linux-kernel - Re: [PATCH] compiler: enable CONFIG_OPTIMIZE

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Message-ID: <CAMuHMdV3VWCP35dOMWaSePz5mhzJp_Y5OViVUqTn7Ocdhn81Og@mail.gmail.com>
Date:   Thu, 26 Sep 2019 11:26:46 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] compiler: enable CONFIG_OPTIMIZE_INLINING forcibly

Hi Yamada-san,

On Thu, Sep 26, 2019 at 11:03 AM Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
> On Thu, Sep 26, 2019 at 5:54 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > On Fri, Aug 30, 2019 at 5:44 AM Masahiro Yamada
> > <yamada.masahiro@...ionext.com> wrote:
> > > Commit 9012d011660e ("compiler: allow all arches to enable
> > > CONFIG_OPTIMIZE_INLINING") allowed all architectures to enable
> > > this option. A couple of build errors were reported by randconfig,
> > > but all of them have been ironed out.
> > >
> > > Towards the goal of removing CONFIG_OPTIMIZE_INLINING entirely
> > > (and it will simplify the 'inline' macro in compiler_types.h),
> > > this commit changes it to always-on option. Going forward, the
> > > compiler will always be allowed to not inline functions marked
> > > 'inline'.
> > >
> > > This is not a problem for x86 since it has been long used by
> > > arch/x86/configs/{x86_64,i386}_defconfig.
> > >
> > > I am keeping the config option just in case any problem crops up for
> > > other architectures.
> > >
> > > The code clean-up will be done after confirming this is solid.
> > >
> > > Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> >
> > This breaks compiling drivers/video/fbdev/c2p*, as the functions in
> > drivers/video/fbdev/c2p_core.h are no longer inlined, leading to calls
> > to the non-existent function c2p_unsupported(), as reported by KISSKB:
> >
> > On Thu, Sep 26, 2019 at 5:02 AM <noreply@...erman.id.au> wrote:
> > > FAILED linux-next/m68k-defconfig/m68k Thu Sep 26, 12:58
> > >
> > > http://kisskb.ellerman.id.au/kisskb/buildresult/13973194/
> > >
> > > Commit:   Add linux-next specific files for 20190925
> > >           d47175169c28eedd2cc2ab8c01f38764cb0269cc
> > > Compiler: m68k-linux-gcc (GCC) 4.6.3 / GNU ld (GNU Binutils) 2.22
> > >
> > > Possible errors
> > > ---------------
> > >
> > > c2p_planar.c:(.text+0xd6): undefined reference to `c2p_unsupported'
> > > c2p_planar.c:(.text+0x1dc): undefined reference to `c2p_unsupported'
> > > c2p_iplan2.c:(.text+0xc4): undefined reference to `c2p_unsupported'
> > > c2p_iplan2.c:(.text+0x150): undefined reference to `c2p_unsupported'
> > > make[1]: *** [Makefile:1074: vmlinux] Error 1
> > > make: *** [Makefile:179: sub-make] Error 2
> >
> > I managed to reproduce this with gcc version 8.3.0 (Ubuntu
> > 8.3.0-6ubuntu1~18.04.1) , and bisected the failure to commit
> > 025f072e5823947c ("compiler: enable CONFIG_OPTIMIZE_INLINING forcibly") .
> >
> > Marking the functions __always_inline instead of inline fixes that.
> > Shall I send a patch to do that?
>
>
> Yes, please.

OK, will do.

> But you do not need to touch _transp() or comp().
> Only functions that call c2p_unsupported().

However, the inlining of these functions is very performance-sensitive too.
So perhaps I should mark all of them __always_inline?

> BTW, c2p_unsupported() can be replaced with BUILD_BUG().
> This will break the build earlier in case
> it cannot be optimized out.

Right. Will do, too.

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds