On 01/06, Roland McGrath wrote: > > > Oh, I am not sure. But I don't understand TIF_SINGLE_STEP on s390, > > absolutely. > > > > For example, why do_signal() sets TIF_SINGLE_STEP? Why can't we do > > I think we could. That would be more consistent with other machines. On > s390, once we set TIF_SINGLE_STEP, we are going to post a SIGTRAP > eventually before going to user mode. But then tracehook_signal_handler() > also gets stepping=1 and the expected meaning of this is that the arch code > is not itself simulating a single-step for the handler setup. So the > tracehook (i.e. ptrace/utrace) code does what it does for "need a fake > single-step". > > In ptrace (including utrace-based ptrace), this winds up with sending a > SIGTRAP. So when we finally do get out of do_signal and TIF_SINGLE_STEP > causes a second SIGTRAP, it's already pending and the second one makes no > difference. Confused again, perhaps I just misunderstood what you mean... Without utrace, tracehook_signal_handler() doesn't send SIGTRAP, it merely does ptrace_notify(SIGTRAP), this means that > But for the general case of utrace, we'll have the UTRACE_SIGNAL_HANDLER > report, followed by a SIGTRAP that appears to be an authentic single-step > trap, but takes place on the same instruction. If the resumption after the > UTRACE_SIGNAL_HANDLER report didn't use stepping, then this is an entirely > unexpected extra SIGTRAP. even without utrace we can have unexpected SIGTRAP. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
