linux-kernel - Re: [PATCH v2 0/2] perf trace: Fix support for the new BPF feature in clang 12

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Message-ID: <Zw61TUe1V97dKWer@google.com>
Date: Tue, 15 Oct 2024 11:32:45 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Howard Chu <howardchu95@...il.com>
Cc: peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
	mark.rutland@....com, alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com,
	kan.liang@...ux.intel.com, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, james.clark@...aro.org,
	alan.maguire@...cle.com
Subject: Re: [PATCH v2 0/2] perf trace: Fix support for the new BPF feature
 in clang 12

On Thu, Oct 10, 2024 at 07:14:00PM -0700, Howard Chu wrote:
> Changes in v2:
> - Resolved a clang-16 build error pointed out by Namhyung Kim
>   <namhyung@...nel.org>
> 
> The new augmentation feature in perf trace, along with the protocol
> change (from payload to payload->value), breaks the clang 12 build.
> 
> perf trace actually builds for any clang version newer than clang 16.
> However, as pointed out by Namhyung Kim <namhyung@...nel.org> and Ian
> Rogers <irogers@...gle.com>, clang 16, which was released in 2023, is
> still too new for most users. Additionally, as James Clark
> <james.clark@...aro.org> noted, some commonly used distributions do not
> yet support clang 16. Therefore, breaking BPF features between clang 12
> and clang 15 is not a good approach.
> 
> This patch series rewrites the BPF program in a way that allows it to
> pass the BPF verifier, even when the BPF bytecode is generated by older
> versions of clang.
> 
> However, I have only tested it till clang 14, as older versions are not
> supported by my distribution.
> 
> Howard Chu (2):
>   perf build: Change the clang check back to 12.0.1
>   perf trace: Rewrite BPF code to pass the verifier

Tested with clang 16.  And I think it's better to change the order of
the commits so it can fix the problem first and then check the version.

Thanks,
Namhyung

> 
>  tools/perf/Makefile.config                    |   4 +-
>  .../bpf_skel/augmented_raw_syscalls.bpf.c     | 122 ++++++++++--------
>  2 files changed, 69 insertions(+), 57 deletions(-)
> 
> -- 
> 2.43.0
>