From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH][RFC] jump_labels/x86: Use either 5 byte or 2 byte jumps
Date: Fri, 07 Oct 2011 15:03:25 -0700
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To: Steven Rostedt <rostedt@goodmis.org>
Cc: Jason Baron <jbaron@redhat.com>, Jeremy Fitzhardinge <jeremy@goop.org>, Richard Henderson <rth@redhat.com>, "David S. Miller" <davem@davemloft.net>, David Daney <david.daney@cavium.com>, Michael Ellerman <michael@ellerman.id.au>, Jan Glauber <jang@linux.vnet.ibm.com>, the arch/x86 maintainers <x86@kernel.org>, Xen Devel <xen-devel@lists.xensource.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>, peterz@infradead.org
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On 10/07/2011 03:00 PM, Steven Rostedt wrote:
>
> Ouch, quite shaken by k.org? I guess I should have substituted go blind
> with being hacked.
>

Well, yes, but I would have said exactly the same thing before.

> The thing is, it may be as simple as an out of tree module screwing up
> the jump table. Or worse, gcc not doing things that we did not expect.
> If this is the case, jump labels can be disabled from modifying code.
>
> But if we just want to do the BUG() case, this will be a big hammer to
> the code and we just prevent any further progress until the issue is
> addressed. Which may be tell people to disable jump labels in their
> code, or use a different compiler.

That is EXACTLY what should happen.  Something is wrong to the point of 
the kernel is *known* to be executing the wrong code.  That is an 
extremely serious condition and should be treated as such.

If you want, you could have a debug option to demote this to WARN, but I 
really don't want to see it by default.

	-hpa