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

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Date:   Thu, 26 Sep 2019 10:54:10 +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>,
        noreply@...erman.id.au
Subject: Re: [PATCH] compiler: enable CONFIG_OPTIMIZE_INLINING forcibly

Hi Yamada-san,

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?

Thanks!

> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -327,7 +327,7 @@ config HEADERS_CHECK
>           relevant for userspace, say 'Y'.
>
>  config OPTIMIZE_INLINING
> -       bool "Allow compiler to uninline functions marked 'inline'"
> +       def_bool y
>         help
>           This option determines if the kernel forces gcc to inline the functions
>           developers have marked 'inline'. Doing so takes away freedom from gcc to
> @@ -338,8 +338,6 @@ config OPTIMIZE_INLINING
>           decision will become the default in the future. Until then this option
>           is there to test gcc for this.
>
> -         If unsure, say N.
> -
>  config DEBUG_SECTION_MISMATCH
>         bool "Enable full Section mismatch analysis"
>         help

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