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llvm-6502/lib/MC/ELFObjectWriter.cpp
Rafael Espindola 9936b80df5 Compute the ELF SectionKind from the flags. 
Any code creating an MCSectionELF knows ELF and already provides the flags.

SectionKind is an abstraction used by common code that uses a plain
MCSection.

Use the flags to compute the SectionKind. This removes a lot of
guessing and boilerplate from the MCSectionELF construction.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227476 91177308-0d34-0410-b5e6-96231b3b80d8
2015-01-29 17:33:21 +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/MCELFObjectWriter.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCELF.h"
#include "llvm/MC/MCELFSymbolFlags.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCValue.h"
#include "llvm/MC/StringTableBuilder.h"
#include "llvm/Support/Compression.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ELF.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/ErrorHandling.h"
#include <vector>
using namespace llvm;
#undef DEBUG_TYPE
#define DEBUG_TYPE "reloc-info"
namespace {
class FragmentWriter {
bool IsLittleEndian;
public:
FragmentWriter(bool IsLittleEndian);
template <typename T> void write(MCDataFragment &F, T Val);
};
typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
class SymbolTableWriter {
MCAssembler &Asm;
FragmentWriter &FWriter;
bool Is64Bit;
SectionIndexMapTy &SectionIndexMap;
// The symbol .symtab fragment we are writting to.
MCDataFragment *SymtabF;
// .symtab_shndx fragment we are writting to.
MCDataFragment *ShndxF;
// The numbel of symbols written so far.
unsigned NumWritten;
void createSymtabShndx();
template <typename T> void write(MCDataFragment &F, T Value);
public:
SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
SectionIndexMapTy &SectionIndexMap,
MCDataFragment *SymtabF);
void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
uint8_t other, uint32_t shndx, bool Reserved);
};
struct ELFRelocationEntry {
uint64_t Offset; // Where is the relocation.
const MCSymbol *Symbol; // The symbol to relocate with.
unsigned Type; // The type of the relocation.
uint64_t Addend; // The addend to use.
ELFRelocationEntry(uint64_t Offset, const MCSymbol *Symbol, unsigned Type,
uint64_t Addend)
: Offset(Offset), Symbol(Symbol), Type(Type), Addend(Addend) {}
};
class ELFObjectWriter : public MCObjectWriter {
FragmentWriter FWriter;
protected:
static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data,
bool Used, bool Renamed);
static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
static bool IsELFMetaDataSection(const MCSectionData &SD);
static uint64_t DataSectionSize(const MCSectionData &SD);
static uint64_t GetSectionFileSize(const MCAsmLayout &Layout,
const MCSectionData &SD);
static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout,
const MCSectionData &SD);
void WriteDataSectionData(MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCSectionELF &Section);
/*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;
StringRef Name;
// Support lexicographic sorting.
bool operator<(const ELFSymbolData &RHS) const {
unsigned LHSType = MCELF::GetType(*SymbolData);
unsigned RHSType = MCELF::GetType(*RHS.SymbolData);
if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
return false;
if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
return true;
if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
return SectionIndex < RHS.SectionIndex;
return Name < RHS.Name;
}
};
/// The target specific ELF writer instance.
std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
DenseMap<const MCSymbol *, const MCSymbol *> Renames;
llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
Relocations;
StringTableBuilder ShStrTabBuilder;
/// @}
/// @name Symbol Table Data
/// @{
StringTableBuilder StrTabBuilder;
std::vector<uint64_t> FileSymbolData;
std::vector<ELFSymbolData> LocalSymbolData;
std::vector<ELFSymbolData> ExternalSymbolData;
std::vector<ELFSymbolData> UndefinedSymbolData;
/// @}
bool NeedsGOT;
// This holds the symbol table index of the last local symbol.
unsigned LastLocalSymbolIndex;
// This holds the .strtab section index.
unsigned StringTableIndex;
// This holds the .symtab section index.
unsigned SymbolTableIndex;
unsigned ShstrtabIndex;
// TargetObjectWriter wrappers.
bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
bool hasRelocationAddend() const {
return TargetObjectWriter->hasRelocationAddend();
}
unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
bool IsPCRel) const {
return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
}
public:
ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_ostream &_OS,
bool IsLittleEndian)
: MCObjectWriter(_OS, IsLittleEndian), FWriter(IsLittleEndian),
TargetObjectWriter(MOTW), NeedsGOT(false) {}
virtual ~ELFObjectWriter();
void WriteWord(uint64_t W) {
if (is64Bit())
Write64(W);
else
Write32(W);
}
template <typename T> void write(MCDataFragment &F, T Value) {
FWriter.write(F, Value);
}
void WriteHeader(const MCAssembler &Asm,
uint64_t SectionDataSize,
unsigned NumberOfSections);
void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
const MCAsmLayout &Layout);
void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm,
const MCAsmLayout &Layout,
SectionIndexMapTy &SectionIndexMap);
bool shouldRelocateWithSymbol(const MCAssembler &Asm,
const MCSymbolRefExpr *RefA,
const MCSymbolData *SD, uint64_t C,
unsigned Type) const;
void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment *Fragment, const MCFixup &Fixup,
MCValue Target, bool &IsPCRel,
uint64_t &FixedValue) override;
uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
const MCSymbol *S);
// Map from a group section to the signature symbol
typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
// Map from a signature symbol to the group section
typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
// Map from a section to the section with the relocations
typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy;
// Map from a section to its offset
typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy;
/// Compute the symbol table data
///
/// \param Asm - The assembler.
/// \param SectionIndexMap - Maps a section to its index.
/// \param RevGroupMap - Maps a signature symbol to the group section.
