCSectionELF &Section =
853 static_cast<const MCSectionELF &>(it->getSection());
854 if (Section.getType() == ELF::SHT_GROUP ||
855 Section.getType() == ELF::SHT_REL ||
856 Section.getType() == ELF::SHT_RELA)
857 continue;
858 SectionIndexMap[&Section] = Index++;
859 const MCSectionELF *RelSection = RelMap.lookup(&Section);
860 if (RelSection)
861 SectionIndexMap[RelSection] = Index++;
862 }
863 }
864
ComputeSymbolTable(MCAssembler & Asm,const SectionIndexMapTy & SectionIndexMap,RevGroupMapTy RevGroupMap,unsigned NumRegularSections)865 void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm,
866 const SectionIndexMapTy &SectionIndexMap,
867 RevGroupMapTy RevGroupMap,
868 unsigned NumRegularSections) {
869 // FIXME: Is this the correct place to do this?
870 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
871 if (NeedsGOT) {
872 StringRef Name = "_GLOBAL_OFFSET_TABLE_";
873 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
874 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
875 Data.setExternal(true);
876 MCELF::SetBinding(Data, ELF::STB_GLOBAL);
877 }
878
879 // Index 0 is always the empty string.
880 StringMap<uint64_t> StringIndexMap;
881 StringTable += '\x00';
882
883 // FIXME: We could optimize suffixes in strtab in the same way we
884 // optimize them in shstrtab.
885
886 // Add the data for the symbols.
887 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
888 ie = Asm.symbol_end(); it != ie; ++it) {
889 const MCSymbol &Symbol = it->getSymbol();
890
891 bool Used = UsedInReloc.count(&Symbol);
892 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
893 bool isSignature = RevGroupMap.count(&Symbol);
894
895 if (!isInSymtab(Asm, *it,
896 Used || WeakrefUsed || isSignature,
897 Renames.count(&Symbol)))
898 continue;
899
900 ELFSymbolData MSD;
901 MSD.SymbolData = it;
902 const MCSymbol &RefSymbol = Symbol.AliasedSymbol();
903
904 // Undefined symbols are global, but this is the first place we
905 // are able to set it.
906 bool Local = isLocal(*it, isSignature, Used);
907 if (!Local && MCELF::GetBinding(*it) == ELF::STB_LOCAL) {
908 MCSymbolData &SD = Asm.getSymbolData(RefSymbol);
909 MCELF::SetBinding(*it, ELF::STB_GLOBAL);
910 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
911 }
912
913 if (RefSymbol.isUndefined() && !Used && WeakrefUsed)
914 MCELF::SetBinding(*it, ELF::STB_WEAK);
915
916 if (it->isCommon()) {
917 assert(!Local);
918 MSD.SectionIndex = ELF::SHN_COMMON;
919 } else if (Symbol.isAbsolute() || RefSymbol.isVariable()) {
920 MSD.SectionIndex = ELF::SHN_ABS;
921 } else if (RefSymbol.isUndefined()) {
922 if (isSignature && !Used)
923 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]);
924 else
925 MSD.SectionIndex = ELF::SHN_UNDEF;
926 } else {
927 const MCSectionELF &Section =
928 static_cast<const MCSectionELF&>(RefSymbol.getSection());
929 MSD.SectionIndex = SectionIndexMap.lookup(&Section);
930 if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
931 NeedsSymtabShndx = true;
932 assert(MSD.SectionIndex && "Invalid section index!");
933 }
934
935 // The @@@ in symbol version is replaced with @ in undefined symbols and
936 // @@ in defined ones.
937 StringRef Name = Symbol.getName();
938 SmallString<32> Buf;
939
940 size_t Pos = Name.find("@@@");
941 if (Pos != StringRef::npos) {
942 Buf += Name.substr(0, Pos);
943 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
944 Buf += Name.substr(Pos + Skip);
945 Name = Buf;
946 }
947
948 uint64_t &Entry = StringIndexMap[Name];
949 if (!Entry) {
950 Entry = StringTable.size();
951 StringTable += Name;
952 StringTable += '\x00';
953 }
954 MSD.StringIndex = Entry;
955 if (MSD.SectionIndex == ELF::SHN_UNDEF)
956 UndefinedSymbolData.push_back(MSD);
957 else if (Local)
958 LocalSymbolData.push_back(MSD);
959 else
960 ExternalSymbolData.push_back(MSD);
961 }
962
963 // Symbols are required to be in lexicographic order.
