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For PC relative relocations where symbols are defined in the same section they

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are referenced, ignore the relocation entry and patch the relocatable field with
the computed symbol offset directly


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76414 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bruno Cardoso Lopes 2009-07-20 08:52:02 +00:00
parent 1488670076
commit 0a38dc5fda
5 changed files with 114 additions and 43 deletions
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13
include/llvm/Target/TargetELFWriterInfo.h
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@ -105,16 +105,25 @@ namespace llvm {
/// ELF relocation entry.
virtual bool hasRelocationAddend() const = 0;
/// getAddendForRelTy - Gets the addend value for an ELF relocation entry
/// based on the target relocation type. If addend is not used returns 0.
/// getDefaultAddendForRelTy - Gets the default addend value for a
/// relocation entry based on the target ELF relocation type.
virtual long int getDefaultAddendForRelTy(unsigned RelTy) const = 0;
/// getRelTySize - Returns the size of relocatable field in bits
virtual unsigned getRelocationTySize(unsigned RelTy) const = 0;
/// isPCRelativeRel - True if the relocation type is pc relative
virtual bool isPCRelativeRel(unsigned RelTy) const = 0;
/// getJumpTableRelocationTy - Returns the machine relocation type used
/// to reference a jumptable.
virtual unsigned getAbsoluteLabelMachineRelTy() const = 0;
/// computeRelocation - Some relocatable fields could be relocated
/// directly, avoiding the emission of a relocation symbol, compute the
/// final relocation value for this symbol.
virtual long int computeRelocation(unsigned SymOffset, unsigned RelOffset,
unsigned RelTy) const = 0;
};
} // end llvm namespace

