linux-kernel - Re: [PATCH perf/core 11/22] selftests/bpf: Use 5-byte nop for x86 usdt probes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAEf4BzbxCqgPErQVBV7Ojz23ZEqYKvxi0Y4j8hq6FgXVvdQo9A@mail.gmail.com>
Date: Wed, 23 Apr 2025 10:33:18 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
	Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, x86@...nel.org, 
	Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, 
	John Fastabend <john.fastabend@...il.com>, Hao Luo <haoluo@...gle.com>, 
	Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Alan Maguire <alan.maguire@...cle.com>, David Laight <David.Laight@...lab.com>, 
	Thomas Weißschuh <thomas@...ch.de>, 
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH perf/core 11/22] selftests/bpf: Use 5-byte nop for x86
 usdt probes

On Mon, Apr 21, 2025 at 2:46 PM Jiri Olsa <jolsa@...nel.org> wrote:
>
> Using 5-byte nop for x86 usdt probes so we can switch
> to optimized uprobe them.
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  tools/testing/selftests/bpf/sdt.h | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>

So sdt.h is an exact copy/paste from systemtap-sdt sources. I'd prefer
to not modify it unnecessarily.

How about we copy/paste usdt.h ([0]) and use *that* for your
benchmarks? I've already anticipated the need to change nop
instruction, so you won't even need to modify the usdt.h file itself,
just

#define USDT_NOP .byte 0x0f, 0x1f, 0x44, 0x00, 0x00

before #include "usdt.h"


  [0] https://github.com/libbpf/usdt/blob/main/usdt.h

> diff --git a/tools/testing/selftests/bpf/sdt.h b/tools/testing/selftests/bpf/sdt.h
> index 1fcfa5160231..1d62c06f5ddc 100644
> --- a/tools/testing/selftests/bpf/sdt.h
> +++ b/tools/testing/selftests/bpf/sdt.h
> @@ -236,6 +236,13 @@ __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
>
> @@ -288,7 +295,7 @@ __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)          \
> --
> 2.49.0
>