miri native_calls: ensure we actually expose *mutable* provenance to the memory FFI can access

Author: RalfJung

src/alloc_addresses/mod.rs

@@ -198,8 +198,8 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 }
                 AllocKind::Dead => unreachable!(),
             };
-            // Ensure this pointer's provenance is exposed, so that it can be used by FFI code.
-            return interp_ok(base_ptr.expose_provenance().try_into().unwrap());
+            // We don't have to expose this pointer yet, we do that in `prepare_for_native_call`.
+            return interp_ok(base_ptr.addr().try_into().unwrap());
         }
         // We are not in native lib mode, so we control the addresses ourselves.
         if let Some((reuse_addr, clock)) = global_state.reuse.take_addr(

src/shims/native_lib.rs

@@ -266,7 +266,7 @@ fn imm_to_carg<'tcx>(v: &ImmTy<'tcx>, cx: &impl HasDataLayout) -> InterpResult<'
             CArg::USize(v.to_scalar().to_target_usize(cx)?.try_into().unwrap()),
         ty::RawPtr(..) => {
             let s = v.to_scalar().to_pointer(cx)?.addr();
-            // This relies on the `expose_provenance` in `addr_from_alloc_id`.
+            // This relies on the `expose_provenance` in `prepare_for_native_call`.
             CArg::RawPtr(std::ptr::with_exposed_provenance_mut(s.bytes_usize()))
         }
         _ => throw_unsup_format!("unsupported argument type for native call: {}", v.layout.ty),