The following code crashes the interpreter on Linux:

#!/usr/bin/python3

import mmap

with open('test', 'wb') as f:
    f.write(bytes(1))

with open('test', 'r+b') as f:
    m = mmap.mmap(f.fileno(), 0)
    f.truncate()
    a = m[:]

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It's not specific to the zero size truncation, it's enough if the file size decreases beyond a page border.