Kernel#syscall

static VALUE
rb_f_syscall(int argc, VALUE *argv, VALUE _)
{
    VALUE arg[8];
#if SIZEOF_VOIDP == 8 && defined(HAVE___SYSCALL) && SIZEOF_INT != 8 /* mainly *BSD */
# define SYSCALL __syscall
# define NUM2SYSCALLID(x) NUM2LONG(x)
# define RETVAL2NUM(x) LONG2NUM(x)
# if SIZEOF_LONG == 8
    long num, retval = -1;
# elif SIZEOF_LONG_LONG == 8
    long long num, retval = -1;
# else
#  error ---->> it is asserted that __syscall takes the first argument and returns retval in 64bit signed integer. <<----
# endif
#elif defined(__linux__)
# define SYSCALL syscall
# define NUM2SYSCALLID(x) NUM2LONG(x)
# define RETVAL2NUM(x) LONG2NUM(x)
    /*
     * Linux man page says, syscall(2) function prototype is below.
     *
     *     int syscall(int number, ...);
     *
     * But, it's incorrect. Actual one takes and returned long. (see unistd.h)
     */
    long num, retval = -1;
#else
# define SYSCALL syscall
# define NUM2SYSCALLID(x) NUM2INT(x)
# define RETVAL2NUM(x) INT2NUM(x)
    int num, retval = -1;
#endif
    int i;

    if (RTEST(ruby_verbose)) {
        rb_category_warning(RB_WARN_CATEGORY_DEPRECATED,
            "We plan to remove a syscall function at future release. DL(Fiddle) provides safer alternative.");
    }

    if (argc == 0)
        rb_raise(rb_eArgError, "too few arguments for syscall");
    if (argc > numberof(arg))
        rb_raise(rb_eArgError, "too many arguments for syscall");
    num = NUM2SYSCALLID(argv[0]); ++argv;
    for (i = argc - 1; i--; ) {
        VALUE v = rb_check_string_type(argv[i]);

        if (!NIL_P(v)) {
            StringValue(v);
            rb_str_modify(v);
            arg[i] = (VALUE)StringValueCStr(v);
        }
        else {
            arg[i] = (VALUE)NUM2LONG(argv[i]);
        }
    }

    switch (argc) {
      case 1:
        retval = SYSCALL(num);
        break;
      case 2:
        retval = SYSCALL(num, arg[0]);
        break;
      case 3:
        retval = SYSCALL(num, arg[0],arg[1]);
        break;
      case 4:
        retval = SYSCALL(num, arg[0],arg[1],arg[2]);
        break;
      case 5:
        retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3]);
        break;
      case 6:
        retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4]);
        break;
      case 7:
        retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5]);
        break;
      case 8:
        retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6]);
        break;
    }

    if (retval == -1)
        rb_sys_fail(0);
    return RETVAL2NUM(retval);
#undef SYSCALL
#undef NUM2SYSCALLID
#undef RETVAL2NUM
}