[Info-vax] Editors, was: Re: VT keyboard replacement

[Robert A. Brooks]

On 11/21/2021 10:19 PM, Michael Moroney wrote:
> On 11/21/2021 4:32 AM, alanfe... at gmail.com wrote:
> 
>> BTW, why did it take so long for someone to fix the hard-coded 22-line
>> limit on EDT? How long could it have taken? Well, I'm very happy about it
>> now!
> 
> That "someone" is myself.  As to why did it "take so long", EDT was
> considered obsolete for decades. Nobody was actively maintaining it. I just
> recently posted some comments about fixing it. It was an unofficial fix, I
> just did it one day. But EDT fans may be happy to know that EDT was the first
> editor to run on x86. I forget why EVE/TPU took longer, it may have been a
> compiler bug that affected it but not EDT. A different problem prevented EDT
> from working out of the box however.

Both editors were affected by the change on X86 where code is placed in 64-bit 
space by default.  This default can be overriden with the LINK qualifier
/SEGMENT_ATTRIBUTE=CODE=P0.

The problem was that in both editors (and other areas of the operating system 
and layered products), certain data PSECTS were marked as EXECUTABLE.  This 
worked on VAX, Alpha, and IA64, and was likely a VAX-era optimization to keep 
certain data co-located with the relevant code.  This does not work on X86; 
Reagan can give the details.

Both editors are written in BLISS, and early BLISS compilers (or perhaps the
GEM-to-LLVM converter) did not deal with the GLOBAL BIND syntax correctly.

I drew the short straw for both editors and had the pleasure of of tracking down 
where in the code was failing, coming up with stripped-down reproducers, and 
bringing my findings to Reagan so he could puzzle it out.

-- 
                  -- Rob