LXR linux/tools/testing/selftests/vDSO/vdso_standalone_test

   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
  19extern void *vdso_sym(const char *version, const char *name);
  20extern void vdso_init_from_sysinfo_ehdr(uintptr_t base);
  21extern void vdso_init_from_auxv(void *auxv);
  22
  23/* We need a libc functions... */
  24int 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. */
  40static 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
  56static 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
  61static inline void linux_exit(int code)
  62{
  63        x86_syscall3(__NR_exit, code, 0, 0);
  64}
  65
  66void 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 */
 115asm (
 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