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

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Message-ID: <20241011021403.4089793-1-howardchu95@gmail.com>
Date: Thu, 10 Oct 2024 19:14:00 -0700
From: Howard Chu <howardchu95@...il.com>
To: peterz@...radead.org
Cc: mingo@...hat.com,
	acme@...nel.org,
	namhyung@...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,
	Howard Chu <howardchu95@...il.com>
Subject: [PATCH v2 0/2] perf trace: Fix support for the new BPF feature in clang 12

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

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

-- 
2.43.0