[wasm] Fix decoding of shared global index space

src/wasm/module-decoder.cc

Index: src/wasm/module-decoder.cc
diff --git a/src/wasm/module-decoder.cc b/src/wasm/module-decoder.cc
index 0f8637f32eeb1785c8a45bad1f585510d13e1f64..10c66b858ed8596c92842da01bb7e956c32df3cf 100644
--- a/src/wasm/module-decoder.cc
+++ b/src/wasm/module-decoder.cc
@@ -397,7 +397,12 @@ class ModuleDecoder : public Decoder {
     // ===== Global section ==================================================
     if (section_iter.section_code() == kGlobalSectionCode) {
       uint32_t globals_count = consume_u32v("globals count");
-      module->globals.reserve(SafeReserve(globals_count));
+      uint32_t imported_globals = static_cast<uint32_t>(module->globals.size());
+      if (!IsWithinLimit(kMaxReserve, globals_count, imported_globals)) {

[Derek Schuff, 2016/10/12 05:35:19]

OK, so I was afraid this would be a problem; I was trying to worry about the sum
of the imported + defined globals overflowing some nebulous limit, but obviously
kMaxReserve is too small (it's causing the test failure). So, any suggestions?
INT_MAX? Just cast to int64 and do UINT_MAX? Something in between?

+        error(pos, pos, "too many imported+defined globals: %u + %u",
+              imported_globals, globals_count);
+      }
+      module->globals.reserve(SafeReserve(imported_globals + globals_count));
       for (uint32_t i = 0; ok() && i < globals_count; ++i) {
         TRACE("DecodeGlobal[%d] module+%d\n", i,
               static_cast<int>(pc_ - start_));
@@ -405,7 +410,7 @@ class ModuleDecoder : public Decoder {
         module->globals.push_back(
             {kAstStmt, false, WasmInitExpr(), 0, false, false});
         WasmGlobal* global = &module->globals.back();
-        DecodeGlobalInModule(module, i, global);
+        DecodeGlobalInModule(module, i + imported_globals, global);
       }
       section_iter.advance();
     }
@@ -617,7 +622,6 @@ class ModuleDecoder : public Decoder {
 
   uint32_t SafeReserve(uint32_t count) {
     // Avoid OOM by only reserving up to a certain size.
-    const uint32_t kMaxReserve = 20000;
     return count < kMaxReserve ? count : kMaxReserve;
   }
 
@@ -656,6 +660,8 @@ class ModuleDecoder : public Decoder {
   ModuleResult result_;
   ModuleOrigin origin_;
 
+  static const uint32_t kMaxReserve = 20000;
+
   uint32_t off(const byte* ptr) { return static_cast<uint32_t>(ptr - start_); }
 
   // Decodes a single global entry inside a module starting at {pc_}.
@@ -669,7 +675,10 @@ class ModuleDecoder : public Decoder {
       case WasmInitExpr::kGlobalIndex: {
         uint32_t other_index = global->init.val.global_index;
         if (other_index >= index) {
-          error("invalid global index in init expression");
+          error(pos, pos,
+                "invalid global index in init expression, "
+                "index %u, other_index %u",
+                index, other_index);
         } else if (module->globals[other_index].type != global->type) {
           error(pos, pos,
                 "type mismatch in global initialization "