From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Tue, 21 Aug 2012 20:48:36 +0000 (+0000)
Subject: Fix unaligned memory accesses when performing relocations in X86 JIT. There's
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;ds=sidebyside;h=fca01b5e2b509f2e9aeeb1cc51aea89c3722cb2e;p=oota-llvm.git

Fix unaligned memory accesses when performing relocations in X86 JIT. There's
no cost to using memcpy here: the fixed code is optimized by LLVM to perfect
machine code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162311 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/X86/X86JITInfo.cpp b/lib/Target/X86/X86JITInfo.cpp
index 0168d12231f..7ac4cec8673 100644
--- a/lib/Target/X86/X86JITInfo.cpp
+++ b/lib/Target/X86/X86JITInfo.cpp
@@ -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;
     }
   }