Problem with gcc linker

[Alex Chen]

I sent the following question to the wrong group, so I am posting it 
here again.  Please bear with me if you have already seen it.

I am using gcc with the following version info on 64-bit Ubunut 10.10.
=============
g++ (Ubuntu/Linaro 4.4.4-14ubuntu5) 4.4.5
Copyright (C) 2010 Free Software Foundation, Inc.
---------------
GNU ld (GNU Binutils for Ubuntu) 2.20.51-system.20100908
Copyright 2010 Free Software Foundation, Inc.
============
My project consists of several shared libraries (.so file) and one 
executable. The program 'myprog' is linked with, say, libA.so, libB.so, 
libC.so, libD.so, and these libraries are put in /usr/local/lib.  This 
path is used to build the libraries and the program, i.e. the -L flag of 
the linker.  At first everything seems to work fine for a while, but all 
of a sudden the generated program 'myprog' would not run any more 
because the loader says the program cannot find certain libraries. I use 
Eclipse C++ plug-in and Code::Blocks for IDE and both experience the 
same problem.  I run 'ldd myprog' and it shows something like:
       linux-vdso.so.1 =>  (0x00007fff45539000)
       libA.so => not found
       libB.so => not found
       libC.so => /usr/local/lib/libC.so (0x00007fa6dd84a000)
       libD.so => /usr/local/lib/libD.so (0x00007fa6dda4a000)
       libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x00007fa6ddc4a000)
       libm.so.6 => /lib/libm.so.6 (0x00007fa6dd9c7000)
       libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x00007fa6dd7b1000)
       libc.so.6 => /lib/libc.so.6 (0x00007fa6dd42d000)
       libpthread.so.0 => /lib/libpthread.so.0 (0x00007fa6dd210000)
       librt.so.1 => /lib/librt.so.1 (0x00007fa6dca07000)
       libltdl.so.7 => /usr/lib/libltdl.so.7 (0x00007fa6dc7fd000)
       libdbus-1.so.3 => /lib/libdbus-1.so.3 (0x00007fa6dc5ba000)
       /lib64/ld-linux-x86-64.so.2 (0x00007fa6e03b8000)
The srtange thing is that those missing libraries are in /usr/local/lib 
and only some libraries are flagged as 'not found' while some libraries 
are fine.

Out of desperation, I made libA.so and libB.so static libraries libA.a 
and libB.a, and have libC.so link with them.  But the linker now says 
libC.so has unresolved symbols like:
   /usr/local/lib/libC.so: undefined reference to `O::O()'
   /usr/local/lib/libC.so: undefined reference to `O::Dump(char const*,  
char const*)'
   /usr/local/lib/libC.so: undefined reference to 
`Address::Address(string const&)'
   /usr/local/lib/libC.so: undefined reference to `B::B(char const*,  
char const*)'
   /usr/local/lib/libC.so: undefined reference to `B::Init(string const&)'
when it tries to link 'myprog'. (Not when it is building libC.so)

When I use 'nm -C libA.a', and 'nm -C libB.a' the symbol are all there:
libA.a
0000000000003514 T O::O()
0000000000002f8c T O::Dump(char const*,  char const*)
0000000000002c36 T Address::Address(string const&)
libB.a
0000000000004538 T B::B(char const*,  char const*)
000000000000cf2c T B::Init(string const&)

But when I use 'nm -C -D libC.so' these symbol are flags as 'U'.
                  U O::O()
                  U O::Dump(char const*,  char const*)
                  U Address::Address(string const&)
                  U B::B(char const*,  char const*)
                  U B::Init(string const&)
Strange thing is that only certain symbols from are unresolved.  Other 
symbols from the same libraries are there.

Can anyone shed some light on how the linker generate the shared/static 
libraries and why some libraries are not linked while some are, even 
when they are all available from the same location.

Alex