The EXECIO command can be used in REXX execs that execute in both the TSO/E address space and non-TSO/E address spaces.
You can use the EXECIO command to do various types of I/O tasks, such as copy information to and from a data set to add, delete, or update the information.
Restrictions: The EXECIO command does not support I/O on files allocated to data sets with spanned, track overflow, or undefined record formats.
An I/O data set must be either sequential or a single member of a PDS. Before the EXECIO command can perform I/O to or from the data set, the data set must be allocated to a file that is specified on the EXECIO command. The EXECIO command does not perform the allocation.
I don't know if you can "open a PDS of format U", but you certainly can't read one.
There is a specific MVS utility that deals with processing the information contained in a loadlib.
It might be more helpful if you would describe what you want to do with this PDS and what process you want to follow to accomplish your goal.
we could find some discrepancy with few load modules in the Loadlib library. Hence we need to get all the compilation dates of the load module in two different environment. The Loadlib library is of U format.