When vforked child is traced, the debugging events are not generated

until child performs exec().  The behaviour is reasonable when a
debugger is the real parent, because the parent is stopped until
exec(), and sending a debugging event to the debugger would deadlock
both parent and child.

On the other hand, when debugger is not the parent of the vforked
child, not sending debugging signals makes it impossible to debug
across vfork.

Fix the issue by declining generating debug signals only when vfork()
was done and child called ptrace(PT_TRACEME).  Set a new process flag
P_PPTRACE from the attach code for PT_TRACEME, if P_PPWAIT flag is
set, which indicates that the process was created with vfork() and
still did not execed. Check P_PPTRACE from issignal(), instead of
refusing the trace outright for the P_PPWAIT case.  The scope of
P_PPTRACE is exactly contained in the scope of P_PPWAIT.

Found and tested by:  zont
Reviewed by:	pluknet
MFC after:	2 weeks

1 files changed, 1 insertions, 1 deletions

diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index 3a9a3a4..82f0344 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -266,7 +266,7 @@ exit1(struct thread *td, int rv)
 	PROC_LOCK(p);
 	rv = p->p_xstat;	/* Event handler could change exit status */
 	stopprofclock(p);
-	p->p_flag &= ~(P_TRACED | P_PPWAIT);
+	p->p_flag &= ~(P_TRACED | P_PPWAIT | P_PPTRACE);
 
 	/*
 	 * Stop the real interval timer.  If the handler is currently