/// \param NumRegularSections - Number of non-relocation sections.
void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
const SectionIndexMapTy &SectionIndexMap,
const RevGroupMapTy &RevGroupMap,
unsigned NumRegularSections);
void ComputeIndexMap(MCAssembler &Asm,
SectionIndexMapTy &SectionIndexMap,
const RelMapTy &RelMap);
void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout,
RelMapTy &RelMap);
void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
const RelMapTy &RelMap);
void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
SectionIndexMapTy &SectionIndexMap,
const RelMapTy &RelMap);
// Create the sections that show up in the symbol table. Currently
// those are the .note.GNU-stack section and the group sections.
void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
GroupMapTy &GroupMap,
RevGroupMapTy &RevGroupMap,
SectionIndexMapTy &SectionIndexMap,
const RelMapTy &RelMap);
void ExecutePostLayoutBinding(MCAssembler &Asm,
const MCAsmLayout &Layout) override;
void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap,
const MCAsmLayout &Layout,
const SectionIndexMapTy &SectionIndexMap,
const SectionOffsetMapTy &SectionOffsetMap);
void ComputeSectionOrder(MCAssembler &Asm,
std::vector<const MCSectionELF*> &Sections);
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
IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
const MCSymbolData &DataA,
const MCFragment &FB,
bool InSet,
bool IsPCRel) const override;
void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
void WriteSection(MCAssembler &Asm,
const SectionIndexMapTy &SectionIndexMap,
uint32_t GroupSymbolIndex,
uint64_t Offset, uint64_t Size, uint64_t Alignment,
const MCSectionELF &Section);
};
}
FragmentWriter::FragmentWriter(bool IsLittleEndian)
: IsLittleEndian(IsLittleEndian) {}
template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
if (IsLittleEndian)
Val = support::endian::byte_swap<T, support::little>(Val);
else
Val = support::endian::byte_swap<T, support::big>(Val);
const char *Start = (const char *)&Val;
F.getContents().append(Start, Start + sizeof(T));
}
void SymbolTableWriter::createSymtabShndx() {
if (ShndxF)
return;
MCContext &Ctx = Asm.getContext();
const MCSectionELF *SymtabShndxSection =
Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
MCSectionData *SymtabShndxSD =
&Asm.getOrCreateSectionData(*SymtabShndxSection);
SymtabShndxSD->setAlignment(4);
ShndxF = new MCDataFragment(SymtabShndxSD);
unsigned Index = SectionIndexMap.size() + 1;
SectionIndexMap[SymtabShndxSection] = Index;
for (unsigned I = 0; I < NumWritten; ++I)
write(*ShndxF, uint32_t(0));
}
template <typename T>
void SymbolTableWriter::write(MCDataFragment &F, T Value) {
FWriter.write(F, Value);
}
SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter,
bool Is64Bit,
SectionIndexMapTy &SectionIndexMap,
MCDataFragment *SymtabF)
: Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit),
SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr),
NumWritten(0) {}
void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
uint64_t size, uint8_t other,
uint32_t shndx, bool Reserved) {
bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
if (LargeIndex)
createSymtabShndx();
if (ShndxF) {
if (LargeIndex)
write(*ShndxF, shndx);
else
write(*ShndxF, uint32_t(0));
}
uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
raw_svector_ostream OS(SymtabF->getContents());
if (Is64Bit) {
write(*SymtabF, name); // st_name
write(*SymtabF, info); // st_info
write(*SymtabF, other); // st_other
write(*SymtabF, Index); // st_shndx
write(*SymtabF, value); // st_value
write(*SymtabF, size); // st_size
} else {
write(*SymtabF, name); // st_name
write(*SymtabF, uint32_t(value)); // st_value
write(*SymtabF, uint32_t(size)); // st_size
write(*SymtabF, info); // st_info
write(*SymtabF, other); // st_other
write(*SymtabF, Index); // st_shndx
}
++NumWritten;
}
bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
const MCFixupKindInfo &FKI =
Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
}
bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
switch (Variant) {
default:
return false;
case MCSymbolRefExpr::VK_GOT:
case MCSymbolRefExpr::VK_PLT:
case MCSymbolRefExpr::VK_GOTPCREL:
case MCSymbolRefExpr::VK_GOTOFF:
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;
}
}
ELFObjectWriter::~ELFObjectWriter()
{}
// Emit the ELF header.
void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
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(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
// e_ident[EI_OSABI]
Write8(TargetObjectWriter->getOSABI());
Write8(0); // e_ident[EI_ABIVERSION]
WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
Write16(ELF::ET_REL); // e_type
Write16(TargetObjectWriter->getEMachine()); // 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
// e_flags = whatever the target wants
Write32(Asm.getELFHeaderEFlags());
// 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
if (NumberOfSections >= ELF::SHN_LORESERVE)
Write16(ELF::SHN_UNDEF);
else
Write16(NumberOfSections);
// e_shstrndx = Section # of '.shstrtab'
if (ShstrtabIndex >= ELF::SHN_LORESERVE)
Write16(ELF::SHN_XINDEX);
else
Write16(ShstrtabIndex);
}
uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
const MCAsmLayout &Layout) {
if (Data.isCommon() && Data.isExternal())
return Data.getCommonAlignment();
uint64_t Res;
if (!Layout.getSymbolOffset(&Data, Res))
return 0;
if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
Res |= 1;
return Res;
}
void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
const MCAsmLayout &Layout) {
// The presence of symbol versions causes undefined symbols and
// versions declared with @@@ to be renamed.
for (MCSymbolData &OriginalData : Asm.symbols()) {
const MCSymbol &Alias = OriginalData.getSymbol();
// Not an alias.
if (!Alias.isVariable())
continue;
auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
if (!Ref)
continue;
const MCSymbol &Symbol = Ref->getSymbol();
MCSymbolData &SD = Asm.getSymbolData(Symbol);
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.
