Chris Lattner | 35f0a4f | 2005-06-27 06:29:00 +0000 | [diff] [blame^] | 1 | //===-- ELFWriter.cpp - Target-independent ELF Writer code ----------------===// |
| 2 | // |
| 3 | // The LLVM Compiler Infrastructure |
| 4 | // |
| 5 | // This file was developed by the LLVM research group and is distributed under |
| 6 | // the University of Illinois Open Source License. See LICENSE.TXT for details. |
| 7 | // |
| 8 | //===----------------------------------------------------------------------===// |
| 9 | // |
| 10 | // This file implements the target-independent ELF writer. This file writes out |
| 11 | // the ELF file in the following order: |
| 12 | // |
| 13 | // #1. ELF Header |
| 14 | // #2. '.data' section |
| 15 | // #3. '.bss' section |
| 16 | // ... |
| 17 | // #X. '.shstrtab' section |
| 18 | // #Y. Section Table |
| 19 | // |
| 20 | // The entries in the section table are laid out as: |
| 21 | // #0. Null entry [required] |
| 22 | // #1. ".data" entry - global variables with initializers. [ if needed ] |
| 23 | // #2. ".bss" entry - global variables without initializers. [ if needed ] |
| 24 | // #3. ".text" entry - the program code |
| 25 | // ... |
| 26 | // #N. ".shstrtab" entry - String table for the section names. |
| 27 | |
| 28 | // |
| 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! |
| 31 | // |
| 32 | //===----------------------------------------------------------------------===// |
| 33 | |
| 34 | #include "llvm/CodeGen/ELFWriter.h" |
| 35 | #include "llvm/Module.h" |
| 36 | #include "llvm/Target/TargetMachine.h" |
| 37 | using namespace llvm; |
| 38 | |
| 39 | ELFWriter::ELFWriter(std::ostream &o, TargetMachine &tm) : O(o), TM(tm) { |
| 40 | e_machine = 0; // e_machine defaults to 'No Machine' |
| 41 | e_flags = 0; // e_flags defaults to 0, no flags. |
| 42 | |
| 43 | is64Bit = TM.getTargetData().getPointerSizeInBits() == 64; |
| 44 | isLittleEndian = TM.getTargetData().isLittleEndian(); |
| 45 | } |
| 46 | |
| 47 | // doInitialization - Emit the file header and all of the global variables for |
| 48 | // the module to the ELF file. |
| 49 | bool ELFWriter::doInitialization(Module &M) { |
| 50 | outbyte(0x7F); // EI_MAG0 |
| 51 | outbyte('E'); // EI_MAG1 |
| 52 | outbyte('L'); // EI_MAG2 |
| 53 | outbyte('F'); // EI_MAG3 |
| 54 | outbyte(is64Bit ? 2 : 1); // EI_CLASS |
| 55 | outbyte(isLittleEndian ? 1 : 2); // EI_DATA |
| 56 | outbyte(1); // EI_VERSION |
| 57 | for (unsigned i = OutputBuffer.size(); i != 16; ++i) |
| 58 | outbyte(0); // EI_PAD up to 16 bytes. |
| 59 | |
| 60 | // This should change for shared objects. |
| 61 | outhalf(1); // e_type = ET_REL |
| 62 | outhalf(e_machine); // e_machine = whatever the target wants |
| 63 | outword(1); // e_version = 1 |
| 64 | outaddr(0); // e_entry = 0 -> no entry point in .o file |
| 65 | outaddr(0); // e_phoff = 0 -> no program header for .o |
| 66 | |
| 67 | ELFHeader_e_shoff_Offset = OutputBuffer.size(); |
| 68 | outaddr(0); // e_shoff |
| 69 | outword(e_flags); // e_flags = whatever the target wants |
| 70 | |
| 71 | assert(!is64Bit && "These sizes need to be adjusted for 64-bit!"); |
| 72 | outhalf(52); // e_ehsize = ELF header size |
| 73 | outhalf(0); // e_phentsize = prog header entry size |
| 74 | outhalf(0); // e_phnum = # prog header entries = 0 |
| 75 | outhalf(40); // e_shentsize = sect header entry size |
| 76 | |
| 77 | |
