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

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Message-ID: <20191012144550.GN25745@shell.armlinux.org.uk>
Date:   Sat, 12 Oct 2019 15:45:50 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Stefan Wahren <wahrenst@....net>
Cc:     Will Deacon <will@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        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>,
        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 Sat, Oct 12, 2019 at 12:15:42PM +0200, Stefan Wahren wrote:
> Hi,
> 
> Am 03.10.19 um 18:36 schrieb Will Deacon:
> > On Wed, Oct 02, 2019 at 01:39:40PM -0700, Linus Torvalds 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. 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.
> > It's clear that opinions are divided on this issue, but you can add
> > an enthusiastic:
> >
> > Acked-by: Will Deacon <will@...nel.org>
> >
> > if you go ahead with the revert. I'm all for allowing the compiler to
> > make its own inlining decisions, but not when the potential for
> > miscompilation isn't fully understood and the proposed alternatives turn
> > the source into an unreadable mess. Perhaps we can do something different
> > for 5.5 (arch opt-in? clang only? invert the logic? work to move functions
> > over to __always_inline /before/ flipping the CONFIG option? ...?)
> 
> what's the status on this?
> 
> In need to prepare my pull requests for 5.5 and all recent kernelci
> targets (including linux-next) with bcm2835_defconfig are still broken.

I merged the patches late on Thursday, it may have been too late for
linux-next to pick them up - and because of the time difference between
UK and Australia, it means they won't be in linux-next until next week
(basically, tomorrow).  linux-next is basically a Sunday to Thursday
operation from my point of view.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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