Using blaslapack

[Tijl Coosemans]

On Mon, 16 Oct 2017 09:20:26 +0300 Gleb Popov <6yearold at gmail.com> wrote:
> I'm porting an application (DLib, https://reviews.freebsd.org/D12559) that
> uses BLAS and LAPACK, and I have some questions.
> 
> 1. Is there any pure C implementation that does not require Fortran
> compiler?

Probably not, BLAS and LAPACK are Fortran libraries.  Any implementation
in C still provides Fortran wrappers.  And often these implementations
only implement performance critical functions and use the original
Fortran for everything else.

> 2. My application looks for cblas_ddot function in BLAS library, but the
> default library (netlib) doesn't seem to have that. It has ddot, though, so
> I'm not sure if it is a wrong check on app's side, or netlib is indeed
> doesn't suit there. For now I've used openblas, but I'm also not sure if it
> is a right choice.

It's part of CBLAS which is also included in OpenBLAS.

> 3. How to link properly to any of BLAS libraries? All BLAS implementations
> blaslapack.mk features require Fortran. This implies USE_GCC=yes, so these
> are compiled with GCC, not Clang. Now when I try to link Clang-compiled
> DLib to GCC-compiled openblas, I get undefined references:
> 
> //usr/local/lib/gcc6/libgfortran.so.3: undefined reference to
> `__getf2 at GCC_4.6.0'
> //usr/local/lib/gcc6/libgfortran.so.3: undefined reference to
> `__floatunditf at GCC_4.6.0'
> //usr/local/lib/gcc6/libgfortran.so.3: undefined reference to
> `__subtf3 at GCC_4.6.0'
> //usr/local/lib/gcc6/libgfortran.so.3: undefined reference to
> `__multf3 at GCC_4.6.0'
> //usr/local/lib/gcc6/libgfortran.so.3: undefined reference to
> `__unordtf2 at GCC_4.6.0'
> //usr/local/lib/gcc6/libgfortran.so.3: undefined reference to
> `__lttf2 at GCC_4.6.0'
> //usr/local/lib/gcc6/libgfortran.so.3: undefined reference to
> `__addtf3 at GCC_4.6.0'
> //usr/local/lib/gcc6/libgfortran.so.3: undefined reference to
> `__gttf2 at GCC_4.6.0'
> //usr/local/lib/gcc6/libgfortran.so.3: undefined reference to
> `__divtf3 at GCC_4.6.0'
> //usr/local/lib/gcc6/libgfortran.so.3: undefined reference to
> `__letf2 at GCC_4.6.0'
> //usr/local/lib/gcc6/libgfortran.so.3: undefined reference to
> `__netf2 at GCC_4.6.0'
> //usr/local/lib/gcc6/libgfortran.so.3: undefined reference to
> `__floatditf at GCC_4.6.0'
> //usr/local/lib/gcc6/libgfortran.so.3: undefined reference to
> `__eqtf2 at GCC_4.6.0'
> //usr/local/lib/gcc6/libgfortran.so.3: undefined reference to
> `__floatsitf at GCC_4.6.0'
> 
> I've tracked these symbols to /usr/local/lib/gcc6/libgcc_s.so. But there is
> also /usr/lib/libgcc_s.so and it doesn't have such symbols. I suspect this
> is the source of the error, but I wasn't able to fix it. Passing -Wl,-rpath
> as advised by lang/gcc6 pkg-message doesn't help. The only workaround I
> came up with is USE_GCC=yes to compile DLib itself, but that's pretty
> unsatisfactory.

This is a known problem.  If your port depends on another port that
has USES=fortran the easiest is to add USES=fortran to your port as
well.  C code will still be built with Clang then.