wag is a WebAssembly compiler implemented as a Go package.

• License: 3-clause BSD
• Author: Timo Savola timo.savola@iki.fi

Features

• The input is a wasm32 binary module.

• The output is executable x86-64 machine code. Support for 64-bit ARM is in development. (Support for non-64-bit or non-little-endian CPU architectures isn't planned.)

• It is only a compiler. A runtime environment for the compiled program, including all import functions, needs to be implemented separately. (But see wasys for a combined compiler and runtime.)

• Single-pass, fast ahead-of-time compilation. Early functions can be executed while the latter functions are still being compiled, even while the source is still being downloaded.

• The generated code requires minimal runtime support; it's designed to be executed in an isolated environment. Calling standard library ABIs is not supported, but see wasys for an example program which exposes syscalls as WebAssembly import functions.

• Supports snapshot-and-restore across compiler versions and CPU architectures. Could also support limited form of code swapping during snapshot and restore.

Status

• Supports WebAssembly version 1 (MVP).

• The Go package API hasn't been finalized (but it's getting there).

Testing

Requires Linux, Go, make, clang and libcapstone. About 75% of the WebAssembly spec testsuite is run, by first converting the tests to binary format:

1. go get -t github.com/tsavola/wag
2. make -C $GOPATH/src/github.com/tsavola/wag/testdata/wabt
3. go test -v -bench=. github.com/tsavola/wag/...

Screenshot #1

$ go get github.com/tsavola/wag/cmd/wasys
$ wasys -v $GOPATH/src/github.com/tsavola/wag/testdata/hello.wasm
import write(i32, i32, i32) i32
import openat(i32, i32, i32, i32) i32
import read(i32, i32, i32) i32
import close(i32) i32
import pipe2(i32, i32) i32
import _exit(i32)
hello, world

Screenshot #2

=== RUN   TestSnapshot
--- PASS: TestSnapshot (0.00s)
    snapshot_test.go:80: print output:
        10
        --- snapshotting ---
        current memory limit: 0x6a96051ca000
        current stack ptr:    0x6a960533ffc0
        globals+memory addr:  0x6a96051ba000
        stack addr:           0x6a960533f000
        globals+memory size:  65536
        memory size:          65536
        stack offset:         4032
        stacktrace:
        #1  func-3
        #2  func-2
        --- shot snapped ---
        20
    snapshot_test.go:88: resuming
    snapshot_test.go:100: print output:
        20
        30
        330
        40
        440