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POGCC 4.5 vs 4.4 linking with dependencies
 

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    <p>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 I am observing a similar failure with this simple test case.</p> <p>What I am basically trying to do is have one shared library (libb) depend on another shared library (liba). When loading libb, I assume that liba should be loaded as well - even though libb is not necessarily using the symbols in liba.</p> <p>What I am observing is when I compile with GCC 4.4, I observe that the liba is loaded, but if I compile with GCC 4.5, libb is not loaded.</p> <p>I have a small test case that consists of two files, a.c and b.c . The contents of the files:</p> <pre><code>//a.c int a(){ return 0; } //b.c int b(){ return 0; } //c.c #include &lt;stdio.h&gt; int a(); int b(); int main() { printf("%d\n", a()+b()); return 0; } //test.sh $CC -o liba.so a.c -shared $CC -o libb.so b.c -shared -L. -la -Wl,-rpath-link . $CC c.c -L. -lb -Wl,-rpath-link . LD_LIBRARY_PATH=. ./a.out </code></pre> <p>This is my output with different versions of GCC</p> <pre><code>$ CC=gcc-4.4 ./test.sh 1 $ CC=gcc-4.5 ./test.sh /tmp/cceJhAqy.o: In function `main': c.c:(.text+0xf): undefined reference to `a' collect2: ld returned 1 exit status ./test.sh: line 4: ./a.out: No such file or directory $ CC=gcc-4.6 ./test.sh /tmp/ccoovR0x.o: In function `main': c.c:(.text+0xf): undefined reference to `a' collect2: ld returned 1 exit status ./test.sh: line 4: ./a.out: No such file or directory $ </code></pre> <p>Can anyone explain what is happening? Another extra bit of information is that ldd on libb.so does show liba.so on GCC 4.4 but not on GCC 4.5.</p> <p><strong>EDIT</strong></p> <p>I changed test.sh to the following:</p> <pre><code>$CC -shared -o liba.so a.c $CC -L. -Wl,--no-as-needed -Wl,--copy-dt-needed-entries -la -shared -o libb.so b.c -Wl,-rpath-link . $CC -L. c.c -lb -Wl,-rpath-link . LD_LIBRARY_PATH=. ./a.out </code></pre> <p>This gave the following output with GCC 4.5:</p> <pre><code>/usr/bin/ld: /tmp/cc5IJ8Ks.o: undefined reference to symbol 'a' /usr/bin/ld: note: 'a' is defined in DSO ./liba.so so try adding it to the linker command line ./liba.so: could not read symbols: Invalid operation collect2: ld returned 1 exit status ./test.sh: line 4: ./a.out: No such file or directory </code></pre>
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    2. COOn Debian 6.0.3, the packaged GCC 4.4 handles the example without problems. The packaged GCC 4.3 complains about a missing `-fPIC` flag.
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