1 //===-- ELFWriter.cpp - Target-independent ELF Writer code ----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by Chris Lattner and is distributed under the
6 // University of Illinois Open Source 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 "llvm/CodeGen/ELFWriter.h"
35 #include "llvm/Module.h"
36 #include "llvm/CodeGen/MachineCodeEmitter.h"
37 #include "llvm/CodeGen/MachineConstantPool.h"
38 #include "llvm/Target/TargetMachine.h"
39 #include "llvm/Support/Mangler.h"
43 //===----------------------------------------------------------------------===//
44 // ELFCodeEmitter Implementation
45 //===----------------------------------------------------------------------===//
48 /// ELFCodeEmitter - This class is used by the ELFWriter to emit the code for
49 /// functions to the ELF file.
50 class ELFCodeEmitter : public MachineCodeEmitter {
52 ELFWriter::ELFSection *ES; // Section to write to.
53 std::vector<unsigned char> *OutBuffer;
56 ELFCodeEmitter(ELFWriter &ew) : EW(ew), OutBuffer(0) {}
58 void startFunction(MachineFunction &F);
59 bool finishFunction(MachineFunction &F);
61 void addRelocation(const MachineRelocation &MR) {
62 assert(0 && "relo not handled yet!");
64 virtual uint64_t getConstantPoolEntryAddress(unsigned Index) {
65 assert(0 && "CP not implementated yet!");
68 virtual uint64_t getJumpTableEntryAddress(unsigned Index) {
69 assert(0 && "JT not implementated yet!");
73 virtual void emitJumpTableInfo(MachineJumpTableInfo *MJTI,
74 std::map<MachineBasicBlock*,uint64_t> &MBBM){
75 assert(0 && "JT not implementated yet!");
79 /// JIT SPECIFIC FUNCTIONS - DO NOT IMPLEMENT THESE HERE!
80 void startFunctionStub(unsigned StubSize) {
81 assert(0 && "JIT specific function called!");
84 void *finishFunctionStub(const Function *F) {
85 assert(0 && "JIT specific function called!");
92 /// startFunction - This callback is invoked when a new machine function is
93 /// about to be emitted.
94 void ELFCodeEmitter::startFunction(MachineFunction &F) {
95 // Align the output buffer to the appropriate alignment.
96 unsigned Align = 16; // FIXME: GENERICIZE!!
97 // Get the ELF Section that this function belongs in.
98 ES = &EW.getSection(".text", ELFWriter::ELFSection::SHT_PROGBITS,
99 ELFWriter::ELFSection::SHF_EXECINSTR |
100 ELFWriter::ELFSection::SHF_ALLOC);
101 OutBuffer = &ES->SectionData;
102 std::cerr << "FIXME: This code needs to be updated for changes in the"
103 << " CodeEmitter interfaces. In particular, this should set "
104 << "BufferBegin/BufferEnd/CurBufferPtr, not deal with OutBuffer!";
107 // Upgrade the section alignment if required.
108 if (ES->Align < Align) ES->Align = Align;
110 // Add padding zeros to the end of the buffer to make sure that the
111 // function will start on the correct byte alignment within the section.
112 size_t SectionOff = OutBuffer->size();
113 ELFWriter::align(*OutBuffer, Align);
115 FnStart = OutBuffer->size();
118 /// finishFunction - This callback is invoked after the function is completely
120 bool ELFCodeEmitter::finishFunction(MachineFunction &F) {
121 // We now know the size of the function, add a symbol to represent it.
122 ELFWriter::ELFSym FnSym(F.getFunction());
124 // Figure out the binding (linkage) of the symbol.
125 switch (F.getFunction()->getLinkage()) {
127 // appending linkage is illegal for functions.
128 assert(0 && "Unknown linkage type!");
129 case GlobalValue::ExternalLinkage:
130 FnSym.SetBind(ELFWriter::ELFSym::STB_GLOBAL);
132 case GlobalValue::LinkOnceLinkage:
133 case GlobalValue::WeakLinkage:
134 FnSym.SetBind(ELFWriter::ELFSym::STB_WEAK);
136 case GlobalValue::InternalLinkage:
137 FnSym.SetBind(ELFWriter::ELFSym::STB_LOCAL);
141 ES->Size = OutBuffer->size();
143 FnSym.SetType(ELFWriter::ELFSym::STT_FUNC);
144 FnSym.SectionIdx = ES->SectionIdx;
145 FnSym.Value = FnStart; // Value = Offset from start of Section.
146 FnSym.Size = OutBuffer->size()-FnStart;
148 // Finally, add it to the symtab.
