On 05/10/2018 11:36 AM, Peter Maydell wrote:
> Some versions of gcc produce a spurious warning if the result of
> __atomic_compare_echange_n() is not used and the type involved
> is a signed 8 bit value:
> error: value computed is not used [-Werror=unused-value]
> This has been seen on at least
> gcc (Ubuntu 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609
>
> Work around this by using an explicit cast to void to indicate
> that we don't care about the return value.
>
> We don't currently use our atomic_cmpxchg() macro on any signed
> 8 bit types, but the upcoming support for the Arm v8.1-Atomics
> will require it.
>
> Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4...@amsat.org>
> ---
> Sending out my workaround as an actual patch. If this is OK I'll
> put in via target-arm.next as it's a dependency for the v8.1-atomics
> series.
>
> include/qemu/atomic.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h
> index d73c9e14d7..9ed39effd3 100644
> --- a/include/qemu/atomic.h
> +++ b/include/qemu/atomic.h
> @@ -187,7 +187,7 @@
> /* Returns the eventual value, failed or not */
> #define atomic_cmpxchg__nocheck(ptr, old, new) ({ \
> typeof_strip_qual(*ptr) _old = (old); \
> - __atomic_compare_exchange_n(ptr, &_old, new, false, \
> + (void)__atomic_compare_exchange_n(ptr, &_old, new, false, \
> __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \
> _old; \
> })
>
