On Mon, 2009-08-03 at 12:19 +0530, Srikar Dronamraju wrote: > > ... > > > > > > and the corresponding function call graph was: > > > > > > 3854 zsh(1350): uprobe_report_signal action=0x0 > > > engine=0xffff88003ac36078 tsk=0xffff880037d0a470 regs=0xffff880059097f58 > > > info > > > 3867 zsh(1350): utrace_attach_pid pid=0xffff880078e8d680 flags=0x1 > > > ops=0xffffffff81443be0 data=0x0 > > > 3881 zsh(1350): utrace_attach_task target=0xffff880037d0a470 > > > flags=0x1 ops=0xffffffff81443be0 data=0x0 > > > 3890 zsh(1350): matching_engine utrace=0xffff880037d0aad8 flags=0x1 > > > ops=0xffffffff81443be0 data=0x0 > > > 3901 zsh(1350): matching_engine return=0xffff880078d190f0 > > > 3907 zsh(1350): utrace_attach_task return=0xffff880078d190f0 > > > 3914 zsh(1350): put_task_struct t=0xffff880037d0a470 > > > 3918 zsh(1350): put_task_struct > > > 3923 zsh(1350): utrace_attach_pid return=0xffff880078d190f0 > > > > I can't think of why utrace_attach_pid() would get called here. > > utrace_attach_pid is from xol_get_area(). So its clear that this was the > first time uprobe_report_signal was called. Also the call to > uretprobe_set_trampoline (below) confirms that this was the first time > uprobe_report_signal was called.
Yes, indeed. ... > > > So as per my analysis, gdb_utrace_report_signal was called, followed by > uprobe_report_signal. Since gdb_utrace_report_signal requested for > UTRACE_STOP as resume action for SIGTRAP, the thread got stopped. > uprobes was waiting for either the singlestep to occur (or the process to > exit/exec or some other event) before it could signal the process to be > quiesced. Uprobes attempts to handle this situation. Before returning (UTRACE_SINGLESTEP | UTRACE_SIGNAL_IGN), uprobe_report_signal() registers to be notified of quiesce events. If report_signal for some other engine (e.g., gdbstub's) requests a UTRACE_STOP, that'll override uprobe_report_signal()'s UTRACE_SINGLESTEP. But uprobe_report_quiesce() should get called as a result and re-assert UTRACE_SINGLESTEP. Assuming gdbstub's report_quiesce callback eventually returns something other than UTRACE_STOP, the UTRACE_SINGLESTEP should take effect. That was my thinking, anyway. I can't guarantee that it actually works that way. > ... > > -- > Thanks and Regards > Srikar Jim
