Re: [Xen-devel] [PATCH v2] autoconf: fix python-dev detection on old python versions

[Roger Pau Monnà <roger.pau@xxxxxxxxxxxxx>]

2012/3/30 Ian Campbell <Ian.Campbell@xxxxxxxxxx>:
> On Fri, 2012-03-30 at 09:26 +0100, Roger Pau Monnà wrote:
>> 2012/3/30 Ian Campbell <Ian.Campbell@xxxxxxxxxx>:
>> > On Fri, 2012-03-30 at 08:35 +0100, Roger Pau Monne wrote:
>> >> Replaced the use of python-config (that is only present in Python >= 
>> >> 2.5.x)
>> >> with the distutils python module.
>> >>
>> >> Please run ./autogen.sh after applying the patch.
>> >>
>> >> Again, this has only been tested on OS X Python 2.7.
>> >>
>> >> Changes since v1:
>> >>
>> >> Â* Added Python LDFLAGS to library test.
>> >>
>> >> Signed-off-by: Roger Pau Monne <roger.pau@xxxxxxxxxxxxx>
>> >> Cc: Zhang, Yang Z <yang.z.zhang@xxxxxxxxx>
>> >> Cc: KUWAMURA Shin'ya <kuwa@xxxxxxxxxxxxxx>
>> >> Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
>> >> ---
>> >> Âtools/m4/python_devel.m4 | Â 36 +++++++++++++++++-------------------
>> >> Â1 files changed, 17 insertions(+), 19 deletions(-)
>> >>
>> >> diff --git a/tools/m4/python_devel.m4 b/tools/m4/python_devel.m4
>> >> index 3bcca7b..dada92a 100644
>> >> --- a/tools/m4/python_devel.m4
>> >> +++ b/tools/m4/python_devel.m4
>> >> @@ -1,27 +1,25 @@
>> >> ÂAC_DEFUN([AX_CHECK_PYTHON_DEVEL], [
>> >> +ac_python_version=`$PYTHON -c 'import distutils.sysconfig; \
>> >> + Â Âprint distutils.sysconfig.get_config_var("VERSION")'`
>> >> Âac_previous_cppflags=$CPPFLAGS
>> >> -CPPFLAGS="$CFLAGS `$PYTHON-config --includes`"
>> >> +CPPFLAGS="$CFLAGS `$PYTHON -c 'import distutils.sysconfig; \
>> >> + Â Âprint "-I" + distutils.sysconfig.get_config_var("INCLUDEPY")'`"
>> >> +CPPFLAGS="$CPPFLAGS `$PYTHON -c 'import distutils.sysconfig; \
>> >> + Â Âprint distutils.sysconfig.get_config_var("CFLAGS")'`"
>> >
>> > This mixes up CPPFLAGS and CFLAGS in what looks like a very strange way
>> > to me, is it right?
>>
>> Yes, this is kind of a work around, since the header preprocessor
>> check ignores CFLAGS and only uses CPPFLAGS, so if CFLAGS are used,
>> the preprocessor check fails, although the header is there.
>
> Which check is this?

AC_CHECK_HEADER, it checks header usability (by trying to include it
in a sample program) and presence, by checking the paths. The
usability check fails if the header path is not added to CPPFLAGS,
because CFLAGS are ignored by the preprocessor on this tests (which is
really strange strange...)

>
>> > [...]
>> >
>> >> +LDFLAGS="$LDFLAGS `$PYTHON -c 'import distutils.sysconfig; \
>> >> + Â Âprint distutils.sysconfig.get_config_var("LIBS")'`"
>> >> +LDFLAGS="$LDFLAGS `$PYTHON -c 'import distutils.sysconfig; \
>> >> + Â Âprint "-L" + distutils.sysconfig.get_python_lib(plat_specific=1,\
>> >> + Â Âstandard_lib=1) + "/config"'`"
>> >> +LDFLAGS="$LDFLAGS `$PYTHON -c 'import distutils.sysconfig; \
>> >> + Â Âprint distutils.sysconfig.get_config_var("LINKFORSHARED")'`"
>> >
>> > Elsewhere in the Xen build system we would call these LDLIBS_<blah>
>> > and/or SHLIBS_<blah> (see tools/Rules.mk for examples). I think in the
>> > case of libpython, which is not built in tree you would only want to use
>> > SHLIBS_PYTHON.
>> >
>> > On a similar note do we really want to add the python stuff to the
>> > global CFLAGS and LDFLABS etc? Wouldn't it be better to have
>> > CFLAGS_PYTHON etc and to use them explicitly in tools/python/Makefile
>> > rather than using them for all compilations?
>>
>> This is only added to CFLAGS/LDFLAGS temporary, to perform the checks,
>> and on the build system they are automatically added by setup.py.
>
> AH, great then!
>
>>
>> > Although that might require other build system changes which could be
>> > done later in the interests of fixing getting a fix for people using
>> > python 2.3/2.4 into the tree.
>> >
>> >> +LDFLAGS="$LDFLAGS `$PYTHON -c 'import distutils.sysconfig; \
>> >> + Â Âprint distutils.sysconfig.get_config_var("LDFLAGS")'`"
>> >> +
>> >> ÂAC_CHECK_HEADER([Python.h], [],
>> >> Â Â Â[AC_MSG_ERROR([Unable to find Python development headers])],)
>> >> -AC_CHECK_LIB($python_lib, PyArg_ParseTuple, [],
>> >> +AC_CHECK_LIB(python$ac_python_version, PyArg_ParseTuple, [],
>> >> Â Â Â[AC_MSG_ERROR([Unable to find a suitable python development 
>> >> library])])
>> >> ÂCPPFLAGS=$ac_previous_cppflags
>> >> ÂLDLFAGS=$ac_previous_ldflags
>> >
>> >
>>
>> I will have to check again, maybe python-config script has the clue to
>> what parameters have to be passed to link against libpython. I'm in a
>> hurry, so I don't think I will have time to look into this until the
>> following week, sorry (I'm not leaving it apart).
>
>

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