From 7aa8707639ede0605d7182bc13047b6e4549e5b1 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Jana=20D=C3=B6nszelmann?= Date: Tue, 29 Jul 2025 20:51:46 +0200 Subject: [PATCH] make no_mangle explicit on foreign items --- .../src/back/symbol_export.rs | 2 +- .../rustc_codegen_ssa/src/codegen_attrs.rs | 21 +++++++ .../src/middle/codegen_fn_attrs.rs | 7 ++- compiler/rustc_middle/src/mir/mono.rs | 2 +- .../src/cross_crate_inline.rs | 2 +- compiler/rustc_passes/src/check_attr.rs | 36 ++++++------ compiler/rustc_passes/src/dead.rs | 2 +- compiler/rustc_passes/src/reachable.rs | 5 +- compiler/rustc_symbol_mangling/src/lib.rs | 55 ++++++++++--------- .../clippy/clippy_lints/src/missing_inline.rs | 2 +- src/tools/miri/src/bin/miri.rs | 2 +- src/tools/miri/src/helpers.rs | 2 +- tests/run-make/wasm-panic-small/rmake.rs | 2 +- 13 files changed, 85 insertions(+), 55 deletions(-) diff --git a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs index 7e124f65324a5..0494666bda923 100644 --- a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs +++ b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs @@ -569,7 +569,7 @@ fn symbol_export_level(tcx: TyCtxt<'_>, sym_def_id: DefId) -> SymbolExportLevel // core/std/allocators/etc. For example symbols used to hook up allocation // are not considered for export let codegen_fn_attrs = tcx.codegen_fn_attrs(sym_def_id); - let is_extern = codegen_fn_attrs.contains_extern_indicator(); + let is_extern = codegen_fn_attrs.contains_extern_indicator(tcx, sym_def_id); let std_internal = codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL); diff --git a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs index 7f54a47327af8..287787eb3d1ff 100644 --- a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs +++ b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs @@ -443,6 +443,27 @@ fn apply_overrides(tcx: TyCtxt<'_>, did: LocalDefId, codegen_fn_attrs: &mut Code if tcx.should_inherit_track_caller(did) { codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER; } + + // Foreign items by default use no mangling for their symbol name. + if tcx.is_foreign_item(did) { + // There's a few exceptions to this rule though: + if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) { + // * `#[rustc_std_internal_symbol]` mangles the symbol name in a special way + // both for exports and imports through foreign items. This is handled further, + // during symbol mangling logic. + } else if codegen_fn_attrs.link_name.is_some() { + // * This can be overridden with the `#[link_name]` attribute + } else { + // NOTE: there's one more exception that we cannot apply here. On wasm, + // some items cannot be `no_mangle`. + // However, we don't have enough information here to determine that. + // As such, no_mangle foreign items on wasm that have the same defid as some + // import will *still* be mangled despite this. + // + // if none of the exceptions apply; apply no_mangle + codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE; + } + } } fn check_result( diff --git a/compiler/rustc_middle/src/middle/codegen_fn_attrs.rs b/compiler/rustc_middle/src/middle/codegen_fn_attrs.rs index 94384e64afd15..52341df074085 100644 --- a/compiler/rustc_middle/src/middle/codegen_fn_attrs.rs +++ b/compiler/rustc_middle/src/middle/codegen_fn_attrs.rs @@ -3,6 +3,7 @@ use std::borrow::Cow; use rustc_abi::Align; use rustc_ast::expand::autodiff_attrs::AutoDiffAttrs; use rustc_hir::attrs::{InlineAttr, InstructionSetAttr, OptimizeAttr}; +use rustc_hir::def_id::DefId; use rustc_macros::{HashStable, TyDecodable, TyEncodable}; use rustc_span::Symbol; use rustc_target::spec::SanitizerSet; @@ -193,7 +194,11 @@ impl CodegenFnAttrs { /// * `#[linkage]` is present /// /// Keep this in sync with the logic for the unused_attributes for `#[inline]` lint. - pub fn contains_extern_indicator(&self) -> bool { + pub fn contains_extern_indicator(&self, tcx: TyCtxt<'_>, did: DefId) -> bool { + if tcx.is_foreign_item(did) { + return false; + } + self.flags.contains(CodegenFnAttrFlags::NO_MANGLE) || self.