compiler/rustc_codegen_ssa/src/codegen_attrs.rs

   1 use rustc_ast::{ast, MetaItemKind, NestedMetaItem};
   2 use rustc_attr::{list_contains_name, InlineAttr, InstructionSetAttr, OptimizeAttr};
   3 use rustc_errors::struct_span_err;
   4 use rustc_hir as hir;
   5 use rustc_hir::def::DefKind;
   6 use rustc_hir::def_id::{DefId, LocalDefId, LOCAL_CRATE};
   7 use rustc_hir::{lang_items, weak_lang_items::WEAK_LANG_ITEMS, LangItem};
   8 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
   9 use rustc_middle::mir::mono::Linkage;
  10 use rustc_middle::ty::query::Providers;
  11 use rustc_middle::ty::{self as ty, DefIdTree, TyCtxt};
  12 use rustc_session::{lint, parse::feature_err};
  13 use rustc_span::{sym, Span};
  14 use rustc_target::spec::{abi, SanitizerSet};
  15
  16 use crate::target_features::from_target_feature;
  17 use crate::{errors::ExpectedUsedSymbol, target_features::check_target_feature_trait_unsafe};
  18
  19 fn linkage_by_name(tcx: TyCtxt<'_>, def_id: LocalDefId, name: &str) -> Linkage {
  20     use rustc_middle::mir::mono::Linkage::*;
  21
  22     // Use the names from src/llvm/docs/LangRef.rst here. Most types are only
  23     // applicable to variable declarations and may not really make sense for
  24     // Rust code in the first place but allow them anyway and trust that the
  25     // user knows what they're doing. Who knows, unanticipated use cases may pop
  26     // up in the future.
  27     //
  28     // ghost, dllimport, dllexport and linkonce_odr_autohide are not supported
  29     // and don't have to be, LLVM treats them as no-ops.
  30     match name {
  31         "appending" => Appending,
  32         "available_externally" => AvailableExternally,
  33         "common" => Common,
  34         "extern_weak" => ExternalWeak,
  35         "external" => External,
  36         "internal" => Internal,
  37         "linkonce" => LinkOnceAny,
  38         "linkonce_odr" => LinkOnceODR,
  39         "private" => Private,
  40         "weak" => WeakAny,
  41         "weak_odr" => WeakODR,
  42         _ => tcx.sess.span_fatal(tcx.def_span(def_id), "invalid linkage specified"),
  43     }
  44 }
  45
  46 fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: DefId) -> CodegenFnAttrs {
  47     if cfg!(debug_assertions) {
  48         let def_kind = tcx.def_kind(did);
  49         assert!(
  50             def_kind.has_codegen_attrs(),
  51             "unexpected `def_kind` in `codegen_fn_attrs`: {def_kind:?}",
  52         );
  53     }
  54
  55     let did = did.expect_local();
  56     let attrs = tcx.hir().attrs(tcx.hir().local_def_id_to_hir_id(did));
  57     let mut codegen_fn_attrs = CodegenFnAttrs::new();
  58     if tcx.should_inherit_track_caller(did) {
  59         codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
  60     }
  61
  62     let supported_target_features = tcx.supported_target_features(LOCAL_CRATE);
  63
  64     // In some cases, attribute are only valid on functions, but it's the `check_attr`
  65     // pass that check that they aren't used anywhere else, rather this module.
  66     // In these cases, we bail from performing further checks that are only meaningful for
  67     // functions (such as calling `fn_sig`, which ICEs if given a non-function). We also
  68     // report a delayed bug, just in case `check_attr` isn't doing its job.