149 EW.SymbolTable.push_back(FnSym);
153 //===----------------------------------------------------------------------===//
154 // ELFWriter Implementation
155 //===----------------------------------------------------------------------===//
157 ELFWriter::ELFWriter(std::ostream &o, TargetMachine &tm) : O(o), TM(tm) {
158 e_machine = 0; // e_machine defaults to 'No Machine'
159 e_flags = 0; // e_flags defaults to 0, no flags.
161 is64Bit = TM.getTargetData().getPointerSizeInBits() == 64;
162 isLittleEndian = TM.getTargetData().isLittleEndian();
164 // Create the machine code emitter object for this target.
165 MCE = new ELFCodeEmitter(*this);
169 ELFWriter::~ELFWriter() {
173 // doInitialization - Emit the file header and all of the global variables for
174 // the module to the ELF file.
175 bool ELFWriter::doInitialization(Module &M) {
176 Mang = new Mangler(M);
178 // Local alias to shortenify coming code.
179 std::vector<unsigned char> &FH = FileHeader;
181 outbyte(FH, 0x7F); // EI_MAG0
182 outbyte(FH, 'E'); // EI_MAG1
183 outbyte(FH, 'L'); // EI_MAG2
184 outbyte(FH, 'F'); // EI_MAG3
185 outbyte(FH, is64Bit ? 2 : 1); // EI_CLASS
186 outbyte(FH, isLittleEndian ? 1 : 2); // EI_DATA
187 outbyte(FH, 1); // EI_VERSION
188 FH.resize(16); // EI_PAD up to 16 bytes.
190 // This should change for shared objects.
191 outhalf(FH, 1); // e_type = ET_REL
192 outhalf(FH, e_machine); // e_machine = whatever the target wants
193 outword(FH, 1); // e_version = 1
194 outaddr(FH, 0); // e_entry = 0 -> no entry point in .o file
195 outaddr(FH, 0); // e_phoff = 0 -> no program header for .o
197 ELFHeader_e_shoff_Offset = FH.size();
198 outaddr(FH, 0); // e_shoff
199 outword(FH, e_flags); // e_flags = whatever the target wants
201 outhalf(FH, is64Bit ? 64 : 52); // e_ehsize = ELF header size
202 outhalf(FH, 0); // e_phentsize = prog header entry size
203 outhalf(FH, 0); // e_phnum = # prog header entries = 0
204 outhalf(FH, is64Bit ? 64 : 40); // e_shentsize = sect hdr entry size
207 ELFHeader_e_shnum_Offset = FH.size();
208 outhalf(FH, 0); // e_shnum = # of section header ents
209 ELFHeader_e_shstrndx_Offset = FH.size();
210 outhalf(FH, 0); // e_shstrndx = Section # of '.shstrtab'
212 // Add the null section, which is required to be first in the file.
213 getSection("", 0, 0);
215 // Start up the symbol table. The first entry in the symtab is the null
217 SymbolTable.push_back(ELFSym(0));
222 void ELFWriter::EmitGlobal(GlobalVariable *GV) {
223 // If this is an external global, emit it now. TODO: Note that it would be
224 // better to ignore the symbol here and only add it to the symbol table if
226 if (!GV->hasInitializer()) {
227 ELFSym ExternalSym(GV);
228 ExternalSym.SetBind(ELFSym::STB_GLOBAL);
229 ExternalSym.SetType(ELFSym::STT_NOTYPE);
230 ExternalSym.SectionIdx = ELFSection::SHN_UNDEF;
231 SymbolTable.push_back(ExternalSym);
235 const Type *GVType = (const Type*)GV->getType();
236 unsigned Align = TM.getTargetData().getTypeAlignment(GVType);
237 unsigned Size = TM.getTargetData().getTypeSize(GVType);
239 // If this global has a zero initializer, it is part of the .bss or common
241 if (GV->getInitializer()->isNullValue()) {
242 // If this global is part of the common block, add it now. Variables are
243 // part of the common block if they are zero initialized and allowed to be
244 // merged with other symbols.
245 if (GV->hasLinkOnceLinkage() || GV->hasWeakLinkage()) {
246 ELFSym CommonSym(GV);
247 // Value for common symbols is the alignment required.
248 CommonSym.Value = Align;
249 CommonSym.Size = Size;
250 CommonSym.SetBind(ELFSym::STB_GLOBAL);
251 CommonSym.SetType(ELFSym::STT_OBJECT);
252 // TODO SOMEDAY: add ELF visibility.
253 CommonSym.SectionIdx = ELFSection::SHN_COMMON;
254 SymbolTable.push_back(CommonSym);
258 // Otherwise, this symbol is part of the .bss section. Emit it now.