OriginalData.setExternal(SD.isExternal());
MCELF::SetBinding(OriginalData, MCELF::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));
}
}
static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
uint8_t Type = newType;
// Propagation rules:
// IFUNC > FUNC > OBJECT > NOTYPE
// TLS_OBJECT > OBJECT > NOTYPE
//
// dont let the new type degrade the old type
switch (origType) {
default:
break;
case ELF::STT_GNU_IFUNC:
if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
Type = ELF::STT_GNU_IFUNC;
break;
case ELF::STT_FUNC:
if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
Type == ELF::STT_TLS)
Type = ELF::STT_FUNC;
break;
case ELF::STT_OBJECT:
if (Type == ELF::STT_NOTYPE)
Type = ELF::STT_OBJECT;
break;
case ELF::STT_TLS:
if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
Type = ELF::STT_TLS;
break;
}
return Type;
}
void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
const MCAsmLayout &Layout) {
MCSymbolData &OrigData = *MSD.SymbolData;
assert((!OrigData.getFragment() ||
(&OrigData.getFragment()->getParent()->getSection() ==
&OrigData.getSymbol().getSection())) &&
"The symbol's section doesn't match the fragment's symbol");
const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
// This has to be in sync with when computeSymbolTable uses SHN_ABS or
// SHN_COMMON.
bool IsReserved = !Base || OrigData.isCommon();
// Binding and Type share the same byte as upper and lower nibbles
uint8_t Binding = MCELF::GetBinding(OrigData);
uint8_t Type = MCELF::GetType(OrigData);
MCSymbolData *BaseSD = nullptr;
if (Base) {
BaseSD = &Layout.getAssembler().getSymbolData(*Base);
Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
}
uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
// Other and Visibility share the same byte with Visibility using the lower
// 2 bits
uint8_t Visibility = MCELF::GetVisibility(OrigData);
uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
Other |= Visibility;
uint64_t Value = SymbolValue(OrigData, Layout);
uint64_t Size = 0;
const MCExpr *ESize = OrigData.getSize();
if (!ESize && Base)
ESize = BaseSD->getSize();
if (ESize) {
int64_t Res;
if (!ESize->EvaluateAsAbsolute(Res, Layout))
report_fatal_error("Size expression must be absolute.");
Size = Res;
}
// Write out the symbol table entry
Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
MSD.SectionIndex, IsReserved);
}
void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
MCAssembler &Asm,
const MCAsmLayout &Layout,
SectionIndexMapTy &SectionIndexMap) {
// The string table must be emitted first because we need the index
// into the string table for all the symbol names.
// FIXME: Make sure the start of the symbol table is aligned.
SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF);
// The first entry is the undefined symbol entry.
Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
ELF::STV_DEFAULT, ELF::SHN_ABS, true);
}
// Write the symbol table entries.
LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
ELFSymbolData &MSD = LocalSymbolData[i];
WriteSymbol(Writer, MSD, Layout);
}
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(Writer, MSD, Layout);
if (MCELF::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(Writer, MSD, Layout);
if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
LastLocalSymbolIndex++;
}
}
// It is always valid to create a relocation with a symbol. It is preferable
// to use a relocation with a section if that is possible. Using the section
// allows us to omit some local symbols from the symbol table.
bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
const MCSymbolRefExpr *RefA,
const MCSymbolData *SD,
uint64_t C,
unsigned Type) const {
// A PCRel relocation to an absolute value has no symbol (or section). We
// represent that with a relocation to a null section.
if (!RefA)
return false;
MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
switch (Kind) {
default:
break;
// The .odp creation emits a relocation against the symbol ".TOC." which
// create a R_PPC64_TOC relocation. However the relocation symbol name
// in final object creation should be NULL, since the symbol does not
// really exist, it is just the reference to TOC base for the current
// object file. Since the symbol is undefined, returning false results
// in a relocation with a null section which is the desired result.
case MCSymbolRefExpr::VK_PPC_TOCBASE:
return false;
// These VariantKind cause the relocation to refer to something other than
// the symbol itself, like a linker generated table. Since the address of
// symbol is not relevant, we cannot replace the symbol with the
// section and patch the difference in the addend.
case MCSymbolRefExpr::VK_GOT:
case MCSymbolRefExpr::VK_PLT:
case MCSymbolRefExpr::VK_GOTPCREL:
case MCSymbolRefExpr::VK_Mips_GOT:
case MCSymbolRefExpr::VK_PPC_GOT_LO:
case MCSymbolRefExpr::VK_PPC_GOT_HI:
case MCSymbolRefExpr::VK_PPC_GOT_HA:
return true;
}
// An undefined symbol is not in any section, so the relocation has to point
// to the symbol itself.
const MCSymbol &Sym = SD->getSymbol();
if (Sym.isUndefined())
return true;
unsigned Binding = MCELF::GetBinding(*SD);
switch(Binding) {
default:
llvm_unreachable("Invalid Binding");
case ELF::STB_LOCAL:
break;
case ELF::STB_WEAK:
// If the symbol is weak, it might be overridden by a symbol in another
// file. The relocation has to point to the symbol so that the linker
// can update it.
return true;
case ELF::STB_GLOBAL:
// Global ELF symbols can be preempted by the dynamic linker. The relocation
// has to point to the symbol for a reason analogous to the STB_WEAK case.
return true;
}
// If a relocation points to a mergeable section, we have to be careful.