80
lib/CodeGen/ELFWriter.cpp
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@ -145,7 +145,7 @@ bool ELFWriter::doInitialization(Module &M) {
return false;
}
/// Get jump table section on the section name returned by TAI
// Get jump table section on the section name returned by TAI
ELFSection &ELFWriter::getJumpTableSection() {
unsigned Align = TM.getTargetData()->getPointerABIAlignment();
return getSection(TAI->getJumpTableDataSection(),
@ -153,7 +153,7 @@ ELFSection &ELFWriter::getJumpTableSection() {
ELFSection::SHF_ALLOC, Align);
}
/// Get a constant pool section based on the section name returned by TAI
// Get a constant pool section based on the section name returned by TAI
ELFSection &ELFWriter::getConstantPoolSection(MachineConstantPoolEntry &CPE) {
std::string CstPoolName =
TAI->SelectSectionForMachineConst(CPE.getType())->getName();
@ -163,6 +163,19 @@ ELFSection &ELFWriter::getConstantPoolSection(MachineConstantPoolEntry &CPE) {
CPE.getAlignment());
}
// Return the relocation section of section 'S'. 'RelA' is true
// if the relocation section contains entries with addends.
ELFSection &ELFWriter::getRelocSection(ELFSection &S) {
unsigned SectionHeaderTy = TEW->hasRelocationAddend() ?
ELFSection::SHT_RELA : ELFSection::SHT_REL;
std::string RelSName(".rel");
if (TEW->hasRelocationAddend())
RelSName.append("a");
RelSName.append(S.getName());
return getSection(RelSName, SectionHeaderTy, 0, TEW->getPrefELFAlignment());
}
// getGlobalELFVisibility - Returns the ELF specific visibility type
unsigned ELFWriter::getGlobalELFVisibility(const GlobalValue *GV) {
switch (GV->getVisibility()) {
@ -474,20 +487,32 @@ bool ELFWriter::doFinalization(Module &M) {
return false;
}
// RelocateField - Patch relocatable field with 'Offset' in 'BO'
// using a 'Value' of known 'Size'
void ELFWriter::RelocateField(BinaryObject &BO, uint32_t Offset,
int64_t Value, unsigned Size) {
if (Size == 32)
BO.fixWord32(Value, Offset);
else if (Size == 64)
BO.fixWord64(Value, Offset);
else
llvm_unreachable("don't know howto patch relocatable field");
}
/// EmitRelocations - Emit relocations
void ELFWriter::EmitRelocations() {
// True if the target uses the relocation entry to hold the addend,
// otherwise the addend is written directly to the relocatable field.
bool HasRelA = TEW->hasRelocationAddend();
// Create Relocation sections for each section which needs it.
for (unsigned i=0, e=SectionList.size(); i != e; ++i) {
ELFSection &S = *SectionList[i];
// This section does not have relocations
if (!S.hasRelocations()) continue;
// Get the relocation section for section 'S'
bool HasRelA = TEW->hasRelocationAddend();
ELFSection &RelSec = getRelocSection(S.getName(), HasRelA,
TEW->getPrefELFAlignment());
ELFSection &RelSec = getRelocSection(S);
// 'Link' - Section hdr idx of the associated symbol table
// 'Info' - Section hdr idx of the section to which the relocation applies
@ -502,18 +527,15 @@ void ELFWriter::EmitRelocations() {
MRE = Relos.end(); MRI != MRE; ++MRI) {
MachineRelocation &MR = *MRI;
// Holds the relocatable field address as an offset from the
// beginning of the section where it lives
unsigned Offset = MR.getMachineCodeOffset();
// Relocatable field offset from the section start
unsigned RelOffset = MR.getMachineCodeOffset();
// Symbol index in the symbol table
unsigned SymIdx = 0;
// Target specific ELF relocation type
// Target specific relocation field type and size
unsigned RelType = TEW->getRelocationType(MR.getRelocationType());
// Constant addend used to compute the value to be stored
// into the relocatable field
unsigned RelTySize = TEW->getRelocationTySize(RelType);
int64_t Addend = 0;
// There are several machine relocations types, and each one of
@ -533,29 +555,33 @@ void ELFWriter::EmitRelocations() {
} else {
// Get the symbol index for the section symbol
unsigned SectionIdx = MR.getConstantVal();
SymIdx = SectionList[SectionIdx]->getSymbolTableIndex();
Addend = (uint64_t)MR.getResultPointer();
// For pc relative relocations where symbols are defined in the same
// section they are referenced, ignore the relocation entry and patch
// the relocatable field with the symbol offset directly.
if (S.SectionIdx == SectionIdx && TEW->isPCRelativeRel(RelType)) {
int64_t Value = TEW->computeRelocation(Addend, RelOffset, RelType);
RelocateField(S, RelOffset, Value, RelTySize);
continue;
}
// Handle Jump Table Index relocation
if ((SectionIdx == getJumpTableSection().SectionIdx) &&
TEW->hasCustomJumpTableIndexRelTy())
TEW->hasCustomJumpTableIndexRelTy()) {
RelType = TEW->getJumpTableIndexRelTy();
SymIdx = SectionList[SectionIdx]->getSymbolTableIndex();
Addend = (uint64_t)MR.getResultPointer();
RelTySize = TEW->getRelocationTySize(RelType);
}
}
// The target without addend on the relocation symbol must be
// patched in the relocation place itself to contain the addend
if (!HasRelA) {
if (TEW->getRelocationTySize(RelType) == 32)
S.fixWord32(Addend, Offset);
else if (TEW->getRelocationTySize(RelType) == 64)
S.fixWord64(Addend, Offset);
else
llvm_unreachable("don't know howto patch relocatable field");
}
if (!HasRelA)
RelocateField(S, RelOffset, Addend, RelTySize);
// Get the relocation entry and emit to the relocation section
ELFRelocation Rel(Offset, SymIdx, RelType, HasRelA, Addend);
ELFRelocation Rel(RelOffset, SymIdx, RelType, HasRelA, Addend);
EmitRelocation(RelSec, Rel, HasRelA);
}
}

