| //===-- ELFWriter.cpp - Target-independent ELF Writer code ----------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file was developed by the LLVM research group and is distributed under |
| // the University of Illinois Open Source License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements the target-independent ELF writer. This file writes out |
| // the ELF file in the following order: |
| // |
| // #1. ELF Header |
| // #2. '.data' section |
| // #3. '.bss' section |
| // ... |
| // #X. '.shstrtab' section |
| // #Y. Section Table |
| // |
| // The entries in the section table are laid out as: |
| // #0. Null entry [required] |
| // #1. ".data" entry - global variables with initializers. [ if needed ] |
| // #2. ".bss" entry - global variables without initializers. [ if needed ] |
| // #3. ".text" entry - the program code |
| // ... |
| // #N. ".shstrtab" entry - String table for the section names. |
| |
| // |
| // NOTE: This code should eventually be extended to support 64-bit ELF (this |
| // won't be hard), but we haven't done so yet! |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/CodeGen/ELFWriter.h" |
| #include "llvm/Module.h" |
| #include "llvm/Target/TargetMachine.h" |
| using namespace llvm; |
| |
| ELFWriter::ELFWriter(std::ostream &o, TargetMachine &tm) : O(o), TM(tm) { |
| e_machine = 0; // e_machine defaults to 'No Machine' |
| e_flags = 0; // e_flags defaults to 0, no flags. |
| |
| is64Bit = TM.getTargetData().getPointerSizeInBits() == 64; |
| isLittleEndian = TM.getTargetData().isLittleEndian(); |
| } |
| |
| // doInitialization - Emit the file header and all of the global variables for |
| // the module to the ELF file. |
| bool ELFWriter::doInitialization(Module &M) { |
| outbyte(0x7F); // EI_MAG0 |
| outbyte('E'); // EI_MAG1 |
| outbyte('L'); // EI_MAG2 |
| outbyte('F'); // EI_MAG3 |
| outbyte(is64Bit ? 2 : 1); // EI_CLASS |
| outbyte(isLittleEndian ? 1 : 2); // EI_DATA |
| outbyte(1); // EI_VERSION |
| for (unsigned i = OutputBuffer.size(); i != 16; ++i) |
| outbyte(0); // EI_PAD up to 16 bytes. |
| |
| // This should change for shared objects. |
| outhalf(1); // e_type = ET_REL |
| outhalf(e_machine); // e_machine = whatever the target wants |
| outword(1); // e_version = 1 |
| outaddr(0); // e_entry = 0 -> no entry point in .o file |
| outaddr(0); // e_phoff = 0 -> no program header for .o |
| |
| ELFHeader_e_shoff_Offset = OutputBuffer.size(); |
| outaddr(0); // e_shoff |
| outword(e_flags); // e_flags = whatever the target wants |
| |
| assert(!is64Bit && "These sizes need to be adjusted for 64-bit!"); |
| outhalf(52); // e_ehsize = ELF header size |
| outhalf(0); // e_phentsize = prog header entry size |
| outhalf(0); // e_phnum = # prog header entries = 0 |
| outhalf(40); // e_shentsize = sect header entry size |
| |
| |
| ELFHeader_e_shnum_Offset = OutputBuffer.size(); |
| outhalf(0); // e_shnum = # of section header ents |
| ELFHeader_e_shstrndx_Offset = OutputBuffer.size(); |
| outhalf(0); // e_shstrndx = Section # of '.shstrtab' |
| |
| // Add the null section. |
| SectionList.push_back(ELFSection()); |
| |
| // Okay, the ELF header has been completed, emit the .data section next. |
| ELFSection DataSection(".data", OutputBuffer.size()); |
| for (Module::global_iterator I = M.global_begin(), E = M.global_end(); |
| I != E; ++I) |
| EmitDATASectionGlobal(I); |
| |
| // If the .data section is nonempty, add it to our list. |
| if ((DataSection.Size = OutputBuffer.size()-DataSection.Offset)) { |
| DataSection.Align = 4; // FIXME: Compute! |
| SectionList.push_back(DataSection); |
| } |
| |
| // Okay, emit the .bss section next. |
| ELFSection BSSSection(".bss", OutputBuffer.size()); |
| for (Module::global_iterator I = M.global_begin(), E = M.global_end(); |
| I != E; ++I) |
| EmitBSSSectionGlobal(I); |
| |
| // If the .bss section is nonempty, add it to our list. |
| if ((BSSSection.Size = OutputBuffer.size()-BSSSection.Offset)) { |
| BSSSection.Align = 4; // FIXME: Compute! |
| SectionList.push_back(BSSSection); |
| } |
| |
| return false; |
| } |
| |
| // isCOMM - A global variable should be emitted to the common area if it is zero |
| // initialized and has linkage that permits it to be merged with other globals. |
| static bool isCOMM(GlobalVariable *GV) { |
| return GV->getInitializer()->isNullValue() && |
