1 //===-- ELFWriter.cpp - Target-independent ELF Writer code ----------------===//
3 // The LLVM Compiler Infrastructure
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.
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.
30 // NOTE: This code should eventually be extended to support 64-bit ELF (this
31 // won't be hard), but we haven't done so yet!
33 //===----------------------------------------------------------------------===//
35 #include "llvm/CodeGen/ELFWriter.h"
36 #include "llvm/Module.h"
37 #include "llvm/Target/TargetMachine.h"
40 ELFWriter::ELFWriter(std::ostream &o, TargetMachine &tm) : O(o), TM(tm) {
41 e_machine = 0; // e_machine defaults to 'No Machine'
42 e_flags = 0; // e_flags defaults to 0, no flags.
44 is64Bit = TM.getTargetData().getPointerSizeInBits() == 64;
45 isLittleEndian = TM.getTargetData().isLittleEndian();
48 // doInitialization - Emit the file header and all of the global variables for
49 // the module to the ELF file.
50 bool ELFWriter::doInitialization(Module &M) {
51 outbyte(0x7F); // EI_MAG0
52 outbyte('E'); // EI_MAG1
53 outbyte('L'); // EI_MAG2
54 outbyte('F'); // EI_MAG3
55 outbyte(is64Bit ? 2 : 1); // EI_CLASS
56 outbyte(isLittleEndian ? 1 : 2); // EI_DATA
57 outbyte(1); // EI_VERSION
58 for (unsigned i = OutputBuffer.size(); i != 16; ++i)
59 outbyte(0); // EI_PAD up to 16 bytes.
61 // This should change for shared objects.
62 outhalf(1); // e_type = ET_REL
63 outhalf(e_machine); // e_machine = whatever the target wants
64 outword(1); // e_version = 1
65 outaddr(0); // e_entry = 0 -> no entry point in .o file
66 outaddr(0); // e_phoff = 0 -> no program header for .o
68 ELFHeader_e_shoff_Offset = OutputBuffer.size();
69 outaddr(0); // e_shoff
70 outword(e_flags); // e_flags = whatever the target wants
72 assert(!is64Bit && "These sizes need to be adjusted for 64-bit!");
73 outhalf(52); // e_ehsize = ELF header size
74 outhalf(0); // e_phentsize = prog header entry size
75 outhalf(0); // e_phnum = # prog header entries = 0
76 outhalf(40); // e_shentsize = sect header entry size
79 ELFHeader_e_shnum_Offset = OutputBuffer.size();
80 outhalf(0); // e_shnum = # of section header ents
81 ELFHeader_e_shstrndx_Offset = OutputBuffer.size();
82 outhalf(0); // e_shstrndx = Section # of '.shstrtab'
84 // Add the null section.
85 SectionList.push_back(ELFSection());
87 // Start up the symbol table. The first entry in the symtab is the null
89 SymbolTable.push_back(ELFSym(0));
93 // FIXME: Should start the .text section.
97 void ELFWriter::EmitGlobal(GlobalVariable *GV, ELFSection &DataSection,
98 ELFSection &BSSSection) {
99 // If this is an external global, emit it...
100 assert(GV->hasInitializer() && "FIXME: unimp");
102 // If this global has a zero initializer, it is part of the .bss or common
104 if (GV->getInitializer()->isNullValue()) {
105 // If this global is part of the common block, add it now. Variables are
106 // part of the common block if they are zero initialized and allowed to be
107 // merged with other symbols.
108 if (GV->hasLinkOnceLinkage() || GV->hasWeakLinkage()) {
109 ELFSym CommonSym(GV);
110 // Value for common symbols is the alignment required.
111 const Type *GVType = (const Type*)GV->getType();
112 CommonSym.Value = TM.getTargetData().getTypeAlignment(GVType);
113 CommonSym.Size = TM.getTargetData().getTypeSize(GVType);
114 CommonSym.SetBind(ELFSym::STB_GLOBAL);
115 CommonSym.SetType(ELFSym::STT_OBJECT);
116 // TODO SOMEDAY: add ELF visibility.
117 CommonSym.SectionIdx = ELFSection::SHN_COMMON;
118 SymbolTable.push_back(CommonSym);
122 // FIXME: Implement the .bss section.
126 // FIXME: handle .rodata
127 //assert(!GV->isConstant() && "unimp");
129 // FIXME: handle .data
130 //assert(0 && "unimp");
134 bool ELFWriter::runOnMachineFunction(MachineFunction &MF) {
138 /// doFinalization - Now that the module has been completely processed, emit
139 /// the ELF file to 'O'.
140 bool ELFWriter::doFinalization(Module &M) {
141 // Okay, the .text section has now been finalized.
142 // FIXME: finalize the .text section.
144 // Okay, the ELF header and .text sections have been completed, build the
145 // .data, .bss, and "common" sections next.
146 ELFSection DataSection(".data", OutputBuffer.size());
147 ELFSection BSSSection (".bss");
148 for (Module::global_iterator I = M.global_begin(), E = M.global_end();
150 EmitGlobal(I, DataSection, BSSSection);
152 // If the .data section is nonempty, add it to our list.
153 if (DataSection.Size) {
154 DataSection.Align = 4; // FIXME: Compute!
155 // FIXME: Set the right flags and stuff.
156 SectionList.push_back(DataSection);
159 // If the .bss section is nonempty, add it to our list.
160 if (BSSSection.Size) {
161 BSSSection.Offset = OutputBuffer.size();
162 BSSSection.Align = 4; // FIXME: Compute!
163 // FIXME: Set the right flags and stuff.
164 SectionList.push_back(BSSSection);
167 // Emit the symbol table now, if non-empty.
170 // FIXME: Emit the relocations now.
