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/DerivedTypes.h"
38 #include "llvm/CodeGen/FileWriters.h"
39 #include "llvm/CodeGen/MachineCodeEmitter.h"
40 #include "llvm/CodeGen/MachineConstantPool.h"
41 #include "llvm/CodeGen/MachineFunctionPass.h"
42 #include "llvm/Target/TargetData.h"
43 #include "llvm/Target/TargetELFWriterInfo.h"
44 #include "llvm/Target/TargetMachine.h"
45 #include "llvm/Support/Mangler.h"
46 #include "llvm/Support/OutputBuffer.h"
47 #include "llvm/Support/Streams.h"
48 #include "llvm/Support/raw_ostream.h"
52 char ELFWriter::ID = 0;
53 /// AddELFWriter - Concrete function to add the ELF writer to the function pass
55 MachineCodeEmitter *llvm::AddELFWriter(PassManagerBase &PM,
58 ELFWriter *EW = new ELFWriter(O, TM);
60 return &EW->getMachineCodeEmitter();
63 //===----------------------------------------------------------------------===//
64 // ELFCodeEmitter Implementation
65 //===----------------------------------------------------------------------===//
68 /// ELFCodeEmitter - This class is used by the ELFWriter to emit the code for
69 /// functions to the ELF file.
70 class ELFCodeEmitter : public MachineCodeEmitter {
73 ELFWriter::ELFSection *ES; // Section to write to.
74 std::vector<unsigned char> *OutBuffer;
77 explicit ELFCodeEmitter(ELFWriter &ew) : EW(ew), TM(EW.TM), OutBuffer(0) {}
79 void startFunction(MachineFunction &F);
80 bool finishFunction(MachineFunction &F);
82 void addRelocation(const MachineRelocation &MR) {
83 assert(0 && "relo not handled yet!");
86 virtual void StartMachineBasicBlock(MachineBasicBlock *MBB) {
89 virtual uintptr_t getConstantPoolEntryAddress(unsigned Index) const {
90 assert(0 && "CP not implementated yet!");
93 virtual uintptr_t getJumpTableEntryAddress(unsigned Index) const {
94 assert(0 && "JT not implementated yet!");
98 virtual uintptr_t getMachineBasicBlockAddress(MachineBasicBlock *MBB) const {
99 assert(0 && "JT not implementated yet!");
103 virtual uintptr_t getLabelAddress(uint64_t Label) const {
104 assert(0 && "Label address not implementated yet!");
109 virtual void emitLabel(uint64_t LabelID) {
110 assert(0 && "emit Label not implementated yet!");
115 virtual void setModuleInfo(llvm::MachineModuleInfo* MMI) { }
118 /// JIT SPECIFIC FUNCTIONS - DO NOT IMPLEMENT THESE HERE!
119 void startGVStub(const GlobalValue* F, unsigned StubSize,
120 unsigned Alignment = 1) {
121 assert(0 && "JIT specific function called!");
124 void *finishGVStub(const GlobalValue *F) {
125 assert(0 && "JIT specific function called!");
132 /// startFunction - This callback is invoked when a new machine function is
133 /// about to be emitted.
134 void ELFCodeEmitter::startFunction(MachineFunction &F) {
135 // Align the output buffer to the appropriate alignment.
136 unsigned Align = 16; // FIXME: GENERICIZE!!
137 // Get the ELF Section that this function belongs in.
138 ES = &EW.getSection(".text", ELFWriter::ELFSection::SHT_PROGBITS,
139 ELFWriter::ELFSection::SHF_EXECINSTR |
140 ELFWriter::ELFSection::SHF_ALLOC);
141 OutBuffer = &ES->SectionData;
142 cerr << "FIXME: This code needs to be updated for changes in the "
143 << "CodeEmitter interfaces. In particular, this should set "
144 << "BufferBegin/BufferEnd/CurBufferPtr, not deal with OutBuffer!";
147 // Upgrade the section alignment if required.
148 if (ES->Align < Align) ES->Align = Align;
150 // Add padding zeros to the end of the buffer to make sure that the
151 // function will start on the correct byte alignment within the section.
