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"
34 #include "ELFWriter.h"
35 #include "ELFCodeEmitter.h"
36 #include "llvm/Constants.h"
37 #include "llvm/Module.h"
38 #include "llvm/PassManager.h"
39 #include "llvm/DerivedTypes.h"
40 #include "llvm/CodeGen/BinaryObject.h"
41 #include "llvm/CodeGen/FileWriters.h"
42 #include "llvm/CodeGen/MachineCodeEmitter.h"
43 #include "llvm/CodeGen/ObjectCodeEmitter.h"
44 #include "llvm/CodeGen/MachineCodeEmitter.h"
45 #include "llvm/CodeGen/MachineConstantPool.h"
46 #include "llvm/Target/TargetAsmInfo.h"
47 #include "llvm/Target/TargetData.h"
48 #include "llvm/Target/TargetELFWriterInfo.h"
49 #include "llvm/Target/TargetMachine.h"
50 #include "llvm/Support/Mangler.h"
51 #include "llvm/Support/Streams.h"
52 #include "llvm/Support/raw_ostream.h"
53 #include "llvm/Support/Debug.h"
56 char ELFWriter::ID = 0;
57 /// AddELFWriter - Concrete function to add the ELF writer to the function pass
59 ObjectCodeEmitter *llvm::AddELFWriter(PassManagerBase &PM,
62 ELFWriter *EW = new ELFWriter(O, TM);
64 return (ObjectCodeEmitter*) &EW->getMachineCodeEmitter();
67 //===----------------------------------------------------------------------===//
68 // ELFWriter Implementation
69 //===----------------------------------------------------------------------===//
71 ELFWriter::ELFWriter(raw_ostream &o, TargetMachine &tm)
72 : MachineFunctionPass(&ID), O(o), TM(tm),
73 is64Bit(TM.getTargetData()->getPointerSizeInBits() == 64),
74 isLittleEndian(TM.getTargetData()->isLittleEndian()),
75 ElfHdr(isLittleEndian, is64Bit) {
77 TAI = TM.getTargetAsmInfo();
78 TEW = TM.getELFWriterInfo();
80 // Create the machine code emitter object for this target.
81 MCE = new ELFCodeEmitter(*this);
83 // Inital number of sections
87 ELFWriter::~ELFWriter() {
91 // doInitialization - Emit the file header and all of the global variables for
92 // the module to the ELF file.
93 bool ELFWriter::doInitialization(Module &M) {
94 Mang = new Mangler(M);
98 // Fields e_shnum e_shstrndx are only known after all section have
99 // been emitted. They locations in the ouput buffer are recorded so
100 // to be patched up later.
104 // emitWord method behaves differently for ELF32 and ELF64, writing
105 // 4 bytes in the former and 8 in the last for *_off and *_addr elf types
107 ElfHdr.emitByte(0x7f); // e_ident[EI_MAG0]
108 ElfHdr.emitByte('E'); // e_ident[EI_MAG1]
109 ElfHdr.emitByte('L'); // e_ident[EI_MAG2]
110 ElfHdr.emitByte('F'); // e_ident[EI_MAG3]
112 ElfHdr.emitByte(TEW->getEIClass()); // e_ident[EI_CLASS]
113 ElfHdr.emitByte(TEW->getEIData()); // e_ident[EI_DATA]
114 ElfHdr.emitByte(EV_CURRENT); // e_ident[EI_VERSION]
115 ElfHdr.emitAlignment(16); // e_ident[EI_NIDENT-EI_PAD]
117 ElfHdr.emitWord16(ET_REL); // e_type
118 ElfHdr.emitWord16(TEW->getEMachine()); // e_machine = target
119 ElfHdr.emitWord32(EV_CURRENT); // e_version
120 ElfHdr.emitWord(0); // e_entry, no entry point in .o file
121 ElfHdr.emitWord(0); // e_phoff, no program header for .o
122 ELFHdr_e_shoff_Offset = ElfHdr.size();
123 ElfHdr.emitWord(0); // e_shoff = sec hdr table off in bytes
124 ElfHdr.emitWord32(TEW->getEFlags()); // e_flags = whatever the target wants
125 ElfHdr.emitWord16(TEW->getHdrSize()); // e_ehsize = ELF header size
126 ElfHdr.emitWord16(0); // e_phentsize = prog header entry size
127 ElfHdr.emitWord16(0); // e_phnum = # prog header entries = 0
129 // e_shentsize = Section header entry size
130 ElfHdr.emitWord16(TEW->getSHdrSize());
132 // e_shnum = # of section header ents
133 ELFHdr_e_shnum_Offset = ElfHdr.size();
134 ElfHdr.emitWord16(0); // Placeholder
136 // e_shstrndx = Section # of '.shstrtab'
137 ELFHdr_e_shstrndx_Offset = ElfHdr.size();
138 ElfHdr.emitWord16(0); // Placeholder
140 // Add the null section, which is required to be first in the file.
