1 //===-- ELFWriter.cpp - Target-independent ELF Writer code ----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the target-independent ELF writer. This file writes out
11 // the ELF file in the following order:
14 // #2. '.text' section
15 // #3. '.data' section
16 // #4. '.bss' section (conceptual position in file)
18 // #X. '.shstrtab' section
21 // The entries in the section table are laid out as:
22 // #0. Null entry [required]
23 // #1. ".text" entry - the program code
24 // #2. ".data" entry - global variables with initializers. [ if needed ]
25 // #3. ".bss" entry - global variables without initializers. [ if needed ]
27 // #N. ".shstrtab" entry - String table for the section names.
29 //===----------------------------------------------------------------------===//
31 #define DEBUG_TYPE "elfwriter"
33 #include "ELFWriter.h"
34 #include "ELFCodeEmitter.h"
35 #include "llvm/Constants.h"
36 #include "llvm/Module.h"
37 #include "llvm/PassManager.h"
38 #include "llvm/DerivedTypes.h"
39 #include "llvm/CodeGen/BinaryObject.h"
40 #include "llvm/CodeGen/FileWriters.h"
41 #include "llvm/CodeGen/MachineCodeEmitter.h"
42 #include "llvm/CodeGen/ObjectCodeEmitter.h"
43 #include "llvm/CodeGen/MachineCodeEmitter.h"
44 #include "llvm/CodeGen/MachineConstantPool.h"
45 #include "llvm/Target/TargetAsmInfo.h"
46 #include "llvm/Target/TargetData.h"
47 #include "llvm/Target/TargetELFWriterInfo.h"
48 #include "llvm/Target/TargetLowering.h"
49 #include "llvm/Target/TargetLoweringObjectFile.h"
50 #include "llvm/Target/TargetMachine.h"
51 #include "llvm/Support/Mangler.h"
52 #include "llvm/Support/Streams.h"
53 #include "llvm/Support/raw_ostream.h"
54 #include "llvm/Support/Debug.h"
55 #include "llvm/Support/ErrorHandling.h"
59 char ELFWriter::ID = 0;
61 /// AddELFWriter - Add the ELF writer to the function pass manager
62 ObjectCodeEmitter *llvm::AddELFWriter(PassManagerBase &PM,
65 ELFWriter *EW = new ELFWriter(O, TM);
67 return EW->getObjectCodeEmitter();
70 //===----------------------------------------------------------------------===//
71 // ELFWriter Implementation
72 //===----------------------------------------------------------------------===//
74 ELFWriter::ELFWriter(raw_ostream &o, TargetMachine &tm)
75 : MachineFunctionPass(&ID), O(o), TM(tm),
76 is64Bit(TM.getTargetData()->getPointerSizeInBits() == 64),
77 isLittleEndian(TM.getTargetData()->isLittleEndian()),
78 ElfHdr(isLittleEndian, is64Bit) {
80 TAI = TM.getTargetAsmInfo();
81 TEW = TM.getELFWriterInfo();
83 // Create the object code emitter object for this target.
84 ElfCE = new ELFCodeEmitter(*this);
86 // Inital number of sections
90 ELFWriter::~ELFWriter() {
94 // doInitialization - Emit the file header and all of the global variables for
95 // the module to the ELF file.
96 bool ELFWriter::doInitialization(Module &M) {
97 Mang = new Mangler(M);
101 // Fields e_shnum e_shstrndx are only known after all section have
102 // been emitted. They locations in the ouput buffer are recorded so
103 // to be patched up later.
