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Diffstat (limited to 'compiler/rustc_target/src/spec/wasm32_wasi.rs')
| -rw-r--r-- | compiler/rustc_target/src/spec/wasm32_wasi.rs | 112 |
1 files changed, 112 insertions, 0 deletions
diff --git a/compiler/rustc_target/src/spec/wasm32_wasi.rs b/compiler/rustc_target/src/spec/wasm32_wasi.rs new file mode 100644 index 000000000..280457d68 --- /dev/null +++ b/compiler/rustc_target/src/spec/wasm32_wasi.rs @@ -0,0 +1,112 @@ +//! 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. +//! +//! 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! + +use super::wasm_base; +use super::{crt_objects, LinkerFlavor, LldFlavor, Target}; + +pub fn target() -> Target { + let mut options = wasm_base::options(); + + options.os = "wasi".into(); + options.linker_flavor = LinkerFlavor::Lld(LldFlavor::Wasm); + options.add_pre_link_args(LinkerFlavor::Gcc, &["--target=wasm32-wasi"]); + + options.pre_link_objects_fallback = crt_objects::pre_wasi_fallback(); + options.post_link_objects_fallback = crt_objects::post_wasi_fallback(); + + // 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; + + 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, + } +} |