Executing WebAssembly in Teaclave

Teaclave integrates WebAssembly Micro Runtime as an executor, which can interpret WebAssembly bytecode in a sandboxed environment. Theoretically, source code written in any language which can be compiled to WebAssembly should also be executable in Teaclave. However, in order to be more secure, Teaclave cannot provide interfaces such as syscalls to legacy applications, so the source code should:

1. Be self-contained: not depending on libraries which are not provided by Teaclave, including standard libraries.
2. Contains no syscall: no system call-related code.
3. Implement required interface: exporting an int entrypoint(int argc, char* argv[]) function which is compatible with Teaclave WAMR calling convention (see examples for more details).

Currently, Teaclave file system APIs are supported. We also provide examples for compiling and executing from source code of various languages.

NOTE

In current Teaclave client SDK, when passing arguments to the registered function, each (key, value) pair is converted into two string pointers in argv and you should expect argc is as twice as the actual number of arguments. The calling convention is subject to further changes.

From C

clang supporting wasm32 can be used for compiling Teaclave-compatible WASM bytecode. Remember to add following options while compiling:

--target=wasm32 \
-nostdlib \
-Wl,--no-entry \
-Wl,--export-all, \
-Wl,--allow-undefined 

You can also use clang provided by wasi-sdk, and the option --target=wasm32 is not needed for this version. We also provide an example payload written in C.

Alternatively, C and C++ code can be compiled with zig:

zig cc  -Os --target=wasm32-freestanding -shared -o example.wasm example.c
zig c++ -Os --target=wasm32-freestanding -shared -o example.wasm example.cpp

From Rust

First of all, your cargo should support wasm32 target and wasm-gc is required to reduce the size of generated binary. You can easily run the following commands to install dependencies:

rustup target add wasm32-unknown-unknown
cargo install wasm-gc

There should be an exported entrypoint function in the source code, so you can simply use cargo to create a new library and generate it with cargo build --target wasm32-unknown-unknown. Please also add crate-type = ["cdylib"] in the [lib] section into your Cargo.toml file to let cargo generate WASM file. To reduce the size of WASM file, run:

cargo build --target wasm32-unknown-unknown --release
wasm-gc target/wasm32-unknown-unknown/release/[WASM FILENAME]

For detailed optimization options and function signature, please refer to the example payload.

References

• Compiling Rust to WebAssembly: A Simple Example