Easy check for unresolved symbols in shared libraries?

Check out the linker option -z defs / --no-undefined. When creating a shared object, it will cause the link to fail if there are unresolved symbols.

If you are using gcc to invoke the linker, you'll use the compiler -Wl option to pass the option to the linker:

gcc -shared ... -Wl,-z,defs

As an example, consider the following file:

#include <stdio.h>

void forgot_to_define(FILE *fp);

void doit(const char *filename)
{
    FILE *fp = fopen(filename, "r");
    if (fp != NULL)
    {
        forgot_to_define(fp);
        fclose(fp);
    }
}

Now, if you build that into a shared object, it will succeed:

> gcc -shared -fPIC -o libsilly.so silly.c && echo succeeded || echo failed
succeeded

But if you add -z defs, the link will fail and tell you about your missing symbol:

> gcc -shared -fPIC -o libsilly.so silly.c -Wl,-z,defs && echo succeeded || echo failed
/tmp/cccIwwbn.o: In function `doit':
silly.c:(.text+0x2c): undefined reference to `forgot_to_define'
collect2: ld returned 1 exit status
failed

On Linux (which you appear to be using) ldd -r a.out should give you exactly the answer you are looking for.

UPDATE: a trivial way to create a.out against which to check:

 echo "int main() { return 0; }" | g++ -xc++ - ./libMySharedLib.so
 ldd -r ./a.out

What about a testsuite ? You create mock executables that link to the symbols you need. If the linking fails, it means that your library interface is incomplete.