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 wasm binary module.
-
The output is machine code.
-
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 an example 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
directly supported, but see wasys for an example which exposes
syscalls as WebAssembly import functions. -
Supports snapshot-and-restore across compiler versions and CPU architectures.
-
Supports breakpoint debugging via recompilation.
-
Cross-compilation is supported via Go build tags. If
wagamd64is
specified, the x86-64 code generator is used regardless of host architecture,
and CPU feature detection is disabled with pessimistic assumptions. Likewise
forwagarm64(but feature detection is not used for ARM64).
Status
-
Supports WebAssembly version 1 (wasm32). No wasm extensions are supported.
-
Supports x86-64 and ARM64 code generation.
-
Generated x86-64 code requires SSE4.1 ROUNDSS/ROUNDSD instructions.
Security
Spectre variant 1: Out-of-bounds linear memory
access detection requires that addressable but unallocated memory is
inaccessible. It naturally prevents conditional branch exploitation.
Spectre variant 2: On x86, Retpoline
is used to protect the runtime environment (although user programs shouldn't be
able to inject arbitrary addresses into the branch target buffer).
Testing
Requires Linux, Go, make, cmake, clang++ and libcapstone. About 75% of the
WebAssembly spec testsuite is run, by first converting the tests to binary
format:
git clone --recurse-submodules https://github.com/tsavola/wag.gitcd wagmake check
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