linux-kernel - Re: [PATCH] linux/compiler-clang.h: define HAVE_BUILTIN

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Message-ID: <202102251213.5815C9B33@keescook>
Date:   Thu, 25 Feb 2021 12:14:17 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Arnd Bergmann <arnd@...db.de>, Miguel Ojeda <ojeda@...nel.org>,
        Marco Elver <elver@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Randy Dunlap <rdunlap@...radead.org>,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] linux/compiler-clang.h: define HAVE_BUILTIN_BSWAP*

On Thu, Feb 25, 2021 at 12:06:37PM -0800, Andrew Morton wrote:
> On Thu, 25 Feb 2021 12:03:48 -0800 Kees Cook <keescook@...omium.org> wrote:
> 
> > On Thu, Feb 25, 2021 at 05:45:09PM +0100, Arnd Bergmann wrote:
> > > From: Arnd Bergmann <arnd@...db.de>
> > > 
> > > Separating compiler-clang.h from compiler-gcc.h inadventently dropped the
> > > definitions of the three HAVE_BUILTIN_BSWAP macros, which requires falling
> > > back to the open-coded version and hoping that the compiler detects it.
> > > 
> > > Since all versions of clang support the __builtin_bswap interfaces,
> > > add back the flags and have the headers pick these up automatically.
> > > 
> > > This results in a 4% improvement of compilation speed for arm defconfig.
> > > 
> > > Fixes: 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h mutually exclusive")
> > > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > 
> > Cc: stable@...r.kernel.org
> 
> I figured 4% better compile time isn't significant enough to justify a
> backport.  Thoughts?

It's a trivial change, so I think it's worth it?

> 
> > Reviewed-by: Kees Cook <keescook@...omium.org>
> 

-- 
Kees Cook