Dave's z/Architecture assembler tips

Attend Conference sessions
Subscribe to the IBM mainframe Assembler newsgroup and mailing list
Misc S/390 assembler tips
Use a REXX exec to quickly find macros
Convert "BC" to Extended Mnemonics easier
An Assembler Programmer's view of Linux for S/390 and zSeries [2006-01-01]

There have been many good sessions for S/390 Assembler programmers at the various SHARE conferences. Here are a few that I've been to that I recommend:

PC Routines for Dummies by Bob Shannon MVS Expo - Session I05 - October 26-30, 1998
Doing it with Mirrors - Reflections of Virtual Storage by Bob Shannon SHARE 90 - Session 2818 - 25 February 1998
Maintaining Integrity for Authorized User Code by Peter Sawyer (Hitachi Data Systems)
Share 81 - Session O312 - Share 81 - August 17, 1993

Perhaps you can locate one of these sessions on a CDROM or go to a future session.

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Misc S/390 assembler tips

Turn on the "HILITE" option of ISPF edit to help your code come alive.
I taught myself assembler by looking at programs on the CBT tape (back when it came only on a reel tape).
When you upgrade to a new level of z/OS, look at the Conversion manual and be the first one on your block to use one of the new APIs (macros).
If you have MVS Quickref, don't forget that it's loaded with assembler information.
I've heard one person say that he didn't really understand assembler language until he looked at the OP CODES generated by the assembler. Sometimes, you may leave out a comma and generate the wrong OP CODE from what you intended.

gottfried.wimmer @ dsi.at sent me his Assembler tips:

SLR to clear Regs (should be the fastest Instr.) .... but you the Cond code is set (la rx,0 preserves it).
MVCL to clear dynamic storage
it's a good practice to code all variables in an instream macro (esp. for RENT-Programming)
NEVER use things like MVC ABC+4(5),=c'ABCDEF'

I try to use the symbolic capabilities of the (H-) Compiler, i.e. to compute the LRECL of an outputfile based on the length of a structure:

rl   dc   al2(rle-rl,0)
f1   dc   cl20' '
f2   dc   10xl2'00'
f3   dc   pl5'0'
rle  equ  *
    .....
Out  dcb  dsorg=ps,ddname=o,macrf=gm,lrecl=rle-rl

Maybe I should have put it in the S/390 assembler FAQ style entry...

Use a REXX exec to quickly find macros

Instead of doing individual searches on each of your various macro libraries, modify the following exec for an easy search facility:

FINDMAC IECSDSL1

Here is the findmac source.

Convert "BC" to Extended Mnemonics easier

A guy I know writes brilliant Assembler code, I don't come anywhere close. He does one thing that makes his code hard to follow for us mortals, he doesn't use Extended Mnemonics for branching. I've written an ISPF edit macro called IEFBR549 that shows the Extended Mnemonics for BC (branching) instructions. Here are some sample ISPF editor lines with the inserted info lines:


 014700          LTR   R15,R15                  SUCESSFUL?
 014800          BC    8,CHKAUTH                YES, CHECK FOR USER AUTHORITY
 ======          BZ    CHKAUTH        After Test Under Mask
 ======          BZ    CHKAUTH      * After Arithmetic Instructions
 ======          BE    CHKAUTH        After Compare Instructions
 014900          MVC   PUTLINE(L'$CON006),$CON006 COPY STAX ERROR MSG
 015000          SLR   R15,R15                  SELECT LINE PRINT ROUTINE
 015100          BAL   R14,$PRINT               PRINT ERROR MSG.
 015200          BC    15,FINISH                EXIT
 ======          B     FINISH       * General

I show all known types of branches based on the condition code. and attempt to flag the one I think is the right one but you should verify the instruction type. Please look at the disclaimers in the source code before using this ISPF edit macro.

An Assembler Programmer's view of Linux for S/390 and zSeries

[2006-01-01]

Share presentation: Session 8139 (PDF) By David Bond of Tachyon Software LLC.

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