Update a few aspects of the adapter build (#17)

* Update a few aspects of the adapter build

* Use the `wasm32-unknown-unknown` target for the adapter and specify
  flags in `.cargo/config.toml` to avoid having to pass the same flags
  everywhere. This allows using `wasm32-wasi` for tests to ensure the
  flags only apply to the adapter.

* Use `opt-level=s` since speed is not of the utmost concern for this
  wasm but since it's likely to be included in many places size is
  likely more important.

* Use `strip = 'debuginfo'` for the release build to remove the standard
  library's debugging information which isn't necessary.

* Remove `debug = 0` from the `dev` profile to have debugging
  information for development.

* Add a small `README.md` describing what's here for now.

* Move `command` support behind a `command` feature

This commit adds a `command` feature to main crate to avoid importing
the `_start` function when the `command` feature is disabled, making
this adapter useful for non-command WASI programs as well.

For now this still emits the `command` export in the final component but
with `use` in `*.wit` files it should be easier to avoid that export.

Author: alexcrichton

.cargo/config.toml

@@ -1,2 +1,18 @@
-[target.wasm32-wasi]
-#rustflags = ['-Clink-arg=--import-memory']
+# The adapter module created in this repository can technically be either
+# compiled for wasm32-wasi or the unknown-unknown target but the unknown version
+# is used to be able to specify custom flags here. That way the wasi tests don't
+# use these custom flags but the adapter does.
+[target.wasm32-unknown-unknown]
+rustflags = [
+  # The adapter must import its memory from the main module so pass this for LLD
+  # to generate the right memory import.
+  '-Clink-arg=--import-memory',
+  # The adapter will allocate its own stack and doesn't use the --stack-first
+  # layout that LLD has by default. Set the stack size from LLD to zero here to
+  # ensure that the memory imported into the module has a minimum size of 0 as
+  # opposed to 1MB which might not be compatible with some WASI-using modules.
+  '-Clink-arg=-zstack-size=0',
+  # Currently all locations that will run this adapter have this feature enabled
+  # and this avoid generating a `memcpy` function in the adapter itself.
+  '-Ctarget-feature=+bulk-memory',
+]

.github/workflows/main.yml

@@ -29,15 +29,15 @@ jobs:
     steps:
     - uses: actions/checkout@v3
     - run: rustup update stable && rustup default stable
-    - run: rustup target add wasm32-wasi
-    - run: cargo build --target wasm32-wasi
-      env:
-        RUSTFLAGS: -Clink-args=--import-memory -Ctarget-feature=+bulk-memory -Clink-args=-zstack-size=0
-    - run: cargo run -p verify -- ./target/wasm32-wasi/debug/wasi_snapshot_preview1.wasm
-    - run: cargo build --release --target wasm32-wasi
-      env:
-        RUSTFLAGS: -Clink-args=--import-memory -Ctarget-feature=+bulk-memory -Clink-args=-zstack-size=0
-    - run: cargo run -p verify -- ./target/wasm32-wasi/release/wasi_snapshot_preview1.wasm
+    - run: rustup target add wasm32-wasi wasm32-unknown-unknown
+    - run: cargo build --target wasm32-unknown-unknown
+    - run: cargo run -p verify -- ./target/wasm32-unknown-unknown/debug/wasi_snapshot_preview1.wasm
+    - run: cargo build --target wasm32-unknown-unknown --features command
+    - run: cargo run -p verify -- ./target/wasm32-unknown-unknown/debug/wasi_snapshot_preview1.wasm
+    - run: cargo build --release --target wasm32-unknown-unknown
+    - run: cargo run -p verify -- ./target/wasm32-unknown-unknown/release/wasi_snapshot_preview1.wasm
+    - run: cargo build --release --target wasm32-unknown-unknown --features command
+    - run: cargo run -p verify -- ./target/wasm32-unknown-unknown/release/wasi_snapshot_preview1.wasm
     - run: cargo test -p host
 
   build:
@@ -49,14 +49,18 @@ jobs:
     steps:
     - uses: actions/checkout@v3
     - run: rustup update stable && rustup default stable
-    - run: rustup target add wasm32-wasi
-    - run: cargo build --target wasm32-wasi --release
-      env:
-        RUSTFLAGS: -Clink-args=--import-memory -Ctarget-feature=+bulk-memory -Clink-args=-zstack-size=0
+    - run: rustup target add wasm32-wasi wasm32-unknown-unknown
+    - run: cargo build --target wasm32-unknown-unknown --release --features command
+    - run: mv target/wasm32-unknown-unknown/release/wasi_snapshot_preview1.wasm wasi_snapshot_preview1.command.wasm
+    - uses: actions/upload-artifact@v3
+      with:
+        name: wasi_snapshot_preview1.command.wasm
+        path: wasi_snapshot_preview1.command.wasm
+    - run: cargo build --target wasm32-unknown-unknown --release
     - uses: actions/upload-artifact@v3
       with:
         name: wasi_snapshot_preview1.wasm
-        path: target/wasm32-wasi/release/wasi_snapshot_preview1.wasm
+        path: target/wasm32-unknown-unknown/release/wasi_snapshot_preview1.wasm
 
