1 files changed, 76 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/gc/unsafe.go b/src/cmd/compile/internal/gc/unsafe.go
new file mode 100644
index 0000000..2233961
--- /dev/null
+++ b/src/cmd/compile/internal/gc/unsafe.go
@@ -0,0 +1,76 @@
+// Copyright 2009 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.
+
+package gc
+
+// evalunsafe evaluates a package unsafe operation and returns the result.
+func evalunsafe(n *Node) int64 {
+	switch n.Op {
+	case OALIGNOF, OSIZEOF:
+		n.Left = typecheck(n.Left, ctxExpr)
+		n.Left = defaultlit(n.Left, nil)
+		tr := n.Left.Type
+		if tr == nil {
+			return 0
+		}
+		dowidth(tr)
+		if n.Op == OALIGNOF {
+			return int64(tr.Align)
+		}
+		return tr.Width
+
+	case OOFFSETOF:
+		// must be a selector.
+		if n.Left.Op != OXDOT {
+			yyerror("invalid expression %v", n)
+			return 0
+		}
+
+		// Remember base of selector to find it back after dot insertion.
+		// Since r->left may be mutated by typechecking, check it explicitly
+		// first to track it correctly.
+		n.Left.Left = typecheck(n.Left.Left, ctxExpr)
+		base := n.Left.Left
+
+		n.Left = typecheck(n.Left, ctxExpr)
+		if n.Left.Type == nil {
+			return 0
+		}
+		switch n.Left.Op {
+		case ODOT, ODOTPTR:
+			break
+		case OCALLPART:
+			yyerror("invalid expression %v: argument is a method value", n)
+			return 0
+		default:
+			yyerror("invalid expression %v", n)
+			return 0
+		}
+
+		// Sum offsets for dots until we reach base.
+		var v int64
+		for r := n.Left; r != base; r = r.Left {
+			switch r.Op {
+			case ODOTPTR:
+				// For Offsetof(s.f), s may itself be a pointer,
+				// but accessing f must not otherwise involve
+				// indirection via embedded pointer types.
+				if r.Left != base {
+					yyerror("invalid expression %v: selector implies indirection of embedded %v", n, r.Left)
+					return 0
+				}
+				fallthrough
+			case ODOT:
+				v += r.Xoffset
+			default:
+				Dump("unsafenmagic", n.Left)
+				Fatalf("impossible %#v node after dot insertion", r.Op)
+			}
+		}
+		return v
+	}
+
+	Fatalf("unexpected op %v", n.Op)
+	return 0
+}