1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
|
/* Testing the alias analysis on ill-defined codes
where it should remain conservative. */
#include <stddef.h>
#include <stdint.h>
/* For testing with GCC */
#define NOINLINE __attribute__((noinline))
/* Passing a pointer through a long long */
void NOINLINE set1(long long x)
{
int * p = (int *) (uintptr_t) x;
*p = 1;
}
int get1(void)
{
int x = 0;
set1((uintptr_t) &x);
return x;
}
/* Passing a pointer through a double */
void NOINLINE set2(double x)
{
int * p = (int *) (uintptr_t) x;
*p = 1;
}
int get2(void)
{
int x = 0;
set2((uintptr_t) &x);
return x;
}
/* Tagging a pointer */
void NOINLINE set3(uintptr_t x)
{
int * p = (int *) (x & ~1);
*p = 1;
}
int get3(void)
{
int x = 0;
set3((uintptr_t) &x | 1);
return x;
}
/* XOR-ing a pointer */
static uintptr_t key = 0xDEADBEEF;
void NOINLINE set4(uintptr_t x)
{
int * p = (int *) (x ^ key);
*p = 1;
}
int get4(void)
{
int x = 0;
set4((uintptr_t) &x ^ key);
return x;
}
/* Byte-swapping a pointer. For 32/64 bit compatibility, we just swap
the two low bytes, but that's in the spirit. */
static inline uintptr_t bswap(uintptr_t x)
{
return (x & ~((uintptr_t) 0xFFFF))
| ((x >> 8) & 0xFF)
| ((x << 8) & 0xFF00);
}
void NOINLINE set5(uintptr_t x)
{
int * p = (int *) bswap(x);
*p = 1;
}
int get5(void)
{
int x = 0;
set5(bswap((uintptr_t) &x));
return x;
}
/* Even more fun with xor. This one manufactures a pointer to one object
from a pointer to another, distinct object. Neither GCC nor CompCert
promise to implement the expected behavior, but both happen to do it.
*/
int g;
void NOINLINE set6(int * p, uintptr_t z)
{
int * q = (int *) ((uintptr_t) p ^ z);
*q = 1;
}
int get6(void)
{
int y = 0;
uintptr_t z = (uintptr_t) &g ^ (uintptr_t) &y;
set6(&g, z);
int res1 = y;
g = 0;
set6(&y, z);
int res2 = g;
return res1 & res2;
}
/* Aligning pointers the hard way */
int offset = 3; /* but not const */
int get7(void)
{
union { int i; char c[4]; } u; /* force alignment to 4 */
u.c[0] = 0;
uintptr_t x = (uintptr_t) &(u.c[offset]);
x = x & ~3;
*((char *) x) = 1;
return u.c[0];
}
/* This is an example where wild pointer arithmetic is used to jump
from one object to another. Like GCC and Clang, we don't preserve the
expected behavior. */
ptrdiff_t NOINLINE delta8(int * p)
{
return p - &g;
}
int get8(void)
{
int x;
ptrdiff_t d = delta8(&x);
x = 0;
*(&g + d) = 1;
return x;
}
/* Test harness */
#include <stdio.h>
int main()
{
printf("Test 1: %d\n", get1());
printf("Test 2: %d\n", get2());
printf("Test 3: %d\n", get3());
printf("Test 4: %d\n", get4());
printf("Test 5: %d\n", get5());
printf("Test 6: %d\n", get6());
printf("Test 7: %d\n", get7());
printf("Test 8: %d\n", get8());
return 0;
}
|
