linux-kernel - Re: [PATCH 2/2] selftests/fpu: Add an FPU selftest

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Date:   Tue, 23 Jun 2020 12:28:31 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        jpa@...nelbug.mail.kapsi.fi, Dave Hansen <dave.hansen@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] selftests/fpu: Add an FPU selftest

On Mon, Jun 22, 2020 at 12:37:12PM -0700, Andy Lutomirski wrote:
> It’s this whole mess:
> 
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383

It really is a mess because our option detection doesn't really work. I did:

ifdef CONFIG_CC_IS_GCC
  ifeq ($(call cc-option-yn,-mpreferred-stack-boundary=3),y)
        dummy := $(error "gcc supports -mpreferred-stack-boundary=3")
  endif
  ...

and doing:

$ make CC=gcc-4.8 HOSTCC=gcc-4.8 V=1 lib/test_fpu.ko

gives

lib/Makefile:110: *** "gcc supports -mpreferred-stack-boundary=3".  Stop.

That same compiler, however, says:

$ gcc-4.8 -mpreferred-stack-boundary=3 -c /tmp/foo.c
/tmp/foo.c:1:0: error: -mpreferred-stack-boundary=3 is not between 4 and 12

so I need to dig deep into cc-option* fun.

Or, I can be lazy and simply cut off all compiler versions to >= 8
and be done with it. If people wanna run selftests, they can upgrade
toolchain too...

-- 
Regards/Gruss,
    Boris.

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