     - uses: marvinpinto/action-automatic-releases@latest
       if: github.event_name == 'push' && github.ref == 'refs/heads/main'
@@ -65,4 +69,6 @@ jobs:
         automatic_release_tag: latest
         prerelease: true
         title: "Latest Build"
-        files: target/wasm32-wasi/release/wasi_snapshot_preview1.wasm
+        files: |
+          target/wasm32-unknown-unknown/release/wasi_snapshot_preview1.wasm
+          wasi_snapshot_preview1.command.wasm

Cargo.toml

@@ -22,12 +22,18 @@ crate-type = ["cdylib"]
 # that could theoretically change in the future.
 panic = 'abort'
 
+[profile.release.package.wasi_snapshot_preview1]
+opt-level = 's'
+strip = 'debuginfo'
+
 # Make dev look like a release build since this adapter module won't work with
 # a debug build that uses data segments and such.
 [profile.dev.package.wasi_snapshot_preview1]
 incremental = false
-opt-level = 3
-debug = 0
+opt-level = 's'
 # Omit integer overflow checks, which include failure messages which require
 # string initializers.
 overflow-checks = false
+
+[features]
+command = []

README.md

@@ -0,0 +1,56 @@
+# `wasi_snapshot_preview1.wasm`
+
+> **Note**: This repository is a work in progress. This is intended to be an
+> internal tool which not everyone has to look at but many might rely on. You
+> may need to reach out via issues or
+> [Zulip](https://bytecodealliance.zulipchat.com/) to learn more about this
+> repository.
+
+This repository currently contains an implementation of a WebAssembly module:
+`wasi_snapshot_preview1.wasm`. This module bridges the `wasi_snapshot_preview1`
+ABI to the preview2 ABI of the component model. At this time the preview2 APIs
+themselves are not done being specified so a local copy of `wit/*.wit` is used
+instead.
+
+## Building
+
+This adapter can be built with:
+
+```sh
+$ cargo build --target wasm32-unknown-unknown --release
+```
+
+And the artifact will be located at
+`target/wasm32-unknown-unknown/release/wasi_snapshot_preview1.wasm`.
+Alternatively the latest copy of this can be [downloaded from the releases
+page][latest-release]
+
+[latest-release]: https://github.com/bytecodealliance/preview2-prototyping/releases/tag/latest
+
+## Using
+
+With a `wasi_snapshot_preview1.wasm` file on-hand you can create a component
+from a module that imports WASI functions using the [`wasm-tools`
+CLI](https://github.com/bytecodealliance/wasm-tools)
+
+```sh
+$ cat foo.rs
+fn main() {
+    println!("Hello, world!");
+}
+$ rustc foo.rs --target wasm32-wasi
+$ wasm-tools print foo.wasm | grep '(import'
+  (import "wasi_snapshot_preview1" "fd_write" (func ...
+  (import "wasi_snapshot_preview1" "environ_get" (func ...
+  (import "wasi_snapshot_preview1" "environ_sizes_get" ...
+  (import "wasi_snapshot_preview1" "proc_exit" (func ...
+$ wasm-tools component new foo.wasm --adapt wasi_snapshot_preview1.wasm -o component.wasm
+
+# Inspect the generated `component.wasm`
+$ wasm-tools validate component.wasm --features component-model
+$ wasm-tools component wit component.wasm
+```
+
+Here the `component.wasm` that's generated is a ready-to-run component which
+imports wasi preview2 functions and is compatible with the wasi-preview1-using
+module internally.

src/lib.rs

@@ -25,13 +25,19 @@ mod bindings {
     });
 }
 
-#[export_name = "command"]
-unsafe extern "C" fn command_entrypoint(
+#[no_mangle]
+pub unsafe extern "C" fn command(
     stdin: u32,
     stdout: u32,
     args_ptr: *const WasmStr,
     args_len: usize,
 ) {
+    // TODO: ideally turning off `command` would remove this import and the
+    // `*.wit` metadata entirely but doing that ergonomically will likely
+    // require some form of `use` to avoid duplicating lots of `*.wit` bits.
+    if !cfg!(feature = "command") {
+        unreachable();
+    }
     State::with_mut(|state| {
         state.push_desc(Descriptor::File(File {
             fd: stdin,
@@ -1430,7 +1436,7 @@ struct State {
     args: Option<&'static [WasmStr]>,
 }
 
-struct WasmStr {
+pub struct WasmStr {
     ptr: *const u8,
     len: usize,
 }

test-programs/macros/build.rs

@@ -14,17 +14,14 @@ fn main() {
     cmd.arg("build")
         .arg("--release")
         .current_dir("../../")
-        .arg("--target=wasm32-wasi")
+        .arg("--target=wasm32-unknown-unknown")
+        .arg("--features=command")
         .env("CARGO_TARGET_DIR", &out_dir)
-        .env(
-            "RUSTFLAGS",
-            "-Clink-args=--import-memory -Clink-args=-zstack-size=0",
-        )
         .env_remove("CARGO_ENCODED_RUSTFLAGS");
     let status = cmd.status().unwrap();
     assert!(status.success());
 
-    let wasi_adapter = out_dir.join("wasm32-wasi/release/wasi_snapshot_preview1.wasm");
+    let wasi_adapter = out_dir.join("wasm32-unknown-unknown/release/wasi_snapshot_preview1.wasm");
     println!("wasi adapter: {:?}", &wasi_adapter);
     let wasi_adapter = fs::read(&wasi_adapter).unwrap();