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llvm-mirror/lib/CodeGen/ELFWriter.cpp
Evan Cheng c9bc5a9011 Goodbye TargetAsmInfo. This eliminate last bit of CodeGen and Target in llvm-mc. 
There is still a bit more refactoring left to do in Targets. But we are now very
close to fixing all the layering issues in MC.

llvm-svn: 135611
2011-07-20 19:50:42 +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/MachineCodeEmitter.h"
#include "llvm/CodeGen/ObjectCodeEmitter.h"
#include "llvm/CodeGen/MachineCodeEmitter.h"
#include "llvm/CodeGen/MachineConstantPool.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/Target/Mangler.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetELFWriterInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetLoweringObjectFile.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallString.h"
using namespace llvm;
char ELFWriter::ID = 0;
//===----------------------------------------------------------------------===//
// ELFWriter Implementation
//===----------------------------------------------------------------------===//
ELFWriter::ELFWriter(raw_ostream &o, TargetMachine &tm)
: MachineFunctionPass(ID), O(o), TM(tm),
OutContext(*new MCContext(*TM.getMCAsmInfo(), *TM.getRegisterInfo(),
&TM.getTargetLowering()->getObjFileLowering())),
TLOF(TM.getTargetLowering()->getObjFileLowering()),
is64Bit(TM.getTargetData()->getPointerSizeInBits() == 64),
isLittleEndian(TM.getTargetData()->isLittleEndian()),
ElfHdr(isLittleEndian, is64Bit) {
MAI = TM.getMCAsmInfo();
TEW = TM.getELFWriterInfo();
// Create the object code emitter object for this target.
ElfCE = new ELFCodeEmitter(*this);
// Initial number of sections
NumSections = 0;
}
ELFWriter::~ELFWriter() {
delete ElfCE;
delete &OutContext;
while(!SymbolList.empty()) {
delete SymbolList.back();
SymbolList.pop_back();
}
while(!PrivateSyms.empty()) {
delete PrivateSyms.back();
PrivateSyms.pop_back();
}
while(!SectionList.empty()) {
delete SectionList.back();
SectionList.pop_back();
}
// Release the name mangler object.
delete Mang; Mang = 0;
}
// doInitialization - Emit the file header and all of the global variables for
// the module to the ELF file.
bool ELFWriter::doInitialization(Module &M) {
// Initialize TargetLoweringObjectFile.
const_cast<TargetLoweringObjectFile&>(TLOF).Initialize(OutContext, TM);
Mang = new Mangler(OutContext, *TM.getTargetData());
// 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(ELF::EV_CURRENT); // e_ident[EI_VERSION]
ElfHdr.emitAlignment(16); // e_ident[EI_NIDENT-EI_PAD]
ElfHdr.emitWord16(ELF::ET_REL); // e_type
ElfHdr.emitWord16(TEW->getEMachine()); // e_machine = target
ElfHdr.emitWord32(ELF::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();
// The first entry in the symtab is the null symbol and the second
// is a local symbol containing the module/file name
SymbolList.push_back(new ELFSym());
SymbolList.push_back(ELFSym::getFileSym());
return false;
}
// AddPendingGlobalSymbol - Add a global to be processed and to
// the global symbol lookup, use a zero index because the table
// index will be determined later.
void ELFWriter::AddPendingGlobalSymbol(const GlobalValue *GV,
bool AddToLookup /* = false */) {
PendingGlobals.insert(GV);
if (AddToLookup)
GblSymLookup[GV] = 0;
}
// AddPendingExternalSymbol - Add the external to be processed
// and to the external symbol lookup, use a zero index because
// the symbol table index will be determined later.