  69     let validate_fn_only_attr = |attr_sp| -> bool {
  70         let def_kind = tcx.def_kind(did);
  71         if let DefKind::Fn | DefKind::AssocFn | DefKind::Variant | DefKind::Ctor(..) = def_kind {
  72             true
  73         } else {
  74             tcx.sess.delay_span_bug(attr_sp, "this attribute can only be applied to functions");
  75             false
  76         }
  77     };
  78
  79     let mut inline_span = None;
  80     let mut link_ordinal_span = None;
  81     let mut no_sanitize_span = None;
  82     for attr in attrs.iter() {
  83         if attr.has_name(sym::cold) {
  84             codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD;
  85         } else if attr.has_name(sym::rustc_allocator) {
  86             codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR;
  87         } else if attr.has_name(sym::ffi_returns_twice) {
  88             codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_RETURNS_TWICE;
  89         } else if attr.has_name(sym::ffi_pure) {
  90             codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_PURE;
  91         } else if attr.has_name(sym::ffi_const) {
  92             codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_CONST;
  93         } else if attr.has_name(sym::rustc_nounwind) {
  94             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
  95         } else if attr.has_name(sym::rustc_reallocator) {
  96             codegen_fn_attrs.flags |= CodegenFnAttrFlags::REALLOCATOR;
  97         } else if attr.has_name(sym::rustc_deallocator) {
  98             codegen_fn_attrs.flags |= CodegenFnAttrFlags::DEALLOCATOR;
  99         } else if attr.has_name(sym::rustc_allocator_zeroed) {
 100             codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR_ZEROED;
 101         } else if attr.has_name(sym::naked) {
 102             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NAKED;
 103         } else if attr.has_name(sym::no_mangle) {
 104             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
 105         } else if attr.has_name(sym::no_coverage) {
 106             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_COVERAGE;
 107         } else if attr.has_name(sym::rustc_std_internal_symbol) {
 108             codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
 109         } else if attr.has_name(sym::used) {
 110             let inner = attr.meta_item_list();
 111             match inner.as_deref() {
 112                 Some([item]) if item.has_name(sym::linker) => {
 113                     if !tcx.features().used_with_arg {
 114                         feature_err(
 115                             &tcx.sess.parse_sess,
 116                             sym::used_with_arg,
 117                             attr.span,
 118                             "`#[used(linker)]` is currently unstable",
 119                         )
 120                         .emit();
 121                     }
 122                     codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED_LINKER;
 123                 }
 124                 Some([item]) if item.has_name(sym::compiler) => {
 125                     if !tcx.features().used_with_arg {
 126                         feature_err(
 127                             &tcx.sess.parse_sess,
 128                             sym::used_with_arg,
 129                             attr.span,
 130                             "`#[used(compiler)]` is currently unstable",
 131                         )
 132                         .emit();
 133                     }
 134                     codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED;
 135                 }
 136                 Some(_) => {
 137                     tcx.sess.emit_err(ExpectedUsedSymbol { span: attr.span });
 138                 }
 139                 None => {
 140                     // Unfortunately, unconditionally using `llvm.used` causes
 141                     // issues in handling `.init_array` with the gold linker,
 142                     // but using `llvm.compiler.used` caused a nontrival amount
 143                     // of unintentional ecosystem breakage -- particularly on
 144                     // Mach-O targets.
 145                     //
 146                     // As a result, we emit `llvm.compiler.used` only on ELF
 147                     // targets. This is somewhat ad-hoc, but actually follows
 148                     // our pre-LLVM 13 behavior (prior to the ecosystem
 149                     // breakage), and seems to match `clang`'s behavior as well
 150                     // (both before and after LLVM 13), possibly because they
 151                     // have similar compatibility concerns to us. See
 152                     // https://github.com/rust-lang/rust/issues/47384#issuecomment-1019080146
 153                     // and following comments for some discussion of this, as
 154                     // well as the comments in `rustc_codegen_llvm` where these
 155                     // flags are handled.
 156                     //
 157                     // Anyway, to be clear: this is still up in the air
 158                     // somewhat, and is subject to change in the future (which
 159                     // is a good thing, because this would ideally be a bit
 160                     // more firmed up).
