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exec-all.h: Use stl_p to avoid undefined behaviour patching x86 jumps 

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)

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>
This commit is contained in:
Peter Maydell 2014-03-28 15:29:46 +00:00 committed by Richard Henderson
parent 06b4f00d53
commit 86360ad71d
1 changed files with 1 additions and 1 deletions
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2
include/exec/exec-all.h
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@ -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__)