Commit ff64846b authored by Tamir Duberstein's avatar Tamir Duberstein Committed by Miguel Ojeda
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rust: alloc: satisfy POSIX alignment requirement 



ISO C's `aligned_alloc` is partially implementation-defined; on some
systems it inherits stricter requirements from POSIX's `posix_memalign`.

This causes the call added in commit dd09538f ("rust: alloc:
implement `Cmalloc` in module allocator_test") to fail on macOS because
it doesn't meet the requirements of `posix_memalign`.

Adjust the call to meet the POSIX requirement and add a comment. This
fixes failures in `make rusttest` on macOS.

Acked-by: default avatarDanilo Krummrich <dakr@kernel.org>
Cc: stable@vger.kernel.org
Fixes: dd09538f ("rust: alloc: implement `Cmalloc` in module allocator_test")
Signed-off-by: default avatarTamir Duberstein <tamird@gmail.com>
Reviewed-by: default avatarGary Guo <gary@garyguo.net>
Link: https://lore.kernel.org/r/20250213-aligned-alloc-v7-1-d2a2d0be164b@gmail.com


[ Added Cc: stable. - Miguel ]
Signed-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
parent df27cef1

rust/kernel/alloc/allocator_test.rs

+18 −0
Original line number Diff line number Diff line
@@ -62,6 +62,24 @@ unsafe fn realloc( 
            ));

        }



        // ISO C (ISO/IEC 9899:2011) defines `aligned_alloc`:

        //

        // > The value of alignment shall be a valid alignment supported by the implementation

        // [...].

        //

        // As an example of the "supported by the implementation" requirement, POSIX.1-2001 (IEEE

        // 1003.1-2001) defines `posix_memalign`:

        //

        // > The value of alignment shall be a power of two multiple of sizeof (void *).

        //

        // and POSIX-based implementations of `aligned_alloc` inherit this requirement. At the time

        // of writing, this is known to be the case on macOS (but not in glibc).

        //

        // Satisfy the stricter requirement to avoid spurious test failures on some platforms.

        let min_align = core::mem::size_of::<*const crate::ffi::c_void>();

        let layout = layout.align_to(min_align).map_err(|_| AllocError)?;

        let layout = layout.pad_to_align();



        // SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or

        // exceeds the given size and alignment requirements.

        let dst = unsafe { libc_aligned_alloc(layout.align(), layout.size()) } as *mut u8;