# VS WASM Debugger Extension<no value>
This tool is designed to help with the debugging of WASM modules. It is a Visual Studio extension which modifies part of Visual Studio's debugger to make WASM debugging easier, since - by default - it has some issues.

{{< callout context="caution" title="IMPORTANT!" icon="outline/alert-triangle" >}}

Debugging tools cannot be attached to the simulation executable by default. If you try to do this, the simulation will crash. In order to be able to debug your WASM modules, you **must** pass in the argument `-AllowDebugger` to the exe. When using this mode, a debugger can be attached to the simulation, but note that some content will be "hidden" (ie: encrypted packages).

{{< /callout >}}

 

 

### The Problem

WASM is used to generate DLLs that can then be used in add-on packages. These WASM files are created from C++ and then converted into DLLs by the package building process. However, sometimes there may be issues with the final DLL due to the way that the WASM compiler and subsequent transition back to C++ for the DLL works. This, in turn, can make debugging the final DLL to find any issues rather complicated, due to some incompatibilities between the WASM environment and the C++ Debugger.

 

To illustrate this, let's look some possible issues when viewing the call stack of a compiled DLL. Within Visual Studio, navigating through the call stack is indeed possible, *but* the data displayed in "Locals" will be wrong, which makes it basically unusable. Let's consider the following code:

``` wasm
class C
    {
    public:
        void Func1()
        {
            WASM_FORCE_DEBUG;
            Func2(m_i, m_f);
        }
    private:
      void Func4(bool b)
        {
            WASM_FORCE_DEBUG;
        }
      void Func3(int iArr[5], float fArr[5])
        {
            WASM_FORCE_DEBUG;
            Func4(false);
        }
      void Func2(int i, float f)
        {
            WASM_FORCE_DEBUG;
            int iArr[5] = { i, i + 1, i + 2, i + 3, i + 4 };
            float fArr[5] = { f, f + 1, f + 2, f + 3, f + 4 };
            Func3(iArr, fArr);
        }
        int m_i = 1;
        float m_f = 10.f;
    };
```

 

By executing this code and putting a breakpoint in `Func4`, here is the callstack you will get:

{{< image-center
    src="images/6_Programming/WASM/wasm_debug/wasmdebug_1_callstack.png"
    alt="A Test Code CallStack In Visual Studio" >}}

 

And here are the "Locals", that you would have for `Func4`:

{{< image-center
    src="images/6_Programming/WASM/wasm_debug/wasmdebug_2_locals.png"
    alt="Test Code Func4 Correct Local Variables" >}}

 

Everything looks correct and is fine for `Func4` it seems. However:

{{< image-center
    src="images/6_Programming/WASM/wasm_debug/wasmdebug_3_func3.png"
    alt="Test Code Func3 Incorrect Local Variables" >}}

 

In the case of `Func3`s local variables, `fArr` and `iArr` are displayed as `nullptr`, which is obviously not the case. And if we check a little bit further:

{{< image-center
    src="images/6_Programming/WASM/wasm_debug/wasmdebug_4_func2.png"
    alt="Test Code Func2 Incorrect Local Variables" >}}

 

In the case of `Func2`, we have some absolute nonsense displayed, eg: `this` is displayed as `nullptr`, arrays are wrong, etc… And finally:

{{< image-center
    src="images/6_Programming/WASM/wasm_debug/wasmdebug_5_func1.png"
    alt="Test Code Func1 Correct Local Variables" >}}

 

In the case of `Func1`s local variables, everything seems to be great again!

 

So, as you can, see Visual Studio has some important issues when debugging WASM, most of which we can resolve using the **VS WASM Debugger Extension**.

 

 

### Using The VS WASM Debugger Extension

This section gives instructions for using the VS WASM Debugger Extension.

{{< callout context="caution" title="IMPORTANT!" icon="outline/alert-triangle" >}}

Ensure that you have the **most up to date version** of the extension, as new functionality may have been added in the latest SDK update.

{{< /callout >}}

 

#### Installing

The SDK [Tools](../../introduction/sdk-contents/#tools) folder contains a folder for the extension that contains the following file: `WasmExtension.vsix`. This extension should be installed in Visual Studio (see [here](https://docs.microsoft.com/en-us/visualstudio/ide/finding-and-using-visual-studio-extensions?view=vs-2022#install-without-using-the-manage-extensions-dialog-box "Install without using the Manage Extensions dialog box") for information).

 

#### Debugging

After installing the extension, when debugging your code, you will see a new local variable in every main function scope:

<img src="images/6_Programming/WASM/wasm_debug/wasmdebug_6_newlocals.png" class="center" />

This variable will be recognized by the extension and will automatically update its environment according to the stack frame inspected, preventing most of the issues outlined in the sections above.

{{< callout context="note" title="NOTE" icon="outline/bulb" >}}

The extension won't do anything if you are not working with a MSFS WASM file or you are working with an incompatible MSFS WASM file (by incompatible we mean: outdated, built in Release mode, etc…).

{{< /callout >}}

 

#### Uninstall

If, for whatever reason, you need to uninstall - or disable - the extension, this is done by going to the **Extensions** menu in Visual Studio, then selecting the **Manage Extensions** option. In the window that opens, go to the **Installed** group, then find the WASM Debugging extension and select either "Disable" or "Uninstall".