feat(c-api) Handle initialized but empty results in wasm_func_call

CHANGELOG.md

@@ -8,6 +8,7 @@
 ## **[Unreleased]**
 
 - [#1710](https://github.com/wasmerio/wasmer/pull/1710) Memory for function call trampolines is now owned by the Artifact.
+- [#1783](https://github.com/wasmerio/wasmer/pull/1783) Handle initialized but empty results in `wasm_func_call` in the Wasm C API.
 
 ### Added
 

lib/c-api/src/wasm_c_api/externals/function.rs

@@ -154,18 +154,34 @@ pub unsafe extern "C" fn wasm_func_call(
                 .into_iter()
                 .map(TryInto::try_into)
                 .collect::<Result<Vec<Val>, _>>()
-                .expect("Argument conversion failed")
+                .expect("Arguments conversion failed")
         })
         .unwrap_or_default();
 
     match func.inner.call(&params) {
         Ok(wasm_results) => {
-            *results = wasm_results
+            let vals = wasm_results
                 .into_iter()
                 .map(TryInto::try_into)
                 .collect::<Result<Vec<wasm_val_t>, _>>()
-                .expect("Argument conversion failed")
-                .into();
+                .expect("Results conversion failed");
+
+            // `results` is an uninitialized vector. Set a new value.
+            if results.size == 0 || results.data.is_null() {
+                *results = vals.into();
+            }
+            // `results` is an initialized but empty vector. Fill it
+            // item per item.
+            else {
+                let slice = results
+                    .into_slice_mut()
+                    .expect("`wasm_func_call`, results' size is greater than 0 but data is NULL");
+
+                for (result, value) in slice.iter_mut().zip(vals.iter()) {
+                    (*result).kind = value.kind;
+                    (*result).of = value.of;
+                }
+            }
 
             None
         }

lib/c-api/src/wasm_c_api/macros.rs

@@ -64,6 +64,16 @@ macro_rules! wasm_declare_vec {
                 }
             }
 
+            impl [<wasm_ $name _vec_t>] {
+                pub unsafe fn into_slice_mut(&self) -> Option<&mut [[<wasm_ $name _t>]]>{
+                    if self.data.is_null() {
+                        return None;
+                    }
+
+                    Some(::std::slice::from_raw_parts_mut(self.data, self.size))
+                }
+            }
+
             // TODO: investigate possible memory leak on `init` (owned pointer)
             #[no_mangle]
             pub unsafe extern "C" fn [<wasm_ $name _vec_new>](out: *mut [<wasm_ $name _vec_t>], length: usize, init: *mut [<wasm_ $name _t>]) {

lib/c-api/tests/wasm_c_api/CMakeLists.txt

@@ -4,7 +4,7 @@ project (WasmerWasmCApiTests)
 # Examples as tests from the `wasm-c-api` repository.
 add_executable(wasm-c-api-callback wasm-c-api/example/callback.c)
 #add_executable(wasm-c-api-finalize wasm-c-api/example/finalize.c)
-#add_executable(wasm-c-api-global wasm-c-api/example/global.c)
+add_executable(wasm-c-api-global wasm-c-api/example/global.c)
 add_executable(wasm-c-api-hello wasm-c-api/example/hello.c)
 #add_executable(wasm-c-api-hostref wasm-c-api/example/hostref.c)
 #add_executable(wasm-c-api-memory wasm-c-api/example/memory.c)
@@ -57,12 +57,12 @@ add_test(NAME wasm-c-api-callback
 #         WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/wasm-c-api/example/
 #)
 
-#target_link_libraries(wasm-c-api-global general ${WASMER_LIB})
-#target_compile_options(wasm-c-api-global PRIVATE ${COMPILER_OPTIONS})
-#add_test(NAME wasm-c-api-global
-#         COMMAND wasm-c-api-global
-#         WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/wasm-c-api/example/
-#)
+target_link_libraries(wasm-c-api-global general ${WASMER_LIB})
+target_compile_options(wasm-c-api-global PRIVATE ${COMPILER_OPTIONS})
+add_test(NAME wasm-c-api-global
+         COMMAND wasm-c-api-global
+         WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/wasm-c-api/example/
+)
 
 target_link_libraries(wasm-c-api-hello general ${WASMER_LIB})
 target_compile_options(wasm-c-api-hello PRIVATE ${COMPILER_OPTIONS})