Re: [PATCH] Use __attribute__((noreturn)) for function pointer

[Rich Felker <dalias@libc.org>]

On Fri, Jun 14, 2019 at 09:42:09AM -0700, Matthew Maurer wrote:
> _Noreturn doesn't actually exist in C99 - that's a C11ism. Even in C11, it
> cannot be used on a function pointer type.
> __attribute__((noreturn)) is a GNU C extension (which we're allowed to use,
> unlike C11), and is allowed to be placed on function pointer types.

> From adeca3acc1e4c1b727e8524542c201b436ba8a5b Mon Sep 17 00:00:00 2001
> From: Matthew Maurer <mmaurer@google.com>
> Date: Thu, 13 Jun 2019 12:33:38 -0700
> Subject: [PATCH] Use __attribute__((noreturn)) for function pointer
> 
> _Noreturn is a C11 construct, and may only be used at the site of a
> function definition.
> __attribute__((noreturn)) is a GNU C extension which may be used on
> function pointers.
> GCC with any standard permits _Noreturn in the position it's used
> (likely because it implements it in terms of attribute noreturn), but
> Clang will reject it for any standard past C11, and warn pre-C11.
> 
> Musl is written in C99 with GNU C extensions, so
> __attribute__((noreturn)) is both more correct in that sense and allows
> us to compile with Clang set to higher language standards.
> ---
>  src/internal/dynlink.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/internal/dynlink.h b/src/internal/dynlink.h
> index cbe0a6fe..d2bf6b41 100644
> --- a/src/internal/dynlink.h
> +++ b/src/internal/dynlink.h
> @@ -95,7 +95,7 @@ struct fdpic_dummy_loadmap {
>  #define DYN_CNT 32
>  
>  typedef void (*stage2_func)(unsigned char *, size_t *);
> -typedef _Noreturn void (*stage3_func)(size_t *);
> +typedef __attribute__((noreturn)) void (*stage3_func)(size_t *);
>  
>  hidden void *__dlsym(void *restrict, const char *restrict, void *restrict);
>  
> -- 
> 2.22.0.410.gd8fdbe21b5-goog
> 

Just remove it. There's no sense having nonstandard C here for
something that's completely inconsequential. It wasn't important, and
probably the only reason I wrote it was wrongly thinking the function
pointer type had to match the _Noreturn of the function definition.

Rich