1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * vdso_test.c: Sample code to test parse_vdso.c on x86
4 * Copyright (c) 2011-2014 Andy Lutomirski
5 *
6 * You can amuse yourself by compiling with:
7 * gcc -std=gnu99 -nostdlib
8 * -Os -fno-asynchronous-unwind-tables -flto -lgcc_s
9 * vdso_standalone_test_x86.c parse_vdso.c
10 * to generate a small binary. On x86_64, you can omit -lgcc_s
11 * if you want the binary to be completely standalone.
12 */
13
14 #include <sys/syscall.h>
15 #include <sys/time.h>
16 #include <unistd.h>
17 #include <stdint.h>
18
19 #include "parse_vdso.h"
20
21 /* We need some libc functions... */
22 int strcmp(const char *a, const char *b)
23 {
24 /* This implementation is buggy: it never returns -1. */
25 while (*a || *b) {
26 if (*a != *b)
27 return 1;
28 if (*a == 0 || *b == 0)
29 return 1;
30 a++;
31 b++;
32 }
33
34 return 0;
35 }
36
37 /*
38 * The clang build needs this, although gcc does not.
39 * Stolen from lib/string.c.
40 */
41 void *memcpy(void *dest, const void *src, size_t count)
42 {
43 char *tmp = dest;
44 const char *s = src;
45
46 while (count--)
47 *tmp++ = *s++;
48 return dest;
49 }
50
51 /* ...and two syscalls. This is x86-specific. */
52 static inline long x86_syscall3(long nr, long a0, long a1, long a2)
53 {
54 long ret;
55 #ifdef __x86_64__
56 asm volatile ("syscall" : "=a" (ret) : "a" (nr),
57 "D" (a0), "S" (a1), "d" (a2) :
58 "cc", "memory", "rcx",
59 "r8", "r9", "r10", "r11" );
60 #else
61 asm volatile ("int $0x80" : "=a" (ret) : "a" (nr),
62 "b" (a0), "c" (a1), "d" (a2) :
63 "cc", "memory" );
64 #endif
65 return ret;
66 }
67
68 static inline long linux_write(int fd, const void *data, size_t len)
69 {
70 return x86_syscall3(__NR_write, fd, (long)data, (long)len);
71 }
72
73 static inline void linux_exit(int code)
74 {
75 x86_syscall3(__NR_exit, code, 0, 0);
76 }
77
78 void to_base10(char *lastdig, time_t n)
79 {
80 while (n) {
81 *lastdig = (n % 10) + '';
82 n /= 10;
83 lastdig--;
84 }
85 }
86
87 void c_main(void **stack)
88 {
89 /* Parse the stack */
90 long argc = (long)*stack;
91 stack += argc + 2;
92
93 /* Now we're pointing at the environment. Skip it. */
94 while(*stack)
95 stack++;
96 stack++;
97
98 /* Now we're pointing at auxv. Initialize the vDSO parser. */
99 vdso_init_from_auxv((void *)stack);
100
101 /* Find gettimeofday. */
102 typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
103 gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday");
104
105 if (!gtod)
106 linux_exit(1);
107
108 struct timeval tv;
109 long ret = gtod(&tv, 0);
110
111 if (ret == 0) {
112 char buf[] = "The time is .000000\n";
113 to_base10(buf + 31, tv.tv_sec);
114 to_base10(buf + 38, tv.tv_usec);
115 linux_write(1, buf, sizeof(buf) - 1);
116 } else {
117 linux_exit(ret);
118 }
119
120 linux_exit(0);
121 }
122
123 /*
124 * This is the real entry point. It passes the initial stack into
125 * the C entry point.
126 */
127 asm (
128 ".text\n"
129 ".global _start\n"
130 ".type _start,@function\n"
131 "_start:\n\t"
132 #ifdef __x86_64__
133 "mov %rsp,%rdi\n\t"
134 "jmp c_main"
135 #else
136 "push %esp\n\t"
137 "call c_main\n\t"
138 "int $3"
139 #endif
140 );
141
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