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

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Date:   Thu, 3 Oct 2019 11:10:11 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Will Deacon <will@...nel.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Stefan Wahren <wahrenst@....net>,
        Kees Cook <keescook@...gle.com>, Arnd Bergmann <arnd@...db.de>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] compiler: enable CONFIG_OPTIMIZE_INLINING forcibly

On Thu, Oct 3, 2019 at 5:46 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Wed, Oct 2, 2019 at 5:56 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> >
> > >
> > > Then use the C preprocessor to force the inlining.  I'm sorry it's not
> > > as pretty as static inline functions.
> >
> > Which makes us lose the baby^H^H^H^Htype checking performed
> > on function parameters, requiring to add more ugly checks.
>
> I'm 100% agreed on this.
>
> If the inline change is being pushed by people who say "you should
> have used macros instead if you wanted inlining", then I will just
> revert that stupid commit that is causing problems.
>
> No, the preprocessor is not the answer.
>
> That said, code that relies on inlining for _correctness_ should use
> "__always_inline" and possibly even have a comment about why.
>
> But I am considering just undoing commit 9012d011660e ("compiler:
> allow all arches to enable CONFIG_OPTIMIZE_INLINING") entirely.

No, please do not.

Macrofying the 'inline' is a horrid mistake that makes incorrect code work.
It would eternally prevent people from writing portable, correct code.
Please do not encourage to hide problems.


> The
> advantages are questionable, and when the advantages are balanced
> against actual regressions and the arguments are "use macros", that
> just shows how badly thought out this was.
>
>                 Linus



-- 
Best Regards
Masahiro Yamada