// If the offset is zero, a relocation with the section will encode the
// same information. With a non-zero offset, the situation is different.
// For example, a relocation can point 42 bytes past the end of a string.
// If we change such a relocation to use the section, the linker would think
// that it pointed to another string and subtracting 42 at runtime will
// produce the wrong value.
auto &Sec = cast<MCSectionELF>(Sym.getSection());
unsigned Flags = Sec.getFlags();
if (Flags & ELF::SHF_MERGE) {
if (C != 0)
return true;
// It looks like gold has a bug (http://sourceware.org/PR16794) and can
// only handle section relocations to mergeable sections if using RELA.
if (!hasRelocationAddend())
return true;
}
// Most TLS relocations use a got, so they need the symbol. Even those that
// are just an offset (@tpoff), require a symbol in gold versions before
// 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
// http://sourceware.org/PR16773.
if (Flags & ELF::SHF_TLS)
return true;
// If the symbol is a thumb function the final relocation must set the lowest
// bit. With a symbol that is done by just having the symbol have that bit
// set, so we would lose the bit if we relocated with the section.
// FIXME: We could use the section but add the bit to the relocation value.
if (Asm.isThumbFunc(&Sym))
return true;
if (TargetObjectWriter->needsRelocateWithSymbol(*SD, Type))
return true;
return false;
}
static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
const MCSymbol &Sym = Ref.getSymbol();
if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
return &Sym;
if (!Sym.isVariable())
return nullptr;
const MCExpr *Expr = Sym.getVariableValue();
const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
if (!Inner)
return nullptr;
if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
return &Inner->getSymbol();
return nullptr;
}
void ELFObjectWriter::RecordRelocation(MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup, MCValue Target,
bool &IsPCRel, uint64_t &FixedValue) {
const MCSectionData *FixupSection = Fragment->getParent();
uint64_t C = Target.getConstant();
uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
"Should not have constructed this");
// Let A, B and C being the components of Target and R be the location of
// the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
// If it is pcrel, we want to compute (A - B + C - R).
// In general, ELF has no relocations for -B. It can only represent (A + C)
// or (A + C - R). If B = R + K and the relocation is not pcrel, we can
// replace B to implement it: (A - R - K + C)
if (IsPCRel)
Asm.getContext().FatalError(
Fixup.getLoc(),
"No relocation available to represent this relative expression");
const MCSymbol &SymB = RefB->getSymbol();
if (SymB.isUndefined())
Asm.getContext().FatalError(
Fixup.getLoc(),
Twine("symbol '") + SymB.getName() +
"' can not be undefined in a subtraction expression");
assert(!SymB.isAbsolute() && "Should have been folded");
const MCSection &SecB = SymB.getSection();
if (&SecB != &FixupSection->getSection())
Asm.getContext().FatalError(
Fixup.getLoc(), "Cannot represent a difference across sections");
const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
uint64_t K = SymBOffset - FixupOffset;
IsPCRel = true;
C -= K;
}
// We either rejected the fixup or folded B into C at this point.
const MCSymbolRefExpr *RefA = Target.getSymA();
const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
C += Layout.getSymbolOffset(SymAD);
uint64_t Addend = 0;
if (hasRelocationAddend()) {
Addend = C;
C = 0;
}
FixedValue = C;
// FIXME: What is this!?!?
MCSymbolRefExpr::VariantKind Modifier =
RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
if (RelocNeedsGOT(Modifier))
NeedsGOT = true;
if (!RelocateWithSymbol) {
const MCSection *SecA =
(SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
MCSymbol *SectionSymbol =
ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
: nullptr;
ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
Relocations[FixupSection].push_back(Rec);
return;
}
if (SymA) {
if (const MCSymbol *R = Renames.lookup(SymA))
SymA = R;
if (const MCSymbol *WeakRef = getWeakRef(*RefA))
WeakrefUsedInReloc.insert(WeakRef);
else
UsedInReloc.insert(SymA);
}
ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
Relocations[FixupSection].push_back(Rec);
return;
}
uint64_t
ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
const MCSymbol *S) {
const MCSymbolData &SD = Asm.getSymbolData(*S);
return SD.getIndex();
}
bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
const MCSymbolData &Data, bool Used,
bool Renamed) {
const MCSymbol &Symbol = Data.getSymbol();
if (Symbol.isVariable()) {
const MCExpr *Expr = Symbol.getVariableValue();
if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
return false;
}
}
if (Used)
return true;
if (Renamed)
return false;
if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
return true;
if (Symbol.isVariable()) {
const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
if (Base && Base->isUndefined())
return false;
}
bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
return false;
if (Symbol.isTemporary())
return false;
return true;
}
bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
if (Data.isExternal())
return false;
const MCSymbol &Symbol = Data.getSymbol();
if (Symbol.isDefined())
return true;
if (isUsedInReloc)
return false;
return true;
}
void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
SectionIndexMapTy &SectionIndexMap,
const RelMapTy &RelMap) {
unsigned Index = 1;
for (MCAssembler::iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
const MCSectionELF &Section =
static_cast<const MCSectionELF &>(it->getSection());
if (Section.getType() != ELF::SHT_GROUP)
continue;
SectionIndexMap[&Section] = Index++;
}
for (MCAssembler::iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
const MCSectionELF &Section =
static_cast<const MCSectionELF &>(it->getSection());
if (Section.getType() == ELF::SHT_GROUP ||
Section.getType() == ELF::SHT_REL ||
Section.getType() == ELF::SHT_RELA)
continue;
SectionIndexMap[&Section] = Index++;
const MCSectionELF *RelSection = RelMap.lookup(&Section);
if (RelSection)
SectionIndexMap[RelSection] = Index++;
}
}
void
ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
const SectionIndexMapTy &SectionIndexMap,
const RevGroupMapTy &RevGroupMap,
unsigned NumRegularSections) {
// FIXME: Is this the correct place to do this?
// FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
if (NeedsGOT) {
StringRef Name = "_GLOBAL_OFFSET_TABLE_";
MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
Data.setExternal(true);
MCELF::SetBinding(Data, ELF::STB_GLOBAL);
}
// Add the data for the symbols.
for (MCSymbolData &SD : Asm.symbols()) {
const MCSymbol &Symbol = SD.getSymbol();
bool Used = UsedInReloc.count(&Symbol);
bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
bool isSignature = RevGroupMap.count(&Symbol);
if (!isInSymtab(Layout, SD,
Used || WeakrefUsed || isSignature,
Renames.count(&Symbol)))
continue;
ELFSymbolData MSD;
MSD.SymbolData = &SD;
const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
// Undefined symbols are global, but this is the first place we
// are able to set it.
bool Local = isLocal(SD, Used);
if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
assert(BaseSymbol);
MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
MCELF::SetBinding(SD, ELF::STB_GLOBAL);
MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
}
if (!BaseSymbol) {
MSD.SectionIndex = ELF::SHN_ABS;
} else if (SD.isCommon()) {
assert(!Local);
MSD.SectionIndex = ELF::SHN_COMMON;
} else if (BaseSymbol->isUndefined()) {
if (isSignature && !Used)
MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap.lookup(&Symbol));
else
MSD.SectionIndex = ELF::SHN_UNDEF;
if (!Used && WeakrefUsed)
MCELF::SetBinding(SD, ELF::STB_WEAK);
} else {
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(BaseSymbol->getSection());
MSD.SectionIndex = SectionIndexMap.lookup(&Section);
assert(MSD.SectionIndex && "Invalid section index!");
}
// The @@@ in symbol version is replaced with @ in undefined symbols and @@
// in defined ones.
//
// FIXME: All name handling should be done before we get to the writer,
// including dealing with GNU-style version suffixes. Fixing this isn’t
// trivial.
//
// We thus have to be careful to not perform the symbol version replacement
// blindly:
//
// The ELF format is used on Windows by the MCJIT engine. Thus, on
// Windows, the ELFObjectWriter can encounter symbols mangled using the MS
// Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
// C++ name mangling can legally have "@@@" as a sub-string. In that case,
// the EFLObjectWriter should not interpret the "@@@" sub-string as
// specifying GNU-style symbol versioning. The ELFObjectWriter therefore
// checks for the MSVC C++ name mangling prefix which is either "?", "@?",
// "__imp_?" or "__imp_@?".
//
// It would have been interesting to perform the MS mangling prefix check
// only when the target triple is of the form *-pc-windows-elf. But, it
// seems that this information is not easily accessible from the
// ELFObjectWriter.
StringRef Name = Symbol.getName();
if (!Name.startswith("?") && !Name.startswith("@?") &&
!Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
// This symbol isn't following the MSVC C++ name mangling convention. We
// can thus safely interpret the @@@ in symbol names as specifying symbol
// versioning.
SmallString<32> Buf;
size_t Pos = Name.find("@@@");
if (Pos != StringRef::npos) {
Buf += Name.substr(0, Pos);
unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
Buf += Name.substr(Pos + Skip);
Name = Buf;
}
}
// Sections have their own string table
if (MCELF::GetType(SD) != ELF::STT_SECTION)
MSD.Name = StrTabBuilder.add(Name);
if (MSD.SectionIndex == ELF::SHN_UNDEF)
UndefinedSymbolData.push_back(MSD);
else if (Local)
LocalSymbolData.push_back(MSD);
else
ExternalSymbolData.push_back(MSD);
}
for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
StrTabBuilder.add(*i);
StrTabBuilder.finalize(StringTableBuilder::ELF);
for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
for (ELFSymbolData &MSD : LocalSymbolData)
MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
? 0
: StrTabBuilder.getOffset(MSD.Name);
for (ELFSymbolData &MSD : ExternalSymbolData)
MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
for (ELFSymbolData& MSD : UndefinedSymbolData)
MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
// 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.
unsigned Index = FileSymbolData.size() + 1;
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 ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm,
MCAsmLayout &Layout,
RelMapTy &RelMap) {
for (MCAssembler::const_iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
const MCSectionData &SD = *it;
if (Relocations[&SD].empty())
continue;
MCContext &Ctx = Asm.getContext();
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);
unsigned Flags = 0;
StringRef Group = "";
if (Section.getFlags() & ELF::SHF_GROUP) {
Flags = ELF::SHF_GROUP;
Group = Section.getGroup()->getName();
}
const MCSectionELF *RelaSection =
Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ?
ELF::SHT_RELA : ELF::SHT_REL, Flags,
EntrySize, Group);
RelMap[&Section] = RelaSection;
Asm.getOrCreateSectionData(*RelaSection);
}
}
static SmallVector<char, 128>
getUncompressedData(MCAsmLayout &Layout,
MCSectionData::FragmentListType &Fragments) {
SmallVector<char, 128> UncompressedData;
for (const MCFragment &F : Fragments) {
const SmallVectorImpl<char> *Contents;
switch (F.getKind()) {
case MCFragment::FT_Data:
Contents = &cast<MCDataFragment>(F).getContents();
break;
case MCFragment::FT_Dwarf:
Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
break;
case MCFragment::FT_DwarfFrame:
Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
break;
default:
llvm_unreachable(
"Not expecting any other fragment types in a debug_* section");
}
UncompressedData.append(Contents->begin(), Contents->end());
}
return UncompressedData;
}
// Include the debug info compression header:
// "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
// useful for consumers to preallocate a buffer to decompress into.