void ELFWriter::AddPendingExternalSymbol(const char *External) {
PendingExternals.insert(External);
ExtSymLookup[External] = 0;
}
ELFSection &ELFWriter::getDataSection() {
const MCSectionELF *Data = (const MCSectionELF *)TLOF.getDataSection();
return getSection(Data->getSectionName(), Data->getType(),
Data->getFlags(), 4);
}
ELFSection &ELFWriter::getBSSSection() {
const MCSectionELF *BSS = (const MCSectionELF *)TLOF.getBSSSection();
return getSection(BSS->getSectionName(), BSS->getType(), BSS->getFlags(), 4);
}
// getCtorSection - Get the static constructor section
ELFSection &ELFWriter::getCtorSection() {
const MCSectionELF *Ctor = (const MCSectionELF *)TLOF.getStaticCtorSection();
return getSection(Ctor->getSectionName(), Ctor->getType(), Ctor->getFlags());
}
// getDtorSection - Get the static destructor section
ELFSection &ELFWriter::getDtorSection() {
const MCSectionELF *Dtor = (const MCSectionELF *)TLOF.getStaticDtorSection();
return getSection(Dtor->getSectionName(), Dtor->getType(), Dtor->getFlags());
}
// getTextSection - Get the text section for the specified function
ELFSection &ELFWriter::getTextSection(const Function *F) {
const MCSectionELF *Text =
(const MCSectionELF *)TLOF.SectionForGlobal(F, Mang, TM);
return getSection(Text->getSectionName(), Text->getType(), Text->getFlags());
}
// getJumpTableSection - Get a read only section for constants when
// emitting jump tables. TODO: add PIC support
ELFSection &ELFWriter::getJumpTableSection() {
const MCSectionELF *JT =
(const MCSectionELF *)TLOF.getSectionForConstant(SectionKind::getReadOnly());
return getSection(JT->getSectionName(), JT->getType(), JT->getFlags(),
TM.getTargetData()->getPointerABIAlignment());
}
// getConstantPoolSection - Get a constant pool section based on the machine
// constant pool entry type and relocation info.
ELFSection &ELFWriter::getConstantPoolSection(MachineConstantPoolEntry &CPE) {
SectionKind Kind;
switch (CPE.getRelocationInfo()) {
default: llvm_unreachable("Unknown section kind");
case 2: Kind = SectionKind::getReadOnlyWithRel(); break;
case 1:
Kind = SectionKind::getReadOnlyWithRelLocal();
break;
case 0:
switch (TM.getTargetData()->getTypeAllocSize(CPE.getType())) {
case 4: Kind = SectionKind::getMergeableConst4(); break;
case 8: Kind = SectionKind::getMergeableConst8(); break;
case 16: Kind = SectionKind::getMergeableConst16(); break;
default: Kind = SectionKind::getMergeableConst(); break;
}
}
const MCSectionELF *CPSect =
(const MCSectionELF *)TLOF.getSectionForConstant(Kind);
return getSection(CPSect->getSectionName(), CPSect->getType(),
CPSect->getFlags(), CPE.getAlignment());
}
// getRelocSection - Return the relocation section of section 'S'. 'RelA'
// is true if the relocation section contains entries with addends.
ELFSection &ELFWriter::getRelocSection(ELFSection &S) {
unsigned SectionType = TEW->hasRelocationAddend() ?
ELF::SHT_RELA : ELF::SHT_REL;
std::string SectionName(".rel");
if (TEW->hasRelocationAddend())
SectionName.append("a");
SectionName.append(S.getName());
return getSection(SectionName, SectionType, 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 ELF::STV_DEFAULT;
case GlobalValue::HiddenVisibility:
return ELF::STV_HIDDEN;
case GlobalValue::ProtectedVisibility:
return ELF::STV_PROTECTED;
}
return 0;
}
// getGlobalELFBinding - Returns the ELF specific binding type
unsigned ELFWriter::getGlobalELFBinding(const GlobalValue *GV) {
if (GV->hasInternalLinkage())
return ELF::STB_LOCAL;
if (GV->isWeakForLinker() && !GV->hasCommonLinkage())
return ELF::STB_WEAK;
return ELF::STB_GLOBAL;
}
// getGlobalELFType - Returns the ELF specific type for a global
unsigned ELFWriter::getGlobalELFType(const GlobalValue *GV) {
if (GV->isDeclaration())
return ELF::STT_NOTYPE;
if (isa<Function>(GV))
return ELF::STT_FUNC;
return ELF::STT_OBJECT;
}
// IsELFUndefSym - True if the global value must be marked as a symbol
// which points to a SHN_UNDEF section. This means that the symbol has
// no definition on the module.
static bool IsELFUndefSym(const GlobalValue *GV) {
return GV->isDeclaration() || (isa<Function>(GV));
}
// AddToSymbolList - Update the symbol lookup and If the symbol is
// private add it to PrivateSyms list, otherwise to SymbolList.
void ELFWriter::AddToSymbolList(ELFSym *GblSym) {
assert(GblSym->isGlobalValue() && "Symbol must be a global value");
const GlobalValue *GV = GblSym->getGlobalValue();
if (GV->hasPrivateLinkage()) {
// For a private symbols, keep track of the index inside
// the private list since it will never go to the symbol
// table and won't be patched up later.
PrivateSyms.push_back(GblSym);
GblSymLookup[GV] = PrivateSyms.size()-1;
} else {
// Non private symbol are left with zero indices until
// they are patched up during the symbol table emition
// (where the indicies are created).
