[issue20162] Test test_hash_distribution fails on RHEL 6.5 / ppc64
Yury V. Zaytsev
report at bugs.python.org
Tue Jan 7 19:05:30 CET 2014
Yury V. Zaytsev added the comment:
Hi Christian,
Dave says "it's not a compiler bug; the code is slightly violating the C standard, and the compiler optimizes based on a strict reading of the rules".
If I compile with -O2 and higher (while -O3 is the default for Python, as far as I can understand), the compiler correctly warns me about possible issues; as you can see, the macro itself is not at fault, even.
It's just that in my particular (rare) mix of circumstances: being big endian, using the macro instead of the glibc function due to the first part of the bug, etc. it results in miscompilation, and in your case, it remains a warning, but the result still works.
I think the "clean" solutions to this problem are as follows:
1) Do not break strict aliasing (use memcpy() instead or something)
2) Disable strict aliasing based optimizations (-fno-strict-aliasing)
In addition, fixing the first part of the bug (wrongly using a macro even if le64toh is available), will mask the second part for me again, but I'm not sure if it will re-surface at some point later or not :)
Hope that helps!
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