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llvm-mirror/lib/CodeGen/ELFWriter.cpp
Bruno Cardoso Lopes 2015382398 Support adding relocations for data sections, handling the cases where 
global declared symbols are initialized with references from other global
symbols.

llvm-svn: 76540
2009-07-21 06:51:32 +00:00

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//===-- ELFWriter.cpp - Target-independent ELF Writer code ----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file 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.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "elfwriter"
#include "ELF.h"
#include "ELFWriter.h"
#include "ELFCodeEmitter.h"
#include "llvm/Constants.h"
#include "llvm/Module.h"
#include "llvm/PassManager.h"
#include "llvm/DerivedTypes.h"
#include "llvm/CodeGen/BinaryObject.h"
#include "llvm/CodeGen/FileWriters.h"
#include "llvm/CodeGen/MachineCodeEmitter.h"
#include "llvm/CodeGen/ObjectCodeEmitter.h"
#include "llvm/CodeGen/MachineCodeEmitter.h"
#include "llvm/CodeGen/MachineConstantPool.h"
#include "llvm/Target/TargetAsmInfo.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetELFWriterInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/Mangler.h"
#include "llvm/Support/Streams.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
using namespace llvm;
char ELFWriter::ID = 0;
/// AddELFWriter - Add the ELF writer to the function pass manager
ObjectCodeEmitter *llvm::AddELFWriter(PassManagerBase &PM,
raw_ostream &O,
TargetMachine &TM) {
ELFWriter *EW = new ELFWriter(O, TM);
PM.add(EW);
return EW->getObjectCodeEmitter();
}
//===----------------------------------------------------------------------===//
// ELFWriter Implementation
//===----------------------------------------------------------------------===//
ELFWriter::ELFWriter(raw_ostream &o, TargetMachine &tm)
: MachineFunctionPass(&ID), O(o), TM(tm),
is64Bit(TM.getTargetData()->getPointerSizeInBits() == 64),
isLittleEndian(TM.getTargetData()->isLittleEndian()),
ElfHdr(isLittleEndian, is64Bit) {
TAI = TM.getTargetAsmInfo();
TEW = TM.getELFWriterInfo();
// Create the object code emitter object for this target.
ElfCE = new ELFCodeEmitter(*this);
// Inital number of sections
NumSections = 0;
}
ELFWriter::~ELFWriter() {
delete ElfCE;
}
// 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);
// ELF Header
// ----------
// Fields e_shnum e_shstrndx are only known after all section have
// been emitted. They locations in the ouput buffer are recorded so
// to be patched up later.
//
// Note
// ----
// emitWord method behaves differently for ELF32 and ELF64, writing
// 4 bytes in the former and 8 in the last for *_off and *_addr elf types
ElfHdr.emitByte(0x7f); // e_ident[EI_MAG0]
ElfHdr.emitByte('E'); // e_ident[EI_MAG1]
ElfHdr.emitByte('L'); // e_ident[EI_MAG2]
ElfHdr.emitByte('F'); // e_ident[EI_MAG3]
ElfHdr.emitByte(TEW->getEIClass()); // e_ident[EI_CLASS]
ElfHdr.emitByte(TEW->getEIData()); // e_ident[EI_DATA]
ElfHdr.emitByte(EV_CURRENT); // e_ident[EI_VERSION]
ElfHdr.emitAlignment(16); // e_ident[EI_NIDENT-EI_PAD]
ElfHdr.emitWord16(ET_REL); // e_type
ElfHdr.emitWord16(TEW->getEMachine()); // e_machine = target
ElfHdr.emitWord32(EV_CURRENT); // e_version
ElfHdr.emitWord(0); // e_entry, no entry point in .o file
ElfHdr.emitWord(0); // e_phoff, no program header for .o
ELFHdr_e_shoff_Offset = ElfHdr.size();
ElfHdr.emitWord(0); // e_shoff = sec hdr table off in bytes
ElfHdr.emitWord32(TEW->getEFlags()); // e_flags = whatever the target wants
ElfHdr.emitWord16(TEW->getHdrSize()); // e_ehsize = ELF header size
ElfHdr.emitWord16(0); // e_phentsize = prog header entry size
ElfHdr.emitWord16(0); // e_phnum = # prog header entries = 0
// e_shentsize = Section header entry size
ElfHdr.emitWord16(TEW->getSHdrSize());
// e_shnum = # of section header ents
ELFHdr_e_shnum_Offset = ElfHdr.size();
ElfHdr.emitWord16(0); // Placeholder
// e_shstrndx = Section # of '.shstrtab'
ELFHdr_e_shstrndx_Offset = ElfHdr.size();
ElfHdr.emitWord16(0); // Placeholder
// Add the null section, which is required to be first in the file.
