7 files changed, 82 insertions, 12 deletions
diff --git a/emscripten.py b/emscripten.py
index 939ddbe8..e2aef648 100755
--- a/emscripten.py
+++ b/emscripten.py
@@ -477,7 +477,7 @@ def emscript(infile, settings, outfile, libraries=[], compiler_engine=None,
     if '_rand' in exported_implemented_functions or '_srand' in exported_implemented_functions:
       basic_vars += ['___rand_seed']
 
-    asm_runtime_funcs = ['stackAlloc', 'stackSave', 'stackRestore', 'setThrew'] + ['setTempRet%d' % i for i in range(10)]
+    asm_runtime_funcs = ['stackAlloc', 'stackSave', 'stackRestore', 'setThrew'] + ['setTempRet%d' % i for i in range(10)] + ['getTempRet%d' % i for i in range(10)]
     # function tables
     function_tables = ['dynCall_' + table for table in last_forwarded_json['Functions']['tables']]
     function_tables_impls = []
@@ -632,6 +632,10 @@ function setTempRet%d(value) {
   value = value|0;
   tempRet%d = value;
 }
+''' % (i, i) for i in range(10)]) + ''.join(['''
+function getTempRet%d() {
+  return tempRet%d|0;
+}
 ''' % (i, i) for i in range(10)])] + [PostSets.js + '\n'] + funcs_js + ['''
   %s
 
@@ -644,9 +648,11 @@ function setTempRet%d(value) {
 
     if not settings.get('SIDE_MODULE'):
       funcs_js.append('''
-Runtime.stackAlloc = function(size) { return asm['stackAlloc'](size) };
-Runtime.stackSave = function() { return asm['stackSave']() };
-Runtime.stackRestore = function(top) { asm['stackRestore'](top) };
+Runtime.stackAlloc = asm['stackAlloc'];
+Runtime.stackSave = asm['stackSave'];
+Runtime.stackRestore = asm['stackRestore'];
+Runtime.setTempRet0 = asm['setTempRet0'];
+Runtime.getTempRet0 = asm['getTempRet0'];
 ''')
 
     # Set function table masks
@@ -1058,7 +1064,7 @@ def emscript_fast(infile, settings, outfile, libraries=[], compiler_engine=None,
     if '_rand' in exported_implemented_functions or '_srand' in exported_implemented_functions:
       basic_vars += ['___rand_seed']
 
-    asm_runtime_funcs = ['stackAlloc', 'stackSave', 'stackRestore', 'setThrew'] + ['setTempRet%d' % i for i in range(10)]
+    asm_runtime_funcs = ['stackAlloc', 'stackSave', 'stackRestore', 'setThrew', 'setTempRet0', 'getTempRet0']
     # function tables
     function_tables = ['dynCall_' + table for table in last_forwarded_json['Functions']['tables']]
     function_tables_impls = []
@@ -1208,12 +1214,14 @@ function copyTempDouble(ptr) {
   HEAP8[tempDoublePtr+6>>0] = HEAP8[ptr+6>>0];
   HEAP8[tempDoublePtr+7>>0] = HEAP8[ptr+7>>0];
 }
-''' + ''.join(['''
-function setTempRet%d(value) {
+function setTempRet0(value) {
   value = value|0;
-  tempRet%d = value;
+  tempRet0 = value;
+}
+function getTempRet0() {
+  return tempRet0|0;
 }
-''' % (i, i) for i in range(10)])] + funcs_js + ['''
+'''] + funcs_js + ['''
   %s
 
   return %s;
@@ -1225,9 +1233,11 @@ function setTempRet%d(value) {
 
     if not settings.get('SIDE_MODULE'):
       funcs_js.append('''
-Runtime.stackAlloc = function(size) { return asm['stackAlloc'](size) };
-Runtime.stackSave = function() { return asm['stackSave']() };
-Runtime.stackRestore = function(top) { asm['stackRestore'](top) };
+Runtime.stackAlloc = asm['stackAlloc'];
+Runtime.stackSave = asm['stackSave'];
+Runtime.stackRestore = asm['stackRestore'];
+Runtime.setTempRet0 = asm['setTempRet0'];
+Runtime.getTempRet0 = asm['getTempRet0'];
 ''')
 
