linux-kernel - [PATCH] perf trace: Fix wrong size to bpf_map__update

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Message-ID: <20250324152756.3879571-1-tmricht@linux.ibm.com>
Date: Mon, 24 Mar 2025 16:27:56 +0100
From: Thomas Richter <tmricht@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-perf-users@...r.kernel.org, acme@...nel.org, namhyung@...nel.org,
        irogers@...gle.com, james.clark@...aro.org
Cc: agordeev@...ux.ibm.com, gor@...ux.ibm.com, sumanthk@...ux.ibm.com,
        hca@...ux.ibm.com, Thomas Richter <tmricht@...ux.ibm.com>
Subject: [PATCH] perf trace: Fix wrong size to bpf_map__update_elem call

In linux-next
commit c760174401f6 ("perf cpumap: Reduce cpu size from int to int16_t")
causes the perf tests 100 126 to fail on s390:

Output before:
 # ./perf test 100
 100: perf trace BTF general tests         : FAILED!
 #

The root cause is the change from int to int16_t for the
cpu maps. The size of the CPU key value pair changes from
four bytes to two bytes. However a two byte key size is
not supported for bpf_map__update_elem().
Note: validate_map_op() in libbpf.c emits warning
 libbpf: map '__augmented_syscalls__': \
	 unexpected key size 2 provided, expected 4
when key size is set to int16_t.

Therefore change to variable size back to 4 bytes for
invocation of bpf_map__update_elem().

Output after:
 # ./perf test 100
 100: perf trace BTF general tests         : Ok
 #

Fixes: c760174401f6 ("perf cpumap: Reduce cpu size from int to int16_t")
Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
Cc: Ian Rogers <irogers@...gle.com>
Cc: James Clark <james.clark@...aro.org>
---
 tools/perf/builtin-trace.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 092c5f6404ba..464c97a11852 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -4375,10 +4375,12 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
 		 * CPU the bpf-output event's file descriptor.
 		 */
 		perf_cpu_map__for_each_cpu(cpu, i, trace->syscalls.events.bpf_output->core.cpus) {
+			int mycpu = cpu.cpu;
+
 			bpf_map__update_elem(trace->skel->maps.__augmented_syscalls__,
-					&cpu.cpu, sizeof(int),
+					&mycpu, sizeof(int),
 					xyarray__entry(trace->syscalls.events.bpf_output->core.fd,
-						       cpu.cpu, 0),
+						       mycpu, 0),
 					sizeof(__u32), BPF_ANY);
 		}
 	}
-- 
2.48.1