gc: bug292

Fixes #843.

R=ken2
CC=golang-dev
https://golang.org/cl/1729051

src/cmd/gc/go.h

@@ -1145,7 +1145,7 @@ void	typechecklist(NodeList *l, int top);
 /*
  *	unsafe.c
  */
-Node*	unsafenmagic(Node *fn, NodeList *args);
+Node*	unsafenmagic(Node *n);
 
 /*
  *	walk.c

src/cmd/gc/print.c

@@ -267,6 +267,7 @@ exprfmt(Fmt *f, Node *n, int prec)
 		fmtprint(f, "struct literal");
 		break;
 
+	case OXDOT:
 	case ODOT:
 	case ODOTPTR:
 	case ODOTINTER:

src/cmd/gc/typecheck.c

@@ -690,7 +690,7 @@ typecheck(Node **np, int top)
 	 */
 	case OCALL:
 		l = n->left;
-		if(l->op == ONAME && (r = unsafenmagic(l, n->list)) != N) {
+		if(l->op == ONAME && (r = unsafenmagic(n)) != N) {
 			n = r;
 			goto reswitch;
 		}

src/cmd/gc/unsafe.c

@@ -11,13 +11,18 @@
  * rewrite with a constant
  */
 Node*
-unsafenmagic(Node *fn, NodeList *args)
+unsafenmagic(Node *nn)
 {
 	Node *r, *n;
 	Sym *s;
 	Type *t, *tr;
 	long v;
 	Val val;
+	Node *fn;
+	NodeList *args;
+
+	fn = nn->left;
+	args = nn->list;
 
 	if(safemode || fn == N || fn->op != ONAME || (s = fn->sym) == S)
 		goto no;
@@ -35,13 +40,14 @@ unsafenmagic(Node *fn, NodeList *args)
 		defaultlit(&r, T);
 		tr = r->type;
 		if(tr == T)
-			goto no;
+			goto bad;
 		v = tr->width;
 		goto yes;
 	}
 	if(strcmp(s->name, "Offsetof") == 0) {
+		typecheck(&r, Erv);
 		if(r->op != ODOT && r->op != ODOTPTR)
-			goto no;
+			goto bad;
 		typecheck(&r, Erv);
 		v = r->xoffset;
 		goto yes;
@@ -51,7 +57,7 @@ unsafenmagic(Node *fn, NodeList *args)
 		defaultlit(&r, T);
 		tr = r->type;
 		if(tr == T)
-			goto no;
+			goto bad;
 
 		// make struct { byte; T; }
 		t = typ(TSTRUCT);
@@ -70,9 +76,15 @@ unsafenmagic(Node *fn, NodeList *args)
 no:
 	return N;
 
+bad:
+	yyerror("invalid expression %#N", nn);
+	v = 0;
+	goto ret;
+
 yes:
 	if(args->next != nil)
 		yyerror("extra arguments for %S", s);
+ret:
 	// any side effects disappear; ignore init
 	val.ctype = CTINT;
 	val.u.xval = mal(sizeof(*n->val.u.xval));

test/fixedbugs/bug292.go

@@ -0,0 +1,22 @@
+// $G $D/$F.go && $L $F.$A && ./$A.out
+
+// Copyright 2010 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// http://code.google.com/p/go/issues/detail?id=843
+
+package main
+
+import "unsafe"
+
+type T struct {
+	X, Y uint8
+}
+
+func main() {
+	var t T
+	if unsafe.Offsetof(t.X) != 0 || unsafe.Offsetof(t.Y) != 1 {
+		println("BUG", unsafe.Offsetof(t.X), unsafe.Offsetof(t.Y))
+	}
+}