On 2018-11-16 1:47 AM, Ward Able, Grant wrote:
Can someone point me to a reasonably simple example?
If you can do branch instructions then you can do branch-relative
instructions. Apart from RR instructions (BR, BASR, BALR, BASSM, BSM,
BAKR and any others I've missed) replace the B that starts the branch
instruction mnemonic with BR, or as I prefer to do, with J (for jump).
eg. BNH -> JNH and BCT -> JCT and BAS -> JAS etc.
Put all the stuff which needs to be cover by a base register after all
the instructions, and start the area with a label, and "use" that.
eg.
LARL R11,Static
USING Static,R11
...
Static DC 0D My module's constants and literals and non-RENT variables
Then all you need to cover is code generated by macros, which is why
Peter mentioned ARCHLVL (look up the SYSSTATE macro) to cover macros
with logic to test it, and the IEABRCX macro to cover the rest.
IEABRCX DEFINE
will define and activate the facility where the older "branch"
instructions will be converted to newer "branch relative" instructions
when encountered by the assembler in the source code. With IEABRCX you
could even leave the old branch source code as-is, but personally I
prefer to use the newer mnemonics to make it obvious that the code is
probably not covered by a base register, and to keep the listing a bit
tidier.
IEABRCX is "better" than IEABRC because you can turn it on and off as
needed. The most well known scenario where you might was to turn it off
(I'd say) is if you have a branch table where you use the index register
of the branch-on-condition instruction to provide an index into a table
of branch (or even jump) instructions.
That's probably enough to get you started. Have fun with it.
Cheers,
Greg P.
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