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(FunctionPassManager &FPM,
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(unsigned StubSize, unsigned Alignment = 1) {
118 assert(0 && "JIT specific function called!");
121 void *finishFunctionStub(const Function *F) {
122 assert(0 && "JIT specific function called!");
129 /// startFunction - This callback is invoked when a new machine function is
130 /// about to be emitted.
131 void ELFCodeEmitter::startFunction(MachineFunction &F) {
132 // Align the output buffer to the appropriate alignment.
133 unsigned Align = 16; // FIXME: GENERICIZE!!
134 // Get the ELF Section that this function belongs in.
135 ES = &EW.getSection(".text", ELFWriter::ELFSection::SHT_PROGBITS,
136 ELFWriter::ELFSection::SHF_EXECINSTR |
137 ELFWriter::ELFSection::SHF_ALLOC);
138 OutBuffer = &ES->SectionData;
139 cerr << "FIXME: This code needs to be updated for changes in the "
140 << "CodeEmitter interfaces. In particular, this should set "
141 << "BufferBegin/BufferEnd/CurBufferPtr, not deal with OutBuffer!";
144 // Upgrade the section alignment if required.
145 if (ES->Align < Align) ES->Align = Align;
147 // Add padding zeros to the end of the buffer to make sure that the
148 // function will start on the correct byte alignment within the section.
149 OutputBuffer OB(*OutBuffer,
150 TM.getTargetData()->getPointerSizeInBits() == 64,
151 TM.getTargetData()->isLittleEndian());
153 FnStart = OutBuffer->size();
156 /// finishFunction - This callback is invoked after the function is completely
158 bool ELFCodeEmitter::finishFunction(MachineFunction &F) {
159 // We now know the size of the function, add a symbol to represent it.
160 ELFWriter::ELFSym FnSym(F.getFunction());
162 // Figure out the binding (linkage) of the symbol.
163 switch (F.getFunction()->getLinkage()) {
165 // appending linkage is illegal for functions.
166 assert(0 && "Unknown linkage type!");
167 case GlobalValue::ExternalLinkage:
168 FnSym.SetBind(ELFWriter::ELFSym::STB_GLOBAL);
170 case GlobalValue::LinkOnceLinkage:
171 case GlobalValue::WeakLinkage:
172 FnSym.SetBind(ELFWriter::ELFSym::STB_WEAK);
174 case GlobalValue::InternalLinkage:
175 FnSym.SetBind(ELFWriter::ELFSym::STB_LOCAL);
179 ES->Size = OutBuffer->size();
181 FnSym.SetType(ELFWriter::ELFSym::STT_FUNC);
182 FnSym.SectionIdx = ES->SectionIdx;
183 FnSym.Value = FnStart; // Value = Offset from start of Section.
184 FnSym.Size = OutBuffer->size()-FnStart;
186 // Finally, add it to the symtab.
187 EW.SymbolTable.push_back(FnSym);
191 //===----------------------------------------------------------------------===//
192 // ELFWriter Implementation
193 //===----------------------------------------------------------------------===//
195 ELFWriter::ELFWriter(std::ostream &o, TargetMachine &tm)
196 : MachineFunctionPass((intptr_t)&ID), O(o), TM(tm) {
197 e_flags = 0; // e_flags defaults to 0, no flags.
199 is64Bit = TM.getTargetData()->getPointerSizeInBits() == 64;
200 isLittleEndian = TM.getTargetData()->isLittleEndian();
202 // Create the machine code emitter object for this target.
203 MCE = new ELFCodeEmitter(*this);
207 ELFWriter::~ELFWriter() {
211 // doInitialization - Emit the file header and all of the global variables for
212 // the module to the ELF file.
213 bool ELFWriter::doInitialization(Module &M) {
214 Mang = new Mangler(M);
216 // Local alias to shortenify coming code.
217 std::vector<unsigned char> &FH = FileHeader;
218 OutputBuffer FHOut(FH, is64Bit, isLittleEndian);
220 FHOut.outbyte(0x7F); // EI_MAG0
221 FHOut.outbyte('E'); // EI_MAG1
222 FHOut.outbyte('L'); // EI_MAG2
223 FHOut.outbyte('F'); // EI_MAG3
224 FHOut.outbyte(is64Bit ? 2 : 1); // EI_CLASS
225 FHOut.outbyte(isLittleEndian ? 1 : 2); // EI_DATA
226 FHOut.outbyte(1); // EI_VERSION
227 FH.resize(16); // EI_PAD up to 16 bytes.
229 // This should change for shared objects.
