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llvm-6502/lib/MC/ELFObjectWriter.cpp
Rafael Espindola d179886f05 Be more strict on when we produce an undefined reference. In gas a file with 
just

.type   foo,@object

will produce an undefined reference to foo. On the other hand, a file with
just

.weakref bar, foo

will not. It is somewhat hard to support both in MC since both statements
should create the symbols. It should be possible if we really need to by
adding to the flags, but hopefully that is not necessary.

With this patch we do not produce a undefined reference in any of those cases.
The assembly file needs an actual use for the undefined reference to be
present.

This is in preparation for a patch implementing .weakref.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117735 91177308-0d34-0410-b5e6-96231b3b80d8
2010-10-29 23:09:31 +00:00

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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(MCSymbolRefExpr::VariantKind Variant) {
switch (Variant) {
default:
return false;
case MCSymbolRefExpr::VK_GOT:
case MCSymbolRefExpr::VK_PLT:
case MCSymbolRefExpr::VK_GOTPCREL:
case MCSymbolRefExpr::VK_TPOFF:
case MCSymbolRefExpr::VK_TLSGD:
case MCSymbolRefExpr::VK_GOTTPOFF:
case MCSymbolRefExpr::VK_INDNTPOFF:
case MCSymbolRefExpr::VK_NTPOFF:
case MCSymbolRefExpr::VK_GOTNTPOFF:
case MCSymbolRefExpr::VK_TLSLDM:
case MCSymbolRefExpr::VK_DTPOFF:
case MCSymbolRefExpr::VK_TLSLD:
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;
DenseMap<const MCSymbol *, const MCSymbol *> Renames;
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;
uint16_t EMachine;
// 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,
uint16_t _EMachine, bool _HasRelAddend,
Triple::OSType _OSType)
: NeedsGOT(false), Writer(_Writer), OS(Writer->getStream()),
Is64Bit(_Is64Bit), HasRelocationAddend(_HasRelAddend),
OSType(_OSType), EMachine(_EMachine) {
}
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
Write16(EMachine); // 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 (MCFragment *FF = Data.getFragment())
return Layout.getSymbolAddress(&Data) -
Layout.getSectionAddress(FF->getParent());
return 0;
}
static const MCSymbol &AliasedSymbol(const MCSymbol &Symbol) {
const MCSymbol *S = &Symbol;
while (S->isVariable()) {
const MCExpr *Value = S->getVariableValue();
if (Value->getKind() != MCExpr::SymbolRef)
return *S;
const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Value);
S = &Ref->getSymbol();
}
return *S;
}
void ELFObjectWriterImpl::ExecutePostLayoutBinding(MCAssembler &Asm) {
// The presence of symbol versions causes undefined symbols and
// versions declared with @@@ to be renamed.
for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
ie = Asm.symbol_end(); it != ie; ++it) {
const MCSymbol &Alias = it->getSymbol();
const MCSymbol &Symbol = AliasedSymbol(Alias);
MCSymbolData &SD = Asm.getSymbolData(Symbol);
// Undefined symbols are global, but this is the first place we
// are able to set it.
if (Symbol.isUndefined() && !Symbol.isVariable()) {
if (GetBinding(SD) == ELF::STB_LOCAL) {
SetBinding(SD, ELF::STB_GLOBAL);
SetBinding(*it, ELF::STB_GLOBAL);
}
}
// Not an alias.
if (&Symbol == &Alias)
continue;
StringRef AliasName = Alias.getName();
size_t Pos = AliasName.find('@');
if (Pos == StringRef::npos)
continue;
// Aliases defined with .symvar copy the binding from the symbol they alias.
// This is the first place we are able to copy this information.
it->setExternal(SD.isExternal());
SetBinding(*it, GetBinding(SD));
StringRef Rest = AliasName.substr(Pos);
if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
continue;
// FIXME: produce a better error message.
if (Symbol.isUndefined() && Rest.startswith("@@") &&
!Rest.startswith("@@@"))
report_fatal_error("A @@ version cannot be undefined");
Renames.insert(std::make_pair(&Symbol, &Alias));
}
}
void ELFObjectWriterImpl::WriteSymbol(MCDataFragment *F, ELFSymbolData &MSD,
const MCAsmLayout &Layout) {
MCSymbolData &OrigData = *MSD.SymbolData;
MCSymbolData &Data =
Layout.getAssembler().getSymbolData(AliasedSymbol(OrigData.getSymbol()));
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)) {
assert(!Res.getSymA() || !Res.getSymA()->getSymbol().isDefined());
assert(!Res.getSymB() || !Res.getSymB()->getSymbol().isDefined());
Size = Res.getConstant();
}
} 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;
MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind();
const MCSectionELF &Sec2 =
static_cast<const MCSectionELF&>(F.getParent()->getSection());
if (Section.getKind().isBSS())
return false;
if (&Sec2 != &Section &&
(Kind == MCSymbolRefExpr::VK_PLT ||
Kind == MCSymbolRefExpr::VK_GOTPCREL ||
Kind == MCSymbolRefExpr::VK_GOTOFF))
return true;
if (Section.getFlags() & MCSectionELF::SHF_MERGE)
return Target.getConstant() != 0;
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;
const MCSymbol *Renamed = 0;