     # Set function table masks
diff --git a/src/runtime.js b/src/runtime.js
index 63610d3b..4466a308 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -96,6 +96,15 @@ function unInline(name_, params) {
 }
 
 var Runtime = {
+  // When a 64 bit long is returned from a compiled function the least significant
+  // 32 bit word is passed in the return value, but the most significant 32 bit
+  // word is placed in tempRet0. This provides an accessor for that value.
+  setTempRet0: function(value) {
+    tempRet0 = value;
+  },
+  getTempRet0: function() {
+    return tempRet0;
+  },
   stackSave: function() {
     return STACKTOP;
   },
diff --git a/tests/return64bit/test.c b/tests/return64bit/test.c
new file mode 100644
index 00000000..e75ee5c1
--- /dev/null
+++ b/tests/return64bit/test.c
@@ -0,0 +1,6 @@
+
+// This is just a trivial test function, the key bit of interest is that it returns a 64 bit long.
+long long test() {
+    long long x = ((long long)1234 << 32) + 5678;
+    return x;
+}
diff --git a/tests/return64bit/testbind.js b/tests/return64bit/testbind.js
new file mode 100644
index 00000000..f2cc0e7b
--- /dev/null
+++ b/tests/return64bit/testbind.js
@@ -0,0 +1,18 @@
+// This code represents a simple native JavaScript binding to a test C function
+// that returns a 64 bit long. Notice that the least significant 32 bits are
+// returned in the normal return value, but the most significant 32 bits are
+// returned via the accessor method Runtime.getTempRet0()
+
+var Module = {
+    'noExitRuntime' : true
+};
+
+Module['runtest'] = function() {
+    var low = _test();
+    var high = Runtime.getTempRet0();
+
+    console.log("low = " + low);
+    console.log("high = " + high);
+};
+
+
diff --git a/tests/return64bit/testbindend.js b/tests/return64bit/testbindend.js
new file mode 100644
index 00000000..2218f14d
--- /dev/null
+++ b/tests/return64bit/testbindend.js
@@ -0,0 +1,2 @@
+
+})(); // End of self calling lambda used to wrap library.
diff --git a/tests/return64bit/testbindstart.js b/tests/return64bit/testbindstart.js
new file mode 100644
index 00000000..4956806b
--- /dev/null
+++ b/tests/return64bit/testbindstart.js
@@ -0,0 +1,3 @@
+
+(function() { // Start of self-calling lambda used to avoid polluting global namespace.
+
diff --git a/tests/test_core.py b/tests/test_core.py
index fb53897a..04271192 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -6528,6 +6528,28 @@ def process(filename):
     if self.emcc_args is None: return self.skip('needs emcc')
     self.do_run_from_file(path_from_root('tests', 'test_locale.c'), path_from_root('tests', 'test_locale.out'))
 
+  def test_64bit_return_value(self):
+    # This test checks that the most significant 32 bits of a 64 bit long are correctly made available
+    # to native JavaScript applications that wish to interact with compiled code returning 64 bit longs.
+    # The MS 32 bits should be available in Runtime.getTempRet0() even when compiled with -O2 --closure 1
+    # Run with ./runner.py test_64bit_return_value
+
+    # Compile test.c and wrap it in a native JavaScript binding so we can call our compiled function from JS.
+    Popen([PYTHON, EMCC, path_from_root('tests', 'return64bit', 'test.c'), '--pre-js', path_from_root('tests', 'return64bit', 'testbindstart.js'), '--pre-js', path_from_root('tests', 'return64bit', 'testbind.js'), '--post-js', path_from_root('tests', 'return64bit', 'testbindend.js'), '-s', 'EXPORTED_FUNCTIONS=["_test"]', '-o', 'test.js', '-O2', '--closure', '1'], stdout=PIPE, stderr=PIPE).communicate()
+
+    # Simple test program to load the test.js binding library and call the binding to the
+    # C function returning the 64 bit long.
+    open(os.path.join(self.get_dir(), 'testrun.js'), 'w').write('''
+      var test = require("./test.js");
+      test.runtest();
+    ''')
+
+    # Run the test and confirm the output is as expected.
+    if NODE_JS in JS_ENGINES:
+      out = run_js('testrun.js', engine=NODE_JS, full_output=True)
+      assert "low = 5678" in out
+      assert "high = 1234" in out
+
 # Generate tests for everything
 def make_run(fullname, name=-1, compiler=-1, embetter=0, quantum_size=0,
     typed_arrays=0, emcc_args=None, env=None):