15
lib/CodeGen/ELFWriter.h
View File

@ -171,18 +171,6 @@ namespace llvm {
ELFSection::SHF_EXECINSTR | ELFSection::SHF_ALLOC);
}
/// Return the relocation section of section 'S'. 'RelA' is true
/// if the relocation section contains entries with addends.
ELFSection &getRelocSection(std::string SName, bool RelA, unsigned Align) {
std::string RelSName(".rel");
unsigned SHdrTy = RelA ? ELFSection::SHT_RELA : ELFSection::SHT_REL;
if (RelA) RelSName.append("a");
RelSName.append(SName);
return getSection(RelSName, SHdrTy, 0, Align);
}
ELFSection &getNonExecStackSection() {
return getSection(".note.GNU-stack", ELFSection::SHT_PROGBITS, 0, 1);
}
@ -215,6 +203,7 @@ namespace llvm {
ELFSection &getJumpTableSection();
ELFSection &getConstantPoolSection(MachineConstantPoolEntry &CPE);
ELFSection &getRelocSection(ELFSection &S);
// Helpers for obtaining ELF specific info.
unsigned getGlobalELFBinding(const GlobalValue *GV);
@ -244,6 +233,8 @@ namespace llvm {
void EmitSymbolTable();
void EmitStringTable();
void OutputSectionsAndSectionTable();
void RelocateField(BinaryObject &BO, uint32_t Offset, int64_t Value,
unsigned Size);
unsigned SortSymbols();
};
}

36
lib/Target/X86/X86ELFWriterInfo.cpp
View File

@ -103,8 +103,44 @@ unsigned X86ELFWriterInfo::getRelocationTySize(unsigned RelTy) const {
return 0;
}
bool X86ELFWriterInfo::isPCRelativeRel(unsigned RelTy) const {
if (is64Bit) {
switch(RelTy) {
case R_X86_64_PC32:
return true;
case R_X86_64_32:
case R_X86_64_32S:
case R_X86_64_64:
return false;
default:
llvm_unreachable("unknown x86_64 relocation type");
}
} else {
switch(RelTy) {
case R_386_PC32:
return true;
case R_386_32:
return false;
default:
llvm_unreachable("unknown x86 relocation type");
}
}
return 0;
}
unsigned X86ELFWriterInfo::getAbsoluteLabelMachineRelTy() const {
return is64Bit ?
X86::reloc_absolute_dword : X86::reloc_absolute_word;
}
long int X86ELFWriterInfo::computeRelocation(unsigned SymOffset,
unsigned RelOffset,
unsigned RelTy) const {
if (RelTy == R_X86_64_PC32 || RelTy == R_386_PC32)
return SymOffset - (RelOffset + 4);
else
assert("computeRelocation unknown for this relocation type");
return 0;
}

13
lib/Target/X86/X86ELFWriterInfo.h
View File

@ -59,16 +59,25 @@ namespace llvm {
/// for a jump table index.
virtual unsigned getJumpTableIndexRelTy() const { return R_X86_64_32S; }
/// getAddendForRelTy - Gets the addend value for an ELF relocation entry
/// based on the target relocation type
/// getDefaultAddendForRelTy - Gets the default addend value for a
/// relocation entry based on the target ELF relocation type.
virtual long int getDefaultAddendForRelTy(unsigned RelTy) const;
/// getRelTySize - Returns the size of relocatable field in bits
virtual unsigned getRelocationTySize(unsigned RelTy) const;
/// isPCRelativeRel - True if the relocation type is pc relative
virtual bool isPCRelativeRel(unsigned RelTy) const;
/// getJumpTableRelocationTy - Returns the machine relocation type used
/// to reference a jumptable.
virtual unsigned getAbsoluteLabelMachineRelTy() const;
/// computeRelocation - Some relocatable fields could be relocated
/// directly, avoiding the relocation symbol emission, compute the
/// final relocation value for this symbol.
virtual long int computeRelocation(unsigned SymOffset, unsigned RelOffset,
unsigned RelTy) const;
};
} // end llvm namespace