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) || self.export_name.is_some() diff --git a/compiler/rustc_middle/src/mir/mono.rs b/compiler/rustc_middle/src/mir/mono.rs index e5864660575c5..3afd946b30a2a 100644 --- a/compiler/rustc_middle/src/mir/mono.rs +++ b/compiler/rustc_middle/src/mir/mono.rs @@ -151,7 +151,7 @@ impl<'tcx> MonoItem<'tcx> { // instantiation: // We emit an unused_attributes lint for this case, which should be kept in sync if possible. let codegen_fn_attrs = tcx.codegen_instance_attrs(instance.def); - if codegen_fn_attrs.contains_extern_indicator() + if codegen_fn_attrs.contains_extern_indicator(tcx, instance.def.def_id()) || codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) { return InstantiationMode::GloballyShared { may_conflict: false }; diff --git a/compiler/rustc_mir_transform/src/cross_crate_inline.rs b/compiler/rustc_mir_transform/src/cross_crate_inline.rs index b186c2bd7758f..03fdf9fbac538 100644 --- a/compiler/rustc_mir_transform/src/cross_crate_inline.rs +++ b/compiler/rustc_mir_transform/src/cross_crate_inline.rs @@ -18,7 +18,7 @@ fn cross_crate_inlinable(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool { let codegen_fn_attrs = tcx.codegen_fn_attrs(def_id); // If this has an extern indicator, then this function is globally shared and thus will not // generate cgu-internal copies which would make it cross-crate inlinable. - if codegen_fn_attrs.contains_extern_indicator() { + if codegen_fn_attrs.contains_extern_indicator(tcx, def_id.into()) { return false; } diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs index 10c532b436aa1..22e2a887b61a2 100644 --- a/compiler/rustc_passes/src/check_attr.rs +++ b/compiler/rustc_passes/src/check_attr.rs @@ -561,7 +561,24 @@ impl<'tcx> CheckAttrVisitor<'tcx> { match target { Target::Fn | Target::Closure - | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => {} + | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => { + // `#[inline]` is ignored if the symbol must be codegened upstream because it's exported. + if let Some(did) = hir_id.as_owner() + && self.tcx.def_kind(did).has_codegen_attrs() + && kind != &InlineAttr::Never + { + let attrs = self.tcx.codegen_fn_attrs(did); + // Not checking naked as `#[inline]` is forbidden for naked functions anyways. + if attrs.contains_extern_indicator(self.tcx, did.into()) { + self.tcx.emit_node_span_lint( + UNUSED_ATTRIBUTES, + hir_id, + attr_span, + errors::InlineIgnoredForExported {}, + ); + } + } + } Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => { self.tcx.emit_node_span_lint( UNUSED_ATTRIBUTES, @@ -588,23 +605,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> { self.dcx().emit_err(errors::InlineNotFnOrClosure { attr_span, defn_span }); } } - - // `#[inline]` is ignored if the symbol must be codegened upstream because it's exported. - if let Some(did) = hir_id.as_owner() - && self.tcx.def_kind(did).has_codegen_attrs() - && kind != &InlineAttr::Never - { - let attrs = self.tcx.codegen_fn_attrs(did); - // Not checking naked as `#[inline]` is forbidden for naked functions anyways. - if attrs.contains_extern_indicator() { - self.tcx.emit_node_span_lint( - UNUSED_ATTRIBUTES, - hir_id, - attr_span, - errors::InlineIgnoredForExported {}, - ); - } - } } /// Checks that `#[coverage(..)]