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98eedc3a AL |
1 | /* |
2 | * vdso_test.c: Sample code to test parse_vdso.c on x86_64 | |
3 | * Copyright (c) 2011 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 | |
9 | * vdso_test.c parse_vdso.c -o vdso_test | |
10 | * to generate a small binary with no dependencies at all. | |
11 | */ | |
12 | ||
13 | #include <sys/syscall.h> | |
14 | #include <sys/time.h> | |
15 | #include <unistd.h> | |
16 | #include <stdint.h> | |
17 | ||
18 | extern void *vdso_sym(const char *version, const char *name); | |
19 | extern void vdso_init_from_sysinfo_ehdr(uintptr_t base); | |
20 | extern void vdso_init_from_auxv(void *auxv); | |
21 | ||
22 | /* We need a libc functions... */ | |
23 | int strcmp(const char *a, const char *b) | |
24 | { | |
25 | /* This implementation is buggy: it never returns -1. */ | |
26 | while (*a || *b) { | |
27 | if (*a != *b) | |
28 | return 1; | |
29 | if (*a == 0 || *b == 0) | |
30 | return 1; | |
31 | a++; | |
32 | b++; | |
33 | } | |
34 | ||
35 | return 0; | |
36 | } | |
37 | ||
38 | /* ...and two syscalls. This is x86_64-specific. */ | |
39 | static inline long linux_write(int fd, const void *data, size_t len) | |
40 | { | |
41 | ||
42 | long ret; | |
43 | asm volatile ("syscall" : "=a" (ret) : "a" (__NR_write), | |
44 | "D" (fd), "S" (data), "d" (len) : | |
45 | "cc", "memory", "rcx", | |
46 | "r8", "r9", "r10", "r11" ); | |
47 | return ret; | |
48 | } | |
49 | ||
50 | static inline void linux_exit(int code) | |
51 | { | |
52 | asm volatile ("syscall" : : "a" (__NR_exit), "D" (code)); | |
53 | } | |
54 | ||
55 | void to_base10(char *lastdig, uint64_t n) | |
56 | { | |
57 | while (n) { | |
58 | *lastdig = (n % 10) + '0'; | |
59 | n /= 10; | |
60 | lastdig--; | |
61 | } | |
62 | } | |
63 | ||
64 | __attribute__((externally_visible)) void c_main(void **stack) | |
65 | { | |
66 | /* Parse the stack */ | |
67 | long argc = (long)*stack; | |
68 | stack += argc + 2; | |
69 | ||
70 | /* Now we're pointing at the environment. Skip it. */ | |
71 | while(*stack) | |
72 | stack++; | |
73 | stack++; | |
74 | ||
75 | /* Now we're pointing at auxv. Initialize the vDSO parser. */ | |
76 | vdso_init_from_auxv((void *)stack); | |
77 | ||
78 | /* Find gettimeofday. */ | |
79 | typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz); | |
80 | gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday"); | |
81 | ||
82 | if (!gtod) | |
83 | linux_exit(1); | |
84 | ||
85 | struct timeval tv; | |
86 | long ret = gtod(&tv, 0); | |
87 | ||
88 | if (ret == 0) { | |
89 | char buf[] = "The time is .000000\n"; | |
90 | to_base10(buf + 31, tv.tv_sec); | |
91 | to_base10(buf + 38, tv.tv_usec); | |
92 | linux_write(1, buf, sizeof(buf) - 1); | |
93 | } else { | |
94 | linux_exit(ret); | |
95 | } | |
96 | ||
97 | linux_exit(0); | |
98 | } | |
99 | ||
100 | /* | |
101 | * This is the real entry point. It passes the initial stack into | |
102 | * the C entry point. | |
103 | */ | |
104 | asm ( | |
105 | ".text\n" | |
106 | ".global _start\n" | |
107 | ".type _start,@function\n" | |
108 | "_start:\n\t" | |
109 | "mov %rsp,%rdi\n\t" | |
110 | "jmp c_main" | |
111 | ); |