[PATCH] selftests/user_events: Avoid taking address of packed member in perf_test

Ankit Khushwaha
2025-10-27T11:34:54Z

Accessing 'reg.write_index' directly triggers a -Waddress-of-packed-member
warning due to potential unaligned pointer access:

perf_test.c:239:38: warning: taking address of packed member 'write_index'
of class or structure 'user_reg' may result in an unaligned pointer value
[-Waddress-of-packed-member]
239 | ASSERT_NE(-1, write(self->data_fd, &reg.write_index,
| ^~~~~~~~~~~~~~~

Use memcpy() instead to safely copy the value and avoid unaligned pointer
access across architectures.

Signed-off-by: Ankit Khushwaha <ankitkhushwaha.linux@gmail.com>
---
tools/testing/selftests/user_events/perf_test.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/user_events/perf_test.c b/tools/testing/selftests/user_events/perf_test.c
index 201459d8094d..e4385f4aa231 100644
--- a/tools/testing/selftests/user_events/perf_test.c
+++ b/tools/testing/selftests/user_events/perf_test.c
@@ -201,6 +201,7 @@ TEST_F(user, perf_empty_events) {
struct perf_event_mmap_page *perf_page;
int page_size = sysconf(_SC_PAGESIZE);
int id, fd;
+ __u32 write_index;
__u32 *val;

reg.size = sizeof(reg);
@@ -236,7 +237,8 @@ TEST_F(user, perf_empty_events) {
ASSERT_EQ(1 << reg.enable_bit, self->check);

/* Ensure write shows up at correct offset */
- ASSERT_NE(-1, write(self->data_fd, &reg.write_index,
+ memcpy(&write_index, &reg.write_index, sizeof(reg.write_index));
+ ASSERT_NE(-1, write(self->data_fd, &write_index,
sizeof(reg.write_index)));
val = (void *)(((char *)perf_page) + perf_page->data_offset);
ASSERT_EQ(PERF_RECORD_SAMPLE, *val);
--
2.51.0