1 /*
2  * Copyright (C) 2014 Oracle.
3  *
4  * This program is free software; you can redistribute it and/or
5  * modify it under the terms of the GNU General Public License
6  * as published by the Free Software Foundation; either version 2
7  * of the License, or (at your option) any later version.
8  *
9  * This program is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  * GNU General Public License for more details.
13  *
14  * You should have received a copy of the GNU General Public License
15  * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
16  */
17 
18 #include "smatch.h"
19 
20 static int my_id;
21 
22 static void match_binop(struct expression *expr)
23 {
24 	struct symbol *type;
25 	sval_t bits;
26 
27 	if (expr->op != SPECIAL_RIGHTSHIFT)
28 		return;
29 
30 	if (!get_implied_value(expr->right, &bits))
31 		return;
32 
33 	type = get_type(expr->left);
34 	if (!type)
35 		return;
36 	if (type_bits(type) == -1 || type_bits(type) > bits.value)
37 		return;
38 	sm_warning("right shifting more than type allows %d vs %lld", type_bits(type), bits.value);
39 }
40 
41 static void match_binop2(struct expression *expr)
42 {
43 	struct expression *left;
44 	struct expression *tmp;
45 	sval_t mask, shift;
46 
47 	if (expr->op != SPECIAL_RIGHTSHIFT)
48 		return;
49 
50 	left = strip_expr(expr->left);
51 	tmp = get_assigned_expr(left);
52 	if (tmp)
53 		left = tmp;
54 	if (left->type != EXPR_BINOP || left->op != '&')
55 		return;
56 
57 	if (!get_implied_value(expr->right, &shift))
58 		return;
59 	if (!get_implied_value(left->right, &mask))
60 		return;
61 
62 	if (mask.uvalue >> shift.uvalue)
63 		return;
64 
65 	sm_warning("mask and shift to zero");
66 }
67 
68 static void match_assign(struct expression *expr)
69 {
70 	struct symbol *type;
71 	sval_t bits;
72 
73 	if (expr->op != SPECIAL_SHR_ASSIGN)
74 		return;
75 
76 	if (!get_implied_value(expr->right, &bits))
77 		return;
78 	type = get_type(expr->left);
79 	if (!type)
80 		return;
81 	if (type_bits(type) > bits.value)
82 		return;
83 	sm_warning("right shift assign to zero");
84 }
85 
86 void check_shift_to_zero(int id)
87 {
88 	my_id = id;
89 
90 	add_hook(&match_binop, BINOP_HOOK);
91 	add_hook(&match_binop2, BINOP_HOOK);
92 
93 	add_hook(&match_assign, ASSIGNMENT_HOOK);
94 
95 }
96