[PATCH] powerpc/futex: fix warning: 'oldval' may be used uninitialized in this function

[PATCH] powerpc/futex: fix warning: 'oldval' may be used uninitialized in this function

[Christophe Leroy]

  CC      kernel/futex.o
kernel/futex.c: In function 'do_futex':
kernel/futex.c:1676:17: warning: 'oldval' may be used uninitialized in this function [-Wmaybe-uninitialized]
   return oldval == cmparg;
                 ^
kernel/futex.c:1651:6: note: 'oldval' was declared here
  int oldval, ret;
      ^

This is because arch_futex_atomic_op_inuser() only sets *oval
if ret is NUL and GCC doesn't see that it will use it only when
ret is NUL.

Anyway, the non-NUL ret path is an error path that won't suffer from
setting *oval, and as *oval is a local var in futex_atomic_op_inuser()
it will have no impact.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/include/asm/futex.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/futex.h b/arch/powerpc/include/asm/futex.h
index 3a6aa57b9d90..eea28ca679db 100644
--- a/arch/powerpc/include/asm/futex.h
+++ b/arch/powerpc/include/asm/futex.h
@@ -60,8 +60,7 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
 
 	pagefault_enable();
 
-	if (!ret)
-		*oval = oldval;
+	*oval = oldval;
 
 	prevent_write_to_user(uaddr, sizeof(*uaddr));
 	return ret;
-- 
2.13.3

Re: [PATCH] powerpc/futex: fix warning: 'oldval' may be used uninitialized in this function

[Michael Ellerman]

Christophe Leroy <christophe.leroy@c-s.fr> writes:
>   CC      kernel/futex.o
> kernel/futex.c: In function 'do_futex':
> kernel/futex.c:1676:17: warning: 'oldval' may be used uninitialized in this function [-Wmaybe-uninitialized]
>    return oldval == cmparg;
>                  ^
> kernel/futex.c:1651:6: note: 'oldval' was declared here
>   int oldval, ret;
>       ^
>
> This is because arch_futex_atomic_op_inuser() only sets *oval
> if ret is NUL and GCC doesn't see that it will use it only when

I prefer 0 to "NUL", as ret is an int. I'll reword it. But otherwise
this looks OK.

cheers

> ret is NUL.
>
> Anyway, the non-NUL ret path is an error path that won't suffer from
> setting *oval, and as *oval is a local var in futex_atomic_op_inuser()
> it will have no impact.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
>  arch/powerpc/include/asm/futex.h | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/futex.h b/arch/powerpc/include/asm/futex.h
> index 3a6aa57b9d90..eea28ca679db 100644
> --- a/arch/powerpc/include/asm/futex.h
> +++ b/arch/powerpc/include/asm/futex.h
> @@ -60,8 +60,7 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
>  
>  	pagefault_enable();
>  
> -	if (!ret)
> -		*oval = oldval;
> +	*oval = oldval;
>  
>  	prevent_write_to_user(uaddr, sizeof(*uaddr));
>  	return ret;
> -- 
> 2.13.3

Re: [PATCH] powerpc/futex: fix warning: 'oldval' may be used uninitialized in this function

[Michael Ellerman]

On Wed, 2019-08-14 at 09:25:52 UTC, Christophe Leroy wrote:
> CC      kernel/futex.o
> kernel/futex.c: In function 'do_futex':
> kernel/futex.c:1676:17: warning: 'oldval' may be used uninitialized in this function [-Wmaybe-uninitialized]
>    return oldval == cmparg;
>                  ^
> kernel/futex.c:1651:6: note: 'oldval' was declared here
>   int oldval, ret;
>       ^
> 
> This is because arch_futex_atomic_op_inuser() only sets *oval
> if ret is NUL and GCC doesn't see that it will use it only when
> ret is NUL.
> 
> Anyway, the non-NUL ret path is an error path that won't suffer from
> setting *oval, and as *oval is a local var in futex_atomic_op_inuser()
> it will have no impact.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/38a0d0cdb46d3f91534e5b9839ec2d67be14c59d

cheers