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Add wasm32-wasi-threads target + WASI threads
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compiler/rustc_target/src/spec/wasm32_wasi_preview1_threads.rs
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//! The `wasm32-wasi-preview1-threads` target is a new and still (as of July 2023) an | ||
//! experimental target. The definition in this file is likely to be tweaked | ||
//! over time and shouldn't be relied on too much. | ||
//! | ||
//! The `wasi-threads` 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 | ||
//! threads, filesystem access, network access, etc. | ||
//! | ||
//! You can see more about the proposal at <https://github.com/WebAssembly/wasi-threads>. | ||
//! | ||
//! 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-preview1-threads | ||
//! 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-preview1-threads` 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-preview1-threads` 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-preview1-threads` and is configured with the `wasm32-wasi-preview1-threads` 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-preview1-threads` 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! | ||
use super::crt_objects::{self, LinkSelfContainedDefault}; | ||
use super::{wasm_base, Cc, LinkerFlavor, Target}; | ||
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pub fn target() -> Target { | ||
let mut options = wasm_base::options(); | ||
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options.os = "wasi".into(); | ||
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options.add_pre_link_args( | ||
LinkerFlavor::WasmLld(Cc::No), | ||
&["--import-memory", "--export-memory", "--shared-memory"], | ||
); | ||
options.add_pre_link_args( | ||
LinkerFlavor::WasmLld(Cc::Yes), | ||
&[ | ||
"--target=wasm32-wasi-threads", | ||
"-Wl,--import-memory", | ||
"-Wl,--export-memory,", | ||
"-Wl,--shared-memory", | ||
], | ||
); | ||
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options.pre_link_objects_self_contained = crt_objects::pre_wasi_self_contained(); | ||
options.post_link_objects_self_contained = crt_objects::post_wasi_self_contained(); | ||
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// FIXME: Figure out cases in which WASM needs to link with a native toolchain. | ||
options.link_self_contained = LinkSelfContainedDefault::True; | ||
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// 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; | ||
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// Allow `+crt-static` to create a "cdylib" output which is just a wasm file | ||
// without a main function. | ||
options.crt_static_allows_dylibs = true; | ||
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// WASI's `sys::args::init` function ignores its arguments; instead, | ||
// `args::args()` makes the WASI API calls itself. | ||
options.main_needs_argc_argv = false; | ||
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// And, WASI mangles the name of "main" to distinguish between different | ||
// signatures. | ||
options.entry_name = "__main_void".into(); | ||
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options.singlethread = false; | ||
options.features = "+atomics,+bulk-memory,+mutable-globals".into(); | ||
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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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