Prevent libtool from moving flags

[Akim Demaille]

Hi!

I have a library that, when loading, invokes functions in the main application. 
 So dependencies are really resolved in reverse: the main program does not 
"need" the libraries, it is the libraries that use the main program to inform 
it that they are there.

In such a case, some distros, such as Ubuntu, will completely drop the 
dependency on the library.  The workaround is well known: use 
-Wl,--no-as-needed.

Unfortunately, libtool moves the options around, and since 
-Wl,--(no-)?-as-needed applies to the libraries that are _after_ it, the result 
is disastrous:

# ./libtool --tag=CXX --mode=link g++-4.9 -Xlinker --no-as-needed 
-Wl,--no-as-needed -g -O2 -std=c++14 -avoid-version -module 
-L/usr/lib/python3.4/config-3.4m-x86_64-linux-gnu -L/usr/lib -lpthread -ldl  
-lutil -lm  -lpython3.4m -Xlinker -export-dynamic -Wl,-O1 
-Wl,-Bsymbolic-functions -o python/vcsn_cxx.la -rpath 
/usr/local/lib/python3.4/site-packages python/python_vcsn_cxx_la-vcsn_cxx.lo 
-lboost_python-py34 -lpthread -ldl  -lutil -lm  -lpython3.4m 
lib/liblal_char_b.la  lib/liblal_char_q.la  lib/liblal_char_z.la lib/libvcsn.la
libtool: warning: 
'/usr/lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu/libltdl.la' seems 
to be moved
libtool: link: rm -fr  python/.libs/vcsn_cxx.la python/.libs/vcsn_cxx.lai 
python/.libs/vcsn_cxx.so
libtool: link: g++-4.9  -fPIC -DPIC -shared -nostdlib 
/usr/lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu/crti.o 
/usr/lib/gcc/x86_64-linux-gnu/4.9/crtbeginS.o  
python/.libs/python_vcsn_cxx_la-vcsn_cxx.o   -Wl,-rpath 
-Wl,/build/vcsn/_build/lib/.libs -Wl,-rpath -Wl,/usr/local/lib/vcsn 
-L/usr/lib/python3.4/config-3.4m-x86_64-linux-gnu -L/usr/lib 
-lboost_python-py34 -lpthread -lutil -lpython3.4m lib/.libs/liblal_char_b.so 
lib/.libs/liblal_char_q.so lib/.libs/liblal_char_z.so lib/.libs/libvcsn.so 
-L/usr/lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu 
-lboost_filesystem -lboost_system /usr/lib/x86_64-linux-gnu/libltdl.so -ldl 
-lrt -L/usr/lib/gcc/x86_64-linux-gnu/4.9 
-L/usr/lib/gcc/x86_64-linux-gnu/4.9/../../../../lib -L/lib/x86_64-linux-gnu 
-L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib 
-L/usr/lib/gcc/x86_64-linux-gnu/4.9/../../.. -lstdc++ -lm -lc -lgcc_s 
/usr/lib/gcc/x86_64-linux-gnu/4.9/crtendS.o 
/usr/lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu/crtn.o  
-Wl,--no-as-needed -Wl,--no-as-needed -g -O2 -Wl,-export-dynamic -Wl,-O1 
-Wl,-Bsymbolic-functions   -pthread -Wl,-soname -Wl,vcsn_cxx.so -o 
python/.libs/vcsn_cxx.so
libtool: link: ( cd "python/.libs" && rm -f "vcsn_cxx.la" && ln -s 
"../vcsn_cxx.la" "vcsn_cxx.la" )

So basically:

$ libtool --tag=CXX --mode=link g++-4.9 -Wl,--no-as-needed lib/liblal_char_b.la 
...

becomes

$ g++-4.9 lib/liblal_char_b.la...  -Wl,--no-as-needed

so -Wl,--no-as-needed has no effects, it is too late.

I have read the faq, and I do know that there is a workaround: "./configure 
CXX='g++ -Wl,--no-as-needed'", and yes it works.  But I meant to say that it 
would be nice if options could stay where they are :)

Cheers!