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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Thu, 25 Feb 2021 13:01:04 -0800
Message-ID: <CAKwvOdmHSgDMMgwowTWyvy4voyD_TtTY811jtKsZR+kUciittg@mail.gmail.com>
Subject: Re: [PATCH] linux/compiler-clang.h: define HAVE_BUILTIN_BSWAP*
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        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 <clang-built-linux@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Thu, Feb 25, 2021 at 12:06 PM Andrew Morton
<akpm@linux-foundation.org> 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?

If I made a mistake in 815f0ddb346c, then it would be important to
correct it since 815f0ddb346c has existed for a few stable branches
(first landed in v4.19-rc1).
Acked-by: Nick Desaulniers <ndesaulniers@google.com>

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


-- 
Thanks,
~Nick Desaulniers