[PAC] Enable support for FPTR_TYPE_DISCR in ABI Version

Also remove error messages/tests that used to guarded it.

Author: jchlanda

compiler/rustc_session/src/diagnostics.rs

@@ -381,12 +381,6 @@ pub(crate) struct StackProtectorNotSupportedForTarget<'a> {
     pub(crate) target_triple: &'a TargetTuple,
 }
 
-#[derive(Diagnostic)]
-#[diag("function pointer type discrimination is not supported")]
-pub(crate) struct PointerAuthenticationTypeDiscriminationNotSupportedForTarget<'a> {
-    pub(crate) target_triple: &'a TargetTuple,
-}
-
 #[derive(Diagnostic)]
 #[diag(
     "`-Z pointer-authentication` is not supported for target {$target_triple} and will be ignored"

compiler/rustc_session/src/session.rs

@@ -209,8 +209,7 @@ impl PointerAuthConfig {
         const GOT: u32 = 8;
         const GOTOS: u32 = 9;
         const TYPEINFO_VT_PTR_DISCR: u32 = 10;
-        // FIXME(jchlanda) We don't yet support function pointer type discrimination.
-        // const FPTR_TYPE_DISCR: u32 = 11;
+        const FPTR_TYPE_DISCR: u32 = 11;
 
         let pauth_abi_version: u32 = (u32::from(self.intrinsics) << INTRINSICS)
             | (u32::from(self.function_pointers.is_some()) << CALLS)
@@ -228,7 +227,10 @@ impl PointerAuthConfig {
             })) << INIT_FINI_ADDR_DISC)
             | (u32::from(self.elf_got) << GOT)
             | (u32::from(self.indirect_gotos) << GOTOS)
-            | (u32::from(self.typeinfo_vt_ptr_discrimination) << TYPEINFO_VT_PTR_DISCR);
+            | (u32::from(self.typeinfo_vt_ptr_discrimination) << TYPEINFO_VT_PTR_DISCR)
+            | (u32::from(self.function_pointers.as_ref().is_some_and(|schema| {
+                matches!(schema.discrimination_kind, PointerAuthDiscrimination::Type)
+            })) << FPTR_TYPE_DISCR);
 
         pauth_abi_version
     }
@@ -1446,19 +1448,6 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
         sess.dcx().emit_err(diagnostics::LinkerPluginToWindowsNotSupported);
     }
 
-    if sess
-        .pointer_auth_config
-        .as_ref()
-        .and_then(|cfg| cfg.function_pointers.as_ref())
-        .is_some_and(|schema| matches!(schema.discrimination_kind, PointerAuthDiscrimination::Type))
-    {
-        sess.dcx().emit_err(
-            diagnostics::PointerAuthenticationTypeDiscriminationNotSupportedForTarget {
-                target_triple: &sess.opts.target_triple,
-            },
-        );
-    }
-
     if sess.target.cfg_abi != CfgAbi::Pauthtest
         && !sess.opts.unstable_opts.pointer_authentication.is_empty()
     {