linux-kernel - Re: PROPOSAL: Extend inline asm syntax with size spec

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Message-ID: <20181010081906.GA5533@zn.tnic>
Date:   Wed, 10 Oct 2018 10:19:06 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Segher Boessenkool <segher@...nel.crashing.org>,
        Ingo Molnar <mingo@...nel.org>
Cc:     Richard Biener <rguenther@...e.de>, Michael Matz <matz@...e.de>,
        gcc@....gnu.org, Nadav Amit <namit@...are.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Alok Kataria <akataria@...are.com>,
        Christopher Li <sparse@...isli.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H. Peter Anvin" <hpa@...or.com>, Jan Beulich <JBeulich@...e.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
        linux-sparse@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        virtualization@...ts.linux-foundation.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        linux-xtensa@...ux-xtensa.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: PROPOSAL: Extend inline asm syntax with size spec

On Wed, Oct 10, 2018 at 03:03:25AM -0500, Segher Boessenkool wrote:
> The code immediately after this makes it size 1, even for things like
> asm(""), I suppose this works better for the inliner.  But that's a detail
> (and it might change); the description says "consider this asm as minimum
> length and cost for inlining decisions", which works for either 0 or 1.

Thanks for implementing this, much appreciated. If you need people to
test stuff, lemme know.

> You can think of it as meaning "we want this asm inlined always", and then
> whether that actually happens depends on if the function around it is
> inlined or not.

My only concern is how we would catch the other extremity where the
inline asm grows too big and we end up inlining it everywhere and thus
getting fat. The 0day bot already builds tinyconfigs but we should be
looking at vmlinux size growth too.

Thx.

-- 
Regards/Gruss,
    Boris.

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