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Based on kernel version 3.13. Page generated on 2014-01-20 22:04 EST.

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		);
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