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SubjectRe: [PATCH] x86: fix and improve cmpxchg_double{,_local}()
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Le mardi 03 janvier 2012 à 16:00 +0100, Eric Dumazet a écrit :

> While looking at your patch, I discovered that atomic64_add() /
> atomic64_inc() on 32bit are completely buggy. Oh well...
>
> Generated code :
>
> c03bc00c <atomic64_add_return_cx8>:
> c03bc00c: 55 push %ebp
> c03bc00d: 53 push %ebx
> c03bc00e: 56 push %esi
> c03bc00f: 57 push %edi
> c03bc010: 89 c6 mov %eax,%esi
> c03bc012: 89 d7 mov %edx,%edi
> c03bc014: 89 cd mov %ecx,%ebp
> c03bc016: 89 d8 mov %ebx,%eax
> c03bc018: 89 ca mov %ecx,%edx
> c03bc01a: f0 0f c7 4d 00 lock cmpxchg8b 0x0(%ebp)
> c03bc01f: 89 c3 mov %eax,%ebx
> c03bc021: 89 d1 mov %edx,%ecx
> c03bc023: 01 f3 add %esi,%ebx
> c03bc025: 11 f9 adc %edi,%ecx
> c03bc027: f0 0f c7 4d 00 lock cmpxchg8b 0x0(%ebp)
> c03bc02c: 75 f9 jne c03bc027 <atomic64_add_return_cx8+0x1b>
> c03bc02e: 89 d8 mov %ebx,%eax
> c03bc030: 89 ca mov %ecx,%edx
> c03bc032: 5f pop %edi
> c03bc033: 5e pop %esi
> c03bc034: 5b pop %ebx
> c03bc035: 5d pop %ebp
> c03bc036: c3 ret
>
> The ' jne c03bc027' should really be 'jne c03bc01f'
>
> No idea how old is this bug.
>

Very old it seems...

arch/x86/lib/atomic64_cx8_32.S

all "jxx 1b" are wrong if a LOCK_PREFIX is included after the 1: label

1:
inst1
LOCK_PREFIX
cmpxchg8b (%ebp)
jne 1b / jumps to beginning of LOCK_PREFIX, inst1 is not replayed





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