[PAC] Include discriminator in FnAbi, add llvm.ptrauth.resign

This patch introduces the following:

* Extends `FnAbi` (`callconv`) with a `ptrauth_type_discriminator`
  field. This field is only used when emitting pointer authentication
  call bundles. It is stored in `FnAbi` because the call site is not
  guaranteed to have access to an `Instance`, so the discriminator
  cannot always be computed on demand.
* Adds support for `llvm.ptrauth.resign`. This intrinsic will be used
  when support for semantic transmute is added.
* Performs a minor API redesign as groundwork for allowing call sites to
  modify schemas in place.

Author: jchlanda

compiler/rustc_codegen_gcc/src/builder.rs

@@ -1843,6 +1843,17 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
     fn fptosi_sat(&mut self, val: RValue<'gcc>, dest_ty: Type<'gcc>) -> RValue<'gcc> {
         self.fptoint_sat(true, val, dest_ty)
     }
+
+    fn ptrauth_resign(
+        &mut self,
+        _value: Self::Value,
+        _old_key: u32,
+        _old_discriminator: u64,
+        _new_key: u32,
+        _new_discriminator: u64,
+    ) -> Self::Value {
+        bug!("Resigning of pointers not implemented");
+    }
 }
 
 impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {

compiler/rustc_codegen_gcc/src/common.rs

@@ -247,7 +247,7 @@ impl<'gcc, 'tcx> ConstCodegenMethods for CodegenCx<'gcc, 'tcx> {
         cv: Scalar,
         layout: abi::Scalar,
         ty: Type<'gcc>,
-        _schema: Option<&PointerAuthSchema>,
+        _schema: Option<PointerAuthSchema>,
     ) -> RValue<'gcc> {
         let bitsize = if layout.is_bool() { 1 } else { layout.size(self).bits() };
         match cv {

compiler/rustc_codegen_gcc/src/context.rs

@@ -401,7 +401,7 @@ impl<'gcc, 'tcx> MiscCodegenMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
     fn get_fn_addr(
         &self,
         instance: Instance<'tcx>,
-        _pointer_auth_schema: Option<&PointerAuthSchema>,
+        _pointer_auth_schema: Option<PointerAuthSchema>,
     ) -> RValue<'gcc> {
         let func_name = self.tcx.symbol_name(instance).name;
 

compiler/rustc_codegen_gcc/src/int.rs

@@ -375,6 +375,7 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
             fixed_count: 3,
             conv: CanonAbi::C,
             can_unwind: false,
+            ptrauth_type_discriminator: 0,
         };
         fn_abi.adjust_for_foreign_abi(self.cx, ExternAbi::C { unwind: false });
 

compiler/rustc_codegen_llvm/src/builder.rs

@@ -1542,6 +1542,30 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         let cold_inline = llvm::AttributeKind::Cold.create_attr(self.llcx);
         attributes::apply_to_callsite(llret, llvm::AttributePlace::Function, &[cold_inline]);
     }
+
+    fn ptrauth_resign(
+        &mut self,
+        value: &'ll Value,
+        old_key: u32,
+        old_discriminator: u64,
+        new_key: u32,
+        new_discriminator: u64,
+    ) -> &'ll Value {
+        let ptr_as_int = self.ptrtoint(value, self.type_i64());
+        let resigned_int = self.call_intrinsic(
+            "llvm.ptrauth.resign",
+            &[],
+            &[
+                ptr_as_int,
+                self.const_i32(old_key as i32),
+                self.const_i64(old_discriminator as i64),
+                self.const_i32(new_key as i32),
+                self.const_i64(new_discriminator as i64),
+            ],
+        );
+
+        self.inttoptr(resigned_int, self.val_ty(value))
+    }
 }
 
