Openblas installation points to generic BLAS/LAPACK

[vermashresth]

Hi,
I installed `libopenblas-dev' using apt-get on my Ubuntu 16.04 system. At the end of installation, the update-alternatives sets the following

update-alternatives: using /usr/lib/openblas-base/libblas.so to provide /usr/lib/libblas.so (libblas.so) in auto mode update-alternatives: using /usr/lib/openblas-base/liblapack.so to provide /usr/lib/liblapack.so (liblapack.so) in auto mode

But the libraries it is poitning to, doesn't contain any OpenBLAS specific functions such as openblas_get_num_threads as it gives not found in cmake.

I also verified this by doing
readelf -Ws /usr/lib/liblapack.so >> res.txt
grep "openblas" res.txt
And the output was none, same for libblas.so

the file '/usr/lib/libopenblas.so" however contains all the openblas specific functions.

Any reason why is it so?

[martin-frbg]

You will probably need to ask the Ubuntu folks who packaged openblas. The standard build of OpenBLAS will contain all functions (including BLAS and LAPACK) in a single libopenblas.so file that may have to be symlinked to the libblas, liblapack names for compatibility with other programs if you want to switch implementations at will. There is some background discussion in issue #296

[martin-frbg]

See also https://github.com/xianyi/OpenBLAS/wiki/Faq#debianlts - what comes with Ubuntu 16.04 is probably a bit old (0.2.18 from early last year I guess)

[brada4]

libblas.so that gcc -lblas reads is netlib reference blas to keep peoples code portable.
you can update that alternative to point to openblas, but probably you need to do -lopenblas instead.

me being author of particular FAQ paragraph - I intentionally left that part out to keep it working like debian packagers intended.

I dont know why you get libblas.so symlinked anywhere, when I wrote faq it was just libblas.so.3 and liblapack.so.3, i.e dynamic loaded not linker libs.

[isuruf]

What debian does is it creates a libblas.so.3 which links against libopenblas.so, but exports only the symbols from the blas API. So, when you do -lblas you are linking against a library which in turn links against libopenblas. If you want openblas symbols, use -lopenblas

[brada4]

@vermashresth can you close the issue? We dont maintain that package and 'ubuntu-support-status' on my 16.04 says vendor does not either.

[vermashresth]

@brada4 Sure, sorry for late reply. It does seem to be an issue from package side because it worked fine on Ubuntu 14.04 and @isuruf 's answer works too. Thanks for the help!