Re: [PATCH] linux/compiler-clang.h: define HAVE_BUILTIN_BSWAP*

[Andrew Morton]

On Thu, 25 Feb 2021 12:03:48 -0800 Kees Cook <keescook@xxxxxxxxxxxx> wrote:

> On Thu, Feb 25, 2021 at 05:45:09PM +0100, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@xxxxxxxx>
> > 
> > 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@xxxxxxxx>
> 
> Cc: stable@xxxxxxxxxxxxxxx

I figured 4% better compile time isn't significant enough to justify a
backport.  Thoughts?

> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>