static bool
prependCompressionHeader(uint64_t Size,
SmallVectorImpl<char> &CompressedContents) {
static const StringRef Magic = "ZLIB";
if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
return false;
if (sys::IsLittleEndianHost)
sys::swapByteOrder(Size);
CompressedContents.insert(CompressedContents.begin(),
Magic.size() + sizeof(Size), 0);
std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
std::copy(reinterpret_cast<char *>(&Size),
reinterpret_cast<char *>(&Size + 1),
CompressedContents.begin() + Magic.size());
return true;
}
// Return a single fragment containing the compressed contents of the whole
// section. Null if the section was not compressed for any reason.
static std::unique_ptr<MCDataFragment>
getCompressedFragment(MCAsmLayout &Layout,
MCSectionData::FragmentListType &Fragments) {
std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
// Gather the uncompressed data from all the fragments, recording the
// alignment fragment, if seen, and any fixups.
SmallVector<char, 128> UncompressedData =
getUncompressedData(Layout, Fragments);
SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
zlib::Status Success = zlib::compress(
StringRef(UncompressedData.data(), UncompressedData.size()),
CompressedContents);
if (Success != zlib::StatusOK)
return nullptr;
if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
return nullptr;
return CompressedFragment;
}
typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
DefiningSymbolMap;
static void UpdateSymbols(const MCAsmLayout &Layout,
const std::vector<MCSymbolData *> &Symbols,
MCFragment &NewFragment) {
for (MCSymbolData *Sym : Symbols) {
Sym->setOffset(Sym->getOffset() +
Layout.getFragmentOffset(Sym->getFragment()));
Sym->setFragment(&NewFragment);
}
}
static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
const DefiningSymbolMap &DefiningSymbols,
const MCSectionELF &Section,
MCSectionData &SD) {
StringRef SectionName = Section.getSectionName();
MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
std::unique_ptr<MCDataFragment> CompressedFragment =
getCompressedFragment(Layout, Fragments);
// Leave the section as-is if the fragments could not be compressed.
if (!CompressedFragment)
return;
// Update the fragment+offsets of any symbols referring to fragments in this
// section to refer to the new fragment.
auto I = DefiningSymbols.find(&SD);
if (I != DefiningSymbols.end())
UpdateSymbols(Layout, I->second, *CompressedFragment);
// Invalidate the layout for the whole section since it will have new and
// different fragments now.
Layout.invalidateFragmentsFrom(&Fragments.front());
Fragments.clear();
// Complete the initialization of the new fragment
CompressedFragment->setParent(&SD);
CompressedFragment->setLayoutOrder(0);
Fragments.push_back(CompressedFragment.release());
// Rename from .debug_* to .zdebug_*
Asm.getContext().renameELFSection(&Section,
(".z" + SectionName.drop_front(1)).str());
}
void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
MCAsmLayout &Layout) {
if (!Asm.getContext().getAsmInfo()->compressDebugSections())
return;
DefiningSymbolMap DefiningSymbols;
for (MCSymbolData &SD : Asm.symbols())
if (MCFragment *F = SD.getFragment())
DefiningSymbols[F->getParent()].push_back(&SD);
for (MCSectionData &SD : Asm) {
const MCSectionELF &Section =
static_cast<const MCSectionELF &>(SD.getSection());
StringRef SectionName = Section.getSectionName();
// Compressing debug_frame requires handling alignment fragments which is
// more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
// for writing to arbitrary buffers) for little benefit.
if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
continue;
CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
}
}
void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
const RelMapTy &RelMap) {
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());
const MCSectionELF *RelaSection = RelMap.lookup(&Section);
if (!RelaSection)
continue;
MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
RelaSD.setAlignment(is64Bit() ? 8 : 4);
MCDataFragment *F = new MCDataFragment(&RelaSD);
WriteRelocationsFragment(Asm, F, &*it);
}
}
void ELFObjectWriter::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
}
// ELF doesn't require relocations to be in any order. We sort by the r_offset,
// just to match gnu as for easier comparison. The use type is an arbitrary way
// of making the sort deterministic.
static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
const ELFRelocationEntry &A = *AP;
const ELFRelocationEntry &B = *BP;
if (A.Offset != B.Offset)
return B.Offset - A.Offset;
if (B.Type != A.Type)
return A.Type - B.Type;
llvm_unreachable("ELFRelocs might be unstable!");
}
static void sortRelocs(const MCAssembler &Asm,
std::vector<ELFRelocationEntry> &Relocs) {
array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
}
void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
MCDataFragment *F,
const MCSectionData *SD) {
std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
sortRelocs(Asm, Relocs);
for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
const ELFRelocationEntry &Entry = Relocs[e - i - 1];
unsigned Index =
Entry.Symbol ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 0;
if (is64Bit()) {
write(*F, Entry.Offset);
if (TargetObjectWriter->isN64()) {
write(*F, uint32_t(Index));
write(*F, TargetObjectWriter->getRSsym(Entry.Type));
write(*F, TargetObjectWriter->getRType3(Entry.Type));
write(*F, TargetObjectWriter->getRType2(Entry.Type));
write(*F, TargetObjectWriter->getRType(Entry.Type));
} else {
struct ELF::Elf64_Rela ERE64;
ERE64.setSymbolAndType(Index, Entry.Type);
write(*F, ERE64.r_info);
}
if (hasRelocationAddend())
write(*F, Entry.Addend);
} else {
write(*F, uint32_t(Entry.Offset));
struct ELF::Elf32_Rela ERE32;
ERE32.setSymbolAndType(Index, Entry.Type);
write(*F, ERE32.r_info);
if (hasRelocationAddend())
write(*F, uint32_t(Entry.Addend));
}
}
}
void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
MCAsmLayout &Layout,
SectionIndexMapTy &SectionIndexMap,
const RelMapTy &RelMap) {
MCContext &Ctx = Asm.getContext();
MCDataFragment *F;
unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
// We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
const MCSectionELF *ShstrtabSection =
Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
ShstrtabSD.setAlignment(1);
const MCSectionELF *SymtabSection =
Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
EntrySize, "");
MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
SymtabSD.setAlignment(is64Bit() ? 8 : 4);
const MCSectionELF *StrtabSection;
StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
StrtabSD.setAlignment(1);
ComputeIndexMap(Asm, SectionIndexMap, RelMap);
ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection);
SymbolTableIndex = SectionIndexMap.lookup(SymtabSection);
StringTableIndex = SectionIndexMap.lookup(StrtabSection);
// Symbol table
F = new MCDataFragment(&SymtabSD);
WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
F = new MCDataFragment(&StrtabSD);
F->getContents().append(StrTabBuilder.data().begin(),
StrTabBuilder.data().end());
F = new MCDataFragment(&ShstrtabSD);
// Section header string table.
