linux-kernel - Re: [PATCH] string.h: Mark 34 functions with __must

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Date:   Wed, 9 Oct 2019 17:30:01 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Markus Elfring <Markus.Elfring@....de>,
        kernel-janitors@...r.kernel.org,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Joe Perches <joe@...ches.com>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] string.h: Mark 34 functions with __must_check

On Wed, Oct 09, 2019 at 04:21:20PM +0200, Rasmus Villemoes wrote:
> On 09/10/2019 15.56, Dan Carpenter wrote:
> > That's because glibc strlen is annotated with __attribute_pure__ which
> > means it has no side effects.
> 
> I know, except it has nothing to do with glibc headers. Just try the
> same thing in the kernel. gcc itself knows this about __builtin_strlen()
> etc. If anything, we could annotate some of our non-standard functions
> (say, memchr_inv) with __pure - then we'd both get the Wunused-value in
> the nonsense cases, and allow gcc to optimize or reorder the calls.

Huh.  You're right.  GCC already knows.  So this patch is pointless like
you say.

regards,
dan carpenter