107 // emitWord method behaves differently for ELF32 and ELF64, writing
108 // 4 bytes in the former and 8 in the last for *_off and *_addr elf types
110 ElfHdr.emitByte(0x7f); // e_ident[EI_MAG0]
111 ElfHdr.emitByte('E'); // e_ident[EI_MAG1]
112 ElfHdr.emitByte('L'); // e_ident[EI_MAG2]
113 ElfHdr.emitByte('F'); // e_ident[EI_MAG3]
115 ElfHdr.emitByte(TEW->getEIClass()); // e_ident[EI_CLASS]
116 ElfHdr.emitByte(TEW->getEIData()); // e_ident[EI_DATA]
117 ElfHdr.emitByte(EV_CURRENT); // e_ident[EI_VERSION]
118 ElfHdr.emitAlignment(16); // e_ident[EI_NIDENT-EI_PAD]
120 ElfHdr.emitWord16(ET_REL); // e_type
121 ElfHdr.emitWord16(TEW->getEMachine()); // e_machine = target
122 ElfHdr.emitWord32(EV_CURRENT); // e_version
123 ElfHdr.emitWord(0); // e_entry, no entry point in .o file
124 ElfHdr.emitWord(0); // e_phoff, no program header for .o
125 ELFHdr_e_shoff_Offset = ElfHdr.size();
126 ElfHdr.emitWord(0); // e_shoff = sec hdr table off in bytes
127 ElfHdr.emitWord32(TEW->getEFlags()); // e_flags = whatever the target wants
128 ElfHdr.emitWord16(TEW->getHdrSize()); // e_ehsize = ELF header size
129 ElfHdr.emitWord16(0); // e_phentsize = prog header entry size
130 ElfHdr.emitWord16(0); // e_phnum = # prog header entries = 0
132 // e_shentsize = Section header entry size
133 ElfHdr.emitWord16(TEW->getSHdrSize());
135 // e_shnum = # of section header ents
136 ELFHdr_e_shnum_Offset = ElfHdr.size();
137 ElfHdr.emitWord16(0); // Placeholder
139 // e_shstrndx = Section # of '.shstrtab'
140 ELFHdr_e_shstrndx_Offset = ElfHdr.size();
141 ElfHdr.emitWord16(0); // Placeholder
143 // Add the null section, which is required to be first in the file.
146 // The first entry in the symtab is the null symbol and the second
147 // is a local symbol containing the module/file name
148 SymbolList.push_back(new ELFSym());
149 SymbolList.push_back(ELFSym::getFileSym());
154 // addGlobalSymbol - Add a global to be processed and to the
155 // global symbol lookup, use a zero index for non private symbols
156 // because the table index will be determined later.
157 void ELFWriter::addGlobalSymbol(const GlobalValue *GV) {
158 PendingGlobals.insert(GV);
161 // addExternalSymbol - Add the external to be processed and to the
162 // external symbol lookup, use a zero index because the symbol
163 // table index will be determined later
164 void ELFWriter::addExternalSymbol(const char *External) {
165 PendingExternals.insert(External);
166 ExtSymLookup[External] = 0;
169 // Get jump table section on the section name returned by TAI
170 ELFSection &ELFWriter::getJumpTableSection() {
171 unsigned Align = TM.getTargetData()->getPointerABIAlignment();
172 return getSection(TAI->getJumpTableDataSection(),
173 ELFSection::SHT_PROGBITS,
174 ELFSection::SHF_ALLOC, Align);
177 // Get a constant pool section based on the section name returned by TAI
178 ELFSection &ELFWriter::getConstantPoolSection(MachineConstantPoolEntry &CPE) {
180 switch (CPE.getRelocationInfo()) {
181 default: llvm_unreachable("Unknown section kind");
182 case 2: Kind = SectionKind::get(SectionKind::ReadOnlyWithRel,false); break;
184 Kind = SectionKind::get(SectionKind::ReadOnlyWithRelLocal,false);
187 switch (TM.getTargetData()->getTypeAllocSize(CPE.getType())) {
188 case 4: Kind = SectionKind::get(SectionKind::MergeableConst4,false); break;
189 case 8: Kind = SectionKind::get(SectionKind::MergeableConst8,false); break;
190 case 16: Kind = SectionKind::get(SectionKind::MergeableConst16,false);break;
191 default: Kind = SectionKind::get(SectionKind::MergeableConst,false); break;
195 const TargetLoweringObjectFile &TLOF =
196 TM.getTargetLowering()->getObjFileLowering();
198 return getSection(TLOF.getSectionForMergeableConstant(Kind)->getName(),
199 ELFSection::SHT_PROGBITS,
200 ELFSection::SHF_MERGE | ELFSection::SHF_ALLOC,
204 // Return the relocation section of section 'S'. 'RelA' is true
205 // if the relocation section contains entries with addends.
206 ELFSection &ELFWriter::getRelocSection(ELFSection &S) {
207 unsigned SectionHeaderTy = TEW->hasRelocationAddend() ?
