[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] [PATCH 1/8] exec-all.h: Use stl_p to avoid undefined behavi
From: |
Richard Henderson |
Subject: |
[Qemu-devel] [PATCH 1/8] exec-all.h: Use stl_p to avoid undefined behaviour patching x86 jumps |
Date: |
Fri, 28 Mar 2014 17:27:07 -0700 |
From: Peter Maydell <address@hidden>
The code which patches x86 jump instructions assumes it can do an
unaligned write of a uint32_t. This is actually safe on x86, but it's
still undefined behaviour. We have infrastructure for doing efficient
unaligned accesses which doesn't engage in undefined behaviour, so
use it.
This is technically fractionally less efficient, at least with gcc 4.6;
instead of one instruction:
7b2: 89 3e mov %edi,(%rsi)
we get an extra spurious store to the stack slot:
7b2: 89 7c 24 64 mov %edi,0x64(%rsp)
7b6: 89 3e mov %edi,(%rsi)
Signed-off-by: Peter Maydell <address@hidden>
Signed-off-by: Richard Henderson <address@hidden>
---
include/exec/exec-all.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
index f9ac332..1c49a21 100644
--- a/include/exec/exec-all.h
+++ b/include/exec/exec-all.h
@@ -229,7 +229,7 @@ void ppc_tb_set_jmp_target(unsigned long jmp_addr, unsigned
long addr);
static inline void tb_set_jmp_target1(uintptr_t jmp_addr, uintptr_t addr)
{
/* patch the branch destination */
- *(uint32_t *)jmp_addr = addr - (jmp_addr + 4);
+ stl_p((void*)jmp_addr, addr - (jmp_addr + 4));
/* no need to flush icache explicitly */
}
#elif defined(__aarch64__)
--
1.9.0
- [Qemu-devel] [PATCH 0/8] tcg: tidy the type of code_ptr, Richard Henderson, 2014/03/28
- [Qemu-devel] [PATCH 1/8] exec-all.h: Use stl_p to avoid undefined behaviour patching x86 jumps,
Richard Henderson <=
- [Qemu-devel] [PATCH 2/8] tcg: Avoid stores to unaligned addresses, Richard Henderson, 2014/03/28
- [Qemu-devel] [PATCH 3/8] tcg: Avoid undefined behaviour patching code at unaligned addresses, Richard Henderson, 2014/03/28
- [Qemu-devel] [PATCH 4/8] tcg: Define tcg_itype for code pointers, Richard Henderson, 2014/03/28
- [Qemu-devel] [PATCH 5/8] tcg-ppc64: Define TCG_TARGET_ITYPE_SIZE, Richard Henderson, 2014/03/28
- [Qemu-devel] [PATCH 6/8] tcg-ppc: Define TCG_TARGET_ITYPE_SIZE, Richard Henderson, 2014/03/28
- [Qemu-devel] [PATCH 7/8] tcg-aarch64: Define TCG_TARGET_ITYPE_SIZE, Richard Henderson, 2014/03/28
- [Qemu-devel] [PATCH 8/8] tcg-sparc: Define TCG_TARGET_ITYPE_SIZE, Richard Henderson, 2014/03/28
- Re: [Qemu-devel] [PATCH 0/8] tcg: tidy the type of code_ptr, Peter Maydell, 2014/03/29