Re: [PATCH 2/2] use the correct attributes for ___errno_location

[Rich Felker <dalias@libc.org>]

On Sat, Jun 29, 2019 at 04:22:44PM -0500, Samuel Holland wrote:
> In the public header, __errno_location is declared with the "const"
> attribute, conditional on __GNUC__. Ensure that its internal alias has
> the same attributes.
> ---
>  src/errno/__errno_location.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/src/errno/__errno_location.c b/src/errno/__errno_location.c
> index 7f9d6027..b59919c3 100644
> --- a/src/errno/__errno_location.c
> +++ b/src/errno/__errno_location.c
> @@ -6,4 +6,8 @@ int *__errno_location(void)
>  	return &__pthread_self()->errno_val;
>  }
>  
> -weak_alias(__errno_location, ___errno_location);
> +weak_alias(__errno_location, ___errno_location)
> +#ifdef __GNUC__
> +__attribute__((const))
> +#endif
> +;
> -- 
> 2.21.0

Thanks for catching this. It's probably a significant regression in
codegen. I think the attribute should be on the declaration in
src/include/errno.h though, not on the weak_alias definition. Most
importantly this is needed for it to affect codegen in the callers.
But it's also for consistency with the approach of having attributes
on the declarations rather than the definitions (to ensure everyone
gets a consistent view of them), and to avoid assumptions about what
the weak_alias macro expands to.

Rich