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

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Message-ID: <aSfcTS3xf64zLdbR@kernel.org>
Date: Thu, 27 Nov 2025 07:06:21 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Ankit Khushwaha <ankitkhushwaha.linux@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Peter Xu <peterx@...hat.com>,
	David Hildenbrand <david@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Shuah Khan <shuah@...nel.org>, linux-mm@...ck.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: Re: [PATCH] selftests/mm/uffd: initialize char variable to Null

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@...il.com>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.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.