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llvm-mirror/lib/CodeGen/ELFWriter.cpp
Chris Lattner e2bd5bc939 remove the SelectSectionForMachineConst hook, replacing it with 
a new getSectionForMergableConstant hook.  This removes one dependence
of TAI on Type, and provides the hook with enough info to make the 
right decision based on whether the global has relocations etc.

llvm-svn: 76705
2009-07-22 00:28:43 +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) {
uint64_t Size = TM.getTargetData()->getTypeAllocSize(CPE.getType());
std::string CstPoolName =
TAI->getSectionForMergableConstant(Size,CPE.getRelocationInfo())->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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