1 files changed, 61 insertions, 37 deletions

diff --git a/rust/kernel/allocator.rs b/rust/kernel/allocator.rs
index 397a3dd57a9b..a8f3d5be1af1 100644
--- a/rust/kernel/allocator.rs
+++ b/rust/kernel/allocator.rs
@@ -9,11 +9,41 @@ use crate::bindings;
 
 struct KernelAllocator;
 
+/// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
+///
+/// # Safety
+///
+/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
+/// - `new_layout` must have a non-zero size.
+unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: bindings::gfp_t) -> *mut u8 {
+    // Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
+    let layout = new_layout.pad_to_align();
+
+    let mut size = layout.size();
+
+    if layout.align() > bindings::BINDINGS_ARCH_SLAB_MINALIGN {
+        // The alignment requirement exceeds the slab guarantee, thus try to enlarge the size
+        // to use the "power-of-two" size/alignment guarantee (see comments in `kmalloc()` for
+        // more information).
+        //
+        // Note that `layout.size()` (after padding) is guaranteed to be a multiple of
+        // `layout.align()`, so `next_power_of_two` gives enough alignment guarantee.
+        size = size.next_power_of_two();
+    }
+
+    // SAFETY:
+    // - `ptr` is either null or a pointer returned from a previous `k{re}alloc()` by the
+    //   function safety requirement.
+    // - `size` is greater than 0 since it's either a `layout.size()` (which cannot be zero
+    //    according to the function safety requirement) or a result from `next_power_of_two()`.
+    unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags) as *mut u8 }
+}
+
 unsafe impl GlobalAlloc for KernelAllocator {
     unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
-        // `krealloc()` is used instead of `kmalloc()` because the latter is
-        // an inline function and cannot be bound to as a result.
-        unsafe { bindings::krealloc(ptr::null(), layout.size(), bindings::GFP_KERNEL) as *mut u8 }
+        // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
+        // requirement.
+        unsafe { krealloc_aligned(ptr::null_mut(), layout, bindings::GFP_KERNEL) }
     }
 
     unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
@@ -21,44 +51,38 @@ unsafe impl GlobalAlloc for KernelAllocator {
             bindings::kfree(ptr as *const core::ffi::c_void);
         }
     }
-}
-
-#[global_allocator]
-static ALLOCATOR: KernelAllocator = KernelAllocator;
 
-// `rustc` only generates these for some crate types. Even then, we would need
-// to extract the object file that has them from the archive. For the moment,
-// let's generate them ourselves instead.
-//
-// Note that `#[no_mangle]` implies exported too, nowadays.
-#[no_mangle]
-fn __rust_alloc(size: usize, _align: usize) -> *mut u8 {
-    unsafe { bindings::krealloc(core::ptr::null(), size, bindings::GFP_KERNEL) as *mut u8 }
-}
+    unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
+        // SAFETY:
+        // - `new_size`, when rounded up to the nearest multiple of `layout.align()`, will not
+        //   overflow `isize` by the function safety requirement.
+        // - `layout.align()` is a proper alignment (i.e. not zero and must be a power of two).
+        let layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
 
-#[no_mangle]
-fn __rust_dealloc(ptr: *mut u8, _size: usize, _align: usize) {
-    unsafe { bindings::kfree(ptr as *const core::ffi::c_void) };
-}
+        // SAFETY:
+        // - `ptr` is either null or a pointer allocated by this allocator by the function safety
+        //   requirement.
+        // - the size of `layout` is not zero because `new_size` is not zero by the function safety
+        //   requirement.
+        unsafe { krealloc_aligned(ptr, layout, bindings::GFP_KERNEL) }
+    }
 
-#[no_mangle]
-fn __rust_realloc(ptr: *mut u8, _old_size: usize, _align: usize, new_size: usize) -> *mut u8 {
-    unsafe {
-        bindings::krealloc(
-            ptr as *const core::ffi::c_void,
-            new_size,
-            bindings::GFP_KERNEL,
-        ) as *mut u8
+    unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
+        // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
+        // requirement.
+        unsafe {
+            krealloc_aligned(
+                ptr::null_mut(),
+                layout,
+                bindings::GFP_KERNEL | bindings::__GFP_ZERO,
+            )
+        }
     }
 }
 
+#[global_allocator]
+static ALLOCATOR: KernelAllocator = KernelAllocator;
+
+// See <https://github.com/rust-lang/rust/pull/86844>.
 #[no_mangle]
-fn __rust_alloc_zeroed(size: usize, _align: usize) -> *mut u8 {
-    unsafe {
-        bindings::krealloc(
-            core::ptr::null(),
-            size,
-            bindings::GFP_KERNEL | bindings::__GFP_ZERO,
-        ) as *mut u8
-    }
-}
+static __rust_no_alloc_shim_is_unstable: u8 = 0;