1 /*
2 * vdso_test.c: Sample code to test parse_vdso.c on x86
3 * Copyright (c) 2011-2014 Andy Lutomirski
4 * Subject to the GNU General Public License, version 2
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 extern void *vdso_sym(const char *version, const char *name);
20 extern void vdso_init_from_sysinfo_ehdr(uintptr_t base);
21 extern void vdso_init_from_auxv(void *auxv);
22
23 /* We need a libc functions... */
strcmp(const char * a,const char * b)24 int strcmp(const char *a, const char *b)
25 {
26 /* This implementation is buggy: it never returns -1. */
27 while (*a || *b) {
28 if (*a != *b)
29 return 1;
30 if (*a == 0 || *b == 0)
31 return 1;
32 a++;
33 b++;
34 }
35
36 return 0;
37 }
38
39 /* ...and two syscalls. This is x86-specific. */
x86_syscall3(long nr,long a0,long a1,long a2)40 static inline long x86_syscall3(long nr, long a0, long a1, long a2)
41 {
42 long ret;
43 #ifdef __x86_64__
44 asm volatile ("syscall" : "=a" (ret) : "a" (nr),
45 "D" (a0), "S" (a1), "d" (a2) :
46 "cc", "memory", "rcx",
47 "r8", "r9", "r10", "r11" );
48 #else
49 asm volatile ("int $0x80" : "=a" (ret) : "a" (nr),
50 "b" (a0), "c" (a1), "d" (a2) :
51 "cc", "memory" );
52 #endif
53 return ret;
54 }
55
linux_write(int fd,const void * data,size_t len)56 static inline long linux_write(int fd, const void *data, size_t len)
57 {
58 return x86_syscall3(__NR_write, fd, (long)data, (long)len);
59 }
60
linux_exit(int code)61 static inline void linux_exit(int code)
62 {
63 x86_syscall3(__NR_exit, code, 0, 0);
64 }
65
to_base10(char * lastdig,time_t n)66 void to_base10(char *lastdig, time_t n)
67 {
68 while (n) {
69 *lastdig = (n % 10) + '0';
70 n /= 10;
71 lastdig--;
72 }
73 }
74
c_main(void ** stack)75 __attribute__((externally_visible)) void c_main(void **stack)
76 {
77 /* Parse the stack */
78 long argc = (long)*stack;
79 stack += argc + 2;
80
81 /* Now we're pointing at the environment. Skip it. */
82 while(*stack)
83 stack++;
84 stack++;
85
86 /* Now we're pointing at auxv. Initialize the vDSO parser. */
87 vdso_init_from_auxv((void *)stack);
88
89 /* Find gettimeofday. */
90 typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
91 gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday");
92
93 if (!gtod)
94 linux_exit(1);
95
96 struct timeval tv;
97 long ret = gtod(&tv, 0);
98
99 if (ret == 0) {
100 char buf[] = "The time is .000000\n";
101 to_base10(buf + 31, tv.tv_sec);
102 to_base10(buf + 38, tv.tv_usec);
103 linux_write(1, buf, sizeof(buf) - 1);
104 } else {
105 linux_exit(ret);
106 }
107
108 linux_exit(0);
109 }
110
111 /*
112 * This is the real entry point. It passes the initial stack into
113 * the C entry point.
114 */
115 asm (
116 ".text\n"
117 ".global _start\n"
118 ".type _start,@function\n"
119 "_start:\n\t"
120 #ifdef __x86_64__
121 "mov %rsp,%rdi\n\t"
122 "jmp c_main"
123 #else
124 "push %esp\n\t"
125 "call c_main\n\t"
126 "int $3"
127 #endif
128 );
129