230 FHOut.outhalf(1); // e_type = ET_REL
231 FHOut.outword(TM.getELFWriterInfo()->getEMachine()); // target-defined
232 FHOut.outword(1); // e_version = 1
233 FHOut.outaddr(0); // e_entry = 0 -> no entry point in .o file
234 FHOut.outaddr(0); // e_phoff = 0 -> no program header for .o
236 ELFHeader_e_shoff_Offset = FH.size();
237 FHOut.outaddr(0); // e_shoff
238 FHOut.outword(e_flags); // e_flags = whatever the target wants
240 FHOut.outhalf(is64Bit ? 64 : 52); // e_ehsize = ELF header size
241 FHOut.outhalf(0); // e_phentsize = prog header entry size
242 FHOut.outhalf(0); // e_phnum = # prog header entries = 0
243 FHOut.outhalf(is64Bit ? 64 : 40); // e_shentsize = sect hdr entry size
246 ELFHeader_e_shnum_Offset = FH.size();
247 FHOut.outhalf(0); // e_shnum = # of section header ents
248 ELFHeader_e_shstrndx_Offset = FH.size();
249 FHOut.outhalf(0); // e_shstrndx = Section # of '.shstrtab'
251 // Add the null section, which is required to be first in the file.
252 getSection("", 0, 0);
254 // Start up the symbol table. The first entry in the symtab is the null
256 SymbolTable.push_back(ELFSym(0));
261 void ELFWriter::EmitGlobal(GlobalVariable *GV) {
262 // If this is an external global, emit it now. TODO: Note that it would be
263 // better to ignore the symbol here and only add it to the symbol table if
265 if (!GV->hasInitializer()) {
266 ELFSym ExternalSym(GV);
267 ExternalSym.SetBind(ELFSym::STB_GLOBAL);
268 ExternalSym.SetType(ELFSym::STT_NOTYPE);
269 ExternalSym.SectionIdx = ELFSection::SHN_UNDEF;
270 SymbolTable.push_back(ExternalSym);
274 const Type *GVType = (const Type*)GV->getType();
275 unsigned Align = TM.getTargetData()->getPreferredAlignment(GV);
276 unsigned Size = TM.getTargetData()->getABITypeSize(GVType);
278 // If this global has a zero initializer, it is part of the .bss or common
280 if (GV->getInitializer()->isNullValue()) {
281 // If this global is part of the common block, add it now. Variables are
282 // part of the common block if they are zero initialized and allowed to be
283 // merged with other symbols.
284 if (GV->hasLinkOnceLinkage() || GV->hasWeakLinkage()) {
285 ELFSym CommonSym(GV);
286 // Value for common symbols is the alignment required.
287 CommonSym.Value = Align;
288 CommonSym.Size = Size;
289 CommonSym.SetBind(ELFSym::STB_GLOBAL);
290 CommonSym.SetType(ELFSym::STT_OBJECT);
291 // TODO SOMEDAY: add ELF visibility.
292 CommonSym.SectionIdx = ELFSection::SHN_COMMON;
293 SymbolTable.push_back(CommonSym);
297 // Otherwise, this symbol is part of the .bss section. Emit it now.
299 // Handle alignment. Ensure section is aligned at least as much as required
301 ELFSection &BSSSection = getBSSSection();
302 BSSSection.Align = std::max(BSSSection.Align, Align);
304 // Within the section, emit enough virtual padding to get us to an alignment
307 BSSSection.Size = (BSSSection.Size + Align - 1) & ~(Align-1);
310 BSSSym.Value = BSSSection.Size;
312 BSSSym.SetType(ELFSym::STT_OBJECT);
314 switch (GV->getLinkage()) {
315 default: // weak/linkonce handled above
316 assert(0 && "Unexpected linkage type!");
317 case GlobalValue::AppendingLinkage: // FIXME: This should be improved!
318 case GlobalValue::ExternalLinkage:
319 BSSSym.SetBind(ELFSym::STB_GLOBAL);
321 case GlobalValue::InternalLinkage:
322 BSSSym.SetBind(ELFSym::STB_LOCAL);
326 // Set the idx of the .bss section
327 BSSSym.SectionIdx = BSSSection.SectionIdx;
328 SymbolTable.push_back(BSSSym);
330 // Reserve space in the .bss section for this symbol.
