Embedding WebAssembly in Rust

下町.rs の資料です。
https://shitamachi.connpass.com/event/173972/

Transcript

1. Embedding WebAssembly in Rust 下町.rs @TaigaMerlin
2. Agenda • Introduction • WebAssembly overview • WebAssembly ABI • WebAssembly toolchain • Embedding WebAssembly into Rust @TaigaMerlin
3. Introduction 半導体 電子回路 信号処理 ソフト
6. I like binaries 00000000 00 61 73 6d 01 00 00 00 01 6a 10 60 02 7f 7f 01 |.asm.....j.`....| 00000010 7f 60 02 7f 7f 00 60 01 7f 00 60 03 7f 7f 7f 01 |.`....`...`.....| 00000020 7f 60 03 7f 7f 7f 00 60 01 7f 01 7f 60 04 7f 7f |.`.....`....`...| 00000030 7f 7f 00 60 00 00 60 01 7f 01 7e 60 00 01 7f 60 |...`..`...~`...`| 00000040 04 7f 7f 7f 7f 01 7f 60 05 7f 7f 7f 7f 7f 00 60 |.......`.......`| 00000050 05 7f 7f 7f 7f 7f 01 7f 60 06 7f 7f 7f 7f 7f 7f |........`.......| 00000060 01 7f 60 07 7f 7f 7f 7f 7f 7f 7f 01 7f 60 03 7e |..`..........`.~| 00000070 7f 7f 01 7f 02 eb 01 06 16 77 61 73 69 5f 73 6e |.........wasi_sn| 00000080 61 70 73 68 6f 74 5f 70 72 65 76 69 65 77 31 09 |apshot_preview1.| 00000090 70 72 6f 63 5f 65 78 69 74 00 02 16 77 61 73 69 |proc_exit...wasi| 000000a0 5f 73 6e 61 70 73 68 6f 74 5f 70 72 65 76 69 65 |_snapshot_previe| 000000b0 77 31 08 66 64 5f 77 72 69 74 65 00 0a 16 77 61 |w1.fd_write...wa| 000000c0 73 69 5f 73 6e 61 70 73 68 6f 74 5f 70 72 65 76 |si_snapshot_prev| 000000d0 69 65 77 31 0e 66 64 5f 70 72 65 73 74 61 74 5f |iew1.fd_prestat_| 000000e0 67 65 74 00 00 16 77 61 73 69 5f 73 6e 61 70 73 |get...wasi_snaps| 000000f0 68 6f 74 5f 70 72 65 76 69 65 77 31 13 66 64 5f |hot_preview1.fd_| 00000100 70 72 65 73 74 61 74 5f 64 69 72 5f 6e 61 6d 65 |prestat_dir_name| 00000110 00 03 16 77 61 73 69 5f 73 6e 61 70 73 68 6f 74 |...wasi_snapshot| @TaigaMerlin
7. Binary code format that runs in a host environment
8. Not just for the web! (See WASI)
9. WebAssembly overview
10. WebAssembly Runtime
11. WebAssembly Runtime
12. Imports and Exports
13. WebAssembly ABIs • ABI: Application Binary Interface • What functions does the host provide? (what can be imported?) • What functions should the module expose? (what should be exported?) • WASM modules are sandboxed ◦ do not have access to stdout ◦ nothing runs until called upon • Commonly used ◦ Emscripten (POSIX-like) => wasm32-unknown-emscripten ◦ WASI (WebAssembly System Interface, capability based) => wasm32-wasi ▪ Officially supported since Rust 1.36
14. WASI is supported on multiple platforms
15. Quick overview of the toolchain
16. WASM toolchain Compile time
17. WASM toolchain Runtime JIT
18. WASM toolchain ???
19. ZIP爆弾、ありますよね 関係ないが、46MB => 4.5PBいけるらしいです
20. コンパイラいじめ、ご存知ですか？ はい、コンパイラの「テスター」とも言えますね
21. JIT爆弾もあるんですよ
22. WASM toolchain ???
23. Backend comparison
24. Let’s look at some binaries!
25. Rust WASM module: fn main() { eprintln!(“hello world”); } ---- $ cargo wasi build --release
26. WASI Imports and Exports $ wasm-objdump -x target/wasm32-wasi/release/shitamachi-rs.rustc.wasm [...] Import[6]: - func[0] sig=1 <__wasi_proc_exit> <- wasi_snapshot_preview1.proc_exit - func[1] sig=9 <_ZN4wasi13lib_generated22wasi_snapshot_preview18fd_write17h62539b3299a4581fE> <- wasi_snapshot_preview1.fd_write - func[2] sig=3 <__wasi_fd_prestat_get> <- wasi_snapshot_preview1.fd_prestat_get - func[3] sig=8 <__wasi_fd_prestat_dir_name> <- wasi_snapshot_preview1.fd_prestat_dir_name - func[4] sig=3 <__wasi_environ_sizes_get> <- wasi_snapshot_preview1.environ_sizes_get - func[5] sig=3 <__wasi_environ_get> <- wasi_snapshot_preview1.environ_get Export[6]: - memory[0] -> "memory" - func[163] <_start> -> "_start" - func[150] <__original_main> -> "__original_main" - func[190] <main> -> "main" - global[1] -> "__data_end" - global[2] -> "__heap_base" [...]