260 // Handle alignment. Ensure section is aligned at least as much as required
262 ELFSection &BSSSection = getBSSSection();
263 BSSSection.Align = std::max(BSSSection.Align, Align);
265 // Within the section, emit enough virtual padding to get us to an alignment
268 BSSSection.Size = (BSSSection.Size + Align - 1) & ~(Align-1);
271 BSSSym.Value = BSSSection.Size;
273 BSSSym.SetType(ELFSym::STT_OBJECT);
275 switch (GV->getLinkage()) {
276 default: // weak/linkonce handled above
277 assert(0 && "Unexpected linkage type!");
278 case GlobalValue::AppendingLinkage: // FIXME: This should be improved!
279 case GlobalValue::ExternalLinkage:
280 BSSSym.SetBind(ELFSym::STB_GLOBAL);
282 case GlobalValue::InternalLinkage:
283 BSSSym.SetBind(ELFSym::STB_LOCAL);
287 // Set the idx of the .bss section
288 BSSSym.SectionIdx = BSSSection.SectionIdx;
289 SymbolTable.push_back(BSSSym);
291 // Reserve space in the .bss section for this symbol.
292 BSSSection.Size += Size;
296 // FIXME: handle .rodata
297 //assert(!GV->isConstant() && "unimp");
299 // FIXME: handle .data
300 //assert(0 && "unimp");
304 bool ELFWriter::runOnMachineFunction(MachineFunction &MF) {
305 // Nothing to do here, this is all done through the MCE object above.
309 /// doFinalization - Now that the module has been completely processed, emit
310 /// the ELF file to 'O'.
311 bool ELFWriter::doFinalization(Module &M) {
312 // Okay, the ELF header and .text sections have been completed, build the
313 // .data, .bss, and "common" sections next.
314 for (Module::global_iterator I = M.global_begin(), E = M.global_end();
318 // Emit the symbol table now, if non-empty.
321 // FIXME: Emit the relocations now.
323 // Emit the string table for the sections in the ELF file we have.
324 EmitSectionTableStringTable();
326 // Emit the sections to the .o file, and emit the section table for the file.
327 OutputSectionsAndSectionTable();
329 // We are done with the abstract symbols.
333 // Release the name mangler object.
334 delete Mang; Mang = 0;
338 /// EmitSymbolTable - If the current symbol table is non-empty, emit the string
339 /// table for it and then the symbol table itself.
340 void ELFWriter::EmitSymbolTable() {
341 if (SymbolTable.size() == 1) return; // Only the null entry.
343 // FIXME: compact all local symbols to the start of the symtab.
344 unsigned FirstNonLocalSymbol = 1;
346 ELFSection &StrTab = getSection(".strtab", ELFSection::SHT_STRTAB, 0);
349 DataBuffer &StrTabBuf = StrTab.SectionData;
351 // Set the zero'th symbol to a null byte, as required.
352 outbyte(StrTabBuf, 0);
353 SymbolTable[0].NameIdx = 0;
355 for (unsigned i = 1, e = SymbolTable.size(); i != e; ++i) {
356 // Use the name mangler to uniquify the LLVM symbol.
357 std::string Name = Mang->getValueName(SymbolTable[i].GV);
360 SymbolTable[i].NameIdx = 0;
362 SymbolTable[i].NameIdx = Index;
364 // Add the name to the output buffer, including the null terminator.
365 StrTabBuf.insert(StrTabBuf.end(), Name.begin(), Name.end());
367 // Add a null terminator.
368 StrTabBuf.push_back(0);
370 // Keep track of the number of bytes emitted to this section.
371 Index += Name.size()+1;
374 assert(Index == StrTabBuf.size());
377 // Now that we have emitted the string table and know the offset into the
378 // string table of each symbol, emit the symbol table itself.
379 ELFSection &SymTab = getSection(".symtab", ELFSection::SHT_SYMTAB, 0);
380 SymTab.Align = is64Bit ? 8 : 4;
381 SymTab.Link = SymTab.SectionIdx; // Section Index of .strtab.
382 SymTab.Info = FirstNonLocalSymbol; // First non-STB_LOCAL symbol.
383 SymTab.EntSize = 16; // Size of each symtab entry. FIXME: wrong for ELF64
384 DataBuffer &SymTabBuf = SymTab.SectionData;
386 if (!is64Bit) { // 32-bit and 64-bit formats are shuffled a bit.
