[gentoo-soc] [GSoC] Weekly Report : May 27-June 2 -- BLAS/LAPACK Runtime Switch

[Mo Zhou]

Hi Benda,

During May 9 - May 27, I created a demonstration overlay
for our initial implimentation [3] (eselect + symlink).
The C++ demo program shipped by that git repo suggests
the draft implementation is working correctly.

During May 27 - June 2, I posted about the proposed
solution on Gentoo-dev to wait for comments. Unfortunately,
it seems that simply porting Debian's solution to Gentoo
is not the best choice, and there are people against it.

I redesigned the solution based on ld.so.conf:

1. sci-libs/lapack could expose all its shared objects
   and headers in the public dirs (i.e. /usr/include,
   /usr/$(get_libdir)/ ).

2. optimized implementations build additional libblas.so
   and liblapack.so objects with patched build systems.
   We hint ld.so with ld.so.conf via eselect, so any
   program linked against libblas.so and liblapack.so
   could make use of this mechanism.

The second point is different from our private discussion
in telegram. And different from my draft implementation,
the redesigned solution will introduce a new USE flag for
BLAS/LAPACK reverse dependencies to decide whether the
program should link against switchable BLAS/LAPACK or
specified BLAS/LAPACK.

Although there are negative responses against the first
proposal, we are not far from the original schedule --
this week I'm going to implement the redesigned solution
for sci-libs/lapack and ask Gentoo-dev for comments again.

Thanks,
Mo.

Reference:

1. Drawback of the eselect+symlink solution:
https://bugs.gentoo.org/632618
2. The eselect+ld.so.conf solution: https://bugs.gentoo.org/531842
3. My Overlay: https://github.com/cdluminate/my-overlay