Re: Re: Assembler Clarification

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for z/OS, there is no "heap"-type stack, but yes, there is a "mainframe" 
form of a stack, called the save area trace. it is a noncontiguous 
doubly-linked (i.e., backwards and forwards) stack.
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Actually, it's more properly named a doubly-linked list.  :-) "SAVE AREA 
TRACE" is what dump processing calls it when it's printed out.

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there is no pc-style "heap" with program linkage and register saving, 
but iirc there are heaps used in some areas of z/OS (advanced stuff; PC 
/ PR instructions, etc).
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PC/PR linkages have been established since MVS/XA and use hardware 
stacks, but the old "traditional" S/360 types of linkages still work 
just fine. z/OS uses a variety of linkage conventions, including BALR, 
BAKR, BASSM and PC/PR, depending on the requirements. PC/PR are 
especially useful since they allow a Address Space Switch event. Much 
faster than SVC events for some supervisor services, like 
ENQ/DEQ/RESERVE and STORAGE (replacement for GETMAIN/FREEMAIN). SVC 
events are really very slow, because of the hardware and software 
overhead in processing an interrupt.

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for more information, you could read the Principles Of Operation (POPs) 
for z/OS and Assembler Language Reference / Macros. POPs will explain 
the instructions; the ASM manuals should show you program linkage 
methodology (program linkage methodology remains basically unchanged 
since the 1960's). it's not "light reading" (i used to read POPs when i 
had insomnia...)
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I found that Program Logic manuals served equally well for insomnia. :-) 
"Supervisor Services" also has a fair description of program linkage 
conventions.

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also please note that while DOS/VS(E), (z/)VM, and z/OS all use pretty 
much the same instruction set, they all have different linkage 
methodologies.
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Most, if not all, the various linkage conventions are available on all 
those systems. Most of the "dependance" is based on the available 
instruction set.

Rick 
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