linux-kernel - Re: [PATCH v4 14/17] x86/asm/entry/64: Migrate error and interrupt exit work to C

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Message-ID: <20150702163339.GM4001@pd.tnic>
Date:	Thu, 2 Jul 2015 18:33:39 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4 14/17] x86/asm/entry/64: Migrate error and interrupt
 exit work to C

On Thu, Jul 02, 2015 at 09:09:23AM -0700, Andy Lutomirski wrote:
> You mean link-time asm optimizations?  Turning off frame pointers in
> leaf functions as long as rbp is still preserved might not be so
> terrible either.

Is there a gcc switch for that?

> I'm torn on this one.  In principle, you're right, or we could have a
> macro CALL_ENTER_FROM_USER_MODE that does nothing if context tracking
> is off.  OTOH, that's also kind of messy.

Yeah, I'm torn too.

If you have something better, cool. Otherwise it is a judgement call for
tip people.

> If we move even more of this stuff into C, then this problem goes
> away.  "call enter_from_user_mode" turns into "enter_from_user_mode()"
> or similar.

... and that should be optimized away, I'd guess, if the body's empty.
Something like empty body removal or whatever...

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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