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//===-- ELFWriter.cpp - Target-independent ELF Writer code ----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by Chris Lattner 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/CodeGen/MachineCodeEmitter.h"
#include "llvm/CodeGen/MachineConstantPool.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/Mangler.h"
using namespace llvm;
//===----------------------------------------------------------------------===//
// ELFCodeEmitter Implementation
//===----------------------------------------------------------------------===//
namespace llvm {
/// ELFCodeEmitter - This class is used by the ELFWriter to emit the code for
/// functions to the ELF file.
class ELFCodeEmitter : public MachineCodeEmitter {
ELFWriter &EW;
ELFWriter::ELFSection *ES; // Section to write to.
std::vector<unsigned char> *OutBuffer;
size_t FnStart;
public:
ELFCodeEmitter(ELFWriter &ew) : EW(ew), OutBuffer(0) {}
void startFunction(MachineFunction &F);
void finishFunction(MachineFunction &F);
void emitConstantPool(MachineConstantPool *MCP) {
if (MCP->isEmpty()) return;
assert(0 && "unimp");
}
virtual void emitByte(unsigned char B) {
OutBuffer->push_back(B);
}
virtual void emitWordAt(unsigned W, unsigned *Ptr) {
assert(0 && "ni");
}
virtual void emitWord(unsigned W) {
assert(0 && "ni");
}
virtual uint64_t getCurrentPCValue() {
return OutBuffer->size();
}
virtual uint64_t getCurrentPCOffset() {
return OutBuffer->size()-FnStart;
}
void addRelocation(const MachineRelocation &MR) {
assert(0 && "relo not handled yet!");
}
virtual uint64_t getConstantPoolEntryAddress(unsigned Index) {
assert(0 && "CP not implementated yet!");
return 0;
}
/// JIT SPECIFIC FUNCTIONS - DO NOT IMPLEMENT THESE HERE!
void startFunctionStub(unsigned StubSize) {
assert(0 && "JIT specific function called!");
abort();
}
void *finishFunctionStub(const Function *F) {
assert(0 && "JIT specific function called!");
abort();
return 0;
}
};
}
/// startFunction - This callback is invoked when a new machine function is
/// about to be emitted.
void ELFCodeEmitter::startFunction(MachineFunction &F) {
// Align the output buffer to the appropriate alignment.
unsigned Align = 16; // FIXME: GENERICIZE!!
// Get the ELF Section that this function belongs in.
ES = &EW.getSection(".text", ELFWriter::ELFSection::SHT_PROGBITS,
ELFWriter::ELFSection::SHF_EXECINSTR |
ELFWriter::ELFSection::SHF_ALLOC);
OutBuffer = &ES->SectionData;
// Upgrade the section alignment if required.
if (ES->Align < Align) ES->Align = Align;
// Add padding zeros to the end of the buffer to make sure that the
// function will start on the correct byte alignment within the section.
size_t SectionOff = OutBuffer->size();
ELFWriter::align(*OutBuffer, Align);
FnStart = OutBuffer->size();
}
/// finishFunction - This callback is invoked after the function is completely
/// finished.
void ELFCodeEmitter::finishFunction(MachineFunction &F) {
// We now know the size of the function, add a symbol to represent it.
ELFWriter::ELFSym FnSym(F.getFunction());
// Figure out the binding (linkage) of the symbol.
switch (F.getFunction()->getLinkage()) {
default:
// appending linkage is illegal for functions.
assert(0 && "Unknown linkage type!");
case GlobalValue::ExternalLinkage:
FnSym.SetBind(ELFWriter::ELFSym::STB_GLOBAL);
break;
case GlobalValue::LinkOnceLinkage:
case GlobalValue::WeakLinkage:
FnSym.SetBind(ELFWriter::ELFSym::STB_WEAK);
break;
case GlobalValue::InternalLinkage:
FnSym.SetBind(ELFWriter::ELFSym::STB_LOCAL);
break;
}
ES->Size = OutBuffer->size();
FnSym.SetType(ELFWriter::ELFSym::STT_FUNC);
FnSym.SectionIdx = ES->SectionIdx;
FnSym.Value = FnStart; // Value = Offset from start of Section.