getNullSection();
return false;
}
// Get jump table section on the section name returned by TAI
ELFSection &ELFWriter::getJumpTableSection() {
unsigned Align = TM.getTargetData()->getPointerABIAlignment();
return getSection(TAI->getJumpTableDataSection(),
ELFSection::SHT_PROGBITS,
ELFSection::SHF_ALLOC, Align);
}
// Get a constant pool section based on the section name returned by TAI
ELFSection &ELFWriter::getConstantPoolSection(MachineConstantPoolEntry &CPE) {
std::string CstPoolName =
TAI->SelectSectionForMachineConst(CPE.getType())->getName();
return getSection(CstPoolName,
ELFSection::SHT_PROGBITS,
ELFSection::SHF_MERGE | ELFSection::SHF_ALLOC,
CPE.getAlignment());
}
// Return the relocation section of section 'S'. 'RelA' is true
// if the relocation section contains entries with addends.
ELFSection &ELFWriter::getRelocSection(ELFSection &S) {
unsigned SectionHeaderTy = TEW->hasRelocationAddend() ?
ELFSection::SHT_RELA : ELFSection::SHT_REL;
std::string RelSName(".rel");
if (TEW->hasRelocationAddend())
RelSName.append("a");
RelSName.append(S.getName());
return getSection(RelSName, SectionHeaderTy, 0, TEW->getPrefELFAlignment());
}
// getGlobalELFVisibility - Returns the ELF specific visibility type
unsigned ELFWriter::getGlobalELFVisibility(const GlobalValue *GV) {
switch (GV->getVisibility()) {
default:
llvm_unreachable("unknown visibility type");
case GlobalValue::DefaultVisibility:
return ELFSym::STV_DEFAULT;
case GlobalValue::HiddenVisibility:
return ELFSym::STV_HIDDEN;
case GlobalValue::ProtectedVisibility:
return ELFSym::STV_PROTECTED;
}
return 0;
}
// getGlobalELFBinding - Returns the ELF specific binding type
unsigned ELFWriter::getGlobalELFBinding(const GlobalValue *GV) {
if (GV->hasInternalLinkage())
return ELFSym::STB_LOCAL;
if (GV->hasWeakLinkage())
return ELFSym::STB_WEAK;
return ELFSym::STB_GLOBAL;
}
// getGlobalELFType - Returns the ELF specific type for a global
unsigned ELFWriter::getGlobalELFType(const GlobalValue *GV) {
if (GV->isDeclaration())
return ELFSym::STT_NOTYPE;
if (isa<Function>(GV))
return ELFSym::STT_FUNC;
return ELFSym::STT_OBJECT;
}
// getElfSectionFlags - Get the ELF Section Header flags based
// on the flags defined in ELFTargetAsmInfo.
