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llvm-project/llvm/lib/MC/ELFObjectWriter.cpp

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//===- lib/MC/ELFObjectWriter.cpp - ELF File Writer -------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements ELF object file writer information.
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/ELFObjectWriter.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCELFSymbolFlags.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/ELF.h"
#include "llvm/Target/TargetAsmBackend.h"
#include "../Target/X86/X86FixupKinds.h"
#include <vector>
using namespace llvm;
static unsigned GetType(const MCSymbolData &SD) {
uint32_t Type = (SD.getFlags() & (0xf << ELF_STT_Shift)) >> ELF_STT_Shift;
assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT ||
Type == ELF::STT_FUNC || Type == ELF::STT_SECTION ||
Type == ELF::STT_FILE || Type == ELF::STT_COMMON ||
Type == ELF::STT_TLS);
return Type;
}
static unsigned GetBinding(const MCSymbolData &SD) {
uint32_t Binding = (SD.getFlags() & (0xf << ELF_STB_Shift)) >> ELF_STB_Shift;
assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
Binding == ELF::STB_WEAK);
return Binding;
}
static void SetBinding(MCSymbolData &SD, unsigned Binding) {
assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
Binding == ELF::STB_WEAK);
uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift);
SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift));
}
static unsigned GetVisibility(MCSymbolData &SD) {
unsigned Visibility =
(SD.getFlags() & (0xf << ELF_STV_Shift)) >> ELF_STV_Shift;
assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL ||
Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED);
return Visibility;
}
static bool isFixupKindX86PCRel(unsigned Kind) {
switch (Kind) {
default:
return false;
case X86::reloc_pcrel_1byte:
case X86::reloc_pcrel_4byte:
case X86::reloc_riprel_4byte:
case X86::reloc_riprel_4byte_movq_load:
return true;
}
}
static bool RelocNeedsGOT(unsigned Type) {
switch (Type) {
default:
return false;
case ELF::R_X86_64_GOT32:
case ELF::R_X86_64_PLT32:
case ELF::R_X86_64_GOTPCREL:
return true;
}
}
namespace {
class ELFObjectWriterImpl {
/*static bool isFixupKindX86RIPRel(unsigned Kind) {
return Kind == X86::reloc_riprel_4byte ||
Kind == X86::reloc_riprel_4byte_movq_load;
}*/
/// ELFSymbolData - Helper struct for containing some precomputed information
/// on symbols.
struct ELFSymbolData {
MCSymbolData *SymbolData;
uint64_t StringIndex;
uint32_t SectionIndex;
// Support lexicographic sorting.
bool operator<(const ELFSymbolData &RHS) const {
if (GetType(*SymbolData) == ELF::STT_FILE)
return true;
if (GetType(*RHS.SymbolData) == ELF::STT_FILE)
return false;
return SymbolData->getSymbol().getName() <
RHS.SymbolData->getSymbol().getName();
}
};
/// @name Relocation Data
/// @{
struct ELFRelocationEntry {
// Make these big enough for both 32-bit and 64-bit
uint64_t r_offset;
int Index;
unsigned Type;
const MCSymbol *Symbol;
uint64_t r_addend;
// Support lexicographic sorting.
bool operator<(const ELFRelocationEntry &RE) const {
return RE.r_offset < r_offset;
}
};
SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
llvm::DenseMap<const MCSectionData*,
std::vector<ELFRelocationEntry> > Relocations;
DenseMap<const MCSection*, uint64_t> SectionStringTableIndex;
/// @}
/// @name Symbol Table Data
/// @{
SmallString<256> StringTable;
std::vector<ELFSymbolData> LocalSymbolData;
std::vector<ELFSymbolData> ExternalSymbolData;
std::vector<ELFSymbolData> UndefinedSymbolData;
/// @}
int NumRegularSections;
bool NeedsGOT;
ELFObjectWriter *Writer;
raw_ostream &OS;
unsigned Is64Bit : 1;
bool HasRelocationAddend;
Triple::OSType OSType;
// This holds the symbol table index of the last local symbol.
unsigned LastLocalSymbolIndex;
// This holds the .strtab section index.
