why post to the cobol forum ???
ISRSUPC is not certainly written in COBOL
running an AMBLIST on the load module will tell
to save You the stress of the research here is the jcl snippet to use
000005 //IDR EXEC PGM=AMBLIST
000006 //SYSPRINT DD SYSOUT=*
000007 //SYSLIB DD DISP=SHR,DSN=ISP.SISPLPA
000008 //SYSIN DD *
000009 LISTIDR DDN=SYSLIB,MEMBER=ISRSUPC
PLX-390 is then IBM IUO language and compiler used for system related programming