On 15 Mar 2022 10:16, Joel Sherrill wrote:
> This is not provided by the newlib malloc implementation but may
> be available in external implementations.
> ---
>  newlib/libc/include/malloc.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/newlib/libc/include/malloc.h b/newlib/libc/include/malloc.h
> index a9dc5bca6..e73095e1e 100644
> --- a/newlib/libc/include/malloc.h
> +++ b/newlib/libc/include/malloc.h
> @@ -137,6 +137,10 @@ extern void __malloc_lock(struct _reent *);
>  
>  extern void __malloc_unlock(struct _reent *);
>  
> +#if __GNU_VISIBLE
> +extern size_t malloc_usable_size(void *);
> +#endif
> +

i'm confused.  isn't this prototype already defined in this header file
on line 101 above where you added this ?
-mike