Investigate wasm32-wasi build support

[lopopolo]

Investigate compiling Artichoke on the wasm32-wasi target. Such an artifact would be able to be run with wasmtime [GitHub] or wasmer [GitHub].

Notes

Since Artichoke has C dependencies (mruby, oniguruma) and depends on the cc crate, it is necessary to provide a C (or soon C++) compiler that can target wasm32-wasi as well as a suitable libc and sysroot.

wasi-sdk provides these things and bundles wasi-libc.

Status

2022-07-23

Artichoke is not able to build for WASI. Per WebAssembly/wasi-sdk#Notable Limitations:

This repository does not yet support C++ exceptions. C++ code is
supported only with -fno-exceptions for now. Similarly, there is not
yet support for setjmp/longjmp. Work on support for exception handling
is underway at the language level which will support both of these
features.

Currently, Artichoke's configuration of mruby uses setjmp/longjmp. After #1904 is merged, Artichoke's configuration of mruby will use C++ exceptions.

The compilation errors look like:

  running: "/wasi-sdk/wasi-sdk-16.0/bin/clang" "--sysroot=/wasi-sdk/wasi-sdk-16.0/share/wasi-sysroot" "-O0" "-ffunction-sections" "-fdata-sections" "-fPIC" "-g" "-fno-omit-frame-pointer" "--target=wasm32-wasi" "-I" "/app2/artichoke-backend/vendor/mruby/include" "-I" "/app2/artichoke-backend/vendor/mruby/mrbgems/mruby-class-ext/include" "-I" "/app2/artichoke-backend/vendor/mruby/mrbgems/mruby-compiler/core" "-I" "/app2/artichoke-backend/vendor/mruby/mrbgems/mruby-error/include" "-I" "/app2/artichoke-backend/vendor/mruby/mrbgems/mruby-eval/include" "-I" "/app2/artichoke-backend/vendor/mruby/mrbgems/mruby-fiber/include" "-I" "/app2/artichoke-backend/vendor/mruby/mrbgems/mruby-metaprog/include" "-I" "/app2/artichoke-backend/vendor/mruby/mrbgems/mruby-method/include" "-I" "/app2/artichoke-backend/vendor/mruby/mrbgems/mruby-pack/include" "-I" "/app2/artichoke-backend/vendor/mruby/mrbgems/mruby-proc-ext/include" "-I" "/app2/artichoke-backend/vendor/mruby/mrbgems/mruby-sprintf/include" "-I" "/app2/artichoke-backend/vendor/mruby/include" "-I" "/app2/artichoke-backend/cext/mrbsys/include" "-I" "/app2/artichoke-backend/vendor/mruby/include" "-DARTICHOKE" "-DMRB_ARY_NO_EMBED" "-DMRB_GC_TURN_OFF_GENERATIONAL" "-DMRB_INT64" "-DMRB_NO_BOXING" "-DMRB_NO_PRESYM" "-DMRB_NO_STDIO" "-DMRB_UTF8_STRING" "-o" "/app2/target/wasm32-wasi/debug/build/artichoke-backend-128c0ff89637f957/out/vendor/mruby/src/error.o" "-c" "vendor/mruby/src/error.c"
  cargo:warning=In file included from vendor/mruby/src/error.c:17:
  cargo:warning=/app2/artichoke-backend/vendor/mruby/include/mruby/throw.h:33:10: fatal error: 'setjmp.h' file not found
  cargo:warning=#include <setjmp.h>
  cargo:warning=         ^~~~~~~~~~
  cargo:warning=1 error generated.
  exit status: 1

There is an open RFC against wasi-sdk to add support for Wasm exceptions:

• [RFC] Add Wasm exception support WebAssembly/wasi-sdk#198

Build Steps

I'm not sure whether the wasi-sdk works on non-Linux environments. The below steps use Docker on macOS.

lopopolo@macos:/path/to/artichoke# cargo clean
lopopolo@macos:/path/to/artichoke# docker run -it -v `pwd`:/app rust:1.62.1 bash
root@ec467dc9a04d:/# rustup target add wasm32-wasi
info: downloading component 'rust-std' for 'wasm32-wasi'
info: installing component 'rust-std' for 'wasm32-wasi'
 17.0 MiB /  17.0 MiB (100 %)  14.9 MiB/s in  1s ETA:  0s
root@ec467dc9a04d:/# mkdir /app2
root@ec467dc9a04d:/# cp -r app/* app2/
root@ec467dc9a04d:/# mkdir wasi-sdk
root@ec467dc9a04d:/# cd wasi-sdk/
root@ec467dc9a04d:/wasi-sdk# export WASI_VERSION=16
root@ec467dc9a04d:/wasi-sdk# export WASI_VERSION_FULL=${WASI_VERSION}.0
root@ec467dc9a04d:/wasi-sdk# wget https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-${WASI_VERSION}/wasi-sdk-${WASI_VERSION_FULL}-linux.tar.gz
... snip ...
root@ec467dc9a04d:/wasi-sdk# tar xvf wasi-sdk-${WASI_VERSION_FULL}-linux.tar.gz
... snip ...
root@ec467dc9a04d:/wasi-sdk# export WASI_SDK_PATH=`pwd`/wasi-sdk-${WASI_VERSION_FULL}
root@ec467dc9a04d:/wasi-sdk# export CC="${WASI_SDK_PATH}/bin/clang --sysroot=${WASI_SDK_PATH}/share/wasi-sysroot"
root@ec467dc9a04d:/wasi-sdk# cd /app2
root@ec467dc9a04d:/app2# cargo build --target wasm32-wasi --no-default-features --features kitchen-sink
... snip ...
The following warnings were emitted during compilation:

warning: In file included from vendor/mruby/src/error.c:17:
warning: /app2/artichoke-backend/vendor/mruby/include/mruby/throw.h:33:10: fatal error: 'setjmp.h' file not found
warning: #include <setjmp.h>
warning:          ^~~~~~~~~~
warning: 1 error generated.

error: failed to run custom build command for `artichoke-backend v0.13.0 (/app2/artichoke-backend)`
... snip ...
warning: build failed, waiting for other jobs to finish...

[lopopolo]

TODO: add O-wasm-wasi label.

[lopopolo]

This ticket is likely to be the solution to:

• Add support for the wasm32-unknown-unknown build target #54