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Fix unaligned memory accesses when performing relocations in X86 JIT. There's

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no cost to using memcpy here: the fixed code is optimized by LLVM to perfect
machine code.

llvm-svn: 162311
This commit is contained in:
Richard Smith 2012-08-21 20:48:36 +00:00
parent 2735d2748d
commit d1addbb679
1 changed files with 13 additions and 4 deletions
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17
lib/Target/X86/X86JITInfo.cpp
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@ -532,6 +532,15 @@ uintptr_t X86JITInfo::getPICJumpTableEntry(uintptr_t BB, uintptr_t Entry) {
#endif
}
template<typename T> void addUnaligned(void *Pos, T Delta) {
T Value;
std::memcpy(reinterpret_cast<char*>(&Value), reinterpret_cast<char*>(Pos),
sizeof(T));
Value += Delta;
std::memcpy(reinterpret_cast<char*>(Pos), reinterpret_cast<char*>(&Value),
sizeof(T));
}
/// relocate - Before the JIT can run a block of code that has been emitted,
/// it must rewrite the code to contain the actual addresses of any
/// referenced global symbols.
@ -545,24 +554,24 @@ void X86JITInfo::relocate(void *Function, MachineRelocation *MR,
// PC relative relocation, add the relocated value to the value already in
// memory, after we adjust it for where the PC is.
ResultPtr = ResultPtr -(intptr_t)RelocPos - 4 - MR->getConstantVal();
*((unsigned*)RelocPos) += (unsigned)ResultPtr;
addUnaligned<unsigned>(RelocPos, ResultPtr);
break;
}
case X86::reloc_picrel_word: {
// PIC base relative relocation, add the relocated value to the value
// already in memory, after we adjust it for where the PIC base is.
ResultPtr = ResultPtr - ((intptr_t)Function + MR->getConstantVal());
*((unsigned*)RelocPos) += (unsigned)ResultPtr;
addUnaligned<unsigned>(RelocPos, ResultPtr);
break;
}
case X86::reloc_absolute_word:
case X86::reloc_absolute_word_sext:
// Absolute relocation, just add the relocated value to the value already
// in memory.
*((unsigned*)RelocPos) += (unsigned)ResultPtr;
addUnaligned<unsigned>(RelocPos, ResultPtr);
break;
case X86::reloc_absolute_dword:
*((intptr_t*)RelocPos) += ResultPtr;
addUnaligned<intptr_t>(RelocPos, ResultPtr);
break;
}
}