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, time_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 ); 129