143 lines · c
1// SPDX-License-Identifier: GPL-2.0-only2/*3 * vdso_test.c: Sample code to test parse_vdso.c on x864 * Copyright (c) 2011-2014 Andy Lutomirski5 *6 * You can amuse yourself by compiling with:7 * gcc -std=gnu99 -nostdlib8 * -Os -fno-asynchronous-unwind-tables -flto -lgcc_s9 * vdso_standalone_test_x86.c parse_vdso.c10 * to generate a small binary. On x86_64, you can omit -lgcc_s11 * 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... */22int 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 */41void *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. */52static 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#else61 asm volatile ("int $0x80" : "=a" (ret) : "a" (nr),62 "b" (a0), "c" (a1), "d" (a2) :63 "cc", "memory" );64#endif65 return ret;66}67 68static 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 73static inline void linux_exit(int code)74{75 x86_syscall3(__NR_exit, code, 0, 0);76}77 78void to_base10(char *lastdig, time_t n)79{80 while (n) {81 *lastdig = (n % 10) + '0';82 n /= 10;83 lastdig--;84 }85}86 87void 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 into125 * the C entry point.126 */127asm (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 "and $-16,%rsp\n\t"135 "sub $8,%rsp\n\t"136 "jmp c_main"137#else138 "push %esp\n\t"139 "call c_main\n\t"140 "int $3"141#endif142 );143