for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(it->getSection());
ShStrTabBuilder.add(Section.getSectionName());
}
ShStrTabBuilder.finalize(StringTableBuilder::ELF);
F->getContents().append(ShStrTabBuilder.data().begin(),
ShStrTabBuilder.data().end());
}
void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
MCAsmLayout &Layout,
GroupMapTy &GroupMap,
RevGroupMapTy &RevGroupMap,
SectionIndexMapTy &SectionIndexMap,
const RelMapTy &RelMap) {
MCContext &Ctx = Asm.getContext();
// Build the groups
for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
it != ie; ++it) {
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(it->getSection());
if (!(Section.getFlags() & ELF::SHF_GROUP))
continue;
const MCSymbol *SignatureSymbol = Section.getGroup();
Asm.getOrCreateSymbolData(*SignatureSymbol);
const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
if (!Group) {
Group = Ctx.CreateELFGroupSection();
MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
Data.setAlignment(4);
MCDataFragment *F = new MCDataFragment(&Data);
write(*F, uint32_t(ELF::GRP_COMDAT));
}
GroupMap[Group] = SignatureSymbol;
}
ComputeIndexMap(Asm, SectionIndexMap, RelMap);
// Add sections to the groups
for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
it != ie; ++it) {
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(it->getSection());
if (!(Section.getFlags() & ELF::SHF_GROUP))
continue;
const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
// FIXME: we could use the previous fragment
MCDataFragment *F = new MCDataFragment(&Data);
uint32_t Index = SectionIndexMap.lookup(&Section);
write(*F, Index);
}
}
void ELFObjectWriter::WriteSection(MCAssembler &Asm,
const SectionIndexMapTy &SectionIndexMap,
uint32_t GroupSymbolIndex,
uint64_t Offset, uint64_t Size,
uint64_t Alignment,
const MCSectionELF &Section) {
uint64_t sh_link = 0;
uint64_t sh_info = 0;
switch(Section.getType()) {
case ELF::SHT_DYNAMIC:
sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
sh_info = 0;
break;
case ELF::SHT_REL:
case ELF::SHT_RELA: {
const MCSectionELF *SymtabSection;
const MCSectionELF *InfoSection;
SymtabSection =
Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 0);
sh_link = SectionIndexMap.lookup(SymtabSection);
assert(sh_link && ".symtab not found");
// Remove ".rel" and ".rela" prefixes.
unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
StringRef SectionName = Section.getSectionName().substr(SecNameLen);
StringRef GroupName =
Section.getGroup() ? Section.getGroup()->getName() : "";
InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS,
0, 0, GroupName);
sh_info = SectionIndexMap.lookup(InfoSection);
break;
}
case ELF::SHT_SYMTAB:
case ELF::SHT_DYNSYM:
sh_link = StringTableIndex;
sh_info = LastLocalSymbolIndex;
break;
case ELF::SHT_SYMTAB_SHNDX:
sh_link = SymbolTableIndex;
break;
case ELF::SHT_PROGBITS:
case ELF::SHT_STRTAB:
case ELF::SHT_NOBITS:
case ELF::SHT_NOTE:
case ELF::SHT_NULL:
case ELF::SHT_ARM_ATTRIBUTES:
case ELF::SHT_INIT_ARRAY:
case ELF::SHT_FINI_ARRAY:
case ELF::SHT_PREINIT_ARRAY:
case ELF::SHT_X86_64_UNWIND:
case ELF::SHT_MIPS_REGINFO:
case ELF::SHT_MIPS_OPTIONS:
case ELF::SHT_MIPS_ABIFLAGS:
// Nothing to do.
