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 a libc functions... */
22int 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/* ...and two syscalls. This is x86-specific. */
38static inline long x86_syscall3(long nr, long a0, long a1, long a2)
39{
40 long ret;
41#ifdef __x86_64__
42 asm volatile ("syscall" : "=a" (ret) : "a" (nr),
43 "D" (a0), "S" (a1), "d" (a2) :
44 "cc", "memory", "rcx",
45 "r8", "r9", "r10", "r11" );
46#else
47 asm volatile ("int $0x80" : "=a" (ret) : "a" (nr),
48 "b" (a0), "c" (a1), "d" (a2) :
49 "cc", "memory" );
50#endif
51 return ret;
52}
53
54static inline long linux_write(int fd, const void *data, size_t len)
55{
56 return x86_syscall3(nr: __NR_write, a0: fd, a1: (long)data, a2: (long)len);
57}
58
59static inline void linux_exit(int code)
60{
61 x86_syscall3(nr: __NR_exit, a0: code, a1: 0, a2: 0);
62}
63
64void to_base10(char *lastdig, time_t n)
65{
66 while (n) {
67 *lastdig = (n % 10) + '0';
68 n /= 10;
69 lastdig--;
70 }
71}
72
73__attribute__((externally_visible)) void c_main(void **stack)
74{
75 /* Parse the stack */
76 long argc = (long)*stack;
77 stack += argc + 2;
78
79 /* Now we're pointing at the environment. Skip it. */
80 while(*stack)
81 stack++;
82 stack++;
83
84 /* Now we're pointing at auxv. Initialize the vDSO parser. */
85 vdso_init_from_auxv(auxv: (void *)stack);
86
87 /* Find gettimeofday. */
88 typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
89 gtod_t gtod = (gtod_t)vdso_sym(version: "LINUX_2.6", name: "__vdso_gettimeofday");
90
91 if (!gtod)
92 linux_exit(code: 1);
93
94 struct timeval tv;
95 long ret = gtod(&tv, 0);
96
97 if (ret == 0) {
98 char buf[] = "The time is .000000\n";
99 to_base10(buf + 31, tv.tv_sec);
100 to_base10(buf + 38, tv.tv_usec);
101 linux_write(1, buf, sizeof(buf) - 1);
102 } else {
103 linux_exit(code: ret);
104 }
105
106 linux_exit(code: 0);
107}
108
109/*
110 * This is the real entry point. It passes the initial stack into
111 * the C entry point.
112 */
113asm (
114 ".text\n"
115 ".global _start\n"
116 ".type _start,@function\n"
117 "_start:\n\t"
118#ifdef __x86_64__
119 "mov %rsp,%rdi\n\t"
120 "jmp c_main"
121#else
122 "push %esp\n\t"
123 "call c_main\n\t"
124 "int $3"
125#endif
126 );
127

source code of linux/tools/testing/selftests/vDSO/vdso_standalone_test_x86.c