Wasm - Write Perl extensions using Wasm


version 0.21



 package MathStuff;
 use strict;
 use warnings;
 use base qw( Exporter );
 use Wasm
   -api => 0,
   -exporter => 'ok',
   -wat => q{
       (func (export "add") (param i32 i32) (result i32)
         local.get 0
         local.get 1
       (func (export "subtract") (param i32 i32) (result i32)
         local.get 0
         local.get 1
       (memory (export "frooble") 2 3)

 use MathStuff qw( add subtract );
 print add(1,2), "\n";      # prints 3
 print subtract(3,2), "\n", # prints 1


WARNING: WebAssembly and Wasmtime are a moving target and the interface for these modules is under active development. Use with caution.

The goal of this project is for Perl and WebAssembly to be able to call each other transparently without having to know or care which module is implemented in which language. Perl subroutines and WebAssembly functions can easily be imported and exported between Perl and WebAssembly (see Wasm::Func for details). WebAssembly global variables can be imported into Perl using tied scalars (see Wasm::Global for details). WebAssembly linear memory can be queried and manipulated by Perl (see Wasm::Memory for details). Perl can throw or catch traps into or out of WebAssembly (see Wasm::Trap for details). WebAssembly can optionally be loaded directly by Perl without writing any Perl wrappers at all (see Wasm::Hook for details).

The example above shows WebAssembly Text (WAT) inlined into the Perl code for readability. In most cases you will want to compile your WebAssembly from a higher level language (Rust, C, Go, etc.), and install it alongside your Perl Module (.pm file) and use the -self option below. That is for lib/ you would install the Wasm file into lib/Math.wasm, and use the -self option.

Modules using Wasm can optionally use Exporter to export WebAssembly functions into other modules. Using -export 'ok' functions can be imported from a calling module on requests. -export 'all' will export all exported functions by default.

The current implementation uses Wasm::Wasmtime, which is itself based on the Rust project Wasmtime. This module doesn't expose the Wasm::Wasmtime interface, and implementation could be changed in the future.



 use Wasm -api => 0;

As of this writing, since the API is subject to change, this must be provided and set to 0.


 use Wasm -api => 0, -exporter => 'all';
 use Wasm -api => 0, -exporter => 'ok';

Configure the caller as an Exporter, with all the functions in the WebAssembly either @EXPORT (all) or @EXPORT_OK (ok).


 use Wasm -api => 0, -file => $file;

Path to a WebAssembly file in either WebAssembly Text (.wat) or WebAssembly binary (.wasm) format.


 use Wasm -api => 0, -global => [ $name, $type, $mutability, $init ];

Creates a global variable for the calling Pure-Perl module that can be imported into WebAssembly. If you use this option you cannot specify the -wat or -file or -self options. For a detailed example see Wasm::Global.


 use Wasm -api => 0, -package => $package;

Install subroutines in to $package namespace instead of the calling namespace.


 use Wasm -api => 0, -self;

Look for a WebAssembly Text (.wat) or WebAssembly binary (.wasm) file with the same base name as the Perl source this is called from.

For example if you are calling this from lib/Foo/, it will look for lib/Foo/Bar.wat and lib/Foo/Bar.wasm. If both exist, then it will use the newer of the two.


 use Wasm -api => 0, -wat => $wat;

String containing WebAssembly Text (WAT). Helpful for inline WebAssembly inside your Perl source file.



This hash maps the Wasm module names to the files from which the Wasm was loaded. It is roughly analogous to the %INC hash in Perl.


As mentioned before as of this writing this dist is a work in progress. I won't intentionally break stuff without a compelling reason, but practicality may demand it in some situations.

This interface is implemented using the bundled Wasm::Wasmtime family of modules, which depends on the Wasmtime project.

The default way of handling out-of-bounds memory errors is to allocate large PROT_NONE pages at startup. While these pages do not consume many resources in practice (at least in the way that they are used by Wasmtime), they can cause out-of-memory errors on Linux systems with virtual memory limits (ulimit -v in the bash shell). Similar techniques are common in other modern programming languages, and this is more a limitation of the Linux kernel than anything else. Setting the limits on the virtual memory address size probably doesn't do what you think it is doing and you are probably better off finding a way to place limits on process memory.

However, as a workaround for environments that choose to set a virtual memory address size limit anyway, Wasmtime provides configurations to not allocate the large PROT_NONE pages at some performance cost. The testing plugin Test2::Plugin::Wasm tries to detect environments that have the virtual memory address size limits and sets this configuration for you. For production you can set the environment variable PERL_WASM_WASMTIME_MEMORY to tune the appropriate memory settings exactly as you want to (see the environment section of Wasm::Wasmtime).



Interface to WebAssembly functions from Perl, and Perl subroutines from WebAssembly.


Interface to WebAssembly globals from Perl, and Perl globals from WebAssembly.


Interface to WebAssembly memory from Perl.


Interface to WebAssembly traps.


Perl WebAssembly command line tool. Run WebAssembly programs from the command line, or dump their export/import interfaces.


Low level interface to wasmtime.


Load WebAssembly modules as though they were Perl modules.


Graham Ollis <>


This software is copyright (c) 2020 by Graham Ollis.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.