Cross-compiling Template Haskell via -fexternal-interpreter and IPC

[Ben Gamari]

Explicitly CCing Simon Marlow to ensure he sees this.


Alberto Valverde <alberto at toscat.net> writes:

> Hello,
>
> I'm trying to put together a GHC 8.0.1 cross-compiler with Template Haskell
> support. Initially to target Windows (32bits) from a Linux host but a
> similar procedure should enable to target other platforms too. I'd like to
> contribute the patches back so I'm asking for advice on how to implement it
> in order to increase the chances of them being accepted.
>
> I've managed to get a working stage 1 cross-compiler with some patches
> which correctly builds all stage1 libs and GHC + stage 2 compiler and
> ghc-iserv.exe. However, compiling TH by using wine and ghc-iserver.exe
> fails because the file descriptor ids that GHC passes as arguments to "wine
> ghc-iserv.exe" don't make sense in the emulated windows world.
>
Ahh, right. Out of curiosity what toolchain are you using to build your
stage 1 cross compiler?

> I've hacked around this to test the feasibility of the approach by using
> stdin/stdout instead of creating new pipes and, surprisingly, managed to
> cross-compile a simple Template Haskell program.
>
Well done!

> I'm considering using a socket for communicating between both processes as
> a more permanent solution but this would incur in a dependency on the
> "network" package. Would this be acceptable?
>
It would be nice if we could avoid it; GHC depending upon a library has
the very unfortunate effect that any user code also needing to link
against GHC or one of its libraries now has no choice in the version of
that library. We go to some lengths to try to keep the dependency
footprint of GHC small for this reason.

> Named pipes have also crossed my mind but I'm not sure how well they're
> supported by wine.
>
It would be great if there were some way we could make this work with
named pipes. Not only does it side-step the dependency issue, but it
feels like the right way forward.

Cheers,

- Ben
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