Re: [Xen-devel] [PATCH v9 1/5] xen: introduce ptrdiff_t, fix uintptr_t

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.02.19 at 02:13, <sstabellini@xxxxxxxxxx> wrote:
> --- a/xen/include/xen/types.h
> +++ b/xen/include/xen/types.h
> @@ -52,7 +52,8 @@ typedef __u32 __be32;
>  typedef __u64 __le64;
>  typedef __u64 __be64;
>  
> -typedef unsigned int __attribute__((__mode__(__pointer__))) uintptr_t;
> +typedef unsigned long __attribute__((__mode__(__pointer__))) uintptr_t;

I don't understand this change: The mode attribute discards any width
association derived from the specified base type.

> +typedef long ptrdiff_t;

FTR I'm unconvinced of this, or the need to use uintptr_t in the first
place in the macros you introduce: The entire UNIX world implies
sizeof(long) == sizeof(void*) afaik.

But if we really want to have ptrdiff_t, then I think we should either
follow the uintptr_t model and use attribute((mode())), or we should
leverage the compiler's __PTRDIFF_TYPE__ (and then also
__UINTPTR_TYPE__ for uintptr_t, at least if available - not sure what
its availability depends on, but it's conditional in gcc's
c_stddef_cpp_builtins()).

Jan



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