152 OutputBuffer OB(*OutBuffer,
153 TM.getTargetData()->getPointerSizeInBits() == 64,
154 TM.getTargetData()->isLittleEndian());
156 FnStart = OutBuffer->size();
159 /// finishFunction - This callback is invoked after the function is completely
161 bool ELFCodeEmitter::finishFunction(MachineFunction &F) {
162 // We now know the size of the function, add a symbol to represent it.
163 ELFWriter::ELFSym FnSym(F.getFunction());
165 // Figure out the binding (linkage) of the symbol.
166 switch (F.getFunction()->getLinkage()) {
168 // appending linkage is illegal for functions.
169 assert(0 && "Unknown linkage type!");
170 case GlobalValue::ExternalLinkage:
171 FnSym.SetBind(ELFWriter::ELFSym::STB_GLOBAL);
173 case GlobalValue::LinkOnceLinkage:
174 case GlobalValue::WeakLinkage:
175 FnSym.SetBind(ELFWriter::ELFSym::STB_WEAK);
177 case GlobalValue::InternalLinkage:
178 FnSym.SetBind(ELFWriter::ELFSym::STB_LOCAL);
182 ES->Size = OutBuffer->size();
184 FnSym.SetType(ELFWriter::ELFSym::STT_FUNC);
185 FnSym.SectionIdx = ES->SectionIdx;
186 FnSym.Value = FnStart; // Value = Offset from start of Section.
187 FnSym.Size = OutBuffer->size()-FnStart;
189 // Finally, add it to the symtab.
190 EW.SymbolTable.push_back(FnSym);
194 //===----------------------------------------------------------------------===//
195 // ELFWriter Implementation
196 //===----------------------------------------------------------------------===//
198 ELFWriter::ELFWriter(raw_ostream &o, TargetMachine &tm)
199 : MachineFunctionPass(&ID), O(o), TM(tm) {
200 e_flags = 0; // e_flags defaults to 0, no flags.
202 is64Bit = TM.getTargetData()->getPointerSizeInBits() == 64;
203 isLittleEndian = TM.getTargetData()->isLittleEndian();
205 // Create the machine code emitter object for this target.
206 MCE = new ELFCodeEmitter(*this);
210 ELFWriter::~ELFWriter() {
214 // doInitialization - Emit the file header and all of the global variables for
215 // the module to the ELF file.
216 bool ELFWriter::doInitialization(Module &M) {
217 Mang = new Mangler(M);
219 // Local alias to shortenify coming code.
220 std::vector<unsigned char> &FH = FileHeader;
221 OutputBuffer FHOut(FH, is64Bit, isLittleEndian);
223 FHOut.outbyte(0x7F); // EI_MAG0
224 FHOut.outbyte('E'); // EI_MAG1
225 FHOut.outbyte('L'); // EI_MAG2
226 FHOut.outbyte('F'); // EI_MAG3
227 FHOut.outbyte(is64Bit ? 2 : 1); // EI_CLASS
228 FHOut.outbyte(isLittleEndian ? 1 : 2); // EI_DATA
229 FHOut.outbyte(1); // EI_VERSION
230 FH.resize(16); // EI_PAD up to 16 bytes.
232 // This should change for shared objects.
233 FHOut.outhalf(1); // e_type = ET_REL
234 FHOut.outhalf(TM.getELFWriterInfo()->getEMachine()); // target-defined
235 FHOut.outword(1); // e_version = 1
236 FHOut.outaddr(0); // e_entry = 0 -> no entry point in .o file
237 FHOut.outaddr(0); // e_phoff = 0 -> no program header for .o
239 ELFHeader_e_shoff_Offset = FH.size();
240 FHOut.outaddr(0); // e_shoff
241 FHOut.outword(e_flags); // e_flags = whatever the target wants
243 FHOut.outhalf(is64Bit ? 64 : 52); // e_ehsize = ELF header size
244 FHOut.outhalf(0); // e_phentsize = prog header entry size
245 FHOut.outhalf(0); // e_phnum = # prog header entries = 0
246 FHOut.outhalf(is64Bit ? 64 : 40); // e_shentsize = sect hdr entry size
249 ELFHeader_e_shnum_Offset = FH.size();
250 FHOut.outhalf(0); // e_shnum = # of section header ents
251 ELFHeader_e_shstrndx_Offset = FH.size();
252 FHOut.outhalf(0); // e_shstrndx = Section # of '.shstrtab'
254 // Add the null section, which is required to be first in the file.