964 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
965 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
966 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
967
968 // Set the symbol indices. Local symbols must come before all other
969 // symbols with non-local bindings.
970 unsigned Index = 1;
971 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
972 LocalSymbolData[i].SymbolData->setIndex(Index++);
973
974 Index += NumRegularSections;
975
976 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
977 ExternalSymbolData[i].SymbolData->setIndex(Index++);
978 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
979 UndefinedSymbolData[i].SymbolData->setIndex(Index++);
980
981 if (Index >= ELF::SHN_LORESERVE)
982 NeedsSymtabShndx = true;
983 }
984
CreateRelocationSections(MCAssembler & Asm,MCAsmLayout & Layout,RelMapTy & RelMap)985 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm,
986 MCAsmLayout &Layout,
987 RelMapTy &RelMap) {
988 for (MCAssembler::const_iterator it = Asm.begin(),
989 ie = Asm.end(); it != ie; ++it) {
990 const MCSectionData &SD = *it;
991 if (Relocations[&SD].empty())
992 continue;
993
994 MCContext &Ctx = Asm.getContext();
995 const MCSectionELF &Section =
996 static_cast<const MCSectionELF&>(SD.getSection());
997
998 const StringRef SectionName = Section.getSectionName();
999 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1000 RelaSectionName += SectionName;
1001
1002 unsigned EntrySize;
1003 if (hasRelocationAddend())
1004 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1005 else
1006 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1007
1008 const MCSectionELF *RelaSection =
1009 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ?
1010 ELF::SHT_RELA : ELF::SHT_REL, 0,
1011 SectionKind::getReadOnly(),
1012 EntrySize, "");
1013 RelMap[&Section] = RelaSection;
1014 Asm.getOrCreateSectionData(*RelaSection);
1015 }
1016 }
1017
WriteRelocations(MCAssembler & Asm,MCAsmLayout & Layout,const RelMapTy & RelMap)1018 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
1019 const RelMapTy &RelMap) {
1020 for (MCAssembler::const_iterator it = Asm.begin(),
1021 ie = Asm.end(); it != ie; ++it) {
1022 const MCSectionData &SD = *it;
1023 const MCSectionELF &Section =
1024 static_cast<const MCSectionELF&>(SD.getSection());
1025
1026 const MCSectionELF *RelaSection = RelMap.lookup(&Section);
1027 if (!RelaSection)
1028 continue;
1029 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
1030 RelaSD.setAlignment(is64Bit() ? 8 : 4);
1031
1032 MCDataFragment *F = new MCDataFragment(&RelaSD);
1033 WriteRelocationsFragment(Asm, F, &*it);
1034 }
1035 }
1036
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)1037 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1038 uint64_t Flags, uint64_t Address,
1039 uint64_t Offset, uint64_t Size,
1040 uint32_t Link, uint32_t Info,
1041 uint64_t Alignment,
1042 uint64_t EntrySize) {
1043 Write32(Name); // sh_name: index into string table
1044 Write32(Type); // sh_type
1045 WriteWord(Flags); // sh_flags
1046 WriteWord(Address); // sh_addr
1047 WriteWord(Offset); // sh_offset
1048 WriteWord(Size); // sh_size
1049 Write32(Link); // sh_link
1050 Write32(Info); // sh_info
1051 WriteWord(Alignment); // sh_addralign
1052 WriteWord(EntrySize); // sh_entsize
1053 }
1054
WriteRelocationsFragment(const MCAssembler & Asm,MCDataFragment * F,const MCSectionData * SD)1055 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1056 MCDataFragment *F,
1057 const MCSectionData *SD) {
1058 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1059
1060 // Sort the relocation entries. Most targets just sort by r_offset, but some
1061 // (e.g., MIPS) have additional constraints.
