cmd/gc, runtime: treat slices and strings like pointers in garbage collection
Before, a slice with cap=0 or a string with len=0 might have its
base pointer pointing beyond the actual slice/string data into
the next block. The collector had to ignore slices and strings with
cap=0 in order to avoid misinterpreting the base pointer.
Now, a slice with cap=0 or a string with len=0 still has a base
pointer pointing into the actual slice/string data, no matter what.
The collector can now always scan the pointer, which means
strings and slices are no longer special.
Fixes #8404.
LGTM=khr, josharian
R=josharian, khr, dvyukov
CC=golang-codereviews
https://golang.org/cl/112570044
diff --git a/src/pkg/reflect/all_test.go b/src/pkg/reflect/all_test.go
index d978169..9a2a9f2 100644
--- a/src/pkg/reflect/all_test.go
+++ b/src/pkg/reflect/all_test.go
@@ -2494,6 +2494,15 @@
if vs != s[3:5] {
t.Errorf("s.Slice(3, 5) = %q; expected %q", vs, s[3:5])
}
+
+ rv := ValueOf(&xs).Elem()
+ rv = rv.Slice(3, 4)
+ ptr2 := rv.Pointer()
+ rv = rv.Slice(5, 5)
+ ptr3 := rv.Pointer()
+ if ptr3 != ptr2 {
+ t.Errorf("xs.Slice(3,4).Slice3(5,5).Pointer() = %#x, want %#x", ptr3, ptr2)
+ }
}
func TestSlice3(t *testing.T) {
@@ -2532,6 +2541,15 @@
s := "hello world"
rv = ValueOf(&s).Elem()
shouldPanic(func() { rv.Slice3(1, 2, 3) })
+
+ rv = ValueOf(&xs).Elem()
+ rv = rv.Slice3(3, 5, 7)
+ ptr2 := rv.Pointer()
+ rv = rv.Slice3(4, 4, 4)
+ ptr3 := rv.Pointer()
+ if ptr3 != ptr2 {
+ t.Errorf("xs.Slice3(3,5,7).Slice3(4,4,4).Pointer() = %#x, want %#x", ptr3, ptr2)
+ }
}
func TestSetLenCap(t *testing.T) {
