Finally, the actual fix.
ptrace_detach_task(sig = -1) is very buggy. Somehow I completely forgot
that implicit detach can race with the running tracee. Depending on how
exactly it races with ptrace_report_signal() we can have the following
problems:
1) If the tracer exits right after
Unlike powepc, x86 always calls tracehook_report_syscall_exit(step)
with step = 0, and sends the trap by hand.
This results in unnecessary SIGTRAP when PTRACE_SINGLESTEP follows
the syscall-exit stop.
Change syscall_trace_leave() to pass the correct step argument to
tracehook and remove the
