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On ELF we need to know which symbols are used in relocations to decide if

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they should be in the symbol table or not. Instead of "guessing", just compute
the symbol table after the relocations are known.

llvm-svn: 115619
This commit is contained in:
Rafael Espindola 2010-10-05 15:11:03 +00:00
parent 9e6ce12abf
commit 5f53528867
7 changed files with 50 additions and 80 deletions
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2
include/llvm/MC/ELFObjectWriter.h
View File

@ -44,7 +44,7 @@ public:
bool IsPCRel,
const MCFragment *DF) const;
virtual void WriteObject(const MCAssembler &Asm, const MCAsmLayout &Layout);
virtual void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout);
};
} // End llvm namespace

2
include/llvm/MC/MCObjectWriter.h
View File

@ -90,7 +90,7 @@ public:
/// This routine is called by the assembler after layout and relaxation is
/// complete, fixups have been evaluated and applied, and relocations
/// generated.
virtual void WriteObject(const MCAssembler &Asm,
virtual void WriteObject(MCAssembler &Asm,
const MCAsmLayout &Layout) = 0;
/// @}

2
include/llvm/MC/MachObjectWriter.h
View File

@ -41,7 +41,7 @@ public:
bool IsPCRel,
const MCFragment *DF) const;
virtual void WriteObject(const MCAssembler &Asm, const MCAsmLayout &Layout);
virtual void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout);
};
} // End llvm namespace

67
lib/MC/ELFObjectWriter.cpp
View File

@ -12,6 +12,7 @@
//===----------------------------------------------------------------------===//
#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"
@ -102,7 +103,9 @@ namespace {
struct ELFRelocationEntry {
// Make these big enough for both 32-bit and 64-bit
uint64_t r_offset;
uint64_t r_info;
int Index;
unsigned Type;
const MCSymbol *Symbol;
uint64_t r_addend;
// Support lexicographic sorting.
@ -111,6 +114,8 @@ namespace {
}
};
SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
llvm::DenseMap<const MCSectionData*,
std::vector<ELFRelocationEntry> > Relocations;
DenseMap<const MCSection*, uint64_t> SectionStringTableIndex;
@ -126,6 +131,8 @@ namespace {
/// @}
int NumRegularSections;
ELFObjectWriter *Writer;
raw_ostream &OS;
@ -262,8 +269,6 @@ namespace {
void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout);
void ExecutePostLayoutBinding(MCAssembler &Asm) {
// Compute symbol table information.
ComputeSymbolTable(Asm);
}
void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
@ -279,7 +284,7 @@ namespace {
bool IsPCRel,
const MCFragment *DF) const;
void WriteObject(const MCAssembler &Asm, const MCAsmLayout &Layout);
void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout);
};
}
@ -526,12 +531,13 @@ void ELFObjectWriterImpl::RecordRelocation(const MCAssembler &Asm,
MCValue Target,
uint64_t &FixedValue) {
int64_t Addend = 0;
unsigned Index = 0;
int Index = 0;
int64_t Value = Target.getConstant();
const MCSymbol *Symbol = 0;
bool IsPCRel = isFixupKindX86PCRel(Fixup.getKind());
if (!Target.isAbsolute()) {
const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
Symbol = &Target.getSymA()->getSymbol();
MCSymbolData &SD = Asm.getSymbolData(*Symbol);
MCFragment *F = SD.getFragment();
@ -560,13 +566,15 @@ void ELFObjectWriterImpl::RecordRelocation(const MCAssembler &Asm,
bool RelocOnSymbol = ShouldRelocOnSymbol(SD, Target);
if (!RelocOnSymbol) {
Index = F->getParent()->getOrdinal() + LocalSymbolData.size() + 1;
Index = F->getParent()->getOrdinal();
MCSectionData *FSD = F->getParent();
// Offset of the symbol in the section
Value += Layout.getSymbolAddress(&SD) - Layout.getSectionAddress(FSD);
} else
Index = getSymbolIndexInSymbolTable(Asm, Symbol);
} else {
UsedInReloc.insert(Symbol);
Index = -1;
}
Addend = Value;
// Compensate for the addend on i386.
if (Is64Bit)
@ -641,15 +649,9 @@ void ELFObjectWriterImpl::RecordRelocation(const MCAssembler &Asm,
ELFRelocationEntry ERE;
if (Is64Bit) {
struct ELF::Elf64_Rela ERE64;
ERE64.setSymbolAndType(Index, Type);
ERE.r_info = ERE64.r_info;
} else {
struct ELF::Elf32_Rela ERE32;
ERE32.setSymbolAndType(Index, Type);
ERE.r_info = ERE32.r_info;
}
ERE.Index = Index;
ERE.Type = Type;
ERE.Symbol = Symbol;
ERE.r_offset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
@ -671,11 +673,12 @@ ELFObjectWriterImpl::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
return SD.getIndex() + /* empty symbol */ 1;
// External or undefined symbol.
return SD.getIndex() + Asm.size() + /* empty symbol */ 1;
return SD.getIndex() + NumRegularSections + /* empty symbol */ 1;
}
void ELFObjectWriterImpl::ComputeSymbolTable(MCAssembler &Asm) {
// Build section lookup table.
NumRegularSections = Asm.size();
DenseMap<const MCSection*, uint8_t> SectionIndexMap;
unsigned Index = 1;
for (MCAssembler::iterator it = Asm.begin(),
@ -698,6 +701,9 @@ void ELFObjectWriterImpl::ComputeSymbolTable(MCAssembler &Asm) {
if (it->isExternal() || Symbol.isUndefined())
continue;
if (Symbol.isTemporary() && !UsedInReloc.count(&Symbol))
continue;
uint64_t &Entry = StringIndexMap[Symbol.getName()];
if (!Entry) {
Entry = StringTable.size();
@ -734,6 +740,10 @@ void ELFObjectWriterImpl::ComputeSymbolTable(MCAssembler &Asm) {
if (Symbol.isVariable())
continue;
if (Symbol.isUndefined() && !UsedInReloc.count(&Symbol)
&& Symbol.isTemporary())
continue;
uint64_t &Entry = StringIndexMap[Symbol.getName()];
if (!Entry) {
Entry = StringTable.size();
@ -843,13 +853,19 @@ void ELFObjectWriterImpl::WriteRelocationsFragment(const MCAssembler &Asm,
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);
String64(buf, entry.r_info);
struct ELF::Elf64_Rela ERE64;
ERE64.setSymbolAndType(entry.Index, entry.Type);
String64(buf, ERE64.r_info);
F->getContents() += StringRef(buf, 8);
if (HasRelocationAddend) {
@ -862,7 +878,9 @@ void ELFObjectWriterImpl::WriteRelocationsFragment(const MCAssembler &Asm,
String32(buf, entry.r_offset);
F->getContents() += StringRef(buf, 4);
String32(buf, entry.r_info);
struct ELF::Elf32_Rela ERE32;
ERE32.setSymbolAndType(entry.Index, entry.Type);
String32(buf, ERE32.r_info);
F->getContents() += StringRef(buf, 4);
if (HasRelocationAddend) {
@ -976,8 +994,11 @@ bool ELFObjectWriterImpl::IsFixupFullyResolved(const MCAssembler &Asm,
return !SectionB && BaseSection == SectionA;
}
void ELFObjectWriterImpl::WriteObject(const MCAssembler &Asm,
void ELFObjectWriterImpl::WriteObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
// Compute symbol table information.
ComputeSymbolTable(Asm);
CreateMetadataSections(const_cast<MCAssembler&>(Asm),
const_cast<MCAsmLayout&>(Layout));
@ -1142,7 +1163,7 @@ bool ELFObjectWriter::IsFixupFullyResolved(const MCAssembler &Asm,
IsPCRel, DF);
}
void ELFObjectWriter::WriteObject(const MCAssembler &Asm,
void ELFObjectWriter::WriteObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
((ELFObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);
}

