How to Use the 'wasm2wat' Command (with Examples)

The ‘wasm2wat’ command is a powerful tool that allows developers to convert files from the WebAssembly (Wasm) binary format to a more readable text format known as WebAssembly Text Format (Wat). This conversion is particularly useful when you want to debug, inspect, or share WebAssembly code in a human-readable form. ‘wasm2wat’ is part of the WebAssembly Binary Toolkit (WABT), which provides tools to read, parse, and write wasm and wat files. The command-line tool helps developers better understand the compiled format of WebAssembly modules by translating them back into a text representation.

Use case 1: Convert a file to the text format and display it to the console

Code:

wasm2wat file.wasm

Motivation:

In software development, especially when dealing with WebAssembly, it’s crucial to understand the code you are working with. The binary format of WebAssembly is efficient and compact, yet it’s not human-readable. Converting the binary file to a text format (Wat) allows you to review and debug the code directly. This is especially helpful if you’re developing applications where you need to ensure that the WebAssembly code behaves as expected, or if you’re learning how WebAssembly works by examining examples.

Explanation:

• wasm2wat: This is the command used to perform the conversion from binary to text format.
• file.wasm: This argument specifies the input file, which is the WebAssembly binary file you want to convert. It is required to run the command.

By default, this command will read the input file, convert it to the text (Wat) format, and display the output directly to the console.

Example Output:

(module
  (func $add (param $lhs i32) (param $rhs i32) (result i32)
    get_local $lhs
    get_local $rhs
    i32.add))

Use case 2: Write the output to a given file

Code:

wasm2wat file.wasm -o file.wat

Motivation:

In many situations, especially in collaborative environments or when a record of the Wat file is necessary for documentation or review purposes, you might want the output to be saved directly to a file rather than just being displayed in the console. This allows multiple developers to access and analyze the same copy of the converted WebAssembly text without the need to perform the conversion individually. Furthermore, saving the output to a file ensures that you have a saved version for future reference or further manipulation.

Explanation:

• wasm2wat: Again, this is the command that initiates the conversion process.
• file.wasm: This specifies the input file, the WebAssembly binary needed for conversion.
• -o: This option denotes that output should be directed to a file.
• file.wat: This argument indicates the name of the output file, where the converted WebAssembly text will be stored.

With these arguments, the command will take file.wasm, convert it to the text format, and save the resulting content into file.wat.

Example Output:

A file named file.wat is created containing:

(module
  (func $subtract (param $a i32) (param $b i32) (result i32)
    get_local $a
    get_local $b
    i32.sub))

Conclusion:

The ‘wasm2wat’ command is an essential utility for developers working with WebAssembly. It simplifies the process of converting binary to text format, which is crucial for debugging and understanding the WebAssembly code. Whether you are displaying the conversion on the console or saving it to a file for documentation purposes, this tool enhances the ability to inspect and work with WebAssembly modules effectively.