llvm-6502/lib/CodeGen/ELFWriter.cpp

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//===-- 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. '.text' section
// #3. '.data' section
// #4. '.bss' section (conceptual position in file)
// ...
// #X. '.shstrtab' section
// #Y. Section Table
//
// The entries in the section table are laid out as:
// #0. Null entry [required]
// #1. ".text" entry - the program code
// #2. ".data" entry - global variables with initializers. [ if needed ]
// #3. ".bss" entry - global variables without initializers. [ if needed ]
// ...
// #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());
// Start up the symbol table. The first entry in the symtab is the null
// entry.
SymbolTable.push_back(ELFSym(0));
// FIXME: Should start the .text section.
return false;
}
void ELFWriter::EmitGlobal(GlobalVariable *GV, ELFSection &DataSection,
ELFSection &BSSSection) {
// If this is an external global, emit it...
assert(GV->hasInitializer() && "FIXME: unimp");
// If this global has a zero initializer, it is part of the .bss or common
// section.
if (GV->getInitializer()->isNullValue()) {
// If this global is part of the common block, add it now. Variables are
// part of the common block if they are zero initialized and allowed to be
// merged with other symbols.
if (GV->hasLinkOnceLinkage() || GV->hasWeakLinkage()) {
ELFSym CommonSym(GV);
// Value for common symbols is the alignment required.
const Type *GVType = (const Type*)GV->getType();
CommonSym.Value = TM.getTargetData().getTypeAlignment(GVType);
CommonSym.Size = TM.getTargetData().getTypeSize(GVType);
CommonSym.SetBind(ELFSym::STB_GLOBAL);
CommonSym.SetType(ELFSym::STT_OBJECT);
// TODO SOMEDAY: add ELF visibility.
CommonSym.SectionIdx = ELFSection::SHN_COMMON;
SymbolTable.push_back(CommonSym);
return;
}
// FIXME: Implement the .bss section.
return;
}
// FIXME: handle .rodata
//assert(!GV->isConstant() && "unimp");
// FIXME: handle .data
//assert(0 && "unimp");
}
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) {
// Okay, the .text section has now been finalized.
// FIXME: finalize the .text section.
// Okay, the ELF header and .text sections have been completed, build the
// .data, .bss, and "common" sections next.
ELFSection DataSection(".data", OutputBuffer.size());
ELFSection BSSSection (".bss");
for (Module::global_iterator I = M.global_begin(), E = M.global_end();
I != E; ++I)
EmitGlobal(I, DataSection, BSSSection);
// If the .data section is nonempty, add it to our list.
if (DataSection.Size) {
DataSection.Align = 4; // FIXME: Compute!
// FIXME: Set the right flags and stuff.
SectionList.push_back(DataSection);
}
// If the .bss section is nonempty, add it to our list.
if (BSSSection.Size) {
BSSSection.Offset = OutputBuffer.size();
BSSSection.Align = 4; // FIXME: Compute!
// FIXME: Set the right flags and stuff.
SectionList.push_back(BSSSection);
}
// Emit the symbol table now, if non-empty.
EmitSymbolTable();
// FIXME: Emit the relocations now.
// 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;
}
/// EmitSymbolTable - If the current symbol table is non-empty, emit the string
/// table for it and then the symbol table itself.
void ELFWriter::EmitSymbolTable() {
if (SymbolTable.size() == 1) return; // Only the null entry.
// FIXME: compact all local symbols to the start of the symtab.
unsigned FirstNonLocalSymbol = 1;
SectionList.push_back(ELFSection(".strtab", OutputBuffer.size()));
ELFSection &StrTab = SectionList.back();
StrTab.Type = ELFSection::SHT_STRTAB;
StrTab.Align = 1;
// Set the zero'th symbol to a null byte, as required.
outbyte(0);
SymbolTable[0].NameIdx = 0;
unsigned Index = 1;
for (unsigned i = 1, e = SymbolTable.size(); i != e; ++i) {
// FIXME: USE A MANGLER!!
const std::string &Name = SymbolTable[i].GV->getName();
if (Name.empty()) {
SymbolTable[i].NameIdx = 0;
} else {
SymbolTable[i].NameIdx = Index;
// Add the name to the output buffer, including the null terminator.
OutputBuffer.insert(OutputBuffer.end(), Name.begin(), Name.end());
// Add a null terminator.
OutputBuffer.push_back(0);
// Keep track of the number of bytes emitted to this section.
Index += Name.size()+1;
}
}
StrTab.Size = OutputBuffer.size()-StrTab.Offset;
// Now that we have emitted the string table and know the offset into the
// string table of each symbol, emit the symbol table itself.
assert(!is64Bit && "Should this be 8 byte aligned for 64-bit?"
" (check .Align below also)");
align(4);
SectionList.push_back(ELFSection(".symtab", OutputBuffer.size()));
ELFSection &SymTab = SectionList.back();
SymTab.Type = ELFSection::SHT_SYMTAB;
SymTab.Align = 4; // FIXME: check for ELF64
SymTab.Link = SectionList.size()-2; // Section Index of .strtab.
SymTab.Info = FirstNonLocalSymbol; // First non-STB_LOCAL symbol.
SymTab.EntSize = 16; // Size of each symtab entry. FIXME: wrong for ELF64
assert(!is64Bit && "check this!");
for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
ELFSym &Sym = SymbolTable[i];
outword(Sym.NameIdx);
outaddr(Sym.Value);
outword(Sym.Size);
outbyte(Sym.Info);
outbyte(Sym.Other);
outhalf(Sym.SectionIdx);
}
SymTab.Size = OutputBuffer.size()-SymTab.Offset;
}
/// 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 = ELFSection::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);
}