rustc_target/spec/targets/
wasm64_unknown_unknown.rs

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//! A "bare wasm" target representing a WebAssembly output that makes zero
//! assumptions about its environment.
//!
//! The `wasm64-unknown-unknown` target is intended to encapsulate use cases
//! that do not rely on any imported functionality. The binaries generated are
//! entirely self-contained by default when using the standard library. Although
//! the standard library is available, most of it returns an error immediately
//! (e.g. trying to create a TCP stream or something like that).

use crate::spec::{Cc, LinkerFlavor, Target, base};

pub(crate) fn target() -> Target {
    let mut options = base::wasm::options();
    options.os = "unknown".into();

    options.add_pre_link_args(LinkerFlavor::WasmLld(Cc::No), &[
        // For now this target just never has an entry symbol no matter the output
        // type, so unconditionally pass this.
        "--no-entry",
        "-mwasm64",
    ]);
    options.add_pre_link_args(LinkerFlavor::WasmLld(Cc::Yes), &[
        // Make sure clang uses LLD as its linker and is configured appropriately
        // otherwise
        "--target=wasm64-unknown-unknown",
        "-Wl,--no-entry",
    ]);

    // Any engine that implements wasm64 will surely implement the rest of these
    // features since they were all merged into the official spec by the time
    // wasm64 was designed.
    options.features = "+bulk-memory,+mutable-globals,+sign-ext,+nontrapping-fptoint".into();

    Target {
        llvm_target: "wasm64-unknown-unknown".into(),
        metadata: crate::spec::TargetMetadata {
            description: Some("WebAssembly".into()),
            tier: Some(3),
            host_tools: Some(false),
            std: None, // ?
        },
        pointer_width: 64,
        data_layout: "e-m:e-p:64:64-p10:8:8-p20:8:8-i64:64-i128:128-n32:64-S128-ni:1:10:20".into(),
        arch: "wasm64".into(),
        options,
    }
}