[llvm-commits] CVS: llvm/lib/CodeGen/ELFWriter.cpp
Reid Spencer
reid at x10sys.com
Thu Jul 7 01:41:55 PDT 2005
I didn't realize you were going to implement this. I have a partial
implementation in the same file name(s) that is based on libelf. I don't
see why we would want to re-invent this wheel, but I'm sure you have
your reasons. If you're opposed to libelf, then please remove it from
the lib/CodeGen/ELF directory.
Reid.
On Mon, 2005-06-27 at 01:29 -0500, Chris Lattner wrote:
>
> Changes in directory llvm/lib/CodeGen:
>
> ELFWriter.cpp added (r1.1)
> ---
> Log message:
>
> 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 :)
>
>
> ---
> Diffs of the changes: (+230 -0)
>
> ELFWriter.cpp | 230 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 230 insertions(+)
>
>
> Index: llvm/lib/CodeGen/ELFWriter.cpp
> diff -c /dev/null llvm/lib/CodeGen/ELFWriter.cpp:1.1
> *** /dev/null Mon Jun 27 01:29:10 2005
> --- llvm/lib/CodeGen/ELFWriter.cpp Mon Jun 27 01:29:00 2005
> ***************
> *** 0 ****
> --- 1,230 ----
> + //===-- 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);
> + }
>
>
>
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