331 BSSSection.Size += Size;
335 // FIXME: handle .rodata
336 //assert(!GV->isConstant() && "unimp");
338 // FIXME: handle .data
339 //assert(0 && "unimp");
343 bool ELFWriter::runOnMachineFunction(MachineFunction &MF) {
344 // Nothing to do here, this is all done through the MCE object above.
348 /// doFinalization - Now that the module has been completely processed, emit
349 /// the ELF file to 'O'.
350 bool ELFWriter::doFinalization(Module &M) {
351 // Okay, the ELF header and .text sections have been completed, build the
352 // .data, .bss, and "common" sections next.
353 for (Module::global_iterator I = M.global_begin(), E = M.global_end();
357 // Emit the symbol table now, if non-empty.
360 // FIXME: Emit the relocations now.
362 // Emit the string table for the sections in the ELF file we have.
363 EmitSectionTableStringTable();
365 // Emit the sections to the .o file, and emit the section table for the file.
366 OutputSectionsAndSectionTable();
368 // We are done with the abstract symbols.
372 // Release the name mangler object.
373 delete Mang; Mang = 0;
377 /// EmitSymbolTable - If the current symbol table is non-empty, emit the string
378 /// table for it and then the symbol table itself.
379 void ELFWriter::EmitSymbolTable() {
380 if (SymbolTable.size() == 1) return; // Only the null entry.
382 // FIXME: compact all local symbols to the start of the symtab.
383 unsigned FirstNonLocalSymbol = 1;
385 ELFSection &StrTab = getSection(".strtab", ELFSection::SHT_STRTAB, 0);
388 DataBuffer &StrTabBuf = StrTab.SectionData;
389 OutputBuffer StrTabOut(StrTabBuf, is64Bit, isLittleEndian);
391 // Set the zero'th symbol to a null byte, as required.
392 StrTabOut.outbyte(0);
393 SymbolTable[0].NameIdx = 0;
395 for (unsigned i = 1, e = SymbolTable.size(); i != e; ++i) {
396 // Use the name mangler to uniquify the LLVM symbol.
397 std::string Name = Mang->getValueName(SymbolTable[i].GV);
400 SymbolTable[i].NameIdx = 0;
402 SymbolTable[i].NameIdx = Index;
404 // Add the name to the output buffer, including the null terminator.
405 StrTabBuf.insert(StrTabBuf.end(), Name.begin(), Name.end());
407 // Add a null terminator.
408 StrTabBuf.push_back(0);
410 // Keep track of the number of bytes emitted to this section.
411 Index += Name.size()+1;
414 assert(Index == StrTabBuf.size());
417 // Now that we have emitted the string table and know the offset into the
418 // string table of each symbol, emit the symbol table itself.
419 ELFSection &SymTab = getSection(".symtab", ELFSection::SHT_SYMTAB, 0);
420 SymTab.Align = is64Bit ? 8 : 4;
421 SymTab.Link = SymTab.SectionIdx; // Section Index of .strtab.
422 SymTab.Info = FirstNonLocalSymbol; // First non-STB_LOCAL symbol.
423 SymTab.EntSize = 16; // Size of each symtab entry. FIXME: wrong for ELF64
424 DataBuffer &SymTabBuf = SymTab.SectionData;
425 OutputBuffer SymTabOut(SymTabBuf, is64Bit, isLittleEndian);
427 if (!is64Bit) { // 32-bit and 64-bit formats are shuffled a bit.
428 for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
429 ELFSym &Sym = SymbolTable[i];
430 SymTabOut.outword(Sym.NameIdx);
431 SymTabOut.outaddr32(Sym.Value);
432 SymTabOut.outword(Sym.Size);
433 SymTabOut.outbyte(Sym.Info);
434 SymTabOut.outbyte(Sym.Other);
435 SymTabOut.outhalf(Sym.SectionIdx);
438 for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
439 ELFSym &Sym = SymbolTable[i];
440 SymTabOut.outword(Sym.NameIdx);
441 SymTabOut.outbyte(Sym.Info);
442 SymTabOut.outbyte(Sym.Other);
443 SymTabOut.outhalf(Sym.SectionIdx);
444 SymTabOut.outaddr64(Sym.Value);
445 SymTabOut.outxword(Sym.Size);
449 SymTab.Size = SymTabBuf.size();
452 /// EmitSectionTableStringTable - This method adds and emits a section for the
453 /// ELF Section Table string table: the string table that holds all of the
455 void ELFWriter::EmitSectionTableStringTable() {
456 // First step: add the section for the string table to the list of sections:
457 ELFSection &SHStrTab = getSection(".shstrtab", ELFSection::SHT_STRTAB, 0);
459 // Now that we know which section number is the .shstrtab section, update the
460 // e_shstrndx entry in the ELF header.
