--emit-symbol-map option

emcc

@@ -242,6 +242,14 @@ Options that are modified or new in %s include:
                            performance and otherwise might not be
                            performed in -g2.
 
+  --emit-symbol-map        Save a map file between the minified
+                           global names and the original function names.
+                           This allows you to reconstruct meaningful
+                           stack traces, for example. (This is only
+                           relevant when minifying global names, which
+                           happens in -O2 and above, and when no -g
+                           option to prevent minification was specified.)
+
   --typed-arrays <mode>    0: No typed arrays
                            1: Parallel typed arrays
                            2: Shared (C-like) typed arrays (default)
@@ -778,6 +786,7 @@ try:
   opt_level = 0
   debug_level = 0
   profiling = False
+  emit_symbol_map = False
   js_opts = None
   llvm_opts = None
   llvm_lto = None
@@ -902,6 +911,9 @@ try:
       debug_level = 2
       profiling = True
       newargs[i] = ''
+    elif newargs[i] == '--emit-symbol-map':
+      emit_symbol_map = True
+      newargs[i] = ''
     elif newargs[i] == '--bind':
       bind = True
       newargs[i] = ''
@@ -1718,7 +1730,9 @@ try:
         js_optimizer_queue += ['registerize']
 
     if opt_level >= 2:
-      if debug_level < 2 and shared.Settings.ASM_JS: js_optimizer_queue += ['minifyNames']
+      if debug_level < 2 and shared.Settings.ASM_JS:
+        js_optimizer_queue += ['minifyNames']
+        if emit_symbol_map: js_optimizer_queue += ['symbolMap='+target+'.symbols']
       if debug_level == 0: js_optimizer_queue += ['minifyWhitespace']
 
     if closure and shared.Settings.ASM_JS:

tests/test_other.py

@@ -2669,3 +2669,16 @@ int main()
       }
     ''', [3, 1, 1])
 
+  def test_symbol_map(self):
+    for m in [0, 1]:
+      self.clear()
+      cmd = [PYTHON, EMCC, path_from_root('tests', 'hello_world.c'), '-O2']
+      if m: cmd += ['--emit-symbol-map']
+      print cmd
+      stdout, stderr = Popen(cmd, stderr=PIPE).communicate()
+      assert ('''wrote symbol map file''' in stderr) == m, stderr
+      assert (os.path.exists('a.out.js.symbols') == m), stderr
+      if m:
+        symbols = open('a.out.js.symbols').read()
+        assert ':_main' in symbols
+

tools/js_optimizer.py

@@ -32,6 +32,7 @@ class Minifier:
   def __init__(self, js, js_engine):
     self.js = js
     self.js_engine = js_engine
+    self.symbols_file = None
 
   def minify_shell(self, shell, minify_whitespace, source_map=False):
     # Run through js-optimizer.js to find and minify the global symbols
@@ -61,6 +62,14 @@ class Minifier:
     #print >> sys.stderr, "minified SHELL 3333333333333333", output, "\n44444444444444444444"
     code, metadata = output.split('// EXTRA_INFO:')
     self.globs = json.loads(metadata)
+
+    if self.symbols_file:
+      mapfile = open(self.symbols_file, 'w')
+      for key, value in self.globs.iteritems():
+        mapfile.write(value + ':' + key + '\n')
+      mapfile.close()
+      print >> sys.stderr, 'wrote symbol map file to', self.symbols_file
+
     return code.replace('13371337', '0.0')
 
 
@@ -162,6 +171,12 @@ EMSCRIPTEN_FUNCS();
 
       # we assume there is a maximum of one new name per line
       minifier = Minifier(js, js_engine)
+      def check_symbol_mapping(p):
+        if p.startswith('symbolMap='):
+          minifier.symbols_file = p.split('=')[1]
+          return False
+        return True
+      passes = filter(check_symbol_mapping, passes)
       asm_shell_pre, asm_shell_post = minifier.minify_shell(asm_shell, 'minifyWhitespace' in passes, source_map).split('EMSCRIPTEN_FUNCS();');
       asm_shell_post = asm_shell_post.replace('});', '})');
       pre += asm_shell_pre + '\n' + start_funcs_marker