SymbolList.push_back(GblSym);
GblSymLookup[GV] = 0;
}
}
/// HasCommonSymbols - True if this section holds common symbols, this is
/// indicated on the ELF object file by a symbol with SHN_COMMON section
/// header index.
static bool HasCommonSymbols(const MCSectionELF &S) {
// FIXME: this is wrong, a common symbol can be in .data for example.
if (StringRef(S.getSectionName()).startswith(".gnu.linkonce."))
return true;
return false;
}
// 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);
unsigned SymType = getGlobalELFType(GV);
bool IsUndefSym = IsELFUndefSym(GV);
ELFSym *GblSym = IsUndefSym ? ELFSym::getUndefGV(GV, SymBind)
: ELFSym::getGV(GV, SymBind, SymType, getGlobalELFVisibility(GV));
if (!IsUndefSym) {
assert(isa<GlobalVariable>(GV) && "GV not a global variable!");
const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
// Handle special llvm globals
if (EmitSpecialLLVMGlobal(GVar))
return;
// Get the ELF section where this global belongs from TLOF
const MCSectionELF *S =
(const MCSectionELF *)TLOF.SectionForGlobal(GV, Mang, TM);
ELFSection &ES =
getSection(S->getSectionName(), S->getType(), S->getFlags());
SectionKind Kind = S->getKind();
// 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 (HasCommonSymbols(*S)) { // Symbol must go to a common section
GblSym->SectionIdx = ELF::SHN_COMMON;
// 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.
ES.Align = 1;
GblSym->Value = Align;
} else if (Kind.isBSS() || Kind.isThreadBSS()) { // Symbol goes to BSS.
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 { // The symbol must go to some kind of data section
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);
ES.emitAlignment(Align);
GblSym->Value = ES.size();
// Emit the global to the data section 'ES'
EmitGlobalConstant(GVar->getInitializer(), ES);
}
}
AddToSymbolList(GblSym);
}
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.
GblS.emitZeros(padSize);
}
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)) {
for (unsigned i = 0, e = CVA->getNumOperands(); i != e; ++i)
EmitGlobalConstant(CVA->getOperand(i), GblS);
return;
} else if (isa<ConstantAggregateZero>(CV)) {
GblS.emitZeros(Size);
return;
} else if (const ConstantStruct *CVS = dyn_cast<ConstantStruct>(CV)) {
EmitGlobalConstantStruct(CVS, GblS);
return;
} else if (const ConstantFP *CFP = dyn_cast<ConstantFP>(CV)) {
APInt Val = CFP->getValueAPF().bitcastToAPInt();
if (CFP->getType()->isDoubleTy())
GblS.emitWord64(Val.getZExtValue());
else if (CFP->getType()->isFloatTy())
GblS.emitWord32(Val.getZExtValue());
else if (CFP->getType()->isX86_FP80Ty()) {
unsigned PadSize = TD->getTypeAllocSize(CFP->getType())-
TD->getTypeStoreSize(CFP->getType());
GblS.emitWordFP80(Val.getRawData(), PadSize);
} else if (CFP->getType()->isPPC_FP128Ty())
llvm_unreachable("PPC_FP128Ty global emission not implemented");
return;
} else if (const ConstantInt *CI = dyn_cast<ConstantInt>(CV)) {
if (Size == 1)
GblS.emitByte(CI->getZExtValue());
else if (Size == 2)
GblS.emitWord16(CI->getZExtValue());
else if (Size == 4)
GblS.emitWord32(CI->getZExtValue());
else
EmitGlobalConstantLargeInt(CI, GblS);
return;
} else if (const ConstantVector *CP = dyn_cast<ConstantVector>(CV)) {
VectorType *PTy = CP->getType();
for (unsigned I = 0, E = PTy->getNumElements(); I < E; ++I)
EmitGlobalConstant(CP->getOperand(I), GblS);
return;
} else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(CV)) {
// Resolve a constant expression which returns a (Constant, Offset)
// pair. If 'Res.first' is a GlobalValue, emit a relocation with
// the offset 'Res.second', otherwise emit a global constant like
// it is always done for not contant expression types.
