The work you do to make a subroutine refreshable pretty much takes care of recursion. There's only one R14 slot in a save area.
Similar considerations apply if you're using XPLINK. -- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Assembler List <[email protected]> on behalf of Charles Mills <[email protected]> Sent: Monday, August 6, 2018 7:07 PM To: [email protected] Subject: Re: EX I get the impression that the hardware handles EX like a subroutine call. If a B or J is like a COBOL GOTO, then EX is like a COBOL PERFORM. Subroutine returns are a heckuva lot easier to implement if you only allow subroutine calls to be one deep. You have only one return address pointer to worry about. Charles -----Original Message----- From: IBM Mainframe Assembler List [mailto:[email protected]] On Behalf Of Paul Gilmartin Sent: Monday, August 6, 2018 3:49 PM To: [email protected] Subject: Re: EX On 2018-08-06, at 16:12:37, Dan Greiner wrote: > I was once asked why the execute exception existed. That is, why not just let the hardware - or, in this odd case, the firmware - cascade down a chain of multiple EX instructions, ORing the bits of the R1 field with the subsequent target instruction, whatever instruction that might be. Aside from there being absolutely no practical reason for wasting circuits on such folly, ... > You've been there; I haven't, so I bow to your expertise. I wouldn't have guessed whether it's less hardware to detect the special case and throw an exception, or just to do it.
