[PATCH] drivers/char/random.c: fix uninitialized value warning

[PATCH] drivers/char/random.c: fix uninitialized value warning

[Constantine Shulyupin]

Local variable t should be initialized by arch_get_random_int.
Actually on failure of arch_get_random_int, value is not used.
So, just keep the build clean with less warnings.

warning:
drivers/char/random.c: In function ‘write_pool.constprop’:
drivers/char/random.c:1912:11: warning: ‘t’ may be used uninitialized in this function [-Wmaybe-uninitialized]

Signed-off-by: Constantine Shulyupin <const@MakeLinux.com>
---
 drivers/char/random.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 283fe390e878..8e51846d0673 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1896,7 +1896,7 @@ static int
 write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
 {
 	size_t bytes;
-	__u32 t, buf[16];
+	__u32 t = 0, buf[16];
 	const char __user *p = buffer;
 
 	while (count > 0) {
-- 
2.17.1

Re: [PATCH] drivers/char/random.c: fix uninitialized value warning

[Theodore Y. Ts'o]

On Wed, Jul 18, 2018 at 10:11:52AM +0300, Constantine Shulyupin wrote:
> Local variable t should be initialized by arch_get_random_int.
> Actually on failure of arch_get_random_int, value is not used.
> So, just keep the build clean with less warnings.
> 
> warning:
> drivers/char/random.c: In function ‘write_pool.constprop’:
> drivers/char/random.c:1912:11: warning: ‘t’ may be used uninitialized in this function [-Wmaybe-uninitialized]
> 
> Signed-off-by: Constantine Shulyupin <const@MakeLinux.com>

There was a more significant problem which Arnd pointed out, which is
I had reversed the sense of the test in arch_get_random_int().  I've
since fixed this, and the current random tree is clean of warnings.

						- Ted

Re: [PATCH] drivers/char/random.c: fix uninitialized value warning

[Arnd Bergmann]

On Wed, Jul 18, 2018 at 9:11 AM, Constantine Shulyupin
<const@makelinux.com> wrote:
> Local variable t should be initialized by arch_get_random_int.
> Actually on failure of arch_get_random_int, value is not used.
> So, just keep the build clean with less warnings.
>
> warning:
> drivers/char/random.c: In function ‘write_pool.constprop’:
> drivers/char/random.c:1912:11: warning: ‘t’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>
> Signed-off-by: Constantine Shulyupin <const@MakeLinux.com>

You need to be much more careful with fixes like this one. As Ted explained,
the warning was about a real bug here, and adding an incorrect initialization
just made it harder to find that bug.

There are many cases in which the compiler does have a false-positive or
a false-negative -Wmaybe-uninitialized warning, but in general you should
assume that the compiler is correct. If you add a fake initialization because
you think the compiler is wrong, it's best to link to the gcc bugzilla
describing
that gcc bug, or open a new bug report if it still happens in the
latest compiler
version and hasn't been reported before.

      Arnd