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From Eric Brunson <brun...@brunson.com>
Subject Re: FreeBSD, pthreads unresoved symbols and LD_PRELOAD revisited
Date Sun, 03 Dec 2006 02:41:37 GMT
Graham Dumpleton wrote:
> On 03/12/2006, at 7:34 AM, Jim Gallacher wrote:
>> Eric Brunson wrote:
>>> I apologize if this goes out twice, I think I wrote it on my laptop at
>>> work, then shut it down without hitting send.
>>> While upgrading to 3.3 on Thursday I ran into the previously discussed
>>> "pthread_*" unresolved symbol problem and used the
>>> LD_PRELOAD=/lib/libc_r.so fix, which worked and seemed to get us
>>> most of
>>> the way through our regression testing (such as it is). We spent
>>> several hours tracking down why certain subprocesses were
>>> failing when using Popen and after much trial and error, came to
>>> realize
>>> that *any* module we compiled ourselves was failing, even the 3.1.4
>>> version that we were originally running from ports.  We started coming
>>> to the conclusion that the threaded libc was causing problems with
>>> subprocesses spawning subprocess ("spawn" in our expect scripts was the
>>> culprit that pointed out the problem, then I was able to produce
>>> failing
>>> test cases in bash and ksh scripts).
>>> Comparing build environments between our vanilla source builds and the
>>> ports tree, I found a patch to configure that changes PyLIBS to use the
>>> same libraries that are linked when python is built in the ports
>>> tree. The patch for 3.1.4 applies cleanly with a 'fuzz' warning to
>>> both the
>>> 3.2.10 source and the 3.3-svn source.  The crux of the patch its to
>>> change one line:
>>> -PyLIBS=`grep "^LIB[SMC]=" ${PyLIBPL}/Makefile | cut -f2 -d= | tr
>>> '\011\012\015' '   '`
>>> +PyLIBS=`ldd $PYTHON_BIN | sed -n 's,^.* => [^ ]*/lib\(.*\)\.so[^ ]*
>>> \((.*)\),-l\1,p' | grep -v '^-lc$' | xargs echo`
>>> this enables any version we tried (3.1.4, 3.2.10 or 3.3) to be compiled
>>> then run without modifying the LD_PRELOAD environment variable and also
>>> fixed our problems with subprocess spawning.
>>> Should we try to implement this change in the build environment?  Or is
>>> it enough to have it referenced in the documentation?  I'll probably
>>> add
>>> a wiki article on the problem.
>> The wiki is fine if people want to backport to 3.1.4 or 3.2.10, but
>> it should be fixed in the 3.3 source. Could you open a JIRA issue and
>> attach the patch so we don't loose track of it? I'd definitely like
>> to see a trouble-free build on FreeBSD.
> The 'ldd' program doesn't exist everywhere and so that change can't be
> used.
> Can you explain properly what that one line is achieving.

The change is causing mod_python to be linked with the same libs that
python was when it was built, in the absence of the Makefile.

> If you are trying to force the linking in of additional libraries, eg,
> -lc_r, what happens
> when you set LIBS when running configure. Eg.
>   LIBS=-lc_r ./configure ...
> Even if this doesn't work but it is what you are hoping to achieve, it
> would be better
> to still require it to be a manual override rather than automatic. 

I don't feel the defaults being chosen for the platform are acceptable,
if others using FreeBSD agree, then I think we should change the
defaults.  The simple presence of libpthreads doesn't mean it should be
used in all cases.  Unfortunately I'm not familiar enough with autoconf
to know what's available to be changed.

> That could mean
> making LIBS be used, or have a special configure option to enable
> linking in of
> other libraries.
> Anyway, please explain what the change is doing.

I can tell you what it is doing in this specific case of FreeBSD 6.1 and
the python 2.4.2 ports package, which is to exclude libpthread.  Can we
just make configure automatically exclude pthreads for FreeBSD using any
of the methods you describe (allowing the --with-pthreads to be
specified if the user desires)?  If we're compiling for python 2.5 or
greater, we can simply use the output of "python2.5-config --ldflags",
but for versions before 2.5 that isn't an option. 

I feel like I'm repeating myself, but... the goal is to link against the
same libraries as python, no matter what they are, and this is obviously
a problem since work arounds for our bad link decisions have already
been discussed here and on the developers list.

> Thanks.
> Graham

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