GeezerVison is showing github.com — [3.14] gh-159739: Handle overlapping buffers in struct.pack_into (GH-159985) by jelle-openai · Pull Request #160484 · python/cpython
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Oct 23, 2026
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struct.pack_into() can use the same bytearray as both the destination and an s or p value. The copy then passes overlapping regions to memcpy, which is undefined in C and can produce platform-dependent results or a sanitizer abort. memmove makes the overlapping copy defined.
(cherry picked from commit 31a7d99)
Co-authored-by: Jelle Zijlstra [email protected]
Backport of #159985 to 3.14.
Use overlap-safe copies in the 3.14 implementation of the s and p formats.
Ran test_struct. With an ASan-instrumented _struct, overlapping 8s and 8p copies both triggered memcpy-param-overlap on the original 3.14 code and completed with this change.
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pythonGH-159985)
`struct.pack_into()` can use the same bytearray as both the destination and an `s` or `p` value. The copy then passes overlapping regions to `memcpy`, which is undefined in C and can produce platform-dependent results or a sanitizer abort. `memmove` makes the overlapping copy defined.
(cherry picked from commit 31a7d99)
Co-authored-by: Jelle Zijlstra <[email protected]>
This was referenced Oct 23, 2026
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