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) + '0';
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