On February 24, 2017 12:31:15 AM PST, Peter Zijlstra <pet...@infradead.org> wrote: >On Fri, Feb 24, 2017 at 08:43:25AM +0100, Ingo Molnar wrote: >> The only high level question is whether we trust the trap machinery >to generate >> WARN_ON()s. I believe we do. >> >> BTW.: why not use INT3 instead of all these weird #UD opcodes? It's a >single byte >> opcode and we can do a quick exception table search in do_debug(). >This way we'll >> also have irqs disabled which might help getting the message out >before any irq >> handler comes in and muddies the waters. >> >> In a sense WARN_ON()s and BUG_ON()s can be considered permanently >installed >> in-line kprobes, with a special, built-in handler. > >I've actually been looking into that. There's a bunch of 'fun' details >that I've been checking, but I think I can make that happen. > >My initial patch extended the existing UD2 BUG trap to include the >WARN, >this is what many other architectures already do. Arjan then complained >that some emulators terminate on UD2 and could I please not use that >for >WARN, at which point Borislav called my attention to UD0/UD1. > >So I made the UD0 change and posted (fwiw, there's a lost refresh in >the >patch I posted and it will not actually work). > >I think I'll post an update of said patch and then attempt to do the >INT3 thing in a later patch -- that will require at least one new knob >in the generic BUG code ... > >> BTW. #2: side note, GCC generated crap code here. Why didn't it do: > >I've seen GCC do 'wonderful' things the past few weeks. Absolutely mind >boggling stuff.
Incidentally, as an alternative to a #UD, int $9 could be an alternative (exception vector 9 was discontinued with the 486.) -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
