Four Approaches to Debugging Server-side WebAssembly

Shopify Functions enables customizing the business logic of Shopify’s back end with server-side WebAssembly. There are many benefits to using a WebAssembly environment to host these customizations such as low cold-start latency and robust security compared to other alternatives. However, WebAssembly poses new challenges when debugging.

Shopify logo
Shopify
•
Jeff Charles
•9 min read•intermediate•
--
•View Original
AssemblyScriptHTMLJavaScriptRubyRustWebAssembly

Overview

The article discusses four approaches to debugging server-side WebAssembly, highlighting the benefits of using WebAssembly in Shopify Functions while addressing the unique challenges it presents. It provides insights into various debugging methods, including using native architecture compilers, LLDB with Wasmtime, WebAssembly-specific debuggers, and browser-based debugging tools.

What You'll Learn

1

How to compile code to a native architecture for debugging

2

Why using LLDB with Wasmtime can help diagnose WebAssembly-specific issues

3

When to use WebAssembly-specific debuggers for better memory inspection

4

How to leverage browser-based debugging for WebAssembly modules

Prerequisites & Requirements

  • Familiarity with WebAssembly and debugging concepts
  • Access to debugging tools like LLDB and Wasmtime(optional)

Key Questions Answered

What are the best approaches for debugging server-side WebAssembly?
The article outlines four main approaches: compiling to a native architecture, using LLDB with Wasmtime, employing WebAssembly-specific debuggers, and utilizing browser-based debugging tools. Each method has its advantages and trade-offs depending on the debugging context.
How does compiling to a native architecture improve debugging experience?
Compiling to a native architecture allows developers to use familiar debuggers like LLDB or GDB, which provide better fidelity in variable representation and are essential for debugging interpreted languages like JavaScript or Ruby running in WebAssembly.
What are the limitations of using LLDB with Wasmtime?
While using LLDB with Wasmtime can help diagnose WebAssembly-specific issues, it may result in lower fidelity rendering of local variables compared to native debugging. Additionally, developers need to learn how to effectively use LLDB, which may require some time.
What are the trade-offs of using WebAssembly-specific debuggers?
WebAssembly-specific debuggers like Wasminspect offer standalone tools for inspecting memory and disassembling WebAssembly instructions. However, they lack the feature set of mature debuggers and may not render non-numeric variables effectively.

Technologies & Tools

Backend
Webassembly
Used for customizing Shopify's back end logic.
Tools
Lldb
Debugger for native code and WebAssembly.
Tools
Gdb
Debugger for native code.
Runtime
Wasmtime
WebAssembly runtime used for executing WebAssembly code.
Tools
Wasminspect
WebAssembly-specific debugger for inspecting memory.

Key Actionable Insights

1
Consider compiling your WebAssembly code to a native architecture for debugging to leverage familiar tools like LLDB or GDB.
This approach provides a higher fidelity representation of variables and a more intuitive debugging experience, especially for developers already accustomed to these tools.
2
Utilize LLDB with Wasmtime to debug issues that only occur in a WebAssembly environment.
This method allows you to step through the source code while taking advantage of debug symbols, which can be crucial for diagnosing WebAssembly-specific behaviors.
3
Explore browser-based debugging tools for a more accessible debugging experience.
As tooling improves, browser-based debugging may become the easiest way to debug WebAssembly, requiring less setup compared to other methods.

Common Pitfalls

1
One common pitfall is relying solely on native debugging for issues that only manifest in a WebAssembly environment.
This can lead to missed bugs that are specific to the WebAssembly runtime, necessitating the use of alternative debugging methods.

Related Concepts

Webassembly Debugging Techniques
Native Architecture Debugging
Using Lldb And Wasmtime