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

   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... */
  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/* ...and two syscalls.  This is x86-specific. */
  38static 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
  54static 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
  59static inline void linux_exit(int code)
  60{
  61        x86_syscall3(__NR_exit, code, 0, 0);
  62}
  63
  64void 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 */
 113asm (
 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        );
 127