Re: [PATCH v6] rust: alloc: satisfy POSIX alignment requirement
From: Gary Guo <gary@garyguo.net>
Date: 2025-02-13 11:30:31
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lkml, rust-for-linux
On Thu, 13 Feb 2025 06:26:41 -0500 Tamir Duberstein [off-list ref] wrote:
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 dd09538fb409 ("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>
Fixes: dd09538fb409 ("rust: alloc: implement `Cmalloc` in module allocator_test")
Signed-off-by: Tamir Duberstein <redacted>
---
Changes in v6:
- Replace unsound use of build_error with map_err. (Danilo Krummrich)It's sound, just not correct.
quoted hunk ↗ jump to hunk
- Link to v5: https://lore.kernel.org/r/20250212-aligned-alloc-v5-1-c51e0b17dee9@gmail.com (local) Changes in v5: - Remove errant newline in commit message. (Miguel Ojeda) - Use more succinct expression. (Gary Guo) - Drop and then add Danilo's Acked-by again. - Link to v4: https://lore.kernel.org/r/20250210-aligned-alloc-v4-1-609c3a6fe139@gmail.com (local) Changes in v4: - Revert to `aligned_alloc` and correct rationale. (Miguel Ojeda) - Apply Danilo's Acked-by from v2. - Rebase on v6.14-rc2. - Link to v3: https://lore.kernel.org/r/20250206-aligned-alloc-v3-1-0cbc0ab0306d@gmail.com (local) Changes in v3: - Replace `aligned_alloc` with `posix_memalign` for portability. - Link to v2: https://lore.kernel.org/r/20250202-aligned-alloc-v2-1-5af0b5fdd46f@gmail.com (local) Changes in v2: - Shorten some variable names. (Danilo Krummrich) - Replace shadowing alignment variable with a second call to Layout::align. (Danilo Krummrich) - Link to v1: https://lore.kernel.org/r/20250201-aligned-alloc-v1-1-c99a73f3cbd4@gmail.com (local) --- rust/kernel/alloc/allocator_test.rs | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs index e3240d16040b..e68775078e90 100644 --- a/rust/kernel/alloc/allocator_test.rs +++ b/rust/kernel/alloc/allocator_test.rs@@ -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)?.pad_to_align(); + let layout = layout.pad_to_align();
You're doing two `pad_to_align`s. Best, Gary
+
// 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;
---
base-commit: 8a5aae7dbbfb612509c8a2f112f7e0f79029ed45
change-id: 20250201-aligned-alloc-b52cb2353c82
Best regards,