Pass strings to C on the heap instead of the stack (bellard#32)

* failing memory test

* pass strings on the heap

Makefile

@@ -15,7 +15,7 @@ QUICKJS_DEFINES:=-D_GNU_SOURCE -DCONFIG_VERSION=\"$(QUICKJS_CONFIG_VERSION)\"
 EMCC_EXPORTED_FUNCS+=-s EXPORTED_FUNCTIONS=$(shell cat $(BUILD_WRAPPER)/symbols.json)
 
 CFLAGS_EMCC+=-s WASM=1
-CFLAGS_EMCC+=-s EXTRA_EXPORTED_RUNTIME_METHODS='["cwrap", "addFunction", "removeFunction", "_malloc", "_free"]'
+CFLAGS_EMCC+=-s EXTRA_EXPORTED_RUNTIME_METHODS='["cwrap", "addFunction", "removeFunction", "stringToUTF8", "lengthBytesUTF8", "_malloc", "_free"]'
 CFLAGS_EMCC+=-s NODEJS_CATCH_EXIT=0
 CFLAGS_EMCC+=-s MODULARIZE=1
 CFLAGS_EMCC+=-s EXPORT_NAME=QuickJSRaw

c/interface.c

@@ -30,6 +30,13 @@
 #define QTS_DUMP(value) ;
 #endif
 
+/**
+ * Signal to our FFI code generator that this string argument should be passed as a pointer
+ * allocated by the caller on the heap, not a JS string on the stack.
+ * https://github.com/emscripten-core/emscripten/issues/6860#issuecomment-405818401
+ */
+#define HeapChar const char
+
 void qts_log(char* msg) {
   fputs(PKG, stderr);
   fputs(msg, stderr);
@@ -291,7 +298,7 @@ double QTS_GetFloat64(JSContext *ctx, JSValueConst *value) {
   return result;
 }
 
-JSValue *QTS_NewString(JSContext *ctx, const char* string) {
+JSValue *QTS_NewString(JSContext *ctx, HeapChar *string) {
   return jsvalue_to_heap(JS_NewString(ctx, string));
 }
 
@@ -434,7 +441,7 @@ char *QTS_Dump(JSContext *ctx, JSValueConst *obj) {
   return QTS_GetString(ctx, obj);
 }
 
-JSValue *QTS_Eval(JSContext *ctx, const char* js_code) {
+JSValue *QTS_Eval(JSContext *ctx, HeapChar *js_code) {
   return jsvalue_to_heap(JS_Eval(ctx, js_code, strlen(js_code), "eval.js", JS_EVAL_TYPE_GLOBAL));
 }
 
@@ -470,3 +477,7 @@ JSValue *QTS_NewPromiseCapability(JSContext *ctx, JSValue **resolve_funcs_out) {
   resolve_funcs_out[1] = jsvalue_to_heap(resolve_funcs[1]);
   return jsvalue_to_heap(promise);
 }
+
+void QTS_TestStringArg(const char *string) {
+  // pass
+}