unsigned ELFWriter::getElfSectionFlags(unsigned Flags) {
unsigned ElfSectionFlags = ELFSection::SHF_ALLOC;
if (Flags & SectionFlags::Code)
ElfSectionFlags |= ELFSection::SHF_EXECINSTR;
if (Flags & SectionFlags::Writeable)
ElfSectionFlags |= ELFSection::SHF_WRITE;
if (Flags & SectionFlags::Mergeable)
ElfSectionFlags |= ELFSection::SHF_MERGE;
if (Flags & SectionFlags::TLS)
ElfSectionFlags |= ELFSection::SHF_TLS;
if (Flags & SectionFlags::Strings)
ElfSectionFlags |= ELFSection::SHF_STRINGS;
return ElfSectionFlags;
}
// isELFUndefSym - the symbol has no section and must be placed in
// the symbol table with a reference to the null section.
static bool isELFUndefSym(const GlobalValue *GV) {
return GV->isDeclaration();
}
// isELFBssSym - for an undef or null value, the symbol must go to a bss
// section if it's not weak for linker, otherwise it's a common sym.
static bool isELFBssSym(const GlobalVariable *GV) {
const Constant *CV = GV->getInitializer();
return ((CV->isNullValue() || isa<UndefValue>(CV)) && !GV->isWeakForLinker());
}
// isELFCommonSym - for an undef or null value, the symbol must go to a
// common section if it's weak for linker, otherwise bss.
static bool isELFCommonSym(const GlobalVariable *GV) {
const Constant *CV = GV->getInitializer();
return ((CV->isNullValue() || isa<UndefValue>(CV)) && GV->isWeakForLinker());
}
// isELFDataSym - if the symbol is an initialized but no null constant
// it must go to some kind of data section gathered from TAI
static bool isELFDataSym(const Constant *CV) {
return (!(CV->isNullValue() || isa<UndefValue>(CV)));
}
// EmitGlobal - Choose the right section for global and emit it
void ELFWriter::EmitGlobal(const GlobalValue *GV) {
// Check if the referenced symbol is already emitted
if (GblSymLookup.find(GV) != GblSymLookup.end())
return;
// Handle ELF Bind, Visibility and Type for the current symbol
unsigned SymBind = getGlobalELFBinding(GV);
ELFSym *GblSym = new ELFSym(GV);
GblSym->setBind(SymBind);
GblSym->setVisibility(getGlobalELFVisibility(GV));
GblSym->setType(getGlobalELFType(GV));
if (isELFUndefSym(GV)) {
GblSym->SectionIdx = ELFSection::SHN_UNDEF;
} else {
assert(isa<GlobalVariable>(GV) && "GV not a global variable!");
const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
// Get ELF section from TAI
const Section *S = TAI->SectionForGlobal(GV);
unsigned SectionFlags = getElfSectionFlags(S->getFlags());
// The symbol align should update the section alignment if needed
const TargetData *TD = TM.getTargetData();
unsigned Align = TD->getPreferredAlignment(GVar);
unsigned Size = TD->getTypeAllocSize(GVar->getInitializer()->getType());
GblSym->Size = Size;
if (isELFCommonSym(GVar)) {
GblSym->SectionIdx = ELFSection::SHN_COMMON;
getSection(S->getName(), ELFSection::SHT_NOBITS, SectionFlags, 1);
// A new linkonce section is created for each global in the
// common section, the default alignment is 1 and the symbol
// value contains its alignment.
GblSym->Value = Align;
} else if (isELFBssSym(GVar)) {
ELFSection &ES =
getSection(S->getName(), ELFSection::SHT_NOBITS, SectionFlags);
GblSym->SectionIdx = ES.SectionIdx;
// Update the size with alignment and the next object can
// start in the right offset in the section
if (Align) ES.Size = (ES.Size + Align-1) & ~(Align-1);
ES.Align = std::max(ES.Align, Align);
// GblSym->Value should contain the virtual offset inside the section.
