First stab at making ptrace(2) usable for debugging multi-threaded programs.

It implements a full-stop model where all threads are stopped before handing
over control to the debugger.  Events are reported as before through wait(2);
you will have to call ptrace(PT_GET_PROCESS_STATE, ...) to find out which
thread hit the event.  Since this changes the size of struct ptrace_state,
you will have to recompile gdb.

ok guenther@

7 files changed, 54 insertions, 21 deletions

diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c
index c8a202bd463..ebaca46f136 100644
--- a/sys/kern/kern_exec.c
+++ b/sys/kern/kern_exec.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_exec.c,v 1.128 2012/04/12 10:11:41 mikeb Exp $	*/
+/*	$OpenBSD: kern_exec.c,v 1.129 2012/04/13 16:37:50 kettenis Exp $	*/
 /*	$NetBSD: kern_exec.c,v 1.75 1996/02/09 18:59:28 christos Exp $	*/
 
 /*-
@@ -678,7 +678,7 @@ sys_execve(struct proc *p, void *v, register_t *retval)
 #endif
 
 	atomic_clearbits_int(&pr->ps_flags, PS_INEXEC);
-	single_thread_clear(p);
+	single_thread_clear(p, P_SUSPSIG);
 
 #if NSYSTRACE > 0
 	if (ISSET(p->p_flag, P_SYSTRACE) &&
@@ -716,7 +716,7 @@ bad:
  clrflag:
 #endif
 	atomic_clearbits_int(&pr->ps_flags, PS_INEXEC);
-	single_thread_clear(p);
+	single_thread_clear(p, P_SUSPSIG);
 
 	if (pathbuf != NULL)
 		pool_put(&namei_pool, pathbuf);
diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index 62f927aefe4..2565844fb74 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_exit.c,v 1.112 2012/04/11 15:28:50 kettenis Exp $	*/
+/*	$OpenBSD: kern_exit.c,v 1.113 2012/04/13 16:37:51 kettenis Exp $	*/
 /*	$NetBSD: kern_exit.c,v 1.39 1996/04/22 01:38:25 christos Exp $	*/
 
 /*
@@ -158,6 +158,10 @@ exit1(struct proc *p, int rv, int flags)
 
 	/* unlink ourselves from the active threads */
 	TAILQ_REMOVE(&pr->ps_threads, p, p_thr_link);
+	if (ISSET(p->p_flag, P_SUSPSINGLE)) {
+		if (--pr->ps_singlecount == 0)
+			wakeup(&pr->ps_singlecount);
+	}
 	if ((p->p_flag & P_THREAD) == 0) {
 		/* main thread gotta wait because it has the pid, et al */
 		while (! TAILQ_EMPTY(&pr->ps_threads))
@@ -487,6 +491,21 @@ loop:
 			proc_finish_wait(q, p);
 			return (0);
 		}
+		if (pr->ps_flags & PS_TRACED &&
+		    (pr->ps_flags & PS_WAITED) == 0 && pr->ps_single &&
+		    pr->ps_single->p_stat == SSTOP &&
+		    (pr->ps_single->p_flag & P_SUSPSINGLE) == 0) {
+			atomic_setbits_int(&pr->ps_flags, PS_WAITED);
+			retval[0] = p->p_pid;
+
+			if (SCARG(uap, status)) {
+				status = W_STOPCODE(pr->ps_single->p_xstat);
+				error = copyout(&status, SCARG(uap, status),
+				    sizeof(status));
+			} else
+				error = 0;
+			return (error);
+		}
 		if (p->p_stat == SSTOP &&
 		    (pr->ps_flags & PS_WAITED) == 0 &&
 		    (p->p_flag & P_SUSPSINGLE) == 0 &&
diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index 62ed83d6e0f..e2771d04022 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_fork.c,v 1.138 2012/04/12 12:33:03 deraadt Exp $	*/
+/*	$OpenBSD: kern_fork.c,v 1.139 2012/04/13 16:37:51 kettenis Exp $	*/
 /*	$NetBSD: kern_fork.c,v 1.29 1996/02/09 18:59:34 christos Exp $	*/
 
 /*
@@ -288,6 +288,7 @@ fork1(struct proc *curp, int exitsig, int flags, void *stack, pid_t *tidptr,
 	p->p_stat = SIDL;			/* protect against others */
 	p->p_exitsig = exitsig;
 	p->p_flag = 0;
+	p->p_xstat = 0;
 
 	if (flags & FORK_THREAD) {
 		atomic_setbits_int(&p->p_flag, P_THREAD);
diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index 991744db1d3..c1cb5857ce0 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_sig.c,v 1.140 2012/04/12 10:11:41 mikeb Exp $	*/
+/*	$OpenBSD: kern_sig.c,v 1.141 2012/04/13 16:37:51 kettenis Exp $	*/
 /*	$NetBSD: kern_sig.c,v 1.54 1996/04/22 01:38:32 christos Exp $	*/
 
 /*
@@ -1072,12 +1072,20 @@ issignal(struct proc *p)
 			 */
 			p->p_xstat = signum;
 
+			KERNEL_LOCK();
+			single_thread_set(p, SINGLE_SUSPEND, 0);
+			KERNEL_UNLOCK();
+
 			if (dolock)
 				SCHED_LOCK(s);
 			proc_stop(p, 1);
 			if (dolock)
 				SCHED_UNLOCK(s);
 
+			KERNEL_LOCK();
+			single_thread_clear(p, 0);
+			KERNEL_UNLOCK();
+
 			/*
 			 * If we are no longer being traced, or the parent
 			 * didn't give us a signal, look for more signals.
@@ -1766,7 +1774,7 @@ single_thread_set(struct proc *p, enum single_thread_mode mode, int deep)
 	TAILQ_FOREACH(q, &pr->ps_threads, p_thr_link) {
 		int s;
 
