Messages in this thread | | | From | Roland McGrath <> | Subject | Re: x86: do_debug && PTRACE_SINGLESTEP broken by 08d68323d1f0c34452e614263b212ca556dae47f | Date | Fri, 18 Dec 2009 12:05:03 -0800 (PST) |
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> Please find the trivial test-case below. It hangs, because > PTRACE_SINGLESTEP doesn't trigger the trap.
2.6.33-rc1 x86-64 works for me with either -m64 or -m32 version of that test.
> (not sure this matters, but I did the testing under kvm)
Apparently it does. You should hack some printks into do_debug() and see how kvm is differing from real hardware. (Actually you can probably do this with a notifier added by a module, not that you are shy about recompiling!)
Probably kvm's emulation of the hardware behavior wrt the DR6 bits is not sufficiently faithful. Conceivably, kvm is being consistent with some older hardware and we have encoded assumptions that only newer hardware meets. But I'd guess it's just a plain kvm bug.
Thanks, Roland
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