GoKawiilWasm is not quite a stack machine
April 27, 2026
Everyone knows Wasm is a stack machine. Wikipedia says so, the official Wasm design specification says so, you get it. I thought so too.
That is, until I started writing Wasm code – not compiling for Wasm, but writing the instructions by hand. And I found out that there exists a major difference between Wasm and all other stack-based languages, that makes this claim misleading.
Register vs stack
Let’s back up a bit. What is a stack machine, even?
Say you write a program in a high-level language, and at some point you want to calculate 2 * 3 + 5 * 7 . Low-level languages don’t have a notion of compound expressions: they can only perform one operation at a time. So you need to do two multiplications, save their results, and then perform addition.
Many low-level languages, like x86 assembly, would represent these steps as follows:
a = 2
b = 3
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