1 use super::{cvs, Cc, LinkerFlavor, PanicStrategy, RelocModel, TargetOptions, TlsModel};
3 pub fn options() -> TargetOptions {
7 // By default LLD only gives us one page of stack (64k) which is a
8 // little small. Default to a larger stack closer to other PC platforms
9 // (1MB) and users can always inject their own link-args to override this.
10 concat!($prefix, "-z"),
11 concat!($prefix, "stack-size=1048576"),
12 // By default LLD's memory layout is:
14 // 1. First, a blank page
15 // 2. Next, all static data
16 // 3. Finally, the main stack (which grows down)
18 // This has the unfortunate consequence that on stack overflows you
19 // corrupt static data and can cause some exceedingly weird bugs. To
20 // help detect this a little sooner we instead request that the stack is
21 // placed before static data.
23 // This means that we'll generate slightly larger binaries as references
24 // to static data will take more bytes in the ULEB128 encoding, but
25 // stack overflow will be guaranteed to trap as it underflows instead of
26 // corrupting static data.
27 concat!($prefix, "--stack-first"),
28 // FIXME we probably shouldn't pass this but instead pass an explicit list
29 // of symbols we'll allow to be undefined. We don't currently have a
30 // mechanism of knowing, however, which symbols are intended to be imported
31 // from the environment and which are intended to be imported from other
32 // objects linked elsewhere. This is a coarse approximation but is sure to
33 // hide some bugs and frustrate someone at some point, so we should ideally
34 // work towards a world where we can explicitly list symbols that are
35 // supposed to be imported and have all other symbols generate errors if
36 // they remain undefined.
37 concat!($prefix, "--allow-undefined"),
38 // Rust code should never have warnings, and warnings are often
39 // indicative of bugs, let's prevent them.
40 concat!($prefix, "--fatal-warnings"),
41 // LLD only implements C++-like demangling, which doesn't match our own
42 // mangling scheme. Tell LLD to not demangle anything and leave it up to
43 // us to demangle these symbols later. Currently rustc does not perform
44 // further demangling, but tools like twiggy and wasm-bindgen are intended
46 concat!($prefix, "--no-demangle"),
51 let mut pre_link_args = TargetOptions::link_args(LinkerFlavor::WasmLld(Cc::No), args!(""));
52 super::add_link_args(&mut pre_link_args, LinkerFlavor::WasmLld(Cc::Yes), args!("-Wl,"));
56 families: cvs!["wasm"],
58 // we allow dynamic linking, but only cdylibs. Basically we allow a
59 // final library artifact that exports some symbols (a wasm module) but
60 // we don't allow intermediate `dylib` crate types
61 dynamic_linking: true,
64 // relatively self-explanatory!
65 exe_suffix: ".wasm".into(),
66 dll_prefix: "".into(),
67 dll_suffix: ".wasm".into(),
68 eh_frame_header: false,
70 max_atomic_width: Some(64),
72 // Unwinding doesn't work right now, so the whole target unconditionally
73 // defaults to panic=abort. Note that this is guaranteed to change in
74 // the future once unwinding is implemented. Don't rely on this as we're
75 // basically guaranteed to change it once WebAssembly supports
77 panic_strategy: PanicStrategy::Abort,
79 // Wasm doesn't have atomics yet, so tell LLVM that we're in a single
80 // threaded model which will legalize atomics to normal operations.
83 // no dynamic linking, no need for default visibility!
84 default_hidden_visibility: true,
86 // Symbol visibility takes care of this for the WebAssembly.
87 // Additionally the only known linker, LLD, doesn't support the script
89 limit_rdylib_exports: false,
91 // we use the LLD shipped with the Rust toolchain by default
92 linker: Some("rust-lld".into()),
93 linker_flavor: LinkerFlavor::WasmLld(Cc::No),
97 // This has no effect in LLVM 8 or prior, but in LLVM 9 and later when
98 // PIC code is implemented this has quite a drastic effect if it stays
99 // at the default, `pic`. In an effort to keep wasm binaries as minimal
100 // as possible we're defaulting to `static` for now, but the hope is
101 // that eventually we can ship a `pic`-compatible standard library which
102 // works with `static` as well (or works with some method of generating
103 // non-relative calls and such later on).
104 relocation_model: RelocModel::Static,
106 // When the atomics feature is activated then these two keys matter,
107 // otherwise they're basically ignored by the standard library. In this
108 // mode, however, the `#[thread_local]` attribute works (i.e.
109 // `has_thread_local`) and we need to get it to work by specifying
110 // `local-exec` as that's all that's implemented in LLVM today for wasm.
111 has_thread_local: true,
112 tls_model: TlsModel::LocalExec,
114 // gdb scripts don't work on wasm blobs
115 emit_debug_gdb_scripts: false,
117 // There's more discussion of this at
118 // https://bugs.llvm.org/show_bug.cgi?id=52442 but the general result is
119 // that this isn't useful for wasm and has tricky issues with
120 // representation, so this is disabled.
121 generate_arange_section: false,