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Re: PROPOSAL: Extend inline asm syntax with size spec
- From: Segher Boessenkool <segher at kernel dot crashing dot org>
- To: Richard Biener <rguenther at suse dot de>
- Cc: Michael Matz <matz at suse dot de>, Borislav Petkov <bp at alien8 dot de>, gcc at gcc dot gnu dot org, Nadav Amit <namit at vmware dot com>, Ingo Molnar <mingo at redhat dot com>, linux-kernel at vger dot kernel dot org, x86 at kernel dot org, Masahiro Yamada <yamada dot masahiro at socionext dot com>, Sam Ravnborg <sam at ravnborg dot org>, Alok Kataria <akataria at vmware dot com>, Christopher Li <sparse at chrisli dot org>, Greg Kroah-Hartman <gregkh at linuxfoundation dot org>, "H. Peter Anvin" <hpa at zytor dot com>, Jan Beulich <JBeulich at suse dot com>, Josh Poimboeuf <jpoimboe at redhat dot com>, Juergen Gross <jgross at suse dot com>, Kate Stewart <kstewart at linuxfoundation dot org>, Kees Cook <keescook at chromium dot org>, linux-sparse at vger dot kernel dot org, Peter Zijlstra <peterz at infradead dot org>, Philippe Ombredanne <pombredanne at nexb dot com>, Thomas Gleixner <tglx at linutronix dot de>, virtualization at lists dot linux-foundation dot org, Linus Torvalds <torvalds at linux-foundation dot org>, Chris Zankel <chris at zankel dot net>, Max Filippov <jcmvbkbc at gmail dot com>, linux-xtensa at linux-xtensa dot org
- Date: Wed, 10 Oct 2018 02:53:54 -0500
- Subject: Re: PROPOSAL: Extend inline asm syntax with size spec
- References: <20181003213100.189959-1-namit@vmware.com> <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>
On Wed, Oct 10, 2018 at 09:12:48AM +0200, Richard Biener wrote:
> On Tue, 9 Oct 2018, Segher Boessenkool wrote:
> > On Mon, Oct 08, 2018 at 11:07:46AM +0200, Richard Biener wrote:
> > > On Mon, 8 Oct 2018, Segher Boessenkool wrote:
> > > > On Sun, Oct 07, 2018 at 03:53:26PM +0000, Michael Matz wrote:
> > > > > On Sun, 7 Oct 2018, Segher Boessenkool wrote:
> > > > > > On Sun, Oct 07, 2018 at 11:18:06AM +0200, Borislav Petkov wrote:
> > > > > > > Now, Richard suggested doing something like:
> > > > > > >
> > > > > > > 1) inline asm ("...")
> > > > > >
> > > > > > What would the semantics of this be?
> > > > >
> > > > > The size of the inline asm wouldn't be counted towards the inliner size
> > > > > limits (or be counted as "1").
> > > >
> > > > That sounds like a good option.
> > >
> > > Yes, I also like it for simplicity. It also avoids the requirement
> > > of translating the number (in bytes?) given by the user to
> > > "number of GIMPLE instructions" as needed by the inliner.
> >
> > This patch implements this, for C only so far. And the syntax is
> > "asm inline", which is more in line with other syntax.
> >
> > How does this look?
>
> Looks good. A few nits - you need to document this in extend.texi, the
Yup.
> tree flag use needs documenting in tree-core.h,
Ah yes.
> and we need a testcase
> (I'd suggest one that shows we inline a function with "large" asm inline
> () even at -Os).
I have one. Oh, and I probably should do a comment at the one line of
code that isn't just bookkeeping ;-)
> Oh, and I don't think we want C and C++ to diverge - so you need to
> cook up C++ support as well.
Right, that's why I said "C only so far".
> Can kernel folks give this a second and third thought please so we
> don't implement sth that in the end won't satisfy you guys?
Or actually try it out and see if it has the desired effect! Nothing
beats field trials.
I'll do the C++ thing today hopefully, and send things to gcc-patches@.
Segher