llvm-6502/lib/CodeGen/ELFWriter.cpp
Chris Lattner 35f0a4f24e iniital checkin of ELFWriter implementation
For now, the elf writer is only capable of emitting an empty elf file, with
a section table and a section table string table.  This will be enhanced
in the future :)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22291 91177308-0d34-0410-b5e6-96231b3b80d8
2005-06-27 06:29:00 +00:00

231 lines
8.7 KiB
C++

//===-- 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);
}