make function pointer aliasing configurable

4 files changed, 16 insertions, 11 deletions

diff --git a/emscripten.py b/emscripten.py
index a6ff7390..2b62c93a 100755
--- a/emscripten.py
+++ b/emscripten.py
@@ -329,8 +329,9 @@ def emscript(infile, settings, outfile, libraries=[], compiler_engine=None,
 
   # calculations on merged forwarded data
   forwarded_json['Functions']['indexedFunctions'] = {}
-  i = 2 # universal counter
-  if settings['ASM_JS']: i += 2*settings['RESERVED_FUNCTION_POINTERS']
+  i = settings['FUNCTION_POINTER_ALIGNMENT'] # universal counter
+  if settings['ASM_JS']: i += settings['RESERVED_FUNCTION_POINTERS']*settings['FUNCTION_POINTER_ALIGNMENT']
+  base_fp = i
   table_counters = {} # table-specific counters
   alias = settings['ASM_JS'] and settings['ALIASING_FUNCTION_POINTERS']
   sig = None
@@ -339,12 +340,12 @@ def emscript(infile, settings, outfile, libraries=[], compiler_engine=None,
       sig = forwarded_json['Functions']['implementedFunctions'].get(indexed) or forwarded_json['Functions']['unimplementedFunctions'].get(indexed)
       assert sig, indexed
       if sig not in table_counters:
-        table_counters[sig] = 2 + 2*settings['RESERVED_FUNCTION_POINTERS']
+        table_counters[sig] = base_fp
       curr = table_counters[sig]
-      table_counters[sig] += 2
+      table_counters[sig] += settings['FUNCTION_POINTER_ALIGNMENT']
     else:
       curr = i
-      i += 2
+      i += settings['FUNCTION_POINTER_ALIGNMENT']
     #logging.debug('function indexing', indexed, curr, sig)
     forwarded_json['Functions']['indexedFunctions'][indexed] = curr # make sure not to modify this python object later - we use it in indexize
 
@@ -426,7 +427,7 @@ def emscript(infile, settings, outfile, libraries=[], compiler_engine=None,
       end = raw.rindex(']')
       body = raw[start+1:end].split(',')
       for j in range(settings['RESERVED_FUNCTION_POINTERS']):
-        body[2 + 2*j] = 'jsCall_%s_%s' % (sig, j)
+        body[settings['FUNCTION_POINTER_ALIGNMENT'] * (1 + j)] = 'jsCall_%s_%s' % (sig, j)
       Counter.j = 0
       def fix_item(item):
         Counter.j += 1
diff --git a/src/modules.js b/src/modules.js
index 9662200c..d9888c24 100644
--- a/src/modules.js
+++ b/src/modules.js
@@ -234,7 +234,7 @@ var Types = {
   preciseI64MathUsed: (PRECISE_I64_MATH == 2)
 };
 
-var firstTableIndex = (ASM_JS ? 2*RESERVED_FUNCTION_POINTERS : 0) + 2;
+var firstTableIndex = FUNCTION_POINTER_ALIGNMENT * ((ASM_JS ? RESERVED_FUNCTION_POINTERS : 0) + 1);
 
 var Functions = {
   // All functions that will be implemented in this file. Maps id to signature
@@ -287,7 +287,7 @@ var Functions = {
       ret = this.indexedFunctions[ident];
       if (!ret) {
         ret = this.nextIndex;
-        this.nextIndex += 2; // Need to have indexes be even numbers, see |polymorph| test
+        this.nextIndex += FUNCTION_POINTER_ALIGNMENT;
         this.indexedFunctions[ident] = ret;
       }
       ret = ret.toString();
diff --git a/src/runtime.js b/src/runtime.js
index 00031fed..a281045b 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -347,22 +347,23 @@ var Runtime = {
     for (var i = 0; i < Runtime.functionPointers.length; i++) {
       if (!Runtime.functionPointers[i]) {
         Runtime.functionPointers[i] = func;
-        return 2 + 2*i;
+        return {{{ FUNCTION_POINTER_ALIGNMENT }}}*(1 + i);
       }
     }
     throw 'Finished up all reserved function pointers. Use a higher value for RESERVED_FUNCTION_POINTERS.';
 #else
     var table = FUNCTION_TABLE;
     var ret = table.length;
+    assert(ret % {{{ FUNCTION_POINTER_ALIGNMENT }}} === 0);
     table.push(func);
-    table.push(0);
+    for (var i = 0; i < {{{ FUNCTION_POINTER_ALIGNMENT }}}-1; i++) table.push(0);
     return ret;
 #endif
   },
 
   removeFunction: function(index) {
 #if ASM_JS
-    Runtime.functionPointers[(index-2)/2] = null;
+    Runtime.functionPointers[(index-{{{ FUNCTION_POINTER_ALIGNMENT }}})/{{{ FUNCTION_POINTER_ALIGNMENT }}}] = null;
 #else
     var table = FUNCTION_TABLE;
     table[index] = null;
diff --git a/src/settings.js b/src/settings.js
index 5cf054a9..3eb43f1c 100644
--- a/src/settings.js
+++ b/src/settings.js
@@ -170,6 +170,9 @@ var ALIASING_FUNCTION_POINTERS = 0; // Whether to allow function pointers to ali
                                     // a different type. This can greatly decrease table sizes
                                     // in asm.js, but can break code that compares function
                                     // pointers across different types.
+var FUNCTION_POINTER_ALIGNMENT = 2; // Byte alignment of function pointers - we will fill the
+                                    // tables with zeros on aligned values. 1 means all values
+                                    // are aligned and all will be used (which is optimal).
 
 var ASM_HEAP_LOG = 0; // Simple heap logging, like SAFE_HEAP_LOG but cheaper, and in asm.js