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Date: Mon, 22 Jun 2015 19:02:04 +0300
From: Andriy Gapon <avg@FreeBSD.org>
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Subject: dtrace fbt vs vmm
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It seems that vmm contains functions for which it is not safe to enable fbt
probes.  At least, if I activate all fbt return probes with e.g.

fbt:::return /self->trace && (int)arg1 == 28/ { printf("ret = %#x\n", arg0);
stack();

(this is a part of larger script) while having an active bhyve VM, then I
instantly get what looks like a possible triple-fault.

I haven't investigated this issue further, but if there are any unsafe functions
in vmm it would be nice to blacklist them in the fbt code.
Perhaps blacklisting everything from vmm module could be a stopgap solution.

-- 
Andriy Gapon