CFI: Support function pointers for trait methods

Adds support for both CFI and KCFI for attaching concrete and abstract
types to functions. KCFI does this through generation of `ReifyShim` on
any function pointer that could go in a vtable, and checking the
`ReifyReason` when emitting the instance. CFI does this by attaching
both the concrete and abstract type to every instance.

TypeID codegen tests are switched to be anchored on the left rather than
the right in order to allow emission of additional type attachments.

Fixes #115953

1 files changed, 7 insertions, 2 deletions

diff --git a/compiler/rustc_symbol_mangling/src/typeid.rs b/compiler/rustc_symbol_mangling/src/typeid.rs
index 11657b3b303..862ba285db8 100644
--- a/compiler/rustc_symbol_mangling/src/typeid.rs
+++ b/compiler/rustc_symbol_mangling/src/typeid.rs
@@ -4,7 +4,7 @@
 /// For more information about LLVM CFI and cross-language LLVM CFI support for the Rust compiler,
 /// see design document in the tracking issue #89653.
 use bitflags::bitflags;
-use rustc_middle::ty::{Instance, Ty, TyCtxt};
+use rustc_middle::ty::{Instance, InstanceDef, ReifyReason, Ty, TyCtxt};
 use rustc_target::abi::call::FnAbi;
 use std::hash::Hasher;
 use twox_hash::XxHash64;
@@ -67,8 +67,13 @@ pub fn kcfi_typeid_for_fnabi<'tcx>(
 pub fn kcfi_typeid_for_instance<'tcx>(
     tcx: TyCtxt<'tcx>,
     instance: Instance<'tcx>,
-    options: TypeIdOptions,
+    mut options: TypeIdOptions,
 ) -> u32 {
+    // If we receive a `ReifyShim` intended to produce a function pointer, we need to remain
+    // concrete - abstraction is for vtables.
+    if matches!(instance.def, InstanceDef::ReifyShim(_, Some(ReifyReason::FnPtr))) {
+        options.remove(TypeIdOptions::ERASE_SELF_TYPE);
+    }
     // A KCFI type metadata identifier is a 32-bit constant produced by taking the lower half of the
     // xxHash64 of the type metadata identifier. (See llvm/llvm-project@cff5bef.)
     let mut hash: XxHash64 = Default::default();