On 6/22/2017 4:17 AM, contactmura...@gmail.com wrote:
I am new to SRBs & FRRs. I have a question regarding FRR Parameter address
discussed over here.
When said "If the SRB abends, its FRR receives the address of the FRR parameter area
in R2 (or SDWAPARM)."
Why is it (or SDWAPARM)? That means the contents in R2 can't be trusted all the
times and SDWAPARM always has the correct FRR parameter address no matter what
is in R2?
I am asking this question because of the below scenario.
Suppose my SRB issues a system macro say, 'STORAGE OBTAIN' and for some reason
it fails inside a system program. At that time, R2 might contain some ghost
value. Before control reaches FRR,
- Does the system restores the original contents of R2 that was at the time of
entry into SRB?
- OR in such cases R2 will be corrupted but at the entry point of FRR, the
SDWAPARM field anyways contains the correct address of FRRPARM.
Can someone please help me understand this.
The current registers at entry to the FRR are set by RTM. They are
*not* the registers at the time of the error. The registers at time of
error are only found in the SDWA.
RTM will *always* set R2 to point to the FRR 6 word parameter list
associated with the FRR prior to calling the FRR. The same value is
also stored into SDWAPARM by RTM. There is no guarantee, however, that
*your* program will have executed long enough to fill in any data in the
parameter list after the FRR was set.
Regards,
Greg
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