51
lib/MC/MCELFStreamer.cpp
View File

@ -156,22 +156,6 @@ void MCELFStreamer::InitSections() {
SetSectionText();
}
static bool isSymbolLinkerVisible(const MCAssembler &Asm,
const MCSymbolData &Data) {
const MCSymbol &Symbol = Data.getSymbol();
// Absolute temporary labels are never visible.
if (!Symbol.isInSection())
return false;
if (Asm.getBackend().doesSectionRequireSymbols(Symbol.getSection()))
return true;
if (!Data.isExternal())
return false;
return Asm.isSymbolLinkerVisible(Symbol);
}
void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
@ -179,11 +163,6 @@ void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
// We have to create a new fragment if this is an atom defining symbol,
// fragments cannot span atoms.
if (isSymbolLinkerVisible(getAssembler(), SD))
new MCDataFragment(getCurrentSectionData());
// FIXME: This is wasteful, we don't necessarily need to create a data
// fragment. Instead, we should mark the symbol as pointing into the data
// fragment if it exists, otherwise we should just queue the label and set its
@ -520,36 +499,6 @@ void MCELFStreamer::Finish() {
SectData.setAlignment(ByteAlignment);
}
// FIXME: We create more atoms than it is necessary. Some relocations to
// merge sections can be implemented with section address + offset,
// figure out which ones and why.
// First, scan the symbol table to build a lookup table from fragments to
// defining symbols.
DenseMap<const MCFragment*, MCSymbolData*> DefiningSymbolMap;
for (MCAssembler::symbol_iterator it = getAssembler().symbol_begin(),
ie = getAssembler().symbol_end(); it != ie; ++it) {
if (isSymbolLinkerVisible(getAssembler(), *it) &&
it->getFragment()) {
// An atom defining symbol should never be internal to a fragment.
assert(it->getOffset() == 0 && "Invalid offset in atom defining symbol!");
DefiningSymbolMap[it->getFragment()] = it;
}
}
// Set the fragment atom associations by tracking the last seen atom defining
// symbol.
for (MCAssembler::iterator it = getAssembler().begin(),
ie = getAssembler().end(); it != ie; ++it) {
MCSymbolData *CurrentAtom = 0;
for (MCSectionData::iterator it2 = it->begin(),
ie2 = it->end(); it2 != ie2; ++it2) {
if (MCSymbolData *SD = DefiningSymbolMap.lookup(it2))
CurrentAtom = SD;
it2->setAtom(CurrentAtom);
}
}
this->MCObjectStreamer::Finish();
}

2
lib/MC/MachObjectWriter.cpp
View File

@ -1360,7 +1360,7 @@ bool MachObjectWriter::IsFixupFullyResolved(const MCAssembler &Asm,
IsPCRel, DF);
}
void MachObjectWriter::WriteObject(const MCAssembler &Asm,
void MachObjectWriter::WriteObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
((MachObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);
}

4
lib/MC/WinCOFFObjectWriter.cpp
View File

@ -186,7 +186,7 @@ public:
bool IsPCRel,
const MCFragment *DF) const;
void WriteObject(const MCAssembler &Asm, const MCAsmLayout &Layout);
void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout);
};
}
@ -703,7 +703,7 @@ bool WinCOFFObjectWriter::IsFixupFullyResolved(const MCAssembler &Asm,
return false;
}
void WinCOFFObjectWriter::WriteObject(const MCAssembler &Asm,
void WinCOFFObjectWriter::WriteObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
// Assign symbol and section indexes and offsets.
Header.NumberOfSections = 0;