[Bug driver/81358] libatomic not automatically linked with C11 code

[Joseph Myers]

I should also note the testsuite point I mentioned in the BoF, and related 
points about building target libraries, which mean this is more 
complicated than just the driver specs change:

There is testsuite logic (see gcc/testsuite/lib/atomic-dg.exp) to locate 
libatomic for build-tree testing and set appropriate -L options and 
LD_LIBRARY_PATH.

This is only used in gcc/testsuite/gcc.dg/atomic/atomic.exp at present.  
If the driver specs change to use "--as-needed -latomic --no-as-needed" 
whenever libatomic is built (obviously they shouldn't do so for 
configurations not building libatomic, whether because unsupported for the 
target or because disabled at configure time), linking *any* target 
program will then require libatomic to be somewhere that ld can find it 
(because ld requires a library named with -l to be somewhere it can find, 
even inside --as-needed; it can only know whether a library is needed 
after seeing what symbols it defines).

Thus, that logic would need to be used globally for all testsuites.  In 
addition, all configure tests in target libraries that run link tests, and 
linking of shared target libraries, would need to pass appropriate -L 
options to find libatomic, and we'd need to make sure the target library 
dependencies in toplevel Makefile.def ensure libatomic is built before 
other target libraries are configured for this to work.  I think libgcc 
should still be built before libatomic and so we'd need some driver option 
to disable linking with libatomic that would be passed when linking shared 
libgcc.

-- 
Joseph S. Myers
joseph@codesourcery.com