selftests: coredump: Properly initialize pointer

JIRA: https://issues.redhat.com/browse/RHEL-113598

commit e194d20
Author: Nam Cao <namcao@linutronix.de>
Date:   Fri, 11 Apr 2025 17:09:41 +0200

    selftests: coredump: Properly initialize pointer

    The buffer pointer "line" is not initialized. This pointer is passed to
    getline().

    It can still work if the stack is zero-initialized, because getline() can
    work with a NULL pointer as buffer.

    But this is obviously broken. This bug shows up while running the test on a
    riscv64 machine.

    Fix it by properly initializing the pointer.

    Fixes: 15858da ("selftests: coredump: Add stackdump test")
    Signed-off-by: Nam Cao <namcao@linutronix.de>
    Link: https://lore.kernel.org/4fb9b6fb3e0040481bacc258c44b4aab5c4df35d.1744383419.git.namcao@linutronix.de
    Signed-off-by: Christian Brauner <brauner@kernel.org>

Signed-off-by: Waiman Long <longman@redhat.com>

Author: Waiman-Long

tools/testing/selftests/coredump/stackdump_test.c

@@ -138,10 +138,12 @@ TEST_F(coredump, stackdump)
 	ASSERT_NE(file, NULL);
 
 	/* Step 4: Make sure all stack pointer values are non-zero */
+	line = NULL;
 	for (i = 0; -1 != getline(&line, &line_length, file); ++i) {
 		stack = strtoull(line, NULL, 10);
 		ASSERT_NE(stack, 0);
 	}
+	free(line);
 
 	ASSERT_EQ(i, 1 + NUM_THREAD_SPAWN);