linux-kernel - Re: Kernel broken on processors without performance counters

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Message-ID: <20150723190258.GL25159@twins.programming.kicks-ass.net>
Date:	Thu, 23 Jul 2015 21:02:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jason Baron <jasonbaron0@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mikulas Patocka <mpatocka@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Kees Cook <keescook@...omium.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Vince Weaver <vince@...ter.net>,
	"hillf.zj" <hillf.zj@...baba-inc.com>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Kernel broken on processors without performance counters

On Thu, Jul 23, 2015 at 01:33:36PM -0400, Jason Baron wrote:
> > That would be bad, how can we force it to emit 5 bytes?

> hmm....I don't think that's an issue, the patching code can
> detect if its a 2-byte jump - 0xeb, or 5-byte: 0xe9, and do
> the correct no-op. Same going the other way. See the code
> I posted a few mails back. In fact, this gets us to the
> smaller 2-byte no-ops in cases where we are initialized
> to jump.

Ah yes, I looked right over that.

I think that if we want to go do that, it should be a separate patch
though.
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