Question

A simple question – is there any way to make the g++ linker to link with a specific libstdc++ library version? I didn’t find anything useful in the man page of gcc/g++, neither in other questions here.

Here’s the situation – my application uses a specific shared library, that’s built with libstdc++.so.5 and I want to install and use it on RHEL5. So, when I try to build the application on a RHEL5 machine, I got the warning:

warning: libstdc++.so.5, needed by ..the_shared_library_.. may conflict with libstdc++.so.6

Installing a compat-libstdc++ rpm didn’t help, the program crashes on a destructor of std::string, because of the incapability. So, on this RHEL5 machine I have this:

[root@xxx]# ll /usr/lib/libstd*  
-rwxr-xr-x 1 root root 259532 Aug 21 2006 /usr/lib/libstdc++-3-libc6.2-2-2.10.0.so  
lrwxrwxrwx 1 root root 31 Jul 28 19:35 /usr/lib/libstdc++-libc6.2-2.so.3 -> libstdc++-3-libc6.2-2-2.10.0.so  
lrwxrwxrwx 1 root root 18 Aug 24 15:08 /usr/lib/libstdc++.so.5 -> libstdc++.so.5.0.7  
-rwxr-xr-x 1 root root 733456 Aug 21 2006 /usr/lib/libstdc++.so.5.0.7  

and when I make

[root@xxxx]# ldd my_exe  
libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x00333000)  
...  
libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x00ddf000)

which is bad, as I know it’s undefined behavior :/

So, is there any way to build my executable using only libstdc++.so.5 ? (removing libstdc++.so.6 is not an option because of many reasons. Static linking is not an option, too ).

Thanks a lot!

Answer 1

Here’s the ABI versions table; the default value for the -fabi-version switch changed from 1 to 2 at the same time g++ introduced libstdc++.so.6 with 3.4. This means that to link against the older libstdc++ library you would need to

• find and use the equivalent C++ headers instead of the ones included with your compiler
• recompile all your code (and any other C++ libraries you’re using) with -fabi-version=1

otherwise you run the risk of ABI incompatibilities. I can’t tell you precisely what the changes were but in general it’s best to try and keep all C++ code you have compiled with the same compiler version.

Assuming you don’t want to try and hack things togther like this I think you have two choices:

1. ask your shared library vendor to recompile the library with your version of GCC for you. This may not be trivial as g++ 3.4 introduced a new stricter C++ parser.
2. ask your vendor which version of g++ they used to compile the library in the first place and use that version to compile your own code. RH might provide a compat-gcc compiler as well as the libstdc++ – I can’t remember. However you’ll also need down-level versions of all other libraries and OS-provided C++ libraries that you’re using, so might be easiest to compile on a VM with an older Red Hat version that had the right compiler.