Re: [PATCH][RFC] jump_labels/x86: Use either 5 byte or 2 byte jumps

From: H. Peter Anvin
Date: Fri Oct 07 2011 - 18:03:52 EST

On 10/07/2011 03:00 PM, Steven Rostedt wrote:

Ouch, quite shaken by 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.

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