387 for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
388 ELFSym &Sym = SymbolTable[i];
389 outword(SymTabBuf, Sym.NameIdx);
390 outaddr32(SymTabBuf, Sym.Value);
391 outword(SymTabBuf, Sym.Size);
392 outbyte(SymTabBuf, Sym.Info);
393 outbyte(SymTabBuf, Sym.Other);
394 outhalf(SymTabBuf, Sym.SectionIdx);
397 for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
398 ELFSym &Sym = SymbolTable[i];
399 outword(SymTabBuf, Sym.NameIdx);
400 outbyte(SymTabBuf, Sym.Info);
401 outbyte(SymTabBuf, Sym.Other);
402 outhalf(SymTabBuf, Sym.SectionIdx);
403 outaddr64(SymTabBuf, Sym.Value);
404 outxword(SymTabBuf, Sym.Size);
408 SymTab.Size = SymTabBuf.size();
411 /// EmitSectionTableStringTable - This method adds and emits a section for the
412 /// ELF Section Table string table: the string table that holds all of the
414 void ELFWriter::EmitSectionTableStringTable() {
415 // First step: add the section for the string table to the list of sections:
416 ELFSection &SHStrTab = getSection(".shstrtab", ELFSection::SHT_STRTAB, 0);
418 // Now that we know which section number is the .shstrtab section, update the
419 // e_shstrndx entry in the ELF header.
420 fixhalf(FileHeader, SHStrTab.SectionIdx, ELFHeader_e_shstrndx_Offset);
422 // Set the NameIdx of each section in the string table and emit the bytes for
425 DataBuffer &Buf = SHStrTab.SectionData;
427 for (std::list<ELFSection>::iterator I = SectionList.begin(),
428 E = SectionList.end(); I != E; ++I) {
429 // Set the index into the table. Note if we have lots of entries with
430 // common suffixes, we could memoize them here if we cared.
433 // Add the name to the output buffer, including the null terminator.
434 Buf.insert(Buf.end(), I->Name.begin(), I->Name.end());
436 // Add a null terminator.
439 // Keep track of the number of bytes emitted to this section.
440 Index += I->Name.size()+1;
443 // Set the size of .shstrtab now that we know what it is.
444 assert(Index == Buf.size());
445 SHStrTab.Size = Index;
448 /// OutputSectionsAndSectionTable - Now that we have constructed the file header
449 /// and all of the sections, emit these to the ostream destination and emit the
451 void ELFWriter::OutputSectionsAndSectionTable() {
452 // Pass #1: Compute the file offset for each section.
453 size_t FileOff = FileHeader.size(); // File header first.
455 // Emit all of the section data in order.
456 for (std::list<ELFSection>::iterator I = SectionList.begin(),
457 E = SectionList.end(); I != E; ++I) {
458 // Align FileOff to whatever the alignment restrictions of the section are.
460 FileOff = (FileOff+I->Align-1) & ~(I->Align-1);
462 FileOff += I->SectionData.size();
465 // Align Section Header.
466 unsigned TableAlign = is64Bit ? 8 : 4;
467 FileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
469 // Now that we know where all of the sections will be emitted, set the e_shnum
470 // entry in the ELF header.
471 fixhalf(FileHeader, NumSections, ELFHeader_e_shnum_Offset);
473 // Now that we know the offset in the file of the section table, update the
474 // e_shoff address in the ELF header.
475 fixaddr(FileHeader, FileOff, ELFHeader_e_shoff_Offset);
477 // Now that we know all of the data in the file header, emit it and all of the
479 O.write((char*)&FileHeader[0], FileHeader.size());
480 FileOff = FileHeader.size();
481 DataBuffer().swap(FileHeader);
485 // Emit all of the section data and build the section table itself.
486 while (!SectionList.empty()) {
487 const ELFSection &S = *SectionList.begin();
489 // Align FileOff to whatever the alignment restrictions of the section are.
491 for (size_t NewFileOff = (FileOff+S.Align-1) & ~(S.Align-1);
492 FileOff != NewFileOff; ++FileOff)
494 O.write((char*)&S.SectionData[0], S.SectionData.size());
495 FileOff += S.SectionData.size();
497 outword(Table, S.NameIdx); // sh_name - Symbol table name idx
498 outword(Table, S.Type); // sh_type - Section contents & semantics
499 outword(Table, S.Flags); // sh_flags - Section flags.
500 outaddr(Table, S.Addr); // sh_addr - The mem addr this section is in.
501 outaddr(Table, S.Offset); // sh_offset - Offset from the file start.
502 outword(Table, S.Size); // sh_size - The section size.
503 outword(Table, S.Link); // sh_link - Section header table index link.
504 outword(Table, S.Info); // sh_info - Auxillary information.
505 outword(Table, S.Align); // sh_addralign - Alignment of section.
506 outword(Table, S.EntSize); // sh_entsize - Size of entries in the section.
508 SectionList.pop_front();
511 // Align output for the section table.
512 for (size_t NewFileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
513 FileOff != NewFileOff; ++FileOff)
516 // Emit the section table itself.
517 O.write((char*)&Table[0], Table.size());