Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 25 Feb 2021 12:14:17 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Arnd Bergmann <arnd@kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Arnd Bergmann <arnd@arndb.de>, Miguel Ojeda <ojeda@kernel.org>,
        Marco Elver <elver@google.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        Randy Dunlap <rdunlap@infradead.org>,
        clang-built-linux@googlegroups.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] linux/compiler-clang.h: define HAVE_BUILTIN_BSWAP*
Message-ID: <202102251213.5815C9B33@keescook>
References: <20210225164513.3667778-1-arnd@kernel.org>
 <202102251203.03762F77@keescook>
 <20210225120637.8e2a234f192952829fc5f471@linux-foundation.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20210225120637.8e2a234f192952829fc5f471@linux-foundation.org>
Precedence: bulk

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@chromium.org> wrote:
> 
> > On Thu, Feb 25, 2021 at 05:45:09PM +0100, Arnd Bergmann wrote:
> > > From: Arnd Bergmann <arnd@arndb.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@arndb.de>
> > 
> > Cc: stable@vger.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@chromium.org>
> 

-- 
Kees Cook