Use NonNull<Void> instead of *mut u8 in the Alloc trait

Fixes #49608

Author: glandium

src/doc/nomicon

@@ -30,6 +30,7 @@ looks like:
 #![feature(global_allocator, allocator_api, heap_api)]
 
 use std::alloc::{GlobalAlloc, System, Layout, Void};
+use std::ptr::NonNull;
 
 struct MyAllocator;
 

src/doc/unstable-book/src/language-features/global-allocator.md

@@ -16,6 +16,7 @@
             issue = "32838")]
 
 use core::intrinsics::{min_align_of_val, size_of_val};
+use core::ptr::NonNull;
 use core::usize;
 
 #[doc(inline)]
@@ -120,27 +121,27 @@ unsafe impl GlobalAlloc for Global {
 
 unsafe impl Alloc for Global {
     #[inline]
-    unsafe fn alloc(&mut self, layout: Layout) -> Result<*mut u8, AllocErr> {
+    unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<Void>, AllocErr> {
         GlobalAlloc::alloc(self, layout).into()
     }
 
     #[inline]
-    unsafe fn dealloc(&mut self, ptr: *mut u8, layout: Layout) {
-        GlobalAlloc::dealloc(self, ptr as *mut Void, layout)
+    unsafe fn dealloc(&mut self, ptr: NonNull<Void>, layout: Layout) {
+        GlobalAlloc::dealloc(self, ptr.as_ptr(), layout)
     }
 
     #[inline]
     unsafe fn realloc(&mut self,
-                      ptr: *mut u8,
+                      ptr: NonNull<Void>,
                       layout: Layout,
                       new_size: usize)
-                      -> Result<*mut u8, AllocErr>
+                      -> Result<NonNull<Void>, AllocErr>
     {
-        GlobalAlloc::realloc(self, ptr as *mut Void, layout, new_size).into()
+        GlobalAlloc::realloc(self, ptr.as_ptr(), layout, new_size).into()
     }
 
     #[inline]
-    unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<*mut u8, AllocErr> {
+    unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<Void>, AllocErr> {
         GlobalAlloc::alloc_zeroed(self, layout).into()
     }
 
@@ -195,8 +196,8 @@ mod tests {
             let ptr = Global.alloc_zeroed(layout.clone())
                 .unwrap_or_else(|_| Global.oom());
 
-            let end = ptr.offset(layout.size() as isize);
-            let mut i = ptr;
+            let mut i = ptr.cast::<u8>().as_ptr();
+            let end = i.offset(layout.size() as isize);
             while i < end {
                 assert_eq!(*i, 0);
                 i = i.offset(1);

src/liballoc/alloc.rs

@@ -512,15 +512,13 @@ impl<T: ?Sized> Arc<T> {
     // Non-inlined part of `drop`.
     #[inline(never)]
     unsafe fn drop_slow(&mut self) {
-        let ptr = self.ptr.as_ptr();
-
         // Destroy the data at this time, even though we may not free the box
         // allocation itself (there may still be weak pointers lying around).
         ptr::drop_in_place(&mut self.ptr.as_mut().data);
 
         if self.inner().weak.fetch_sub(1, Release) == 1 {
             atomic::fence(Acquire);
-            Global.dealloc(ptr as *mut u8, Layout::for_value(&*ptr))
+            Global.dealloc(self.ptr.as_void(), Layout::for_value(self.ptr.as_ref()))
         }
     }
 
@@ -558,7 +556,7 @@ impl<T: ?Sized> Arc<T> {
             .unwrap_or_else(|_| Global.oom());
 
