Messages in this thread |  | | | Date | Sun, 20 Dec 2009 10:30:33 +0200 | | From | Avi Kivity <> | | Subject | Re: x86: do_debug && PTRACE_SINGLESTEP broken by 08d68323d1f0c34452e614263b212ca556dae47f |
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On 12/19/2009 01:15 AM, Frederic Weisbecker wrote: > >> 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. >> >
A kvm bug is most likely.
> It looks like in kvm, before entering the guest, we restore its > debug registers: > > vcpu_enter_guest(): > if (unlikely(vcpu->arch.switch_db_regs)) { > set_debugreg(0, 7); > set_debugreg(vcpu->arch.eff_db[0], 0); > set_debugreg(vcpu->arch.eff_db[1], 1); > set_debugreg(vcpu->arch.eff_db[2], 2); > set_debugreg(vcpu->arch.eff_db[3], 3); > } > > > But what happens to dr6, I don't know. >
That's done later, in vmx.c:vmx_vcpu_run():
if (vcpu->arch.switch_db_regs) set_debugreg(vcpu->arch.dr6, 6); Can you describe the failure? I'll try to construct a test case reproducer and work with Jan to fix it.
-- error compiling committee.c: too many arguments to function
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