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Date:   Wed, 10 Oct 2018 13:54:33 -0500
From:   Segher Boessenkool <segher@kernel.crashing.org>
To:     Borislav Petkov <bp@alien8.de>
Cc:     Ingo Molnar <mingo@kernel.org>, Richard Biener <rguenther@suse.de>,
        Michael Matz <matz@suse.de>, gcc@gcc.gnu.org,
        Nadav Amit <namit@vmware.com>, Ingo Molnar <mingo@redhat.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Sam Ravnborg <sam@ravnborg.org>,
        Alok Kataria <akataria@vmware.com>,
        Christopher Li <sparse@chrisli.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Jan Beulich <JBeulich@suse.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Juergen Gross <jgross@suse.com>,
        Kate Stewart <kstewart@linuxfoundation.org>,
        Kees Cook <keescook@chromium.org>,
        linux-sparse@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
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        virtualization@lists.linux-foundation.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Max Filippov <jcmvbkbc@gmail.com>,
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        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: PROPOSAL: Extend inline asm syntax with size spec
Message-ID: <20181010185432.GB29268@gate.crashing.org>
References: <20181007091805.GA30687@zn.tnic> <20181007132228.GJ29268@gate.crashing.org> <alpine.LSU.2.21.1810071534220.7867@wotan.suse.de> <20181008073128.GL29268@gate.crashing.org> <alpine.LSU.2.20.1810081105350.16707@zhemvz.fhfr.qr> <20181009145330.GT29268@gate.crashing.org> <alpine.LSU.2.20.1810100909140.16707@zhemvz.fhfr.qr> <20181010072240.GB103159@gmail.com> <20181010080324.GV29268@gate.crashing.org> <20181010081906.GA5533@zn.tnic>
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On Wed, Oct 10, 2018 at 10:19:06AM +0200, Borislav Petkov wrote:
> 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.

It would be great to hear from kernel people if it works adequately for
what you guys want it for :-)

> > 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.

But this isn't really different from other always_inline concerns afaics?
So you should be able to catch it the same way, too.


Segher