FnSym.Size = OutBuffer->size()-FnStart;
// Finally, add it to the symtab.
EW.SymbolTable.push_back(FnSym);
}
//===----------------------------------------------------------------------===//
// ELFWriter Implementation
//===----------------------------------------------------------------------===//
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();
// Create the machine code emitter object for this target.
MCE = new ELFCodeEmitter(*this);
NumSections = 0;
}
ELFWriter::~ELFWriter() {
delete MCE;
}
// doInitialization - Emit the file header and all of the global variables for
// the module to the ELF file.
bool ELFWriter::doInitialization(Module &M) {
Mang = new Mangler(M);
// Local alias to shortenify coming code.
std::vector<unsigned char> &FH = FileHeader;
outbyte(FH, 0x7F); // EI_MAG0
outbyte(FH, 'E'); // EI_MAG1
outbyte(FH, 'L'); // EI_MAG2
outbyte(FH, 'F'); // EI_MAG3
outbyte(FH, is64Bit ? 2 : 1); // EI_CLASS
outbyte(FH, isLittleEndian ? 1 : 2); // EI_DATA
outbyte(FH, 1); // EI_VERSION
FH.resize(16); // EI_PAD up to 16 bytes.
// This should change for shared objects.
outhalf(FH, 1); // e_type = ET_REL
outhalf(FH, e_machine); // e_machine = whatever the target wants
outword(FH, 1); // e_version = 1
outaddr(FH, 0); // e_entry = 0 -> no entry point in .o file
outaddr(FH, 0); // e_phoff = 0 -> no program header for .o
ELFHeader_e_shoff_Offset = FH.size();
outaddr(FH, 0); // e_shoff
outword(FH, e_flags); // e_flags = whatever the target wants
outhalf(FH, is64Bit ? 64 : 52); // e_ehsize = ELF header size
outhalf(FH, 0); // e_phentsize = prog header entry size
outhalf(FH, 0); // e_phnum = # prog header entries = 0
outhalf(FH, is64Bit ? 64 : 40); // e_shentsize = sect hdr entry size
ELFHeader_e_shnum_Offset = FH.size();
outhalf(FH, 0); // e_shnum = # of section header ents
ELFHeader_e_shstrndx_Offset = FH.size();
outhalf(FH, 0); // e_shstrndx = Section # of '.shstrtab'
// Add the null section, which is required to be first in the file.
getSection("", 0, 0);
// Start up the symbol table. The first entry in the symtab is the null
// entry.
SymbolTable.push_back(ELFSym(0));
return false;
}
void ELFWriter::EmitGlobal(GlobalVariable *GV) {
// If this is an external global, emit it now. TODO: Note that it would be
// better to ignore the symbol here and only add it to the symbol table if
// referenced.
if (!GV->hasInitializer()) {
ELFSym ExternalSym(GV);
ExternalSym.SetBind(ELFSym::STB_GLOBAL);
ExternalSym.SetType(ELFSym::STT_NOTYPE);
ExternalSym.SectionIdx = ELFSection::SHN_UNDEF;
SymbolTable.push_back(ExternalSym);
return;
}
const Type *GVType = (const Type*)GV->getType();
unsigned Align = TM.getTargetData().getTypeAlignment(GVType);
unsigned Size = TM.getTargetData().getTypeSize(GVType);
// 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.
CommonSym.Value = Align;
CommonSym.Size = Size;
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;
}
// Otherwise, this symbol is part of the .bss section. Emit it now.
// Handle alignment. Ensure section is aligned at least as much as required
// by this symbol.
