The Linux Standard Base Specification 2.0.1 for libc places constraints on arguments to some internal functions. The behavior of this function is undefined unless its control parameter is set to a specific value. If the constraints are not met, the behavior of the functions is not defined. It is almost always invoked through a macro defined in a system header file, and the macro ensures that the following constraints are met: The value 1 must be passed to the third. parameter (the version number) of the following file system function:”]
Source: https://owasp.org/www-community/vulnerabilities/Undefined_Behavior