unsigned StringTableIndex;
unsigned ShstrtabIndex;
public:
ELFObjectWriterImpl(ELFObjectWriter *_Writer, bool _Is64Bit,
bool _HasRelAddend, Triple::OSType _OSType)
: NeedsGOT(false), Writer(_Writer), OS(Writer->getStream()),
Is64Bit(_Is64Bit), HasRelocationAddend(_HasRelAddend),
OSType(_OSType) {
}
void Write8(uint8_t Value) { Writer->Write8(Value); }
void Write16(uint16_t Value) { Writer->Write16(Value); }
void Write32(uint32_t Value) { Writer->Write32(Value); }
//void Write64(uint64_t Value) { Writer->Write64(Value); }
void WriteZeros(unsigned N) { Writer->WriteZeros(N); }
//void WriteBytes(StringRef Str, unsigned ZeroFillSize = 0) {
// Writer->WriteBytes(Str, ZeroFillSize);
//}
void WriteWord(uint64_t W) {
if (Is64Bit)
Writer->Write64(W);
else
Writer->Write32(W);
}
void String8(char *buf, uint8_t Value) {
buf[0] = Value;
}
void StringLE16(char *buf, uint16_t Value) {
buf[0] = char(Value >> 0);
buf[1] = char(Value >> 8);
}
void StringLE32(char *buf, uint32_t Value) {
StringLE16(buf, uint16_t(Value >> 0));
StringLE16(buf + 2, uint16_t(Value >> 16));
}
void StringLE64(char *buf, uint64_t Value) {
StringLE32(buf, uint32_t(Value >> 0));
StringLE32(buf + 4, uint32_t(Value >> 32));
}
void StringBE16(char *buf ,uint16_t Value) {
buf[0] = char(Value >> 8);
buf[1] = char(Value >> 0);
}
void StringBE32(char *buf, uint32_t Value) {
StringBE16(buf, uint16_t(Value >> 16));
StringBE16(buf + 2, uint16_t(Value >> 0));
}
void StringBE64(char *buf, uint64_t Value) {
StringBE32(buf, uint32_t(Value >> 32));
StringBE32(buf + 4, uint32_t(Value >> 0));
}
void String16(char *buf, uint16_t Value) {
if (Writer->isLittleEndian())
StringLE16(buf, Value);
else
StringBE16(buf, Value);
}
void String32(char *buf, uint32_t Value) {
if (Writer->isLittleEndian())
StringLE32(buf, Value);
else
StringBE32(buf, Value);
}
void String64(char *buf, uint64_t Value) {
if (Writer->isLittleEndian())
StringLE64(buf, Value);
else
StringBE64(buf, Value);
}
void WriteHeader(uint64_t SectionDataSize, unsigned NumberOfSections);
void WriteSymbolEntry(MCDataFragment *F, uint64_t name, uint8_t info,
uint64_t value, uint64_t size,
uint8_t other, uint16_t shndx);
void WriteSymbol(MCDataFragment *F, ELFSymbolData &MSD,
const MCAsmLayout &Layout);
void WriteSymbolTable(MCDataFragment *F, const MCAssembler &Asm,
const MCAsmLayout &Layout,
unsigned NumRegularSections);
void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment *Fragment, const MCFixup &Fixup,
MCValue Target, uint64_t &FixedValue);
uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
const MCSymbol *S);
/// ComputeSymbolTable - Compute the symbol table data
///
/// \param StringTable [out] - The string table data.
/// \param StringIndexMap [out] - Map from symbol names to offsets in the
/// string table.
void ComputeSymbolTable(MCAssembler &Asm);
void WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
const MCSectionData &SD);
void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) {
for (MCAssembler::const_iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
WriteRelocation(Asm, Layout, *it);
}
}
void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout);
void ExecutePostLayoutBinding(MCAssembler &Asm) {
}
void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
uint64_t Address, uint64_t Offset,
uint64_t Size, uint32_t Link, uint32_t Info,
uint64_t Alignment, uint64_t EntrySize);
void WriteRelocationsFragment(const MCAssembler &Asm, MCDataFragment *F,
const MCSectionData *SD);
bool IsFixupFullyResolved(const MCAssembler &Asm,
const MCValue Target,
bool IsPCRel,
const MCFragment *DF) const;
void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout);
};
}
// Emit the ELF header.
void ELFObjectWriterImpl::WriteHeader(uint64_t SectionDataSize,
unsigned NumberOfSections) {
// ELF Header
// ----------
//
// Note
// ----
// emitWord method behaves differently for ELF32 and ELF64, writing
// 4 bytes in the former and 8 in the latter.
Write8(0x7f); // e_ident[EI_MAG0]
Write8('E'); // e_ident[EI_MAG1]
Write8('L'); // e_ident[EI_MAG2]
Write8('F'); // e_ident[EI_MAG3]
Write8(Is64Bit ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
// e_ident[EI_DATA]
Write8(Writer->isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
// e_ident[EI_OSABI]
switch (OSType) {
case Triple::FreeBSD: Write8(ELF::ELFOSABI_FREEBSD); break;
case Triple::Linux: Write8(ELF::ELFOSABI_LINUX); break;
default: Write8(ELF::ELFOSABI_NONE); break;
}
Write8(0); // e_ident[EI_ABIVERSION]
WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
Write16(ELF::ET_REL); // e_type
// FIXME: Make this configurable
Write16(Is64Bit ? ELF::EM_X86_64 : ELF::EM_386); // e_machine = target
Write32(ELF::EV_CURRENT); // e_version
WriteWord(0); // e_entry, no entry point in .o file
WriteWord(0); // e_phoff, no program header for .o
WriteWord(SectionDataSize + (Is64Bit ? sizeof(ELF::Elf64_Ehdr) :
sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes
// FIXME: Make this configurable.
