make: linking openblas fails on standard linux setup

[ahbarnett]

make fails at link stage on standard linux machine:
ubuntu 22.04 on amd64.
GNU Fortran (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
libopenblas-base:amd64 0.3.20+ds-1

Error:

gfortran -g -w -fdefault-integer-8 -finteger-4-integer-8 -std=legacy -o int2 -lopenblas examples/test_surfsmooth.o src/koornexps.o src/ortho2eva.o src/ortho2eva_new.o src/ortho2exps.o src/orthom.o src/cisurf_loadmsh.o src/cisurf_skeleton.o src/cisurf_plottools.o src/cisurf_tritools.o src/lapack_wrap.o src/pplot2.o lib/tfmm3dlr/tfmm3dlr_expout.o lib/tfmm3dlr/tfmm3dlrwrap_expout.o lib/tfmm3dlr/l3dzero.o lib/tfmm3dlr/treeplot.o lib/tfmm3dlr/prini.o lib/tfmm3dlr/l3dterms.o lib/tfmm3dlr/laprouts3d.o lib/tfmm3dlr/nearfield.o lib/tfmm3dlr/l3dmpmpfinal4.o lib/tfmm3dlr/l3dloclocfinal4.o lib/tfmm3dlr/l3dmplocfinal4.o lib/tfmm3dlr/prinm.o lib/tfmm3dlr/yrecursion.o lib/tfmm3dlr/ftophys.o lib/tfmm3dlr/phystof2.o lib/tfmm3dlr/legeexps.o lib/tfmm3dlr/tree_lr_3d.o lib/tfmm3dlr/rotgen.o lib/tfmm3dlr/numthetafour.o lib/tfmm3dlr/numthetahalf2.o lib/tfmm3dlr/lapweights.o lib/tfmm3dlr/pwrouts2.o lib/tfmm3dlr/hkrand.o lib/tfmm3dlr/dlaran.o lib/tfmm3dlr/rotviarecur3.o lib/tfmm3dlr/rotgen2.o lib/tfmm3dlr/l3dgqbxauxrouts2.o lib/tfmm3dlr/lwtsexp_sep2.o lib/tfmm3dlr/chebexps.o src/Mod_TreeLRD.o src/ModType_Smooth_Surface.o src/Mod_Fast_Sigma.o src/chebtarggridrouts.o src/Mod_Plot_Tools_sigma.o src/Mod_Feval.o src/Mod_Smooth_Surface.o
/bin/ld: src/cisurf_tritools.o: in function `fast_matvec_':
/home/alex/numerics/smooth-surface/src/cisurf_tritools.f90:458: undefined reference to `dgemv_'
ETC...

Cuprit is the link order:

smooth-surface/makefile

Line 151 in 20b53cb

$(FLINK) $(OBJECTS) $(MOD_OBJECTS)

Since -lopenblas is part of FLINK it appears before the object files. But the correct link order is at the end, since it is a dependency of the object files.

Moving -lopenblas to the end fixes it.

Here's a URL on link order:
https://eli.thegreenplace.net/2013/07/09/library-order-in-static-linking

Take-home message:
If object or library AA needs a symbol from library BB, then AA should come before library BB in the command-line invocation of the linker.