Add a 32 bit system to the CI

[perturbing]

Currently our CI only builds on 64-bit systems. We should also run CI on 32-bit targets to catch hidden assumptions. See this comment for context.

[perturbing]

@angerman

In cardano-base we have Cardano.Crypto.PackedBytes, which uses CPP to select different implementations depending on WORD_SIZE_IN_BITS (64 vs 32). Right now our CI only exercises the 64-bit branch, so any 32-bit-specific issues/assumptions could slip through.

Would it be feasible to add a 32-bit job on Hydra by cross-compiling (e.g., to a musl32 target) using haskell.nix?

[angerman]

Yes. @hamishmack should be able to add a 32bit cross target.

[hamishmack]

I tried to get musl32 to build by adding:

             #   inherit compiler-nix-name;
             # });
             # we also want cross compilation to windows.
-            crossPlatforms = p: lib.optional (system == "x86_64-linux") p.ucrt64;
+            crossPlatforms = p: lib.optionals (system == "x86_64-linux") [p.ucrt64 p.musl32];
           };

           # package customizations as needed. Where cabal.project is not

This works for getting the cardano-base library to build, but the tests fail to build as they need th-orphans

With GHC 9.6.7 and 9.8.4 it fails with unknown symbol '_GLOBAL_OFFSET_TABLE_':

$ nix build '.#hydraJobs.x86_64-linux.armv7a-unknown-linux-androideabi.checks.cardano-base:test:tests'
...
[2 of 2] Compiling Language.Haskell.TH.Instances ( src/Language/Haskell/TH/Instances.hs, dist/build/Language/Haskell/TH/Instances.o )
---> Starting iserv-proxy-interpreter on port 8389
---| iserv-proxy-interpreter should have started on 8389
Listening on port 8389
iserv-proxy-interpreter: tmp/nix/store/l6nczjqpqka499gf6bhai05s2w779swb-i686-unknown-linux-musl-ghc-9.8.4/lib/i386-linux-ghc-9.8.4/ghc-prim-0.11.0-inplace/HSghc-prim-0.11.0-inplace.o: unknown symbol `_GLOBAL_OFFSET_TABLE_'
iserv-proxy-interpreter: Could not load Object Code tmp/nix/store/l6nczjqpqka499gf6bhai05s2w779swb-i686-unknown-linux-musl-ghc-9.8.4/lib/i386-linux-ghc-9.8.4/ghc-prim-0.11.0-inplace/HSghc-prim-0.11.0-inplace.o.


<no location info>: error: unable to load unit `ghc-prim-0.11.0'
---> killing iserv-proxy-interpreter...

On GHC 9.10.3 and 9.12.2 it fails with unhandled ELF relocation(Rel) type 10 errors:

$ nix build '.#hydraJobs.x86_64-linux.armv7a-unknown-linux-androideabi.checks.cardano-base:test:tests'
...
[2 of 2] Compiling Language.Haskell.TH.Instances ( src/Language/Haskell/TH/Instances.hs, dist/build/Language/Haskell/TH/Instances.o )
---> Starting iserv-proxy-interpreter on port 5765
---| iserv-proxy-interpreter should have started on 5765
Listening on port 5765
iserv-proxy-interpreter: tmp/nix/store/kh94p53vsiabm4mc580gghggy354vjsy-i686-unknown-linux-musl-ghc-9.12.2/lib/i386-linux-ghc-9.12.2-inplace/ghc-prim-0.13.0-inplace/HSghc-prim-0.13.0-inplace.o: unhandled ELF relocation(Rel) type 10

iserv-proxy-interpreter: Could not load Object Code tmp/nix/store/kh94p53vsiabm4mc580gghggy354vjsy-i686-unknown-linux-musl-ghc-9.12.2/lib/i386-linux-ghc-9.12.2-inplace/ghc-prim-0.13.0-inplace/HSghc-prim-0.13.0-inplace.o.

<no location info>: error: unable to load unit `ghc-prim-0.13.0'

Fixing that will probably be difficult. I'm trying p.armv7a-android-prebuilt instead of p.musl32.