wag

README

wag is a WebAssembly compiler (or assembler?) 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 embedders of the compiler decide what kind of import functions they choose to implement and make available for the WebAssembly programs.

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

• 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.

Status

• Implements WebAssembly binary encoding version 1.

• The Go package API hasn't been finalized.

• The snapshot-and-restore functionality is beta quality.

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 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 open(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:73: 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:81: resuming
	snapshot_test.go:93: print output:
		20
		30
		330
		40
		440