bool IsPCRel = isFixupKindX86PCRel(Fixup.getKind());
if (!Target.isAbsolute()) {
Symbol = &AliasedSymbol(Target.getSymA()->getSymbol());
Renamed = Renames.lookup(Symbol);
if (!Renamed)
Renamed = Symbol;
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(Renamed);
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) {
default:
llvm_unreachable("Unimplemented");
case MCSymbolRefExpr::VK_None:
Type = ELF::R_X86_64_PC32;
break;
case MCSymbolRefExpr::VK_PLT:
Type = ELF::R_X86_64_PLT32;
break;
case MCSymbolRefExpr::VK_GOTPCREL:
Type = ELF::R_X86_64_GOTPCREL;
break;
case MCSymbolRefExpr::VK_GOTTPOFF:
Type = ELF::R_X86_64_GOTTPOFF;
break;
case MCSymbolRefExpr::VK_TLSGD:
Type = ELF::R_X86_64_TLSGD;
break;
case MCSymbolRefExpr::VK_TLSLD:
Type = ELF::R_X86_64_TLSLD;
break;
}
} 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) {
default:
llvm_unreachable("Unimplemented");
case MCSymbolRefExpr::VK_None:
Type = ELF::R_X86_64_32S;
break;
case MCSymbolRefExpr::VK_GOT:
Type = ELF::R_X86_64_GOT32;
break;
case MCSymbolRefExpr::VK_GOTPCREL:
Type = ELF::R_X86_64_GOTPCREL;
break;
case MCSymbolRefExpr::VK_TPOFF:
Type = ELF::R_X86_64_TPOFF32;
break;
case MCSymbolRefExpr::VK_DTPOFF:
Type = ELF::R_X86_64_DTPOFF32;
break;
}
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) {
switch (Modifier) {
default:
llvm_unreachable("Unimplemented");
case MCSymbolRefExpr::VK_None:
Type = ELF::R_386_PC32;
break;
case MCSymbolRefExpr::VK_PLT:
Type = ELF::R_386_PLT32;
break;
}
} else {
switch ((unsigned)Fixup.getKind()) {
default: llvm_unreachable("invalid fixup kind!");
case X86::reloc_global_offset_table:
Type = ELF::R_386_GOTPC;
break;
// 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:
switch (Modifier) {
default:
llvm_unreachable("Unimplemented");
case MCSymbolRefExpr::VK_None:
Type = ELF::R_386_32;
break;
case MCSymbolRefExpr::VK_GOT:
Type = ELF::R_386_GOT32;
break;
case MCSymbolRefExpr::VK_GOTOFF:
Type = ELF::R_386_GOTOFF;
break;
case MCSymbolRefExpr::VK_TLSGD:
Type = ELF::R_386_TLS_GD;
break;
case MCSymbolRefExpr::VK_TPOFF:
Type = ELF::R_386_TLS_LE_32;
break;
case MCSymbolRefExpr::VK_INDNTPOFF:
Type = ELF::R_386_TLS_IE;
break;
case MCSymbolRefExpr::VK_NTPOFF:
Type = ELF::R_386_TLS_LE;
break;
case MCSymbolRefExpr::VK_GOTNTPOFF:
Type = ELF::R_386_TLS_GOTIE;
break;
case MCSymbolRefExpr::VK_TLSLDM:
Type = ELF::R_386_TLS_LDM;
break;
case MCSymbolRefExpr::VK_DTPOFF:
Type = ELF::R_386_TLS_LDO_32;
break;
}
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(Modifier))
NeedsGOT = true;
ELFRelocationEntry ERE;
ERE.Index = Index;
ERE.Type = Type;
ERE.Symbol = Renamed;
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, bool Renamed) {
if (Used)
return true;
if (Renamed)
return false;
const MCSymbol &Symbol = Data.getSymbol();
if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
return true;
const MCSymbol &A = AliasedSymbol(Symbol);
if (!A.isVariable() && A.isUndefined() && !Data.isCommon())
return false;
if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined())
return false;
if (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);
SetBinding(Data, ELF::STB_GLOBAL);
}
// 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 the 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),
Renames.count(&Symbol)))
continue;
ELFSymbolData MSD;
MSD.SymbolData = it;
bool Local = isLocal(*it);
const MCSymbol &RefSymbol = AliasedSymbol(Symbol);
if (it->isCommon()) {
assert(!Local);
MSD.SectionIndex = ELF::SHN_COMMON;
} else if (Symbol.isAbsolute() || RefSymbol.isVariable()) {
MSD.SectionIndex = ELF::SHN_ABS;
} else if (RefSymbol.isUndefined()) {
MSD.SectionIndex = ELF::SHN_UNDEF;
} else {
MSD.SectionIndex = SectionIndexMap.lookup(&RefSymbol.getSection());
assert(MSD.SectionIndex && "Invalid section index!");
}
// The @@@ in symbol version is replaced with @ in undefined symbols and
// @@ in defined ones.
StringRef Name = Symbol.getName();
size_t Pos = Name.find("@@@");
std::string FinalName;
if (Pos != StringRef::npos) {
StringRef Prefix = Name.substr(0, Pos);
unsigned n = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
StringRef Suffix = Name.substr(Pos + n);
FinalName = Prefix.str() + Suffix.str();
} else {
FinalName = Name.str();
}
uint64_t &Entry = StringIndexMap[FinalName];
if (!Entry) {
Entry = StringTable.size();
StringTable += FinalName;
StringTable += '\x00';
}
MSD.StringIndex = Entry;
if (MSD.SectionIndex == ELF::SHN_UNDEF)
UndefinedSymbolData.push_back(MSD);
else if (Local)
LocalSymbolData.push_back(MSD);
else
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:
case ELF::SHT_ARM_ATTRIBUTES:
// Nothing to do.
break;
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,
uint16_t EMachine,
bool IsLittleEndian,
bool HasRelocationAddend)
: MCObjectWriter(OS, IsLittleEndian)
{
Impl = new ELFObjectWriterImpl(this, Is64Bit, EMachine,
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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