DRL T.EXEC (octal 100) - execute code in TSS exec mode.

Usage:

drl    t.exec
zero   <routine locsym>,0

Description:

DRL T.EXEC enters the code at the locsym under TSS's ISR (BAR). On initial entry, the address of the UST of the caller is loaded in X4 and the address of the first UST in the chain (probably the most recent logon) is loaded in x2. X1 is sacred and is used for exit back to TSSK. An exit of "tra 0,1" will result in a re-entry to the routine with the next UST in the chain loaded in x2 (x4 is meaningless at this time). An exit of "tra 1,1" will return to the calling subsystem just after the derail calling sequence.

Notes:

It is the responsibility of the caller to preserve the index and address registers of the subsystem across this derail. On return to the subsystem, everything will have been lost.

The routine at the locsym must be floating code.

The calling subsystem must have .bmasx privilege. This requires that the subsystem be edited into TSSA.