rust: alloc: implement `Cmalloc` in module allocator_test

So far the kernel's `Box` and `Vec` types can't be used by userspace
test cases, since all users of those types (e.g. `CString`) use kernel
allocators for instantiation.

In order to allow userspace test cases to make use of such types as
well, implement the `Cmalloc` allocator within the allocator_test module
and type alias all kernel allocators to `Cmalloc`. The `Cmalloc`
allocator uses libc's `realloc()` function as allocator backend.

Reviewed-by: Benno Lossin <[email protected]>
Reviewed-by: Gary Guo <[email protected]>
Signed-off-by: Danilo Krummrich <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[ Removed the temporary `allow(dead_code)` as discussed in the list and
  fixed typo, added backticks. - Miguel ]
Signed-off-by: Miguel Ojeda <[email protected]>

1 files changed, 0 insertions, 1 deletions

diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index 049fca7a514d..c6024afa3739 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -215,7 +215,6 @@ pub unsafe trait Allocator {
     }
 }
 
-#[allow(dead_code)]
 /// Returns a properly aligned dangling pointer from the given `layout`.
 pub(crate) fn dangling_from_layout(layout: Layout) -> NonNull<u8> {
     let ptr = layout.align() as *mut u8;