On Sun, 11 Jun 2017 14:13:17 -0400, Peter Relson wrote:
>A refreshable program cannot modify itself (or if it can, it would be a
>very interesting and perhaps self-limiting testcase).
>
I believe that if a program is marked REFR but loaded from a
non-authorized library and REFRPROT is not in effect, no error
is reported at that time. Behavior is unpredictable when
a refresh may actually occur.
>... A reentrant program
>can, if written carefully, modify itself, although it is rarely a good idea.
>LPA modules are generally, in effect, refreshable.
>
Does this mean that REFRPROT "in effect" applies to LPA modules?
>As to "why", think about it.
>Page protection did not even exist at the time RENT and REFR were defined.
>And over those 20-30 years, many many programs were incorrectly bound with
>"RENT,REFR" when in fact they were RENT but not REFR. But they worked fine
>given the way the system processed.
>The combination was used indiscriminately, and often thought of as a pair.
>Making it the default would be horribly incompatible.
>
It's like a child whining about a distasteful medicine: in the
end it's good for him and should be done, even as user key
CSA has been disabled (I think).
Programmers who didn't RTFM deserve what they get; it's easy
enough to relink with NO REFR.
>Thus we made it an option and encouraged IBM code and ISV code to fix
>their binder attributes so that REFR could be used in this way, with the
>new processing enabled by use of REFRPROT.
>
Code residing authorized llibraries was strongly "encouraged",
regardless of the REFRPROT setting. I suppose that's true
additionaly for end-user code.
In the Program Management UG and Ref, I see:
RENT
... A reenterable module is ordinarily expected not to modify
its own code. In some cases, MVS protects the reentrant module's
virtual storage so that it cannot be modified except by a
program running in key 0. These cases include programs which
the system treats as having been loaded from an authorized
library, ...
Is that right? It seems to be describing REFR, not RENT. And
the "treats as" waffling? Is that referring to LPA, regardless of
load module attributes? And "include" hints at other cases, not
mentioned.
>And, yes, it is a performance consideration. Not a huge one, but one
>nevertheless.
-- gil
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