Mainframe, MVS and zOS Discussion

Hi,

I'm starting with assembler and looking for a guidance on how is the addressability of a called program set when we make a call for it, in assembler? I looked in to POP but I could not really grasp it - if someone can provide an example it'll be a gerat help.

Addressability starts, typically, with register 15 (BALR 14,15). Once the called program is loaded into memory, its starting address is loaded into register 15, and control transfers to that starting address. The initial code for the called program typically sets up a base register to replace 15 (which may be used in the program and hence should NOT be kept as the base register), save the registers, and set up the save area trace.

Thanks for the indication on save area, this is useful.

Thank you.