CstExprResTy Res = ResolveConstantExpr(CE);
const Constant *Op = Res.first;
if (isa<GlobalValue>(Op))
EmitGlobalDataRelocation(cast<const GlobalValue>(Op),
TD->getTypeAllocSize(Op->getType()),
GblS, Res.second);
else
EmitGlobalConstant(Op, GblS);
return;
} else if (CV->getType()->getTypeID() == Type::PointerTyID) {
// Fill the data entry with zeros or emit a relocation entry
if (isa<ConstantPointerNull>(CV))
GblS.emitZeros(Size);
else
EmitGlobalDataRelocation(cast<const GlobalValue>(CV),
Size, 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.
EmitGlobalDataRelocation(GV, Size, GblS);
return;
}
std::string msg;
raw_string_ostream ErrorMsg(msg);
ErrorMsg << "Constant unimp for type: " << *CV->getType();
report_fatal_error(ErrorMsg.str());
}
// ResolveConstantExpr - Resolve the constant expression until it stop
// yielding other constant expressions.
CstExprResTy ELFWriter::ResolveConstantExpr(const Constant *CV) {
const TargetData *TD = TM.getTargetData();
// There ins't constant expression inside others anymore
if (!isa<ConstantExpr>(CV))
return std::make_pair(CV, 0);
const ConstantExpr *CE = dyn_cast<ConstantExpr>(CV);
switch (CE->getOpcode()) {
case Instruction::BitCast:
return ResolveConstantExpr(CE->getOperand(0));
case Instruction::GetElementPtr: {
const Constant *ptrVal = CE->getOperand(0);
SmallVector<Value*, 8> idxVec(CE->op_begin()+1, CE->op_end());
int64_t Offset = TD->getIndexedOffset(ptrVal->getType(), idxVec);
return std::make_pair(ptrVal, Offset);
}
case Instruction::IntToPtr: {
Constant *Op = CE->getOperand(0);
Op = ConstantExpr::getIntegerCast(Op, TD->getIntPtrType(CV->getContext()),
false/*ZExt*/);
return ResolveConstantExpr(Op);
}
case Instruction::PtrToInt: {
Constant *Op = CE->getOperand(0);
Type *Ty = CE->getType();
// We can emit the pointer value into this slot if the slot is an
// integer slot greater or equal to the size of the pointer.
if (TD->getTypeAllocSize(Ty) == TD->getTypeAllocSize(Op->getType()))
return ResolveConstantExpr(Op);
llvm_unreachable("Integer size less then pointer size");
}
case Instruction::Add:
case Instruction::Sub: {
// Only handle cases where there's a constant expression with GlobalValue
// as first operand and ConstantInt as second, which are the cases we can
// solve direclty using a relocation entry. GlobalValue=Op0, CstInt=Op1
// 1) Instruction::Add => (global) + CstInt
// 2) Instruction::Sub => (global) + -CstInt
const Constant *Op0 = CE->getOperand(0);
const Constant *Op1 = CE->getOperand(1);
assert(isa<ConstantInt>(Op1) && "Op1 must be a ConstantInt");
CstExprResTy Res = ResolveConstantExpr(Op0);
assert(isa<GlobalValue>(Res.first) && "Op0 must be a GlobalValue");
const APInt &RHS = cast<ConstantInt>(Op1)->getValue();
switch (CE->getOpcode()) {
case Instruction::Add:
return std::make_pair(Res.first, RHS.getSExtValue());
case Instruction::Sub:
return std::make_pair(Res.first, (-RHS).getSExtValue());
}
}
}
report_fatal_error(CE->getOpcodeName() +
StringRef(": Unsupported ConstantExpr type"));
return std::make_pair(CV, 0); // silence warning
}
void ELFWriter::EmitGlobalDataRelocation(const GlobalValue *GV, unsigned Size,
ELFSection &GblS, int64_t Offset) {
// Create the relocation entry for the global value
MachineRelocation MR =
MachineRelocation::getGV(GblS.getCurrentPCOffset(),
TEW->getAbsoluteLabelMachineRelTy(),
const_cast<GlobalValue*>(GV),
Offset);
// Fill the data entry with zeros
GblS.emitZeros(Size);
// Add the relocation entry for the current data section
GblS.addRelocation(MR);
}
void ELFWriter::EmitGlobalConstantLargeInt(const ConstantInt *CI,
ELFSection &S) {
const TargetData *TD = TM.getTargetData();
unsigned BitWidth = CI->getBitWidth();
assert(isPowerOf2_32(BitWidth) &&
"Non-power-of-2-sized integers not handled!");
const uint64_t *RawData = CI->getValue().getRawData();
uint64_t Val = 0;
for (unsigned i = 0, e = BitWidth / 64; i != e; ++i) {
Val = (TD->isBigEndian()) ? RawData[e - i - 1] : RawData[i];
S.emitWord64(Val);
}
}
/// EmitSpecialLLVMGlobal - Check to see if the specified global is a
/// special global used by LLVM. If so, emit it and return true, otherwise
/// do nothing and return false.
