RACF® supports callers running in either AMODE(24) or AMODE(31), except for RACROUTE REQUEST=SIGNON, which requires its callers to be in AMODE(31). If all of your RACF exits have AMODE(31) or AMODE(ANY), parameters and parameter lists for the exits can reside above the 16MB address. If you have AMODE(24) exits, RACF data areas are placed below the 16MB address in storage to ensure that your exits process correctly. The RCVT, any task-level ACEEs (pointed to by TCBSENV), and the address space ACEE (pointed to by ASXBSENV) always reside below 16MB.

For best use of virtual storage and best RACF performance, we recommend that you write and link-edit your exits to run in AMODE(31) or AMODE(ANY).

During system IPL, RACF initialization records the AMODE of each installation exit routine it finds. All RACF exit routines, except the RACROUTE REQUEST=FASTAUTH exits, are called in their defined AMODE and must return control to RACF in the mode in which they were called.

RACF calls the RACROUTE REQUEST=FASTAUTH exits and MVS™ calls the SAF router exits in the AMODE (24 or 31) used by the invoker of the service. For this reason, the RACROUTE REQUEST=FASTAUTH and SAF router exits must be capable of running in either mode.

In many cases RACF must copy caller-supplied parameter areas to an area below 16MB, so that the AMODE(24) exit can address the parameter areas. However, when the RACROUTE REQUEST=AUTH or RACROUTE REQUEST=DEFINE exit routines receive the ACCLVL parameter or INSTL parameters, RACF does not know the format or length of the parameters being passed, and therefore cannot copy the parameters into 24-bit storage. Because the parameter list pointing to these parameters is in 24-bit storage, you must modify the exit routines to handle the parameters if the exit routines access these areas, and if they are passed by callers in 31-bit mode.

If a 31-bit caller issues a RACROUTE REQUEST=VERIFY request with the ACEE parameter, and does not specify that the ACEE should be placed below 16MB, it is placed above 16MB, unless a RACF exit is marked (or defaulted to) AMODE(24).

For an ACEE other than an address space ACEE, if a 31-bit caller of RACROUTE REQUEST=LIST requests that the RACLISTed profiles be placed above 16MB, and no installation-supplied RACF exits have AMODE(24), the profiles are placed above 16MB by RACROUTE REQUEST=LIST.