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Rollup merge of rust-lang#126967 - alexcrichton:wasm32-wasip2-tier-2,…
… r=Mark-Simulacrum Promote the `wasm32-wasip2` target to Tier 2 This commit promotes the `wasm32-wasip2` Rust target to tier 2 as proposed in rust-lang/compiler-team#760. There are two major changes in this PR: 1. The `dist-various-2` container, which already produces the other WASI targets, now has an extra target added for `wasm32-wasip2`. 2. A new `wasm-component-ld` binary is added to all host toolchains when LLD is enabled. This is the linker used for the `wasm32-wasip2` target. This new linker is added for all host toolchains to ensure that all host toolchains can produce the `wasm32-wasip2` target. This is similar to how `rust-lld` was originally included for all host toolchains to be able to produce WebAssembly output when the targets were first added. The new linker is developed [here][wasm-component-ld] and is pulled in via a crates.io-based dependency to the tree here. [wasm-component-ld]: https://github.com/bytecodealliance/wasm-component-ld
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| # See the `README.md` in this directory for what this tool is. | ||
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| [package] | ||
| name = "wasm-component-ld-wrapper" | ||
| version = "0.1.0" | ||
| edition = "2021" | ||
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| [[bin]] | ||
| name = "wasm-component-ld" | ||
| path = "src/main.rs" | ||
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| [dependencies] | ||
| wasm-component-ld = "0.5.4" |
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| # `wasm-component-ld` | ||
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| This wrapper is a wrapper around the [`wasm-component-ld`] crates.io crate. That | ||
| crate. That crate is itself a thin wrapper around two pieces: | ||
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| * `wasm-ld` - the LLVM-based linker distributed as part of LLD and packaged in | ||
| Rust as `rust-lld`. | ||
| * [`wit-component`] - a Rust crate for creating a [WebAssembly Component] from a | ||
| core wasm module. | ||
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| This linker is used for Rust's `wasm32-wasip2` target to natively output a | ||
| component instead of a core WebAssembly module, unlike other WebAssembly | ||
| targets. If you're confused about any of this here's an FAQ-style explanation of | ||
| what's going on here: | ||
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| * **What's a component?** - It's a proposal to the WebAssembly standard | ||
| primarily developed at this time by out-of-browser use cases of WebAssembly. | ||
| You can find high-level documentation [here][component docs]. | ||
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| * **What's WASIp2?** - Not to be confused with WASIp1, WASIp0, | ||
| `wasi_snapshot_preview1`, or `wasi_unstable`, it's a version of WASI. Released | ||
| in January 2024 it's the first version of WASI defined in terms of the | ||
| component model. | ||
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| * **Why does this need its own linker?** - like any target that Rust has the | ||
| `wasm32-wasip2` target needs a linker. What makes this different from other | ||
| WebAssembly targets is that WASIp2 is defined at the component level, not core | ||
| WebAssembly level. This means that filesystem functions take a `string` | ||
| instead of `i32 i32`, for example. This means that the raw output of LLVM and | ||
| `wasm-ld`, a core WebAssembly module, is not suitable. | ||
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| * **Isn't writing a linker really hard?** - Generally, yes, but this linker | ||
| works by first asking `wasm-ld` to do all the hard work. It invokes `wasm-ld` | ||
| and then uses the output core WebAssembly module to create a component. | ||
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| * **How do you create a component from a core module?** - this is the purpose of | ||
| the [`wit-component`] crate, notably the `ComponentEncoder` type. This uses | ||
| component type information embedded in the core module and a general set of | ||
| conventions/guidelines with what the core module imports/exports. A component | ||
| is then hooked up to codify all of these conventions in a component itself. | ||
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| * **Why not require users to run `wit-component` themselves?** - while possible | ||
| it adds friction to the usage `wasm32-wasip2` target. More importantly though | ||
| the "module only" output of the `wasm32-wasip2` target is not ready right now. | ||
| The standard library still imports from `wasi_snapshot_preview1` and it will | ||
| take time to migrate all usage to WASIp2. | ||
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| * **What exactly does this linker do?** - the `wasm-component-ld` has the same | ||
| CLI interface and flags as `wasm-ld`, plus some more that are | ||
| component-specific. These flags are used to forward most flags to `wasm-ld` to | ||
| produce a core wasm module. After the core wasm module is produced the | ||
| `wit-component` crate will read custom sections in the final binary which | ||
| contain component type information. After merging all this type information | ||
| together a component is produced which wraps the core module. | ||
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| If you've got any other questions about this linker or its operation don't | ||
| hesitate to reach out to the maintainers of the `wasm32-wasip2` target. | ||
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| [`wasm-component-ld`]: https://crates.io/crates/wasm-component-ld | ||
| [`wit-component`]: https://crates.io/crates/wit-component | ||
| [WebAssembly Component]: https://github.com/webassembly/component-model | ||
| [component docs]: https://component-model.bytecodealliance.org/ |
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| // See the `README.md` in this directory for what this tool is. | ||
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| // The source for this crate lives at | ||
| // https://github.com/bytecodealliance/wasm-component-ld and the binary is | ||
| // independently used in other projects such as `wasi-sdk` so the `main` | ||
| // function is just reexported here to delegate. A Cargo dependency is used to | ||
| // facilitate version management in the Rust repository and work well with | ||
| // vendored/offline builds. | ||
| use wasm_component_ld::main; |