Fix review comments

Author: bjorn3

src/shims/foreign_items.rs

@@ -164,15 +164,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     let symbol_name = tcx.symbol_name(instance).name;
                     let is_weak = attrs.linkage == Some(Linkage::WeakAny);
                     if symbol_name == link_name.as_str() {
-                        if let Some(SymbolTarget {
-                            instance: original_instance,
-                            cnum: original_cnum,
-                            is_weak: original_is_weak,
-                        }) = symbol_target
+                        if let Some(original) = &symbol_target
                         {
                             // There is more than one definition with this name. What we do now
                             // depends on whether one or both definitions are weak.
-                            match (is_weak, original_is_weak) {
+                            match (is_weak, original.is_weak) {
                                 (false, true) => {
                                     // Original definition is a weak definition. Override it.
 
@@ -193,14 +189,14 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 
                                     // Make sure we are consistent wrt what is 'first' and 'second'.
                                     let original_span =
-                                        tcx.def_span(original_instance.def_id()).data();
+                                        tcx.def_span(original.instance.def_id()).data();
                                     let span = tcx.def_span(def_id).data();
                                     if original_span < span {
                                         throw_machine_stop!(
                                             TerminationInfo::MultipleSymbolDefinitions {
                                                 link_name,
                                                 first: original_span,
-                                                first_crate: tcx.crate_name(original_cnum),
+                                                first_crate: tcx.crate_name(original.cnum),
                                                 second: span,
                                                 second_crate: tcx.crate_name(cnum),
                                             }
@@ -212,7 +208,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                                                 first: span,
                                                 first_crate: tcx.crate_name(cnum),
                                                 second: original_span,
-                                                second_crate: tcx.crate_name(original_cnum),
+                                                second_crate: tcx.crate_name(original.cnum),
                                             }
                                         );
                                     }
@@ -229,6 +225,9 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     interp_ok(())
                 })?;
 
+                // Once we identified the instance corresponding to the symbol, ensure
+                // it is a function. It is okay to encounter non-functions in the search above
+                // as long as the final instance we arrive at is a function.
                 if let Some(SymbolTarget { instance, .. }) = symbol_target {
                     if !matches!(tcx.def_kind(instance.def_id()), DefKind::Fn | DefKind::AssocFn) {
                         throw_ub_format!(