feat(hal): add nicer addr->NonNull conversion (#509)

This is just a bit more convenient.

Author: hawkw

hal-core/src/addr.rs

@@ -152,6 +152,18 @@ pub trait Address:
         );
         ptr::with_exposed_provenance_mut(self.as_usize())
     }
+
+    /// Converts this address into a `Option<NonNull<T>>` from a
+    /// `VAddr`, returning `None` if the address is null.
+    ///
+    /// # Panics
+    ///
+    /// - If `self` is not aligned for a `T`-typed value.
+    #[inline]
+    #[track_caller]
+    fn as_non_null<T>(self) -> Option<ptr::NonNull<T>> {
+        ptr::NonNull::new(self.as_mut_ptr::<T>())
+    }
 }
 
 #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
@@ -369,6 +381,18 @@ macro_rules! impl_addrs {
                 pub fn as_mut_ptr<T>(self) -> *mut T {
                     Address::as_mut_ptr(self)
                 }
+
+                /// Converts this address into a `Option<NonNull<T>>` from a
+                /// `VAddr`, returning `None` if the address is null.
+                ///
+                /// # Panics
+                ///
+                /// - If `self` is not aligned for a `T`-typed value.
+                #[inline]
+                #[track_caller]
+                pub fn as_non_null<T>(self) -> Option<ptr::NonNull<T>> {
+                    ptr::NonNull::new(self.as_mut_ptr::<T>())
+                }
             }
         )+
     }

hal-x86_64/src/mm.rs

@@ -303,7 +303,7 @@ impl<R: level::Recursive> PageTable<R> {
         tracing::trace!(next.addr = ?vaddr, "found next table virtual address");
         // XXX(eliza): this _probably_ could be be a `new_unchecked`...if, after
         // all this, the next table address is null...we're probably pretty fucked!
-        Some(unsafe { &*NonNull::new(vaddr.as_mut_ptr())?.as_ptr() })
+        Some(unsafe { vaddr.as_non_null()?.as_ref() })
     }
 
     #[inline]
@@ -336,7 +336,7 @@ impl<R: level::Recursive> PageTable<R> {
         tracing::trace!(next.addr = ?vaddr, "found next table virtual address");
         // XXX(eliza): this _probably_ could be be a `new_unchecked`...if, after
         // all this, the next table address is null...we're probably pretty fucked!
-        Some(unsafe { &mut *NonNull::new(vaddr.as_ptr())?.as_ptr() })
+        Some(unsafe { vaddr.as_non_null()?.as_mut() })
     }
 
     fn create_next_table<S: Size>(