Re: Re: Assembler Clarification

Hi - yes, recursion, multi-tasking, pipelining, etc, others are still
catching up! No stack, thanks! So, no stack overflows, no security problems
in that sense, no code injection, no push / pop nightmare, etc.

Now : try IBM System/370 Systems Principles of Operation - it explains these
very nicely (already 1970!) -

http://bitsavers.org/pdf/ibm/370/princOps/GA22-7000-0_370_Principles_Of_Operation_Jun70.pdf

have a nice day - tuomo

ps. there are later versions of "Principles of Operation" but this isn't too
bad.

On Sun, May 9, 2010 at 21:01, Ron Hudson <[email protected]> wrote:

>
>
> The return address is stored in a register? No recursion... right?
>
> Is there a stack?
>
>
>
> On Sun, May 9, 2010 at 2:16 PM, peter.thingsted <[email protected]> wrote:
>
>>
>>
>> The first thing a program needs to do is to save the contents of the
>> general registers (16 of them ) in memory.
>>
>> The general registers are to be thought of as separate electronic pieces
>> of storage - outside the main storage.
>>
>> You need to save the contents of these registers when your program starts
>> running, and restore them after your program has finished doing whatever it
>> is programmed to do.
>>
>> One register (14) is especially important to preserve, because it contains
>> the return address of the calling program, i.e. the program that was running
>> just before your assembler program. So the very last instruction in your
>> program should be a BR 14, i.e branch to the machine instruction stored in
>> the memory location that register 14 poinded to when YOUR program took over.
>>
>> You can play with one register for good effects just before your BR 14
>> instucton. You can put a value in register 15, e.g. a big fat zero by coding
>> SR 15,15. This signals that all ended well. It is customary (but not
>> required or in any way enforced) that you can put various powers of 2 into
>> reg 15 to signal any number of abnormal situations thet your program
>> detected.
>>
>> The latter here is part of what we call the linkage conventions. Note that
>> they are conventions not enforced by any part of MVS - but you best know
>> these conventions otherwise your program wil not cooperate well with all the
>> other programs that taken together constitute the MVS sustem.
>>
>> Rgs,
>>
>> Peter
>> mvsaudit.org
>>
>>
>> --- In [email protected] <turnkey-mvs%40yahoogroups.com>, Ron
>> Hudson <hudson.ra@...> wrote:
>> >
>> > Hey Wizards of Assembly Language..
>> >
>> > It looks to me like one of the first things a program does in setting up
>> > it's own environment
>> > is tell the CPU where to put the registers? Are do the registers
>> actually
>> > reside in memory?
>> > Does each program get it's own set of registers? Gee that would make
>> context
>> > changes
>> > really easy..
>> >
>> > (Not starting assembly language just yet but interested...)
>> >
>> > Thanks.
>> >
>>
>>
>  
>