172 // Emit the string table for the sections in the ELF file we have.
173 EmitSectionTableStringTable();
175 // Emit the .o file section table.
178 // Emit the .o file to the specified stream.
179 O.write((char*)&OutputBuffer[0], OutputBuffer.size());
181 // Free the output buffer.
182 std::vector<unsigned char>().swap(OutputBuffer);
186 /// EmitSymbolTable - If the current symbol table is non-empty, emit the string
187 /// table for it and then the symbol table itself.
188 void ELFWriter::EmitSymbolTable() {
189 if (SymbolTable.size() == 1) return; // Only the null entry.
191 // FIXME: compact all local symbols to the start of the symtab.
192 unsigned FirstNonLocalSymbol = 1;
194 SectionList.push_back(ELFSection(".strtab", OutputBuffer.size()));
195 ELFSection &StrTab = SectionList.back();
196 StrTab.Type = ELFSection::SHT_STRTAB;
199 // Set the zero'th symbol to a null byte, as required.
201 SymbolTable[0].NameIdx = 0;
203 for (unsigned i = 1, e = SymbolTable.size(); i != e; ++i) {
204 // FIXME: USE A MANGLER!!
205 const std::string &Name = SymbolTable[i].GV->getName();
208 SymbolTable[i].NameIdx = 0;
210 SymbolTable[i].NameIdx = Index;
212 // Add the name to the output buffer, including the null terminator.
213 OutputBuffer.insert(OutputBuffer.end(), Name.begin(), Name.end());
215 // Add a null terminator.
216 OutputBuffer.push_back(0);
218 // Keep track of the number of bytes emitted to this section.
219 Index += Name.size()+1;
223 StrTab.Size = OutputBuffer.size()-StrTab.Offset;
225 // Now that we have emitted the string table and know the offset into the
226 // string table of each symbol, emit the symbol table itself.
227 assert(!is64Bit && "Should this be 8 byte aligned for 64-bit?"
228 " (check .Align below also)");
231 SectionList.push_back(ELFSection(".symtab", OutputBuffer.size()));
232 ELFSection &SymTab = SectionList.back();
233 SymTab.Type = ELFSection::SHT_SYMTAB;
234 SymTab.Align = 4; // FIXME: check for ELF64
235 SymTab.Link = SectionList.size()-2; // Section Index of .strtab.
236 SymTab.Info = FirstNonLocalSymbol; // First non-STB_LOCAL symbol.
237 SymTab.EntSize = 16; // Size of each symtab entry. FIXME: wrong for ELF64
239 assert(!is64Bit && "check this!");
240 for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
241 ELFSym &Sym = SymbolTable[i];
242 outword(Sym.NameIdx);
247 outhalf(Sym.SectionIdx);
250 SymTab.Size = OutputBuffer.size()-SymTab.Offset;
253 /// EmitSectionTableStringTable - This method adds and emits a section for the
254 /// ELF Section Table string table: the string table that holds all of the
256 void ELFWriter::EmitSectionTableStringTable() {
257 // First step: add the section for the string table to the list of sections:
258 SectionList.push_back(ELFSection(".shstrtab", OutputBuffer.size()));
259 SectionList.back().Type = ELFSection::SHT_STRTAB;
261 // Now that we know which section number is the .shstrtab section, update the
262 // e_shstrndx entry in the ELF header.
263 fixhalf(SectionList.size()-1, ELFHeader_e_shstrndx_Offset);
265 // Set the NameIdx of each section in the string table and emit the bytes for
269 for (unsigned i = 0, e = SectionList.size(); i != e; ++i) {
270 // Set the index into the table. Note if we have lots of entries with
271 // common suffixes, we could memoize them here if we cared.
272 SectionList[i].NameIdx = Index;
274 // Add the name to the output buffer, including the null terminator.
275 OutputBuffer.insert(OutputBuffer.end(), SectionList[i].Name.begin(),
276 SectionList[i].Name.end());
277 // Add a null terminator.
278 OutputBuffer.push_back(0);
280 // Keep track of the number of bytes emitted to this section.
281 Index += SectionList[i].Name.size()+1;
284 // Set the size of .shstrtab now that we know what it is.
285 SectionList.back().Size = Index;
288 /// EmitSectionTable - Now that we have emitted the entire contents of the file
289 /// (all of the sections), emit the section table which informs the reader where
290 /// the boundaries are.
291 void ELFWriter::EmitSectionTable() {
292 // Now that all of the sections have been emitted, set the e_shnum entry in
294 fixhalf(SectionList.size(), ELFHeader_e_shnum_Offset);
296 // Now that we know the offset in the file of the section table (which we emit
297 // next), update the e_shoff address in the ELF header.
298 fixaddr(OutputBuffer.size(), ELFHeader_e_shoff_Offset);
300 // Emit all of the section table entries.
301 for (unsigned i = 0, e = SectionList.size(); i != e; ++i) {
302 const ELFSection &S = SectionList[i];
303 outword(S.NameIdx); // sh_name - Symbol table name idx
304 outword(S.Type); // sh_type - Section contents & semantics
305 outword(S.Flags); // sh_flags - Section flags.
306 outaddr(S.Addr); // sh_addr - The mem address this section appears in.
307 outaddr(S.Offset); // sh_offset - The offset from the start of the file.
308 outword(S.Size); // sh_size - The section size.
309 outword(S.Link); // sh_link - Section header table index link.
310 outword(S.Info); // sh_info - Auxillary information.
311 outword(S.Align); // sh_addralign - Alignment of section.
312 outword(S.EntSize); // sh_entsize - Size of each entry in the section.
315 // Release the memory allocated for the section list.
316 std::vector<ELFSection>().swap(SectionList);