Write32(0); // e_flags = whatever the target wants
// e_ehsize = ELF header size
Write16(Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
Write16(0); // e_phentsize = prog header entry size
Write16(0); // e_phnum = # prog header entries = 0
// e_shentsize = Section header entry size
Write16(Is64Bit ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
// e_shnum = # of section header ents
Write16(NumberOfSections);
// e_shstrndx = Section # of '.shstrtab'
Write16(ShstrtabIndex);
}
void ELFObjectWriterImpl::WriteSymbolEntry(MCDataFragment *F, uint64_t name,
uint8_t info, uint64_t value,
uint64_t size, uint8_t other,
uint16_t shndx) {
if (Is64Bit) {
char buf[8];
String32(buf, name);
F->getContents() += StringRef(buf, 4); // st_name
String8(buf, info);
F->getContents() += StringRef(buf, 1); // st_info
String8(buf, other);
F->getContents() += StringRef(buf, 1); // st_other
String16(buf, shndx);
F->getContents() += StringRef(buf, 2); // st_shndx
String64(buf, value);
F->getContents() += StringRef(buf, 8); // st_value
String64(buf, size);
F->getContents() += StringRef(buf, 8); // st_size
} else {
char buf[4];
String32(buf, name);
F->getContents() += StringRef(buf, 4); // st_name
String32(buf, value);
F->getContents() += StringRef(buf, 4); // st_value
String32(buf, size);
F->getContents() += StringRef(buf, 4); // st_size
String8(buf, info);
F->getContents() += StringRef(buf, 1); // st_info
String8(buf, other);
F->getContents() += StringRef(buf, 1); // st_other
String16(buf, shndx);
F->getContents() += StringRef(buf, 2); // st_shndx
}
}
static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout) {
if (Data.isCommon() && Data.isExternal())
return Data.getCommonAlignment();
const MCSymbol &Symbol = Data.getSymbol();
if (!Symbol.isInSection())
return 0;
if (!Data.isCommon() && !(Data.getFlags() & ELF_STB_Weak))
if (MCFragment *FF = Data.getFragment())
return Layout.getSymbolAddress(&Data) -
Layout.getSectionAddress(FF->getParent());
return 0;
}
void ELFObjectWriterImpl::WriteSymbol(MCDataFragment *F, ELFSymbolData &MSD,
const MCAsmLayout &Layout) {
MCSymbolData &OrigData = *MSD.SymbolData;
MCSymbolData *AliasData = NULL;
if (OrigData.Symbol->isVariable()) {
const MCExpr *Value = OrigData.getSymbol().getVariableValue();
assert (Value->getKind() == MCExpr::SymbolRef && "Unimplemented");
const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Value);
AliasData = &Layout.getAssembler().getSymbolData(Ref->getSymbol());
}
MCSymbolData &Data = AliasData ? *AliasData : OrigData;
uint8_t Binding = GetBinding(OrigData);
uint8_t Visibility = GetVisibility(OrigData);
uint8_t Type = GetType(Data);
uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
uint8_t Other = Visibility;
uint64_t Value = SymbolValue(Data, Layout);
uint64_t Size = 0;
const MCExpr *ESize;
assert(!(Data.isCommon() && !Data.isExternal()));
ESize = Data.getSize();
if (Data.getSize()) {
MCValue Res;
if (ESize->getKind() == MCExpr::Binary) {
const MCBinaryExpr *BE = static_cast<const MCBinaryExpr *>(ESize);
if (BE->EvaluateAsRelocatable(Res, &Layout)) {
uint64_t AddressA = 0;
uint64_t AddressB = 0;
const MCSymbol &SymA = Res.getSymA()->getSymbol();
const MCSymbol &SymB = Res.getSymB()->getSymbol();
if (SymA.isDefined()) {
MCSymbolData &A = Layout.getAssembler().getSymbolData(SymA);
AddressA = Layout.getSymbolAddress(&A);
}
if (SymB.isDefined()) {
MCSymbolData &B = Layout.getAssembler().getSymbolData(SymB);
AddressB = Layout.getSymbolAddress(&B);
}
Size = AddressA - AddressB;
}
} else if (ESize->getKind() == MCExpr::Constant) {
Size = static_cast<const MCConstantExpr *>(ESize)->getValue();
} else {
assert(0 && "Unsupported size expression");
}
}
// Write out the symbol table entry
WriteSymbolEntry(F, MSD.StringIndex, Info, Value,
Size, Other, MSD.SectionIndex);
}
void ELFObjectWriterImpl::WriteSymbolTable(MCDataFragment *F,
const MCAssembler &Asm,
const MCAsmLayout &Layout,
unsigned NumRegularSections) {
// The string table must be emitted first because we need the index
// into the string table for all the symbol names.
assert(StringTable.size() && "Missing string table");
// FIXME: Make sure the start of the symbol table is aligned.