` is applied to a function/closure/method, diff --git a/compiler/rustc_passes/src/dead.rs b/compiler/rustc_passes/src/dead.rs index fa9d0c7b1b7d4..1c76e4e7166d7 100644 --- a/compiler/rustc_passes/src/dead.rs +++ b/compiler/rustc_passes/src/dead.rs @@ -701,7 +701,7 @@ fn has_allow_dead_code_or_lang_attr( // #[used], #[no_mangle], #[export_name], etc also keeps the item alive // forcefully, e.g., for placing it in a specific section. - cg_attrs.contains_extern_indicator() + cg_attrs.contains_extern_indicator(tcx, def_id.into()) || cg_attrs.flags.contains(CodegenFnAttrFlags::USED_COMPILER) || cg_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER) } diff --git a/compiler/rustc_passes/src/reachable.rs b/compiler/rustc_passes/src/reachable.rs index 2f78c22c7483b..6cd8a54ecf434 100644 --- a/compiler/rustc_passes/src/reachable.rs +++ b/compiler/rustc_passes/src/reachable.rs @@ -183,7 +183,7 @@ impl<'tcx> ReachableContext<'tcx> { } else { CodegenFnAttrs::EMPTY }; - let is_extern = codegen_attrs.contains_extern_indicator(); + let is_extern = codegen_attrs.contains_extern_indicator(self.tcx, search_item.into()); if is_extern { self.reachable_symbols.insert(search_item); } @@ -423,8 +423,9 @@ fn has_custom_linkage(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool { if !tcx.def_kind(def_id).has_codegen_attrs() { return false; } + let codegen_attrs = tcx.codegen_fn_attrs(def_id); - codegen_attrs.contains_extern_indicator() + codegen_attrs.contains_extern_indicator(tcx, def_id.into()) // FIXME(nbdd0121): `#[used]` are marked as reachable here so it's picked up by // `linked_symbols` in cg_ssa. They won't be exported in binary or cdylib due to their // `SymbolExportLevel::Rust` export level but may end up being exported in dylibs. diff --git a/compiler/rustc_symbol_mangling/src/lib.rs b/compiler/rustc_symbol_mangling/src/lib.rs index 6bcb7f6e093c4..f3c96f641902e 100644 --- a/compiler/rustc_symbol_mangling/src/lib.rs +++ b/compiler/rustc_symbol_mangling/src/lib.rs @@ -218,32 +218,33 @@ fn compute_symbol_name<'tcx>( } } - // Foreign items by default use no mangling for their symbol name. There's a - // few exceptions to this rule though: - // - // * This can be overridden with the `#[link_name]` attribute - // - // * On the wasm32 targets there is a bug (or feature) in LLD [1] where the - // same-named symbol when imported from different wasm modules will get - // hooked up incorrectly. As a result foreign symbols, on the wasm target, - // with a wasm import module, get mangled. Additionally our codegen will - // deduplicate symbols based purely on the symbol name, but for wasm this - // isn't quite right because the same-named symbol on wasm can come from - // different modules. For these reasons if `#[link(wasm_import_module)]` - // is present we mangle everything on wasm because the demangled form will - // show up in the `wasm-import-name` custom attribute in LLVM IR. - // - // * `#[rustc_std_internal_symbol]` mangles the symbol name in a special way - // both for exports and imports through foreign items. This is handled above. - // [1]: https://bugs.llvm.org/show_bug.cgi?id=44316 - if tcx.is_foreign_item(def_id) - && (!tcx.sess.target.is_like_wasm - || !tcx.wasm_import_module_map(def_id.krate).contains_key(&def_id)) + let wasm_import_module_exception_force_mangling = { + // * On the wasm32 targets there is a bug (or feature) in LLD [1] where the + // same-named symbol when imported from different wasm modules will get + // hooked up incorrectly. As a result foreign symbols, on the wasm target, + // with a wasm import module, get mangled. Additionally our codegen will + // deduplicate symbols based purely on the symbol name, but for wasm this + // isn't