Re: [PATCHv3 perf/core 1/2] uprobes/x86: Add support to emulate nop instructions

[Andrii Nakryiko]

On Mon, Apr 14, 2025 at 1:36 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> Adding support to emulate all nop instructions as the original uprobe
> instruction.
>
> This change speeds up uprobe on top of all nop instructions and is a
> preparation for usdt probe optimization, that will be done on top of
> nop5 instruction.
>
> With this change the usdt probe on top of nop5 won't take the performance
> hit compared to usdt probe on top of standard nop instruction.
>
> Suggested-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> v3 changes:
>  - use insn->length as index to x86_nops [Andrii]
>
>  arch/x86/kernel/uprobes.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index 9194695662b2..6d383839e839 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -840,6 +840,11 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
>         insn_byte_t p;
>         int i;
>
> +       /* x86_nops[insn->length]; same as jmp with .offs = 0 */
> +       if (insn->length <= ASM_NOP_MAX &&
> +           !memcmp(insn->kaddr, x86_nops[insn->length], insn->length))
> +               goto setup;
> +

LGTM, thanks!

Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>


>         switch (opc1) {
>         case 0xeb:      /* jmp 8 */
>         case 0xe9:      /* jmp 32 */
> --
> 2.49.0
>