         // Initialize the real ArcInner
-        let inner = set_data_ptr(ptr as *mut T, mem) as *mut ArcInner<T>;
+        let inner = set_data_ptr(ptr as *mut T, mem.as_ptr() as *mut u8) as *mut ArcInner<T>;
 
         ptr::write(&mut (*inner).strong, atomic::AtomicUsize::new(1));
         ptr::write(&mut (*inner).weak, atomic::AtomicUsize::new(1));
@@ -625,7 +623,7 @@ impl<T: Clone> ArcFromSlice<T> for Arc<[T]> {
         // In the event of a panic, elements that have been written
         // into the new ArcInner will be dropped, then the memory freed.
         struct Guard<T> {
-            mem: *mut u8,
+            mem: NonNull<u8>,
             elems: *mut T,
             layout: Layout,
             n_elems: usize,
@@ -639,7 +637,7 @@ impl<T: Clone> ArcFromSlice<T> for Arc<[T]> {
                     let slice = from_raw_parts_mut(self.elems, self.n_elems);
                     ptr::drop_in_place(slice);
 
-                    Global.dealloc(self.mem, self.layout.clone());
+                    Global.dealloc(self.mem.as_void(), self.layout.clone());
                 }
             }
         }
@@ -655,7 +653,7 @@ impl<T: Clone> ArcFromSlice<T> for Arc<[T]> {
             let elems = &mut (*ptr).data as *mut [T] as *mut T;
 
             let mut guard = Guard{
-                mem: mem,
+                mem: NonNull::new_unchecked(mem),
                 elems: elems,
                 layout: layout,
                 n_elems: 0,
@@ -1147,8 +1145,6 @@ impl<T: ?Sized> Drop for Weak<T> {
     /// assert!(other_weak_foo.upgrade().is_none());
     /// ```
     fn drop(&mut self) {
-        let ptr = self.ptr.as_ptr();
-
         // If we find out that we were the last weak pointer, then its time to
         // deallocate the data entirely. See the discussion in Arc::drop() about
         // the memory orderings
@@ -1160,7 +1156,7 @@ impl<T: ?Sized> Drop for Weak<T> {
         if self.inner().weak.fetch_sub(1, Release) == 1 {
             atomic::fence(Acquire);
             unsafe {
-                Global.dealloc(ptr as *mut u8, Layout::for_value(&*ptr))
+                Global.dealloc(self.ptr.as_void(), Layout::for_value(self.ptr.as_ref()))
             }
         }
     }

src/liballoc/arc.rs

@@ -236,7 +236,7 @@ impl<K, V> Root<K, V> {
     pub fn pop_level(&mut self) {
         debug_assert!(self.height > 0);
 
-        let top = self.node.ptr.as_ptr() as *mut u8;
+        let top = self.node.ptr;
 
         self.node = unsafe {
             BoxedNode::from_ptr(self.as_mut()
@@ -249,7 +249,7 @@ impl<K, V> Root<K, V> {
         self.as_mut().as_leaf_mut().parent = ptr::null();
 
         unsafe {
-            Global.dealloc(top, Layout::new::<InternalNode<K, V>>());
+            Global.dealloc(NonNull::from(top).as_void(), Layout::new::<InternalNode<K, V>>());
         }
     }
 }
@@ -433,9 +433,9 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::Leaf> {
             marker::Edge
         >
     > {
-        let ptr = self.as_leaf() as *const LeafNode<K, V> as *const u8 as *mut u8;
+        let node = self.node;
         let ret = self.ascend().ok();
-        Global.dealloc(ptr, Layout::new::<LeafNode<K, V>>());
+        Global.dealloc(node.as_void(), Layout::new::<LeafNode<K, V>>());
         ret
     }
 }
@@ -454,9 +454,9 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::Internal> {
             marker::Edge
         >
     > {
-        let ptr = self.as_internal() as *const InternalNode<K, V> as *const u8 as *mut u8;
+        let node = self.node;
         let ret = self.ascend().ok();
-        Global.dealloc(ptr, Layout::new::<InternalNode<K, V>>());
+        Global.dealloc(node.as_void(), Layout::new::<InternalNode<K, V>>());
         ret
     }
 }
@@ -1239,12 +1239,12 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
                 }
 
