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rust: alloc: satisfy POSIX alignment requirement

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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 dd09538fb4 ("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: Danilo Krummrich <dakr@kernel.org>
Cc: stable@vger.kernel.org
Fixes: dd09538fb4 ("rust: alloc: implement `Cmalloc` in module allocator_test")
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Reviewed-by: Gary 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: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Tamir Duberstein
2025-02-13 06:34:18 -05:00
committed by Miguel Ojeda
parent df27cef153
commit ff64846bee
1 changed files with 18 additions and 0 deletions
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18
rust/kernel/alloc/allocator_test.rs
View File

@@ -62,6 +62,24 @@ unsafe impl Allocator for Cmalloc {
));
}
// 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;