support emcc --separate-asm output

3 files changed, 27 insertions, 8 deletions

diff --git a/README.md b/README.md
index 2c2914b89..25c401fad 100644
--- a/README.md
+++ b/README.md
@@ -32,12 +32,18 @@ Set `ASM2WASM_DEBUG=1` in the env to see debug info, about asm.js nodes as they
 
 ## Starting from C/C++ Source
 
-[Grab Emscripten](http://kripken.github.io/emscripten-site/docs/getting_started/downloads.html), and build
+[Grab Emscripten](http://kripken.github.io/emscripten-site/docs/getting_started/downloads.html), and build the source file into asm.js, for example using
 
-Limitations:
+```
+emcc src.cpp -o a.html --separate-asm
+```
+
+That will emit `a.html`, `a.js`, and `a.asm.js`. That last file is the asm.js module, which you can pass into `asm2wasm`.
+
+## TODO
 
  * WebAssembly lacks global variables, so `asm2wasm` maps them onto addresses in memory. This requires that you have some reserved space for those variables. You can do that with `emcc -s GLOBAL_BASE=1000`. We still need to write the code to copy the globals there.
- * Emscripten emits asm.js and JavaScript, that work together using web APIs to do things like print, render, etc. Not sure if there is a way to test that full output yet.
+ * Emscripten emits asm.js and JavaScript, that work together using web APIs to do things like print, render, etc. Need to figure out how to test that.
 
 ## Testing
 
@@ -49,5 +55,7 @@ Limitations:
 
 ## License & Contributing
 
-Same as Emscripten: MIT license. This code is sync'ed with Emscripten's repo.
+Same as Emscripten: MIT license.
+
+For changes to `src/`, please make pulls into emscripten's `asm2wasm` branch (this code is sync'ed with there, for convenience).
 
diff --git a/src/asm2wasm.cpp b/src/asm2wasm.cpp
index f46d86c13..bdba9dac0 100644
--- a/src/asm2wasm.cpp
+++ b/src/asm2wasm.cpp
@@ -980,13 +980,24 @@ int main(int argc, char **argv) {
   fclose(f);
   input[num] = 0;
 
-  /*
-  // Separate asm modules look like
+  // emcc --separate-asm modules look like
   //
   //    Module["asm"] = (function(global, env, buffer) {
+  //      ..
+  //    });
   //
-  // , we can remove the part until the function.
-  */
+  // we need to clean that up.
+  if (*input == 'M') {
+    while (*input != 'f') {
+      input++;
+      num--;
+    }
+    char *end = input + num - 1;
+    while (*end != '}') {
+      *end = 0;
+      end--;
+    }
+  }
 
   if (debug) std::cerr << "parsing...\n";
   cashew::Parser<Ref, ValueBuilder> builder;
diff --git a/test/hello_world.wasm b/test/hello_world.wast
index 66dd61c42..66dd61c42 100644
--- a/test/hello_world.wasm
+++ b/test/hello_world.wast