On 08/08, Sebastian Andrzej Siewior wrote:
>
> On 08/08/2012 02:57 PM, Oleg Nesterov wrote:
>>> +static int insn_changes_flags(struct arch_uprobe *auprobe)
>>> +{
>>> + /* popf reads flags from stack */
>>> + if (auprobe->insn[0] == 0x9d)
>>> + return 1;
>>
>> Ah, somehow I didn't think about this before.
>>
>> ->insn[0] doesn't look right, we should skip the prefixes.
>
> Why? I tried 'lock popf' and I got invalid instruction. The same for
> 'rep popf'.
int main(void)
{
asm volatile ("pushf; rep; popf");
return 0;
}
objdump:
00000000040047c <main>:
40047c: 55 push %rbp
40047d: 48 89 e5 mov %rsp,%rbp
400480: 9c pushfq
400481: f3 9d repz popfq
400483: b8 00 00 00 00 mov $0x0,%eax
400488: c9 leaveq
400489: c3 retq
OK, probably nobody should do this (although the kernel should not
assume this imho), but
asm volatile ("pushfw; popfw");
doesn't look bad and the code is
000000000040047c <main>:
40047c: 55 push %rbp
40047d: 48 89 e5 mov %rsp,%rbp
400480: 66 9c pushfw
400482: 66 9d popfw
400484: b8 00 00 00 00 mov $0x0,%eax
400489: c9 leaveq
40048a: c3 retq
And in any case it would be better to re-use auprobe->fixups.
Oleg.
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