 161                     let is_like_elf = !(tcx.sess.target.is_like_osx
 162                         || tcx.sess.target.is_like_windows
 163                         || tcx.sess.target.is_like_wasm);
 164                     codegen_fn_attrs.flags |= if is_like_elf {
 165                         CodegenFnAttrFlags::USED
 166                     } else {
 167                         CodegenFnAttrFlags::USED_LINKER
 168                     };
 169                 }
 170             }
 171         } else if attr.has_name(sym::cmse_nonsecure_entry) {
 172             if validate_fn_only_attr(attr.span)
 173                 && !matches!(tcx.fn_sig(did).skip_binder().abi(), abi::Abi::C { .. })
 174             {
 175                 struct_span_err!(
 176                     tcx.sess,
 177                     attr.span,
 178                     E0776,
 179                     "`#[cmse_nonsecure_entry]` requires C ABI"
 180                 )
 181                 .emit();
 182             }
 183             if !tcx.sess.target.llvm_target.contains("thumbv8m") {
 184                 struct_span_err!(tcx.sess, attr.span, E0775, "`#[cmse_nonsecure_entry]` is only valid for targets with the TrustZone-M extension")
 185                     .emit();
 186             }
 187             codegen_fn_attrs.flags |= CodegenFnAttrFlags::CMSE_NONSECURE_ENTRY;
 188         } else if attr.has_name(sym::thread_local) {
 189             codegen_fn_attrs.flags |= CodegenFnAttrFlags::THREAD_LOCAL;
 190         } else if attr.has_name(sym::track_caller) {
 191             if !tcx.is_closure(did.to_def_id())
 192                 && validate_fn_only_attr(attr.span)
 193                 && tcx.fn_sig(did).skip_binder().abi() != abi::Abi::Rust
 194             {
 195                 struct_span_err!(tcx.sess, attr.span, E0737, "`#[track_caller]` requires Rust ABI")
 196                     .emit();
 197             }
 198             if tcx.is_closure(did.to_def_id()) && !tcx.features().closure_track_caller {
 199                 feature_err(
 200                     &tcx.sess.parse_sess,
 201                     sym::closure_track_caller,
 202                     attr.span,
 203                     "`#[track_caller]` on closures is currently unstable",
 204                 )
 205                 .emit();
 206             }
 207             codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
 208         } else if attr.has_name(sym::export_name) {
 209             if let Some(s) = attr.value_str() {
 210                 if s.as_str().contains('\0') {
 211                     // `#[export_name = ...]` will be converted to a null-terminated string,
 212                     // so it may not contain any null characters.
 213                     struct_span_err!(
 214                         tcx.sess,
 215                         attr.span,
 216                         E0648,
 217                         "`export_name` may not contain null characters"
 218                     )
 219                     .emit();
 220                 }
 221                 codegen_fn_attrs.export_name = Some(s);
 222             }
 223         } else if attr.has_name(sym::target_feature) {
 224             if !tcx.is_closure(did.to_def_id())
 225                 && tcx.fn_sig(did).skip_binder().unsafety() == hir::Unsafety::Normal
 226             {
 227                 if tcx.sess.target.is_like_wasm || tcx.sess.opts.actually_rustdoc {
 228                     // The `#[target_feature]` attribute is allowed on
 229                     // WebAssembly targets on all functions, including safe
 230                     // ones. Other targets require that `#[target_feature]` is
 231                     // only applied to unsafe functions (pending the
 232                     // `target_feature_11` feature) because on most targets
 233                     // execution of instructions that are not supported is
 234                     // considered undefined behavior. For WebAssembly which is a
 235                     // 100% safe target at execution time it's not possible to
 236                     // execute undefined instructions, and even if a future
 237                     // feature was added in some form for this it would be a
 238                     // deterministic trap. There is no undefined behavior when
 239                     // executing WebAssembly so `#[target_feature]` is allowed
 240                     // on safe functions (but again, only for WebAssembly)
 241                     //
 242                     // Note that this is also allowed if `actually_rustdoc` so
 243                     // if a target is documenting some wasm-specific code then
 244                     // it's not spuriously denied.