// The first entry is the undefined symbol entry.
unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
F->getContents().append(EntrySize, '\x00');
// Write the symbol table entries.
LastLocalSymbolIndex = LocalSymbolData.size() + 1;
for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
ELFSymbolData &MSD = LocalSymbolData[i];
WriteSymbol(F, MSD, Layout);
}
// Write out a symbol table entry for each regular section.
unsigned Index = 1;
for (MCAssembler::const_iterator it = Asm.begin();
Index <= NumRegularSections; ++it, ++Index) {
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(it->getSection());
// Leave out relocations so we don't have indexes within
// the relocations messed up
if (Section.getType() == ELF::SHT_RELA || Section.getType() == ELF::SHT_REL)
continue;
WriteSymbolEntry(F, 0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT, Index);
LastLocalSymbolIndex++;
}
for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
ELFSymbolData &MSD = ExternalSymbolData[i];
MCSymbolData &Data = *MSD.SymbolData;
assert(((Data.getFlags() & ELF_STB_Global) ||
(Data.getFlags() & ELF_STB_Weak)) &&
"External symbol requires STB_GLOBAL or STB_WEAK flag");
WriteSymbol(F, MSD, Layout);
if (GetBinding(Data) == ELF::STB_LOCAL)
LastLocalSymbolIndex++;
}
for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
ELFSymbolData &MSD = UndefinedSymbolData[i];
MCSymbolData &Data = *MSD.SymbolData;
WriteSymbol(F, MSD, Layout);
if (GetBinding(Data) == ELF::STB_LOCAL)
LastLocalSymbolIndex++;
}
}
static bool ShouldRelocOnSymbol(const MCSymbolData &SD,
const MCValue &Target,
const MCFragment &F) {
const MCSymbol &Symbol = SD.getSymbol();
if (Symbol.isUndefined())
return true;
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(Symbol.getSection());
if (SD.isExternal())
return true;
if (Section.getFlags() & MCSectionELF::SHF_MERGE)
return Target.getConstant() != 0;
MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind();
const MCSectionELF &Sec2 =
static_cast<const MCSectionELF&>(F.getParent()->getSection());
if (&Sec2 != &Section &&
(Kind == MCSymbolRefExpr::VK_PLT || Kind == MCSymbolRefExpr::VK_GOTPCREL))
return true;
return false;
}
// FIXME: this is currently X86/X86_64 only
void ELFObjectWriterImpl::RecordRelocation(const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
uint64_t &FixedValue) {
int64_t Addend = 0;
int Index = 0;
int64_t Value = Target.getConstant();
const MCSymbol *Symbol = 0;
bool IsPCRel = isFixupKindX86PCRel(Fixup.getKind());
if (!Target.isAbsolute()) {
Symbol = &Target.getSymA()->getSymbol();
MCSymbolData &SD = Asm.getSymbolData(*Symbol);
MCFragment *F = SD.getFragment();
if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
const MCSymbol &SymbolB = RefB->getSymbol();
MCSymbolData &SDB = Asm.getSymbolData(SymbolB);
IsPCRel = true;
MCSectionData *Sec = Fragment->getParent();
// Offset of the symbol in the section
int64_t a = Layout.getSymbolAddress(&SDB) - Layout.getSectionAddress(Sec);
// Ofeset of the relocation in the section
int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
Value += b - a;
}
// Check that this case has already been fully resolved before we get
// here.
if (Symbol->isDefined() && !SD.isExternal() &&
IsPCRel &&
&Fragment->getParent()->getSection() == &Symbol->getSection()) {
llvm_unreachable("We don't need a relocation in this case.");
return;
}
bool RelocOnSymbol = ShouldRelocOnSymbol(SD, Target, *Fragment);
if (!RelocOnSymbol) {
Index = F->getParent()->getOrdinal();
MCSectionData *FSD = F->getParent();
// Offset of the symbol in the section
Value += Layout.getSymbolAddress(&SD) - Layout.getSectionAddress(FSD);
} else {
UsedInReloc.insert(Symbol);
Index = -1;
}
Addend = Value;
// Compensate for the addend on i386.
