linux-kernel - Re: [PATCH v5 02/10] x86: Compile-time asm code validation

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Message-ID: <20150611140110.GB11517@treble.redhat.com>
Date:	Thu, 11 Jun 2015 09:01:10 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Michal Marek <mmarek@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	live-patching@...r.kernel.org, X86 ML <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v5 02/10] x86: Compile-time asm code validation

On Thu, Jun 11, 2015 at 08:08:07AM +0200, Ingo Molnar wrote:
> 
> * Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> 
> > I should also mention that my proposed ia32_ptregs_common patch, which 
> > duplicated the needed code, was more optimized for performance than code size.
> > 
> > But if you're more worried about code size, we could turn ia32_ptregs_common 
> > into a proper callable function, and then replace
> > 
> >    jmp ia32_ptregs_common
> > 
> > with:
> > 
> >    call ia32_ptregs_common
> >    ret
> > 
> > So it becomes a regular call instead of a tail call.  It only adds a few 
> > instructions and the function is self-contained.  Would that be good enough?
> 
> No, debug info should not slow down the kernel, especially not code we write in 
> assembly partly for performance.

Ok.  I'll work on adding support for external jumps.

-- 
Josh
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