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Date:   Thu, 25 Feb 2021 12:06:37 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Kees Cook <keescook@chromium.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: <20210225120637.8e2a234f192952829fc5f471@linux-foundation.org>
In-Reply-To: <202102251203.03762F77@keescook>
References: <20210225164513.3667778-1-arnd@kernel.org>
        <202102251203.03762F77@keescook>
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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?

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