if (Is64Bit)
Value = 0;
}
FixedValue = Value;
// determine the type of the relocation
MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
unsigned Type;
if (Is64Bit) {
if (IsPCRel) {
switch (Modifier) {
case MCSymbolRefExpr::VK_None:
Type = ELF::R_X86_64_PC32;
break;
case MCSymbolRefExpr::VK_PLT:
Type = ELF::R_X86_64_PLT32;
break;
case llvm::MCSymbolRefExpr::VK_GOTPCREL:
Type = ELF::R_X86_64_GOTPCREL;
break;
default:
llvm_unreachable("Unimplemented");
}
} else {
switch ((unsigned)Fixup.getKind()) {
default: llvm_unreachable("invalid fixup kind!");
case FK_Data_8: Type = ELF::R_X86_64_64; break;
case X86::reloc_signed_4byte:
case X86::reloc_pcrel_4byte:
assert(isInt<32>(Target.getConstant()));
switch (Modifier) {
case MCSymbolRefExpr::VK_None:
Type = ELF::R_X86_64_32S;
break;
case MCSymbolRefExpr::VK_GOT:
Type = ELF::R_X86_64_GOT32;
break;
case llvm::MCSymbolRefExpr::VK_GOTPCREL:
Type = ELF::R_X86_64_GOTPCREL;
break;
default:
llvm_unreachable("Unimplemented");
}
break;
case FK_Data_4:
Type = ELF::R_X86_64_32;
break;
case FK_Data_2: Type = ELF::R_X86_64_16; break;
case X86::reloc_pcrel_1byte:
case FK_Data_1: Type = ELF::R_X86_64_8; break;
}
}
} else {
if (IsPCRel) {
Type = ELF::R_386_PC32;
} else {
switch ((unsigned)Fixup.getKind()) {
default: llvm_unreachable("invalid fixup kind!");
// FIXME: Should we avoid selecting reloc_signed_4byte in 32 bit mode
// instead?
case X86::reloc_signed_4byte:
case X86::reloc_pcrel_4byte:
case FK_Data_4: Type = ELF::R_386_32; break;
case FK_Data_2: Type = ELF::R_386_16; break;
case X86::reloc_pcrel_1byte:
case FK_Data_1: Type = ELF::R_386_8; break;
}
}
}
if (RelocNeedsGOT(Type))
NeedsGOT = true;
ELFRelocationEntry ERE;
ERE.Index = Index;
ERE.Type = Type;
ERE.Symbol = Symbol;
ERE.r_offset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
if (HasRelocationAddend)
ERE.r_addend = Addend;
else
ERE.r_addend = 0; // Silence compiler warning.
Relocations[Fragment->getParent()].push_back(ERE);
}
uint64_t
ELFObjectWriterImpl::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
const MCSymbol *S) {
MCSymbolData &SD = Asm.getSymbolData(*S);
// Local symbol.
if (!SD.isExternal() && !S->isUndefined())
return SD.getIndex() + /* empty symbol */ 1;
// External or undefined symbol.
return SD.getIndex() + NumRegularSections + /* empty symbol */ 1;
}
static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data,
bool Used) {
const MCSymbol &Symbol = Data.getSymbol();
if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined())
return false;
if (!Used && Symbol.isTemporary())
return false;
return true;
}
static bool isLocal(const MCSymbolData &Data) {
if (Data.isExternal())
return false;
const MCSymbol &Symbol = Data.getSymbol();
if (Symbol.isUndefined() && !Symbol.isVariable())
return false;
return true;
}
void ELFObjectWriterImpl::ComputeSymbolTable(MCAssembler &Asm) {
// FIXME: Is this the correct place to do this?
if (NeedsGOT) {
llvm::StringRef Name = "_GLOBAL_OFFSET_TABLE_";
MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
Data.setExternal(true);
}
// Build section lookup table.
NumRegularSections = Asm.size();
DenseMap<const MCSection*, uint32_t> SectionIndexMap;
unsigned Index = 1;
for (MCAssembler::iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it, ++Index)
SectionIndexMap[&it->getSection()] = Index;
// Index 0 is always the empty string.