ELFSection &BSSSection = getBSSSection();
BSSSection.Align = std::max(BSSSection.Align, Align);
// Within the section, emit enough virtual padding to get us to an alignment
// boundary.
if (Align)
BSSSection.Size = (BSSSection.Size + Align - 1) & ~(Align-1);
ELFSym BSSSym(GV);
BSSSym.Value = BSSSection.Size;
BSSSym.Size = Size;
BSSSym.SetType(ELFSym::STT_OBJECT);
switch (GV->getLinkage()) {
default: // weak/linkonce handled above
assert(0 && "Unexpected linkage type!");
case GlobalValue::AppendingLinkage: // FIXME: This should be improved!
case GlobalValue::ExternalLinkage:
BSSSym.SetBind(ELFSym::STB_GLOBAL);
break;
case GlobalValue::InternalLinkage:
BSSSym.SetBind(ELFSym::STB_LOCAL);
break;
}
// Set the idx of the .bss section
BSSSym.SectionIdx = BSSSection.SectionIdx;
SymbolTable.push_back(BSSSym);
// Reserve space in the .bss section for this symbol.
BSSSection.Size += Size;
return;
}
// FIXME: handle .rodata
//assert(!GV->isConstant() && "unimp");
// FIXME: handle .data
//assert(0 && "unimp");
}
bool ELFWriter::runOnMachineFunction(MachineFunction &MF) {
// Nothing to do here, this is all done through the MCE object above.
return false;
}
/// doFinalization - Now that the module has been completely processed, emit
/// the ELF file to 'O'.
bool ELFWriter::doFinalization(Module &M) {
// Okay, the ELF header and .text sections have been completed, build the
// .data, .bss, and "common" sections next.
for (Module::global_iterator I = M.global_begin(), E = M.global_end();
I != E; ++I)
EmitGlobal(I);
// 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 sections to the .o file, and emit the section table for the file.
OutputSectionsAndSectionTable();
// We are done with the abstract symbols.
SectionList.clear();
NumSections = 0;
// Release the name mangler object.
delete Mang; Mang = 0;
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;
ELFSection &StrTab = getSection(".strtab", ELFSection::SHT_STRTAB, 0);
StrTab.Align = 1;
DataBuffer &StrTabBuf = StrTab.SectionData;
// Set the zero'th symbol to a null byte, as required.
outbyte(StrTabBuf, 0);
SymbolTable[0].NameIdx = 0;
unsigned Index = 1;
for (unsigned i = 1, e = SymbolTable.size(); i != e; ++i) {
// Use the name mangler to uniquify the LLVM symbol.
std::string Name = Mang->getValueName(SymbolTable[i].GV);
if (Name.empty()) {
SymbolTable[i].NameIdx = 0;
} else {
SymbolTable[i].NameIdx = Index;
// Add the name to the output buffer, including the null terminator.
StrTabBuf.insert(StrTabBuf.end(), Name.begin(), Name.end());
// Add a null terminator.
StrTabBuf.push_back(0);
// Keep track of the number of bytes emitted to this section.
Index += Name.size()+1;
}
}
assert(Index == StrTabBuf.size());
StrTab.Size = Index;
// Now that we have emitted the string table and know the offset into the
// string table of each symbol, emit the symbol table itself.
ELFSection &SymTab = getSection(".symtab", ELFSection::SHT_SYMTAB, 0);
SymTab.Align = is64Bit ? 8 : 4;
SymTab.Link = SymTab.SectionIdx; // Section Index of .strtab.
SymTab.Info = FirstNonLocalSymbol; // First non-STB_LOCAL symbol.
SymTab.EntSize = 16; // Size of each symtab entry. FIXME: wrong for ELF64
DataBuffer &SymTabBuf = SymTab.SectionData;
if (!is64Bit) { // 32-bit and 64-bit formats are shuffled a bit.
for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
ELFSym &Sym = SymbolTable[i];
outword(SymTabBuf, Sym.NameIdx);
outaddr32(SymTabBuf, Sym.Value);
outword(SymTabBuf, Sym.Size);
outbyte(SymTabBuf, Sym.Info);
outbyte(SymTabBuf, Sym.Other);
outhalf(SymTabBuf, Sym.SectionIdx);
}
} else {
for (unsigned i = 0, e = SymbolTable.size(); i != e; ++i) {
ELFSym &Sym = SymbolTable[i];
outword(SymTabBuf, Sym.NameIdx);
outbyte(SymTabBuf, Sym.Info);
outbyte(SymTabBuf, Sym.Other);
outhalf(SymTabBuf, Sym.SectionIdx);
outaddr64(SymTabBuf, Sym.Value);
outxword(SymTabBuf, Sym.Size);
}
}
SymTab.Size = SymTabBuf.size();
}
/// 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:
ELFSection &SHStrTab = getSection(".shstrtab", ELFSection::SHT_STRTAB, 0);
// Now that we know which section number is the .shstrtab section, update the
// e_shstrndx entry in the ELF header.
