Paging? The conventional wisdom has always been to stay within one base register, so for systems with 4K pages that isn't an issue. I tend to use LOCTR so that constants aren't always at the end of the source code. I normally put labels on the same line as the instructions and inserting code has never been a problem. I will admit to using self-modifying code when I was a callow youth, but I stopped doing that and started making any new code reentrant and refreshable sometime around the end of the 1960s.
-- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Assembler List [ASSEMBLER-LIST@LISTSERV.UGA.EDU] on behalf of MELVYN MALTZ [0000072265160664-dmarc-requ...@listserv.uga.edu] Sent: Tuesday, June 2, 2020 4:01 PM To: ASSEMBLER-LIST@LISTSERV.UGA.EDU Subject: Re: z/OS HLASM: EQU for statement labels Hi Guys, I thought I would put my 2 cents worth in I know that 55 years of Assembler coding doesn't count for much these days :-) Labels... Even back in the 60's I was taught never to put a label on an instruction I only break that rule now for the subject of an EX (and its variants) In the old days of real storage I used to code label EQU * and this was fine Then paging came along and the recommendation was to keep in-line data close to the instructions using it (locality of reference). As people have mentioned this sometimes resulted in odd addresses and S0C1 abends (before unalignment was detected) So I switched to label DS 0H in coding Have to state the obvious...DS 0H might not be appropriate for some data as there are now many instructions that rely on specific alignments I consider... DS 0H label EQU * to be overkill and I would deduct 2 points With changes in architecture, we now move in-line data to avoid cache problems And did you know that this code...popular in ancient times is a performance disaster now ONETIME NOP THERE MVI ONETIME+1,X'F0' Returning CC from a subroutine... Have to point out that IBM do this in the VSAM TESTCB macro Melvyn Maltz. ----- Original Message ----- From: "David Woolbright" <woolbright_da...@columbusstate.edu> To: <ASSEMBLER-LIST@LISTSERV.UGA.EDU> Sent: Tuesday, June 02, 2020 5:58 PM Subject: Re: z/OS HLASM: EQU for statement labels I’’m just a humble academic so I hesitate to weigh in. I trained assembler programmers for one large credit card processing company for many years and their standard was to use EQU * as the target of all branches, mainly so new lines could be added easily. I’ve never had an odd address created accidentally using this technique, but it’s also the case that the assembler will warn you in cases where you do have an unfavorable address. I’m in the process of revising many years of teaching material into book format, so your opinions on this matter to me. Using EQU for targets would seem to be a stylistic point on which reasonable people could disagree, but perhaps I’m wrong. > On Jun 2, 2020, at 11:49 AM, Seymour J Metz <sme...@gmu.edu> wrote: > >> Is this useful? > > Only if you're a sadist. > > > -- > Shmuel (Seymour J.) Metz > http://mason.gmu.edu/~smetz3 > > ________________________________________ > From: IBM Mainframe Assembler List [ASSEMBLER-LIST@LISTSERV.UGA.EDU] on > behalf of Paul Gilmartin [00000014e0e4a59b-dmarc-requ...@listserv.uga.edu] > Sent: Tuesday, June 2, 2020 11:40 AM > To: ASSEMBLER-LIST@LISTSERV.UGA.EDU > Subject: Re: z/OS HLASM: EQU for statement labels > > On 2020-06-02, at 09:33:48, Charles Mills wrote: >> >> I don't claim any benefit to the technique, it's just my habit. Actually >> I think the cleanest is a DS 0H followed by label EQU *. That clearly >> shows what is going on: re-establishing halfword alignment followed by >> mapping a label to an address. >> > I found it ironic that: > LABEL CNOP ... > assigns the address of the beginning of the padding rather > than the end to LABEL. Is this useful? > > Fortunately, > LABEL DS 0H > does the opposite so your 2-instruction construct is otiose. > > -- gil
