Re: [PATCH 1/2] uprobes/x86: Add support to emulate nop5 instruction

[Oleg Nesterov <oleg@redhat.com>]

On 04/09, Oleg Nesterov wrote:
>
> For the moment, lets forget about compat tasks on a 64-bit kernel, can't
> we simply do something like below?

...

> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -840,12 +840,16 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
>  	insn_byte_t p;
>  	int i;
>  
> +	/* prefix* + nop[i]; same as jmp with .offs = 0 */
> +	for (i = 1; i <= ASM_NOP_MAX; ++i) {
> +		if (!memcmp(insn->kaddr, x86_nops[i], i))
> +			goto setup;
> +	}
> +
>  	switch (opc1) {
>  	case 0xeb:	/* jmp 8 */
>  	case 0xe9:	/* jmp 32 */
>  		break;
> -	case 0x90:	/* prefix* + nop; same as jmp with .offs = 0 */
> -		goto setup;

OK, I guess we can't remove this "case 0x90" because of prefixes, please
ignore this part.

Oleg.