[PATCH 128] introduce suppress_sigtrap() to prevent unwanted send_sigtrap()

[Roland McGrath]

> I don't understand how the discussed changes in syscall_trace_leave() path
> can make any difference here.

All that part does is move all decisions about what to do into the
tracehook/utrace/ptrace layers out of arch code.

> 	The PTRACE_O_TRACEFORK tracee calls fork(), stops in SYSCALL_ENTRY.
> 
> 	The tracer does PTRACE_SINGLESTEP. utrace_control(UTRACE_SINGLESTEP)
> 	sets TIF_SINGLESTEP.
> 
> 	The tracee resumes, it must report PTRACE_EVENT_FORK. But, unlike
> 	upstream, we don't stop inside do_fork(), the tracee will stop
> 	in utrace_resume(). Before that, it passes syscall_trace_leave(),
> 	and since TIF_SINGLESTEP is set the tracee gets SIGTRAP.

After the arch/tracehook cleanup we've been discussing, what happens here
is consistent across machines.  It reaches tracehook_report_syscall_exit()
with step=1, and nothing else magical happens when after returns.  So that
is the hook into utrace/higher code that decides what to do.  Its options
here are just like all other "stacked events" cases.


Thanks,
Roland