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

[James Clark <james.clark@linaro.org>]

On 11/10/2024 3:14 am, Howard Chu wrote:
> Changes in v2:
> - Resolved a clang-16 build error pointed out by Namhyung Kim
>    <namhyung@kernel.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@kernel.org> and Ian
> Rogers <irogers@google.com>, clang 16, which was released in 2023, is
> still too new for most users. Additionally, as James Clark
> <james.clark@linaro.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
> 
>   tools/perf/Makefile.config                    |   4 +-
>   .../bpf_skel/augmented_raw_syscalls.bpf.c     | 122 ++++++++++--------
>   2 files changed, 69 insertions(+), 57 deletions(-)
> 


Tested with clang 15:

$ sudo perf trace -e write --max-events=100 -- echo hello

    0.000 ( 0.014 ms): echo/976249 write(fd: 1, buf: hello\10, count: 6)
                                             =

Tested-by: James Clark <james.clark@linaro.org>