quite right because the same-named symbol on wasm can come from + // different modules. For these reasons if `#[link(wasm_import_module)]` + // is present we mangle everything on wasm because the demangled form will + // show up in the `wasm-import-name` custom attribute in LLVM IR. + // + // [1]: https://bugs.llvm.org/show_bug.cgi?id=44316 + // + // So, on wasm if a foreign item loses its `#[no_mangle]`, it might *still* + // be mangled if we're forced to. Note: I don't like this. + // These kinds of exceptions should be added during the `codegen_attrs` query. + // However, we don't have the wasm import module map there yet. + tcx.is_foreign_item(def_id) + && tcx.sess.target.is_like_wasm + && tcx.wasm_import_module_map(LOCAL_CRATE).contains_key(&def_id.into()) + }; + + if let Some(name) = attrs.link_name + && !wasm_import_module_exception_force_mangling { - if let Some(name) = attrs.link_name { - return name.to_string(); - } - return tcx.item_name(def_id).to_string(); + // Use provided name + return name.to_string(); } if let Some(name) = attrs.export_name { @@ -251,7 +252,9 @@ fn compute_symbol_name<'tcx>( return name.to_string(); } - if attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE) { + if attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE) + && !wasm_import_module_exception_force_mangling + { // Don't mangle return tcx.item_name(def_id).to_string(); } diff --git a/src/tools/clippy/clippy_lints/src/missing_inline.rs b/src/tools/clippy/clippy_lints/src/missing_inline.rs index d02952eb48702..b16924babd1c5 100644 --- a/src/tools/clippy/clippy_lints/src/missing_inline.rs +++ b/src/tools/clippy/clippy_lints/src/missing_inline.rs @@ -190,5 +190,5 @@ impl<'tcx> LateLintPass<'tcx> for MissingInline { /// and a rustc warning would be triggered, see #15301 fn fn_is_externally_exported(cx: &LateContext<'_>, def_id: DefId) -> bool { let attrs = cx.tcx.codegen_fn_attrs(def_id); - attrs.contains_extern_indicator() + attrs.contains_extern_indicator(cx.tcx, def_id) } diff --git a/src/tools/miri/src/bin/miri.rs b/src/tools/miri/src/bin/miri.rs index ae1b25f8857a0..d9e374c414cad 100644 --- a/src/tools/miri/src/bin/miri.rs +++ b/src/tools/miri/src/bin/miri.rs @@ -279,7 +279,7 @@ impl rustc_driver::Callbacks for MiriBeRustCompilerCalls { return None; } let codegen_fn_attrs = tcx.codegen_fn_attrs(local_def_id); - if codegen_fn_attrs.contains_extern_indicator() + if codegen_fn_attrs.contains_extern_indicator(tcx, local_def_id.into()) || codegen_fn_attrs .flags .contains(CodegenFnAttrFlags::USED_COMPILER) diff --git a/src/tools/miri/src/helpers.rs b/src/tools/miri/src/helpers.rs index 43cb1c9ae053c..a8e2151afe610 100644 --- a/src/tools/miri/src/helpers.rs +++ b/src/tools/miri/src/helpers.rs @@ -132,7 +132,7 @@ pub fn iter_exported_symbols<'tcx>( for def_id in crate_items.definitions() { let exported = tcx.def_kind(def_id).has_codegen_attrs() && { let codegen_attrs = tcx.codegen_fn_attrs(def_id); - codegen_attrs.contains_extern_indicator() + codegen_attrs.contains_extern_indicator(tcx, def_id.into()) || codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) || codegen_attrs.flags.contains(CodegenFnAttrFlags::USED_COMPILER) || codegen_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER) diff --git a/tests/run-make/wasm-panic-small/rmake.rs b/tests/run-make/wasm-panic-small/rmake.rs index e69fbac96356a..ea0b6faf037c5 100644 --- a/tests/run-make/wasm-panic-small/rmake.rs +++ b/tests/run-make/wasm-panic-small/rmake.rs @@ -24,5 +24,5 @@ fn test(cfg: &str) { let bytes = rfs::read("foo.wasm"); println!("{}", bytes.len()); - assert!(bytes.len() < 40_000); + assert!(bytes.len() < 40_000, "bytes len was: {}", bytes.len()); }