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

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Date:   Thu, 3 Oct 2019 10:08:09 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
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 10:01 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> 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.

Side note: what might be an actual advantage would be to have a mode
where you see when the compiler would choose to not inline things.

Maybe we have things that are marked "inline" that simply shouldn't
be. We do tend to have this history of adding small helper functions
to header files, and then they grow and grow and grow. And now they
shouldn't be in a header file any more, but they still are.

So having a "compiler doesn't want to inline this" flag might be
useful for finding those, but it might also be useful for people
looking for what triggers bugs.

But honestly, the last time I saw somebody argue for "I don't want
inlining", it was the broken "I want to compiler the kernel with no
optimizations so that it's easier to look at the resulting code". That
was just a _bad_ bad patch. And if it is concerns like that that are
driving this "compiler doesn't have to inline", then we should stop it
immediately.

             Linus