Re: [PATCH bpf-next 09/13] selftests/bpf: Use 5-byte nop for x86 usdt probes

[Andrii Nakryiko]

On Wed, Dec 11, 2024 at 5:35 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> Using 5-byte nop for x86 usdt probes so we can switch
> to optimized uprobe them.
>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  tools/testing/selftests/bpf/sdt.h | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>

This change will make it impossible to run latest selftests on older
kernels. Let's do what we did with -DENABLE_ATOMICS_TESTS and allow to
disable this through Makefile, ok?


> diff --git a/tools/testing/selftests/bpf/sdt.h b/tools/testing/selftests/bpf/sdt.h
> index ca0162b4dc57..7ac9291f45f1 100644
> --- a/tools/testing/selftests/bpf/sdt.h
> +++ b/tools/testing/selftests/bpf/sdt.h
> @@ -234,6 +234,13 @@ __extension__ extern unsigned long long __sdt_unsp;
>  #define _SDT_NOP       nop
>  #endif
>
> +/* Use 5 byte nop for x86_64 to allow optimizing uprobes. */
> +#if defined(__x86_64__)
> +# define _SDT_DEF_NOP _SDT_ASM_5(990:  .byte 0x0f, 0x1f, 0x44, 0x00, 0x00)
> +#else
> +# define _SDT_DEF_NOP _SDT_ASM_1(990:  _SDT_NOP)
> +#endif
> +
>  #define _SDT_NOTE_NAME "stapsdt"
>  #define _SDT_NOTE_TYPE 3
>
> @@ -286,7 +293,7 @@ __extension__ extern unsigned long long __sdt_unsp;
>
>  #define _SDT_ASM_BODY(provider, name, pack_args, args, ...)                  \
>    _SDT_DEF_MACROS                                                            \
> -  _SDT_ASM_1(990:      _SDT_NOP)                                             \
> +  _SDT_DEF_NOP                                                               \
>    _SDT_ASM_3(          .pushsection .note.stapsdt,_SDT_ASM_AUTOGROUP,"note") \
>    _SDT_ASM_1(          .balign 4)                                            \
>    _SDT_ASM_3(          .4byte 992f-991f, 994f-993f, _SDT_NOTE_TYPE)          \
> --
> 2.47.0
>