461 OutputBuffer FHOut(FileHeader, is64Bit, isLittleEndian);
462 FHOut.fixhalf(SHStrTab.SectionIdx, ELFHeader_e_shstrndx_Offset);
464 // Set the NameIdx of each section in the string table and emit the bytes for
467 DataBuffer &Buf = SHStrTab.SectionData;
469 for (std::list<ELFSection>::iterator I = SectionList.begin(),
470 E = SectionList.end(); I != E; ++I) {
471 // Set the index into the table. Note if we have lots of entries with
472 // common suffixes, we could memoize them here if we cared.
475 // Add the name to the output buffer, including the null terminator.
476 Buf.insert(Buf.end(), I->Name.begin(), I->Name.end());
478 // Add a null terminator.
481 // Keep track of the number of bytes emitted to this section.
482 Index += I->Name.size()+1;
485 // Set the size of .shstrtab now that we know what it is.
486 assert(Index == Buf.size());
487 SHStrTab.Size = Index;
490 /// OutputSectionsAndSectionTable - Now that we have constructed the file header
491 /// and all of the sections, emit these to the ostream destination and emit the
493 void ELFWriter::OutputSectionsAndSectionTable() {
494 // Pass #1: Compute the file offset for each section.
495 size_t FileOff = FileHeader.size(); // File header first.
497 // Emit all of the section data in order.
498 for (std::list<ELFSection>::iterator I = SectionList.begin(),
499 E = SectionList.end(); I != E; ++I) {
500 // Align FileOff to whatever the alignment restrictions of the section are.
502 FileOff = (FileOff+I->Align-1) & ~(I->Align-1);
504 FileOff += I->SectionData.size();
507 // Align Section Header.
508 unsigned TableAlign = is64Bit ? 8 : 4;
509 FileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
511 // Now that we know where all of the sections will be emitted, set the e_shnum
512 // entry in the ELF header.
513 OutputBuffer FHOut(FileHeader, is64Bit, isLittleEndian);
514 FHOut.fixhalf(NumSections, ELFHeader_e_shnum_Offset);
516 // Now that we know the offset in the file of the section table, update the
517 // e_shoff address in the ELF header.
518 FHOut.fixaddr(FileOff, ELFHeader_e_shoff_Offset);
520 // Now that we know all of the data in the file header, emit it and all of the
522 O.write((char*)&FileHeader[0], FileHeader.size());
523 FileOff = FileHeader.size();
524 DataBuffer().swap(FileHeader);
527 OutputBuffer TableOut(Table, is64Bit, isLittleEndian);
529 // Emit all of the section data and build the section table itself.
530 while (!SectionList.empty()) {
531 const ELFSection &S = *SectionList.begin();
533 // Align FileOff to whatever the alignment restrictions of the section are.
535 for (size_t NewFileOff = (FileOff+S.Align-1) & ~(S.Align-1);
536 FileOff != NewFileOff; ++FileOff)
538 O.write((char*)&S.SectionData[0], S.SectionData.size());
539 FileOff += S.SectionData.size();
541 TableOut.outword(S.NameIdx); // sh_name - Symbol table name idx
542 TableOut.outword(S.Type); // sh_type - Section contents & semantics
543 TableOut.outword(S.Flags); // sh_flags - Section flags.
544 TableOut.outaddr(S.Addr); // sh_addr - The mem addr this section is in.
545 TableOut.outaddr(S.Offset); // sh_offset - Offset from the file start.
546 TableOut.outword(S.Size); // sh_size - The section size.
547 TableOut.outword(S.Link); // sh_link - Section header table index link.
548 TableOut.outword(S.Info); // sh_info - Auxillary information.
549 TableOut.outword(S.Align); // sh_addralign - Alignment of section.
550 TableOut.outword(S.EntSize); // sh_entsize - Size of entries in the section
552 SectionList.pop_front();
555 // Align output for the section table.
556 for (size_t NewFileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
557 FileOff != NewFileOff; ++FileOff)
560 // Emit the section table itself.
561 O.write((char*)&Table[0], Table.size());