27. Demo: run it in wasmer
28. Demo: run it in wasmer $ ~/.wasmer/bin/wasmer ./target/wasm32-wasi/release/shitamachi-rs.wasm hello world
29. That wasn’t too interesting...
30. Let’s make it more interesting • Wasmer is an embeddable WASM runtime • We can write our own Rust program that will run WASM code fn main() -> error::Result<()> { let wasm_bytes = include_bytes!("my-module.wasm"); let import_object = imports! {}; let instance = instantiate(wasm_bytes, &import_object)?; instance.call("my_function", &[])?; Ok(()) }
31. Let’s fake implement the required WASI functions! let wasm_bytes = include_bytes!("print.wasm"); let import_object = imports! { "wasi_snapshot_preview1" => { "proc_exit" => func!(wasi_proc_exit), "fd_write" => func!(wasi_fd_write), "fd_prestat_get" => func!(wasi_fd_prestat_get), "fd_prestat_dir_name" => func!(wasi_fd_prestat_dir_name), "environ_sizes_get" => func!(wasi_environ_sizes_get), "environ_get" => func!(wasi_environ_get), }, }; let instance = instantiate(wasm_bytes, &import_object)?; instance.call("_start", &[])?;
32. With some hacks like this... fn wasi_fd_prestat_get(_ctx: &mut Ctx, _fd: u32, _ptr: WasmPtr<__wasi_prestat_t>) -> u16 { println!("fd_prestat_get"); return __WASI_EBADF; } fn wasi_fd_prestat_dir_name( _ctx: &mut Ctx, _fd: u32, _path: WasmPtr<u8, Array>, _path_len: u32, ) -> u16 { println!("fd_prestat_dir_name"); return __WASI_EBADF; }
33. And more late night hacks... fn wasi_fd_write(ctx: &mut Ctx, fd: u32, iovs: WasmPtr<__wasi_ciovec_t, Array>, iovs_len: u32, nwritten: WasmPtr<u32> ) -> u32 { let memory = ctx.memory(0); let iovs_ptr = iovs.deref(memory, 0, iovs_len).unwrap(); let nwritten_ptr = nwritten.deref(memory).unwrap(); let total_len = iovs_ptr.iter().map(|iov| iov.get().buf_len).fold(0, |acc, x| acc + x); let data_arr = iovs_ptr.iter().map(|iov| get_array(&*ctx, iov.get())) .flat_map(|s| s.into_iter()).collect::<Vec<u8>>(); let data_str = std::str::from_utf8(data_arr.as_slice()).unwrap(); println!("wasi_fd_write fd={} byte_len={} bytes={}", fd, total_len, data_str); nwritten_ptr.set(total_len); return 0; }
34. And we can see the WASI syscalls! $ cargo run Compiling wasmer-test v0.1.0 (/code/wasmer-test) Finished dev [unoptimized + debuginfo] target(s) in 2.60s Running `target/debug/wasmer-test` environ_sizes_get fd_prestat_get wasi_fd_write fd=1 byte_len=11 bytes= hello world • It’s printing to stdout via a call into a host-provided fd_write() function • WASI syscalls allow modules to access restricted resources
35. • We are going to run JavaScript in the browser! • Via a JavaScript interpreter compiled to WASM • Running on top of the V8 engine • https://webassembly.sh/?run-command=quickjs Let’s take a look at QuickJS on webassembly.sh
36. Wrapping up • WASI is still highly experimental and not stable • Rust has full WASI support built into the toolchain • The inner workings of WASM/WASI are quite simple • Rust x WASI has many interesting cross-platform use cases @TaigaMerlin
37. Thank you for listening @TaigaMerlin