208 ELFSection::SHT_RELA : ELFSection::SHT_REL;
209 std::string RelSName(".rel");
210 if (TEW->hasRelocationAddend())
211 RelSName.append("a");
212 RelSName.append(S.getName());
214 return getSection(RelSName, SectionHeaderTy, 0, TEW->getPrefELFAlignment());
217 // getGlobalELFVisibility - Returns the ELF specific visibility type
218 unsigned ELFWriter::getGlobalELFVisibility(const GlobalValue *GV) {
219 switch (GV->getVisibility()) {
221 llvm_unreachable("unknown visibility type");
222 case GlobalValue::DefaultVisibility:
223 return ELFSym::STV_DEFAULT;
224 case GlobalValue::HiddenVisibility:
225 return ELFSym::STV_HIDDEN;
226 case GlobalValue::ProtectedVisibility:
227 return ELFSym::STV_PROTECTED;
232 // getGlobalELFBinding - Returns the ELF specific binding type
233 unsigned ELFWriter::getGlobalELFBinding(const GlobalValue *GV) {
234 if (GV->hasInternalLinkage())
235 return ELFSym::STB_LOCAL;
237 if (GV->hasWeakLinkage())
238 return ELFSym::STB_WEAK;
240 return ELFSym::STB_GLOBAL;
243 // getGlobalELFType - Returns the ELF specific type for a global
244 unsigned ELFWriter::getGlobalELFType(const GlobalValue *GV) {
245 if (GV->isDeclaration())
246 return ELFSym::STT_NOTYPE;
248 if (isa<Function>(GV))
249 return ELFSym::STT_FUNC;
251 return ELFSym::STT_OBJECT;
254 // getElfSectionFlags - Get the ELF Section Header flags based
255 // on the flags defined in ELFTargetAsmInfo.
256 unsigned ELFWriter::getElfSectionFlags(SectionKind Kind) {
257 unsigned ElfSectionFlags = ELFSection::SHF_ALLOC;
260 ElfSectionFlags |= ELFSection::SHF_EXECINSTR;
261 if (Kind.isWriteable())
262 ElfSectionFlags |= ELFSection::SHF_WRITE;
263 if (Kind.isMergeableConst())
264 ElfSectionFlags |= ELFSection::SHF_MERGE;
265 if (Kind.isThreadLocal())
266 ElfSectionFlags |= ELFSection::SHF_TLS;
267 if (Kind.isMergeableCString())
268 ElfSectionFlags |= ELFSection::SHF_STRINGS;
270 return ElfSectionFlags;
273 // isELFUndefSym - the symbol has no section and must be placed in
274 // the symbol table with a reference to the null section.
275 static bool isELFUndefSym(const GlobalValue *GV) {
276 return GV->isDeclaration();
279 // isELFBssSym - for an undef or null value, the symbol must go to a bss
280 // section if it's not weak for linker, otherwise it's a common sym.
281 static bool isELFBssSym(const GlobalVariable *GV) {
282 const Constant *CV = GV->getInitializer();
283 return ((CV->isNullValue() || isa<UndefValue>(CV)) && !GV->isWeakForLinker());
286 // isELFCommonSym - for an undef or null value, the symbol must go to a
287 // common section if it's weak for linker, otherwise bss.
288 static bool isELFCommonSym(const GlobalVariable *GV) {
289 const Constant *CV = GV->getInitializer();
290 return ((CV->isNullValue() || isa<UndefValue>(CV)) && GV->isWeakForLinker());
293 // isELFDataSym - if the symbol is an initialized but no null constant
294 // it must go to some kind of data section gathered from TAI
295 static bool isELFDataSym(const Constant *CV) {
296 return (!(CV->isNullValue() || isa<UndefValue>(CV)));
299 // EmitGlobal - Choose the right section for global and emit it
300 void ELFWriter::EmitGlobal(const GlobalValue *GV) {
302 // Check if the referenced symbol is already emitted
303 if (GblSymLookup.find(GV) != GblSymLookup.end())
306 // If the global is a function already emited in the text section
307 // just add it to the global symbol lookup with a zero index to be
309 if (isa<Function>(GV) && !GV->isDeclaration()) {
310 GblSymLookup[GV] = 0;
314 // Handle ELF Bind, Visibility and Type for the current symbol
315 unsigned SymBind = getGlobalELFBinding(GV);
316 ELFSym *GblSym = ELFSym::getGV(GV, SymBind, getGlobalELFType(GV),
317 getGlobalELFVisibility(GV));
319 if (isELFUndefSym(GV)) {
320 GblSym->SectionIdx = ELFSection::SHN_UNDEF;
322 assert(isa<GlobalVariable>(GV) && "GV not a global variable!");
323 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
325 const TargetLoweringObjectFile &TLOF =
326 TM.getTargetLowering()->getObjFileLowering();
328 // Get the ELF section where this global belongs from TLOF
329 const Section *S = TLOF.SectionForGlobal(GV, Mang, TM);
330 unsigned SectionFlags = getElfSectionFlags(S->getKind());
332 // The symbol align should update the section alignment if needed
333 const TargetData *TD = TM.getTargetData();
334 unsigned Align = TD->getPreferredAlignment(GVar);
335 unsigned Size = TD->getTypeAllocSize(GVar->getInitializer()->getType());
338 if (isELFCommonSym(GVar)) {
339 GblSym->SectionIdx = ELFSection::SHN_COMMON;
340 getSection(S->getName(), ELFSection::SHT_NOBITS, SectionFlags, 1);
342 // A new linkonce section is created for each global in the
343 // common section, the default alignment is 1 and the symbol
344 // value contains its alignment.
