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The alignment test introduced in pythongh-140557 guards against empty-allocation optimisations handing out oddly-aligned pointers, as had been observed for the empty `bytearray` used by pickle protocol 5. It compared every array buffer against the maximum alignment of any array element type, which over-specifies the requirement: an allocation only needs to be aligned for the type stored in it. This failed on 32-bit platforms using mimalloc for single-byte element types such as 'B', where the tiny allocation region only guarantees 4-byte alignment rather than the 8-byte alignment of `double`. Check instead that each array's buffer, empty or allocated, is aligned to at least the alignment of its element type. The alignment is derived from `struct` rather than from `itemsize`, since the two differ for types such as `Zf` and `Zd`. Co-authored-by: Jake Lishman <jake@binhbar.com>
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The alignment test introduced in gh-140557 guards against empty-allocation optimisations handing out oddly-aligned pointers, as had been observed for the empty
bytearrayused by pickle protocol 5. It compared every array buffer against the maximum alignment of any array element type, which over-specifies the requirement: an allocation only needs to be aligned for the type stored in it. This failed on 32-bit platforms using mimalloc for single-byte element types such as 'B', where the tiny allocation region only guarantees 4-byte alignment rather than the 8-byte alignment ofdouble.Check instead that each array's buffer, empty or allocated, is aligned to at least the alignment of its element type. The alignment is derived from
structrather than fromitemsize, since the two differ for types such asZfandZd.I took @jakelishman's PR and added the fixes from review by @colesbury in GH-145026