fix(bindings): use max_align_t for allocator alignment#5745
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jmayclin
approved these changes
Feb 18, 2026
maddeleine
approved these changes
Feb 18, 2026
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Goal
Fix the alignment used in the Rust bindings custom allocator to match the C malloc alignment contract.
We would like to thank Joshua Rogers (https://joshua.hu/) of AISLE Research Team (https://aisle.com/) for reporting this issue.
Why
The custom allocator was using
size_of::<usize>()(8 bytes on 64-bit) for alignment, but C'smallocis required to return memory "suitably aligned for any built-in type." On platforms like x86_64 Linux,max_align_thas a 16-byte alignment requirement (due tolong double), so the previous alignment could return under-aligned memory for C code.How
Changed the alignment constant from
size_of::<usize>()toalign_of::<libc::max_align_t>(), which matches the C standard's alignment guarantee formalloc.Callouts
This isn't expected to have an effect in practice as most allocators I tested (default Rust allocator, jemalloc, mimalloc), already align to 16-bytes regardless of the specified alignment.
Testing
Existing tests
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.