345 GblSym->Value = Align;
347 } else if (isELFBssSym(GVar)) {
349 getSection(S->getName(), ELFSection::SHT_NOBITS, SectionFlags);
350 GblSym->SectionIdx = ES.SectionIdx;
352 // Update the size with alignment and the next object can
353 // start in the right offset in the section
354 if (Align) ES.Size = (ES.Size + Align-1) & ~(Align-1);
355 ES.Align = std::max(ES.Align, Align);
357 // GblSym->Value should contain the virtual offset inside the section.
358 // Virtual because the BSS space is not allocated on ELF objects
359 GblSym->Value = ES.Size;
362 } else if (isELFDataSym(GV)) {
364 getSection(S->getName(), ELFSection::SHT_PROGBITS, SectionFlags);
365 GblSym->SectionIdx = ES.SectionIdx;
367 // GblSym->Value should contain the symbol offset inside the section,
368 // and all symbols should start on their required alignment boundary
369 ES.Align = std::max(ES.Align, Align);
370 GblSym->Value = (ES.size() + (Align-1)) & (-Align);
371 ES.emitAlignment(ES.Align);
373 // Emit the global to the data section 'ES'
374 EmitGlobalConstant(GVar->getInitializer(), ES);
378 if (GV->hasPrivateLinkage()) {
379 // For a private symbols, keep track of the index inside the
380 // private list since it will never go to the symbol table and
381 // won't be patched up later.
382 PrivateSyms.push_back(GblSym);
383 GblSymLookup[GV] = PrivateSyms.size()-1;
385 // Non private symbol are left with zero indices until they are patched
386 // up during the symbol table emition (where the indicies are created).
387 SymbolList.push_back(GblSym);
388 GblSymLookup[GV] = 0;
392 void ELFWriter::EmitGlobalConstantStruct(const ConstantStruct *CVS,
395 // Print the fields in successive locations. Pad to align if needed!
396 const TargetData *TD = TM.getTargetData();
397 unsigned Size = TD->getTypeAllocSize(CVS->getType());
398 const StructLayout *cvsLayout = TD->getStructLayout(CVS->getType());
399 uint64_t sizeSoFar = 0;
400 for (unsigned i = 0, e = CVS->getNumOperands(); i != e; ++i) {
401 const Constant* field = CVS->getOperand(i);
403 // Check if padding is needed and insert one or more 0s.
404 uint64_t fieldSize = TD->getTypeAllocSize(field->getType());
405 uint64_t padSize = ((i == e-1 ? Size : cvsLayout->getElementOffset(i+1))
406 - cvsLayout->getElementOffset(i)) - fieldSize;
407 sizeSoFar += fieldSize + padSize;
409 // Now print the actual field value.
410 EmitGlobalConstant(field, GblS);
412 // Insert padding - this may include padding to increase the size of the
413 // current field up to the ABI size (if the struct is not packed) as well
414 // as padding to ensure that the next field starts at the right offset.