| 78 | ELFHeader_e_shnum_Offset = OutputBuffer.size(); |
| 79 | outhalf(0); // e_shnum = # of section header ents |
| 80 | ELFHeader_e_shstrndx_Offset = OutputBuffer.size(); |
| 81 | outhalf(0); // e_shstrndx = Section # of '.shstrtab' |
| 82 | |
| 83 | // Add the null section. |
| 84 | SectionList.push_back(ELFSection()); |
| 85 | |
| 86 | // Okay, the ELF header has been completed, emit the .data section next. |
| 87 | ELFSection DataSection(".data", OutputBuffer.size()); |
| 88 | for (Module::global_iterator I = M.global_begin(), E = M.global_end(); |
| 89 | I != E; ++I) |
| 90 | EmitDATASectionGlobal(I); |
| 91 | |
| 92 | // If the .data section is nonempty, add it to our list. |
| 93 | if ((DataSection.Size = OutputBuffer.size()-DataSection.Offset)) { |
| 94 | DataSection.Align = 4; // FIXME: Compute! |
| 95 | SectionList.push_back(DataSection); |
| 96 | } |
| 97 | |
| 98 | // Okay, emit the .bss section next. |
| 99 | ELFSection BSSSection(".bss", OutputBuffer.size()); |
| 100 | for (Module::global_iterator I = M.global_begin(), E = M.global_end(); |
| 101 | I != E; ++I) |
| 102 | EmitBSSSectionGlobal(I); |
| 103 | |
| 104 | // If the .bss section is nonempty, add it to our list. |
| 105 | if ((BSSSection.Size = OutputBuffer.size()-BSSSection.Offset)) { |
| 106 | BSSSection.Align = 4; // FIXME: Compute! |
| 107 | SectionList.push_back(BSSSection); |
| 108 | } |
| 109 | |
| 110 | return false; |
| 111 | } |
| 112 | |
| 113 | // isCOMM - A global variable should be emitted to the common area if it is zero |
| 114 | // initialized and has linkage that permits it to be merged with other globals. |
| 115 | static bool isCOMM(GlobalVariable *GV) { |
| 116 | return GV->getInitializer()->isNullValue() && |
| 117 | (GV->hasLinkOnceLinkage() || GV->hasInternalLinkage() || |
| 118 | GV->hasWeakLinkage()); |
| 119 | } |
| 120 | |
| 121 | // EmitDATASectionGlobal - Emit a global variable to the .data section if it |
| 122 | // belongs there. |
| 123 | void ELFWriter::EmitDATASectionGlobal(GlobalVariable *GV) { |
| 124 | if (!GV->hasInitializer()) return; |
| 125 | |
| 126 | // Do not emit a symbol here if it should be emitted to the common area. |
| 127 | if (isCOMM(GV)) return; |
| 128 | |
| 129 | EmitGlobal(GV); |
| 130 | } |
| 131 | |
| 132 | void ELFWriter::EmitBSSSectionGlobal(GlobalVariable *GV) { |
| 133 | if (!GV->hasInitializer()) return; |
| 134 | |
| 135 | // FIXME: We don't support BSS yet! |
| 136 | return; |
| 137 | |
| 138 | EmitGlobal(GV); |
| 139 | } |
| 140 | |
| 141 | void ELFWriter::EmitGlobal(GlobalVariable *GV) { |
| 142 | } |
| 143 | |
| 144 | |
| 145 | bool ELFWriter::runOnMachineFunction(MachineFunction &MF) { |
| 146 | return false; |
| 147 | } |
| 148 | |
| 149 | /// doFinalization - Now that the module has been completely processed, emit |
| 150 | /// the ELF file to 'O'. |
| 151 | bool ELFWriter::doFinalization(Module &M) { |
| 152 | // Emit the string table for the sections in the ELF file we have. |
| 153 | EmitSectionTableStringTable(); |
| 154 | |
| 155 | // Emit the .o file section table. |
| 156 | EmitSectionTable(); |
| 157 | |
| 158 | // Emit the .o file to the specified stream. |
| 159 | O.write((char*)&OutputBuffer[0], OutputBuffer.size()); |
| 160 | |
| 161 | // Free the output buffer. |
| 162 | std::vector<unsigned char>().swap(OutputBuffer); |
| 163 | return false; |
| 164 | } |
| 165 | |
