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diff --git a/nixpkgs/doc/languages-frameworks/emscripten.section.md b/nixpkgs/doc/languages-frameworks/emscripten.section.md new file mode 100644 index 000000000000..20d358f2e9e3 --- /dev/null +++ b/nixpkgs/doc/languages-frameworks/emscripten.section.md @@ -0,0 +1,167 @@ +# Emscripten {#emscripten} + +[Emscripten](https://github.com/kripken/emscripten): An LLVM-to-JavaScript Compiler + +If you want to work with `emcc`, `emconfigure` and `emmake` as you are used to from Ubuntu and similar distributions, + +```console +nix-shell -p emscripten +``` + +A few things to note: + +* `export EMCC_DEBUG=2` is nice for debugging +* The build artifact cache in `~/.emscripten` sometimes creates issues and needs to be removed from time to time + +## Examples {#declarative-usage} + +Let's see two different examples from `pkgs/top-level/emscripten-packages.nix`: + +* `pkgs.zlib.override` +* `pkgs.buildEmscriptenPackage` + +A special requirement of the `pkgs.buildEmscriptenPackage` is the `doCheck = true`. +This means each Emscripten package requires that a [`checkPhase`](#ssec-check-phase) is implemented. + +* Use `export EMCC_DEBUG=2` from within a phase to get more detailed debug output what is going wrong. +* The cache at `~/.emscripten` requires to set `HOME=$TMPDIR` in individual phases. + This makes compilation slower but also more deterministic. + +::: {.example #usage-1-pkgs.zlib.override} + +# Using `pkgs.zlib.override {}` + +This example uses `zlib` from Nixpkgs, but instead of compiling **C** to **ELF** it compiles **C** to **JavaScript** since we were using `pkgs.zlib.override` and changed `stdenv` to `pkgs.emscriptenStdenv`. + +A few adaptions and hacks were put in place to make it work. +One advantage is that when `pkgs.zlib` is updated, it will automatically update this package as well. + + +```nix +(pkgs.zlib.override { + stdenv = pkgs.emscriptenStdenv; +}).overrideAttrs +(old: rec { + buildInputs = old.buildInputs ++ [ pkg-config ]; + # we need to reset this setting! + env = (old.env or { }) // { NIX_CFLAGS_COMPILE = ""; }; + configurePhase = '' + # FIXME: Some tests require writing at $HOME + HOME=$TMPDIR + runHook preConfigure + + #export EMCC_DEBUG=2 + emconfigure ./configure --prefix=$out --shared + + runHook postConfigure + ''; + dontStrip = true; + outputs = [ "out" ]; + buildPhase = '' + emmake make + ''; + installPhase = '' + emmake make install + ''; + checkPhase = '' + echo "================= testing zlib using node =================" + + echo "Compiling a custom test" + set -x + emcc -O2 -s EMULATE_FUNCTION_POINTER_CASTS=1 test/example.c -DZ_SOLO \ + libz.so.${old.version} -I . -o example.js + + echo "Using node to execute the test" + ${pkgs.nodejs}/bin/node ./example.js + + set +x + if [ $? -ne 0 ]; then + echo "test failed for some reason" + exit 1; + else + echo "it seems to work! very good." + fi + echo "================= /testing zlib using node =================" + ''; + + postPatch = pkgs.lib.optionalString pkgs.stdenv.isDarwin '' + substituteInPlace configure \ + --replace '/usr/bin/libtool' 'ar' \ + --replace 'AR="libtool"' 'AR="ar"' \ + --replace 'ARFLAGS="-o"' 'ARFLAGS="-r"' + ''; +}) +``` + +:::{.example #usage-2-pkgs.buildemscriptenpackage} + +# Using `pkgs.buildEmscriptenPackage {}` + +This `xmlmirror` example features an Emscripten package that is defined completely from this context and no `pkgs.zlib.override` is used. + +```nix +pkgs.buildEmscriptenPackage rec { + name = "xmlmirror"; + + buildInputs = [ pkg-config autoconf automake libtool gnumake libxml2 nodejs openjdk json_c ]; + nativeBuildInputs = [ pkg-config zlib ]; + + src = pkgs.fetchgit { + url = "https://gitlab.com/odfplugfest/xmlmirror.git"; + rev = "4fd7e86f7c9526b8f4c1733e5c8b45175860a8fd"; + hash = "sha256-i+QgY+5PYVg5pwhzcDnkfXAznBg3e8sWH2jZtixuWsk="; + }; + + configurePhase = '' + rm -f fastXmlLint.js* + # a fix for ERROR:root:For asm.js, TOTAL_MEMORY must be a multiple of 16MB, was 234217728 + # https://gitlab.com/odfplugfest/xmlmirror/issues/8 + sed -e "s/TOTAL_MEMORY=234217728/TOTAL_MEMORY=268435456/g" -i Makefile.emEnv + # https://github.com/kripken/emscripten/issues/6344 + # https://gitlab.com/odfplugfest/xmlmirror/issues/9 + sed -e "s/\$(JSONC_LDFLAGS) \$(ZLIB_LDFLAGS) \$(LIBXML20_LDFLAGS)/\$(JSONC_LDFLAGS) \$(LIBXML20_LDFLAGS) \$(ZLIB_LDFLAGS) /g" -i Makefile.emEnv + # https://gitlab.com/odfplugfest/xmlmirror/issues/11 + sed -e "s/-o fastXmlLint.js/-s EXTRA_EXPORTED_RUNTIME_METHODS='[\"ccall\", \"cwrap\"]' -o fastXmlLint.js/g" -i Makefile.emEnv + ''; + + buildPhase = '' + HOME=$TMPDIR + make -f Makefile.emEnv + ''; + + outputs = [ "out" "doc" ]; + + installPhase = '' + mkdir -p $out/share + mkdir -p $doc/share/${name} + + cp Demo* $out/share + cp -R codemirror-5.12 $out/share + cp fastXmlLint.js* $out/share + cp *.xsd $out/share + cp *.js $out/share + cp *.xhtml $out/share + cp *.html $out/share + cp *.json $out/share + cp *.rng $out/share + cp README.md $doc/share/${name} + ''; + checkPhase = '' + + ''; +} +``` + +::: + +## Debugging {#declarative-debugging} + +Use `nix-shell -I nixpkgs=/some/dir/nixpkgs -A emscriptenPackages.libz` and from there you can go trough the individual steps. This makes it easy to build a good `unit test` or list the files of the project. + +1. `nix-shell -I nixpkgs=/some/dir/nixpkgs -A emscriptenPackages.libz` +2. `cd /tmp/` +3. `unpackPhase` +4. cd libz-1.2.3 +5. `configurePhase` +6. `buildPhase` +7. ... happy hacking... |