[petsc-dev] [buildsystem] support for --start-group/--end-group

[Chen Shen]

Hi all,

Currently, there is an option to specify the blas/lapack library
files --with-scalapack-lib=[<list of .a files>]. This is indeed necessary,
because MKL provides a large choice of libraries to link against.

However, MKL static libraries have object inter-dependencies, and requires
--start-group/--end-group linker options. All libraries in the group are
searched repeatedly until all inter-dependencies resolved.
For example, the following options is suggested for a configuration (
http://software.intel.com/en-us/articles/intel-mkl-link-line-advisor/):

$(MKLROOT)/lib/intel64/libmkl_scalapack_lp64.a  -Wl,--start-group
$(MKLROOT)/lib/intel64/libmkl_intel_lp64.a
$(MKLROOT)/lib/intel64/libmkl_sequential.a
$(MKLROOT)/lib/intel64/libmkl_core.a
$(MKLROOT)/lib/intel64/libmkl_blacs_intelmpi_lp64.a -Wl,--end-group
-lpthread

I'd like to propose an extension to the --with-scalapack-lib syntax to
support start/end group. Consider the following example:
--with-blas-lapack-lib=[ /xxx/scalapack_lp64.a,   [/xxx/libmkl_intel_lp64.a,
/xxx/libmkl_sequential.a, libmkl_core.a, /xxx/libmkl_blacs_intelmpi_lp64.a]
]

The embedded list indicates a set of libraries to be grouped up. Would this
be possible?

This isn't a problem if we link to dynamic libraries, because -l for dynamic
libraries doesn't have to be ordered as in the case of static libraries.
I hate the wicked order rule for .a libraries, but have to live with it...

Further, I guess -Bstatic options are dropped somewhere (I haven't checked
it in detail). The final PACKAGES_LIBS macro never contains -Bstatic, so end
application will always link to the static libraries.


Regards,
Shen Chen
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