Re: [RFC PATCH 6/8] READ_ONCE: Drop pointer qualifiers when reading from scalar types

[Luc Van Oostenryck]

On Mon, Jan 13, 2020 at 02:59:54PM +0000, Will Deacon wrote:
> // Insert big fat comment here
> #define unqual_typeof(x)    typeof(({_Atomic typeof(x) ___x __maybe_unused; ___x; }))
> 
> That apparently *requires* GCC 4.8, but I think the question is more about
> whether it's easier to stomach the funny use of _Atomic or the nested
> __builtin_choose_expr() I have here. I'm also worried about how reliable
> the _Atomic thing is, or whether it's just an artifact of how GCC happens
> to work today.

As far as I understand it, it's an artifact of how GCC works today (it
was added to support the type-generic macros in <tgmath.h>).
I also think it's also quite fragile, for example, the unqualified type
is returned if typeof's argument is an expression but not if it's a
'typename'. IOW:
	typeof(_Atomic typeof(const int))
returns 'const int', while
	typeof(({_Atomic typeof(const int) x; x; }))
returns 'int'.

-- Luc