StringMap<uint64_t> StringIndexMap;
StringTable += '\x00';
// Add the data for local symbols.
for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
ie = Asm.symbol_end(); it != ie; ++it) {
const MCSymbol &Symbol = it->getSymbol();
if (!isInSymtab(Asm, *it, UsedInReloc.count(&Symbol)))
continue;
if (!isLocal(*it))
continue;
uint64_t &Entry = StringIndexMap[Symbol.getName()];
if (!Entry) {
Entry = StringTable.size();
StringTable += Symbol.getName();
StringTable += '\x00';
}
ELFSymbolData MSD;
MSD.SymbolData = it;
MSD.StringIndex = Entry;
if (Symbol.isAbsolute()) {
MSD.SectionIndex = ELF::SHN_ABS;
LocalSymbolData.push_back(MSD);
} else {
const MCSymbol *SymbolP = &Symbol;
if (Symbol.isVariable()) {
const MCExpr *Value = Symbol.getVariableValue();
assert (Value->getKind() == MCExpr::SymbolRef && "Unimplemented");
const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Value);
SymbolP = &Ref->getSymbol();
}
MSD.SectionIndex = SectionIndexMap.lookup(&SymbolP->getSection());
assert(MSD.SectionIndex && "Invalid section index!");
LocalSymbolData.push_back(MSD);
}
}
// Now add non-local symbols.
for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
ie = Asm.symbol_end(); it != ie; ++it) {
const MCSymbol &Symbol = it->getSymbol();
if (!isInSymtab(Asm, *it, UsedInReloc.count(&Symbol)))
continue;
if (isLocal(*it))
continue;
uint64_t &Entry = StringIndexMap[Symbol.getName()];
if (!Entry) {
Entry = StringTable.size();
StringTable += Symbol.getName();
StringTable += '\x00';
}
ELFSymbolData MSD;
MSD.SymbolData = it;
MSD.StringIndex = Entry;
// FIXME: There is duplicated code with the local case.
if (it->isCommon()) {
MSD.SectionIndex = ELF::SHN_COMMON;
ExternalSymbolData.push_back(MSD);
} else if (Symbol.isVariable()) {
const MCExpr *Value = Symbol.getVariableValue();
assert (Value->getKind() == MCExpr::SymbolRef && "Unimplemented");
const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Value);
const MCSymbol &RefSymbol = Ref->getSymbol();
if (RefSymbol.isDefined()) {
MSD.SectionIndex = SectionIndexMap.lookup(&RefSymbol.getSection());
assert(MSD.SectionIndex && "Invalid section index!");
ExternalSymbolData.push_back(MSD);
}
} else if (Symbol.isUndefined()) {
MSD.SectionIndex = ELF::SHN_UNDEF;
// FIXME: Undefined symbols are global, but this is the first place we
// are able to set it.
if (GetBinding(*it) == ELF::STB_LOCAL)
SetBinding(*it, ELF::STB_GLOBAL);
UndefinedSymbolData.push_back(MSD);
} else if (Symbol.isAbsolute()) {
MSD.SectionIndex = ELF::SHN_ABS;
ExternalSymbolData.push_back(MSD);
} else {
MSD.SectionIndex = SectionIndexMap.lookup(&Symbol.getSection());
assert(MSD.SectionIndex && "Invalid section index!");
ExternalSymbolData.push_back(MSD);
}
}
// Symbols are required to be in lexicographic order.
array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
// Set the symbol indices. Local symbols must come before all other
// symbols with non-local bindings.
Index = 0;
for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
LocalSymbolData[i].SymbolData->setIndex(Index++);
for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
ExternalSymbolData[i].SymbolData->setIndex(Index++);
for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
UndefinedSymbolData[i].SymbolData->setIndex(Index++);
}
void ELFObjectWriterImpl::WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
const MCSectionData &SD) {
if (!Relocations[&SD].empty()) {
MCContext &Ctx = Asm.getContext();
const MCSection *RelaSection;
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(SD.getSection());
const StringRef SectionName = Section.getSectionName();
std::string RelaSectionName = HasRelocationAddend ? ".rela" : ".rel";
RelaSectionName += SectionName;
unsigned EntrySize;
if (HasRelocationAddend)
EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
else
EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
RelaSection = Ctx.getELFSection(RelaSectionName, HasRelocationAddend ?
