GeezerVison is showing github.com — gh-159739: Handle overlapping mmap writes by jelle-openai · Pull Request #160189 · python/cpython
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jelle-openai
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Oct 22, 2026
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edited by bedevere-app
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Writing a memoryview of an mmap back into an overlapping region, through write() or contiguous slice assignment, used memcpy(), which has undefined behavior for overlapping ranges and can corrupt the mapped data. Use overlap-safe copying for both operations. Backport to 3.15 and 3.14.
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Writing a memoryview of an mmap back into an overlapping region, through write() or contiguous slice assignment, used memcpy(), which has undefined behavior for overlapping ranges and can corrupt the mapped data. Use overlap-safe copying for both operations. Backport to 3.15 and 3.14.
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if (safe_copy_from_slice(self->data, (char *)vbuf.buf, start, step,
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slicelen) < 0)
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{
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/* The source may overlap the destination, so copy it before
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Feels like this can hurt performance, let's look for a better solution.
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