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Diffstat (limited to 'compiler/rustc_target/src/spec/wasm_base.rs')
| -rw-r--r-- | compiler/rustc_target/src/spec/wasm_base.rs | 129 |
1 files changed, 129 insertions, 0 deletions
diff --git a/compiler/rustc_target/src/spec/wasm_base.rs b/compiler/rustc_target/src/spec/wasm_base.rs new file mode 100644 index 000000000..9216d3e7b --- /dev/null +++ b/compiler/rustc_target/src/spec/wasm_base.rs @@ -0,0 +1,129 @@ +use super::crt_objects::CrtObjectsFallback; +use super::{cvs, LinkerFlavor, LldFlavor, PanicStrategy, RelocModel, TargetOptions, TlsModel}; + +pub fn options() -> TargetOptions { + macro_rules! args { + ($prefix:literal) => { + &[ + // By default LLD only gives us one page of stack (64k) which is a + // little small. Default to a larger stack closer to other PC platforms + // (1MB) and users can always inject their own link-args to override this. + concat!($prefix, "-z"), + concat!($prefix, "stack-size=1048576"), + // By default LLD's memory layout is: + // + // 1. First, a blank page + // 2. Next, all static data + // 3. Finally, the main stack (which grows down) + // + // This has the unfortunate consequence that on stack overflows you + // corrupt static data and can cause some exceedingly weird bugs. To + // help detect this a little sooner we instead request that the stack is + // placed before static data. + // + // This means that we'll generate slightly larger binaries as references + // to static data will take more bytes in the ULEB128 encoding, but + // stack overflow will be guaranteed to trap as it underflows instead of + // corrupting static data. + concat!($prefix, "--stack-first"), + // FIXME we probably shouldn't pass this but instead pass an explicit list + // of symbols we'll allow to be undefined. We don't currently have a + // mechanism of knowing, however, which symbols are intended to be imported + // from the environment and which are intended to be imported from other + // objects linked elsewhere. This is a coarse approximation but is sure to + // hide some bugs and frustrate someone at some point, so we should ideally + // work towards a world where we can explicitly list symbols that are + // supposed to be imported and have all other symbols generate errors if + // they remain undefined. + concat!($prefix, "--allow-undefined"), + // Rust code should never have warnings, and warnings are often + // indicative of bugs, let's prevent them. + concat!($prefix, "--fatal-warnings"), + // LLD only implements C++-like demangling, which doesn't match our own + // mangling scheme. Tell LLD to not demangle anything and leave it up to + // us to demangle these symbols later. Currently rustc does not perform + // further demangling, but tools like twiggy and wasm-bindgen are intended + // to do so. + concat!($prefix, "--no-demangle"), + ] + }; + } + + let mut pre_link_args = TargetOptions::link_args(LinkerFlavor::Lld(LldFlavor::Wasm), args!("")); + super::add_link_args(&mut pre_link_args, LinkerFlavor::Gcc, args!("-Wl,")); + + TargetOptions { + is_like_wasm: true, + families: cvs!["wasm"], + + // we allow dynamic linking, but only cdylibs. Basically we allow a + // final library artifact that exports some symbols (a wasm module) but + // we don't allow intermediate `dylib` crate types + dynamic_linking: true, + only_cdylib: true, + + // relatively self-explanatory! + exe_suffix: ".wasm".into(), + dll_prefix: "".into(), + dll_suffix: ".wasm".into(), + eh_frame_header: false, + + max_atomic_width: Some(64), + + // Unwinding doesn't work right now, so the whole target unconditionally + // defaults to panic=abort. Note that this is guaranteed to change in + // the future once unwinding is implemented. Don't rely on this as we're + // basically guaranteed to change it once WebAssembly supports + // exceptions. + panic_strategy: PanicStrategy::Abort, + + // Wasm doesn't have atomics yet, so tell LLVM that we're in a single + // threaded model which will legalize atomics to normal operations. + singlethread: true, + + // no dynamic linking, no need for default visibility! + default_hidden_visibility: true, + + // Symbol visibility takes care of this for the WebAssembly. + // Additionally the only known linker, LLD, doesn't support the script + // arguments just yet + limit_rdylib_exports: false, + + // we use the LLD shipped with the Rust toolchain by default + linker: Some("rust-lld".into()), + lld_flavor: LldFlavor::Wasm, + linker_is_gnu: false, + + pre_link_args, + + crt_objects_fallback: Some(CrtObjectsFallback::Wasm), + + // This has no effect in LLVM 8 or prior, but in LLVM 9 and later when + // PIC code is implemented this has quite a drastic effect if it stays + // at the default, `pic`. In an effort to keep wasm binaries as minimal + // as possible we're defaulting to `static` for now, but the hope is + // that eventually we can ship a `pic`-compatible standard library which + // works with `static` as well (or works with some method of generating + // non-relative calls and such later on). + relocation_model: RelocModel::Static, + + // When the atomics feature is activated then these two keys matter, + // otherwise they're basically ignored by the standard library. In this + // mode, however, the `#[thread_local]` attribute works (i.e. + // `has_thread_local`) and we need to get it to work by specifying + // `local-exec` as that's all that's implemented in LLVM today for wasm. + has_thread_local: true, + tls_model: TlsModel::LocalExec, + + // gdb scripts don't work on wasm blobs + emit_debug_gdb_scripts: false, + + // There's more discussion of this at + // https://bugs.llvm.org/show_bug.cgi?id=52442 but the general result is + // that this isn't useful for wasm and has tricky issues with + // representation, so this is disabled. + generate_arange_section: false, + + ..Default::default() + } +} |