On 10/13, Roland McGrath wrote: > > > But. Suppose we have to attached engines. The first engine gets > > UTRACE_SIGNAL_REPORT and returns "UTRACE_STOP | UTRACE_SIGNAL_IGN". > > Right, that's what it would do. I see, you're saying that the > report.result passed on to the next engine would appear like it had > been a real signal that the previous engine decided to ignore (or > whose sa_handler==SIG_IGN or default action was to ignore). Hmm. > > Well, it's also distinguished by having orig_ka==NULL in the callback. > Any real signal has a non-null orig_ka argument.
Yes, this is what ugdb does. ptrace doesn't, I didn't realize this problem when I was writing that code. > > or yes, it returns UTRACE_SIGNAL_DELIVER after gdb does "signal XX". > > > > Now. The second engine gets UTRACE_SIGNAL_DELIVER or UTRACE_SIGNAL_IGN, > > not UTRACE_SIGNAL_REPORT. > > At least in the UTRACE_SIGNAL_DELIVER case, that's really the true > thing for it to see. The previous engine decided to do a signal > delivery (as directed by return_ka), so the next engine needs to see > this to know what the prevailing state of play is now. Agreed. Currently ugdb doesn't report a signal injected by another engine. > > > I'm not really sure what you mean here. > > > > If ->report_signal(orig_ka) was calles with orig_ka == NULL, then, > > whatever utrace_signal_action(action) we see, originally it was > > either UTRACE_SIGNAL_HANDLER or UTRACE_SIGNAL_REPORT but another engine > > returned, say, UTRACE_SIGNAL_DELIVER/UTRACE_SIGNAL_IGN to deliver/stop. > > Right. But this is in fact just the same for either > UTRACE_SIGNAL_REPORT or UTRACE_SIGNAL_HANDLER. Now I am not sure what you mean... Yes, if the callback returns UTRACE_SIGNAL_REPORT then the next callback will see "orig_ka == NULL" too, sure. But I guess you meant something else. > > > > Not sure about UTRACE_SIGNAL_HOLD, but this is very unlikely race. > > > > > > You probably don't want to use that, but I'm not entirely sure. ptrace > > > doesn't use it, and the signal interception model is pretty much the same. > > > > Yes, agreed. But there is one corner case. Until we generalize > > utrace_stop()->ptrace_notify_stop() hook, the tracee can be reported as > > stopped to gdb, but before it actually stops it can recieve a signal. > > I don't follow this. If we're stopping, then we don't "receive" > (dequeue) any other signal until we get resumed. That should be fine > from gdb's point of view. The next signal is just pending for later. Hmm. Yes. If a callback ever returned UTRACE_STOP, utrace_get_signal() should notice utrace->resume <= UTRACE_REPORT. OK, so ugdb doesn't need this hack. Thanks. Now I am wondering how I managed to test this UTRACE_SIGNAL_HOLD code. I recall, initially it returned "UTRACE_STOP | UTRACE_SIGNAL_HOLD", then the testing showed it doesn't work and I added UTRACE_SIGNAL_REPORT. Probably I added some hacks to simulate the problem which, as you showed, doesn't exist. Oleg.