1062 TargetObjectWriter->sortRelocs(Asm, Relocs);
1063
1064 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1065 ELFRelocationEntry entry = Relocs[e - i - 1];
1066
1067 if (!entry.Index)
1068 ;
1069 else if (entry.Index < 0)
1070 entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol);
1071 else
1072 entry.Index += LocalSymbolData.size();
1073 if (is64Bit()) {
1074 String64(*F, entry.r_offset);
1075 if (TargetObjectWriter->isN64()) {
1076 String32(*F, entry.Index);
1077
1078 String8(*F, TargetObjectWriter->getRSsym(entry.Type));
1079 String8(*F, TargetObjectWriter->getRType3(entry.Type));
1080 String8(*F, TargetObjectWriter->getRType2(entry.Type));
1081 String8(*F, TargetObjectWriter->getRType(entry.Type));
1082 }
1083 else {
1084 struct ELF::Elf64_Rela ERE64;
1085 ERE64.setSymbolAndType(entry.Index, entry.Type);
1086 String64(*F, ERE64.r_info);
1087 }
1088 if (hasRelocationAddend())
1089 String64(*F, entry.r_addend);
1090 } else {
1091 String32(*F, entry.r_offset);
1092
1093 struct ELF::Elf32_Rela ERE32;
1094 ERE32.setSymbolAndType(entry.Index, entry.Type);
1095 String32(*F, ERE32.r_info);
1096
1097 if (hasRelocationAddend())
1098 String32(*F, entry.r_addend);
1099 }
1100 }
1101 }
1102
compareBySuffix(const void * a,const void * b)1103 static int compareBySuffix(const void *a, const void *b) {
1104 const MCSectionELF *secA = *static_cast<const MCSectionELF* const *>(a);
1105 const MCSectionELF *secB = *static_cast<const MCSectionELF* const *>(b);
1106 const StringRef &NameA = secA->getSectionName();
1107 const StringRef &NameB = secB->getSectionName();
1108 const unsigned sizeA = NameA.size();
1109 const unsigned sizeB = NameB.size();
1110 const unsigned len = std::min(sizeA, sizeB);
1111 for (unsigned int i = 0; i < len; ++i) {
1112 char ca = NameA[sizeA - i - 1];
1113 char cb = NameB[sizeB - i - 1];
1114 if (ca != cb)
1115 return cb - ca;
1116 }
1117
1118 return sizeB - sizeA;
1119 }
1120
CreateMetadataSections(MCAssembler & Asm,MCAsmLayout & Layout,SectionIndexMapTy & SectionIndexMap,const RelMapTy & RelMap)1121 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
1122 MCAsmLayout &Layout,
1123 SectionIndexMapTy &SectionIndexMap,
1124 const RelMapTy &RelMap) {
1125 MCContext &Ctx = Asm.getContext();
1126 MCDataFragment *F;
1127
1128 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1129
1130 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1131 const MCSectionELF *ShstrtabSection =
1132 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
1133 SectionKind::getReadOnly());
1134 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1135 ShstrtabSD.setAlignment(1);
1136
1137 const MCSectionELF *SymtabSection =
1138 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1139 SectionKind::getReadOnly(),
1140 EntrySize, "");
1141 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1142 SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1143
1144 MCSectionData *SymtabShndxSD = NULL;
1145
1146 if (NeedsSymtabShndx) {
1147 const MCSectionELF *SymtabShndxSection =
1148 Ctx.getELFSection(".symtab_shndx", ELF::SHT_SYMTAB_SHNDX, 0,
1149 SectionKind::getReadOnly(), 4, "");
1150 SymtabShndxSD = &Asm.getOrCreateSectionData(*SymtabShndxSection);
1151 SymtabShndxSD->setAlignment(4);
1152 }
1153
1154 const MCSectionELF *StrtabSection;
1155 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
1156 SectionKind::getReadOnly());
1157 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1158 StrtabSD.setAlignment(1);
1159
1160 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1161
1162 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection);
1163 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection);
1164 StringTableIndex = SectionIndexMap.lookup(StrtabSection);
1165
1166 // Symbol table
1167 F = new MCDataFragment(&SymtabSD);
1168 MCDataFragment *ShndxF = NULL;
1169 if (NeedsSymtabShndx) {
1170 ShndxF = new MCDataFragment(SymtabShndxSD);
1171 }
1172 WriteSymbolTable(F, ShndxF, Asm, Layout, SectionIndexMap);
1173
1174 F = new MCDataFragment(&StrtabSD);
1175 F->getContents().append(StringTable.begin(), StringTable.end());
1176
1177 F = new MCDataFragment(&ShstrtabSD);
1178
1179 std::vector<const MCSectionELF*> Sections;
1180 for (MCAssembler::const_iterator it = Asm.begin(),
1181 ie = Asm.end(); it != ie; ++it) {
1182 const MCSectionELF &Section =
1183 static_cast<const MCSectionELF&>(it->getSection());
1184 Sections.push_back(&Section);
1185 }
1186 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix);
1187
1188 // Section header string table.