// Virtual because the BSS space is not allocated on ELF objects
GblSym->Value = ES.Size;
ES.Size += Size;
} else if (isELFDataSym(GV)) {
ELFSection &ES =
getSection(S->getName(), ELFSection::SHT_PROGBITS, SectionFlags);
GblSym->SectionIdx = ES.SectionIdx;
// GblSym->Value should contain the symbol offset inside the section,
// and all symbols should start on their required alignment boundary
ES.Align = std::max(ES.Align, Align);
GblSym->Value = (ES.size() + (Align-1)) & (-Align);
ES.emitAlignment(ES.Align);
// Emit the global to the data section 'ES'
EmitGlobalConstant(GVar->getInitializer(), ES);
}
}
// Private symbols must never go to the symbol table.
unsigned SymIdx = 0;
if (GV->hasPrivateLinkage()) {
PrivateSyms.push_back(GblSym);
SymIdx = PrivateSyms.size()-1;
} else {
SymbolList.push_back(GblSym);
}
setGlobalSymLookup(GV, SymIdx);
}
void ELFWriter::EmitGlobalConstantStruct(const ConstantStruct *CVS,
ELFSection &GblS) {
// Print the fields in successive locations. Pad to align if needed!
const TargetData *TD = TM.getTargetData();
unsigned Size = TD->getTypeAllocSize(CVS->getType());
const StructLayout *cvsLayout = TD->getStructLayout(CVS->getType());
uint64_t sizeSoFar = 0;
for (unsigned i = 0, e = CVS->getNumOperands(); i != e; ++i) {
const Constant* field = CVS->getOperand(i);
// Check if padding is needed and insert one or more 0s.
uint64_t fieldSize = TD->getTypeAllocSize(field->getType());
uint64_t padSize = ((i == e-1 ? Size : cvsLayout->getElementOffset(i+1))
- cvsLayout->getElementOffset(i)) - fieldSize;
sizeSoFar += fieldSize + padSize;
// Now print the actual field value.
EmitGlobalConstant(field, GblS);
// Insert padding - this may include padding to increase the size of the
// current field up to the ABI size (if the struct is not packed) as well
// as padding to ensure that the next field starts at the right offset.
for (unsigned p=0; p < padSize; p++)
GblS.emitByte(0);
}
assert(sizeSoFar == cvsLayout->getSizeInBytes() &&
"Layout of constant struct may be incorrect!");
}
void ELFWriter::EmitGlobalConstant(const Constant *CV, ELFSection &GblS) {
const TargetData *TD = TM.getTargetData();
unsigned Size = TD->getTypeAllocSize(CV->getType());
if (const ConstantArray *CVA = dyn_cast<ConstantArray>(CV)) {
if (CVA->isString()) {
std::string GblStr = CVA->getAsString();
GblStr.resize(GblStr.size()-1);
GblS.emitString(GblStr);
} else { // Not a string. Print the values in successive locations
for (unsigned i = 0, e = CVA->getNumOperands(); i != e; ++i)
EmitGlobalConstant(CVA->getOperand(i), GblS);
}
return;
} else if (const ConstantStruct *CVS = dyn_cast<ConstantStruct>(CV)) {
EmitGlobalConstantStruct(CVS, GblS);
return;
} else if (const ConstantFP *CFP = dyn_cast<ConstantFP>(CV)) {
uint64_t Val = CFP->getValueAPF().bitcastToAPInt().getZExtValue();
if (CFP->getType() == Type::DoubleTy)
GblS.emitWord64(Val);
else if (CFP->getType() == Type::FloatTy)
GblS.emitWord32(Val);
else if (CFP->getType() == Type::X86_FP80Ty) {
llvm_unreachable("X86_FP80Ty global emission not implemented");
} else if (CFP->getType() == Type::PPC_FP128Ty)
llvm_unreachable("PPC_FP128Ty global emission not implemented");
return;
} else if (const ConstantInt *CI = dyn_cast<ConstantInt>(CV)) {
if (Size == 4)
GblS.emitWord32(CI->getZExtValue());
else if (Size == 8)
GblS.emitWord64(CI->getZExtValue());
else
llvm_unreachable("LargeInt global emission not implemented");
return;
} else if (const ConstantVector *CP = dyn_cast<ConstantVector>(CV)) {
const VectorType *PTy = CP->getType();
for (unsigned I = 0, E = PTy->getNumElements(); I < E; ++I)
EmitGlobalConstant(CP->getOperand(I), GblS);
return;
} else if (const GlobalValue *GV = dyn_cast<GlobalValue>(CV)) {
// This is a constant address for a global variable or function and
// therefore must be referenced using a relocation entry.
