PR Feedback: To Encoder - Treat data pointer the same as fn in Option handling

Author: jchlanda

compiler/rustc_middle/src/ptrauth/discriminator.rs

@@ -316,17 +316,31 @@ enum ClangDiscTy<'tcx> {
     Void,
 }
 
-// Canonicalize `Option<fn ptr>` to `fn ptr`. This is so that we can express C's null ptr argument.
-// Please see: pauth-fn-ptr-type-discrimination-option-callback.rs,
+// Canonicalize Option-wrapped pointer types used to model C nullable pointers.
+//
+// Rust and Clang should compute identical discriminators for equivalent C APIs.
+// Clang does not distinguish nullable from non-nullable pointer types when
+// computing function pointer authentication discriminators, so
+// `Option<fn>` and `Option<*mut T>` are encoded identically to their
+// underlying pointer types.
+//
+// Although `Option<*mut T>` is not considered FFI-safe by Rust and triggers the
+// `improper_ctypes`/`improper_ctypes_definitions` lints, this is a warning
+// rather than a hard error. Canonicalizing it here preserves Clang-compatible
+// discriminator computation.
+//
+// Please see the following tests for sample use cases:
+// pauth-fn-ptr-type-discrimination-option-callback.rs,
 // pauth-fn-ptr-type-discrimination-option-return.rs and pauth-fn-ptr-type-discrimination-option.rs
 fn canonicalize_c_type<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Ty<'tcx> {
     if let ty::Adt(def, args) = ty.kind()
         && tcx.is_diagnostic_item(sym::Option, def.did())
     {
         let inner = args.type_at(0);
 
-        if matches!(inner.kind(), ty::FnPtr(..)) {
-            return inner;
+        match inner.kind() {
+            ty::FnPtr(..) | ty::RawPtr(..) => return inner,
+            _ => {}
         }
     }
 

tests/codegen-llvm/pauth/pauth-fn-ptr-type-discrimination-option-callback.rs

@@ -25,17 +25,28 @@
 // int f_opt(FnCallback cb);
 // int f_raw(FnCallback cb);
 //
+// int d_opt(void *ctx);
+// int d_raw(void *ctx);
+//
 // int callback_i32(int);
 //
 // int (*T_OPT)(FnCallback) = f_opt;
 // int (*T_RAW)(FnCallback) = f_raw;
 //
+// int (*D_OPT)(void *) = d_opt;
+// int (*D_RAW)(void *) = d_raw;
 // int main(void) {
+//   /* function pointers */
 //   T_OPT(callback_i32);
 //   T_OPT(NULL);
 //
 //   T_RAW(callback_i32);
 //
+//   /* data pointers */
+//   int x = 42;
+//   D_OPT(&x);
+//   D_OPT(NULL);
+//
 //   return 0;
 // }
 // ```
@@ -46,16 +57,23 @@
 #![crate_type = "lib"]
 
 extern crate minicore;
-use minicore::Option;
 use minicore::Option::{None, Some};
+use minicore::{Option, c_void};
 
 extern "C" {
     fn f_opt(cb: Option<unsafe extern "C" fn(i32) -> i32>) -> i32;
     fn f_raw(cb: unsafe extern "C" fn(i32) -> i32) -> i32;
+
+    fn g_opt(ctx: Option<*mut c_void>) -> i32;
+    fn g_raw(ctx: *mut c_void) -> i32;
+
+    fn callback_i32(x: i32) -> i32;
 }
 
 type FnOpt = unsafe extern "C" fn(Option<unsafe extern "C" fn(i32) -> i32>) -> i32;
 type FnRaw = unsafe extern "C" fn(unsafe extern "C" fn(i32) -> i32) -> i32;
+type DataOpt = unsafe extern "C" fn(Option<*mut c_void>) -> i32;
+type DataRaw = unsafe extern "C" fn(*mut c_void) -> i32;
 
 #[used]
 // DISC: @{{.*}}T_OPT = constant ptr ptrauth (ptr @{{.*}}f_opt, i32 0, i64 12410), align 8
@@ -66,13 +84,21 @@ static T_OPT: FnOpt = f_opt;
 // NO_DISC: @{{.*}}T_RAW = constant ptr ptrauth (ptr @{{.*}}f_raw, i32 0), align 8
 static T_RAW: FnRaw = f_raw;
 
-unsafe extern "C" {
-    fn callback_i32(x: i32) -> i32;
-}
+// DISC: @{{.*}}G_OPT = constant ptr ptrauth (ptr @{{.*}}g_opt, i32 0, i64 12410), align 8
+// NO_DISC: @{{.*}}G_OPT = constant ptr ptrauth (ptr @{{.*}}g_opt, i32 0), align 8
+#[used]
+static G_OPT: DataOpt = g_opt;
 
+// DISC: @{{.*}}G_RAW = constant ptr ptrauth (ptr @{{.*}}g_raw, i32 0, i64 12410), align 8
+// NO_DISC: @{{.*}}G_RAW = constant ptr ptrauth (ptr @{{.*}}g_raw, i32 0), align 8
+#[used]
+static G_RAW: DataRaw = g_raw;
 // CHECK-LABEL: main
 pub fn main() {
+    let mut x = 42i32;
+
     unsafe {
+        // Function pointers
         //DISC: call i32 ptrauth (ptr @f_opt, i32 0, i64 12410)(ptr ptrauth (ptr @callback_i32, i32 0, i64 2981)) {{.*}} [ "ptrauth"(i32 0, i64 12410) ]
         //NO_DISC: call i32 ptrauth (ptr @f_opt, i32 0)(ptr ptrauth (ptr @callback_i32, i32 0)) {{.*}} [ "ptrauth"(i32 0, i64 0) ]
         let _ = T_OPT(Some(callback_i32));
@@ -82,5 +108,17 @@ pub fn main() {
         // DISC: call i32 ptrauth (ptr @f_raw, i32 0, i64 12410)(ptr ptrauth (ptr @callback_i32, i32 0, i64 2981)) {{.*}} [ "ptrauth"(i32 0, i64 12410) ]
         // NO_DISC: call i32 ptrauth (ptr @f_raw, i32 0)(ptr ptrauth (ptr @callback_i32, i32 0)) {{.*}} [ "ptrauth"(i32 0, i64 0) ]
         let _ = T_RAW(callback_i32);
+
+        // Data pointers
+        // DISC: call i32 ptrauth (ptr @g_opt, i32 0, i64 12410){{.*}} [ "ptrauth"(i32 0, i64 12410) ]
+        // NO_DISC: call i32 ptrauth (ptr @g_opt, i32 0){{.*}} [ "ptrauth"(i32 0, i64 0) ]
+        let _ = G_OPT(Some((&mut x as *mut i32) as *mut c_void));
+        // DISC: call i32 ptrauth (ptr @g_opt, i32 0, i64 12410){{.*}} [ "ptrauth"(i32 0, i64 12410) ]
+        // NO_DISC: call i32 ptrauth (ptr @g_opt, i32 0){{.*}} [ "ptrauth"(i32 0, i64 0) ]
+        let _ = G_OPT(None);
+
+        // DISC: call i32 ptrauth (ptr @g_raw, i32 0, i64 12410){{.*}} [ "ptrauth"(i32 0, i64 12410) ]
+        // NO_DISC: call i32 ptrauth (ptr @g_raw, i32 0){{.*}} [ "ptrauth"(i32 0, i64 0) ]
+        let _ = G_RAW((&mut x as *mut i32) as *mut c_void);
     }
 }