1189 //
1190 // The first entry of a string table holds a null character so skip
1191 // section 0.
1192 uint64_t Index = 1;
1193 F->getContents().push_back('\x00');
1194
1195 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) {
1196 const MCSectionELF &Section = *Sections[I];
1197
1198 StringRef Name = Section.getSectionName();
1199 if (I != 0) {
1200 StringRef PreviousName = Sections[I - 1]->getSectionName();
1201 if (PreviousName.endswith(Name)) {
1202 SectionStringTableIndex[&Section] = Index - Name.size() - 1;
1203 continue;
1204 }
1205 }
1206 // Remember the index into the string table so we can write it
1207 // into the sh_name field of the section header table.
1208 SectionStringTableIndex[&Section] = Index;
1209
1210 Index += Name.size() + 1;
1211 F->getContents().append(Name.begin(), Name.end());
1212 F->getContents().push_back('\x00');
1213 }
1214 }
1215
CreateIndexedSections(MCAssembler & Asm,MCAsmLayout & Layout,GroupMapTy & GroupMap,RevGroupMapTy & RevGroupMap,SectionIndexMapTy & SectionIndexMap,const RelMapTy & RelMap)1216 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
1217 MCAsmLayout &Layout,
1218 GroupMapTy &GroupMap,
1219 RevGroupMapTy &RevGroupMap,
1220 SectionIndexMapTy &SectionIndexMap,
1221 const RelMapTy &RelMap) {
1222 // Create the .note.GNU-stack section if needed.
1223 MCContext &Ctx = Asm.getContext();
1224 if (Asm.getNoExecStack()) {
1225 const MCSectionELF *GnuStackSection =
1226 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0,
1227 SectionKind::getReadOnly());
1228 Asm.getOrCreateSectionData(*GnuStackSection);
1229 }
1230
1231 // Build the groups
1232 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1233 it != ie; ++it) {
1234 const MCSectionELF &Section =
1235 static_cast<const MCSectionELF&>(it->getSection());
1236 if (!(Section.getFlags() & ELF::SHF_GROUP))
1237 continue;
1238
1239 const MCSymbol *SignatureSymbol = Section.getGroup();
1240 Asm.getOrCreateSymbolData(*SignatureSymbol);
1241 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1242 if (!Group) {
1243 Group = Ctx.CreateELFGroupSection();
1244 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1245 Data.setAlignment(4);
1246 MCDataFragment *F = new MCDataFragment(&Data);
1247 String32(*F, ELF::GRP_COMDAT);
1248 }
1249 GroupMap[Group] = SignatureSymbol;
1250 }
1251
1252 ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1253
1254 // Add sections to the groups
1255 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1256 it != ie; ++it) {
1257 const MCSectionELF &Section =
1258 static_cast<const MCSectionELF&>(it->getSection());
1259 if (!(Section.getFlags() & ELF::SHF_GROUP))
1260 continue;
1261 const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1262 MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1263 // FIXME: we could use the previous fragment
1264 MCDataFragment *F = new MCDataFragment(&Data);
1265 unsigned Index = SectionIndexMap.lookup(&Section);
1266 String32(*F, Index);
1267 }
1268 }
1269
WriteSection(MCAssembler & Asm,const SectionIndexMapTy & SectionIndexMap,uint32_t GroupSymbolIndex,uint64_t Offset,uint64_t Size,uint64_t Alignment,const MCSectionELF & Section)1270 void ELFObjectWriter::WriteSection(MCAssembler &Asm,
1271 const SectionIndexMapTy &SectionIndexMap,
1272 uint32_t GroupSymbolIndex,
1273 uint64_t Offset, uint64_t Size,
1274 uint64_t Alignment,
1275 const MCSectionELF &Section) {
1276 uint64_t sh_link = 0;
1277 uint64_t sh_info = 0;
1278
1279 switch(Section.getType()) {
1280 case ELF::SHT_DYNAMIC:
1281 sh_link = SectionStringTableIndex[&Section];
1282 sh_info = 0;
1283 break;
1284
1285 case ELF::SHT_REL:
1286 case ELF::SHT_RELA: {
1287 const MCSectionELF *SymtabSection;
1288 const MCSectionELF *InfoSection;
1289 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB,
1290 0,
1291 SectionKind::getReadOnly());
1292 sh_link = SectionIndexMap.lookup(SymtabSection);
1293 assert(sh_link && ".symtab not found");
1294
1295 // Remove ".rel" and ".rela" prefixes.