break;
case ELF::SHT_GROUP:
sh_link = SymbolTableIndex;
sh_info = GroupSymbolIndex;
break;
default:
llvm_unreachable("FIXME: sh_type value not supported!");
}
if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
Section.getType() == ELF::SHT_ARM_EXIDX) {
StringRef SecName(Section.getSectionName());
if (SecName == ".ARM.exidx") {
sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
".text", ELF::SHT_PROGBITS, ELF::SHF_EXECINSTR | ELF::SHF_ALLOC));
} else if (SecName.startswith(".ARM.exidx")) {
StringRef GroupName =
Section.getGroup() ? Section.getGroup()->getName() : "";
sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS,
ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, 0, GroupName));
}
}
WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
Section.getType(),
Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
Alignment, Section.getEntrySize());
}
bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
return SD.getOrdinal() == ~UINT32_C(0) &&
!SD.getSection().isVirtualSection();
}
uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
uint64_t Ret = 0;
for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
++i) {
const MCFragment &F = *i;
assert(F.getKind() == MCFragment::FT_Data);
Ret += cast<MCDataFragment>(F).getContents().size();
}
return Ret;
}
uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
const MCSectionData &SD) {
if (IsELFMetaDataSection(SD))
return DataSectionSize(SD);
return Layout.getSectionFileSize(&SD);
}
uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
const MCSectionData &SD) {
if (IsELFMetaDataSection(SD))
return DataSectionSize(SD);
return Layout.getSectionAddressSize(&SD);
}
void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCSectionELF &Section) {
const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
WriteZeros(Padding);
if (IsELFMetaDataSection(SD)) {
for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
++i) {
const MCFragment &F = *i;
assert(F.getKind() == MCFragment::FT_Data);
WriteBytes(cast<MCDataFragment>(F).getContents());
}
} else {
Asm.writeSectionData(&SD, Layout);
}
}
void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm,
const GroupMapTy &GroupMap,
const MCAsmLayout &Layout,
const SectionIndexMapTy &SectionIndexMap,
const SectionOffsetMapTy &SectionOffsetMap) {
const unsigned NumSections = Asm.size() + 1;
std::vector<const MCSectionELF*> Sections;
Sections.resize(NumSections - 1);
for (SectionIndexMapTy::const_iterator i=
SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
const std::pair<const MCSectionELF*, uint32_t> &p = *i;
Sections[p.second - 1] = p.first;
}
// Null section first.
uint64_t FirstSectionSize =
NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
uint32_t FirstSectionLink =
ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
for (unsigned i = 0; i < NumSections - 1; ++i) {
const MCSectionELF &Section = *Sections[i];
const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
uint32_t GroupSymbolIndex;
if (Section.getType() != ELF::SHT_GROUP)
GroupSymbolIndex = 0;
else
GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
GroupMap.lookup(&Section));
uint64_t Size = GetSectionAddressSize(Layout, SD);
WriteSection(Asm, SectionIndexMap, GroupSymbolIndex,
SectionOffsetMap.lookup(&Section), Size,
SD.getAlignment(), Section);
}
}
void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
std::vector<const MCSectionELF*> &Sections) {
for (MCAssembler::iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
const MCSectionELF &Section =
static_cast<const MCSectionELF &>(it->getSection());
if (Section.getType() == ELF::SHT_GROUP)
Sections.push_back(&Section);
}
for (MCAssembler::iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
const MCSectionELF &Section =
static_cast<const MCSectionELF &>(it->getSection());
if (Section.getType() != ELF::SHT_GROUP &&
Section.getType() != ELF::SHT_REL &&
Section.getType() != ELF::SHT_RELA)
Sections.push_back(&Section);
}
for (MCAssembler::iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
const MCSectionELF &Section =
static_cast<const MCSectionELF &>(it->getSection());
if (Section.getType() == ELF::SHT_REL ||
Section.getType() == ELF::SHT_RELA)
Sections.push_back(&Section);
}
}
void ELFObjectWriter::WriteObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
GroupMapTy GroupMap;
RevGroupMapTy RevGroupMap;
SectionIndexMapTy SectionIndexMap;
unsigned NumUserSections = Asm.size();
CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
const unsigned NumUserAndRelocSections = Asm.size();
CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
RevGroupMap, SectionIndexMap, RelMap);
const unsigned AllSections = Asm.size();
const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
unsigned NumRegularSections = NumUserSections + NumIndexedSections;
// Compute symbol table information.
computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
NumRegularSections);
WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
CreateMetadataSections(const_cast<MCAssembler&>(Asm),
const_cast<MCAsmLayout&>(Layout),
SectionIndexMap,
RelMap);
uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
sizeof(ELF::Elf32_Ehdr);
uint64_t FileOff = HeaderSize;
std::vector<const MCSectionELF*> Sections;
ComputeSectionOrder(Asm, Sections);
unsigned NumSections = Sections.size();
SectionOffsetMapTy SectionOffsetMap;
for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
const MCSectionELF &Section = *Sections[i];
const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
// Remember the offset into the file for this section.
SectionOffsetMap[&Section] = FileOff;
// Get the size of the section in the output file (including padding).
FileOff += GetSectionFileSize(Layout, SD);
}
FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
const unsigned SectionHeaderOffset = FileOff - HeaderSize;
uint64_t SectionHeaderEntrySize = is64Bit() ?
sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
FileOff += (NumSections + 1) * SectionHeaderEntrySize;
for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
const MCSectionELF &Section = *Sections[i];
const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
// Remember the offset into the file for this section.
SectionOffsetMap[&Section] = FileOff;
// Get the size of the section in the output file (including padding).
FileOff += GetSectionFileSize(Layout, SD);
}
// Write out the ELF header ...
WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
// ... then the regular sections ...
// + because of .shstrtab
for (unsigned i = 0; i < NumRegularSections + 1; ++i)
WriteDataSectionData(Asm, Layout, *Sections[i]);
uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
WriteZeros(Padding);
// ... then the section header table ...
WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap,
SectionOffsetMap);
// ... and then the remaining sections ...
for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
WriteDataSectionData(Asm, Layout, *Sections[i]);
}
bool
ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
const MCSymbolData &DataA,
const MCFragment &FB,
bool InSet,
bool IsPCRel) const {
if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC)
return false;
return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
Asm, DataA, FB,InSet, IsPCRel);
}
MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
raw_ostream &OS,
bool IsLittleEndian) {
return new ELFObjectWriter(MOTW, OS, IsLittleEndian);
}
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