GCC 4.5 vs 4.4 linking with dependencies

Question

I am observing a difference when trying to do the same operation on GCC 4.4 and GCC 4.5. Because the code I am doing this with is proprietary, I am unable to provide it, but

Answer 1

There seems to have been changes in how DT_NEEDED libraries are treated during linking by ld. Here's the relevant part of current man ld:

With --copy-dt-needed-entries dynamic libraries mentioned on the command line will be recursively searched, following their DT_NEEDED tags to other libraries, in order to resolve symbols required by the output binary. With the default setting however the searching of dynamic libraries that follow it will stop with the dynamic library itself. No DT_NEEDED links will be traversed to resolve symbols.

(part of the --copy-dt-needed-entries section).

Some time between GCC 4.4 and GCC 4.5 (apparently, see some reference here - can't find anything really authoritative), the default was changed from the recursive search, to no recursive search (as you are seeing with the newer GCCs).

In any case, you can (and should) fix it by specifying liba in your final link step:

$CC c.c -L. -lb -la -Wl,-rpath-link .

You can check that this linker setting is indeed (at least part of) the issue by running with your newer compilers and this command line:

$CC c.c -L. -Wl,--copy-dt-needed-entries -lb -Wl,--no-copy-dt-needed-entries \
         -Wl,-rpath-link .