[Numpy-discussion] debian floating point exceptions/numpy/f2py -- sse

Andrew Jaffe a.h.jaffe at gmail.com
Fri Jul 14 11:35:36 CDT 2006

David Cournapeau wrote:
> Andrew Jaffe wrote:
>> Hi All,
>> I have just switched from RHEL to debian, and all of a sudden I started 
>> getting floating point exception errors in various contexts.
>> Apparently, this has to do with some faulty error stuff in glibc, 
>> specifically related to the sse. I would prefer to fix the actual 
>> problem, but I can't seem to be able to get the recommended 'apt-get 
>> source glibc' incantation to work (I'm not root, but I can sudo.)
> What does not work ? The apt-get source part ? The actual building ?
> Basically, if the sources are OK, you just need to do
>  - fakeroot dpkg-source -x name_of_dsc_file
>  - cd name_of_package
>  - fakeroot dpkg-buildpackage
> And that's it

Aha -- I didn't know about fakeroot... Thanks! That was the problem with 
apt-get source. I'm compiling the patched version now... wow, is it slow!

>> I was able to fix some of these issues by simply downgrading ATLAS to 
>> not use sse instructions anymore.
>> But f2py still links with sse and sse2 by default. I can't quite 
>> understand the configuration well enough to work out how to turn it off. 
>> Can someone give me any guidance?
> The way it is supposed to work, at least on debian and ubuntu, is that 
> you never link to the sse/sse2 versions, but to the non-optimized 
> versions. After, the dynamic loader will get the right one (ie optimized 
> if available) instead of the one linked (this of course only works for 
> dynamic linking). You can check which library is picked with a ldconfig 
> - p | grep lapack (for lapack functions, and so on...)

The problem with f2py isn't the atlas/lapack linkage, which it does 
correctly, but the fact that it automatically appends -sse2 to the g77 
compile options; I couldn't figure out how to turn that off! Although 
now I'm not so sure, since I can never get my self-compiled executable 
version of my fortran code to give the same error as when it runs within 

But with the patched glibc, I think I'm alright in any event!



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