415 for (unsigned p=0; p < padSize; p++)
418 assert(sizeSoFar == cvsLayout->getSizeInBytes() &&
419 "Layout of constant struct may be incorrect!");
422 void ELFWriter::EmitGlobalConstant(const Constant *CV, ELFSection &GblS) {
423 const TargetData *TD = TM.getTargetData();
424 unsigned Size = TD->getTypeAllocSize(CV->getType());
426 if (const ConstantArray *CVA = dyn_cast<ConstantArray>(CV)) {
427 if (CVA->isString()) {
428 std::string GblStr = CVA->getAsString();
429 GblStr.resize(GblStr.size()-1);
430 GblS.emitString(GblStr);
431 } else { // Not a string. Print the values in successive locations
432 for (unsigned i = 0, e = CVA->getNumOperands(); i != e; ++i)
433 EmitGlobalConstant(CVA->getOperand(i), GblS);
436 } else if (const ConstantStruct *CVS = dyn_cast<ConstantStruct>(CV)) {
437 EmitGlobalConstantStruct(CVS, GblS);
439 } else if (const ConstantFP *CFP = dyn_cast<ConstantFP>(CV)) {
440 uint64_t Val = CFP->getValueAPF().bitcastToAPInt().getZExtValue();
441 if (CFP->getType() == Type::DoubleTy)
442 GblS.emitWord64(Val);
443 else if (CFP->getType() == Type::FloatTy)
444 GblS.emitWord32(Val);
445 else if (CFP->getType() == Type::X86_FP80Ty) {
446 llvm_unreachable("X86_FP80Ty global emission not implemented");
447 } else if (CFP->getType() == Type::PPC_FP128Ty)
448 llvm_unreachable("PPC_FP128Ty global emission not implemented");
450 } else if (const ConstantInt *CI = dyn_cast<ConstantInt>(CV)) {
452 GblS.emitWord32(CI->getZExtValue());
454 GblS.emitWord64(CI->getZExtValue());
456 llvm_unreachable("LargeInt global emission not implemented");
458 } else if (const ConstantVector *CP = dyn_cast<ConstantVector>(CV)) {
459 const VectorType *PTy = CP->getType();
460 for (unsigned I = 0, E = PTy->getNumElements(); I < E; ++I)
461 EmitGlobalConstant(CP->getOperand(I), GblS);
463 } else if (const GlobalValue *GV = dyn_cast<GlobalValue>(CV)) {
464 // This is a constant address for a global variable or function and
465 // therefore must be referenced using a relocation entry.
467 // Check if the referenced symbol is already emitted
468 if (GblSymLookup.find(GV) == GblSymLookup.end())
471 // Create the relocation entry for the global value
472 MachineRelocation MR =
473 MachineRelocation::getGV(GblS.getCurrentPCOffset(),
474 TEW->getAbsoluteLabelMachineRelTy(),
475 const_cast<GlobalValue*>(GV));
477 // Fill the data entry with zeros
478 for (unsigned i=0; i < Size; ++i)
481 // Add the relocation entry for the current data section
482 GblS.addRelocation(MR);
484 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(CV)) {
485 if (CE->getOpcode() == Instruction::BitCast) {
486 EmitGlobalConstant(CE->getOperand(0), GblS);
489 // See AsmPrinter::EmitConstantValueOnly for other ConstantExpr types
490 llvm_unreachable("Unsupported ConstantExpr type");
493 llvm_unreachable("Unknown global constant type");
497 bool ELFWriter::runOnMachineFunction(MachineFunction &MF) {
498 // Nothing to do here, this is all done through the ElfCE object above.
502 /// doFinalization - Now that the module has been completely processed, emit
503 /// the ELF file to 'O'.
504 bool ELFWriter::doFinalization(Module &M) {
505 // Emit .data section placeholder
508 // Emit .bss section placeholder
511 // Build and emit data, bss and "common" sections.
512 for (Module::global_iterator I = M.global_begin(), E = M.global_end();
516 // Emit all pending globals
517 for (PendingGblsIter I = PendingGlobals.begin(), E = PendingGlobals.end();
521 // Emit all pending externals
522 for (PendingExtsIter I = PendingExternals.begin(), E = PendingExternals.end();
524 SymbolList.push_back(ELFSym::getExtSym(*I));
526 // Emit non-executable stack note
527 if (TAI->getNonexecutableStackDirective())
528 getNonExecStackSection();
530 // Emit a symbol for each section created until now, skip null section
531 for (unsigned i = 1, e = SectionList.size(); i < e; ++i) {
532 ELFSection &ES = *SectionList[i];
533 ELFSym *SectionSym = ELFSym::getSectionSym();
534 SectionSym->SectionIdx = ES.SectionIdx;
535 SymbolList.push_back(SectionSym);
536 ES.Sym = SymbolList.back();
540 EmitStringTable(M.getModuleIdentifier());
542 // Emit the symbol table now, if non-empty.
545 // Emit the relocation sections.
548 // Emit the sections string table.
549 EmitSectionTableStringTable();
551 // Dump the sections and section table to the .o file.
552 OutputSectionsAndSectionTable();
554 // We are done with the abstract symbols.
559 // Release the name mangler object.
560 delete Mang; Mang = 0;
564 // RelocateField - Patch relocatable field with 'Offset' in 'BO'
565 // using a 'Value' of known 'Size'
566 void ELFWriter::RelocateField(BinaryObject &BO, uint32_t Offset,
567 int64_t Value, unsigned Size) {
569 BO.fixWord32(Value, Offset);
571 BO.fixWord64(Value, Offset);
573 llvm_unreachable("don't know howto patch relocatable field");
576 /// EmitRelocations - Emit relocations
577 void ELFWriter::EmitRelocations() {
579 // True if the target uses the relocation entry to hold the addend,
580 // otherwise the addend is written directly to the relocatable field.
