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 // NOTE: This code should eventually be extended to support 64-bit ELF (this
30 // won't be hard), but we haven't done so yet!
32 //===----------------------------------------------------------------------===//
34 #include "ELFWriter.h"
35 #include "llvm/Module.h"
36 #include "llvm/PassManager.h"
37 #include "llvm/CodeGen/FileWriters.h"
38 #include "llvm/CodeGen/MachineCodeEmitter.h"
39 #include "llvm/CodeGen/MachineConstantPool.h"
40 #include "llvm/CodeGen/MachineFunctionPass.h"
41 #include "llvm/Target/TargetData.h"
42 #include "llvm/Target/TargetELFWriterInfo.h"
43 #include "llvm/Target/TargetMachine.h"
44 #include "llvm/Support/Mangler.h"
45 #include "llvm/Support/OutputBuffer.h"
46 #include "llvm/Support/Streams.h"
50 char ELFWriter::ID = 0;
51 /// AddELFWriter - Concrete function to add the ELF writer to the function pass
53 MachineCodeEmitter *llvm::AddELFWriter(PassManagerBase &PM,
56 ELFWriter *EW = new ELFWriter(O, TM);
58 return &EW->getMachineCodeEmitter();
61 //===----------------------------------------------------------------------===//
62 // ELFCodeEmitter Implementation
63 //===----------------------------------------------------------------------===//
66 /// ELFCodeEmitter - This class is used by the ELFWriter to emit the code for
67 /// functions to the ELF file.
68 class ELFCodeEmitter : public MachineCodeEmitter {
71 ELFWriter::ELFSection *ES; // Section to write to.
72 std::vector<unsigned char> *OutBuffer;
75 explicit ELFCodeEmitter(ELFWriter &ew) : EW(ew), TM(EW.TM), OutBuffer(0) {}
77 void startFunction(MachineFunction &F);
78 bool finishFunction(MachineFunction &F);
80 void addRelocation(const MachineRelocation &MR) {
81 assert(0 && "relo not handled yet!");
84 virtual void StartMachineBasicBlock(MachineBasicBlock *MBB) {
87 virtual intptr_t getConstantPoolEntryAddress(unsigned Index) const {
88 assert(0 && "CP not implementated yet!");
91 virtual intptr_t getJumpTableEntryAddress(unsigned Index) const {
92 assert(0 && "JT not implementated yet!");
96 virtual intptr_t getMachineBasicBlockAddress(MachineBasicBlock *MBB) const {
97 assert(0 && "JT not implementated yet!");
101 virtual intptr_t getLabelAddress(uint64_t Label) const {
102 assert(0 && "Label address not implementated yet!");
107 virtual void emitLabel(uint64_t LabelID) {
108 assert(0 && "emit Label not implementated yet!");
113 virtual void setModuleInfo(llvm::MachineModuleInfo* MMI) { }
116 /// JIT SPECIFIC FUNCTIONS - DO NOT IMPLEMENT THESE HERE!
117 void startFunctionStub(const GlobalValue* F, unsigned StubSize,
118 unsigned Alignment = 1) {
119 assert(0 && "JIT specific function called!");
122 void *finishFunctionStub(const GlobalValue *F) {
123 assert(0 && "JIT specific function called!");
130 /// startFunction - This callback is invoked when a new machine function is
131 /// about to be emitted.
132 void ELFCodeEmitter::startFunction(MachineFunction &F) {
133 // Align the output buffer to the appropriate alignment.
134 unsigned Align = 16; // FIXME: GENERICIZE!!
135 // Get the ELF Section that this function belongs in.
136 ES = &EW.getSection(".text", ELFWriter::ELFSection::SHT_PROGBITS,
137 ELFWriter::ELFSection::SHF_EXECINSTR |
138 ELFWriter::ELFSection::SHF_ALLOC);
139 OutBuffer = &ES->SectionData;
140 cerr << "FIXME: This code needs to be updated for changes in the "
141 << "CodeEmitter interfaces. In particular, this should set "
142 << "BufferBegin/BufferEnd/CurBufferPtr, not deal with OutBuffer!";
145 // Upgrade the section alignment if required.
