3 files changed, 17 insertions, 4 deletions
diff --git a/src/runtime/mgc0.c b/src/runtime/mgc0.c
index 7754bad89..083beec22 100644
--- a/src/runtime/mgc0.c
+++ b/src/runtime/mgc0.c
@@ -350,6 +350,9 @@ scanblock(byte *b, uintptr n, byte *ptrmask)
 				x -= (uintptr)arena_start>>PageShift;
 				s = runtime·mheap.spans[x];
 				if(s == nil || k < s->start || obj >= s->limit || s->state != MSpanInUse) {
+					// Sometimes 32-bit heaps have holes.  See issue 9872
+					if(PtrSize == 4 && s == nil)
+						continue;
 					// Stack pointers lie within the arena bounds but are not part of the GC heap.
 					// Ignore them.
 					if(s != nil && s->state == MSpanStack)
diff --git a/src/runtime/syscall_windows.go b/src/runtime/syscall_windows.go
index 5b76ad573..51004b78a 100644
--- a/src/runtime/syscall_windows.go
+++ b/src/runtime/syscall_windows.go
@@ -54,11 +54,13 @@ func compileCallback(fn eface, cleanstack bool) (code uintptr) {
 		panic("compilecallback: output parameter size is wrong")
 	}
 	argsize := uintptr(0)
-	for _, t := range (*[1024](*_type))(unsafe.Pointer(&ft.in[0]))[:len(ft.in)] {
-		if (*t).size > uintptrSize {
-			panic("compilecallback: input parameter size is wrong")
+	if len(ft.in) > 0 {
+		for _, t := range (*[1024](*_type))(unsafe.Pointer(&ft.in[0]))[:len(ft.in)] {
+			if (*t).size > uintptrSize {
+				panic("compilecallback: input parameter size is wrong")
+			}
+			argsize += uintptrSize
 		}
-		argsize += uintptrSize
 	}
 
 	lock(&cbs.lock)
diff --git a/src/runtime/syscall_windows_test.go b/src/runtime/syscall_windows_test.go
index ce8a9ec1b..126bef62e 100644
--- a/src/runtime/syscall_windows_test.go
+++ b/src/runtime/syscall_windows_test.go
@@ -533,3 +533,11 @@ func main() {
 	println(z)
 }
 `
+
+func TestCallbackWithNoInputParameters(t *testing.T) {
+	// Test that NewCallback and NewCallbackCDecl can accept functions without
+	// input parameters, see issue 9871.
+	cb := func() uintptr { return 0 }
+	_ = syscall.NewCallback(cb)
+	_ = syscall.NewCallbackCDecl(cb)
+}