581 bool HasRelA = TEW->hasRelocationAddend();
583 // Create Relocation sections for each section which needs it.
584 for (unsigned i=0, e=SectionList.size(); i != e; ++i) {
585 ELFSection &S = *SectionList[i];
587 // This section does not have relocations
588 if (!S.hasRelocations()) continue;
589 ELFSection &RelSec = getRelocSection(S);
591 // 'Link' - Section hdr idx of the associated symbol table
592 // 'Info' - Section hdr idx of the section to which the relocation applies
593 ELFSection &SymTab = getSymbolTableSection();
594 RelSec.Link = SymTab.SectionIdx;
595 RelSec.Info = S.SectionIdx;
596 RelSec.EntSize = TEW->getRelocationEntrySize();
598 // Get the relocations from Section
599 std::vector<MachineRelocation> Relos = S.getRelocations();
600 for (std::vector<MachineRelocation>::iterator MRI = Relos.begin(),
601 MRE = Relos.end(); MRI != MRE; ++MRI) {
602 MachineRelocation &MR = *MRI;
604 // Relocatable field offset from the section start
605 unsigned RelOffset = MR.getMachineCodeOffset();
607 // Symbol index in the symbol table
610 // Target specific relocation field type and size
611 unsigned RelType = TEW->getRelocationType(MR.getRelocationType());
612 unsigned RelTySize = TEW->getRelocationTySize(RelType);
615 // There are several machine relocations types, and each one of
616 // them needs a different approach to retrieve the symbol table index.
617 if (MR.isGlobalValue()) {
618 const GlobalValue *G = MR.getGlobalValue();
619 SymIdx = GblSymLookup[G];
620 if (G->hasPrivateLinkage()) {
621 // If the target uses a section offset in the relocation:
622 // SymIdx + Addend = section sym for global + section offset
623 unsigned SectionIdx = PrivateSyms[SymIdx]->SectionIdx;
624 Addend = PrivateSyms[SymIdx]->Value;
625 SymIdx = SectionList[SectionIdx]->getSymbolTableIndex();
627 Addend = TEW->getDefaultAddendForRelTy(RelType);
629 } else if (MR.isExternalSymbol()) {
630 const char *ExtSym = MR.getExternalSymbol();
631 SymIdx = ExtSymLookup[ExtSym];
632 Addend = TEW->getDefaultAddendForRelTy(RelType);
634 // Get the symbol index for the section symbol
635 unsigned SectionIdx = MR.getConstantVal();
636 SymIdx = SectionList[SectionIdx]->getSymbolTableIndex();
637 Addend = (uint64_t)MR.getResultPointer();
639 // For pc relative relocations where symbols are defined in the same
640 // section they are referenced, ignore the relocation entry and patch
641 // the relocatable field with the symbol offset directly.
642 if (S.SectionIdx == SectionIdx && TEW->isPCRelativeRel(RelType)) {
643 int64_t Value = TEW->computeRelocation(Addend, RelOffset, RelType);
644 RelocateField(S, RelOffset, Value, RelTySize);
648 // Handle Jump Table Index relocation
649 if ((SectionIdx == getJumpTableSection().SectionIdx) &&
650 TEW->hasCustomJumpTableIndexRelTy()) {
651 RelType = TEW->getJumpTableIndexRelTy();
652 RelTySize = TEW->getRelocationTySize(RelType);
656 // The target without addend on the relocation symbol must be
657 // patched in the relocation place itself to contain the addend
659 RelocateField(S, RelOffset, Addend, RelTySize);
661 // Get the relocation entry and emit to the relocation section
662 ELFRelocation Rel(RelOffset, SymIdx, RelType, HasRelA, Addend);
663 EmitRelocation(RelSec, Rel, HasRelA);
668 /// EmitRelocation - Write relocation 'Rel' to the relocation section 'Rel'
669 void ELFWriter::EmitRelocation(BinaryObject &RelSec, ELFRelocation &Rel,
671 RelSec.emitWord(Rel.getOffset());
672 RelSec.emitWord(Rel.getInfo(is64Bit));
674 RelSec.emitWord(Rel.getAddend());
677 /// EmitSymbol - Write symbol 'Sym' to the symbol table 'SymbolTable'
