Method: Kernel#syscall

Defined in:

io.c

#syscall(num[, args...]) ⇒ Integer

Calls the operating system function identified by num and returns the result of the function or raises SystemCallError if it failed.

Arguments for the function can follow num. They must be either String objects or Integer objects. A String object is passed as a pointer to the byte sequence. An Integer object is passed as an integer whose bit size is same as a pointer. Up to nine parameters may be passed (14 on the Atari-ST).

The function identified by num is system dependent. On some Unix systems, the numbers may be obtained from a header file called syscall.h.

syscall 4, 1, "hello\n", 6   # '4' is write(2) on our box

produces:

hello

Calling syscall on a platform which does not have any way to an arbitrary system function just fails with NotImplementedError.

Note

syscall is essentially unsafe and unportable. Feel free to shoot your foot. DL (Fiddle) library is preferred for safer and a bit more portable programming.

Returns:

• (Integer)

# File 'io.c', line 9114

static VALUE
rb_f_syscall(int argc, VALUE *argv)
{
#ifdef atarist
    VALUE arg[13]; /* yes, we really need that many ! */
#else
    VALUE arg[8];
#endif
#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_warning("We plan to remove a syscall function at future release. DL(Fiddle) provides safer alternative.");
    }

    rb_secure(2);
    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)) {
	    SafeStringValue(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;
#ifdef atarist
      case 9:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
	  arg[7]);
	break;
      case 10:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
	  arg[7], arg[8]);
	break;
      case 11:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
	  arg[7], arg[8], arg[9]);
	break;
      case 12:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
	  arg[7], arg[8], arg[9], arg[10]);
	break;
      case 13:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
	  arg[7], arg[8], arg[9], arg[10], arg[11]);
	break;
      case 14:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
	  arg[7], arg[8], arg[9], arg[10], arg[11], arg[12]);
        break;
#endif
    }

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