255 getSection("", 0, 0);
257 // Start up the symbol table. The first entry in the symtab is the null
259 SymbolTable.push_back(ELFSym(0));
264 void ELFWriter::EmitGlobal(GlobalVariable *GV) {
265 // If this is an external global, emit it now. TODO: Note that it would be
266 // better to ignore the symbol here and only add it to the symbol table if
268 if (!GV->hasInitializer()) {
269 ELFSym ExternalSym(GV);
270 ExternalSym.SetBind(ELFSym::STB_GLOBAL);
271 ExternalSym.SetType(ELFSym::STT_NOTYPE);
272 ExternalSym.SectionIdx = ELFSection::SHN_UNDEF;
273 SymbolTable.push_back(ExternalSym);
277 unsigned Align = TM.getTargetData()->getPreferredAlignment(GV);
279 TM.getTargetData()->getABITypeSize(GV->getType()->getElementType());
281 // If this global has a zero initializer, it is part of the .bss or common
283 if (GV->getInitializer()->isNullValue()) {
284 // If this global is part of the common block, add it now. Variables are
285 // part of the common block if they are zero initialized and allowed to be
286 // merged with other symbols.
287 if (GV->hasLinkOnceLinkage() || GV->hasWeakLinkage() ||
288 GV->hasCommonLinkage()) {
289 ELFSym CommonSym(GV);
290 // Value for common symbols is the alignment required.
291 CommonSym.Value = Align;
292 CommonSym.Size = Size;
293 CommonSym.SetBind(ELFSym::STB_GLOBAL);
294 CommonSym.SetType(ELFSym::STT_OBJECT);
295 // TODO SOMEDAY: add ELF visibility.
296 CommonSym.SectionIdx = ELFSection::SHN_COMMON;
297 SymbolTable.push_back(CommonSym);
301 // Otherwise, this symbol is part of the .bss section. Emit it now.
303 // Handle alignment. Ensure section is aligned at least as much as required
305 ELFSection &BSSSection = getBSSSection();
306 BSSSection.Align = std::max(BSSSection.Align, Align);
308 // Within the section, emit enough virtual padding to get us to an alignment
311 BSSSection.Size = (BSSSection.Size + Align - 1) & ~(Align-1);
314 BSSSym.Value = BSSSection.Size;
316 BSSSym.SetType(ELFSym::STT_OBJECT);
318 switch (GV->getLinkage()) {
319 default: // weak/linkonce/common handled above
320 assert(0 && "Unexpected linkage type!");
321 case GlobalValue::AppendingLinkage: // FIXME: This should be improved!
322 case GlobalValue::ExternalLinkage:
323 BSSSym.SetBind(ELFSym::STB_GLOBAL);
325 case GlobalValue::InternalLinkage:
326 BSSSym.SetBind(ELFSym::STB_LOCAL);
330 // Set the idx of the .bss section
331 BSSSym.SectionIdx = BSSSection.SectionIdx;
332 SymbolTable.push_back(BSSSym);
334 // Reserve space in the .bss section for this symbol.
335 BSSSection.Size += Size;
339 // FIXME: handle .rodata
340 //assert(!GV->isConstant() && "unimp");
342 // FIXME: handle .data
343 //assert(0 && "unimp");
347 bool ELFWriter::runOnMachineFunction(MachineFunction &MF) {
348 // Nothing to do here, this is all done through the MCE object above.
352 /// doFinalization - Now that the module has been completely processed, emit
353 /// the ELF file to 'O'.
354 bool ELFWriter::doFinalization(Module &M) {
355 // Okay, the ELF header and .text sections have been completed, build the
356 // .data, .bss, and "common" sections next.
