tools/testing/selftests/vDSO/vdso_standalone_test_x86.c

   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         "and $-16,%rsp\n\t"
 135         "sub $8,%rsp\n\t"
 136         "jmp c_main"
 137 #else
 138         "push %esp\n\t"
 139         "call c_main\n\t"
 140         "int $3"
 141 #endif
 142         );