Enable cross-compiler development

.github/workflows/riscv64-cross-ci.yml

@@ -0,0 +1,49 @@
+name: RISC-V 64bit cross-compiler CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Prepare git
+        run:
+          git config --global url."git://github.com/ghc/packages-".insteadOf     git://github.com/ghc/packages/ &&
+          git config --global url."http://github.com/ghc/packages-".insteadOf    http://github.com/ghc/packages/ &&
+          git config --global url."https://github.com/ghc/packages-".insteadOf   https://github.com/ghc/packages/ &&
+          git config --global url."ssh://[email protected]/ghc/packages-".insteadOf ssh://[email protected]/ghc/packages/ &&
+          git config --global url."[email protected]:ghc/packages-".insteadOf       [email protected]:ghc/packages/
+
+      - name: Checkout GHC
+        uses: actions/[email protected]
+        with:
+          repository: ghc/ghc
+          submodules: recursive
+
+      - name: Checkout ghc.nix
+        uses: actions/[email protected]
+        with:
+          path: ghc.nix
+
+      - name: Install nix
+        uses: cachix/install-nix-action@v20
+
+      - name: Use cachix
+        uses: cachix/cachix-action@v12
+        with:
+          name: ghc-nix
+          signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
+
+      - name: Run nix-shell - Boot and Configure
+        run: nix-shell --pure ghc.nix/shell.nix --arg withLlvm true --arg crossTarget '"riscv64"' --command "./boot && configure_ghc"
+
+      - name: Run nix-shell - cabal update
+        run: nix-shell --pure ghc.nix/shell.nix --arg withLlvm true --arg crossTarget '"riscv64"' --command "pushd hadrian; cabal update; popd"
+
+      - name: Run nix-shell - Build GHC
+        run: nix-shell --pure ghc.nix/shell.nix  --arg withLlvm true --arg crossTarget '"riscv64"' --command "hadrian/build -j --flavour=quickest"

README.md

@@ -142,6 +142,24 @@ nix develop github:alpmestan/ghc.nix#js-cross
 **Note** for the JavaScript backend, use `bignum=native` or the `native_bignum`
 transformer.
 
+## Building a cross-compiler
+
+Cross-compiling in this section means: GHC is developed/built on one
+architecture (`--build`) to run on the same architecture (`--host`) and target
+another architecture (`--target`).
+
+E.g. develop GHC on *amd64*, run it on *amd64* and let the resulting GHC produce
+binaries for *riscv64*.
+
+The `crossTarget` argument defines the target. The string must be a supported
+architecture in `nixpkgs.pkgsCross`. When `crossTarget` is defined, all required
+environment variables and `configure_ghc` parameters are setup for building a
+cross-compiler.
+
+``` sh
+nix-shell --pure ghc.nix/shell.nix --arg withLlvm true --arg crossTarget '"riscv64"'
+```
+
 ## Cachix
 
 There is a Cachix cache ([ghc-nix](https://app.cachix.org/cache/ghc-nix)) which is filled by our CI. To use it, run the following command and follow the instructions:

flake.nix

@@ -7,7 +7,7 @@
   };
 
   inputs = {
-    nixpkgs.url = "github:nixos/nixpkgs/nixos-23.05";
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-24.05";
     flake-compat = {
       url = "github:edolstra/flake-compat";
       flake = false;