Add fn for splitting borrow of memory & data in Ctx, use in WASI

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## **[Unreleased]**
 
 - [#1060](https://github.com/wasmerio/wasmer/pull/1060) Test the capi with all the backends
+- [#1069](https://github.com/wasmerio/wasmer/pull/1069) Add function `get_memory_and_data` to `Ctx` to help prevent undefined behavior and mutable aliasing. It allows accessing memory while borrowing data mutably for the `Ctx` lifetime. This new function is now being used in `wasmer-wasi`.
 - [#1058](https://github.com/wasmerio/wasmer/pull/1058) Fix minor panic issue when `wasmer::compile_with` called with llvm backend.
 - [#858](https://github.com/wasmerio/wasmer/pull/858) Minor panic fix when wasmer binary with `loader` option run a module without exported `_start` function.
 - [#1056](https://github.com/wasmerio/wasmer/pull/1056) Improved `--invoke` args parsing (supporting `i32`, `i64`, `f32` and `f32`) in Wasmer CLI

lib/runtime-core/src/vm.rs

@@ -401,6 +401,21 @@ impl Ctx {
         }
     }
 
+    /// Get access to [`Memory`] and mutable access to the user defined data
+    /// field as the type, `T`.
+    ///
+    /// This method is required to access both at the same time.
+    /// This is useful for updating a data type that stores information about
+    /// locations in Wasm memory.
+    ///
+    /// # Safety
+    ///
+    /// This function must be called with the same type, `T`, that the `data`
+    /// was initialized with.
+    pub unsafe fn memory_and_data_mut<T>(&mut self, mem_index: u32) -> (&Memory, &mut T) {
+        (self.memory(mem_index), &mut *(self.data as *mut T))
+    }
+
     /// Gives access to the emscripten symbol map, used for debugging
     pub unsafe fn borrow_symbol_map(&self) -> &Option<HashMap<u32, String>> {
         &(*self.module).info.em_symbol_map