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Add a new
wasm32-wasi-preview1 target to rustc
This commit adds a new target called `wasm32-wasi-preview1` to rustc. This new target is explained in these two MCPs: * rust-lang/compiler-team#606 * rust-lang/compiler-team#695 In short, the previous `wasm32-wasi` target is going to be renamed to `wasm32-wasi-preview1` to better live alongside the [new `wasm32-wasi-preview2` target](#119616). This new target is added alongside the `wasm32-wasi` target and has the exact same definition as the previous target. This PR is effectively a rename of `wasm32-wasi` to `wasm32-wasi-preview1`. Note, however, that as explained in rust-lang/compiler-team#695 the previous `wasm32-wasi` target is not being removed at this time. This change will reach stable Rust before even a warning about the rename will be printed. At this time this change is just the start where a new target is introduced and users can start migrating if they support only Nightly for example.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
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| //! The `wasm32-wasi` target is a new and still (as of April 2019) an | ||
| //! experimental target. The definition in this file is likely to be tweaked | ||
| //! over time and shouldn't be relied on too much. | ||
| //! NB: This target is in the process of being renamed to | ||
| //! `wasm32-wasi-preview1`. For more information see: | ||
| //! | ||
| //! The `wasi` target is a proposal to define a standardized set of syscalls | ||
| //! that WebAssembly files can interoperate with. This set of syscalls is | ||
| //! intended to empower WebAssembly binaries with native capabilities such as | ||
| //! filesystem access, network access, etc. | ||
| //! | ||
| //! You can see more about the proposal at <https://wasi.dev>. | ||
| //! | ||
| //! The Rust target definition here is interesting in a few ways. We want to | ||
| //! serve two use cases here with this target: | ||
| //! | ||
| //! * First, we want Rust usage of the target to be as hassle-free as possible, | ||
| //! ideally avoiding the need to configure and install a local wasm32-wasi | ||
| //! toolchain. | ||
| //! | ||
| //! * Second, one of the primary use cases of LLVM's new wasm backend and the | ||
| //! wasm support in LLD is that any compiled language can interoperate with | ||
| //! any other. To that the `wasm32-wasi` target is the first with a viable C | ||
| //! standard library and sysroot common definition, so we want Rust and C/C++ | ||
| //! code to interoperate when compiled to `wasm32-unknown-unknown`. | ||
| //! | ||
| //! You'll note, however, that the two goals above are somewhat at odds with one | ||
| //! another. To attempt to solve both use cases in one go we define a target | ||
| //! that (ab)uses the `crt-static` target feature to indicate which one you're | ||
| //! in. | ||
| //! | ||
| //! ## No interop with C required | ||
| //! | ||
| //! By default the `crt-static` target feature is enabled, and when enabled | ||
| //! this means that the bundled version of `libc.a` found in `liblibc.rlib` | ||
| //! is used. This isn't intended really for interoperation with a C because it | ||
| //! may be the case that Rust's bundled C library is incompatible with a | ||
| //! foreign-compiled C library. In this use case, though, we use `rust-lld` and | ||
| //! some copied crt startup object files to ensure that you can download the | ||
| //! wasi target for Rust and you're off to the races, no further configuration | ||
| //! necessary. | ||
| //! | ||
| //! All in all, by default, no external dependencies are required. You can | ||
| //! compile `wasm32-wasi` binaries straight out of the box. You can't, however, | ||
| //! reliably interoperate with C code in this mode (yet). | ||
| //! | ||
| //! ## Interop with C required | ||
| //! | ||
| //! For the second goal we repurpose the `target-feature` flag, meaning that | ||
| //! you'll need to do a few things to have C/Rust code interoperate. | ||
| //! | ||
| //! 1. All Rust code needs to be compiled with `-C target-feature=-crt-static`, | ||
