when not aliasing tables, keep them all at full size to avoid aliasing through the &M mask in a small table

2 files changed, 19 insertions, 5 deletions

diff --git a/src/modules.js b/src/modules.js
index 8e029b27..e4093078 100644
--- a/src/modules.js
+++ b/src/modules.js
@@ -301,6 +301,7 @@ var Functions = {
     }
     var generated = false;
     var wrapped = {};
+    var maxTable = 0;
     for (var t in tables) {
       if (t == 'pre') continue;
       generated = true;
@@ -355,13 +356,21 @@ var Functions = {
           j += 10;
         }
       }
+      maxTable = Math.max(maxTable, table.length);
+    }
+    if (ASM_JS) maxTable = ceilPowerOfTwo(maxTable);
+    for (var t in tables) {
+      if (t == 'pre') continue;
+      var table = tables[t];
       if (ASM_JS) {
         // asm function table mask must be power of two
-        var fullSize = ceilPowerOfTwo(table.length);
+        // if nonaliasing, then standardize function table size, to avoid aliasing pointers through the &M mask (in a small table using a big index)
+        var fullSize = ALIASING_FUNCTION_POINTERS ? ceilPowerOfTwo(table.length) : maxTable;
         for (var i = table.length; i < fullSize; i++) {
           table[i] = 0;
         }
       }
+      // finalize table
       var indices = table.toString().replace('"', '');
       if (BUILD_AS_SHARED_LIB) {
         // Shared libraries reuse the parent's function table.
diff --git a/tests/runner.py b/tests/runner.py
index b802a68f..1ff917d0 100755
--- a/tests/runner.py
+++ b/tests/runner.py
@@ -7729,15 +7729,20 @@ void*:16
 
       assert 'asm2g' in test_modes
       if self.run_name == 'asm2g':
-        original = open('src.cpp.o.js').read()
         results = {}
-        results[Settings.ALIASING_FUNCTION_POINTERS] = len(open('src.cpp.o.js').read())
+        original = open('src.cpp.o.js').read()
+        results[Settings.ALIASING_FUNCTION_POINTERS] = len(original)
         Settings.ALIASING_FUNCTION_POINTERS = 1 - Settings.ALIASING_FUNCTION_POINTERS
         self.do_run(path_from_root('tests', 'cubescript'), '*\nTemp is 33\n9\n5\nhello, everyone\n*', main_file='command.cpp')
-        results[Settings.ALIASING_FUNCTION_POINTERS] = len(open('src.cpp.o.js').read())
+        final = open('src.cpp.o.js').read()
+        results[Settings.ALIASING_FUNCTION_POINTERS] = len(final)
         open('original.js', 'w').write(original)
         print results
-        assert results[1] < results[0]
+        assert results[1] < 0.99*results[0]
+        assert ' & 3]()' in original, 'small function table exists'
+        assert ' & 3]()' not in final, 'small function table does not exist'
+        assert ' & 255]()' not in original, 'big function table does not exist'
+        assert ' & 255]()' in final, 'big function table exists'
 
     def test_gcc_unmangler(self):
       Settings.NAMED_GLOBALS = 1 # test coverage for this