1 // Copyright 2009 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4
5 #include "go.h"
6
7 /*
8 * look for
9 * unsafe.Sizeof
10 * unsafe.Offsetof
11 * rewrite with a constant
12 */
13 Node*
14 unsafenmagic(Node *nn)
15 {
16 Node *r, *n;
17 Sym *s;
18 Type *t, *tr;
19 long v;
20 Val val;
21 Node *fn;
22 NodeList *args;
23
24 fn = nn->left;
25 args = nn->list;
26
27 if(safemode || fn == N || fn->op != ONAME || (s = fn->sym) == S)
28 goto no;
29 if(s->pkg != unsafepkg)
30 goto no;
31
32 if(args == nil) {
33 yyerror("missing argument for %S", s);
34 goto no;
35 }
36 r = args->n;
37
38 if(strcmp(s->name, "Sizeof") == 0) {
39 typecheck(&r, Erv);
40 defaultlit(&r, T);
41 tr = r->type;
42 if(tr == T)
43 goto bad;
44 dowidth(tr);
45 v = tr->width;
46 goto yes;
47 }
48 if(strcmp(s->name, "Offsetof") == 0) {
49 typecheck(&r, Erv);
50 if(r->op != ODOT && r->op != ODOTPTR)
51 goto bad;
52 typecheck(&r, Erv);
53 v = r->xoffset;
54 goto yes;
55 }
56 if(strcmp(s->name, "Alignof") == 0) {
57 typecheck(&r, Erv);
58 defaultlit(&r, T);
59 tr = r->type;
60 if(tr == T)
61 goto bad;
62
63 // make struct { byte; T; }
64 t = typ(TSTRUCT);
65 t->type = typ(TFIELD);
66 t->type->type = types[TUINT8];
67 t->type->down = typ(TFIELD);
68 t->type->down->type = tr;
69 // compute struct widths
70 dowidth(t);
71
72 // the offset of T is its required alignment
73 v = t->type->down->width;
74 goto yes;
75 }
76
77 no:
78 return N;
79
80 bad:
81 yyerror("invalid expression %#N", nn);
82 v = 0;
83 goto ret;
84
85 yes:
86 if(args->next != nil)
87 yyerror("extra arguments for %S", s);
88 ret:
89 // any side effects disappear; ignore init
90 val.ctype = CTINT;
91 val.u.xval = mal(sizeof(*n->val.u.xval));
92 mpmovecfix(val.u.xval, v);
93 n = nod(OLITERAL, N, N);
94 n->val = val;
95 n->type = types[TUINTPTR];
96 return n;
97 }