1 /*
2 * dataalign.c -- show alignment needs
3 *
4 * Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
5 * Copyright (C) 2001 O'Reilly & Associates
6 *
7 * The source code in this file can be freely used, adapted,
8 * and redistributed in source or binary form, so long as an
9 * acknowledgment appears in derived source files. The citation
10 * should list that the code comes from the book "Linux Device
11 * Drivers" by Alessandro Rubini and Jonathan Corbet, published
12 * by O'Reilly & Associates. No warranty is attached;
13 * we cannot take responsibility for errors or fitness for use.
14 *
15 * This runs with any Linux kernel (not any Unix, because of <linux/types.h>)
16 */
17 #include <stdio.h>
18 #include <sys/utsname.h>
19 #include <linux/types.h>
20
21 /*
22 * Define several data structures, all of them start with a lone char
23 * in order to present an unaligned offset for the next field
24 */
25 struct c {char c; char t;} c;
26 struct s {char c; short t;} s;
27 struct i {char c; int t;} i;
28 struct l {char c; long t;} l;
29 struct ll {char c; long long t;} ll;
30 struct p {char c; void * t;} p;
31 struct u1b {char c; __u8 t;} u1b;
32 struct u2b {char c; __u16 t;} u2b;
33 struct u4b {char c; __u32 t;} u4b;
34 struct u8b {char c; __u64 t;} u8b;
35
36 int main(int argc, char **argv)
37 {
38 struct utsname name;
39
40 uname(&name); /* never fails :) */
41 printf("arch Align: char short int long ptr long-long "
42 " u8 u16 u32 u64\n");
43 printf( "%-12s %3i %3i %3i %3i %3i %3i "
44 "%3i %3i %3i %3i\n",
45 name.machine,
46 /* note that gcc can subtract void * values, but it's not ansi */
47 (int)((void *)(&c.t) - (void *)&c),
48 (int)((void *)(&s.t) - (void *)&s),
49 (int)((void *)(&i.t) - (void *)&i),
50 (int)((void *)(&l.t) - (void *)&l),
51 (int)((void *)(&p.t) - (void *)&p),
52 (int)((void *)(&ll.t) - (void *)&ll),
53 (int)((void *)(&u1b.t) - (void *)&u1b),
54 (int)((void *)(&u2b.t) - (void *)&u2b),
55 (int)((void *)(&u4b.t) - (void *)&u4b),
56 (int)((void *)(&u8b.t) - (void *)&u8b));
57 return 0;
58 }
59
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