                 Global.dealloc(
-                    right_node.node.as_ptr() as *mut u8,
+                    right_node.node.as_void(),
                     Layout::new::<InternalNode<K, V>>(),
                 );
             } else {
                 Global.dealloc(
-                    right_node.node.as_ptr() as *mut u8,
+                    right_node.node.as_void(),
                     Layout::new::<LeafNode<K, V>>(),
                 );
             }

src/liballoc/btree/node.rs

@@ -8,14 +8,20 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-pub use alloc::{Excess, Layout, AllocErr, CannotReallocInPlace};
+#![allow(deprecated)]
+
+pub use alloc::{Layout, AllocErr, CannotReallocInPlace, Void};
 use core::alloc::Alloc as CoreAlloc;
+use core::ptr::NonNull;
 
 #[doc(hidden)]
 pub mod __core {
     pub use core::*;
 }
 
+#[derive(Debug)]
+pub struct Excess(pub *mut u8, pub usize);
+
 /// Compatibility with older versions of #[global_allocator] during bootstrap
 pub unsafe trait Alloc {
     unsafe fn alloc(&mut self, layout: Layout) -> Result<*mut u8, AllocErr>;
@@ -42,13 +48,13 @@ pub unsafe trait Alloc {
                               new_layout: Layout) -> Result<(), CannotReallocInPlace>;
 }
 
-#[allow(deprecated)]
 unsafe impl<T> Alloc for T where T: CoreAlloc {
     unsafe fn alloc(&mut self, layout: Layout) -> Result<*mut u8, AllocErr> {
-        CoreAlloc::alloc(self, layout)
+        CoreAlloc::alloc(self, layout).map(|ptr| ptr.cast().as_ptr())
     }
 
     unsafe fn dealloc(&mut self, ptr: *mut u8, layout: Layout) {
+        let ptr = NonNull::new_unchecked(ptr as *mut Void);
         CoreAlloc::dealloc(self, ptr, layout)
     }
 
@@ -64,35 +70,41 @@ unsafe impl<T> Alloc for T where T: CoreAlloc {
                       ptr: *mut u8,
                       layout: Layout,
                       new_layout: Layout) -> Result<*mut u8, AllocErr> {
-        CoreAlloc::realloc(self, ptr, layout, new_layout.size())
+        let ptr = NonNull::new_unchecked(ptr as *mut Void);
+        CoreAlloc::realloc(self, ptr, layout, new_layout.size()).map(|ptr| ptr.cast().as_ptr())
     }
 
     unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<*mut u8, AllocErr> {
-        CoreAlloc::alloc_zeroed(self, layout)
+        CoreAlloc::alloc_zeroed(self, layout).map(|ptr| ptr.cast().as_ptr())
     }
 
     unsafe fn alloc_excess(&mut self, layout: Layout) -> Result<Excess, AllocErr> {
         CoreAlloc::alloc_excess(self, layout)
+            .map(|e| Excess(e.0 .cast().as_ptr(), e.1))
     }
 
     unsafe fn realloc_excess(&mut self,
                              ptr: *mut u8,
                              layout: Layout,
                              new_layout: Layout) -> Result<Excess, AllocErr> {
+        let ptr = NonNull::new_unchecked(ptr as *mut Void);
         CoreAlloc::realloc_excess(self, ptr, layout, new_layout.size())
+            .map(|e| Excess(e.0 .cast().as_ptr(), e.1))
     }
 
     unsafe fn grow_in_place(&mut self,
                             ptr: *mut u8,
                             layout: Layout,
                             new_layout: Layout) -> Result<(), CannotReallocInPlace> {
+        let ptr = NonNull::new_unchecked(ptr as *mut Void);
         CoreAlloc::grow_in_place(self, ptr, layout, new_layout.size())
     }
 
     unsafe fn shrink_in_place(&mut self,
                               ptr: *mut u8,
                               layout: Layout,
                               new_layout: Layout) -> Result<(), CannotReallocInPlace> {
+        let ptr = NonNull::new_unchecked(ptr as *mut Void);
         CoreAlloc::shrink_in_place(self, ptr, layout, new_layout.size())
     }
 }

src/liballoc/heap.rs

@@ -99,6 +99,7 @@
 #![feature(lang_items)]
 #![feature(libc)]
 #![feature(needs_allocator)]
+#![feature(nonnull_cast)]
 #![feature(nonzero)]
 #![feature(optin_builtin_traits)]
 #![feature(pattern)]