fixhalf(FileHeader, SHStrTab.SectionIdx, 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;
DataBuffer &Buf = SHStrTab.SectionData;
for (std::list<ELFSection>::iterator I = SectionList.begin(),
E = SectionList.end(); 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.
I->NameIdx = Index;
// Add the name to the output buffer, including the null terminator.
Buf.insert(Buf.end(), I->Name.begin(), I->Name.end());
// Add a null terminator.
Buf.push_back(0);
// Keep track of the number of bytes emitted to this section.
Index += I->Name.size()+1;
}
// Set the size of .shstrtab now that we know what it is.
assert(Index == Buf.size());
SHStrTab.Size = Index;
}
/// OutputSectionsAndSectionTable - Now that we have constructed the file header
/// and all of the sections, emit these to the ostream destination and emit the
/// SectionTable.
void ELFWriter::OutputSectionsAndSectionTable() {
// Pass #1: Compute the file offset for each section.
size_t FileOff = FileHeader.size(); // File header first.
// Emit all of the section data in order.
for (std::list<ELFSection>::iterator I = SectionList.begin(),
E = SectionList.end(); I != E; ++I) {
// Align FileOff to whatever the alignment restrictions of the section are.
if (I->Align)
FileOff = (FileOff+I->Align-1) & ~(I->Align-1);
I->Offset = FileOff;
FileOff += I->SectionData.size();
}
// Align Section Header.
unsigned TableAlign = is64Bit ? 8 : 4;
FileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
// Now that we know where all of the sections will be emitted, set the e_shnum
// entry in the ELF header.
fixhalf(FileHeader, NumSections, ELFHeader_e_shnum_Offset);
// Now that we know the offset in the file of the section table, update the
// e_shoff address in the ELF header.
fixaddr(FileHeader, FileOff, ELFHeader_e_shoff_Offset);
// Now that we know all of the data in the file header, emit it and all of the
// sections!
O.write((char*)&FileHeader[0], FileHeader.size());
FileOff = FileHeader.size();
DataBuffer().swap(FileHeader);
DataBuffer Table;
// Emit all of the section data and build the section table itself.
while (!SectionList.empty()) {
const ELFSection &S = *SectionList.begin();
// Align FileOff to whatever the alignment restrictions of the section are.
if (S.Align)
for (size_t NewFileOff = (FileOff+S.Align-1) & ~(S.Align-1);
FileOff != NewFileOff; ++FileOff)
O.put(0xAB);
O.write((char*)&S.SectionData[0], S.SectionData.size());
FileOff += S.SectionData.size();
outword(Table, S.NameIdx); // sh_name - Symbol table name idx
outword(Table, S.Type); // sh_type - Section contents & semantics
outword(Table, S.Flags); // sh_flags - Section flags.
outaddr(Table, S.Addr); // sh_addr - The mem addr this section is in.
outaddr(Table, S.Offset); // sh_offset - Offset from the file start.
outword(Table, S.Size); // sh_size - The section size.
outword(Table, S.Link); // sh_link - Section header table index link.
outword(Table, S.Info); // sh_info - Auxillary information.
outword(Table, S.Align); // sh_addralign - Alignment of section.
outword(Table, S.EntSize); // sh_entsize - Size of entries in the section.
SectionList.pop_front();
}
// Align output for the section table.
for (size_t NewFileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
FileOff != NewFileOff; ++FileOff)
O.put(0xAB);
// Emit the section table itself.
O.write((char*)&Table[0], Table.size());
}
|