146 unsigned ELFWriter::getGlobalELFVisibility(const GlobalValue *GV) {
147 switch (GV->getVisibility()) {
149 assert(0 && "unknown visibility type");
150 case GlobalValue::DefaultVisibility:
151 return ELFSym::STV_DEFAULT;
152 case GlobalValue::HiddenVisibility:
153 return ELFSym::STV_HIDDEN;
154 case GlobalValue::ProtectedVisibility:
155 return ELFSym::STV_PROTECTED;
161 unsigned ELFWriter::getGlobalELFLinkage(const GlobalValue *GV) {
162 if (GV->hasInternalLinkage())
163 return ELFSym::STB_LOCAL;
165 if (GV->hasWeakLinkage())
166 return ELFSym::STB_WEAK;
168 return ELFSym::STB_GLOBAL;
171 // getElfSectionFlags - Get the ELF Section Header based on the
172 // flags defined in ELFTargetAsmInfo.
173 unsigned ELFWriter::getElfSectionFlags(unsigned Flags) {
174 unsigned ElfSectionFlags = ELFSection::SHF_ALLOC;
176 if (Flags & SectionFlags::Code)
177 ElfSectionFlags |= ELFSection::SHF_EXECINSTR;
178 if (Flags & SectionFlags::Writeable)
179 ElfSectionFlags |= ELFSection::SHF_WRITE;
180 if (Flags & SectionFlags::Mergeable)
181 ElfSectionFlags |= ELFSection::SHF_MERGE;
182 if (Flags & SectionFlags::TLS)
183 ElfSectionFlags |= ELFSection::SHF_TLS;
184 if (Flags & SectionFlags::Strings)
185 ElfSectionFlags |= ELFSection::SHF_STRINGS;
187 return ElfSectionFlags;
190 // For global symbols without a section, return the Null section as a
192 ELFSection &ELFWriter::getGlobalSymELFSection(const GlobalVariable *GV,
194 // If this is a declaration, the symbol does not have a section.
195 if (!GV->hasInitializer()) {
196 Sym.SectionIdx = ELFSection::SHN_UNDEF;
197 return getNullSection();
200 // Get the name and flags of the section for the global
201 const Section *S = TAI->SectionForGlobal(GV);
202 unsigned SectionType = ELFSection::SHT_PROGBITS;
203 unsigned SectionFlags = getElfSectionFlags(S->getFlags());
204 DOUT << "Section " << S->getName() << " for global " << GV->getName() << "\n";
206 const TargetData *TD = TM.getTargetData();
207 unsigned Align = TD->getPreferredAlignment(GV);
208 Constant *CV = GV->getInitializer();
210 // If this global has a zero initializer, go to .bss or common section.
211 // Variables are part of the common block if they are zero initialized
212 // and allowed to be merged with other symbols.
