Copy from userspace to MaybeUninit

Co-authored-by: Thalia Archibald <thalia@archibald.dev>

Author: Jethro Beekman

library/std/src/sys/pal/sgx/abi/usercalls/alloc.rs

@@ -6,7 +6,7 @@ use super::super::mem::{is_enclave_range, is_user_range};
 usecrate::arch::asm;
 usecrate::cell::UnsafeCell;
 usecrate::convert::TryInto;
-usecrate::mem::{self,ManuallyDrop};
+usecrate::mem::{self,ManuallyDrop,MaybeUninit};
 usecrate::ops::{CoerceUnsized,Deref,DerefMut,Index,IndexMut};
 usecrate::pin::PinCoerceUnsized;
 usecrate::ptr::{self,NonNull};
@@ -209,6 +209,45 @@ impl<T: ?Sized> NewUserRef<NonNull<T>> for NonNull<UserRef<T>> {
 }
 }
 
+/// A type which can a destination for safely copying from userspace.
+///
+/// # Safety
+///
+/// Requires that `T` and `Self` have identical layouts.
+#[unstable(feature = "sgx_platform", issue = "56975")]
+pubunsafetraitUserSafeCopyDestination<T: ?Sized>{
+/// Returns a pointer for writing to the value.
+fnas_mut_ptr(&mutself) -> *mutT;
+}
+
+#[unstable(feature = "sgx_platform", issue = "56975")]
+unsafeimpl<T>UserSafeCopyDestination<T>forT{
+fnas_mut_ptr(&mutself) -> *mutT{
+selfas_
+}
+}
+
+#[unstable(feature = "sgx_platform", issue = "56975")]
+unsafeimpl<T>UserSafeCopyDestination<[T]>for[T]{
+fnas_mut_ptr(&mutself) -> *mut[T]{
+selfas_
+}
+}
+
+#[unstable(feature = "sgx_platform", issue = "56975")]
+unsafeimpl<T>UserSafeCopyDestination<T>forMaybeUninit<T>{
+fnas_mut_ptr(&mutself) -> *mutT{
+selfas*mutSelfas_
+}
+}
+
+#[unstable(feature = "sgx_platform", issue = "56975")]
+unsafeimpl<T>UserSafeCopyDestination<[T]>for[MaybeUninit<T>]{
+fnas_mut_ptr(&mutself) -> *mut[T]{
+selfas*mutSelfas_
+}
+}
+
 #[unstable(feature = "sgx_platform", issue = "56975")]
 impl<T: ?Sized>User<T>
 where
@@ -544,12 +583,12 @@ where
 /// # Panics
 /// This function panics if the destination doesn't have the same size as
 /// the source. This can happen for dynamically-sized types such as slices.
-pubfncopy_to_enclave(&self,dest:&mutT){
+pubfncopy_to_enclave<U: ?Sized + UserSafeCopyDestination<T>>(&self,dest:&mutU){
 unsafe{
 assert_eq!(size_of_val(dest), size_of_val(&*self.0.get()));
 copy_from_userspace(
 self.0.get()as*constTas*constu8,
- destas*mutTas*mutu8,
+ dest.as_mut_ptr()as*mutu8,
 size_of_val(dest),
 );
 }