// Check if the referenced symbol is already emitted
if (GblSymLookup.find(GV) == GblSymLookup.end())
EmitGlobal(GV);
// Create the relocation entry for the global value
MachineRelocation MR =
MachineRelocation::getGV(GblS.getCurrentPCOffset(),
TEW->getAbsoluteLabelMachineRelTy(),
const_cast<GlobalValue*>(GV));
// Fill the data entry with zeros
for (unsigned i=0; i < Size; ++i)
GblS.emitByte(0);
// Add the relocation entry for the current data section
GblS.addRelocation(MR);
return;
} else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(CV)) {
if (CE->getOpcode() == Instruction::BitCast) {
EmitGlobalConstant(CE->getOperand(0), GblS);
return;
}
// See AsmPrinter::EmitConstantValueOnly for other ConstantExpr types
llvm_unreachable("Unsupported ConstantExpr type");
}
llvm_unreachable("Unknown global constant type");
}
bool ELFWriter::runOnMachineFunction(MachineFunction &MF) {
// Nothing to do here, this is all done through the ElfCE object above.
return false;
}
/// doFinalization - Now that the module has been completely processed, emit
/// the ELF file to 'O'.
bool ELFWriter::doFinalization(Module &M) {
// Emit .data section placeholder
getDataSection();
// Emit .bss section placeholder
getBSSSection();
// Build and emit data, bss and "common" sections.
for (Module::global_iterator I = M.global_begin(), E = M.global_end();
I != E; ++I)
EmitGlobal(I);
// Emit all pending globals
for (SetVector<GlobalValue*>::const_iterator I = PendingGlobals.begin(),
E = PendingGlobals.end(); I != E; ++I)
EmitGlobal(*I);
// Emit non-executable stack note
if (TAI->getNonexecutableStackDirective())
getNonExecStackSection();
// Emit a symbol for each section created until now, skip null section
for (unsigned i = 1, e = SectionList.size(); i < e; ++i) {
ELFSection &ES = *SectionList[i];
ELFSym *SectionSym = new ELFSym(0);
SectionSym->SectionIdx = ES.SectionIdx;
SectionSym->Size = 0;
SectionSym->setBind(ELFSym::STB_LOCAL);
SectionSym->setType(ELFSym::STT_SECTION);
SectionSym->setVisibility(ELFSym::STV_DEFAULT);
SymbolList.push_back(SectionSym);
ES.Sym = SymbolList.back();
}
// Emit string table
EmitStringTable();
// Emit the symbol table now, if non-empty.
EmitSymbolTable();
// Emit the relocation sections.
EmitRelocations();
// Emit the sections string table.
EmitSectionTableStringTable();
// Dump the sections and section table to the .o file.
OutputSectionsAndSectionTable();
// We are done with the abstract symbols.
SymbolList.clear();
SectionList.clear();
NumSections = 0;
// Release the name mangler object.
delete Mang; Mang = 0;
return false;
}
// RelocateField - Patch relocatable field with 'Offset' in 'BO'
// using a 'Value' of known 'Size'
void ELFWriter::RelocateField(BinaryObject &BO, uint32_t Offset,
int64_t Value, unsigned Size) {
if (Size == 32)
BO.fixWord32(Value, Offset);
else if (Size == 64)
BO.fixWord64(Value, Offset);
else
llvm_unreachable("don't know howto patch relocatable field");
}
/// EmitRelocations - Emit relocations
void ELFWriter::EmitRelocations() {
// True if the target uses the relocation entry to hold the addend,
// otherwise the addend is written directly to the relocatable field.
bool HasRelA = TEW->hasRelocationAddend();
// Create Relocation sections for each section which needs it.