| //! indicating that the bundled C standard library in the Rust sysroot will | ||
| //! not be used. | ||
| //! | ||
| //! 2. If you're using rustc to build a linked artifact then you'll need to | ||
| //! specify `-C linker` to a `clang` binary that supports | ||
| //! `wasm32-wasi` and is configured with the `wasm32-wasi` sysroot. This | ||
| //! will cause Rust code to be linked against the libc.a that the specified | ||
| //! `clang` provides. | ||
| //! | ||
| //! 3. If you're building a staticlib and integrating Rust code elsewhere, then | ||
| //! compiling with `-C target-feature=-crt-static` is all you need to do. | ||
| //! | ||
| //! You can configure the linker via Cargo using the | ||
| //! `CARGO_TARGET_WASM32_WASI_LINKER` env var. Be sure to also set | ||
| //! `CC_wasm32-wasi` if any crates in the dependency graph are using the `cc` | ||
| //! crate. | ||
| //! | ||
| //! ## Remember, this is all in flux | ||
| //! | ||
| //! The wasi target is **very** new in its specification. It's likely going to | ||
| //! be a long effort to get it standardized and stable. We'll be following it as | ||
| //! best we can with this target. Don't start relying on too much here unless | ||
| //! you know what you're getting in to! | ||
| //! * https://github.com/rust-lang/compiler-team/issues/607 | ||
| //! * https://github.com/rust-lang/compiler-team/issues/695 | ||
| use crate::spec::crt_objects; | ||
| use crate::spec::LinkSelfContainedDefault; | ||
| use crate::spec::{base, Cc, LinkerFlavor, Target}; | ||
| use crate::spec::Target; | ||
|
|
||
| pub fn target() -> Target { | ||
| let mut options = base::wasm::options(); | ||
|
|
||
| options.os = "wasi".into(); | ||
| options.add_pre_link_args(LinkerFlavor::WasmLld(Cc::Yes), &["--target=wasm32-wasi"]); | ||
|
|
||
| options.pre_link_objects_self_contained = crt_objects::pre_wasi_self_contained(); | ||
| options.post_link_objects_self_contained = crt_objects::post_wasi_self_contained(); | ||
|
|
||
| // FIXME: Figure out cases in which WASM needs to link with a native toolchain. | ||
| options.link_self_contained = LinkSelfContainedDefault::True; | ||
|
|
||
| // Right now this is a bit of a workaround but we're currently saying that | ||
| // the target by default has a static crt which we're taking as a signal | ||
| // for "use the bundled crt". If that's turned off then the system's crt | ||
| // will be used, but this means that default usage of this target doesn't | ||
| // need an external compiler but it's still interoperable with an external | ||
| // compiler if configured correctly. | ||
| options.crt_static_default = true; | ||
| options.crt_static_respected = true; | ||
|
|
||
| // Allow `+crt-static` to create a "cdylib" output which is just a wasm file | ||
| // without a main function. | ||
| options.crt_static_allows_dylibs = true; | ||
|
|
||
| // WASI's `sys::args::init` function ignores its arguments; instead, | ||
| // `args::args()` makes the WASI API calls itself. | ||
| options.main_needs_argc_argv = false; | ||
|
|
||
| // And, WASI mangles the name of "main" to distinguish between different | ||
| // signatures. | ||
| options.entry_name = "__main_void".into(); | ||
|
|
||
| Target { | ||
| llvm_target: "wasm32-wasi".into(), | ||
| pointer_width: 32, | ||
| data_layout: "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-n32:64-S128-ni:1:10:20".into(), | ||
| arch: "wasm32".into(), | ||
| options, | ||
| } | ||
| super::wasm32_wasi_preview1::target() | ||
| } |
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compiler/rustc_target/src/spec/targets/wasm32_wasi_preview1.rs
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| //! The `wasm32-wasi-preview1` enables compiling to WebAssembly using the first | ||
| //! version of the WASI standard, called "preview1". This version of the | ||
| //! standard was never formally specified and WASI has since evolved to a | ||
| //! "preview2". This target in rustc uses the previous version of the proposal. | ||
| //! | ||
| //! This target uses the syscalls defined at | ||
| //! <https://github.com/WebAssembly/WASI/tree/main/legacy/preview1>. | ||
| //! | ||
| //! Note that this target was historically called `wasm32-wasi` originally and | ||