213 if (CV->isNullValue() || isa<UndefValue>(CV)) {
214 SectionType = ELFSection::SHT_NOBITS;
215 ELFSection &ElfS = getSection(S->getName(), SectionType, SectionFlags);
216 if (GV->hasLinkOnceLinkage() || GV->hasWeakLinkage() ||
217 GV->hasCommonLinkage()) {
218 Sym.SectionIdx = ELFSection::SHN_COMMON;
224 Sym.SectionIdx = ElfS.SectionIdx;
225 if (Align) ElfS.Size = (ElfS.Size + Align-1) & ~(Align-1);
226 ElfS.Align = std::max(ElfS.Align, Align);
230 Sym.IsConstant = true;
231 ELFSection &ElfS = getSection(S->getName(), SectionType, SectionFlags);
232 Sym.SectionIdx = ElfS.SectionIdx;
233 ElfS.Align = std::max(ElfS.Align, Align);
237 void ELFWriter::EmitFunctionDeclaration(const Function *F) {
239 GblSym.setBind(ELFSym::STB_GLOBAL);
240 GblSym.setType(ELFSym::STT_NOTYPE);
241 GblSym.setVisibility(ELFSym::STV_DEFAULT);
242 GblSym.SectionIdx = ELFSection::SHN_UNDEF;
243 SymbolList.push_back(GblSym);
246 void ELFWriter::EmitGlobalVar(const GlobalVariable *GV) {
247 unsigned SymBind = getGlobalELFLinkage(GV);
248 unsigned Align=0, Size=0;
250 GblSym.setBind(SymBind);
251 GblSym.setVisibility(getGlobalELFVisibility(GV));
253 if (GV->hasInitializer()) {
254 GblSym.setType(ELFSym::STT_OBJECT);
255 const TargetData *TD = TM.getTargetData();
256 Align = TD->getPreferredAlignment(GV);
257 Size = TD->getTypeAllocSize(GV->getInitializer()->getType());
260 GblSym.setType(ELFSym::STT_NOTYPE);
263 ELFSection &GblSection = getGlobalSymELFSection(GV, GblSym);
265 if (GblSym.IsCommon) {
266 GblSym.Value = Align;
267 } else if (GblSym.IsBss) {
268 GblSym.Value = GblSection.Size;
269 GblSection.Size += Size;
270 } else if (GblSym.IsConstant){
271 // GblSym.Value should contain the symbol index inside the section,
272 // and all symbols should start on their required alignment boundary
273 GblSym.Value = (GblSection.size() + (Align-1)) & (-Align);
274 GblSection.emitAlignment(Align);
275 EmitGlobalConstant(GV->getInitializer(), GblSection);
278 // Local symbols should come first on the symbol table.
279 if (!GV->hasPrivateLinkage()) {
280 if (SymBind == ELFSym::STB_LOCAL)
281 SymbolList.push_front(GblSym);
283 SymbolList.push_back(GblSym);
287 void ELFWriter::EmitGlobalConstantStruct(const ConstantStruct *CVS,
290 // Print the fields in successive locations. Pad to align if needed!
291 const TargetData *TD = TM.getTargetData();
292 unsigned Size = TD->getTypeAllocSize(CVS->getType());
293 const StructLayout *cvsLayout = TD->getStructLayout(CVS->getType());
294 uint64_t sizeSoFar = 0;
295 for (unsigned i = 0, e = CVS->getNumOperands(); i != e; ++i) {
296 const Constant* field = CVS->getOperand(i);
298 // Check if padding is needed and insert one or more 0s.
299 uint64_t fieldSize = TD->getTypeAllocSize(field->getType());
300 uint64_t padSize = ((i == e-1 ? Size : cvsLayout->getElementOffset(i+1))
301 - cvsLayout->getElementOffset(i)) - fieldSize;
302 sizeSoFar += fieldSize + padSize;
304 // Now print the actual field value.
305 EmitGlobalConstant(field, GblS);
307 // Insert padding - this may include padding to increase the size of the
308 // current field up to the ABI size (if the struct is not packed) as well
309 // as padding to ensure that the next field starts at the right offset.
