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

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Message-ID: <20251126160830.52124-1-ankitkhushwaha.linux@gmail.com>
Date: Wed, 26 Nov 2025 21:38:30 +0530
From: Ankit Khushwaha <ankitkhushwaha.linux@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Mike Rapoport <rppt@...nel.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>
Cc: Shuah Khan <shuah@...nel.org>,
	linux-mm@...ck.org,
	linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev,
	Ankit Khushwaha <ankitkhushwaha.linux@...il.com>
Subject: [PATCH] selftests/mm/uffd: initialize char variable to Null

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>
---
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