 245                 } else if !tcx.features().target_feature_11 {
 246                     let mut err = feature_err(
 247                         &tcx.sess.parse_sess,
 248                         sym::target_feature_11,
 249                         attr.span,
 250                         "`#[target_feature(..)]` can only be applied to `unsafe` functions",
 251                     );
 252                     err.span_label(tcx.def_span(did), "not an `unsafe` function");
 253                     err.emit();
 254                 } else {
 255                     check_target_feature_trait_unsafe(tcx, did, attr.span);
 256                 }
 257             }
 258             from_target_feature(
 259                 tcx,
 260                 attr,
 261                 supported_target_features,
 262                 &mut codegen_fn_attrs.target_features,
 263             );
 264         } else if attr.has_name(sym::linkage) {
 265             if let Some(val) = attr.value_str() {
 266                 let linkage = Some(linkage_by_name(tcx, did, val.as_str()));
 267                 if tcx.is_foreign_item(did) {
 268                     codegen_fn_attrs.import_linkage = linkage;
 269                 } else {
 270                     codegen_fn_attrs.linkage = linkage;
 271                 }
 272             }
 273         } else if attr.has_name(sym::link_section) {
 274             if let Some(val) = attr.value_str() {
 275                 if val.as_str().bytes().any(|b| b == 0) {
 276                     let msg = format!(
 277                         "illegal null byte in link_section \
 278                          value: `{}`",
 279                         &val
 280                     );
 281                     tcx.sess.span_err(attr.span, &msg);
 282                 } else {
 283                     codegen_fn_attrs.link_section = Some(val);
 284                 }
 285             }
 286         } else if attr.has_name(sym::link_name) {
 287             codegen_fn_attrs.link_name = attr.value_str();
 288         } else if attr.has_name(sym::link_ordinal) {
 289             link_ordinal_span = Some(attr.span);
 290             if let ordinal @ Some(_) = check_link_ordinal(tcx, attr) {
 291                 codegen_fn_attrs.link_ordinal = ordinal;
 292             }
 293         } else if attr.has_name(sym::no_sanitize) {
 294             no_sanitize_span = Some(attr.span);
 295             if let Some(list) = attr.meta_item_list() {
 296                 for item in list.iter() {
 297                     if item.has_name(sym::address) {
 298                         codegen_fn_attrs.no_sanitize |= SanitizerSet::ADDRESS;
 299                     } else if item.has_name(sym::cfi) {
 300                         codegen_fn_attrs.no_sanitize |= SanitizerSet::CFI;
 301                     } else if item.has_name(sym::kcfi) {
 302                         codegen_fn_attrs.no_sanitize |= SanitizerSet::KCFI;
 303                     } else if item.has_name(sym::memory) {
 304                         codegen_fn_attrs.no_sanitize |= SanitizerSet::MEMORY;
 305                     } else if item.has_name(sym::memtag) {
 306                         codegen_fn_attrs.no_sanitize |= SanitizerSet::MEMTAG;
 307                     } else if item.has_name(sym::shadow_call_stack) {
 308                         codegen_fn_attrs.no_sanitize |= SanitizerSet::SHADOWCALLSTACK;
 309                     } else if item.has_name(sym::thread) {
 310                         codegen_fn_attrs.no_sanitize |= SanitizerSet::THREAD;
 311                     } else if item.has_name(sym::hwaddress) {
 312                         codegen_fn_attrs.no_sanitize |= SanitizerSet::HWADDRESS;
 313                     } else {
 314                         tcx.sess
 315                             .struct_span_err(item.span(), "invalid argument for `no_sanitize`")
 316                             .note("expected one of: `address`, `cfi`, `hwaddress`, `kcfi`, `memory`, `memtag`, `shadow-call-stack`, or `thread`")
 317                             .emit();
 318                     }
 319                 }
 320             }
 321         } else if attr.has_name(sym::instruction_set) {
 322             codegen_fn_attrs.instruction_set = match attr.meta_kind() {
 323                 Some(MetaItemKind::List(ref items)) => match items.as_slice() {
 324                     [NestedMetaItem::MetaItem(set)] => {
 325                         let segments =
 326                             set.path.segments.iter().map(|x| x.ident.name).collect::<Vec<_>>();
 327                         match segments.as_slice() {
 328                             [sym::arm, sym::a32] | [sym::arm, sym::t32] => {
 329                                 if !tcx.sess.target.has_thumb_interworking {
 330                                     struct_span_err!(
 331                                         tcx.sess.diagnostic(),
 332                                         attr.span,
 333                                         E0779,
 334                                         "target does not support `#[instruction_set]`"
 335                                     )
 336                                     .emit();
 337                                     None