357 for (Module::global_iterator I = M.global_begin(), E = M.global_end();
361 // Emit the symbol table now, if non-empty.
364 // FIXME: Emit the relocations now.
366 // Emit the string table for the sections in the ELF file we have.
367 EmitSectionTableStringTable();
369 // Emit the sections to the .o file, and emit the section table for the file.
370 OutputSectionsAndSectionTable();
372 // We are done with the abstract symbols.
376 // Release the name mangler object.
377 delete Mang; Mang = 0;
381 /// EmitSymbolTable - If the current symbol table is non-empty, emit the string
382 /// table for it and then the symbol table itself.
383 void ELFWriter::EmitSymbolTable() {
384 if (SymbolTable.size() == 1) return; // Only the null entry.
386 // FIXME: compact all local symbols to the start of the symtab.
387 unsigned FirstNonLocalSymbol = 1;
389 ELFSection &StrTab = getSection(".strtab", ELFSection::SHT_STRTAB, 0);
392 DataBuffer &StrTabBuf = StrTab.SectionData;
393 OutputBuffer StrTabOut(StrTabBuf, is64Bit, isLittleEndian);
395 // Set the zero'th symbol to a null byte, as required.
396 StrTabOut.outbyte(0);
397 SymbolTable[0].NameIdx = 0;
399 for (unsigned i = 1, e = SymbolTable.size(); i != e; ++i) {
400 // Use the name mangler to uniquify the LLVM symbol.
401 std::string Name = Mang->getValueName(SymbolTable[i].GV);
404 SymbolTable[i].NameIdx = 0;
406 SymbolTable[i].NameIdx = Index;
408 // Add the name to the output buffer, including the null terminator.
409 StrTabBuf.insert(StrTabBuf.end(), Name.begin(), Name.end());
411 // Add a null terminator.
412 StrTabBuf.push_back(0);
414 // Keep track of the number of bytes emitted to this section.
415 Index += Name.size()+1;
418 assert(Index == StrTabBuf.size());
421 // Now that we have emitted the string table and know the offset into the
422 // string table of each symbol, emit the symbol table itself.
423 ELFSection &SymTab = getSection(".symtab", ELFSection::SHT_SYMTAB, 0);
424 SymTab.Align = is64Bit ? 8 : 4;
425 SymTab.Link = SymTab.SectionIdx; // Section Index of .strtab.
426 SymTab.Info = FirstNonLocalSymbol; // First non-STB_LOCAL symbol.
427 SymTab.EntSize = 16; // Size of each symtab entry. FIXME: wrong for ELF64
428 DataBuffer &SymTabBuf = SymTab.SectionData;
429 OutputBuffer SymTabOut(SymTabBuf, is64Bit, isLittleEndian);
431 if (!is64Bit) { // 32-bit and 64-bit formats are shuffled a bit.
432 for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
433 ELFSym &Sym = SymbolTable[i];
434 SymTabOut.outword(Sym.NameIdx);
435 SymTabOut.outaddr32(Sym.Value);
436 SymTabOut.outword(Sym.Size);
437 SymTabOut.outbyte(Sym.Info);
438 SymTabOut.outbyte(Sym.Other);
439 SymTabOut.outhalf(Sym.SectionIdx);
442 for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
443 ELFSym &Sym = SymbolTable[i];
444 SymTabOut.outword(Sym.NameIdx);
445 SymTabOut.outbyte(Sym.Info);
446 SymTabOut.outbyte(Sym.Other);
447 SymTabOut.outhalf(Sym.SectionIdx);
448 SymTabOut.outaddr64(Sym.Value);
449 SymTabOut.outxword(Sym.Size);
453 SymTab.Size = SymTabBuf.size();
456 /// EmitSectionTableStringTable - This method adds and emits a section for the
457 /// ELF Section Table string table: the string table that holds all of the
459 void ELFWriter::EmitSectionTableStringTable() {
460 // First step: add the section for the string table to the list of sections:
461 ELFSection &SHStrTab = getSection(".shstrtab", ELFSection::SHT_STRTAB, 0);
463 // Now that we know which section number is the .shstrtab section, update the
464 // e_shstrndx entry in the ELF header.