for (unsigned i=0, e=SectionList.size(); i != e; ++i) {
ELFSection &S = *SectionList[i];
// This section does not have relocations
if (!S.hasRelocations()) continue;
ELFSection &RelSec = getRelocSection(S);
// 'Link' - Section hdr idx of the associated symbol table
// 'Info' - Section hdr idx of the section to which the relocation applies
ELFSection &SymTab = getSymbolTableSection();
RelSec.Link = SymTab.SectionIdx;
RelSec.Info = S.SectionIdx;
RelSec.EntSize = TEW->getRelocationEntrySize();
// Get the relocations from Section
std::vector<MachineRelocation> Relos = S.getRelocations();
for (std::vector<MachineRelocation>::iterator MRI = Relos.begin(),
MRE = Relos.end(); MRI != MRE; ++MRI) {
MachineRelocation &MR = *MRI;
// Relocatable field offset from the section start
unsigned RelOffset = MR.getMachineCodeOffset();
// Symbol index in the symbol table
unsigned SymIdx = 0;
// Target specific relocation field type and size
unsigned RelType = TEW->getRelocationType(MR.getRelocationType());
unsigned RelTySize = TEW->getRelocationTySize(RelType);
int64_t Addend = 0;
// There are several machine relocations types, and each one of
// them needs a different approach to retrieve the symbol table index.
if (MR.isGlobalValue()) {
const GlobalValue *G = MR.getGlobalValue();
SymIdx = GblSymLookup[G];
if (G->hasPrivateLinkage()) {
// If the target uses a section offset in the relocation:
// SymIdx + Addend = section sym for global + section offset
unsigned SectionIdx = PrivateSyms[SymIdx]->SectionIdx;
Addend = PrivateSyms[SymIdx]->Value;
SymIdx = SectionList[SectionIdx]->getSymbolTableIndex();
} else {
Addend = TEW->getDefaultAddendForRelTy(RelType);
}
} else {
// Get the symbol index for the section symbol
unsigned SectionIdx = MR.getConstantVal();
SymIdx = SectionList[SectionIdx]->getSymbolTableIndex();
Addend = (uint64_t)MR.getResultPointer();
// For pc relative relocations where symbols are defined in the same
// section they are referenced, ignore the relocation entry and patch
// the relocatable field with the symbol offset directly.
if (S.SectionIdx == SectionIdx && TEW->isPCRelativeRel(RelType)) {
int64_t Value = TEW->computeRelocation(Addend, RelOffset, RelType);
RelocateField(S, RelOffset, Value, RelTySize);
continue;
}
// Handle Jump Table Index relocation
if ((SectionIdx == getJumpTableSection().SectionIdx) &&
TEW->hasCustomJumpTableIndexRelTy()) {
RelType = TEW->getJumpTableIndexRelTy();
RelTySize = TEW->getRelocationTySize(RelType);
}
}
// The target without addend on the relocation symbol must be
// patched in the relocation place itself to contain the addend
if (!HasRelA)
RelocateField(S, RelOffset, Addend, RelTySize);
// Get the relocation entry and emit to the relocation section
ELFRelocation Rel(RelOffset, SymIdx, RelType, HasRelA, Addend);
EmitRelocation(RelSec, Rel, HasRelA);
}
}
}
/// EmitRelocation - Write relocation 'Rel' to the relocation section 'Rel'
void ELFWriter::EmitRelocation(BinaryObject &RelSec, ELFRelocation &Rel,
bool HasRelA) {
RelSec.emitWord(Rel.getOffset());
RelSec.emitWord(Rel.getInfo(is64Bit));
if (HasRelA)
RelSec.emitWord(Rel.getAddend());
