That was my point; If the goal is to allow the called program to switch
to amode 31 and return to the caller in the amode it was in, it appears
Binjamin's 2 instructions are sufficient. The original code is checking
to see if they need to do this (and there is a small exposure because
the opcodes could be spoofed or EXECed, as others pointed out, or the
locations preceding the R14 could be unaddressable), and it may be more
efficient to just run the LA and BSM without checking. Tony mentioned
that the code is now used outside its original controlled environment,
so the assumptions abut how it's entered may no longer apply.
My comment on speed was checking the opcodes and branching take some
cycles and the LA, BSM instructions may take fewer.
On 2020-08-12 2:04 p.m., Martin Truebner wrote:
Gary,
Are we to conclude from that this discussion that this is a reliable way
to ensure that an AMODE 31 subroutine returns control to its caller
in the correct amode?
the code Tony had was to ensure that it can switch to whatever mode
a routine to be called from that code needs
without effecting the original caller of the code
From Binjamin's response, it appears that checking the opcode of the
previous instruction was unnecessary and perhaps, depending on the
speed of BSM, actually slowed down the routine.
no no - if BSM is needed (because original caller of the code is 24
and final target is 31) then Binjamin's code is fine (at entry!) ...
but it also is executed if everyone is 24 and there is no need for it.
Gary Weinhold
Senior Application Architect
DATAKINETICS | Data Performance & Optimization
Phone:+1.613.523.5500 x216
Email: [email protected]
Visit us online at www.DKL.com
E-mail Notification: The information contained in this email and any
attachments is confidential and may be subject to copyright or other
intellectual property protection. If you are not the intended recipient, you
are not authorized to use or disclose this information, and we request that you
notify us by reply mail or telephone and delete the original message from your
mail system.