1296 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1297 StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1298
1299 InfoSection = Asm.getContext().getELFSection(SectionName,
1300 ELF::SHT_PROGBITS, 0,
1301 SectionKind::getReadOnly());
1302 sh_info = SectionIndexMap.lookup(InfoSection);
1303 break;
1304 }
1305
1306 case ELF::SHT_SYMTAB:
1307 case ELF::SHT_DYNSYM:
1308 sh_link = StringTableIndex;
1309 sh_info = LastLocalSymbolIndex;
1310 break;
1311
1312 case ELF::SHT_SYMTAB_SHNDX:
1313 sh_link = SymbolTableIndex;
1314 break;
1315
1316 case ELF::SHT_PROGBITS:
1317 case ELF::SHT_STRTAB:
1318 case ELF::SHT_NOBITS:
1319 case ELF::SHT_NOTE:
1320 case ELF::SHT_NULL:
1321 case ELF::SHT_ARM_ATTRIBUTES:
1322 case ELF::SHT_INIT_ARRAY:
1323 case ELF::SHT_FINI_ARRAY:
1324 case ELF::SHT_PREINIT_ARRAY:
1325 case ELF::SHT_X86_64_UNWIND:
1326 case ELF::SHT_MIPS_REGINFO:
1327 case ELF::SHT_MIPS_OPTIONS:
1328 // Nothing to do.
1329 break;
1330
1331 case ELF::SHT_GROUP:
1332 sh_link = SymbolTableIndex;
1333 sh_info = GroupSymbolIndex;
1334 break;
1335
1336 default:
1337 assert(0 && "FIXME: sh_type value not supported!");
1338 break;
1339 }
1340
1341 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1342 Section.getType() == ELF::SHT_ARM_EXIDX) {
1343 StringRef SecName(Section.getSectionName());
1344 if (SecName == ".ARM.exidx") {
1345 sh_link = SectionIndexMap.lookup(
1346 Asm.getContext().getELFSection(".text",
1347 ELF::SHT_PROGBITS,
1348 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
1349 SectionKind::getText()));
1350 } else if (SecName.startswith(".ARM.exidx")) {
1351 sh_link = SectionIndexMap.lookup(
1352 Asm.getContext().getELFSection(SecName.substr(sizeof(".ARM.exidx") - 1),
1353 ELF::SHT_PROGBITS,
1354 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
1355 SectionKind::getText()));
1356 }
1357 }
1358
1359 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(),
1360 Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1361 Alignment, Section.getEntrySize());
1362 }
1363
IsELFMetaDataSection(const MCSectionData & SD)1364 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1365 return SD.getOrdinal() == ~UINT32_C(0) &&
1366 !SD.getSection().isVirtualSection();
1367 }
1368
DataSectionSize(const MCSectionData & SD)1369 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1370 uint64_t Ret = 0;
1371 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1372 ++i) {
1373 const MCFragment &F = *i;
1374 assert(F.getKind() == MCFragment::FT_Data);
1375 Ret += cast<MCDataFragment>(F).getContents().size();
1376 }
1377 return Ret;
1378 }
1379
GetSectionFileSize(const MCAsmLayout & Layout,const MCSectionData & SD)1380 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
1381 const MCSectionData &SD) {
1382 if (IsELFMetaDataSection(SD))
1383 return DataSectionSize(SD);
1384 return Layout.getSectionFileSize(&SD);
1385 }
1386
GetSectionAddressSize(const MCAsmLayout & Layout,const MCSectionData & SD)1387 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1388 const MCSectionData &SD) {
1389 if (IsELFMetaDataSection(SD))
1390 return DataSectionSize(SD);
1391 return Layout.getSectionAddressSize(&SD);
1392 }
1393
WriteDataSectionData(MCAssembler & Asm,const MCAsmLayout & Layout,const MCSectionELF & Section)1394 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
1395 const MCAsmLayout &Layout,
1396 const MCSectionELF &Section) {
1397 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1398
1399 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1400 WriteZeros(Padding);
1401
1402 if (IsELFMetaDataSection(SD)) {
1403 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1404 ++i) {
1405 const MCFragment &F = *i;
1406 assert(F.getKind() == MCFragment::FT_Data);