}
/// EmitSymbol - Write symbol 'Sym' to the symbol table 'SymbolTable'
void ELFWriter::EmitSymbol(BinaryObject &SymbolTable, ELFSym &Sym) {
if (is64Bit) {
SymbolTable.emitWord32(Sym.NameIdx);
SymbolTable.emitByte(Sym.Info);
SymbolTable.emitByte(Sym.Other);
SymbolTable.emitWord16(Sym.SectionIdx);
SymbolTable.emitWord64(Sym.Value);
SymbolTable.emitWord64(Sym.Size);
} else {
SymbolTable.emitWord32(Sym.NameIdx);
SymbolTable.emitWord32(Sym.Value);
SymbolTable.emitWord32(Sym.Size);
SymbolTable.emitByte(Sym.Info);
SymbolTable.emitByte(Sym.Other);
SymbolTable.emitWord16(Sym.SectionIdx);
}
}
/// EmitSectionHeader - Write section 'Section' header in 'SHdrTab'
/// Section Header Table
void ELFWriter::EmitSectionHeader(BinaryObject &SHdrTab,
const ELFSection &SHdr) {
SHdrTab.emitWord32(SHdr.NameIdx);
SHdrTab.emitWord32(SHdr.Type);
if (is64Bit) {
SHdrTab.emitWord64(SHdr.Flags);
SHdrTab.emitWord(SHdr.Addr);
SHdrTab.emitWord(SHdr.Offset);
SHdrTab.emitWord64(SHdr.Size);
SHdrTab.emitWord32(SHdr.Link);
SHdrTab.emitWord32(SHdr.Info);
SHdrTab.emitWord64(SHdr.Align);
SHdrTab.emitWord64(SHdr.EntSize);
} else {
SHdrTab.emitWord32(SHdr.Flags);
SHdrTab.emitWord(SHdr.Addr);
SHdrTab.emitWord(SHdr.Offset);
SHdrTab.emitWord32(SHdr.Size);
SHdrTab.emitWord32(SHdr.Link);
SHdrTab.emitWord32(SHdr.Info);
SHdrTab.emitWord32(SHdr.Align);
SHdrTab.emitWord32(SHdr.EntSize);
}
}
/// EmitStringTable - If the current symbol table is non-empty, emit the string
/// table for it
void ELFWriter::EmitStringTable() {
if (!SymbolList.size()) return; // Empty symbol table.
ELFSection &StrTab = getStringTableSection();
// Set the zero'th symbol to a null byte, as required.
StrTab.emitByte(0);
// Walk on the symbol list and write symbol names into the string table.
unsigned Index = 1;
for (ELFSymIter I=SymbolList.begin(), E=SymbolList.end(); I != E; ++I) {
ELFSym &Sym = *(*I);
// Use the name mangler to uniquify the LLVM symbol.
std::string Name;
if (Sym.GV) Name.append(Mang->getMangledName(Sym.GV));
if (Name.empty()) {
Sym.NameIdx = 0;
} else {
Sym.NameIdx = Index;
StrTab.emitString(Name);
// Keep track of the number of bytes emitted to this section.
Index += Name.size()+1;
}
}
assert(Index == StrTab.size());
StrTab.Size = Index;
}
// SortSymbols - On the symbol table local symbols must come before
// all other symbols with non-local bindings. The return value is
// the position of the first non local symbol.
unsigned ELFWriter::SortSymbols() {
unsigned FirstNonLocalSymbol;
std::vector<ELFSym*> LocalSyms, OtherSyms;
for (ELFSymIter I=SymbolList.begin(), E=SymbolList.end(); I != E; ++I) {
if ((*I)->isLocalBind())
LocalSyms.push_back(*I);
else
OtherSyms.push_back(*I);
}
SymbolList.clear();
FirstNonLocalSymbol = LocalSyms.size();
for (unsigned i = 0; i < FirstNonLocalSymbol; ++i)
SymbolList.push_back(LocalSyms[i]);
for (ELFSymIter I=OtherSyms.begin(), E=OtherSyms.end(); I != E; ++I)
SymbolList.push_back(*I);
LocalSyms.clear();
OtherSyms.clear();
return FirstNonLocalSymbol;
}
/// EmitSymbolTable - Emit the symbol table itself.
void ELFWriter::EmitSymbolTable() {
if (!SymbolList.size()) return; // Empty symbol table.
