On Tue, 14 Sep 2010 13:38:15 -0500, Mike Schwab wrote: >On Tue, Sep 14, 2010 at 12:15 PM, Tony Harminc wrote: ><deleted> >> Well, we had this discussion at great length a few years ago... The >> pre-existing 24- or 31-bit program that's been running for many years >> now gets called by a 64-bit program, issues a GETMAIN which now zeros >> the high half of 64-bit R1, does some stuff, and returns to its >> caller, restoring the only R1 it knows about, which is 32 bits. >> >> The 64-bit caller has had its R1 clobbered by calling the pre-existing >> program, even though the pre-existing program used no 64-bit >> instructions or services and restored R1 as it always has done, and as >> its documentation states.
The programmer who wrote the 64-bit program should not expect that the bits 0-31 of registers 0, 1 and 15 are preserved. > >This is just like a 31 bit program calling a 24 bit program. You have >to save your own registers and set up the with 24 bit addresses before >calling the 24 bit program. No, you don't have to save your own registers if you are a 31-bit program calling a 24-bit program. You do, of course, have to ensure that the called program will get control in AMODE(24) and must expect that it will return in AMODE(24), but that is a very different discussion. An AMODE(64) program does not have to save its registers either. Read the Assembler Services Guide chapter on Linkage Conventions. > >System interrupts do have to restore all 64 bits of the register, but not calls. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
