The user exit should maintain the absolute record number and the relative record number. These fields are set to zero before the OPEN request. The assembler uses the relative record number in diagnostic messages when you specify the FLAG(RECORD) assembler option. If you specify the ADATA assembler option, the assembler includes both fields in the associated data file Source Analysis record.

If you want to provide the assembler with the values for the system variables &SYSIN_DSN, &SYSIN_MEMBER, and &SYSIN_VOLUME, the user exit must set the reason code to 4 and place the values in the data set name, member name, and volume serial fields of the exit-specific information block. You can provide this information during the OPEN call, or whenever the exit supplies a record to the assembler. If the exit is reading records from concatenated data sets, it should supply the data set information with the first record from each data set in the concatenation.

If the exit does not supply the data set information, the system variables are set to null, and the primary input data set details are not shown in the Diagnostic Cross Reference and Assembler Summary section of the listing, nor are they included in the ADATA Job Identification record.