678 void ELFWriter::EmitSymbol(BinaryObject &SymbolTable, ELFSym &Sym) {
680 SymbolTable.emitWord32(Sym.NameIdx);
681 SymbolTable.emitByte(Sym.Info);
682 SymbolTable.emitByte(Sym.Other);
683 SymbolTable.emitWord16(Sym.SectionIdx);
684 SymbolTable.emitWord64(Sym.Value);
685 SymbolTable.emitWord64(Sym.Size);
687 SymbolTable.emitWord32(Sym.NameIdx);
688 SymbolTable.emitWord32(Sym.Value);
689 SymbolTable.emitWord32(Sym.Size);
690 SymbolTable.emitByte(Sym.Info);
691 SymbolTable.emitByte(Sym.Other);
692 SymbolTable.emitWord16(Sym.SectionIdx);
696 /// EmitSectionHeader - Write section 'Section' header in 'SHdrTab'
697 /// Section Header Table
698 void ELFWriter::EmitSectionHeader(BinaryObject &SHdrTab,
699 const ELFSection &SHdr) {
700 SHdrTab.emitWord32(SHdr.NameIdx);
701 SHdrTab.emitWord32(SHdr.Type);
703 SHdrTab.emitWord64(SHdr.Flags);
704 SHdrTab.emitWord(SHdr.Addr);
705 SHdrTab.emitWord(SHdr.Offset);
706 SHdrTab.emitWord64(SHdr.Size);
707 SHdrTab.emitWord32(SHdr.Link);
708 SHdrTab.emitWord32(SHdr.Info);
709 SHdrTab.emitWord64(SHdr.Align);
710 SHdrTab.emitWord64(SHdr.EntSize);
712 SHdrTab.emitWord32(SHdr.Flags);
713 SHdrTab.emitWord(SHdr.Addr);
714 SHdrTab.emitWord(SHdr.Offset);
715 SHdrTab.emitWord32(SHdr.Size);
716 SHdrTab.emitWord32(SHdr.Link);
717 SHdrTab.emitWord32(SHdr.Info);
718 SHdrTab.emitWord32(SHdr.Align);
719 SHdrTab.emitWord32(SHdr.EntSize);
723 /// EmitStringTable - If the current symbol table is non-empty, emit the string
725 void ELFWriter::EmitStringTable(const std::string &ModuleName) {
726 if (!SymbolList.size()) return; // Empty symbol table.
727 ELFSection &StrTab = getStringTableSection();
729 // Set the zero'th symbol to a null byte, as required.
732 // Walk on the symbol list and write symbol names into the string table.
734 for (ELFSymIter I=SymbolList.begin(), E=SymbolList.end(); I != E; ++I) {
738 if (Sym.isGlobalValue())
739 // Use the name mangler to uniquify the LLVM symbol.
740 Name.append(Mang->getMangledName(Sym.getGlobalValue()));
741 else if (Sym.isExternalSym())
742 Name.append(Sym.getExternalSymbol());
743 else if (Sym.isFileType())
744 Name.append(ModuleName);
750 StrTab.emitString(Name);
752 // Keep track of the number of bytes emitted to this section.
753 Index += Name.size()+1;
756 assert(Index == StrTab.size());
760 // SortSymbols - On the symbol table local symbols must come before
761 // all other symbols with non-local bindings. The return value is
762 // the position of the first non local symbol.
763 unsigned ELFWriter::SortSymbols() {
764 unsigned FirstNonLocalSymbol;
765 std::vector<ELFSym*> LocalSyms, OtherSyms;
767 for (ELFSymIter I=SymbolList.begin(), E=SymbolList.end(); I != E; ++I) {
768 if ((*I)->isLocalBind())
769 LocalSyms.push_back(*I);
771 OtherSyms.push_back(*I);
774 FirstNonLocalSymbol = LocalSyms.size();
776 for (unsigned i = 0; i < FirstNonLocalSymbol; ++i)
777 SymbolList.push_back(LocalSyms[i]);
779 for (ELFSymIter I=OtherSyms.begin(), E=OtherSyms.end(); I != E; ++I)
780 SymbolList.push_back(*I);
785 return FirstNonLocalSymbol;
788 /// EmitSymbolTable - Emit the symbol table itself.
789 void ELFWriter::EmitSymbolTable() {
790 if (!SymbolList.size()) return; // Empty symbol table.
792 // Now that we have emitted the string table and know the offset into the
793 // string table of each symbol, emit the symbol table itself.
794 ELFSection &SymTab = getSymbolTableSection();
795 SymTab.Align = TEW->getPrefELFAlignment();
797 // Section Index of .strtab.
798 SymTab.Link = getStringTableSection().SectionIdx;
800 // Size of each symtab entry.