146 if (ES->Align < Align) ES->Align = Align;
148 // Add padding zeros to the end of the buffer to make sure that the
149 // function will start on the correct byte alignment within the section.
150 OutputBuffer OB(*OutBuffer,
151 TM.getTargetData()->getPointerSizeInBits() == 64,
152 TM.getTargetData()->isLittleEndian());
154 FnStart = OutBuffer->size();
157 /// finishFunction - This callback is invoked after the function is completely
159 bool ELFCodeEmitter::finishFunction(MachineFunction &F) {
160 // We now know the size of the function, add a symbol to represent it.
161 ELFWriter::ELFSym FnSym(F.getFunction());
163 // Figure out the binding (linkage) of the symbol.
164 switch (F.getFunction()->getLinkage()) {
166 // appending linkage is illegal for functions.
167 assert(0 && "Unknown linkage type!");
168 case GlobalValue::ExternalLinkage:
169 FnSym.SetBind(ELFWriter::ELFSym::STB_GLOBAL);
171 case GlobalValue::LinkOnceLinkage:
172 case GlobalValue::WeakLinkage:
173 FnSym.SetBind(ELFWriter::ELFSym::STB_WEAK);
175 case GlobalValue::InternalLinkage:
176 FnSym.SetBind(ELFWriter::ELFSym::STB_LOCAL);
180 ES->Size = OutBuffer->size();
182 FnSym.SetType(ELFWriter::ELFSym::STT_FUNC);
183 FnSym.SectionIdx = ES->SectionIdx;
184 FnSym.Value = FnStart; // Value = Offset from start of Section.
185 FnSym.Size = OutBuffer->size()-FnStart;
187 // Finally, add it to the symtab.
188 EW.SymbolTable.push_back(FnSym);
192 //===----------------------------------------------------------------------===//
193 // ELFWriter Implementation
194 //===----------------------------------------------------------------------===//
196 ELFWriter::ELFWriter(std::ostream &o, TargetMachine &tm)
197 : MachineFunctionPass((intptr_t)&ID), O(o), TM(tm) {
198 e_flags = 0; // e_flags defaults to 0, no flags.
200 is64Bit = TM.getTargetData()->getPointerSizeInBits() == 64;
201 isLittleEndian = TM.getTargetData()->isLittleEndian();
203 // Create the machine code emitter object for this target.
204 MCE = new ELFCodeEmitter(*this);
208 ELFWriter::~ELFWriter() {
212 // doInitialization - Emit the file header and all of the global variables for
213 // the module to the ELF file.
214 bool ELFWriter::doInitialization(Module &M) {
215 Mang = new Mangler(M);
217 // Local alias to shortenify coming code.
218 std::vector<unsigned char> &FH = FileHeader;
219 OutputBuffer FHOut(FH, is64Bit, isLittleEndian);
221 FHOut.outbyte(0x7F); // EI_MAG0
222 FHOut.outbyte('E'); // EI_MAG1
223 FHOut.outbyte('L'); // EI_MAG2
224 FHOut.outbyte('F'); // EI_MAG3
225 FHOut.outbyte(is64Bit ? 2 : 1); // EI_CLASS
226 FHOut.outbyte(isLittleEndian ? 1 : 2); // EI_DATA
227 FHOut.outbyte(1); // EI_VERSION
228 FH.resize(16); // EI_PAD up to 16 bytes.
230 // This should change for shared objects.
231 FHOut.outhalf(1); // e_type = ET_REL
232 FHOut.outhalf(TM.getELFWriterInfo()->getEMachine()); // target-defined
233 FHOut.outword(1); // e_version = 1
234 FHOut.outaddr(0); // e_entry = 0 -> no entry point in .o file
235 FHOut.outaddr(0); // e_phoff = 0 -> no program header for .o
237 ELFHeader_e_shoff_Offset = FH.size();
238 FHOut.outaddr(0); // e_shoff
239 FHOut.outword(e_flags); // e_flags = whatever the target wants
241 FHOut.outhalf(is64Bit ? 64 : 52); // e_ehsize = ELF header size
242 FHOut.outhalf(0); // e_phentsize = prog header entry size
243 FHOut.outhalf(0); // e_phnum = # prog header entries = 0
244 FHOut.outhalf(is64Bit ? 64 : 40); // e_shentsize = sect hdr entry size
247 ELFHeader_e_shnum_Offset = FH.size();
248 FHOut.outhalf(0); // e_shnum = # of section header ents
249 ELFHeader_e_shstrndx_Offset = FH.size();
250 FHOut.outhalf(0); // e_shstrndx = Section # of '.shstrtab'
252 // Add the null section, which is required to be first in the file.