310 for (unsigned p=0; p < padSize; p++)
313 assert(sizeSoFar == cvsLayout->getSizeInBytes() &&
314 "Layout of constant struct may be incorrect!");
317 void ELFWriter::EmitGlobalConstant(const Constant *CV, ELFSection &GblS) {
318 const TargetData *TD = TM.getTargetData();
319 unsigned Size = TD->getTypeAllocSize(CV->getType());
321 if (const ConstantArray *CVA = dyn_cast<ConstantArray>(CV)) {
322 if (CVA->isString()) {
323 std::string GblStr = CVA->getAsString();
324 GblStr.resize(GblStr.size()-1);
325 GblS.emitString(GblStr);
326 } else { // Not a string. Print the values in successive locations
327 for (unsigned i = 0, e = CVA->getNumOperands(); i != e; ++i)
328 EmitGlobalConstant(CVA->getOperand(i), GblS);
331 } else if (const ConstantStruct *CVS = dyn_cast<ConstantStruct>(CV)) {
332 EmitGlobalConstantStruct(CVS, GblS);
334 } else if (const ConstantFP *CFP = dyn_cast<ConstantFP>(CV)) {
335 uint64_t Val = CFP->getValueAPF().bitcastToAPInt().getZExtValue();
336 if (CFP->getType() == Type::DoubleTy)
337 GblS.emitWord64(Val);
338 else if (CFP->getType() == Type::FloatTy)
339 GblS.emitWord32(Val);
340 else if (CFP->getType() == Type::X86_FP80Ty) {
341 assert(0 && "X86_FP80Ty global emission not implemented");
342 } else if (CFP->getType() == Type::PPC_FP128Ty)
343 assert(0 && "PPC_FP128Ty global emission not implemented");
345 } else if (const ConstantInt *CI = dyn_cast<ConstantInt>(CV)) {
347 GblS.emitWord32(CI->getZExtValue());
349 GblS.emitWord64(CI->getZExtValue());
351 assert(0 && "LargeInt global emission not implemented");
353 } else if (const ConstantVector *CP = dyn_cast<ConstantVector>(CV)) {
354 const VectorType *PTy = CP->getType();
355 for (unsigned I = 0, E = PTy->getNumElements(); I < E; ++I)
356 EmitGlobalConstant(CP->getOperand(I), GblS);
359 assert(0 && "unknown global constant");
363 bool ELFWriter::runOnMachineFunction(MachineFunction &MF) {
364 // Nothing to do here, this is all done through the MCE object above.
368 /// doFinalization - Now that the module has been completely processed, emit
369 /// the ELF file to 'O'.
370 bool ELFWriter::doFinalization(Module &M) {
371 /// FIXME: This should be removed when moving to ObjectCodeEmiter. Since the
372 /// current ELFCodeEmiter uses CurrBuff, ... it doesn't update S.Data
373 /// vector size for .text sections, so this is a quick dirty fix
374 ELFSection &TS = getTextSection();
376 BinaryData &BD = TS.getData();
377 for (unsigned e=0; e<TS.Size; ++e)
381 // Emit .data section placeholder
384 // Emit .bss section placeholder
387 // Build and emit data, bss and "common" sections.
388 for (Module::global_iterator I = M.global_begin(), E = M.global_end();
394 // Emit all pending globals
395 // TODO: this should be done only for referenced symbols
396 for (SetVector<GlobalValue*>::const_iterator I = PendingGlobals.begin(),
397 E = PendingGlobals.end(); I != E; ++I) {
399 // No need to emit the symbol again
400 if (GblSymLookup.find(*I) != GblSymLookup.end())
403 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(*I)) {
405 } else if (Function *F = dyn_cast<Function>(*I)) {
406 // If function is not in GblSymLookup, it doesn't have a body,
407 // so emit the symbol as a function declaration (no section associated)
408 EmitFunctionDeclaration(F);
410 assert("unknown howto handle pending global");
412 GblSymLookup[*I] = 0;
415 // Emit non-executable stack note
416 if (TAI->getNonexecutableStackDirective())
417 getNonExecStackSection();
419 // Emit a symbol for each section created until now
420 for (std::map<std::string, ELFSection*>::iterator I = SectionLookup.begin(),
421 E = SectionLookup.end(); I != E; ++I) {
422 ELFSection *ES = I->second;
425 if (ES->SectionIdx == 0) continue;
427 ELFSym SectionSym(0);
428 SectionSym.SectionIdx = ES->SectionIdx;
430 SectionSym.setBind(ELFSym::STB_LOCAL);
431 SectionSym.setType(ELFSym::STT_SECTION);
432 SectionSym.setVisibility(ELFSym::STV_DEFAULT);
434 // Local symbols go in the list front
435 SymbolList.push_front(SectionSym);
441 // Emit the symbol table now, if non-empty.