1407 WriteBytes(cast<MCDataFragment>(F).getContents());
1408 }
1409 } else {
1410 Asm.writeSectionData(&SD, Layout);
1411 }
1412 }
1413
WriteSectionHeader(MCAssembler & Asm,const GroupMapTy & GroupMap,const MCAsmLayout & Layout,const SectionIndexMapTy & SectionIndexMap,const SectionOffsetMapTy & SectionOffsetMap)1414 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm,
1415 const GroupMapTy &GroupMap,
1416 const MCAsmLayout &Layout,
1417 const SectionIndexMapTy &SectionIndexMap,
1418 const SectionOffsetMapTy &SectionOffsetMap) {
1419 const unsigned NumSections = Asm.size() + 1;
1420
1421 std::vector<const MCSectionELF*> Sections;
1422 Sections.resize(NumSections - 1);
1423
1424 for (SectionIndexMapTy::const_iterator i=
1425 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
1426 const std::pair<const MCSectionELF*, uint32_t> &p = *i;
1427 Sections[p.second - 1] = p.first;
1428 }
1429
1430 // Null section first.
1431 uint64_t FirstSectionSize =
1432 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1433 uint32_t FirstSectionLink =
1434 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1435 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1436
1437 for (unsigned i = 0; i < NumSections - 1; ++i) {
1438 const MCSectionELF &Section = *Sections[i];
1439 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1440 uint32_t GroupSymbolIndex;
1441 if (Section.getType() != ELF::SHT_GROUP)
1442 GroupSymbolIndex = 0;
1443 else
1444 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1445 GroupMap.lookup(&Section));
1446
1447 uint64_t Size = GetSectionAddressSize(Layout, SD);
1448
1449 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex,
1450 SectionOffsetMap.lookup(&Section), Size,
1451 SD.getAlignment(), Section);
1452 }
1453 }
1454
ComputeSectionOrder(MCAssembler & Asm,std::vector<const MCSectionELF * > & Sections)1455 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
1456 std::vector<const MCSectionELF*> &Sections) {
1457 for (MCAssembler::iterator it = Asm.begin(),
1458 ie = Asm.end(); it != ie; ++it) {
1459 const MCSectionELF &Section =
1460 static_cast<const MCSectionELF &>(it->getSection());
1461 if (Section.getType() == ELF::SHT_GROUP)
1462 Sections.push_back(&Section);
1463 }
1464
1465 for (MCAssembler::iterator it = Asm.begin(),
1466 ie = Asm.end(); it != ie; ++it) {
1467 const MCSectionELF &Section =
1468 static_cast<const MCSectionELF &>(it->getSection());
1469 if (Section.getType() != ELF::SHT_GROUP &&
1470 Section.getType() != ELF::SHT_REL &&
1471 Section.getType() != ELF::SHT_RELA)
1472 Sections.push_back(&Section);
1473 }
1474
1475 for (MCAssembler::iterator it = Asm.begin(),
1476 ie = Asm.end(); it != ie; ++it) {
1477 const MCSectionELF &Section =
1478 static_cast<const MCSectionELF &>(it->getSection());
1479 if (Section.getType() == ELF::SHT_REL ||
1480 Section.getType() == ELF::SHT_RELA)
1481 Sections.push_back(&Section);
1482 }
1483 }
1484
WriteObject(MCAssembler & Asm,const MCAsmLayout & Layout)1485 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1486 const MCAsmLayout &Layout) {
1487 GroupMapTy GroupMap;
1488 RevGroupMapTy RevGroupMap;
1489 SectionIndexMapTy SectionIndexMap;
1490
1491 unsigned NumUserSections = Asm.size();
1492
1493 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
1494 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1495
1496 const unsigned NumUserAndRelocSections = Asm.size();
1497 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
1498 RevGroupMap, SectionIndexMap, RelMap);
1499 const unsigned AllSections = Asm.size();
1500 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
1501
1502 unsigned NumRegularSections = NumUserSections + NumIndexedSections;
1503
1504 // Compute symbol table information.
