diff --git a/libgo/go/runtime/lock_futex.go b/libgo/go/runtime/lock_futex.go
index 4d914b2..9877bc3 100644
--- a/libgo/go/runtime/lock_futex.go
+++ b/libgo/go/runtime/lock_futex.go
@@ -198,13 +198,10 @@
 }
 
 func notetsleep(n *note, ns int64) bool {
-	// Currently OK to sleep in non-g0 for gccgo.  It happens in
-	// stoptheworld because our version of systemstack does not
-	// change to g0.
-	// gp := getg()
-	// if gp != gp.m.g0 && gp.m.preemptoff != "" {
-	//	throw("notetsleep not on g0")
-	// }
+	gp := getg()
+	if gp != gp.m.g0 && gp.m.preemptoff != "" {
+		throw("notetsleep not on g0")
+	}
 
 	return notetsleep_internal(n, ns)
 }
diff --git a/libgo/go/runtime/lock_sema.go b/libgo/go/runtime/lock_sema.go
index e2d7614..57fee19 100644
--- a/libgo/go/runtime/lock_sema.go
+++ b/libgo/go/runtime/lock_sema.go
@@ -251,14 +251,9 @@
 
 func notetsleep(n *note, ns int64) bool {
 	gp := getg()
-
-	// Currently OK to sleep in non-g0 for gccgo.  It happens in
-	// stoptheworld because our version of systemstack does not
-	// change to g0.
-	// if gp != gp.m.g0 && gp.m.preemptoff != "" {
-	//	throw("notetsleep not on g0")
-	// }
-
+	if gp != gp.m.g0 && gp.m.preemptoff != "" {
+		throw("notetsleep not on g0")
+	}
 	semacreate(gp.m)
 	return notetsleep_internal(n, ns, nil, 0)
 }
diff --git a/libgo/go/runtime/proc.go b/libgo/go/runtime/proc.go
index 0907afc..28fbe5b 100644
--- a/libgo/go/runtime/proc.go
+++ b/libgo/go/runtime/proc.go
@@ -32,8 +32,6 @@
 //go:linkname exitsyscall runtime.exitsyscall
 //go:linkname gfget runtime.gfget
 //go:linkname helpgc runtime.helpgc
-//go:linkname stopTheWorldWithSema runtime.stopTheWorldWithSema
-//go:linkname startTheWorldWithSema runtime.startTheWorldWithSema
 //go:linkname kickoff runtime.kickoff
 //go:linkname mstart1 runtime.mstart1
 //go:linkname globrunqput runtime.globrunqput
diff --git a/libgo/go/runtime/stubs.go b/libgo/go/runtime/stubs.go
index cccbd12..9109e4b 100644
--- a/libgo/go/runtime/stubs.go
+++ b/libgo/go/runtime/stubs.go
@@ -51,11 +51,22 @@
 //
 // For the gc toolchain this permits running a function that requires
 // additional stack space in a context where the stack can not be
-// split.  For gccgo, however, stack splitting is not managed by the
-// Go runtime. In effect, all stacks are system stacks. So this gccgo
-// version just runs the function.
+// split. We don't really need additional stack space in gccgo, since
+// stack splitting is handled separately. But to keep things looking
+// the same, we do switch to the g0 stack here if necessary.
 func systemstack(fn func()) {
-	fn()
+	gp := getg()
+	mp := gp.m
+	if gp == mp.g0 || gp == mp.gsignal {
+		fn()
+	} else if gp == mp.curg {
+		mcall(func(origg *g) {
+			fn()
+			gogo(origg)
+		})
+	} else {
+		badsystemstack()
+	}
 }
 
 func badsystemstack() {
@@ -656,3 +667,15 @@
 
 // Temporary for gccgo until we port malloc.go.
 const maxTinySize = 16
+
+// Temporary for gccgo until we port heapdump.go and mgc.go.
+//go:linkname callStopTheWorldWithSema runtime.callStopTheWorldWithSema
+func callStopTheWorldWithSema() {
+	systemstack(stopTheWorldWithSema)
+}
+
+// Temporary for gccgo until we port heapdump.go and mgc.go.
+//go:linkname callStartTheWorldWithSema runtime.callStartTheWorldWithSema
+func callStartTheWorldWithSema() {
+	systemstack(startTheWorldWithSema)
+}
diff --git a/libgo/runtime/heapdump.c b/libgo/runtime/heapdump.c
index ab65d39..8178946 100644
--- a/libgo/runtime/heapdump.c
+++ b/libgo/runtime/heapdump.c
@@ -621,7 +621,7 @@
 	runtime_acquireWorldsema();
 	m = runtime_m();
 	m->preemptoff = runtime_gostringnocopy((const byte*)"write heap dump");
-	runtime_stopTheWorldWithSema();
+	runtime_callStopTheWorldWithSema();
 
 	// Update stats so we can dump them.
 	// As a side effect, flushes all the MCaches so the MSpan.freelist
@@ -641,7 +641,7 @@
 	dumpfd = 0;
 
 	// Start up the world again.
-	runtime_startTheWorldWithSema();
+	runtime_callStartTheWorldWithSema();
 	runtime_releaseWorldsema();
 	m->preemptoff = runtime_gostringnocopy(nil);
 }
diff --git a/libgo/runtime/mgc0.c b/libgo/runtime/mgc0.c
index 13e04f0..0178507 100644
--- a/libgo/runtime/mgc0.c
+++ b/libgo/runtime/mgc0.c
@@ -2097,7 +2097,7 @@
 	a.start_time = runtime_nanotime();
 	a.eagersweep = force >= 2;
 	m->gcing = 1;
-	runtime_stopTheWorldWithSema();
+	runtime_callStopTheWorldWithSema();
 	
 	clearpools();
 
@@ -2122,7 +2122,7 @@
 	m->gcing = 0;
 	m->locks++;
 	runtime_releaseWorldsema();
-	runtime_startTheWorldWithSema();
+	runtime_callStartTheWorldWithSema();
 	m->locks--;
 
 	// now that gc is done, kick off finalizer thread if needed
diff --git a/libgo/runtime/runtime.h b/libgo/runtime/runtime.h
index e38bf06..e12d506 100644
--- a/libgo/runtime/runtime.h
+++ b/libgo/runtime/runtime.h
@@ -382,10 +382,10 @@
 void	runtime_iterate_finq(void (*callback)(FuncVal*, void*, const FuncType*, const PtrType*))
   __asm__(GOSYM_PREFIX "runtime.iterate_finq");
 
-void	runtime_stopTheWorldWithSema(void)
-  __asm__(GOSYM_PREFIX "runtime.stopTheWorldWithSema");
-void	runtime_startTheWorldWithSema(void)
-  __asm__(GOSYM_PREFIX "runtime.startTheWorldWithSema");
+void	runtime_callStopTheWorldWithSema(void)
+  __asm__(GOSYM_PREFIX "runtime.callStopTheWorldWithSema");
+void	runtime_callStartTheWorldWithSema(void)
+  __asm__(GOSYM_PREFIX "runtime.callStartTheWorldWithSema");
 void	runtime_acquireWorldsema(void)
   __asm__(GOSYM_PREFIX "runtime.acquireWorldsema");
 void	runtime_releaseWorldsema(void)