1 files changed, 61 insertions, 0 deletions
diff --git a/src/corruptionCheck.js b/src/corruptionCheck.js
new file mode 100644
index 00000000..0616337b
--- /dev/null
+++ b/src/corruptionCheck.js
@@ -0,0 +1,61 @@
+
+// See settings.js, CORRUPTION_CHECK
+
+var CorruptionChecker = {
+  BUFFER_FACTOR: {{{ CORRUPTION_CHECK }}},
+
+  ptrs: {},
+
+  init: function() {
+    this.realMalloc = _malloc;
+    _malloc = Module['_malloc'] = this.malloc;
+
+    this.realFree = _free;
+    _free = Module['_free'] = this.free;
+  },
+  malloc: function(size) {
+    assert(size > 0); // some mallocs accept zero - fix your code if you want to use this tool
+    var allocation = CorruptionChecker.realMalloc(size*(1+2*CorruptionChecker.BUFFER_FACTOR));
+    var ptr = allocation + size*CorruptionChecker.BUFFER_FACTOR;
+    assert(!CorruptionChecker.ptrs[ptr]);
+    CorruptionChecker.ptrs[ptr] = size;
+    CorruptionChecker.fillBuffer(allocation, size*CorruptionChecker.BUFFER_FACTOR);
+    CorruptionChecker.fillBuffer(allocation + size*(1+CorruptionChecker.BUFFER_FACTOR), size*CorruptionChecker.BUFFER_FACTOR);
+    return ptr;
+  },
+  free: function(ptr) {
+    CorruptionChecker.checkPtr(ptr, true);
+  },
+  canary: function(x) {
+    return (x + (x << 3) + (x&75) - (x&47))&255;
+  },
+  fillBuffer: function(allocation, size) {
+    for (var x = allocation; x < allocation + size; x++) {
+      {{{ makeSetValue('x', 0, 'CorruptionChecker.canary(x)', 'i8') }}};
+    }
+  },
+  checkBuffer: function(allocation, size) {
+    for (var x = allocation; x < allocation + size; x++) {
+      assert(({{{ makeGetValue('x', 0, 'i8') }}}&255) == CorruptionChecker.canary(x), 'Heap corruption detected!');
+    }
+  },
+  checkPtr: function(ptr, free) {
+    var size = CorruptionChecker.ptrs[ptr];
+    assert(size);
+    var allocation = ptr - size*CorruptionChecker.BUFFER_FACTOR;
+    CorruptionChecker.checkBuffer(allocation, size*CorruptionChecker.BUFFER_FACTOR);
+    CorruptionChecker.checkBuffer(allocation + size*(1+CorruptionChecker.BUFFER_FACTOR), size*CorruptionChecker.BUFFER_FACTOR);
+    if (free) {
+      delete CorruptionChecker.ptrs[ptr];
+      CorruptionChecker.realFree(allocation);
+    }
+  },
+  checkAll: function() {
+    for (var ptr in CorruptionChecker.ptrs) {
+      CorruptionChecker.checkPtr(ptr, false);
+    }
+  },
+};
+
+CorruptionChecker.init();
+