Preliminary review for new WINENV support

[Magnus Ihse Bursie]

On 2020-08-24 19:21, Ludovic Henry wrote:
> Hi Magnus,
>
> I want to follow up on this work of yours, as we've particular interest in it for the Windows-AArch64 port.
>
> Let me know how I could assist you in this effort.
The big blockers for this fix is basically these two issues:

>> I have also temporarily disabled the javac server, and building without absolute paths. I believe a better way forward is to address these with improved functionality in separate patches, instead of trying to work around the issues introduced by them in this patch.
Until that is fixed, any integration of this patch is a no-go.

I have been working on those, but a lot of other stuff has kept me from 
gaining much progress; everything from long vacations to preparations to 
the switch to github. Unfortunately, I don't think there's an easy way 
for you to help on those two blockers.

However, there are two more things that I'd like to look into, if 
possible, before integrating my patch, and there you might be able to help.

One is performance. I got a somewhat different performance profile with 
my patch than without -- some things were faster, and some were slower. 
I'd like to understand why some things got slower, and if it is possible 
to do anything about. (Why things got faster I don't care about, I'm 
just happy :))

So maybe you can help me with some performance analysis? With the 
limited availability of tooling for makefiles, this is not really 
trivial. What I usually do is I run with JOBS=1 (to be able to track 
each task individually without effects of concurrency), and 
LOG=info,profile. This will give you time stamps for each individual 
execution in build.log.  And see if there is any interesting differences 
with and without the patch.

The other thing is that WSL2 works awfully bad. :( Maybe there's nothing 
to be done about it, if the thing being shipped is just too buggy, but 
maybe we do things incorrectly, or that unnecessarily triggers bugs. Or 
maybe there are workarounds we could use. But I think it could be worth 
some more effort to try to get it working. Maybe you can help with this?

/Magnus