1505 ComputeSymbolTable(Asm, SectionIndexMap, RevGroupMap, NumRegularSections);
1506
1507
1508 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1509
1510 CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1511 const_cast<MCAsmLayout&>(Layout),
1512 SectionIndexMap,
1513 RelMap);
1514
1515 uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1516 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
1517 sizeof(ELF::Elf32_Ehdr);
1518 uint64_t FileOff = HeaderSize;
1519
1520 std::vector<const MCSectionELF*> Sections;
1521 ComputeSectionOrder(Asm, Sections);
1522 unsigned NumSections = Sections.size();
1523 SectionOffsetMapTy SectionOffsetMap;
1524 for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
1525 const MCSectionELF &Section = *Sections[i];
1526 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1527
1528 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1529
1530 // Remember the offset into the file for this section.
1531 SectionOffsetMap[&Section] = FileOff;
1532
1533 // Get the size of the section in the output file (including padding).
1534 FileOff += GetSectionFileSize(Layout, SD);
1535 }
1536
1537 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1538
1539 const unsigned SectionHeaderOffset = FileOff - HeaderSize;
1540
1541 uint64_t SectionHeaderEntrySize = is64Bit() ?
1542 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
1543 FileOff += (NumSections + 1) * SectionHeaderEntrySize;
1544
1545 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
1546 const MCSectionELF &Section = *Sections[i];
1547 const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1548
1549 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1550
1551 // Remember the offset into the file for this section.
1552 SectionOffsetMap[&Section] = FileOff;
1553
1554 // Get the size of the section in the output file (including padding).
1555 FileOff += GetSectionFileSize(Layout, SD);
1556 }
1557
1558 // Write out the ELF header ...
1559 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
1560
1561 // ... then the regular sections ...
1562 // + because of .shstrtab
1563 for (unsigned i = 0; i < NumRegularSections + 1; ++i)
1564 WriteDataSectionData(Asm, Layout, *Sections[i]);
1565
1566 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1567 WriteZeros(Padding);
1568
1569 // ... then the section header table ...
1570 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap,
1571 SectionOffsetMap);
1572
1573 // ... and then the remaining sections ...
1574 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
1575 WriteDataSectionData(Asm, Layout, *Sections[i]);
1576 }
1577
1578 bool
IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler & Asm,const MCSymbolData & DataA,const MCFragment & FB,bool InSet,bool IsPCRel) const1579 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
1580 const MCSymbolData &DataA,
1581 const MCFragment &FB,
1582 bool InSet,
1583 bool IsPCRel) const {
1584 if (DataA.getFlags() & ELF_STB_Weak)
1585 return false;
1586 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1587 Asm, DataA, FB,InSet, IsPCRel);
1588 }
1589
createELFObjectWriter(MCELFObjectTargetWriter * MOTW,raw_ostream & OS,bool IsLittleEndian)1590 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1591 raw_ostream &OS,
1592 bool IsLittleEndian) {
1593 return new ELFObjectWriter(MOTW, OS, IsLittleEndian);
1594 }
1595