801 SymTab.EntSize = TEW->getSymTabEntrySize();
803 // Reorder the symbol table with local symbols first!
804 unsigned FirstNonLocalSymbol = SortSymbols();
806 // Emit all the symbols to the symbol table.
807 for (unsigned i = 0, e = SymbolList.size(); i < e; ++i) {
808 ELFSym &Sym = *SymbolList[i];
810 // Emit symbol to the symbol table
811 EmitSymbol(SymTab, Sym);
813 // Record the symbol table index for each symbol
814 if (Sym.isGlobalValue())
815 GblSymLookup[Sym.getGlobalValue()] = i;
816 else if (Sym.isExternalSym())
817 ExtSymLookup[Sym.getExternalSymbol()] = i;
819 // Keep track on the symbol index into the symbol table
823 // One greater than the symbol table index of the last local symbol
824 SymTab.Info = FirstNonLocalSymbol;
825 SymTab.Size = SymTab.size();
828 /// EmitSectionTableStringTable - This method adds and emits a section for the
829 /// ELF Section Table string table: the string table that holds all of the
831 void ELFWriter::EmitSectionTableStringTable() {
832 // First step: add the section for the string table to the list of sections:
833 ELFSection &SHStrTab = getSectionHeaderStringTableSection();
835 // Now that we know which section number is the .shstrtab section, update the
836 // e_shstrndx entry in the ELF header.
837 ElfHdr.fixWord16(SHStrTab.SectionIdx, ELFHdr_e_shstrndx_Offset);
839 // Set the NameIdx of each section in the string table and emit the bytes for
843 for (ELFSectionIter I=SectionList.begin(), E=SectionList.end(); I != E; ++I) {
844 ELFSection &S = *(*I);
845 // Set the index into the table. Note if we have lots of entries with
846 // common suffixes, we could memoize them here if we cared.
848 SHStrTab.emitString(S.getName());
850 // Keep track of the number of bytes emitted to this section.
851 Index += S.getName().size()+1;
854 // Set the size of .shstrtab now that we know what it is.
855 assert(Index == SHStrTab.size());
856 SHStrTab.Size = Index;
859 /// OutputSectionsAndSectionTable - Now that we have constructed the file header
860 /// and all of the sections, emit these to the ostream destination and emit the
862 void ELFWriter::OutputSectionsAndSectionTable() {
863 // Pass #1: Compute the file offset for each section.
864 size_t FileOff = ElfHdr.size(); // File header first.
866 // Adjust alignment of all section if needed, skip the null section.
867 for (unsigned i=1, e=SectionList.size(); i < e; ++i) {
868 ELFSection &ES = *SectionList[i];
874 // Update Section size
878 // Align FileOff to whatever the alignment restrictions of the section are.
880 FileOff = (FileOff+ES.Align-1) & ~(ES.Align-1);
886 // Align Section Header.
887 unsigned TableAlign = TEW->getPrefELFAlignment();
888 FileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
890 // Now that we know where all of the sections will be emitted, set the e_shnum
891 // entry in the ELF header.
892 ElfHdr.fixWord16(NumSections, ELFHdr_e_shnum_Offset);
894 // Now that we know the offset in the file of the section table, update the
895 // e_shoff address in the ELF header.
896 ElfHdr.fixWord(FileOff, ELFHdr_e_shoff_Offset);
898 // Now that we know all of the data in the file header, emit it and all of the
900 O.write((char *)&ElfHdr.getData()[0], ElfHdr.size());
901 FileOff = ElfHdr.size();
903 // Section Header Table blob
904 BinaryObject SHdrTable(isLittleEndian, is64Bit);
906 // Emit all of sections to the file and build the section header table.
907 for (ELFSectionIter I=SectionList.begin(), E=SectionList.end(); I != E; ++I) {
908 ELFSection &S = *(*I);
909 DOUT << "SectionIdx: " << S.SectionIdx << ", Name: " << S.getName()
910 << ", Size: " << S.Size << ", Offset: " << S.Offset
911 << ", SectionData Size: " << S.size() << "\n";
913 // Align FileOff to whatever the alignment restrictions of the section are.
916 for (size_t NewFileOff = (FileOff+S.Align-1) & ~(S.Align-1);
917 FileOff != NewFileOff; ++FileOff)
920 O.write((char *)&S.getData()[0], S.Size);
924 EmitSectionHeader(SHdrTable, S);
927 // Align output for the section table.
928 for (size_t NewFileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
929 FileOff != NewFileOff; ++FileOff)
932 // Emit the section table itself.
933 O.write((char *)&SHdrTable.getData()[0], SHdrTable.size());