linux-kernel - Re: [PATCH v2 10/16] x86: probe assembler capabilities via kconfig instead of makefile

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Date:   Thu, 26 Mar 2020 13:00:35 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 10/16] x86: probe assembler capabilities via kconfig
 instead of makefile

On Thu, Mar 26, 2020 at 12:54 PM Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> On Thu, Mar 26, 2020 at 11:49 AM Nick Desaulniers
> <ndesaulniers@...gle.com> wrote:
> >
> > On Thu, Mar 26, 2020 at 1:02 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
> > >
> > > From: "Jason A. Donenfeld" <Jason@...c4.com>
> > >
> > > Doing this probing inside of the Makefiles means we have a maze of
> > > ifdefs inside the source code and child Makefiles that need to make
> > > proper decisions on this too. Instead, we do it at Kconfig time, like
> > > many other compiler and assembler options, which allows us to set up the
> > > dependencies normally for full compilation units. In the process, the
> > > ADX test changes to use %eax instead of %r10 so that it's valid in both
> > > 32-bit and 64-bit mode.
> >
> > Does KConfig generate -D<foo> flags for KBUILD_CFLAGS and KBUILD_AFLAGS?
>
> kconfig sticks everything it's got into include/generated/autoconf.h.
> That's how you're able to use all those #ifdef CONFIG_* macros
> already. This change moves things from a command line -D to the
> autoconf.h file.

Cool, I wondered how that was wired up.  Though seeing the word
"autoconf" brings on PTSD for me.
Patch LGTM.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

>
> > Looks like lib/raid6/test/Makefile also generates some of these?
>
> raid6 has its own crazy thing going on. The test directory compiles
> that code for use in userspace. You might argue that its whole
> situation is non-standard and weird and should be reworked
> differently, but that seems like fodder for a different patchset on
> the linux-raid list.



-- 
Thanks,
~Nick Desaulniers