Index: sys/kern/kern_event.c
===================================================================
--- sys/kern/kern_event.c
+++ sys/kern/kern_event.c
@@ -1528,7 +1528,7 @@
 		if (error == 0)
 			goto retry;
 		/* don't restart after signals... */
-		if (error == ERESTART)
+		if (error == ERESTART && !THREAD_DEBUGGING_SIG(td))
 			error = EINTR;
 		else if (error == EWOULDBLOCK)
 			error = 0;
Index: sys/kern/kern_sig.c
===================================================================
--- sys/kern/kern_sig.c
+++ sys/kern/kern_sig.c
@@ -2499,6 +2499,9 @@
 	td->td_xsig = sig;
 	CTR4(KTR_PTRACE, "ptracestop: tid %d (pid %d) flags %#x sig %d",
 	    td->td_tid, p->p_pid, td->td_dbgflags, sig);
+	thread_lock(td);
+	td->td_flags |= TDF_PTRACESIG;
+	thread_unlock(td);
 	PROC_SLOCK(p);
 	while ((p->p_flag & P_TRACED) && (td->td_dbgflags & TDB_XSIG)) {
 		if (p->p_flag & P_SINGLE_EXIT) {
Index: sys/kern/kern_thread.c
===================================================================
--- sys/kern/kern_thread.c
+++ sys/kern/kern_thread.c
@@ -918,8 +918,11 @@
 			if (p->p_singlethread == td)
 				return (0);	/* Exempt from stopping. */
 		}
-		if ((p->p_flag & P_SINGLE_EXIT) && return_instead)
+		if ((p->p_flag & P_SINGLE_EXIT) && return_instead) {
+			if (THREAD_DEBUGGING_SIG(td))
+				return (ERESTART);
 			return (EINTR);
+		}
 
 		/* Should we goto user boundary if we didn't come from there? */
 		if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
Index: sys/kern/kern_time.c
===================================================================
--- sys/kern/kern_time.c
+++ sys/kern/kern_time.c
@@ -503,7 +503,7 @@
 	error = tsleep_sbt(&nanowait[curcpu], PWAIT | PCATCH, "nanslp",
 	    sbt, prec, C_ABSOLUTE);
 	if (error != EWOULDBLOCK) {
-		if (error == ERESTART)
+		if (error == ERESTART && !THREAD_DEBUGGING_SIG(td))
 			error = EINTR;
 		TIMESEL(&sbtt, tmp);
 		if (rmt != NULL) {
Index: sys/kern/subr_sleepqueue.c
===================================================================
--- sys/kern/subr_sleepqueue.c
+++ sys/kern/subr_sleepqueue.c
@@ -453,9 +453,12 @@
 		ret = thread_suspend_check(1);
 		MPASS(ret == 0 || ret == EINTR || ret == ERESTART);
 	} else {
-		if (SIGISMEMBER(ps->ps_sigintr, sig))
-			ret = EINTR;
-		else
+		if (SIGISMEMBER(ps->ps_sigintr, sig)) {
+			if (THREAD_DEBUGGING_SIGERR(td, EINTR))
+				ret = ERESTART;
+			else
+				ret = EINTR;
+		} else
 			ret = ERESTART;
 		mtx_unlock(&ps->ps_mtx);
 	}
@@ -611,6 +614,8 @@
 
 	if (td->td_flags & TDF_SLEEPABORT) {
 		td->td_flags &= ~TDF_SLEEPABORT;
+		if (THREAD_DEBUGGING_SIGERR(td, td->td_intrval))
+			td->td_intrval = ERESTART;
 		return (td->td_intrval);
 	}
 
Index: sys/kern/subr_trap.c
===================================================================
--- sys/kern/subr_trap.c
+++ sys/kern/subr_trap.c
@@ -216,7 +216,8 @@
 	thread_lock(td);
 	flags = td->td_flags;
 	td->td_flags &= ~(TDF_ASTPENDING | TDF_NEEDSIGCHK | TDF_NEEDSUSPCHK |
-	    TDF_NEEDRESCHED | TDF_ALRMPEND | TDF_PROFPEND | TDF_MACPEND);
+	    TDF_NEEDRESCHED | TDF_ALRMPEND | TDF_PROFPEND | TDF_MACPEND |
+	    TDF_PTRACESIG);
 	thread_unlock(td);
 	PCPU_INC(cnt.v_trap);
 