// 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 = getSymbolTableSection();
SymTab.Align = TEW->getPrefELFAlignment();
// Section Index of .strtab.
SymTab.Link = getStringTableSection().SectionIdx;
// Size of each symtab entry.
SymTab.EntSize = TEW->getSymTabEntrySize();
// The first entry in the symtab is the null symbol
SymbolList.insert(SymbolList.begin(), new ELFSym(0));
// Reorder the symbol table with local symbols first!
unsigned FirstNonLocalSymbol = SortSymbols();
// Emit all the symbols to the symbol table.
for (unsigned i = 0, e = SymbolList.size(); i < e; ++i) {
ELFSym &Sym = *SymbolList[i];
// Emit symbol to the symbol table
EmitSymbol(SymTab, Sym);
// Record the symbol table index for each global value
if (Sym.GV) setGlobalSymLookup(Sym.GV, i);
// Keep track on the symbol index into the symbol table
Sym.SymTabIdx = i;
}
// One greater than the symbol table index of the last local symbol
SymTab.Info = FirstNonLocalSymbol;
SymTab.Size = SymTab.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 = getSectionHeaderStringTableSection();
// Now that we know which section number is the .shstrtab section, update the
// e_shstrndx entry in the ELF header.
ElfHdr.fixWord16(SHStrTab.SectionIdx, ELFHdr_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 (ELFSectionIter I=SectionList.begin(), E=SectionList.end(); I != E; ++I) {
ELFSection &S = *(*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.
S.NameIdx = Index;
SHStrTab.emitString(S.getName());
// Keep track of the number of bytes emitted to this section.
Index += S.getName().size()+1;
}
// Set the size of .shstrtab now that we know what it is.
assert(Index == SHStrTab.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 = ElfHdr.size(); // File header first.
// Adjust alignment of all section if needed, skip the null section.
for (unsigned i=1, e=SectionList.size(); i < e; ++i) {
ELFSection &ES = *SectionList[i];
if (!ES.size()) {
ES.Offset = FileOff;
continue;
}
// Update Section size
if (!ES.Size)
ES.Size = ES.size();
// Align FileOff to whatever the alignment restrictions of the section are.
if (ES.Align)
FileOff = (FileOff+ES.Align-1) & ~(ES.Align-1);
ES.Offset = FileOff;
FileOff += ES.Size;
}
// Align Section Header.
unsigned TableAlign = TEW->getPrefELFAlignment();
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.
ElfHdr.fixWord16(NumSections, ELFHdr_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.
ElfHdr.fixWord(FileOff, ELFHdr_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 *)&ElfHdr.getData()[0], ElfHdr.size());
FileOff = ElfHdr.size();
// Section Header Table blob
BinaryObject SHdrTable(isLittleEndian, is64Bit);
// Emit all of sections to the file and build the section header table.
for (ELFSectionIter I=SectionList.begin(), E=SectionList.end(); I != E; ++I) {
ELFSection &S = *(*I);
DOUT << "SectionIdx: " << S.SectionIdx << ", Name: " << S.getName()
<< ", Size: " << S.Size << ", Offset: " << S.Offset
<< ", SectionData Size: " << S.size() << "\n";
// Align FileOff to whatever the alignment restrictions of the section are.
if (S.size()) {
if (S.Align) {
for (size_t NewFileOff = (FileOff+S.Align-1) & ~(S.Align-1);
FileOff != NewFileOff; ++FileOff)
O << (char)0xAB;
}
O.write((char *)&S.getData()[0], S.Size);
FileOff += S.Size;
}
EmitSectionHeader(SHdrTable, S);
}
// Align output for the section table.
for (size_t NewFileOff = (FileOff+TableAlign-1) & ~(TableAlign-1);
FileOff != NewFileOff; ++FileOff)
O << (char)0xAB;
// Emit the section table itself.
O.write((char *)&SHdrTable.getData()[0], SHdrTable.size());
}
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