 338                                 } else if segments[1] == sym::a32 {
 339                                     Some(InstructionSetAttr::ArmA32)
 340                                 } else if segments[1] == sym::t32 {
 341                                     Some(InstructionSetAttr::ArmT32)
 342                                 } else {
 343                                     unreachable!()
 344                                 }
 345                             }
 346                             _ => {
 347                                 struct_span_err!(
 348                                     tcx.sess.diagnostic(),
 349                                     attr.span,
 350                                     E0779,
 351                                     "invalid instruction set specified",
 352                                 )
 353                                 .emit();
 354                                 None
 355                             }
 356                         }
 357                     }
 358                     [] => {
 359                         struct_span_err!(
 360                             tcx.sess.diagnostic(),
 361                             attr.span,
 362                             E0778,
 363                             "`#[instruction_set]` requires an argument"
 364                         )
 365                         .emit();
 366                         None
 367                     }
 368                     _ => {
 369                         struct_span_err!(
 370                             tcx.sess.diagnostic(),
 371                             attr.span,
 372                             E0779,
 373                             "cannot specify more than one instruction set"
 374                         )
 375                         .emit();
 376                         None
 377                     }
 378                 },
 379                 _ => {
 380                     struct_span_err!(
 381                         tcx.sess.diagnostic(),
 382                         attr.span,
 383                         E0778,
 384                         "must specify an instruction set"
 385                     )
 386                     .emit();
 387                     None
 388                 }
 389             };
 390         } else if attr.has_name(sym::repr) {
 391             codegen_fn_attrs.alignment = match attr.meta_item_list() {
 392                 Some(items) => match items.as_slice() {
 393                     [item] => match item.name_value_literal() {
 394                         Some((sym::align, literal)) => {
 395                             let alignment = rustc_attr::parse_alignment(&literal.kind);
 396
 397                             match alignment {
 398                                 Ok(align) => Some(align),
 399                                 Err(msg) => {
 400                                     struct_span_err!(
 401                                         tcx.sess.diagnostic(),
 402                                         attr.span,
 403                                         E0589,
 404                                         "invalid `repr(align)` attribute: {}",
 405                                         msg
 406                                     )
 407                                     .emit();
 408
 409                                     None
 410                                 }
 411                             }
 412                         }
 413                         _ => None,
 414                     },
 415                     [] => None,
 416                     _ => None,
 417                 },
 418                 None => None,
 419             };
 420         }
 421     }
 422
 423     codegen_fn_attrs.inline = attrs.iter().fold(InlineAttr::None, |ia, attr| {
 424         if !attr.has_name(sym::inline) {
 425             return ia;
 426         }
 427         match attr.meta_kind() {
 428             Some(MetaItemKind::Word) => InlineAttr::Hint,
 429             Some(MetaItemKind::List(ref items)) => {
 430                 inline_span = Some(attr.span);
 431                 if items.len() != 1 {
 432                     struct_span_err!(
 433                         tcx.sess.diagnostic(),
 434                         attr.span,
 435                         E0534,
 436                         "expected one argument"
 437                     )
 438                     .emit();
 439                     InlineAttr::None
 440                 } else if list_contains_name(&items, sym::always) {
 441                     InlineAttr::Always
 442                 } else if list_contains_name(&items, sym::never) {
 443                     InlineAttr::Never
 444                 } else {
 445                     struct_span_err!(
 446                         tcx.sess.diagnostic(),
 447                         items[0].span(),
 448                         E0535,
 449                         "invalid argument"
 450                     )
 451                     .help("valid inline arguments are `always` and `never`")
 452                     .emit();
 453
 454                     InlineAttr::None
 455                 }
 456             }
 457             Some(MetaItemKind::NameValue(_)) => ia,