253 getSection("", 0, 0);
255 // Start up the symbol table. The first entry in the symtab is the null
257 SymbolTable.push_back(ELFSym(0));
262 void ELFWriter::EmitGlobal(GlobalVariable *GV) {
263 // If this is an external global, emit it now. TODO: Note that it would be
264 // better to ignore the symbol here and only add it to the symbol table if
266 if (!GV->hasInitializer()) {
267 ELFSym ExternalSym(GV);
268 ExternalSym.SetBind(ELFSym::STB_GLOBAL);
269 ExternalSym.SetType(ELFSym::STT_NOTYPE);
270 ExternalSym.SectionIdx = ELFSection::SHN_UNDEF;
271 SymbolTable.push_back(ExternalSym);
275 const Type *GVType = (const Type*)GV->getType();
276 unsigned Align = TM.getTargetData()->getPreferredAlignment(GV);
277 unsigned Size = TM.getTargetData()->getABITypeSize(GVType);
279 // If this global has a zero initializer, it is part of the .bss or common
281 if (GV->getInitializer()->isNullValue()) {
282 // If this global is part of the common block, add it now. Variables are
283 // part of the common block if they are zero initialized and allowed to be
284 // merged with other symbols.
285 if (GV->hasLinkOnceLinkage() || GV->hasWeakLinkage() ||
286 GV->hasCommonLinkage()) {
287 ELFSym CommonSym(GV);
288 // Value for common symbols is the alignment required.
289 CommonSym.Value = Align;
290 CommonSym.Size = Size;
291 CommonSym.SetBind(ELFSym::STB_GLOBAL);
292 CommonSym.SetType(ELFSym::STT_OBJECT);
293 // TODO SOMEDAY: add ELF visibility.
294 CommonSym.SectionIdx = ELFSection::SHN_COMMON;
295 SymbolTable.push_back(CommonSym);
299 // Otherwise, this symbol is part of the .bss section. Emit it now.
301 // Handle alignment. Ensure section is aligned at least as much as required
303 ELFSection &BSSSection = getBSSSection();
304 BSSSection.Align = std::max(BSSSection.Align, Align);
306 // Within the section, emit enough virtual padding to get us to an alignment
309 BSSSection.Size = (BSSSection.Size + Align - 1) & ~(Align-1);
312 BSSSym.Value = BSSSection.Size;
314 BSSSym.SetType(ELFSym::STT_OBJECT);
316 switch (GV->getLinkage()) {
317 default: // weak/linkonce/common handled above
318 assert(0 && "Unexpected linkage type!");
319 case GlobalValue::AppendingLinkage: // FIXME: This should be improved!
320 case GlobalValue::ExternalLinkage:
321 BSSSym.SetBind(ELFSym::STB_GLOBAL);
323 case GlobalValue::InternalLinkage:
324 BSSSym.SetBind(ELFSym::STB_LOCAL);
328 // Set the idx of the .bss section
329 BSSSym.SectionIdx = BSSSection.SectionIdx;
330 SymbolTable.push_back(BSSSym);
332 // Reserve space in the .bss section for this symbol.
333 BSSSection.Size += Size;
337 // FIXME: handle .rodata
338 //assert(!GV->isConstant() && "unimp");
340 // FIXME: handle .data
341 //assert(0 && "unimp");
345 bool ELFWriter::runOnMachineFunction(MachineFunction &MF) {
346 // Nothing to do here, this is all done through the MCE object above.
350 /// doFinalization - Now that the module has been completely processed, emit
351 /// the ELF file to 'O'.
352 bool ELFWriter::doFinalization(Module &M) {
353 // Okay, the ELF header and .text sections have been completed, build the
354 // .data, .bss, and "common" sections next.
