bash-3.2$ cat x.c
extern void foo() __attribute__((weak,visibility("hidden")));
extern int puts( char const* );
int main()
{
        foo ? foo() : puts( "foo == null, skipped." );
        return 0;
}
bash-3.2$ /usr/gcc-4.4/bin/gcc -B./ -fPIC -g   -c -o x.o x.c
bash-3.2$ ./ld -shared -o libx.so x.o
./ld: x.o: relocation R_X86_64_PC32 against `foo' can not be used when making a
shared object; recompile with -fPIC
./ld: final link failed: Bad value
bash-3.2$ /usr/gcc-4.4/bin/gcc -B./ -fPIC -g   -c -o x.o x.c -m32
bash-3.2$ ld -m elf_i386 -shared -o libx.so x.o
bash-3.2$ 

Linker should issue clear error message for both cases.