444 // Emit the relocation sections.
447 // Emit the sections string table.
448 EmitSectionTableStringTable();
450 // Dump the sections and section table to the .o file.
451 OutputSectionsAndSectionTable();
453 // We are done with the abstract symbols.
457 // Release the name mangler object.
458 delete Mang; Mang = 0;
462 /// EmitRelocations - Emit relocations
463 void ELFWriter::EmitRelocations() {
465 // Create Relocation sections for each section which needs it.
466 for (std::list<ELFSection>::iterator I = SectionList.begin(),
467 E = SectionList.end(); I != E; ++I) {
469 // This section does not have relocations
470 if (!I->hasRelocations()) continue;
472 // Get the relocation section for section 'I'
473 bool HasRelA = TEW->hasRelocationAddend();
474 ELFSection &RelSec = getRelocSection(I->getName(), HasRelA,
475 TEW->getPrefELFAlignment());
477 // 'Link' - Section hdr idx of the associated symbol table
478 // 'Info' - Section hdr idx of the section to which the relocation applies
479 ELFSection &SymTab = getSymbolTableSection();
480 RelSec.Link = SymTab.SectionIdx;
481 RelSec.Info = I->SectionIdx;
482 RelSec.EntSize = TEW->getRelocationEntrySize();
484 // Get the relocations from Section
485 std::vector<MachineRelocation> Relos = I->getRelocations();
486 for (std::vector<MachineRelocation>::iterator MRI = Relos.begin(),
487 MRE = Relos.end(); MRI != MRE; ++MRI) {
488 MachineRelocation &MR = *MRI;
490 // Offset from the start of the section containing the symbol
491 unsigned Offset = MR.getMachineCodeOffset();
493 // Symbol index in the symbol table
496 // Target specific ELF relocation type
497 unsigned RelType = TEW->getRelocationType(MR.getRelocationType());
499 // Constant addend used to compute the value to be stored
500 // into the relocatable field
503 // There are several machine relocations types, and each one of
504 // them needs a different approach to retrieve the symbol table index.
505 if (MR.isGlobalValue()) {
506 const GlobalValue *G = MR.getGlobalValue();
507 SymIdx = GblSymLookup[G];
508 Addend = TEW->getAddendForRelTy(RelType);
510 unsigned SectionIdx = MR.getConstantVal();
511 // TODO: use a map for this.
