linux-kernel - Re: [linux-stable-rc:linux-5.15.y 6874/8723] arch/arm/lib/xor-neon.c:30:2: warning: This code requires at least version 4.6 of GCC

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Date:   Sun, 31 Jul 2022 01:15:59 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Arnd Bergmann <arnd@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
        kernel test robot <lkp@...el.com>,
        "Justin M. Forbes" <jforbes@...oraproject.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        kbuild-all@...ts.01.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Jason A. Donenfeld" <zx2c4@...nel.org>
Subject: Re: [linux-stable-rc:linux-5.15.y 6874/8723]
 arch/arm/lib/xor-neon.c:30:2: warning: This code requires at least version
 4.6 of GCC

On Sat, Jul 30, 2022 at 04:33:28PM +0200, Greg Kroah-Hartman wrote:
> On Mon, Jul 25, 2022 at 04:35:38PM +0200, Arnd Bergmann wrote:
> > On Mon, Jul 25, 2022 at 2:55 PM Arnd Bergmann <arnd@...nel.org> wrote:
> > 
> > > The other easy workaround would be to just turn off the xor-neon code
> > > when building with clang, e.g. using this Makefile hack:
> > >
> > > diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
> > > index 6d2ba454f25b..8e4fe6421dd2 100644
> > > --- a/arch/arm/lib/Makefile
> > > +++ b/arch/arm/lib/Makefile
> > > @@ -43,8 +43,10 @@ endif
> > >  $(obj)/csumpartialcopy.o:      $(obj)/csumpartialcopygeneric.S
> > >  $(obj)/csumpartialcopyuser.o:  $(obj)/csumpartialcopygeneric.S
> > >
> > > +ifdef CONFIG_CC_IS_CLANG
> > >  ifeq ($(CONFIG_KERNEL_MODE_NEON),y)
> > >    NEON_FLAGS                   := -march=armv7-a -mfloat-abi=softfp -mfpu=neon
> > >    CFLAGS_xor-neon.o            += $(NEON_FLAGS)
> > >    obj-$(CONFIG_XOR_BLOCKS)     += xor-neon.o
> > >  endif
> > > +endif
> > 
> > Nevermind, this does not actually work. Just turning off the warning
> > is probably best then, as actually disabling this code would still
> > be invasive not do much beyond saving a little bit of kernel .text size.
> 
> Ok, if it triggers again, and I get annoyed, I'll write a patch,
> otherwise I'll just leave it alone unless someone else wants to send it
> to me...

The patch is trivial, if your idea is just to remove the #warning,
right? Might as well just do it now and get it over with.

Jason