[wasm] Fix bounds check for zero initial memory.

src/assembler.cc

Index: src/assembler.cc
diff --git a/src/assembler.cc b/src/assembler.cc
index b44bc06ba36aaff6cbd92c6a6f9a1f928e0f35a7..f34952fb07a3714658f522ec1925062b845f44c8 100644
--- a/src/assembler.cc
+++ b/src/assembler.cc
@@ -355,6 +355,22 @@ void RelocInfo::update_wasm_memory_reference(
     uint32_t offset = old_size - current_size_reference;
     DCHECK_GE(new_size, offset);
     uint32_t updated_size_reference = new_size - offset;
+
+    if (old_size == 0) {
+      switch (rmode_) {
+        case RelocInfo::WASM_MEMORY_WORD_SIZE_REFERENCE:
+          updated_size_reference = updated_size_reference - 1;
+          break;
+        case RelocInfo::WASM_MEMORY_DWORD_SIZE_REFERENCE:
+          updated_size_reference = updated_size_reference - 3;
+          break;
+        case RelocInfo::WASM_MEMORY_QWORD_SIZE_REFERENCE:
+          updated_size_reference = updated_size_reference - 7;
+          break;
+        default:
+          DCHECK(rmode_ == RelocInfo::WASM_MEMORY_BYTE_SIZE_REFERENCE);

[bradn, 2016/10/12 18:50:45]

Handle explicit and make default unreachable?

[gdeepti, 2016/10/13 08:42:59]

Got rid of additional RelocInfo modes, code removed in latest patch. 

+      }
+    }
     unchecked_update_wasm_memory_size(updated_size_reference,
                                       icache_flush_mode);
   } else {
@@ -786,8 +802,14 @@ const char* RelocInfo::RelocModeName(RelocInfo::Mode rmode) {
       return "generator continuation";
     case WASM_MEMORY_REFERENCE:
       return "wasm memory reference";
-    case WASM_MEMORY_SIZE_REFERENCE:
-      return "wasm memory size reference";
+    case WASM_MEMORY_BYTE_SIZE_REFERENCE:
+      return "wasm memory size byte reference";
+    case WASM_MEMORY_WORD_SIZE_REFERENCE:
+      return "wasm memory size word reference";
+    case WASM_MEMORY_DWORD_SIZE_REFERENCE:
+      return "wasm memory size dword reference";
+    case WASM_MEMORY_QWORD_SIZE_REFERENCE:
+      return "wasm memory size qword reference";
     case WASM_GLOBAL_REFERENCE:
       return "wasm global value reference";
     case NUMBER_OF_MODES:
@@ -885,7 +907,10 @@ void RelocInfo::Verify(Isolate* isolate) {
     case DEBUG_BREAK_SLOT_AT_TAIL_CALL:
     case GENERATOR_CONTINUATION:
     case WASM_MEMORY_REFERENCE:
-    case WASM_MEMORY_SIZE_REFERENCE:
+    case WASM_MEMORY_BYTE_SIZE_REFERENCE:
+    case WASM_MEMORY_WORD_SIZE_REFERENCE:
+    case WASM_MEMORY_DWORD_SIZE_REFERENCE:
+    case WASM_MEMORY_QWORD_SIZE_REFERENCE:
     case WASM_GLOBAL_REFERENCE:
     case NONE32:
     case NONE64: