The error buffer pointer points to the error text buffer.

The assembler sets this pointer. If you want the assembler to issue a message on behalf of the exit, you must supply the text of the error messages in the area pointed to by the error buffer pointer. The text can be up to 255 characters. The exit must place the length of the text in the error buffer length field. The assembler selects a message number based on the value you place in the error severity field.