Re: [PATCH] selftests/mm/uffd: initialize char variable to Null

Mike Rapoport
2025-11-27T05:06:31Z

On Wed, Nov 26, 2025 at 09:38:30PM +0530, Ankit Khushwaha wrote:
> In "uffd-stress.c" & "uffd-unit-tests.c". address of char variable having
> garbage value (uninitialized) is passed to 'write' syscall triggers
> warning.
>
> uffd-stress.c:246:39: warning: variable 'c' is uninitialized when
> passed as a const pointer argument here
> [-Wuninitialized-const-pointer]
>
> uffd-unit-tests.c:581:31: warning: variable 'c' is uninitialized
> when passed as a const pointer argument here
> [-Wuninitialized-const-pointer]
>
> so the fix is to assign char variable to '\0' to prevent writing of
> garbage value.
>
> Signed-off-by: Ankit Khushwaha <ankitkhushwaha.linux@gmail.com>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
> this warning is raised with clang version 21.1.5 (Fedora 21.1.5-1.fc43).
> ---
> tools/testing/selftests/mm/uffd-stress.c | 2 +-
> tools/testing/selftests/mm/uffd-unit-tests.c | 8 ++++----
> 2 files changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/uffd-stress.c b/tools/testing/selftests/mm/uffd-stress.c
> index b51c89e1cd1a..700fbaa18d44 100644
> --- a/tools/testing/selftests/mm/uffd-stress.c
> +++ b/tools/testing/selftests/mm/uffd-stress.c
> @@ -241,7 +241,7 @@ static int stress(struct uffd_args *args)
> return 1;
>
> for (cpu = 0; cpu < gopts->nr_parallel; cpu++) {
> - char c;
> + char c = '\0';
> if (bounces & BOUNCE_POLL) {
> if (write(gopts->pipefd[cpu*2+1], &c, 1) != 1)
> err("pipefd write error");
> diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
> index f917b4c4c943..f4807242c5b2 100644
> --- a/tools/testing/selftests/mm/uffd-unit-tests.c
> +++ b/tools/testing/selftests/mm/uffd-unit-tests.c
> @@ -543,7 +543,7 @@ static void uffd_minor_test_common(uffd_global_test_opts_t *gopts, bool test_col
> {
> unsigned long p;
> pthread_t uffd_mon;
> - char c;
> + char c = '\0';
> struct uffd_args args = { 0 };
> args.gopts = gopts;
>
> @@ -759,7 +759,7 @@ static void uffd_sigbus_test_common(uffd_global_test_opts_t *gopts, bool wp)
> pthread_t uffd_mon;
> pid_t pid;
> int err;
> - char c;
> + char c = '\0';
> struct uffd_args args = { 0 };
> args.gopts = gopts;
>
> @@ -819,7 +819,7 @@ static void uffd_events_test_common(uffd_global_test_opts_t *gopts, bool wp)
> pthread_t uffd_mon;
> pid_t pid;
> int err;
> - char c;
> + char c = '\0';
> struct uffd_args args = { 0 };
> args.gopts = gopts;
>
> @@ -1125,7 +1125,7 @@ uffd_move_test_common(uffd_global_test_opts_t *gopts,
> {
> unsigned long nr;
> pthread_t uffd_mon;
> - char c;
> + char c = '\0';
> unsigned long long count;
> struct uffd_args args = { 0 };
> char *orig_area_src = NULL, *orig_area_dst = NULL;
> --
> 2.52.0
>

--
Sincerely yours,
Mike.