2019-08-14 09:27:39

by Christophe Leroy

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

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 <[email protected]>
---
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

2019-08-16 12:37:55

by Michael Ellerman

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

Christophe Leroy <[email protected]> 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 <[email protected]>
> ---
> 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

2019-08-22 18:30:17

by Michael Ellerman

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

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 <[email protected]>

Applied to powerpc next, thanks.

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

cheers