bug#74805: 30.0.92; Trying to build scratch/igc on Cygwin

[Ken Brown <kbrown@cornell.edu>]

On 12/12/2024 1:09 AM, Eli Zaretskii wrote:
>> Date: Wed, 11 Dec 2024 17:50:40 -0500
>> From: Ken Brown <kbrown@cornell.edu>
>>
>> I've made a first attempt to port mps to Cygwin.  If anyone else is
>> interested in seeing this or helping, you can find my work at
>>
>>     https://github.com/kbrow1i/mps-cygwin
>>
>> This is a fork of the mps git repo with two commits on top.
> 
> Thanks, good news!  Could you please post the patches here, so that
> they are recorded in our bug tracker?
> 
>> With the current attempt, I can build the scratch/igc branch, but there
>> are many test failures.  For example, when I run the process-tests, I
>> get 19 failures and 8 skipped tests.  But on the master branch I get no
>> failures and only 3 skipped.
>>
>> This probably means that my current attempt to port mps is no good, and
>> I have to go back to the drawing board.
> 
> Did you run the MPS test suite, and if you did, were there any
> failures?  My suggestion is to make sure the MPS test suite passes
> cleanly, including in several consecutive runs (when I ported MPS to
> 32-bit MinGW, I had intermittent failures which only happened once in
> several runs, until I fixed that).

This is an update on my attempts to port the MPS to Cygwin and build the 
scratch/igc branch.  The GitHub repo that I cited above now consists of 
4 branches:

1. The "master" branch is an MPS fork with README.Cygwin added.  This 
file explains in detail what I'm summarizing here.

2. The "w3" branch attempts to use the Windows interface on Cygwin.  For 
example, it uses direct calls to VirtualAlloc instead of Cygwin's mmap. 
This attempt fails because it's not compatible with Cygwin's fork.

3. The "mmap" branch is a straightforward port, mostly imitating the 
FreeBSD port.  It currently (with Cygwin 3.5.5) fails because of a 
limitation of Cygwin's mmap.  But I have a simple patch to Cygwin in the 
works that removes that limitation.  With that patch, 37 of the 38 MPS 
tests pass.  I still need to debug the failing test.  I'm cautiously 
optimistic that I can get this approach to work.  Either way, I expect 
the Cygwin patch to soon be available in a test release of Cygwin 3.6.0 
so that other Cygwin users can try it.

4. The "generic" branch uses generic implementations of some of the MPS 
features.  For example, it uses malloc instead of mmap.  This passes all 
of the MPS tests, and Emacs seems to work well so far in limited 
testing.  I suspect that there may be some performance problems, but I 
haven't seen them yet.

Once I've determined whether or not the mmap approach will work, I'll 
post the MPS patches here either for the mmap branch or the generic branch.

Ken