 impl<'ll> StaticBuilderMethods for Builder<'_, 'll, '_> {
@@ -2059,8 +2083,14 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
         // bundles.
         // Once this is resolved, we should analyze each call and skip direct calls. See the
         // discussion in the rust-lang issue: <https://github.com/rust-lang/rust/issues/152532>
-        let key: u32 = 0;
-        let discriminator: u64 = 0;
+
+        let key: u32 = self.sess().pointer_authentication_fn_ptr_key().unwrap() as u32;
+        let discriminator = if self.sess().pointer_authentication_fn_ptr_type_discrimination() {
+            fn_abi?.ptrauth_type_discriminator
+        } else {
+            0
+        };
+
         Some(llvm::OperandBundleBox::new(
             "ptrauth",
             &[self.const_u32(key), self.const_u64(discriminator)],

compiler/rustc_codegen_llvm/src/common.rs

@@ -30,11 +30,9 @@ pub(crate) fn maybe_sign_fn_ptr<'ll, 'tcx>(
     cx: &CodegenCx<'ll, '_>,
     instance: Instance<'tcx>,
     llfn: &'ll llvm::Value,
-    schema: &PointerAuthSchema,
+    schema: PointerAuthSchema,
 ) -> &'ll llvm::Value {
-    if cx.tcx.sess.pointer_authentication_functions().is_none() {
-        return llfn;
-    }
+    assert!(cx.tcx.sess.pointer_authentication_functions().is_some());
 
     // Only free functions or methods
     let def_id = instance.def_id();
@@ -317,7 +315,7 @@ impl<'ll, 'tcx> ConstCodegenMethods for CodegenCx<'ll, 'tcx> {
         cv: Scalar,
         layout: abi::Scalar,
         llty: &'ll Type,
-        schema: Option<&PointerAuthSchema>,
+        schema: Option<PointerAuthSchema>,
     ) -> &'ll Value {
         let bitsize = if layout.is_bool() { 1 } else { layout.size(self).bits() };
         match cv {

compiler/rustc_codegen_llvm/src/context.rs

@@ -913,7 +913,7 @@ impl<'ll, 'tcx> MiscCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
     fn get_fn_addr(
         &self,
         instance: Instance<'tcx>,
-        pointer_auth_schema: Option<&PointerAuthSchema>,
+        pointer_auth_schema: Option<PointerAuthSchema>,
     ) -> &'ll Value {
         // When pointer authentication metadata is provided, `get_fn_addr` will
         // attempt to sign the pointer using LLVM's `ConstPtrAuth` constant

compiler/rustc_codegen_ssa/src/traits/builder.rs

@@ -667,4 +667,13 @@ pub trait BuilderMethods<'a, 'tcx>:
     fn zext(&mut self, val: Self::Value, dest_ty: Self::Type) -> Self::Value;
 
     fn apply_attrs_to_cleanup_callsite(&mut self, llret: Self::Value);
+
+    fn ptrauth_resign(
+        &mut self,
+        value: Self::Value,
+        old_key: u32,
+        old_discriminator: u64,
+        new_key: u32,
+        new_discriminator: u64,
+    ) -> Self::Value;
 }

compiler/rustc_codegen_ssa/src/traits/consts.rs

@@ -47,7 +47,7 @@ pub trait ConstCodegenMethods: BackendTypes {
         cv: Scalar,
         layout: abi::Scalar,
         llty: Self::Type,
-        schema: Option<&PointerAuthSchema>,
+        schema: Option<PointerAuthSchema>,
     ) -> Self::Value;
 
     fn const_ptr_byte_offset(&self, val: Self::Value, offset: abi::Size) -> Self::Value;

compiler/rustc_codegen_ssa/src/traits/misc.rs

@@ -22,7 +22,7 @@ pub trait MiscCodegenMethods<'tcx>: BackendTypes {
     fn get_fn_addr(
         &self,
         instance: Instance<'tcx>,
-        pointer_auth_schema: Option<&PointerAuthSchema>,
+        pointer_auth_schema: Option<PointerAuthSchema>,
     ) -> Self::Value;
     fn eh_personality(&self) -> Self::Function;
     fn sess(&self) -> &Session;