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 a 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 /* ...and two syscalls.  This is x86-specific. */
  38 static inline long x86_syscall3(long nr, long a0, long a1, long a2)
  39 {
  40         long ret;
  41 #ifdef __x86_64__
  42         asm volatile ("syscall" : "=a" (ret) : "a" (nr),
  43                       "D" (a0), "S" (a1), "d" (a2) :
  44                       "cc", "memory", "rcx",
  45                       "r8", "r9", "r10", "r11" );
  46 #else
  47         asm volatile ("int $0x80" : "=a" (ret) : "a" (nr),
  48                       "b" (a0), "c" (a1), "d" (a2) :
  49                       "cc", "memory" );
  50 #endif
  51         return ret;
  52 }
  53
  54 static inline long linux_write(int fd, const void *data, size_t len)
  55 {
  56         return x86_syscall3(__NR_write, fd, (long)data, (long)len);
  57 }
  58
  59 static inline void linux_exit(int code)
  60 {
  61         x86_syscall3(__NR_exit, code, 0, 0);
  62 }
  63
  64 void to_base10(char *lastdig, time_t n)
  65 {
  66         while (n) {
  67                 *lastdig = (n % 10) + '0';
  68                 n /= 10;
  69                 lastdig--;
  70         }
  71 }
  72
  73 __attribute__((externally_visible)) void c_main(void **stack)
  74 {
  75         /* Parse the stack */
  76         long argc = (long)*stack;
  77         stack += argc + 2;
  78
  79         /* Now we're pointing at the environment.  Skip it. */
  80         while(*stack)
  81                 stack++;
  82         stack++;
  83
  84         /* Now we're pointing at auxv.  Initialize the vDSO parser. */
  85         vdso_init_from_auxv((void *)stack);
  86
  87         /* Find gettimeofday. */
  88         typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
  89         gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday");
  90
  91         if (!gtod)
  92                 linux_exit(1);
  93
  94         struct timeval tv;
  95         long ret = gtod(&tv, 0);
  96
  97         if (ret == 0) {
  98                 char buf[] = "The time is                     .000000\n";
  99                 to_base10(buf + 31, tv.tv_sec);
 100                 to_base10(buf + 38, tv.tv_usec);
 101                 linux_write(1, buf, sizeof(buf) - 1);
 102         } else {
 103                 linux_exit(ret);
 104         }
 105
 106         linux_exit(0);
 107 }
 108
 109 /*
 110  * This is the real entry point.  It passes the initial stack into
 111  * the C entry point.
 112  */
 113 asm (
 114         ".text\n"
 115         ".global _start\n"
 116         ".type _start,@function\n"
 117         "_start:\n\t"
 118 #ifdef __x86_64__
 119         "mov %rsp,%rdi\n\t"
 120         "jmp c_main"
 121 #else
 122         "push %esp\n\t"
 123         "call c_main\n\t"
 124         "int $3"
 125 #endif
 126         );