512 for (std::list<ELFSym>::iterator I = SymbolList.begin(),
513 E = SymbolList.end(); I != E; ++I)
514 if ((SectionIdx == I->SectionIdx) &&
515 (I->getType() == ELFSym::STT_SECTION)) {
516 SymIdx = I->SymTabIdx;
519 Addend = (uint64_t)MR.getResultPointer();
522 // Get the relocation entry and emit to the relocation section
523 ELFRelocation Rel(Offset, SymIdx, RelType, HasRelA, Addend);
524 EmitRelocation(RelSec, Rel, HasRelA);
529 /// EmitRelocation - Write relocation 'Rel' to the relocation section 'Rel'
530 void ELFWriter::EmitRelocation(BinaryObject &RelSec, ELFRelocation &Rel,
532 RelSec.emitWord(Rel.getOffset());
533 RelSec.emitWord(Rel.getInfo(is64Bit));
535 RelSec.emitWord(Rel.getAddend());
538 /// EmitSymbol - Write symbol 'Sym' to the symbol table 'SymbolTable'
539 void ELFWriter::EmitSymbol(BinaryObject &SymbolTable, ELFSym &Sym) {
541 SymbolTable.emitWord32(Sym.NameIdx);
542 SymbolTable.emitByte(Sym.Info);
543 SymbolTable.emitByte(Sym.Other);
544 SymbolTable.emitWord16(Sym.SectionIdx);
545 SymbolTable.emitWord64(Sym.Value);
546 SymbolTable.emitWord64(Sym.Size);
548 SymbolTable.emitWord32(Sym.NameIdx);
549 SymbolTable.emitWord32(Sym.Value);
550 SymbolTable.emitWord32(Sym.Size);
551 SymbolTable.emitByte(Sym.Info);
552 SymbolTable.emitByte(Sym.Other);
553 SymbolTable.emitWord16(Sym.SectionIdx);
557 /// EmitSectionHeader - Write section 'Section' header in 'SHdrTab'
558 /// Section Header Table
559 void ELFWriter::EmitSectionHeader(BinaryObject &SHdrTab,
560 const ELFSection &SHdr) {
561 SHdrTab.emitWord32(SHdr.NameIdx);
562 SHdrTab.emitWord32(SHdr.Type);
564 SHdrTab.emitWord64(SHdr.Flags);
565 SHdrTab.emitWord(SHdr.Addr);
566 SHdrTab.emitWord(SHdr.Offset);
567 SHdrTab.emitWord64(SHdr.Size);
568 SHdrTab.emitWord32(SHdr.Link);
569 SHdrTab.emitWord32(SHdr.Info);
570 SHdrTab.emitWord64(SHdr.Align);
571 SHdrTab.emitWord64(SHdr.EntSize);
573 SHdrTab.emitWord32(SHdr.Flags);
574 SHdrTab.emitWord(SHdr.Addr);
575 SHdrTab.emitWord(SHdr.Offset);
576 SHdrTab.emitWord32(SHdr.Size);
577 SHdrTab.emitWord32(SHdr.Link);
578 SHdrTab.emitWord32(SHdr.Info);
579 SHdrTab.emitWord32(SHdr.Align);
580 SHdrTab.emitWord32(SHdr.EntSize);
584 /// EmitStringTable - If the current symbol table is non-empty, emit the string
586 void ELFWriter::EmitStringTable() {
587 if (!SymbolList.size()) return; // Empty symbol table.
588 ELFSection &StrTab = getStringTableSection();
590 // Set the zero'th symbol to a null byte, as required.
593 // Walk on the symbol list and write symbol names into the
596 for (std::list<ELFSym>::iterator I = SymbolList.begin(),
597 E = SymbolList.end(); I != E; ++I) {
599 // Use the name mangler to uniquify the LLVM symbol.
601 if (I->GV) Name.append(Mang->getValueName(I->GV));
607 StrTab.emitString(Name);
609 // Keep track of the number of bytes emitted to this section.
610 Index += Name.size()+1;
613 assert(Index == StrTab.size());
617 /// EmitSymbolTable - Emit the symbol table itself.
618 void ELFWriter::EmitSymbolTable() {
619 if (!SymbolList.size()) return; // Empty symbol table.
621 unsigned FirstNonLocalSymbol = 1;
622 // Now that we have emitted the string table and know the offset into the
623 // string table of each symbol, emit the symbol table itself.
624 ELFSection &SymTab = getSymbolTableSection();
625 SymTab.Align = TEW->getPrefELFAlignment();
627 // Section Index of .strtab.
628 SymTab.Link = getStringTableSection().SectionIdx;
630 // Size of each symtab entry.