 458             None => ia,
 459         }
 460     });
 461
 462     codegen_fn_attrs.optimize = attrs.iter().fold(OptimizeAttr::None, |ia, attr| {
 463         if !attr.has_name(sym::optimize) {
 464             return ia;
 465         }
 466         let err = |sp, s| struct_span_err!(tcx.sess.diagnostic(), sp, E0722, "{}", s).emit();
 467         match attr.meta_kind() {
 468             Some(MetaItemKind::Word) => {
 469                 err(attr.span, "expected one argument");
 470                 ia
 471             }
 472             Some(MetaItemKind::List(ref items)) => {
 473                 inline_span = Some(attr.span);
 474                 if items.len() != 1 {
 475                     err(attr.span, "expected one argument");
 476                     OptimizeAttr::None
 477                 } else if list_contains_name(&items, sym::size) {
 478                     OptimizeAttr::Size
 479                 } else if list_contains_name(&items, sym::speed) {
 480                     OptimizeAttr::Speed
 481                 } else {
 482                     err(items[0].span(), "invalid argument");
 483                     OptimizeAttr::None
 484                 }
 485             }
 486             Some(MetaItemKind::NameValue(_)) => ia,
 487             None => ia,
 488         }
 489     });
 490
 491     // #73631: closures inherit `#[target_feature]` annotations
 492     if tcx.features().target_feature_11 && tcx.is_closure(did.to_def_id()) {
 493         let owner_id = tcx.parent(did.to_def_id());
 494         if tcx.def_kind(owner_id).has_codegen_attrs() {
 495             codegen_fn_attrs
 496                 .target_features
 497                 .extend(tcx.codegen_fn_attrs(owner_id).target_features.iter().copied());
 498         }
 499     }
 500
 501     // If a function uses #[target_feature] it can't be inlined into general
 502     // purpose functions as they wouldn't have the right target features
 503     // enabled. For that reason we also forbid #[inline(always)] as it can't be
 504     // respected.
 505     if !codegen_fn_attrs.target_features.is_empty() {
 506         if codegen_fn_attrs.inline == InlineAttr::Always {
 507             if let Some(span) = inline_span {
 508                 tcx.sess.span_err(
 509                     span,
 510                     "cannot use `#[inline(always)]` with \
 511                      `#[target_feature]`",
 512                 );
 513             }
 514         }
 515     }
 516
 517     if !codegen_fn_attrs.no_sanitize.is_empty() {
 518         if codegen_fn_attrs.inline == InlineAttr::Always {
 519             if let (Some(no_sanitize_span), Some(inline_span)) = (no_sanitize_span, inline_span) {
 520                 let hir_id = tcx.hir().local_def_id_to_hir_id(did);
 521                 tcx.struct_span_lint_hir(
 522                     lint::builtin::INLINE_NO_SANITIZE,
 523                     hir_id,
 524                     no_sanitize_span,
 525                     "`no_sanitize` will have no effect after inlining",
 526                     |lint| lint.span_note(inline_span, "inlining requested here"),
 527                 )
 528             }
 529         }
 530     }
 531
 532     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
 533         codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_COVERAGE;
 534         codegen_fn_attrs.inline = InlineAttr::Never;
 535     }
 536
 537     // Weak lang items have the same semantics as "std internal" symbols in the
 538     // sense that they're preserved through all our LTO passes and only
 539     // strippable by the linker.
 540     //
 541     // Additionally weak lang items have predetermined symbol names.
 542     if WEAK_LANG_ITEMS.iter().any(|&l| tcx.lang_items().get(l) == Some(did.to_def_id())) {
 543         codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
 544     }
 545     if let Some((name, _)) = lang_items::extract(attrs)
 546         && let Some(lang_item) = LangItem::from_name(name)
 547         && let Some(link_name) = lang_item.link_name()
 548     {
 549         codegen_fn_attrs.export_name = Some(link_name);
 550         codegen_fn_attrs.link_name = Some(link_name);
 551     }
 552     check_link_name_xor_ordinal(tcx, &codegen_fn_attrs, link_ordinal_span);
 553
 554     // Internal symbols to the standard library all have no_mangle semantics in
 555     // that they have defined symbol names present in the function name. This
 556     // also applies to weak symbols where they all have known symbol names.
 557     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
 558         codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
 559     }
 560
 561     // Any linkage to LLVM intrinsics for now forcibly marks them all as never
 562     // unwinds since LLVM sometimes can't handle codegen which `invoke`s
 563     // intrinsic functions.
 564     if let Some(name) = &codegen_fn_attrs.link_name {
 565         if name.as_str().starts_with("llvm.") {
 566             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
 567         }
 568     }
 569
 570     codegen_fn_attrs
 571 }
 572
 573 /// Checks if the provided DefId is a method in a trait impl for a trait which has track_caller
 574 /// applied to the method prototype.