ELF::SHT_RELA : ELF::SHT_REL, 0,
SectionKind::getReadOnly(),
false, EntrySize);
MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
RelaSD.setAlignment(Is64Bit ? 8 : 4);
MCDataFragment *F = new MCDataFragment(&RelaSD);
WriteRelocationsFragment(Asm, F, &SD);
Asm.AddSectionToTheEnd(*Writer, RelaSD, Layout);
}
}
void ELFObjectWriterImpl::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
uint64_t Flags, uint64_t Address,
uint64_t Offset, uint64_t Size,
uint32_t Link, uint32_t Info,
uint64_t Alignment,
uint64_t EntrySize) {
Write32(Name); // sh_name: index into string table
Write32(Type); // sh_type
WriteWord(Flags); // sh_flags
WriteWord(Address); // sh_addr
WriteWord(Offset); // sh_offset
WriteWord(Size); // sh_size
Write32(Link); // sh_link
Write32(Info); // sh_info
WriteWord(Alignment); // sh_addralign
WriteWord(EntrySize); // sh_entsize
}
void ELFObjectWriterImpl::WriteRelocationsFragment(const MCAssembler &Asm,
MCDataFragment *F,
const MCSectionData *SD) {
std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
// sort by the r_offset just like gnu as does
array_pod_sort(Relocs.begin(), Relocs.end());
for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
ELFRelocationEntry entry = Relocs[e - i - 1];
if (entry.Index < 0)
entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol);
else
entry.Index += LocalSymbolData.size() + 1;
if (Is64Bit) {
char buf[8];
String64(buf, entry.r_offset);
F->getContents() += StringRef(buf, 8);
struct ELF::Elf64_Rela ERE64;
ERE64.setSymbolAndType(entry.Index, entry.Type);
String64(buf, ERE64.r_info);
F->getContents() += StringRef(buf, 8);
if (HasRelocationAddend) {
String64(buf, entry.r_addend);
F->getContents() += StringRef(buf, 8);
}
} else {
char buf[4];
String32(buf, entry.r_offset);
F->getContents() += StringRef(buf, 4);
struct ELF::Elf32_Rela ERE32;
ERE32.setSymbolAndType(entry.Index, entry.Type);
String32(buf, ERE32.r_info);
F->getContents() += StringRef(buf, 4);
if (HasRelocationAddend) {
String32(buf, entry.r_addend);
F->getContents() += StringRef(buf, 4);
}
}
}
}
void ELFObjectWriterImpl::CreateMetadataSections(MCAssembler &Asm,
MCAsmLayout &Layout) {
MCContext &Ctx = Asm.getContext();
MCDataFragment *F;
const MCSection *SymtabSection;
unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
unsigned NumRegularSections = Asm.size();
// We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
const MCSection *ShstrtabSection;
ShstrtabSection = Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
SectionKind::getReadOnly(), false);
MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
ShstrtabSD.setAlignment(1);
ShstrtabIndex = Asm.size();
SymtabSection = Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
SectionKind::getReadOnly(),
false, EntrySize);
MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
SymtabSD.setAlignment(Is64Bit ? 8 : 4);
const MCSection *StrtabSection;
StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
SectionKind::getReadOnly(), false);
MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
StrtabSD.setAlignment(1);
StringTableIndex = Asm.size();
WriteRelocations(Asm, Layout);
// Symbol table
F = new MCDataFragment(&SymtabSD);
WriteSymbolTable(F, Asm, Layout, NumRegularSections);
Asm.AddSectionToTheEnd(*Writer, SymtabSD, Layout);
F = new MCDataFragment(&StrtabSD);
F->getContents().append(StringTable.begin(), StringTable.end());
Asm.AddSectionToTheEnd(*Writer, StrtabSD, Layout);
F = new MCDataFragment(&ShstrtabSD);
// Section header string table.
//
// The first entry of a string table holds a null character so skip
// section 0.
uint64_t Index = 1;
F->getContents() += '\x00';
for (MCAssembler::const_iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(it->getSection());
// FIXME: We could merge suffixes like in .text and .rela.text.
// Remember the index into the string table so we can write it
// into the sh_name field of the section header table.
SectionStringTableIndex[&it->getSection()] = Index;
Index += Section.getSectionName().size() + 1;
F->getContents() += Section.getSectionName();
F->getContents() += '\x00';
}
Asm.AddSectionToTheEnd(*Writer, ShstrtabSD, Layout);
}
bool ELFObjectWriterImpl::IsFixupFullyResolved(const MCAssembler &Asm,
const MCValue Target,
bool IsPCRel,
const MCFragment *DF) const {
// If this is a PCrel relocation, find the section this fixup value is
// relative to.
const MCSection *BaseSection = 0;
if (IsPCRel) {
BaseSection = &DF->getParent()->getSection();
assert(BaseSection);
}
const MCSection *SectionA = 0;
const MCSymbol *SymbolA = 0;
if (const MCSymbolRefExpr *A = Target.getSymA()) {
SymbolA = &A->getSymbol();
SectionA = &SymbolA->getSection();
}
const MCSection *SectionB = 0;
if (const MCSymbolRefExpr *B = Target.getSymB()) {
SectionB = &B->getSymbol().getSection();
}
if (!BaseSection)
return SectionA == SectionB;
const MCSymbolData &DataA = Asm.getSymbolData(*SymbolA);
if (DataA.isExternal())
return false;
return !SectionB && BaseSection == SectionA;
}
void ELFObjectWriterImpl::WriteObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
// Compute symbol table information.
