On 12/18, Roland McGrath wrote: > > > 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.
OK, thanks. Hmm. Now I see how wrong I was when I said this code is "obviously wrong" ;) I'll add the debugging printk's and report the output. Sorry for delay, can't do this today. Oleg.