| 166 | /// EmitSectionTableStringTable - This method adds and emits a section for the |
| 167 | /// ELF Section Table string table: the string table that holds all of the |
| 168 | /// section names. |
| 169 | void ELFWriter::EmitSectionTableStringTable() { |
| 170 | // First step: add the section for the string table to the list of sections: |
| 171 | SectionList.push_back(ELFSection(".shstrtab", OutputBuffer.size())); |
| 172 | SectionList.back().Type = 3; // SHT_STRTAB |
| 173 | |
| 174 | // Now that we know which section number is the .shstrtab section, update the |
| 175 | // e_shstrndx entry in the ELF header. |
| 176 | fixhalf(SectionList.size()-1, ELFHeader_e_shstrndx_Offset); |
| 177 | |
| 178 | // Set the NameIdx of each section in the string table and emit the bytes for |
| 179 | // the string table. |
| 180 | unsigned Index = 0; |
| 181 | |
| 182 | for (unsigned i = 0, e = SectionList.size(); i != e; ++i) { |
| 183 | // Set the index into the table. Note if we have lots of entries with |
| 184 | // common suffixes, we could memoize them here if we cared. |
| 185 | SectionList[i].NameIdx = Index; |
| 186 | |
| 187 | // Add the name to the output buffer, including the null terminator. |
| 188 | OutputBuffer.insert(OutputBuffer.end(), SectionList[i].Name.begin(), |
| 189 | SectionList[i].Name.end()); |
| 190 | // Add a null terminator. |
| 191 | OutputBuffer.push_back(0); |
| 192 | |
| 193 | // Keep track of the number of bytes emitted to this section. |
| 194 | Index += SectionList[i].Name.size()+1; |
| 195 | } |
| 196 | |
| 197 | // Set the size of .shstrtab now that we know what it is. |
| 198 | SectionList.back().Size = Index; |
| 199 | } |
| 200 | |
| 201 | /// EmitSectionTable - Now that we have emitted the entire contents of the file |
| 202 | /// (all of the sections), emit the section table which informs the reader where |
| 203 | /// the boundaries are. |
| 204 | void ELFWriter::EmitSectionTable() { |
| 205 | // Now that all of the sections have been emitted, set the e_shnum entry in |
| 206 | // the ELF header. |
| 207 | fixhalf(SectionList.size(), ELFHeader_e_shnum_Offset); |
| 208 | |
| 209 | // Now that we know the offset in the file of the section table (which we emit |
| 210 | // next), update the e_shoff address in the ELF header. |
| 211 | fixaddr(OutputBuffer.size(), ELFHeader_e_shoff_Offset); |
| 212 | |
| 213 | // Emit all of the section table entries. |
| 214 | for (unsigned i = 0, e = SectionList.size(); i != e; ++i) { |
| 215 | const ELFSection &S = SectionList[i]; |
| 216 | outword(S.NameIdx); // sh_name - Symbol table name idx |
| 217 | outword(S.Type); // sh_type - Section contents & semantics |
| 218 | outword(S.Flags); // sh_flags - Section flags. |
| 219 | outaddr(S.Addr); // sh_addr - The mem address this section appears in. |
| 220 | outaddr(S.Offset); // sh_offset - The offset from the start of the file. |
| 221 | outword(S.Size); // sh_size - The section size. |
| 222 | outword(S.Link); // sh_link - Section header table index link. |
| 223 | outword(S.Info); // sh_info - Auxillary information. |
| 224 | outword(S.Align); // sh_addralign - Alignment of section. |
| 225 | outword(S.EntSize); // sh_entsize - Size of each entry in the section. |
| 226 | } |
| 227 | |
| 228 | // Release the memory allocated for the section list. |
| 229 | std::vector<ELFSection>().swap(SectionList); |
| 230 | } |