[issue11277] Crash with mmap and sparse files on Mac OS X

[Nadeem Vawda]

Nadeem Vawda <nadeem.vawda at gmail.com> added the comment:

haypo> Can we just remove the test?

I think so. The test was originally intended to catch the case where crc32() or
adler32() would get a buffer of >=4GB, and then silently truncate the size and
produce an incorrect result (issue10276). However, 2.7's zlib doesn't define
PY_SSIZE_T_CLEAN, so passing in a buffer of >=2GB raises an exception. So the
condition that it was testing for can't happen in 2.7.


sdaoden> Can we remove it?  I would keep it, Apple is preparing the next
sdaoden> major release (uname -a yet states 10.7.0 even though it's
sdaoden> 10.6.7), and maybe then mmap() will fail for 0xDEADBEEF.
sdaoden> Who will be the one which detects that otherwise??

I initially thought the same thing, but it turns out that the OS X sparsefile
crash is also covered by LargeMmapTests.test_large_offset() in test_mmap.
That test had also been failing sporadically before the F_FULLSYNC patch was
committed (see issue11779). So keeping this test around would be redundant.


sdaoden> Unfortunately we cannot test 0x80000000+ no more because
sdaoden> Python prevents that such a buffer can be used - that's a shame.
sdaoden> Maybe we could test 0x7FFFFFFF*2 aka 0xfffffffe in two iterations.

That wouldn't accomplish the same thing. The point of the test is to pick up
truncation issues that occur when you pass in a big buffer. These issues
won't show up if you split the data up into smaller pieces. And in any case,
they can't happen at all in 2.7, because the functions don't accept big
buffers in the first place ;)

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<http://bugs.python.org/issue11277>
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