bool ELFWriter::EmitSpecialLLVMGlobal(const GlobalVariable *GV) {
if (GV->getName() == "llvm.used")
llvm_unreachable("not implemented yet");
// Ignore debug and non-emitted data. This handles llvm.compiler.used.
if (GV->getSection() == "llvm.metadata" ||
GV->hasAvailableExternallyLinkage())
return true;
if (!GV->hasAppendingLinkage()) return false;
assert(GV->hasInitializer() && "Not a special LLVM global!");
const TargetData *TD = TM.getTargetData();
unsigned Align = TD->getPointerPrefAlignment();
if (GV->getName() == "llvm.global_ctors") {
ELFSection &Ctor = getCtorSection();
Ctor.emitAlignment(Align);
EmitXXStructorList(GV->getInitializer(), Ctor);
return true;
}
if (GV->getName() == "llvm.global_dtors") {
ELFSection &Dtor = getDtorSection();
Dtor.emitAlignment(Align);
EmitXXStructorList(GV->getInitializer(), Dtor);
return true;
}
return false;
}
/// EmitXXStructorList - Emit the ctor or dtor list. This just emits out the
/// function pointers, ignoring the init priority.
void ELFWriter::EmitXXStructorList(const Constant *List, ELFSection &Xtor) {
// Should be an array of '{ i32, void ()* }' structs. The first value is the
// init priority, which we ignore.
if (List->isNullValue()) return;
const ConstantArray *InitList = cast<ConstantArray>(List);
for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i) {
if (InitList->getOperand(i)->isNullValue())
continue;
ConstantStruct *CS = cast<ConstantStruct>(InitList->getOperand(i));
if (CS->getOperand(1)->isNullValue())
continue;
// Emit the function pointer.
EmitGlobalConstant(CS->getOperand(1), Xtor);
}
}
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 (PendingGblsIter I = PendingGlobals.begin(), E = PendingGlobals.end();
I != E; ++I)
EmitGlobal(*I);
// Emit all pending externals
for (PendingExtsIter I = PendingExternals.begin(), E = PendingExternals.end();
I != E; ++I)
SymbolList.push_back(ELFSym::getExtSym(*I));
// 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 = ELFSym::getSectionSym();
SectionSym->SectionIdx = ES.SectionIdx;
SymbolList.push_back(SectionSym);
ES.Sym = SymbolList.back();
}
// Emit string table
EmitStringTable(M.getModuleIdentifier());
// 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();
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();
int64_t GlobalOffset = MR.getConstantVal();
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 + GlobalOffset;
SymIdx = SectionList[SectionIdx]->getSymbolTableIndex();
} else {
Addend = TEW->getDefaultAddendForRelTy(RelType, GlobalOffset);
}
} else if (MR.isExternalSymbol()) {
const char *ExtSym = MR.getExternalSymbol();
SymIdx = ExtSymLookup[ExtSym];
Addend = TEW->getDefaultAddendForRelTy(RelType);
} else {
// Get the symbol index for the section symbol
unsigned SectionIdx = MR.getConstantVal();
SymIdx = SectionList[SectionIdx]->getSymbolTableIndex();
// The symbol offset inside the section
int64_t SymOffset = (int64_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(SymOffset, RelOffset, RelType);
RelocateField(S, RelOffset, Value, RelTySize);
continue;
}
Addend = TEW->getDefaultAddendForRelTy(RelType, SymOffset);
}
// The target without addend on the relocation symbol must be
// patched in the relocation place itself to contain the addend
// otherwise write zeros to make sure there is no garbage there
RelocateField(S, RelOffset, HasRelA ? 0 : 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(const std::string &ModuleName) {
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);
std::string Name;
if (Sym.isGlobalValue()) {
SmallString<40> NameStr;
Mang->getNameWithPrefix(NameStr, Sym.getGlobalValue(), false);
Name.append(NameStr.begin(), NameStr.end());
} else if (Sym.isExternalSym())
Name.append(Sym.getExternalSymbol());
else if (Sym.isFileType())
Name.append(ModuleName);
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();
// 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 symbol
if (Sym.isGlobalValue())
GblSymLookup[Sym.getGlobalValue()] = i;
else if (Sym.isExternalSym())
ExtSymLookup[Sym.getExternalSymbol()] = 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);
DEBUG(dbgs() << "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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