ASMA036W Reentrant check failed
Explanation: A machine instruction that might store data into a control section or common area when run has been detected. This message is generated only when reentrant checking is requested by the assembler option RENT or within an RSECT.
This is a known limitation with the ASMA90 assembler.
Based on the TPX Customization Guide chapter titled "Setting Up User Exits", the exit MUST be coded as reentrant programs. This is done via the UENTER & UEXIT macros which are available to help write the exits. ASMA90 does not check this, since it's done via the UENTER and UEXIT macros.
So, the assembler ASMA036W warnings can be ignored. The exit will be reenterant.