linux-kernel - Re: [PATCH v5 00/10] x86/asm: Compile-time asm code validation

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Message-ID: <20150610165056.GC29724@treble.redhat.com>
Date:	Wed, 10 Jun 2015 11:50:56 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 00/10] x86/asm: Compile-time asm code validation

On Wed, Jun 10, 2015 at 10:31:55AM -0500, Josh Poimboeuf wrote:
> On Wed, Jun 10, 2015 at 05:04:12PM +0200, Andi Kleen wrote:
> > It's not needed, but it's an optimization to optimize icache usage.
> > It is optional (-freorder-blocks-and-partition)
> > 
> > In this case gcc splits the function into two (hot and cold)
> > 
> > It's actually a nice optimization and it would be sad from stopping
> > the kernel from using it.
> 
> Sorry if I wasn't clear, I was trying to ask for examples in kernel asm
> code.
> 
> Are you suggesting that we implement this gcc optimization in kernel asm
> code?

If you're wanting something like -freorder-blocks-and-partition for asm
code, maybe we could implement something analagous to the
likely()/unlikely() macros, to allow the hot and cold portions to be
placed into different sections.  (I could then teach asmvalidate how to
validate such code.)

Would that be useful?

-- 
Josh
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