extern void assert_fail(void) __attribute__ ((__noreturn__));
void __fxprintf(int _mode, const char *fmt, ...)
{
	if (_mode) {
		unsigned int len = strlen(fmt) + 1;
		unsigned int wfmt[len];
		for (unsigned int i = 0; i < len; ++i)
			if (fmt[i] & ~0x7f)
				assert_fail();
	}
}