465 OutputBuffer FHOut(FileHeader, is64Bit, isLittleEndian);
466 FHOut.fixhalf(SHStrTab.SectionIdx, ELFHeader_e_shstrndx_Offset);
468 // Set the NameIdx of each section in the string table and emit the bytes for
471 DataBuffer &Buf = SHStrTab.SectionData;
473 for (std::list<ELFSection>::iterator I = SectionList.begin(),
474 E = SectionList.end(); I != E; ++I) {
475 // Set the index into the table. Note if we have lots of entries with
476 // common suffixes, we could memoize them here if we cared.
479 // Add the name to the output buffer, including the null terminator.
480 Buf.insert(Buf.end(), I->Name.begin(), I->Name.end());
482 // Add a null terminator.
485 // Keep track of the number of bytes emitted to this section.
486 Index += I->Name.size()+1;
489 // Set the size of .shstrtab now that we know what it is.
490 assert(Index == Buf.size());
491 SHStrTab.Size = Index;
494 /// OutputSectionsAndSectionTable - Now that we have constructed the file header
495 /// and all of the sections, emit these to the ostream destination and emit the
497 void ELFWriter::OutputSectionsAndSectionTable() {
498 // Pass #1: Compute the file offset for each section.
499 size_t FileOff = FileHeader.size(); // File header first.
501 // Emit all of the section data in order.
502 for (std::list<ELFSection>::iterator I = SectionList.begin(),
503 E = SectionList.end(); I != E; ++I) {
504 // Align FileOff to whatever the alignment restrictions of the section are.
506 FileOff = (FileOff+I->Align-1) & ~(I->Align-1);
508 FileOff += I->SectionData.size();
511 // Align Section Header.
512 unsigned TableAlign = is64Bit ? 8 : 4;
513 FileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
515 // Now that we know where all of the sections will be emitted, set the e_shnum
516 // entry in the ELF header.
517 OutputBuffer FHOut(FileHeader, is64Bit, isLittleEndian);
518 FHOut.fixhalf(NumSections, ELFHeader_e_shnum_Offset);
520 // Now that we know the offset in the file of the section table, update the
521 // e_shoff address in the ELF header.
522 FHOut.fixaddr(FileOff, ELFHeader_e_shoff_Offset);
524 // Now that we know all of the data in the file header, emit it and all of the
526 O.write((char*)&FileHeader[0], FileHeader.size());
527 FileOff = FileHeader.size();
528 DataBuffer().swap(FileHeader);
531 OutputBuffer TableOut(Table, is64Bit, isLittleEndian);
533 // Emit all of the section data and build the section table itself.
534 while (!SectionList.empty()) {
535 const ELFSection &S = *SectionList.begin();
537 // Align FileOff to whatever the alignment restrictions of the section are.
539 for (size_t NewFileOff = (FileOff+S.Align-1) & ~(S.Align-1);
540 FileOff != NewFileOff; ++FileOff)
542 O.write((char*)&S.SectionData[0], S.SectionData.size());
543 FileOff += S.SectionData.size();
545 TableOut.outword(S.NameIdx); // sh_name - Symbol table name idx
546 TableOut.outword(S.Type); // sh_type - Section contents & semantics
547 TableOut.outword(S.Flags); // sh_flags - Section flags.
548 TableOut.outaddr(S.Addr); // sh_addr - The mem addr this section is in.
549 TableOut.outaddr(S.Offset); // sh_offset - Offset from the file start.
550 TableOut.outword(S.Size); // sh_size - The section size.
551 TableOut.outword(S.Link); // sh_link - Section header table index link.
552 TableOut.outword(S.Info); // sh_info - Auxillary information.
553 TableOut.outword(S.Align); // sh_addralign - Alignment of section.
554 TableOut.outword(S.EntSize); // sh_entsize - Size of entries in the section
556 SectionList.pop_front();
559 // Align output for the section table.
560 for (size_t NewFileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
561 FileOff != NewFileOff; ++FileOff)
564 // Emit the section table itself.
565 O.write((char*)&Table[0], Table.size());