-		if (q == p)
+		if (q == p || ISSET(q->p_flag, P_WEXIT))
 			continue;
 		SCHED_LOCK(s);
 		atomic_setbits_int(&q->p_flag, P_SUSPSINGLE);
@@ -1812,7 +1820,7 @@ single_thread_set(struct proc *p, enum single_thread_mode mode, int deep)
 }
 
 void
-single_thread_clear(struct proc *p)
+single_thread_clear(struct proc *p, int flag)
 {
 	struct process *pr = p->p_p;
 	struct proc *q;
@@ -1834,7 +1842,7 @@ single_thread_clear(struct proc *p)
 		 * it back into some sleep queue
 		 */
 		SCHED_LOCK(s);
-		if (q->p_stat == SSTOP && (q->p_flag & P_SUSPSIG) == 0) {
+		if (q->p_stat == SSTOP && (q->p_flag & flag) == 0) {
 			if (q->p_wchan == 0)
 				setrunnable(q);
 			else
diff --git a/sys/kern/sys_process.c b/sys/kern/sys_process.c
index 480f42dd0e3..14a19211c0a 100644
--- a/sys/kern/sys_process.c
+++ b/sys/kern/sys_process.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sys_process.c,v 1.55 2012/04/12 14:40:41 kettenis Exp $	*/
+/*	$OpenBSD: sys_process.c,v 1.56 2012/04/13 16:37:51 kettenis Exp $	*/
 /*	$NetBSD: sys_process.c,v 1.55 1996/05/15 06:17:47 tls Exp $	*/
 
 /*-
@@ -84,7 +84,6 @@ sys_ptrace(struct proc *p, void *v, register_t *retval)
 	} */ *uap = v;
 	struct proc *t;				/* target thread */
 	struct process *tr;			/* target process */
-	struct proc *q;
 	struct uio uio;
 	struct iovec iov;
 	struct ptrace_io_desc piod;
@@ -437,6 +436,9 @@ sys_ptrace(struct proc *p, void *v, register_t *retval)
 		 * from where it stopped."
 		 */
 
+		if (SCARG(uap, pid) < THREAD_PID_OFFSET && tr->ps_single)
+			t = tr->ps_single;
+
 		/* Check that the data is a valid signal number or zero. */
 		if (SCARG(uap, data) < 0 || SCARG(uap, data) >= NSIG)
 			return (EINVAL);
@@ -469,6 +471,9 @@ sys_ptrace(struct proc *p, void *v, register_t *retval)
 		 * from where it stopped."
 		 */
 
+		if (SCARG(uap, pid) < THREAD_PID_OFFSET && tr->ps_single)
+			t = tr->ps_single;
+
 		/* Check that the data is a valid signal number or zero. */
 		if (SCARG(uap, data) < 0 || SCARG(uap, data) >= NSIG)
 			return (EINVAL);
@@ -507,13 +512,7 @@ sys_ptrace(struct proc *p, void *v, register_t *retval)
 			if (SCARG(uap, data) != 0)
 				psignal(t, SCARG(uap, data));
 		}
-		SCHED_LOCK(s);
-		TAILQ_FOREACH(q, &tr->ps_threads, p_thr_link) {
-			if (q != t && q->p_stat == SSTOP) {
-				setrunnable(q);
-			}
-		}
-		SCHED_UNLOCK(s);
+
 		return (0);
 
 	relebad:
@@ -561,6 +560,11 @@ sys_ptrace(struct proc *p, void *v, register_t *retval)
 	case  PT_GET_PROCESS_STATE:
 		if (SCARG(uap, data) != sizeof(*tr->ps_ptstat))
 			return (EINVAL);
+
+		if (tr->ps_single)
+			tr->ps_ptstat->pe_tid =
+			    tr->ps_single->p_pid + THREAD_PID_OFFSET;
+
 		return (copyout(tr->ps_ptstat, SCARG(uap, addr),
 		    sizeof(*tr->ps_ptstat)));
 
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index e882c276629..d3ed87cff35 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: proc.h,v 1.157 2012/04/12 12:33:03 deraadt Exp $	*/
+/*	$OpenBSD: proc.h,v 1.158 2012/04/13 16:37:50 kettenis Exp $	*/
 /*	$NetBSD: proc.h,v 1.44 1996/04/22 01:23:21 christos Exp $	*/
 
 /*-
@@ -545,7 +545,7 @@ enum single_thread_mode {
 	SINGLE_EXIT		/* other threads to unwind and then exit */
 };
 int	single_thread_set(struct proc *, enum single_thread_mode, int);
-void	single_thread_clear(struct proc *);
+void	single_thread_clear(struct proc *, int);
 int	single_thread_check(struct proc *, int);
 
 void	child_return(void *);
diff --git a/sys/sys/ptrace.h b/sys/sys/ptrace.h
index d29b03bcb22..3c8fda30f21 100644
--- a/sys/sys/ptrace.h
+++ b/sys/sys/ptrace.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ptrace.h,v 1.13 2012/02/20 22:23:39 guenther Exp $	*/
+/*	$OpenBSD: ptrace.h,v 1.14 2012/04/13 16:37:50 kettenis Exp $	*/
 /*	$NetBSD: ptrace.h,v 1.21 1996/02/09 18:25:26 christos Exp $	*/
 
 /*-
@@ -76,6 +76,7 @@ typedef struct ptrace_event {
 typedef struct ptrace_state {
 	int	pe_report_event;
 	pid_t	pe_other_pid;
+	pid_t	pe_tid;
 } ptrace_state_t;
 
 #define PT_GET_THREAD_FIRST	15