Get in loser. We're rewinding the stack.

Sandboxing Perl with WebAssembly - Part 2.

In my last post, I expressed frustration at how the lack of exnref support in most WebAssembly runtimes made zeroperl effectively unusable. However, complaining alone doesn’t solve problems—if something is broken, fix it. Don’t accept the status quo or let it derail your goals.

Using libsetjmp from the WASI SDK for setjmp/longjmp breaks compatibility across WebAssembly runtimes, so I decided to implement it myself. Binaryen has an Asyncify feature, which provides more than enough functionality to build a setjmp implementation from scratch.¹

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First, we remove the official library

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Next, we write some (web)assembly

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Then, we run wasm-opt

wasm-opt zeroperl_unopt -O3 \  
--strip-dwarf \  
--enable-bulk-memory \  
--asyncify \  
-o zeroperl.wasm  

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And the moment of truth…

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zeroperl now runs in Wasmer, Wasmtime, and every other WebAssembly runtime I tested.

Enjoy your fully sandboxed and self-contained Perl. All in one tiny WebAssembly module. Source code here.

See part three for how I got asynchronous web APIs working.

1. Okay, not from scratch, I found a solution in the Ruby repo of all places (which itself just mirrors how Emscripten implements setjmp)