Added APIs to support conditional emscripten instantiation

src/apis/emscripten/mod.rs

@@ -4,9 +4,11 @@ use crate::webassembly::{ImportObject, ImportValue};
 mod memory;
 mod process;
 mod io;
+mod utils;
 
 // SYSCALLS
 use super::host;
+pub use self::utils::is_emscripten_module;
 
 pub fn generate_emscripten_env<'a, 'b>() -> ImportObject<&'a str, &'b str> {
     let mut import_object = ImportObject::new();

src/apis/emscripten/tests/is_emscripten_false.wast

@@ -0,0 +1,9 @@
+(module
+ (table 0 anyfunc)
+ (memory $0 1)
+ (export "memory" (memory $0))
+ (export "main" (func $main))
+ (func $main (; 1 ;) (result i32)
+  (i32.const 0)
+ )
+)

src/apis/emscripten/tests/is_emscripten_true.wast

@@ -0,0 +1,17 @@
+(module
+ (type $FUNCSIG$ii (func (param i32) (result i32)))
+ (import "env" "puts" (func $puts (param i32) (result i32)))
+ (table 0 anyfunc)
+ (memory $0 1)
+ (data (i32.const 16) "hello, world!\00")
+ (export "memory" (memory $0))
+ (export "main" (func $main))
+ (func $main (; 1 ;) (result i32)
+  (drop
+   (call $puts
+    (i32.const 16)
+   )
+  )
+  (i32.const 0)
+ )
+)

src/apis/emscripten/utils.rs

@@ -0,0 +1,35 @@
+use crate::webassembly::module::Module;
+
+/// We check if a provided module is an Emscripten generated one
+pub fn is_emscripten_module(module: &Module) -> bool {
+    for (module, field) in &module.info.imported_funcs {
+        if module == "env" {
+            return true;
+        }
+    }
+    return false;
+}
+
+
+#[cfg(test)]
+mod tests {
+    use crate::webassembly::instantiate;
+    use super::is_emscripten_module;
+    use super::super::generate_emscripten_env;
+
+    #[test]
+    fn should_detect_emscripten_files() {
+        let wasm_bytes = include_wast2wasm_bytes!("tests/is_emscripten_true.wast");
+        let import_object = generate_emscripten_env();
+        let result_object = instantiate(wasm_bytes, import_object).expect("Not compiled properly");
+        assert!(is_emscripten_module(&result_object.module));
+    }
+
+    #[test]
+    fn should_detect_non_emscripten_files() {
+        let wasm_bytes = include_wast2wasm_bytes!("tests/is_emscripten_false.wast");
+        let import_object = generate_emscripten_env();
+        let result_object = instantiate(wasm_bytes, import_object).expect("Not compiled properly");
+        assert!(!is_emscripten_module(&result_object.module));
+    }
+}

src/apis/mod.rs

@@ -1,5 +1,4 @@
 pub mod emscripten;
 pub mod host;
 
-pub use self::emscripten::generate_emscripten_env;
-
+pub use self::emscripten::{generate_emscripten_env, is_emscripten_module};

src/main.rs

@@ -71,22 +71,32 @@ fn execute_wasm(wasm_path: PathBuf) -> Result<(), String> {
         wasm_binary = wabt::wat2wasm(wasm_binary)
             .map_err(|err| format!("Can't convert from wast to wasm: {:?}", err))?;
     }
-
+    // TODO: We should instantiate after compilation, so we provide the
+    // emscripten environment conditionally based on the module
     let import_object = apis::generate_emscripten_env();
     let webassembly::ResultObject { module, instance } =
         webassembly::instantiate(wasm_binary, import_object)
             .map_err(|err| format!("Can't instantiate the WebAssembly module: {}", err))?;
 
-    // webassembly::utils::print_instance_offsets(&instance);
-
+    if apis::is_emscripten_module(&module) {
+        let func_index = match module.info.exports.get("main") {
+            Some(&webassembly::Export::Function(index)) => index,
+            _ => panic!("_main emscripten function not found"),
+        };
+        let main: extern fn(u32, u32, &webassembly::Instance) = get_instance_function!(instance, func_index);
+        main(0, 0, &instance);
+    }
+    else {
         let func_index = instance
             .start_func
-        .unwrap_or_else(|| match module.info.exports.get("main").or(module.info.exports.get("_main")) {
+            .unwrap_or_else(|| match module.info.exports.get("main") {
                 Some(&webassembly::Export::Function(index)) => index,
                 _ => panic!("Main function not found"),
             });
-    let main: extern fn(u32, u32, &webassembly::Instance) = get_instance_function!(instance, func_index);
-    main(0, 0, &instance);
+        let main: extern fn(&webassembly::Instance) = get_instance_function!(instance, func_index);
+        main(&instance);
+    }
+
     Ok(())
 }