linux-kernel - Re: [PATCH RFC V2 3/5] jump_label: if a key has already been initialized, don't nop it out

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Date:	Thu, 06 Oct 2011 16:45:45 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jason Baron <jbaron@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"David S. Miller" <davem@...emloft.net>,
	David Daney <david.daney@...ium.com>,
	Michael Ellerman <michael@...erman.id.au>,
	Jan Glauber <jang@...ux.vnet.ibm.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	peterz@...radead.org, rth@...hat.com
Subject: Re: [PATCH RFC V2 3/5] jump_label: if a key has already been
 initialized, don't nop it out

On Thu, 2011-10-06 at 16:33 -0400, Jason Baron wrote:

> > Then have the record_jumplabel.c (or whatever it's called) find all the
> > jmps at run time, and convert them into the appropriate nop.
> > 
> 
> I'd prefer to do this at build-time as hpa said. We don't want there to
> be some race b/w patching in the no-ops and taking an incorrect branch.

Yep, this record_jumplabel.c would execute at build time. Just like the
record_mcount.c does.

> 
> > Then at runtime patching, the jumplabel code could figure out what size
> > jump it needs to replace it.

The runtime patching is when we can figure out what size the compiler
used. That wont change. It should be pretty trivial to do. I can't see
any races here.

-- Steve




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