[PATCH v2] selftests/user_events: Fix type cast for write_index packed member in perf_test

[Ankit Khushwaha]

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,
      |                                             ^~~~~~~~~~~~~~~

Since write(2) works with any alignment. Casting '&reg.write_index'
explicitly to 'void *' to suppress this warning.

Signed-off-by: Ankit Khushwaha <ankitkhushwaha.li...@gmail.com>
---
Changelog:
v2:
- typecast '&reg.write_index' to 'void *' & remove use of memcpy as
 suggested by Andrew.

v1: 
https://lore.kernel.org/linux-kselftest/20251027113439.36059-1-ankitkhushwaha.li...@gmail.com/

---
 tools/testing/selftests/user_events/perf_test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/user_events/perf_test.c 
b/tools/testing/selftests/user_events/perf_test.c
index 201459d8094d..cafec0e52eb3 100644
--- a/tools/testing/selftests/user_events/perf_test.c
+++ b/tools/testing/selftests/user_events/perf_test.c
@@ -236,7 +236,7 @@ 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,
+       ASSERT_NE(-1, write(self->data_fd, (void *)&reg.write_index,
                                                sizeof(reg.write_index)));
        val = (void *)(((char *)perf_page) + perf_page->data_offset);
        ASSERT_EQ(PERF_RECORD_SAMPLE, *val);
--
2.51.0