355 for (Module::global_iterator I = M.global_begin(), E = M.global_end();
359 // Emit the symbol table now, if non-empty.
362 // FIXME: Emit the relocations now.
364 // Emit the string table for the sections in the ELF file we have.
365 EmitSectionTableStringTable();
367 // Emit the sections to the .o file, and emit the section table for the file.
368 OutputSectionsAndSectionTable();
370 // We are done with the abstract symbols.
374 // Release the name mangler object.
375 delete Mang; Mang = 0;
379 /// EmitSymbolTable - If the current symbol table is non-empty, emit the string
380 /// table for it and then the symbol table itself.
381 void ELFWriter::EmitSymbolTable() {
382 if (SymbolTable.size() == 1) return; // Only the null entry.
384 // FIXME: compact all local symbols to the start of the symtab.
385 unsigned FirstNonLocalSymbol = 1;
387 ELFSection &StrTab = getSection(".strtab", ELFSection::SHT_STRTAB, 0);
390 DataBuffer &StrTabBuf = StrTab.SectionData;
391 OutputBuffer StrTabOut(StrTabBuf, is64Bit, isLittleEndian);
393 // Set the zero'th symbol to a null byte, as required.
394 StrTabOut.outbyte(0);
395 SymbolTable[0].NameIdx = 0;
397 for (unsigned i = 1, e = SymbolTable.size(); i != e; ++i) {
398 // Use the name mangler to uniquify the LLVM symbol.
399 std::string Name = Mang->getValueName(SymbolTable[i].GV);
402 SymbolTable[i].NameIdx = 0;
404 SymbolTable[i].NameIdx = Index;
406 // Add the name to the output buffer, including the null terminator.
407 StrTabBuf.insert(StrTabBuf.end(), Name.begin(), Name.end());
409 // Add a null terminator.
410 StrTabBuf.push_back(0);
412 // Keep track of the number of bytes emitted to this section.
413 Index += Name.size()+1;
416 assert(Index == StrTabBuf.size());
419 // Now that we have emitted the string table and know the offset into the
420 // string table of each symbol, emit the symbol table itself.
421 ELFSection &SymTab = getSection(".symtab", ELFSection::SHT_SYMTAB, 0);
422 SymTab.Align = is64Bit ? 8 : 4;
423 SymTab.Link = SymTab.SectionIdx; // Section Index of .strtab.
424 SymTab.Info = FirstNonLocalSymbol; // First non-STB_LOCAL symbol.
425 SymTab.EntSize = 16; // Size of each symtab entry. FIXME: wrong for ELF64
426 DataBuffer &SymTabBuf = SymTab.SectionData;
427 OutputBuffer SymTabOut(SymTabBuf, is64Bit, isLittleEndian);
429 if (!is64Bit) { // 32-bit and 64-bit formats are shuffled a bit.
430 for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
431 ELFSym &Sym = SymbolTable[i];
432 SymTabOut.outword(Sym.NameIdx);
433 SymTabOut.outaddr32(Sym.Value);
434 SymTabOut.outword(Sym.Size);
435 SymTabOut.outbyte(Sym.Info);
436 SymTabOut.outbyte(Sym.Other);
437 SymTabOut.outhalf(Sym.SectionIdx);
440 for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
441 ELFSym &Sym = SymbolTable[i];
442 SymTabOut.outword(Sym.NameIdx);
443 SymTabOut.outbyte(Sym.Info);
444 SymTabOut.outbyte(Sym.Other);
445 SymTabOut.outhalf(Sym.SectionIdx);
446 SymTabOut.outaddr64(Sym.Value);
447 SymTabOut.outxword(Sym.Size);
451 SymTab.Size = SymTabBuf.size();
454 /// EmitSectionTableStringTable - This method adds and emits a section for the
455 /// ELF Section Table string table: the string table that holds all of the
457 void ELFWriter::EmitSectionTableStringTable() {
458 // First step: add the section for the string table to the list of sections:
459 ELFSection &SHStrTab = getSection(".shstrtab", ELFSection::SHT_STRTAB, 0);
461 // Now that we know which section number is the .shstrtab section, update the
462 // e_shstrndx entry in the ELF header.
