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