mark naked functions as InstantiatedMode::GloballyShared

this makes sure that the function prototype is defined correctly, and we don't see LLVM complaining about a global value with invalid linkage

Author: folkertdev

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -643,14 +643,6 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
         }
     }
 
-    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
-        // naked functions are generated using an extern function and global assembly. To
-        // make sure that these can be linked together by LLVM, the linkage should be external,
-        // unless the user explicitly configured something else (in which case any linker errors
-        // they encounter are their responsibility).
-        codegen_fn_attrs.linkage = codegen_fn_attrs.linkage.or(Some(Linkage::External));
-    }
-
     // Weak lang items have the same semantics as "std internal" symbols in the
     // sense that they're preserved through all our LTO passes and only
     // strippable by the linker.

compiler/rustc_middle/src/mir/mono.rs

@@ -1,4 +1,5 @@
 use crate::dep_graph::{DepNode, WorkProduct, WorkProductId};
+use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::ty::{GenericArgs, Instance, InstanceKind, SymbolName, TyCtxt};
 use rustc_attr::InlineAttr;
 use rustc_data_structures::base_n::BaseNString;
@@ -118,7 +119,9 @@ impl<'tcx> MonoItem<'tcx> {
                 let entry_def_id = tcx.entry_fn(()).map(|(id, _)| id);
                 // If this function isn't inlined or otherwise has an extern
                 // indicator, then we'll be creating a globally shared version.
-                if tcx.codegen_fn_attrs(instance.def_id()).contains_extern_indicator()
+                let codegen_fn_attrs = tcx.codegen_fn_attrs(instance.def_id());
+                if codegen_fn_attrs.contains_extern_indicator()
+                    || codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED)
                     || !instance.def.generates_cgu_internal_copy(tcx)
                     || Some(instance.def_id()) == entry_def_id
                 {