linux-hardening - RE: [PATCH] linux/const.h: Explain how __is

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Date:   Wed, 2 Feb 2022 08:49:33 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Rasmus Villemoes' <linux@...musvillemoes.dk>,
        Kees Cook <keescook@...omium.org>,
        Jonathan Corbet <corbet@....net>
CC:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Martin Uecker <Martin.Uecker@....uni-goettingen.de>,
        Ingo Molnar <mingo@...nel.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Rikard Falkeborn <rikard.falkeborn@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>
Subject: RE: [PATCH] linux/const.h: Explain how __is_constexpr() works

From: Rasmus Villemoes
> Sent: 01 February 2022 13:06
...
> > + * - The C standard defines an "integer constant expression" as different
> > + *   from a "null pointer constant" (an integer constant 0 pointer).
> 
> I don't see the point of this bullet. Yes, an ICE is a distinct concept
> from a null pointer constant, obviously. One is defined in terms of the
> other - and your parenthesis is not an accurate paraphrase of the
> definition of a null pointer constant.

>From what I remember a "null pointer constant" is in "integer constant
expression with value 0 cast to a pointer type".
So (void *)(1-1) is just as valid as (void *)0.

Not sure any of it is relevant here.

	David

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