 575 fn should_inherit_track_caller(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 576     if let Some(impl_item) = tcx.opt_associated_item(def_id)
 577         && let ty::AssocItemContainer::ImplContainer = impl_item.container
 578         && let Some(trait_item) = impl_item.trait_item_def_id
 579     {
 580         return tcx
 581             .codegen_fn_attrs(trait_item)
 582             .flags
 583             .intersects(CodegenFnAttrFlags::TRACK_CALLER);
 584     }
 585
 586     false
 587 }
 588
 589 fn check_link_ordinal(tcx: TyCtxt<'_>, attr: &ast::Attribute) -> Option<u16> {
 590     use rustc_ast::{LitIntType, LitKind, MetaItemLit};
 591     if !tcx.features().raw_dylib && tcx.sess.target.arch == "x86" {
 592         feature_err(
 593             &tcx.sess.parse_sess,
 594             sym::raw_dylib,
 595             attr.span,
 596             "`#[link_ordinal]` is unstable on x86",
 597         )
 598         .emit();
 599     }
 600     let meta_item_list = attr.meta_item_list();
 601     let meta_item_list = meta_item_list.as_deref();
 602     let sole_meta_list = match meta_item_list {
 603         Some([item]) => item.lit(),
 604         Some(_) => {
 605             tcx.sess
 606                 .struct_span_err(attr.span, "incorrect number of arguments to `#[link_ordinal]`")
 607                 .note("the attribute requires exactly one argument")
 608                 .emit();
 609             return None;
 610         }
 611         _ => None,
 612     };
 613     if let Some(MetaItemLit { kind: LitKind::Int(ordinal, LitIntType::Unsuffixed), .. }) =
 614         sole_meta_list
 615     {
 616         // According to the table at https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#import-header,
 617         // the ordinal must fit into 16 bits. Similarly, the Ordinal field in COFFShortExport (defined
 618         // in llvm/include/llvm/Object/COFFImportFile.h), which we use to communicate import information
 619         // to LLVM for `#[link(kind = "raw-dylib"_])`, is also defined to be uint16_t.
 620         //
 621         // FIXME: should we allow an ordinal of 0?  The MSVC toolchain has inconsistent support for this:
 622         // both LINK.EXE and LIB.EXE signal errors and abort when given a .DEF file that specifies
 623         // a zero ordinal. However, llvm-dlltool is perfectly happy to generate an import library
 624         // for such a .DEF file, and MSVC's LINK.EXE is also perfectly happy to consume an import
 625         // library produced by LLVM with an ordinal of 0, and it generates an .EXE.  (I don't know yet
 626         // if the resulting EXE runs, as I haven't yet built the necessary DLL -- see earlier comment
 627         // about LINK.EXE failing.)
 628         if *ordinal <= u16::MAX as u128 {
 629             Some(*ordinal as u16)
 630         } else {
 631             let msg = format!("ordinal value in `link_ordinal` is too large: `{}`", &ordinal);
 632             tcx.sess
 633                 .struct_span_err(attr.span, &msg)
 634                 .note("the value may not exceed `u16::MAX`")
 635                 .emit();
 636             None
 637         }
 638     } else {
 639         tcx.sess
 640             .struct_span_err(attr.span, "illegal ordinal format in `link_ordinal`")
 641             .note("an unsuffixed integer value, e.g., `1`, is expected")
 642             .emit();
 643         None
 644     }
 645 }
 646
 647 fn check_link_name_xor_ordinal(
 648     tcx: TyCtxt<'_>,
 649     codegen_fn_attrs: &CodegenFnAttrs,
 650     inline_span: Option<Span>,
 651 ) {
 652     if codegen_fn_attrs.link_name.is_none() || codegen_fn_attrs.link_ordinal.is_none() {
 653         return;
 654     }
 655     let msg = "cannot use `#[link_name]` with `#[link_ordinal]`";
 656     if let Some(span) = inline_span {
 657         tcx.sess.span_err(span, msg);
 658     } else {
 659         tcx.sess.err(msg);
 660     }
 661 }
 662
 663 pub fn provide(providers: &mut Providers) {
 664     *providers = Providers { codegen_fn_attrs, should_inherit_track_caller, ..*providers };
 665 }