I noticed a bug/feature of Python 2.7 (and 3.X) distutils that worries
me a bit. Let's try to compile a simple extension module:
$ python2.7 setup.py build_ext | grep -F .c
gcc -pthread -fno-strict-aliasing -g -O2 -DNDEBUG -g -fwrapv -O2 -Wall
-Wstrict-prototypes -fPIC -I/usr/include/python2.7 -c markupsafe/_speedups.c -o
build/temp.linux-x86_64-2.7/markupsafe/_speedups.o
Everything looks fine until we put some build flags into environment (if
we were building a Debian package, dpkg-buildpackage would do that for
us):
$ eval $(dpkg-buildflags --export=sh)
$ rm -Rf build/
$ python2.7 setup.py build_ext | grep -F .c
gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -g -O2 -fPIC
-I/usr/include/python2.7 -c markupsafe/_speedups.c -o
build/temp.linux-x86_64-2.7/markupsafe/_speedups.o
Please note that "-fno-strict-aliasing" is no longer passed to gcc. I
believe C extensions quite often exploit type punning that breaks strict
aliasing rules, so omitting -fno-string-aliasing has a great potential
for breakage.
My question is: is this is a bug in python2.7/python3.X? Or are we
supposed to fix (all) the extensions that are built via distutils?
--
Jakub Wilk
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