About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / vDSO / vdso_standalone_test_x86.c




Custom Search

Based on kernel version 3.16. Page generated on 2014-08-06 21:41 EST.

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... */
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. */
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	
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	
61	static inline void linux_exit(int code)
62	{
63		x86_syscall3(__NR_exit, code, 0, 0);
64	}
65	
66	void to_base10(char *lastdig, uint64_t n)
67	{
68		while (n) {
69			*lastdig = (n % 10) + '0';
70			n /= 10;
71			lastdig--;
72		}
73	}
74	
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		);
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.