[vlc-devel] [PATCH 1/2] posix/wait: do not use alignof on expression

[Steve Lhomme]

OK for both. Although it would be nice to have a safety check in case 
the underlying type changes and the alignof is not valid anymore.

May a static_assert when compiling with GCC, like
#if defined(__GNUC__) && !defined(__llvm__) && !defined(__INTEL_COMPILER)
static_assert(alignof(*addr) == alignof(atomic_uint), "type mismatch");
#endif


On 2020-08-07 6:44, Marvin Scholz wrote:
> Using alignof not on a type but an expression is a GNU extension and
> causes the following warning:
> 
>     warning: '_Alignof' applied to an expression is a GNU extension
> ---
>   src/posix/wait.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/posix/wait.c b/src/posix/wait.c
> index 584cc493b1a..3fa6890193a 100644
> --- a/src/posix/wait.c
> +++ b/src/posix/wait.c
> @@ -52,7 +52,7 @@ static struct wait_bucket
>   static struct wait_bucket *wait_bucket_get(atomic_uint *addr)
>   {
>       uintptr_t u = (uintptr_t)addr;
> -    size_t idx = (u / alignof (*addr)) % ARRAY_SIZE(wait_buckets);
> +    size_t idx = (u / alignof (atomic_uint)) % ARRAY_SIZE(wait_buckets);
>   
>       return &wait_buckets[idx];
>   }
> -- 
> 2.24.3 (Apple Git-128)
> 
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