ComputeSymbolTable(Asm);
CreateMetadataSections(const_cast<MCAssembler&>(Asm),
const_cast<MCAsmLayout&>(Layout));
// Add 1 for the null section.
unsigned NumSections = Asm.size() + 1;
uint64_t NaturalAlignment = Is64Bit ? 8 : 4;
uint64_t HeaderSize = Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr);
uint64_t FileOff = HeaderSize;
for (MCAssembler::const_iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
const MCSectionData &SD = *it;
FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
// Get the size of the section in the output file (including padding).
uint64_t Size = Layout.getSectionFileSize(&SD);
FileOff += Size;
}
FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
// Write out the ELF header ...
WriteHeader(FileOff - HeaderSize, NumSections);
FileOff = HeaderSize;
// ... then all of the sections ...
DenseMap<const MCSection*, uint64_t> SectionOffsetMap;
DenseMap<const MCSection*, uint32_t> SectionIndexMap;
unsigned Index = 1;
for (MCAssembler::const_iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
const MCSectionData &SD = *it;
uint64_t Padding = OffsetToAlignment(FileOff, SD.getAlignment());
WriteZeros(Padding);
FileOff += Padding;
// Remember the offset into the file for this section.
SectionOffsetMap[&it->getSection()] = FileOff;
SectionIndexMap[&it->getSection()] = Index++;
FileOff += Layout.getSectionFileSize(&SD);
Asm.WriteSectionData(it, Layout, Writer);
}
uint64_t Padding = OffsetToAlignment(FileOff, NaturalAlignment);
WriteZeros(Padding);
FileOff += Padding;
// ... and then the section header table.
// Should we align the section header table?
//
// Null section first.
WriteSecHdrEntry(0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
for (MCAssembler::const_iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
const MCSectionData &SD = *it;
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(SD.getSection());
uint64_t sh_link = 0;
uint64_t sh_info = 0;
switch(Section.getType()) {
case ELF::SHT_DYNAMIC:
sh_link = SectionStringTableIndex[&it->getSection()];
sh_info = 0;
break;
case ELF::SHT_REL:
case ELF::SHT_RELA: {
const MCSection *SymtabSection;
const MCSection *InfoSection;
SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
SectionKind::getReadOnly(),
false);
sh_link = SectionIndexMap[SymtabSection];
// Remove ".rel" and ".rela" prefixes.
unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
StringRef SectionName = Section.getSectionName().substr(SecNameLen);
InfoSection = Asm.getContext().getELFSection(SectionName,
ELF::SHT_PROGBITS, 0,
SectionKind::getReadOnly(),
false);
sh_info = SectionIndexMap[InfoSection];
break;
}
case ELF::SHT_SYMTAB:
case ELF::SHT_DYNSYM:
sh_link = StringTableIndex;
sh_info = LastLocalSymbolIndex;
break;
case ELF::SHT_PROGBITS:
case ELF::SHT_STRTAB:
case ELF::SHT_NOBITS:
case ELF::SHT_NULL:
// Nothing to do.
break;
case ELF::SHT_HASH:
case ELF::SHT_GROUP:
case ELF::SHT_SYMTAB_SHNDX:
default:
assert(0 && "FIXME: sh_type value not supported!");
break;
}
WriteSecHdrEntry(SectionStringTableIndex[&it->getSection()],
Section.getType(), Section.getFlags(),
0,
SectionOffsetMap.lookup(&SD.getSection()),
Layout.getSectionSize(&SD), sh_link,
sh_info, SD.getAlignment(),
Section.getEntrySize());
}
}
ELFObjectWriter::ELFObjectWriter(raw_ostream &OS,
bool Is64Bit,
Triple::OSType OSType,
bool IsLittleEndian,
bool HasRelocationAddend)
: MCObjectWriter(OS, IsLittleEndian)
{
Impl = new ELFObjectWriterImpl(this, Is64Bit, HasRelocationAddend, OSType);
}
ELFObjectWriter::~ELFObjectWriter() {
delete (ELFObjectWriterImpl*) Impl;
}
void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
((ELFObjectWriterImpl*) Impl)->ExecutePostLayoutBinding(Asm);
}
void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup, MCValue Target,
uint64_t &FixedValue) {
((ELFObjectWriterImpl*) Impl)->RecordRelocation(Asm, Layout, Fragment, Fixup,
Target, FixedValue);
}
bool ELFObjectWriter::IsFixupFullyResolved(const MCAssembler &Asm,
const MCValue Target,
bool IsPCRel,
const MCFragment *DF) const {
return ((ELFObjectWriterImpl*) Impl)->IsFixupFullyResolved(Asm, Target,
IsPCRel, DF);
}
void ELFObjectWriter::WriteObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
((ELFObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);
}
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