1 files changed, 23 insertions, 1 deletions

diff --git a/src/wasm-js.cpp b/src/wasm-js.cpp
index 2f9ac639f..3de6319cb 100644
--- a/src/wasm-js.cpp
+++ b/src/wasm-js.cpp
@@ -14,6 +14,9 @@
 using namespace cashew;
 using namespace wasm;
 
+IString GROW_WASM_MEMORY("_growWasmMemory"),
+        NEW_SIZE("newSize");
+
 // global singletons
 Asm2WasmBuilder* asm2wasm = nullptr;
 ModuleInstance* instance = nullptr;
@@ -82,14 +85,32 @@ extern "C" void EMSCRIPTEN_KEEPALIVE load_asm(char *input) {
   Ref asmjs = builder.parseToplevel(input);
 
   module = new Module();
-  module->memory.initial = module->memory.max = EM_ASM_INT_V({
+  module->memory.initial = EM_ASM_INT_V({
     return Module['providedTotalMemory']; // we receive the size of memory from emscripten
   });
+  module->memory.max = memoryGrowth ? -1 : module->memory.initial;
 
   if (wasmJSDebug) std::cerr << "wasming...\n";
   asm2wasm = new Asm2WasmBuilder(*module);
   asm2wasm->processAsm(asmjs);
 
+  if (memoryGrowth) {
+    // create and export a function that just calls memory growth
+    auto growWasmMemory = new Function();
+    growWasmMemory->name = GROW_WASM_MEMORY;
+    growWasmMemory->params.emplace_back(NEW_SIZE, i32); // the new size
+    auto get = new GetLocal();
+    get->name = NEW_SIZE;
+    auto grow = new Host();
+    grow->op = GrowMemory;
+    grow->operands.push_back(get);
+    growWasmMemory->body = grow;
+    module->addFunction(growWasmMemory);
+    auto export_ = new Export();
+    export_->name = export_->value = GROW_WASM_MEMORY;
+    module->addExport(export_);
+  }
+
   if (wasmJSDebug) std::cerr << "optimizing...\n";
   asm2wasm->optimize();
 
@@ -207,6 +228,7 @@ extern "C" void EMSCRIPTEN_KEEPALIVE load_asm(char *input) {
     }
 
     void growMemory(size_t oldSize, size_t newSize) override {
+      // never called from compiled asm.js directly, we have special support for it as the request arrives from outside js
       abort();
     }