| (GV->hasLinkOnceLinkage() || GV->hasInternalLinkage() || |
| GV->hasWeakLinkage()); |
| } |
| |
| // EmitDATASectionGlobal - Emit a global variable to the .data section if it |
| // belongs there. |
| void ELFWriter::EmitDATASectionGlobal(GlobalVariable *GV) { |
| if (!GV->hasInitializer()) return; |
| |
| // Do not emit a symbol here if it should be emitted to the common area. |
| if (isCOMM(GV)) return; |
| |
| EmitGlobal(GV); |
| } |
| |
| void ELFWriter::EmitBSSSectionGlobal(GlobalVariable *GV) { |
| if (!GV->hasInitializer()) return; |
| |
| // FIXME: We don't support BSS yet! |
| return; |
| |
| EmitGlobal(GV); |
| } |
| |
| void ELFWriter::EmitGlobal(GlobalVariable *GV) { |
| } |
| |
| |
| bool ELFWriter::runOnMachineFunction(MachineFunction &MF) { |
| return false; |
| } |
| |
| /// doFinalization - Now that the module has been completely processed, emit |
| /// the ELF file to 'O'. |
| bool ELFWriter::doFinalization(Module &M) { |
| // Emit the string table for the sections in the ELF file we have. |
| EmitSectionTableStringTable(); |
| |
| // Emit the .o file section table. |
| EmitSectionTable(); |
| |
| // Emit the .o file to the specified stream. |
| O.write((char*)&OutputBuffer[0], OutputBuffer.size()); |
| |
| // Free the output buffer. |
| std::vector<unsigned char>().swap(OutputBuffer); |
| return false; |
| } |
| |
| /// EmitSectionTableStringTable - This method adds and emits a section for the |
| /// ELF Section Table string table: the string table that holds all of the |
| /// section names. |
| void ELFWriter::EmitSectionTableStringTable() { |
| // First step: add the section for the string table to the list of sections: |
| SectionList.push_back(ELFSection(".shstrtab", OutputBuffer.size())); |
| SectionList.back().Type = 3; // SHT_STRTAB |
| |
| // Now that we know which section number is the .shstrtab section, update the |
| // e_shstrndx entry in the ELF header. |
| fixhalf(SectionList.size()-1, ELFHeader_e_shstrndx_Offset); |
| |
| // Set the NameIdx of each section in the string table and emit the bytes for |
| // the string table. |
| unsigned Index = 0; |
| |
| for (unsigned i = 0, e = SectionList.size(); i != e; ++i) { |
| // Set the index into the table. Note if we have lots of entries with |
| // common suffixes, we could memoize them here if we cared. |
| SectionList[i].NameIdx = Index; |
| |
| // Add the name to the output buffer, including the null terminator. |
| OutputBuffer.insert(OutputBuffer.end(), SectionList[i].Name.begin(), |
| SectionList[i].Name.end()); |
| // Add a null terminator. |
| OutputBuffer.push_back(0); |
| |
| // Keep track of the number of bytes emitted to this section. |
| Index += SectionList[i].Name.size()+1; |
| } |
| |
| // Set the size of .shstrtab now that we know what it is. |
| SectionList.back().Size = Index; |
| } |
| |
| /// EmitSectionTable - Now that we have emitted the entire contents of the file |
| /// (all of the sections), emit the section table which informs the reader where |
| /// the boundaries are. |
| void ELFWriter::EmitSectionTable() { |
| // Now that all of the sections have been emitted, set the e_shnum entry in |
| // the ELF header. |
| fixhalf(SectionList.size(), ELFHeader_e_shnum_Offset); |
| |
| // Now that we know the offset in the file of the section table (which we emit |
| // next), update the e_shoff address in the ELF header. |
| fixaddr(OutputBuffer.size(), ELFHeader_e_shoff_Offset); |
| |
| // Emit all of the section table entries. |
| for (unsigned i = 0, e = SectionList.size(); i != e; ++i) { |
| const ELFSection &S = SectionList[i]; |
| outword(S.NameIdx); // sh_name - Symbol table name idx |
| outword(S.Type); // sh_type - Section contents & semantics |
| outword(S.Flags); // sh_flags - Section flags. |
| outaddr(S.Addr); // sh_addr - The mem address this section appears in. |
| outaddr(S.Offset); // sh_offset - The offset from the start of the file. |
| outword(S.Size); // sh_size - The section size. |
| outword(S.Link); // sh_link - Section header table index link. |
| outword(S.Info); // sh_info - Auxillary information. |
| outword(S.Align); // sh_addralign - Alignment of section. |
| outword(S.EntSize); // sh_entsize - Size of each entry in the section. |
| } |
| |
| // Release the memory allocated for the section list. |
| std::vector<ELFSection>().swap(SectionList); |
| } |