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

Andrii Nakryiko
2024-12-13T21:58:47Z

On Wed, Dec 11, 2024 at 5:35 AM Jiri Olsa <jolsa@kernel.org> wrote:
>
> Using 5-byte nop for x86 usdt probes so we can switch
> to optimized uprobe them.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> 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
>