631 SymTab.EntSize = TEW->getSymTabEntrySize();
633 // The first entry in the symtab is the null symbol
634 ELFSym NullSym = ELFSym(0);
635 EmitSymbol(SymTab, NullSym);
637 // Emit all the symbols to the symbol table. Skip the null
638 // symbol, cause it's emitted already
640 for (std::list<ELFSym>::iterator I = SymbolList.begin(),
641 E = SymbolList.end(); I != E; ++I, ++Index) {
642 // Keep track of the first non-local symbol
643 if (I->getBind() == ELFSym::STB_LOCAL)
644 FirstNonLocalSymbol++;
646 // Emit symbol to the symbol table
647 EmitSymbol(SymTab, *I);
649 // Record the symbol table index for each global value
651 GblSymLookup[I->GV] = Index;
653 // Keep track on the symbol index into the symbol table
654 I->SymTabIdx = Index;
657 SymTab.Info = FirstNonLocalSymbol;
658 SymTab.Size = SymTab.size();
661 /// EmitSectionTableStringTable - This method adds and emits a section for the
662 /// ELF Section Table string table: the string table that holds all of the
664 void ELFWriter::EmitSectionTableStringTable() {
665 // First step: add the section for the string table to the list of sections:
666 ELFSection &SHStrTab = getSectionHeaderStringTableSection();
668 // Now that we know which section number is the .shstrtab section, update the
669 // e_shstrndx entry in the ELF header.
670 ElfHdr.fixWord16(SHStrTab.SectionIdx, ELFHdr_e_shstrndx_Offset);
672 // Set the NameIdx of each section in the string table and emit the bytes for
676 for (std::list<ELFSection>::iterator I = SectionList.begin(),
677 E = SectionList.end(); I != E; ++I) {
678 // Set the index into the table. Note if we have lots of entries with
679 // common suffixes, we could memoize them here if we cared.
681 SHStrTab.emitString(I->getName());
683 // Keep track of the number of bytes emitted to this section.
684 Index += I->getName().size()+1;
687 // Set the size of .shstrtab now that we know what it is.
688 assert(Index == SHStrTab.size());
689 SHStrTab.Size = Index;
692 /// OutputSectionsAndSectionTable - Now that we have constructed the file header
693 /// and all of the sections, emit these to the ostream destination and emit the
695 void ELFWriter::OutputSectionsAndSectionTable() {
696 // Pass #1: Compute the file offset for each section.
697 size_t FileOff = ElfHdr.size(); // File header first.
699 // Adjust alignment of all section if needed.
700 for (std::list<ELFSection>::iterator I = SectionList.begin(),
701 E = SectionList.end(); I != E; ++I) {
703 // Section idx 0 has 0 offset
712 // Update Section size
716 // Align FileOff to whatever the alignment restrictions of the section are.
718 FileOff = (FileOff+I->Align-1) & ~(I->Align-1);
724 // Align Section Header.
725 unsigned TableAlign = TEW->getPrefELFAlignment();
726 FileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
728 // Now that we know where all of the sections will be emitted, set the e_shnum
729 // entry in the ELF header.
730 ElfHdr.fixWord16(NumSections, ELFHdr_e_shnum_Offset);
732 // Now that we know the offset in the file of the section table, update the
733 // e_shoff address in the ELF header.
734 ElfHdr.fixWord(FileOff, ELFHdr_e_shoff_Offset);
736 // Now that we know all of the data in the file header, emit it and all of the
738 O.write((char *)&ElfHdr.getData()[0], ElfHdr.size());
739 FileOff = ElfHdr.size();
741 // Section Header Table blob
742 BinaryObject SHdrTable(isLittleEndian, is64Bit);
744 // Emit all of sections to the file and build the section header table.
745 while (!SectionList.empty()) {
746 ELFSection &S = *SectionList.begin();
747 DOUT << "SectionIdx: " << S.SectionIdx << ", Name: " << S.getName()
748 << ", Size: " << S.Size << ", Offset: " << S.Offset
749 << ", SectionData Size: " << S.size() << "\n";
751 // Align FileOff to whatever the alignment restrictions of the section are.
754 for (size_t NewFileOff = (FileOff+S.Align-1) & ~(S.Align-1);
755 FileOff != NewFileOff; ++FileOff)
758 O.write((char *)&S.getData()[0], S.Size);
762 EmitSectionHeader(SHdrTable, S);
763 SectionList.pop_front();
766 // Align output for the section table.
767 for (size_t NewFileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
768 FileOff != NewFileOff; ++FileOff)
771 // Emit the section table itself.
772 O.write((char *)&SHdrTable.getData()[0], SHdrTable.size());