linux-kernel - RE: [PATCH v2 next] compiler.h: Move __is

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Date:   Fri, 6 Oct 2023 08:28:04 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Kees Cook' <keescook@...omium.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "'linux@...musvillemoes.dk'" <linux@...musvillemoes.dk>,
        'Steven Rostedt' <rostedt@...dmis.org>,
        "'bvanassche@....org'" <bvanassche@....org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "Nathan Chancellor" <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: RE: [PATCH v2 next] compiler.h: Move __is_constexpr() to compiler.h.

From: Kees Cook
> Sent: 05 October 2023 17:22
> 
> On Thu, Oct 05, 2023 at 11:39:54AM +0000, David Laight wrote:
> > Prior to f747e6667ebb2 __is_constexpr() was in its only user minmax.h.
> > That commit moved it to const.h - but that file just defines ULL(x) and
> >   UL(x) so that constants can be defined for .S and .c files.
> > So apart from the word 'const' it wasn't really a good location.
> > Instead move the definition to compiler.h just before the similar
> >   is_signed_type() and is_unsigned_type().
> > This may not be a good long-term home, but the three definitions
> >   belong together.
> >
> > Signed-off-by: David Laight <david.laight@...lab.com>
> 
> Yeah, this is what I'd expect (a duplicate move in tools/). Thanks!

I did try to run something that might have built 'perf'.
But it complained about a lot of stuff not being installed.

I do wonder if a better home for all these is_xxx() and __is_xxx()
would be at the top of build_bug.h.

While they can be used on their own (eg with __builtin_choose_expr())
they are typically used with the compile-time asserts
(or at least with code that is also doing asserts.)
So there might only be a few places that need the extra #include.

	David

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