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

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Date:   Fri, 4 Oct 2019 02:23:36 +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 Fri, Oct 4, 2019 at 2:02 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Wed, Oct 2, 2019 at 7:11 PM Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
> >
> > 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.
>
> Honestly, if the alternative to hiding problems is "use a macro", then
> I'd rather hide the problems and just make "inline" means "inline".
>
> If "inline" means "it's just a hint, use macros", then inline is useless.

For clarification,
I am not saying "use macros" at all.


I just want to annotate __always_inline for the case
"2. code that if not inlined is somehow not correct."



> If "inline" means "using this means that there are known compiler
> bugs, but we don't know where they trigger", then inline is _worse_
> than useless.
>
> I do not see the big advantage of letting the compiler say "yeah, I'm
> not going to do that, Dave".
>
> And I see a *huge* disadvantage when people are ignoring compiler
> bugs, and are saying "use a macro". Seriously.


Again, not saying "use a macro".



>
> Right now we see the obvious compiler bugs that cause build breakages.
> How many non-obvious compiler bugs do we have? And how sure are you
> that our code is "correct" after fixing a couple of obvious cases?
>
> As to "portable", nobody cares. We're a kernel. We aren't portable,
> and never were.
>
> If this is purely about the fact that x86 is different from other
> architectures, then let's remove the "compiler can do stupid things"
> option on x86 too. It was never clear that it was a huge advantage.
>
>                Linus



-- 
Best Regards
Masahiro Yamada