Add lint againts invalid runtime symbol definitions

Cargo.lock

@@ -4266,6 +4266,7 @@ dependencies = [
  "rustc_parse_format",
  "rustc_session",
  "rustc_span",
+ "rustc_symbol_mangling",
  "rustc_target",
  "rustc_trait_selection",
  "smallvec",

compiler/rustc_error_codes/src/error_codes/E0755.md

@@ -20,7 +20,7 @@ side effects or infinite loops:
 
 extern "C" {
     #[unsafe(ffi_pure)] // ok!
-    pub fn strlen(s: *const i8) -> isize;
+    pub fn strlen(s: *const std::ffi::c_char) -> usize;
 }
 # fn main() {}
 ```

compiler/rustc_error_codes/src/error_codes/E0756.md

@@ -21,7 +21,7 @@ which have no side effects except for their return value:
 
 extern "C" {
     #[unsafe(ffi_const)] // ok!
-    pub fn strlen(s: *const i8) -> i32;
+    pub fn strlen(s: *const std::ffi::c_char) -> usize;
 }
 # fn main() {}
 ```

compiler/rustc_hir/src/lang_items.rs

@@ -447,6 +447,14 @@ language_item_table! {
 
     // Used to fallback `{float}` to `f32` when `f32: From<{float}>`
     From,                    sym::From,                from_trait,                 Target::Trait,          GenericRequirement::Exact(1);
+
+    // Runtime symbols
+    MemCpy,                  sym::memcpy_fn,           memcpy_fn,                  Target::Fn,             GenericRequirement::None;
+    MemMove,                 sym::memmove_fn,          memmove_fn,                 Target::Fn,             GenericRequirement::None;
+    MemSet,                  sym::memset_fn,           memset_fn,                  Target::Fn,             GenericRequirement::None;
+    MemCmp,                  sym::memcmp_fn,           memcmp_fn,                  Target::Fn,             GenericRequirement::None;
+    Bcmp,                    sym::bcmp_fn,             bcmp_fn,                    Target::Fn,             GenericRequirement::None;
+    StrLen,                  sym::strlen_fn,           strlen_fn,                  Target::Fn,             GenericRequirement::None;
 }
 
 /// The requirement imposed on the generics of a lang item

compiler/rustc_hir/src/weak_lang_items.rs

@@ -23,7 +23,28 @@ macro_rules! weak_lang_items {
     }
 }
 
+macro_rules! weak_only_lang_items {
+    ($($item:ident,)*) => {
+        pub static WEAK_ONLY_LANG_ITEMS: &[LangItem] = &[$(LangItem::$item,)*];
+
+        impl LangItem {
+            pub fn is_weak_only(self) -> bool {
+                matches!(self, $(LangItem::$item)|*)
+            }
+        }
+    }
+}
+
 weak_lang_items! {
     PanicImpl,          rust_begin_unwind;
     EhPersonality,      rust_eh_personality;
 }
+
+weak_only_lang_items! {
+    MemCpy,
+    MemMove,
+    MemSet,
+    MemCmp,
+    Bcmp,
+    StrLen,
+}

compiler/rustc_lint/Cargo.toml

@@ -22,6 +22,7 @@ rustc_middle = { path = "../rustc_middle" }
 rustc_parse_format = { path = "../rustc_parse_format" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
+rustc_symbol_mangling = { path = "../rustc_symbol_mangling" }
 rustc_target = { path = "../rustc_target" }
 rustc_trait_selection = { path = "../rustc_trait_selection" }
 smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }

compiler/rustc_lint/src/lib.rs

@@ -72,6 +72,7 @@ mod precedence;
 mod ptr_nulls;
 mod redundant_semicolon;
 mod reference_casting;
+mod runtime_symbols;
 mod shadowed_into_iter;
 mod static_mut_refs;
 mod traits;
@@ -117,6 +118,7 @@ use precedence::*;
 use ptr_nulls::*;
 use redundant_semicolon::*;
 use reference_casting::*;
+use runtime_symbols::*;
 use rustc_hir::def_id::LocalModDefId;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::TyCtxt;
@@ -246,6 +248,7 @@ late_lint_methods!(
             AsyncFnInTrait: AsyncFnInTrait,
             NonLocalDefinitions: NonLocalDefinitions::default(),
             InteriorMutableConsts: InteriorMutableConsts,
+            RuntimeSymbols: RuntimeSymbols,
             ImplTraitOvercaptures: ImplTraitOvercaptures,
             IfLetRescope: IfLetRescope::default(),
             StaticMutRefs: StaticMutRefs,

compiler/rustc_lint/src/lints.rs

@@ -848,6 +848,45 @@ pub(crate) enum UseLetUnderscoreIgnoreSuggestion {
     },
 }
 
+// runtime_symbols.rs
+#[derive(Diagnostic)]
+pub(crate) enum RedefiningRuntimeSymbolsDiag<'tcx> {
+    #[diag(
+        "invalid definition of the runtime `{$symbol_name}` symbol used by the standard library"
+    )]
+    #[note(
+        "expected `{$expected_fn_sig}`
+    found    `{$found_fn_sig}`"
+    )]
+    #[help(
+        "either fix the signature or remove any attributes like `#[unsafe(no_mangle)]`, `#[unsafe(export_name = \"{$symbol_name}\")]`, or `#[link_name = \"{$symbol_name}\"]`"
+    )]
+    FnDefInvalid { symbol_name: String, expected_fn_sig: Ty<'tcx>, found_fn_sig: Ty<'tcx> },
+    #[diag(
+        "suspicious definition of the runtime `{$symbol_name}` symbol used by the standard library"
+    )]
+    #[note(
+        "expected `{$expected_fn_sig}`
+    found    `{$found_fn_sig}`"
+    )]
+    #[help(
+        "either fix the signature or remove any attributes like `#[unsafe(no_mangle)]`, `#[unsafe(export_name = \"{$symbol_name}\")]`, or `#[link_name = \"{$symbol_name}\"]`"
+    )]
+    #[help("allow this lint if the signature is compatible")]
+    FnDefSuspicious { symbol_name: String, expected_fn_sig: Ty<'tcx>, found_fn_sig: Ty<'tcx> },
+    #[diag(
+        "invalid definition of the runtime `{$symbol_name}` symbol used by the standard library"
+    )]
+    #[note(
+        "expected `{$expected_fn_sig}`
+    found    `static {$symbol_name}: {$static_ty}`"
+    )]
+    #[help(
+        "either fix the signature or remove any attributes `#[unsafe(no_mangle)]` or `#[unsafe(export_name = \"{$symbol_name}\")]`"
+    )]
+    Static { symbol_name: String, static_ty: Ty<'tcx>, expected_fn_sig: Ty<'tcx> },
+}
+
 // drop_forget_useless.rs
 #[derive(Diagnostic)]
 #[diag("calls to `std::mem::drop` with a reference instead of an owned value does nothing")]