linux-kernel - [PATCH] perf: write bpf_prog (infos|btfs)

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Message-ID: <20251107173150.135037-1-thomas.falcon@intel.com>
Date: Fri,  7 Nov 2025 11:31:50 -0600
From: Thomas Falcon <thomas.falcon@...el.com>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>
Cc: linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Thomas Falcon <thomas.falcon@...el.com>
Subject: [PATCH] perf: write bpf_prog (infos|btfs)_cnt to data file

With commit f0d0f978f3f58 ("perf header: Don't write empty BPF/BTF
info"), the write_bpf_( prog_info() | btf() ) functions exit
without writing anything if env->bpf_prog.(infos| btfs)_cnt is zero.

process_bpf_( prog_info() | btf() ), however, still expect a "count"
value to exist in the data file. If btf information is empty, for
example, process_bpf_btf will read garbage or some other data as the
number of btf nodes in the data file. As a result, the data file will
not be processed correctly.

Instead, write the count to the data file and exit if it is zero.

Fixes: f0d0f978f3f58 ("perf header: Don't write empty BPF/BTF info")
Signed-off-by: Thomas Falcon <thomas.falcon@...el.com>
---
 tools/perf/util/header.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index db2ad19fa50d..54968881481c 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1022,12 +1022,9 @@ static int write_bpf_prog_info(struct feat_fd *ff,
 
 	down_read(&env->bpf_progs.lock);
 
-	if (env->bpf_progs.infos_cnt == 0)
-		goto out;
-
 	ret = do_write(ff, &env->bpf_progs.infos_cnt,
 		       sizeof(env->bpf_progs.infos_cnt));
-	if (ret < 0)
+	if (ret < 0 || env->bpf_progs.infos_cnt == 0)
 		goto out;
 
 	root = &env->bpf_progs.infos;
@@ -1067,13 +1064,10 @@ static int write_bpf_btf(struct feat_fd *ff,
 
 	down_read(&env->bpf_progs.lock);
 
-	if (env->bpf_progs.btfs_cnt == 0)
-		goto out;
-
 	ret = do_write(ff, &env->bpf_progs.btfs_cnt,
 		       sizeof(env->bpf_progs.btfs_cnt));
 
-	if (ret < 0)
+	if (ret < 0 || env->bpf_progs.btfs_cnt == 0)
 		goto out;
 
 	root = &env->bpf_progs.btfs;
-- 
2.47.3