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Commit | Line | Data |
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f2b60f7d | 1 | use super::crt_objects::LinkSelfContainedDefault; |
5e7ed085 | 2 | use super::{cvs, LinkerFlavor, LldFlavor, PanicStrategy, RelocModel, TargetOptions, TlsModel}; |
532ac7d7 XL |
3 | |
4 | pub fn options() -> TargetOptions { | |
064997fb FG |
5 | macro_rules! args { |
6 | ($prefix:literal) => { | |
7 | &[ | |
8 | // By default LLD only gives us one page of stack (64k) which is a | |
9 | // little small. Default to a larger stack closer to other PC platforms | |
10 | // (1MB) and users can always inject their own link-args to override this. | |
11 | concat!($prefix, "-z"), | |
12 | concat!($prefix, "stack-size=1048576"), | |
13 | // By default LLD's memory layout is: | |
14 | // | |
15 | // 1. First, a blank page | |
16 | // 2. Next, all static data | |
17 | // 3. Finally, the main stack (which grows down) | |
18 | // | |
19 | // This has the unfortunate consequence that on stack overflows you | |
20 | // corrupt static data and can cause some exceedingly weird bugs. To | |
21 | // help detect this a little sooner we instead request that the stack is | |
22 | // placed before static data. | |
23 | // | |
24 | // This means that we'll generate slightly larger binaries as references | |
25 | // to static data will take more bytes in the ULEB128 encoding, but | |
26 | // stack overflow will be guaranteed to trap as it underflows instead of | |
27 | // corrupting static data. | |
28 | concat!($prefix, "--stack-first"), | |
29 | // FIXME we probably shouldn't pass this but instead pass an explicit list | |
30 | // of symbols we'll allow to be undefined. We don't currently have a | |
31 | // mechanism of knowing, however, which symbols are intended to be imported | |
32 | // from the environment and which are intended to be imported from other | |
33 | // objects linked elsewhere. This is a coarse approximation but is sure to | |
34 | // hide some bugs and frustrate someone at some point, so we should ideally | |
35 | // work towards a world where we can explicitly list symbols that are | |
36 | // supposed to be imported and have all other symbols generate errors if | |
37 | // they remain undefined. | |
38 | concat!($prefix, "--allow-undefined"), | |
39 | // Rust code should never have warnings, and warnings are often | |
40 | // indicative of bugs, let's prevent them. | |
41 | concat!($prefix, "--fatal-warnings"), | |
42 | // LLD only implements C++-like demangling, which doesn't match our own | |
43 | // mangling scheme. Tell LLD to not demangle anything and leave it up to | |
44 | // us to demangle these symbols later. Currently rustc does not perform | |
45 | // further demangling, but tools like twiggy and wasm-bindgen are intended | |
46 | // to do so. | |
47 | concat!($prefix, "--no-demangle"), | |
48 | ] | |
49 | }; | |
50 | } | |
532ac7d7 | 51 | |
064997fb FG |
52 | let mut pre_link_args = TargetOptions::link_args(LinkerFlavor::Lld(LldFlavor::Wasm), args!("")); |
53 | super::add_link_args(&mut pre_link_args, LinkerFlavor::Gcc, args!("-Wl,")); | |
532ac7d7 XL |
54 | |
55 | TargetOptions { | |
cdc7bbd5 | 56 | is_like_wasm: true, |
5e7ed085 | 57 | families: cvs!["wasm"], |
cdc7bbd5 | 58 | |
532ac7d7 XL |
59 | // we allow dynamic linking, but only cdylibs. Basically we allow a |
60 | // final library artifact that exports some symbols (a wasm module) but | |
61 | // we don't allow intermediate `dylib` crate types | |
62 | dynamic_linking: true, | |
63 | only_cdylib: true, | |
64 | ||
532ac7d7 | 65 | // relatively self-explanatory! |
5e7ed085 FG |
66 | exe_suffix: ".wasm".into(), |
67 | dll_prefix: "".into(), | |
68 | dll_suffix: ".wasm".into(), | |
1b1a35ee | 69 | eh_frame_header: false, |
532ac7d7 XL |
70 | |
71 | max_atomic_width: Some(64), | |
72 | ||
73 | // Unwinding doesn't work right now, so the whole target unconditionally | |
74 | // defaults to panic=abort. Note that this is guaranteed to change in | |
75 | // the future once unwinding is implemented. Don't rely on this as we're | |
76 | // basically guaranteed to change it once WebAssembly supports | |
77 | // exceptions. | |
78 | panic_strategy: PanicStrategy::Abort, | |
79 | ||
80 | // Wasm doesn't have atomics yet, so tell LLVM that we're in a single | |
81 | // threaded model which will legalize atomics to normal operations. | |
82 | singlethread: true, | |
83 | ||
84 | // no dynamic linking, no need for default visibility! | |
85 | default_hidden_visibility: true, | |
86 | ||
dc9dc135 XL |
87 | // Symbol visibility takes care of this for the WebAssembly. |
88 | // Additionally the only known linker, LLD, doesn't support the script | |
89 | // arguments just yet | |
90 | limit_rdylib_exports: false, | |
91 | ||
532ac7d7 | 92 | // we use the LLD shipped with the Rust toolchain by default |
5e7ed085 | 93 | linker: Some("rust-lld".into()), |
532ac7d7 | 94 | lld_flavor: LldFlavor::Wasm, |
17df50a5 | 95 | linker_is_gnu: false, |
532ac7d7 XL |
96 | |
97 | pre_link_args, | |
98 | ||
f2b60f7d FG |
99 | // FIXME: Figure out cases in which WASM needs to link with a native toolchain. |
100 | link_self_contained: LinkSelfContainedDefault::True, | |
f9f354fc | 101 | |
532ac7d7 | 102 | // This has no effect in LLVM 8 or prior, but in LLVM 9 and later when |
5e7ed085 | 103 | // PIC code is implemented this has quite a drastic effect if it stays |
532ac7d7 XL |
104 | // at the default, `pic`. In an effort to keep wasm binaries as minimal |
105 | // as possible we're defaulting to `static` for now, but the hope is | |
106 | // that eventually we can ship a `pic`-compatible standard library which | |
107 | // works with `static` as well (or works with some method of generating | |
108 | // non-relative calls and such later on). | |
f9f354fc | 109 | relocation_model: RelocModel::Static, |
532ac7d7 | 110 | |
416331ca XL |
111 | // When the atomics feature is activated then these two keys matter, |
112 | // otherwise they're basically ignored by the standard library. In this | |
113 | // mode, however, the `#[thread_local]` attribute works (i.e. | |
a2a8927a | 114 | // `has_thread_local`) and we need to get it to work by specifying |
416331ca | 115 | // `local-exec` as that's all that's implemented in LLVM today for wasm. |
a2a8927a | 116 | has_thread_local: true, |
f9f354fc | 117 | tls_model: TlsModel::LocalExec, |
416331ca | 118 | |
60c5eb7d XL |
119 | // gdb scripts don't work on wasm blobs |
120 | emit_debug_gdb_scripts: false, | |
121 | ||
3c0e092e XL |
122 | // There's more discussion of this at |
123 | // https://bugs.llvm.org/show_bug.cgi?id=52442 but the general result is | |
124 | // that this isn't useful for wasm and has tricky issues with | |
125 | // representation, so this is disabled. | |
126 | generate_arange_section: false, | |
127 | ||
dfeec247 | 128 | ..Default::default() |
532ac7d7 XL |
129 | } |
130 | } |