WebAssembly: node polyfill code and build script

Author: yurydelendik

Makefile

@@ -27,6 +27,14 @@ else
 endif
 CAT ?= $(if $(filter $(OS),Windows_NT),type,cat)
 
+ifdef WASM
+  CFLAGS   += -D_WASM
+  CXXFLAGS += -D_WASM
+endif
+
+ifdef WASM
+	UNAME := WebAssembly
+else
 ifneq (,$(findstring /cygdrive/,$(PATH)))
 	UNAME := Cygwin
 else
@@ -44,6 +52,7 @@ endif
 endif
 endif
 endif
+endif
 
 ifndef LIBSASS_VERSION
 	ifneq ($(wildcard ./.git/ ),)
@@ -161,18 +170,28 @@ ifeq (Windows,$(UNAME))
 		LIB_SHARED  = $(SASS_LIBSASS_PATH)/lib/libsass.dll
 	endif
 else
+ifdef WASM
+	SASSC_BIN = $(SASS_SASSC_PATH)/bin/sassc.wasm
+	SHAREDLIB  = lib/libsass.wasm
+	LIB_SHARED  = $(SASS_LIBSASS_PATH)/lib/libsass.wasm
+else
 ifneq (Cygwin,$(UNAME))
 	CFLAGS   += -fPIC
 	CXXFLAGS += -fPIC
 	LDFLAGS  += -fPIC
 endif
 endif
+endif
 
 include Makefile.conf
 OBJECTS = $(addprefix src/,$(SOURCES:.cpp=.o))
 COBJECTS = $(addprefix src/,$(CSOURCES:.c=.o))
 RCOBJECTS = $(RESOURCES:.rc=.o)
 
+ifdef WASM
+WASMOBJECTS = wasm/libcxxabi_stubs.o
+endif
+
 DEBUG_LVL ?= NONE
 
 CLEANUPS ?=
@@ -198,15 +217,18 @@ debug-shared: shared
 lib:
 	$(MKDIR) lib
 
-lib/libsass.a: $(COBJECTS) $(OBJECTS) | lib
-	$(AR) rcvs $@ $(COBJECTS) $(OBJECTS)
+lib/libsass.a: $(COBJECTS) $(OBJECTS) $(WASMOBJECTS) | lib
+	$(AR) rcvs $@ $(COBJECTS) $(OBJECTS) $(WASMOBJECTS)
 
 lib/libsass.so: $(COBJECTS) $(OBJECTS) | lib
 	$(CXX) -shared $(LDFLAGS) -o $@ $(COBJECTS) $(OBJECTS) $(LDLIBS)
 
 lib/libsass.dll: $(COBJECTS) $(OBJECTS) $(RCOBJECTS) | lib
 	$(CXX) -shared $(LDFLAGS) -o $@ $(COBJECTS) $(OBJECTS) $(RCOBJECTS) $(LDLIBS) -s -Wl,--subsystem,windows,--out-implib,lib/libsass.a
 
+lib/libsass.wasm: $(COBJECTS) $(OBJECTS) $(WASMOBJECTS) | lib
+	$(CXX) $(LDFLAGS) -o $@ $(COBJECTS) $(OBJECTS) $(WASMOBJECTS) $(LDLIBS)
+
 %.o: %.c
 	$(CC) $(CFLAGS) -c -o $@ $<
 
@@ -269,7 +291,9 @@ $(SASSC_BIN): $(BUILD)
 	$(MAKE) -C $(SASS_SASSC_PATH) build-$(BUILD)-dev
 
 sassc: $(SASSC_BIN)
+ifndef WASM
 	$(SASSC_BIN) -v
+endif
 
 version: $(SASSC_BIN)
 	$(SASSC_BIN) -v
@@ -286,7 +310,7 @@ test_probe: $(SASSC_BIN)
 	$(RUBY_BIN) $(SASS_SPEC_PATH)/sass-spec.rb -c $(SASSC_BIN) --impl libsass --probe-todo $(LOG_FLAGS) $(SASS_SPEC_PATH)/$(SASS_SPEC_SPEC_DIR)
 
 clean-objects: | lib
-	-$(RM) lib/*.a lib/*.so lib/*.dll lib/*.la
+	-$(RM) lib/*.a lib/*.so lib/*.dll lib/*.la lib/*.wasm
 	-$(RMDIR) lib
 clean: clean-objects
 	$(RM) $(CLEANUPS)

