check link ordinal make sure target is foreign function

compiler/rustc_passes/src/check_attr.rs

@@ -146,6 +146,9 @@ impl CheckAttrVisitor<'_> {
                 | sym::stable
                 | sym::rustc_allowed_through_unstable_modules
                 | sym::rustc_promotable => self.check_stability_promotable(&attr, span, target),
+                sym::link_ordinal => {
+                    self.check_link_ordinal(&attr, span, target)
+                },
                 _ => true,
             };
             is_valid &= attr_is_valid;
@@ -1861,6 +1864,16 @@ impl CheckAttrVisitor<'_> {
         }
     }
 
+    fn check_link_ordinal(&self, attr: &Attribute, _span: Span, target: Target) -> bool {
+        match target {
+            Target::ForeignFn => true,
+            _ => {
+                self.tcx.sess.emit_err(errors::LinkOrdinal { attr_span: attr.span });
+                false
+            }
+        }
+    }
+
     fn check_deprecated(&self, hir_id: HirId, attr: &Attribute, _span: Span, target: Target) {
         match target {
             Target::Closure | Target::Expression | Target::Statement | Target::Arm => {

compiler/rustc_passes/src/errors.rs

@@ -551,6 +551,13 @@ pub struct ConstTrait {
     pub attr_span: Span,
 }
 
+#[derive(SessionDiagnostic)]
+#[error(passes::link_ordinal)]
+pub struct LinkOrdinal {
+    #[primary_span]
+    pub attr_span: Span
+}
+
 #[derive(SessionDiagnostic)]
 #[error(passes::stability_promotable)]
 pub struct StabilityPromotable {