linux-kernel - Re: [PATCH v2 4/6] compiler-gcc.h: add asm

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Message-ID: <CAKwvOdnaBD3Dg3pmZqX2-=Cd0n30ByMT7KUNZKhq0bsDdFeXpg@mail.gmail.com>
Date:   Fri, 6 Sep 2019 18:04:54 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Segher Boessenkool <segher@...nel.crashing.org>
Cc:     Jakub Jelinek <jakub@...hat.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "gcc-patches@....gnu.org" <gcc-patches@....gnu.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH v2 4/6] compiler-gcc.h: add asm_inline definition

On Fri, Sep 6, 2019 at 5:14 PM Segher Boessenkool
<segher@...nel.crashing.org> wrote:
>
> On Fri, Sep 06, 2019 at 04:42:58PM -0700, Nick Desaulniers via gcc-patches wrote:
> > Just to prove my point about version checks being brittle, it looks
> > like Rasmus' version check isn't even right.  GCC supported `asm
> > inline` back in the 8.3 release, not 9.1 as in this patch:
>
> Yes, I backported it so that it is available in 7.5, 8.3, and 9.1, so
> that more users will have this available sooner.  (7.5 has not been
> released yet, but asm inline has been supported in GCC 7 since Jan 2
> this year).

Ah, ok that makes sense.

How would you even write a version check for that?

Which looks better?

#if __GNU_MAJOR__ > 9 || __GNU_MAJOR__ == 8 && __GNU_MINOR__ >= 3 ||
__GNU_MAJOR__ == 7 && __GNU_MINOR__ >= 5 || __CLANG_MAJOR__ == 42
// make use of `asm inline`
#endif

or

#ifdef __CC_HAS_ASM_INLINE__
// make use of `asm inline`
#endif

>
> > Or was it "broken" until 9.1?  Lord knows, as `asm inline` wasn't in
> > any release notes or bug reports I can find:
>
> https://gcc.gnu.org/ml/gcc-patches/2019-02/msg01143.html
>
> It never was accepted, and I dropped the ball.

Ah, ok, that's fine, so documentation was at least written.  Tracking
when and where patches land (or don't) is difficult when patch files
are emailed around.  I try to keep track of when and where our kernel
patches land, but I frequently drop the ball there.

> > Segher, next time there's discussion about new C extensions for the
> > kernel, can you please include me in the discussions?
>
> You can lurk on gcc-patches@ and/or gcc@?

Please "interrupt" me when you're aware of such discussions, rather
than me "polling" a mailing list.  (I will buy you a tasty beverage of
your preference).  I'm already subscribed to more mailing lists than I
have time to read.

> But I'll try to remember, sure.
> Not that I am involved in all such discussions myself, mind.

But you _did_ implement `asm inline`. ;)
-- 
Thanks,
~Nick Desaulniers