463 OutputBuffer FHOut(FileHeader, is64Bit, isLittleEndian);
464 FHOut.fixhalf(SHStrTab.SectionIdx, ELFHeader_e_shstrndx_Offset);
466 // Set the NameIdx of each section in the string table and emit the bytes for
469 DataBuffer &Buf = SHStrTab.SectionData;
471 for (std::list<ELFSection>::iterator I = SectionList.begin(),
472 E = SectionList.end(); I != E; ++I) {
473 // Set the index into the table. Note if we have lots of entries with
474 // common suffixes, we could memoize them here if we cared.
477 // Add the name to the output buffer, including the null terminator.
478 Buf.insert(Buf.end(), I->Name.begin(), I->Name.end());
480 // Add a null terminator.
483 // Keep track of the number of bytes emitted to this section.
484 Index += I->Name.size()+1;
487 // Set the size of .shstrtab now that we know what it is.
488 assert(Index == Buf.size());
489 SHStrTab.Size = Index;
492 /// OutputSectionsAndSectionTable - Now that we have constructed the file header
493 /// and all of the sections, emit these to the ostream destination and emit the
495 void ELFWriter::OutputSectionsAndSectionTable() {
496 // Pass #1: Compute the file offset for each section.
497 size_t FileOff = FileHeader.size(); // File header first.
499 // Emit all of the section data in order.
500 for (std::list<ELFSection>::iterator I = SectionList.begin(),
501 E = SectionList.end(); I != E; ++I) {
502 // Align FileOff to whatever the alignment restrictions of the section are.
504 FileOff = (FileOff+I->Align-1) & ~(I->Align-1);
506 FileOff += I->SectionData.size();
509 // Align Section Header.
510 unsigned TableAlign = is64Bit ? 8 : 4;
511 FileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
513 // Now that we know where all of the sections will be emitted, set the e_shnum
514 // entry in the ELF header.
515 OutputBuffer FHOut(FileHeader, is64Bit, isLittleEndian);
516 FHOut.fixhalf(NumSections, ELFHeader_e_shnum_Offset);
518 // Now that we know the offset in the file of the section table, update the
519 // e_shoff address in the ELF header.
520 FHOut.fixaddr(FileOff, ELFHeader_e_shoff_Offset);
522 // Now that we know all of the data in the file header, emit it and all of the
524 O.write((char*)&FileHeader[0], FileHeader.size());
525 FileOff = FileHeader.size();
526 DataBuffer().swap(FileHeader);
529 OutputBuffer TableOut(Table, is64Bit, isLittleEndian);
531 // Emit all of the section data and build the section table itself.
532 while (!SectionList.empty()) {
533 const ELFSection &S = *SectionList.begin();
535 // Align FileOff to whatever the alignment restrictions of the section are.
537 for (size_t NewFileOff = (FileOff+S.Align-1) & ~(S.Align-1);
538 FileOff != NewFileOff; ++FileOff)
540 O.write((char*)&S.SectionData[0], S.SectionData.size());
541 FileOff += S.SectionData.size();
543 TableOut.outword(S.NameIdx); // sh_name - Symbol table name idx
544 TableOut.outword(S.Type); // sh_type - Section contents & semantics
545 TableOut.outword(S.Flags); // sh_flags - Section flags.
546 TableOut.outaddr(S.Addr); // sh_addr - The mem addr this section is in.
547 TableOut.outaddr(S.Offset); // sh_offset - Offset from the file start.
548 TableOut.outword(S.Size); // sh_size - The section size.
549 TableOut.outword(S.Link); // sh_link - Section header table index link.
550 TableOut.outword(S.Info); // sh_info - Auxillary information.
551 TableOut.outword(S.Align); // sh_addralign - Alignment of section.
552 TableOut.outword(S.EntSize); // sh_entsize - Size of entries in the section
554 SectionList.pop_front();
557 // Align output for the section table.
558 for (size_t NewFileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
559 FileOff != NewFileOff; ++FileOff)
562 // Emit the section table itself.
563 O.write((char*)&Table[0], Table.size());