src/file.cpp

@@ -58,6 +58,9 @@ namespace Sass {
     std::string get_cwd()
     {
       const size_t wd_len = 4096;
+      #ifdef _WASM
+        std::string cwd = "/";
+      #else
       #ifndef _WIN32
         char wd[wd_len];
         char* pwd = getcwd(wd, wd_len);
@@ -73,6 +76,7 @@ namespace Sass {
         //convert backslashes to forward slashes
         replace(cwd.begin(), cwd.end(), '\\', '/');
       #endif
+      #endif
       if (cwd[cwd.length() - 1] != '/') cwd += '/';
       return cwd;
     }

src/plugins.cpp

@@ -13,8 +13,10 @@
 #include <sys/types.h>
 #include <dirent.h>
 #include <errno.h>
+#ifndef _WASM
 #include <dlfcn.h>
 #endif
+#endif
 
 namespace Sass {
 
@@ -62,6 +64,7 @@ namespace Sass {
     typedef Sass_Function_List (*__plugin_load_fns__)(void);
     typedef Sass_Importer_List (*__plugin_load_imps__)(void);
 
+#ifndef _WASM
     if (LOAD_LIB(plugin, path))
     {
       // try to load initial function to query libsass version suppor
@@ -107,6 +110,9 @@ namespace Sass {
       std::cerr << "failed loading plugin <" << path << ">" << std::endl;
       if (const char* dlopen_error = dlerror()) std::cerr << dlopen_error << std::endl;
     }
+#else
+    std::cerr << "loading plugin unsupported <" << path << ">" << std::endl;
+#endif
 
     return false;
 

wasm/.gitignore

@@ -0,0 +1,3 @@
+*.sass
+*.css
+*.css.map

wasm/Makefile

@@ -0,0 +1,18 @@
+WASI_SDK ?= ~/bin/wasi-sdk
+MAKE_OPTS = \
+	CC=$(WASI_SDK)/bin/clang \
+	CXX=$(WASI_SDK)/bin/clang++ \
+	AR=$(WASI_SDK)/bin/llvm-ar \
+	WASM=1
+WABT ?= ~/Work/wabt
+
+build:
+	$(MAKE) -C .. $(MAKE_OPTS) sassc
+
+clean:
+	$(MAKE) -C .. $(MAKE_OPTS) clean-all
+
+wasi_polyfill.wasm: wasi_polyfill.wat
+	$(WABT)/bin/wat2wasm wasi_polyfill.wat -o wasi_polyfill.wasm
+
+.PHONY: build clean

wasm/README.md

@@ -0,0 +1,22 @@
+# Building
+
+To build `../sassc/bin/sassc.wasm`:
+
+* Clone https://github.com/yurydelendik/sassc into parent (libsass) folder
+* Run `make`
+
+To rebuild `wasi_polyfill.wasm`: `make wasi_polyfill.wasm`
+
+# Running
+
+Examples:
+
+```
+node run.js -v
+node run.js $PWD/test.sass
+node run.js $PWD/test.sass $PWD/test.css
+```
+
+Note: Use full path for the file names and only in the current dir (hence `$PWD/` prefix).
+
+

wasm/libcxxabi_stubs.c

@@ -0,0 +1,25 @@
+#include <stdlib.h> 
+
+// -fno-exceptions is not an option with libsass yet,
+// stubbing libc++abi functions
+
+void __cxa_throw(void *thrown_exception, void *tinfo,
+                 void (*dest)(void *))
+{
+    abort();
+}
+
+void *__cxa_allocate_exception(size_t thrown_size)
+{
+    abort();
+}
+
+void __cxa_rethrow()
+{
+    abort();
+}
+
+void* __cxa_begin_catch(void* exceptionObject)
+{
+    abort();
+}

wasm/run.js

@@ -0,0 +1,25 @@
+const wp = require('./wasi_polyfill.js');
+const fs = require('fs');
+
+async function init() {
+  const host = new wp.createWasiHost();
+  const { instance: wrapper } = await WebAssembly.instantiate(
+    fs.readFileSync("wasi_polyfill.wasm"),
+    {"wasi_polyfill": host}
+  );
+  const { instance: sassc } = await WebAssembly.instantiate(
+    fs.readFileSync("../sassc/bin/sassc.wasm"),
+    {"wasi_unstable": wrapper.exports}
+  );
+  host.args = ["../sassc/bin/sassc.wasm", ...process.argv.slice(2)];
+  host.memory = sassc.exports.memory;
+  return sassc.exports;
+}
+
+init().then(sassc => {
+  try {
+    sassc._start();
+  } catch (e) {
+    if (e.message != "proc_exit") throw e;
+  }
+}, console.error);