Auto merge of #123071 - rcvalle:rust-cfi-fix-method-fn-ptr-cast, r=compiler-errors

CFI: Fix methods as function pointer cast

Fix casting between methods and function pointers by assigning a secondary type id to methods with their concrete self so they can be used as function pointers.

This was split off from #116404.

cc `@compiler-errors` `@workingjubilee`

2 files changed, 13 insertions, 1 deletions

diff --git a/compiler/rustc_symbol_mangling/src/typeid.rs b/compiler/rustc_symbol_mangling/src/typeid.rs
index 1d28d2b732f..fc1e8e46e8d 100644
--- a/compiler/rustc_symbol_mangling/src/typeid.rs
+++ b/compiler/rustc_symbol_mangling/src/typeid.rs
@@ -13,9 +13,20 @@ bitflags! {
     /// Options for typeid_for_fnabi.
     #[derive(Clone, Copy, Debug)]
     pub struct TypeIdOptions: u32 {
+        /// Generalizes pointers for compatibility with Clang
+        /// `-fsanitize-cfi-icall-generalize-pointers` option for cross-language LLVM CFI and KCFI
+        /// support.
         const GENERALIZE_POINTERS = 1;
+        /// Generalizes repr(C) user-defined type for extern function types with the "C" calling
+        /// convention (or extern types) for cross-language LLVM CFI and  KCFI support.
         const GENERALIZE_REPR_C = 2;
+        /// Normalizes integers for compatibility with Clang
+        /// `-fsanitize-cfi-icall-experimental-normalize-integers` option for cross-language LLVM
+        /// CFI and  KCFI support.
         const NORMALIZE_INTEGERS = 4;
+        /// Do not perform self type erasure for attaching a secondary type id to methods with their
+        /// concrete self so they can be used as function pointers.
+        const NO_SELF_TYPE_ERASURE = 8;
     }
 }
 
diff --git a/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs b/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs
index 04b92fbd33b..7fd5cfeb48b 100644
--- a/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs
+++ b/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs
@@ -1144,7 +1144,8 @@ pub fn typeid_for_instance<'tcx>(
         instance.args = strip_receiver_auto(tcx, instance.args);
     }
 
-    if let Some(impl_id) = tcx.impl_of_method(instance.def_id())
+    if !options.contains(EncodeTyOptions::NO_SELF_TYPE_ERASURE)
+        && let Some(impl_id) = tcx.impl_of_method(instance.def_id())
         && let Some(trait_ref) = tcx.impl_trait_ref(impl_id)
     {
         let impl_method = tcx.associated_item(instance.def_id());