| //! was since renamed to `wasm32-wasi-preview1` after the preview2 target was | ||
| //! introduced. | ||
| use crate::spec::crt_objects; | ||
| use crate::spec::LinkSelfContainedDefault; | ||
| use crate::spec::{base, Cc, LinkerFlavor, Target}; | ||
|
|
||
| pub fn target() -> Target { | ||
| let mut options = base::wasm::options(); | ||
|
|
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| options.os = "wasi".into(); | ||
| options.add_pre_link_args(LinkerFlavor::WasmLld(Cc::Yes), &["--target=wasm32-wasi"]); | ||
|
|
||
| options.pre_link_objects_self_contained = crt_objects::pre_wasi_self_contained(); | ||
| options.post_link_objects_self_contained = crt_objects::post_wasi_self_contained(); | ||
|
|
||
| // FIXME: Figure out cases in which WASM needs to link with a native toolchain. | ||
| options.link_self_contained = LinkSelfContainedDefault::True; | ||
|
|
||
| // Right now this is a bit of a workaround but we're currently saying that | ||
| // the target by default has a static crt which we're taking as a signal | ||
| // for "use the bundled crt". If that's turned off then the system's crt | ||
| // will be used, but this means that default usage of this target doesn't | ||
| // need an external compiler but it's still interoperable with an external | ||
| // compiler if configured correctly. | ||
| options.crt_static_default = true; | ||
| options.crt_static_respected = true; | ||
|
|
||
| // Allow `+crt-static` to create a "cdylib" output which is just a wasm file | ||
| // without a main function. | ||
| options.crt_static_allows_dylibs = true; | ||
|
|
||
| // WASI's `sys::args::init` function ignores its arguments; instead, | ||
| // `args::args()` makes the WASI API calls itself. | ||
| options.main_needs_argc_argv = false; | ||
|
|
||
| // And, WASI mangles the name of "main" to distinguish between different | ||
| // signatures. | ||
| options.entry_name = "__main_void".into(); | ||
|
|
||
| Target { | ||
| llvm_target: "wasm32-wasi".into(), | ||
| pointer_width: 32, | ||
| data_layout: "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-n32:64-S128-ni:1:10:20".into(), | ||
| arch: "wasm32".into(), | ||
| options, | ||
| } | ||
| } |
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119 changes: 119 additions & 0 deletions
119
src/doc/rustc/src/platform-support/wasm32-wasi-preview1.md
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| # `wasm32-wasi-preview1` | ||
|
|
||
| **Tier: 2** | ||
|
|
||
| The `wasm32-wasi-preview1` target is a WebAssembly compilation target which | ||
| assumes that the [WASI Preview1] set of "syscalls" are available for use in the | ||
| standard library. Historically this target in the Rust compiler was one of the | ||
| first for WebAssembly where Rust and C code are explicitly intended to | ||
| interoperate as well. | ||
|
|
||
| There's a bit of history to the target and current development which is also | ||
| worth explaining before going much further. Historically this target was | ||
| originally called `wasm32-wasi` in both rustc and Clang. This was first added | ||
| to Rust in 2019. In the intervening years leading up to 2024 the WASI standard | ||
| continued to be developed and was eventually "rebased" on top of the [Component | ||
| Model]. This was a large change to the WASI specification and was released as | ||
| 0.2.0 ("preview 2" colloquially) in January 2024. The previous target's name in | ||
| rustc, `wasm32-wasi`, was then renamed to `wasm32-wasi-preview1`, to avoid | ||
| confusion with this new target to be added to rustc as `wasm32-wasi-preview2`. | ||
| Some more context can be found in these MCPs: | ||
|
|
||
| * [Rename wasm32-wasi target to wasm32-wasi-preview1](https://github.com/rust-lang/compiler-team/issues/607) | ||
| * [Smooth the renaming transition of wasm32-wasi](https://github.com/rust-lang/compiler-team/issues/695) | ||
|
|
||
| At this point the `wasm32-wasi-preview1` target is intended for historical | ||
| compatibility with the first version of the WASI standard. As of now (January | ||
| 2024) the 0.2.0 target of WASI ("preview2") is relatively new. The state of | ||
