cmd/gc: fix Offsetof computation.
The offset of an embedded field s.X must be relative to s
and not to the implicit s.Field of which X is a direct field.
Moreover, no indirections may happen on the path.
Fixes #4909.
R=nigeltao, ality, daniel.morsing, iant, gri, r
CC=golang-dev
https://golang.org/cl/8287043
diff --git a/test/sizeof.go b/test/sizeof.go
index a6abdd5..9aa9567 100644
--- a/test/sizeof.go
+++ b/test/sizeof.go
@@ -4,8 +4,6 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
-// Test unsafe.Sizeof, unsafe.Alignof, and unsafe.Offsetof all return uintptr.
-
package main
import "unsafe"
@@ -18,8 +16,143 @@
func isUintptr(uintptr) {}
+type T2 struct {
+ A int32
+ U2
+}
+
+type U2 struct {
+ B int32
+ C int32
+}
+
+var t2 T2
+var p2 *T2
+
func main() {
+ // Test unsafe.Sizeof, unsafe.Alignof, and unsafe.Offsetof all return uintptr.
isUintptr(unsafe.Sizeof(t))
isUintptr(unsafe.Alignof(t))
isUintptr(unsafe.Offsetof(t.X))
+
+ // Test correctness of Offsetof with respect to embedded fields (issue 4909).
+ if unsafe.Offsetof(t2.C) != 8 {
+ println(unsafe.Offsetof(t2.C), "!= 8")
+ panic("unsafe.Offsetof(t2.C) != 8")
+ }
+ if unsafe.Offsetof(p2.C) != 8 {
+ println(unsafe.Offsetof(p2.C), "!= 8")
+ panic("unsafe.Offsetof(p2.C) != 8")
+ }
+ if unsafe.Offsetof(t2.U2.C) != 4 {
+ println(unsafe.Offsetof(t2.U2.C), "!= 4")
+ panic("unsafe.Offsetof(t2.U2.C) != 4")
+ }
+ if unsafe.Offsetof(p2.U2.C) != 4 {
+ println(unsafe.Offsetof(p2.U2.C), "!= 4")
+ panic("unsafe.Offsetof(p2.U2.C) != 4")
+ }
+ testDeep()
+ testNotEmbedded()
+}
+
+type (
+ S1 struct {
+ A int32
+ S2
+ }
+ S2 struct {
+ B int32
+ S3
+ }
+ S3 struct {
+ C int32
+ S4
+ }
+ S4 struct {
+ D int32
+ S5
+ }
+ S5 struct {
+ E int32
+ S6
+ }
+ S6 struct {
+ F int32
+ S7
+ }
+ S7 struct {
+ G int32
+ S8
+ }
+ S8 struct {
+ H int32
+ *S1
+ }
+)
+
+func testDeep() {
+ var s1 S1
+ switch {
+ case unsafe.Offsetof(s1.A) != 0:
+ panic("unsafe.Offsetof(s1.A) != 0")
+ case unsafe.Offsetof(s1.B) != 4:
+ panic("unsafe.Offsetof(s1.B) != 4")
+ case unsafe.Offsetof(s1.C) != 8:
+ panic("unsafe.Offsetof(s1.C) != 8")
+ case unsafe.Offsetof(s1.D) != 12:
+ panic("unsafe.Offsetof(s1.D) != 12")
+ case unsafe.Offsetof(s1.E) != 16:
+ panic("unsafe.Offsetof(s1.E) != 16")
+ case unsafe.Offsetof(s1.F) != 20:
+ panic("unsafe.Offsetof(s1.F) != 20")
+ case unsafe.Offsetof(s1.G) != 24:
+ panic("unsafe.Offsetof(s1.G) != 24")
+ case unsafe.Offsetof(s1.H) != 28:
+ panic("unsafe.Offsetof(s1.H) != 28")
+ case unsafe.Offsetof(s1.S1) != 32:
+ panic("unsafe.Offsetof(s1.S1) != 32")
+ case unsafe.Offsetof(s1.S1.S2.S3.S4.S5.S6.S7.S8.S1.S2) != 4:
+ panic("unsafe.Offsetof(s1.S1.S2.S3.S4.S5.S6.S7.S8.S1.S2) != 4")
+ }
+}
+
+func testNotEmbedded() {
+ type T2 struct {
+ B int32
+ C int32
+ }
+ type T1 struct {
+ A int32
+ T2
+ }
+ type T struct {
+ Dummy int32
+ F T1
+ P *T1
+ }
+
+ var t T
+ var p *T
+ switch {
+ case unsafe.Offsetof(t.F.B) != 4:
+ panic("unsafe.Offsetof(t.F.B) != 4")
+ case unsafe.Offsetof(t.F.C) != 8:
+ panic("unsafe.Offsetof(t.F.C) != 8")
+
+ case unsafe.Offsetof(t.P.B) != 4:
+ panic("unsafe.Offsetof(t.P.B) != 4")
+ case unsafe.Offsetof(t.P.C) != 8:
+ panic("unsafe.Offsetof(t.P.C) != 8")
+
+ case unsafe.Offsetof(p.F.B) != 4:
+ panic("unsafe.Offsetof(p.F.B) != 4")
+ case unsafe.Offsetof(p.F.C) != 8:
+ panic("unsafe.Offsetof(p.F.C) != 8")
+
+ case unsafe.Offsetof(p.P.B) != 4:
+ panic("unsafe.Offsetof(p.P.B) != 4")
+ case unsafe.Offsetof(p.P.C) != 8:
+ panic("unsafe.Offsetof(p.P.C) != 8")
+ }
}
