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// 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
}
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