Index: sys/kern/sys_generic.c
===================================================================
--- sys/kern/sys_generic.c
+++ sys/kern/sys_generic.c
@@ -1119,7 +1119,7 @@
 
 done:
 	/* select is not restarted after signals... */
-	if (error == ERESTART)
+	if (error == ERESTART && !THREAD_DEBUGGING_SIG(td))
 		error = EINTR;
 	if (error == EWOULDBLOCK)
 		error = 0;
@@ -1403,7 +1403,7 @@
 
 done:
 	/* poll is not restarted after signals... */
-	if (error == ERESTART)
+	if (error == ERESTART && !THREAD_DEBUGGING_SIG(td))
 		error = EINTR;
 	if (error == EWOULDBLOCK)
 		error = 0;
Index: sys/kern/sys_process.c
===================================================================
--- sys/kern/sys_process.c
+++ sys/kern/sys_process.c
@@ -856,6 +856,9 @@
 		data = SIGSTOP;
 		CTR2(KTR_PTRACE, "PT_ATTACH: pid %d, oppid %d", p->p_pid,
 		    p->p_oppid);
+		thread_lock(td2);
+		td2->td_flags |= TDF_PTRACESIG;
+		thread_unlock(td2);
 		goto sendsig;	/* in PT_CONTINUE below */
 
 	case PT_CLEARSTEP:
@@ -905,6 +908,10 @@
 		if (data < 0 || data > _SIG_MAXSIG) {
 			error = EINVAL;
 			break;
+		} else if (data == 0) {
+			thread_lock(td2);
+			td2->td_flags |= TDF_PTRACESIG;
+			thread_unlock(td2);
 		}
 
 		switch (req) {
@@ -1035,19 +1042,8 @@
 		uio.uio_rw = write ? UIO_WRITE : UIO_READ;
 		uio.uio_td = td;
 		error = proc_rwmem(p, &uio);
-		if (uio.uio_resid != 0) {
-			/*
-			 * XXX proc_rwmem() doesn't currently return ENOSPC,
-			 * so I think write() can bogusly return 0.
-			 * XXX what happens for short writes?  We don't want
-			 * to write partial data.
-			 * XXX proc_rwmem() returns EPERM for other invalid
-			 * addresses.  Convert this to EINVAL.  Does this
-			 * clobber returns of EPERM for other reasons?
-			 */
-			if (error == 0 || error == ENOSPC || error == EPERM)
-				error = EINVAL;	/* EOF */
-		}
+		if (uio.uio_resid != 0 && error == 0)
+			error = EINVAL;	/* EOF */
 		if (!write)
 			td->td_retval[0] = tmp;
 		if (error == 0) {
Index: sys/sys/proc.h
===================================================================
--- sys/sys/proc.h
+++ sys/sys/proc.h
@@ -391,7 +391,7 @@
 #define	TDF_THRWAKEUP	0x00100000 /* Libthr thread must not suspend itself. */
 #define	TDF_UNUSED21	0x00200000 /* --available-- */
 #define	TDF_SWAPINREQ	0x00400000 /* Swapin request due to wakeup. */
-#define	TDF_UNUSED23	0x00800000 /* --available-- */
+#define	TDF_PTRACESIG	0x00800000 /* ERESTART from ptrace-generated signal */
 #define	TDF_SCHED0	0x01000000 /* Reserved for scheduler private use */
 #define	TDF_SCHED1	0x02000000 /* Reserved for scheduler private use */
 #define	TDF_SCHED2	0x04000000 /* Reserved for scheduler private use */
@@ -769,6 +769,14 @@
 
 #define	SESS_LEADER(p)	((p)->p_session->s_leader == (p))
 
+#define THREAD_DEBUGGING_SIGERR(td, err)				\
+	(((td)->td_proc->p_flag & P_TRACED) != 0 &&			\
+	    ((td)->td_flags & TDF_PTRACESIG) != 0 &&			\
+	    (err) == EINTR)
+
+#define THREAD_DEBUGGING_SIG(td)					\
+	(((td)->td_proc->p_flag & P_TRACED) != 0 &&			\
+	    ((td)->td_flags & TDF_PTRACESIG) != 0)
 
 #define	STOPEVENT(p, e, v) do {						\
 	WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,			\