| WASI will likely change in few years after which point this documentation will | ||
| probably receive another update. | ||
|
|
||
| [WASI Preview1]: https://github.com/WebAssembly/WASI/tree/main/legacy/preview1 | ||
| [Component Model]: https://github.com/webassembly/component-model | ||
|
|
||
| Today the `wasm32-wasi-preview1` target will generate core WebAssembly modules | ||
| which will import functions from the `wasi_snapshot_preview1` module for | ||
| OS-related functionality (e.g. printing). | ||
|
|
||
| ## Target maintainers | ||
|
|
||
| When this target was added to the compiler platform-specific documentation here | ||
| was not maintained at that time. This means that the list below is not | ||
| exhaustive and there are more interested parties in this target. That being | ||
| said since when this document was last updated those interested in maintaining | ||
| this target are: | ||
|
|
||
| - Alex Crichton, https://github.com/alexcrichton | ||
|
|
||
| ## Requirements | ||
|
|
||
| This target is cross-compiled. The target includes support for `std` itself, | ||
| but not all of the standard library works. For example spawning a thread will | ||
| always return an error (see the `wasm32-wasi-preview1-threads` target for | ||
| example). Another example is that spawning a process will always return an | ||
| error. Operations such as opening a file, however, will be implemented by | ||
| calling WASI-defined APIs. | ||
|
|
||
| The WASI targets for Rust are explicitly intended to interoperate with other | ||
| languages compiled to WebAssembly, for example C/C++. Any ABI differences or | ||
| mismatches are considered bugs that need to be fixed. | ||
|
|
||
| By default the WASI targets in Rust ship in rustup with a precompiled copy of | ||
| [`wasi-libc`] meaning that a WebAssembly-targetting-Clang is not required to | ||
| use the WASI targets from Rust. If there is no actual interoperation with C | ||
| then `rustup target add wasm32-wasi` is all that's needed to get started with | ||
| WASI. | ||
|
|
||
| Note that this behavior can be controlled with `-Clinker` and | ||
| `-Clink-self-contained`, however. By specifying `clang` as a linker and | ||
| disabling the `link-self-contained` option an external version of `libc.a` can | ||
| be used instead. | ||
|
|
||
| [`wasi-libc`]: https://github.com/WebAssembly/wasi-libc | ||
|
|
||
| ## Building the target | ||
|
|
||
| To build this target a compiled version of [`wasi-libc`] is required to be | ||
| present at build time. This can be installed through | ||
| [`wasi-sdk`](https://github.com/WebAssembly/wasi-sdk) as well. This is the | ||
| configured with: | ||
|
|
||
| ```toml | ||
| [target.wasm32-wasi-preview1] | ||
| wasi-root = ".../wasi-libc/sysroot" | ||
| ``` | ||
|
|
||
| Additionally users will need to enable LLD when building Rust from source as | ||
| LLVM's `wasm-ld` driver for LLD is required when linking WebAssembly code | ||
| together. | ||
|
|
||
| ## Building Rust programs | ||
|
|
||
| The `wasm32-wasi-preview1` target is shipped with rustup so users can install | ||
| the target with: | ||
|
|
||
| ```text | ||
| rustup target add wasm32-wasi-preview1 | ||
| ``` | ||
|
|
||
| > **Note**: the `wasm32-wasi-preview1` target is new and may only be available | ||
| > on nightly by the time you're reading this. If `wasm32-wasi-preview` isn't | ||
| > available on stable Rust then `wasm32-wasi` should be available instead. | ||
| Rust programs can be built for that target: | ||
|
|
||
| ```text | ||
| rustc --target wasm32-wasi-preview1 your-code.rs | ||
| ``` | ||
|
|
||
| ## Cross-compilation | ||
|
|
||
| This target can be cross-compiled from any hosts. | ||
|
|
||
| ## Testing | ||
|
|
||
| Currently the WASI target is not tested in rust-lang/rust CI. This means that | ||
| tests in the repository are not guaranteed to pass. This is theoretically | ||
| possibly by installing a standalone WebAssembly runtime and using it as a | ||
| "runner" for all tests, but there are various failures that will need to be | ||
| waded through to adjust tests to work on the WASI target. |
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