linux-hardening - Re: [PATCH] compiler.h: Explain how __is

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Date: Fri, 1 Mar 2024 17:46:55 -0800
From: Kees Cook <keescook@...omium.org>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Rasmus Villemoes <linux@...musvillemoes.dk>,
	"Gustavo A . R . Silva" <gustavoars@...nel.org>,
	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	David Laight <David.Laight@...lab.com>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Martin Uecker <Martin.Uecker@....uni-goettingen.de>,
	Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
	Miguel Ojeda <ojeda@...nel.org>, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] compiler.h: Explain how __is_constexpr() works

On Sat, Mar 02, 2024 at 03:17:32AM +0200, Andy Shevchenko wrote:
> Thu, Feb 29, 2024 at 08:44:37PM -0800, Kees Cook kirjoitti:
> > The __is_constexpr() macro is dark magic. Shed some light on it with
> > a comment to explain how and why it works.
> 
> I was under impression that somebody did it already once and it fell through
> cracks when has been moved (?) to compiler.h.

I tried to do it before (see the v1).

> 
> Ah, now I see it, https://lore.kernel.org/all/YKeghxRY4FeOKuwb@smile.fi.intel.com/.
> It was asked, but till now never fulfilled (maybe Reported-by:/Closes: tag?).

Sure! akpm was hardly the first to ask about it, but yeah, makes for
some good tags.

Reported-by: Andrew Morton <akpm@...ux-foundation.org>
Closes: https://lore.kernel.org/all/20210520134112.ee15f156f1b7dbd3d8f16471@linux-foundation.org/

:)

> And explanation before was given here:
> https://stackoverflow.com/questions/49481217/linux-kernels-is-constexpr-macro.

Sure, but I wanted something that lived with the macro and everyone was
happy with the details.

-Kees

-- 
Kees Cook