IBM Mainframe Forum

Hi, could anyone let know, how is the addressability of a called program set when we make a call for it. What all instructions are involved and how is the data of the calling program saved in savearea. Thanx

Hello Rahul and welcome to the forums,

how is the addressability of a called program set when we make a call for it

When you call a sub-program, the addressability is done the same as when the main program is invoked by the operating system. This is usually known as the "standard linkage convention".

how is the data of the calling program saved in savearea

The caller's data is not saved in the savearea. The save area stores register content.

Since no one have helped you I will give this information.

The POPs manual is the king of manuals when dealing with assembler.
POP is the Principle of Operations.

The actual instructions are as follows and should be built into a startup macro.
This the from my days in the 370 market place.

an online version can be found here. http://publibz.boulder.ibm.com/cgi-bin/ ... 0504121320


Assembler codeing can begin in any collum other then 1. if its in col. 1 then its a label.

The called pgm must have the follwing instructions to follow the rules.

your special code

to return to caller



Have at it. Any questions. TKS

tsjurseth wrote: stm r14,r12,12(r13) save the callers registers into the new pgms save area. ( of couse this is non-reentrant)

IIRC, r13 is pointing to a save area in the calling program, isn't it?

balr r12,0 set addresserrablilty with r12 for use as base reg
using *,r12 give address ability to the next 4096 bytes with addressability

Why use another register, isn't r15 already pointing to the entyry point?

tsjurseth wrote: stm r14,r12,12(r13) save the callers registers into the new pgms save area. ( of couse this is non-reentrant)

IIRC, r13 is pointing to a save area in the calling program, isn't it?

In the calling program or provided by the calling program, yes.
(It could well be "provided by" the calling program and be entirely re-entrant..)

balr r12,0 set addresserrablilty with r12 for use as base reg
using *,r12 give address ability to the next 4096 bytes with addressability

Why use another register, isn't r15 already pointing to the entyry point?

Yes, but if your module is going to do anything non-trivial, such as use any system or
I/O macros, R15 is going to get modified. Much safer, and more standard-observant,
to provide your own base register.

dickvb wrote:In the calling program or provided by the calling program, yes.

'Standard linkage'......

Yes, but if your module is going to do anything non-trivial, such as use any system or
I/O macros, R15 is going to get modified. Much safer, and more standard-observant,
to provide your own base register.

Correct, but I'd assumed the programmer would know that....grin.....