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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/