[nSLUG] Help? libstdc++ question/confusion

Dop Ganger nslug at fop.ns.ca
Wed Jan 14 08:10:25 AST 2009

On Wed, 14 Jan 2009, Mike Spencer wrote:

> So I copy the real lib over to the same dir on the new box (nudel),
> create the corresponding symlink:
>     nudel-root$  mount bogus:/
>     nudel-root$ pwd
>      /usr/i486-slackware-linux/lib
>    nudel-root$ cp \
>      /mnt/bogus/usr/i486-slackware-linux/lib/libstdc++-2-libc6.1-1-2.9.0.so .
>    nudel-root$ ln -s libstdc++-2-libc6.1-1-2.9.0.so  libstdc++-libc6.1-1.so.2
> and now the app in question segfaults.

Did you run ldconfig to reinitialise the library cache?

I think you might be better off using LD_PRELOAD rather than overwriting 

> What can I do to fix this?

If ldconfig doesn't fix it, something like strace -f -s 500 netscape > 
/tmp/netscape.trace 2>&1 should give you a hint - /tmp/netscape.trace will 
be a trace of all system calls, signals, etc so might give you more 
information on just where it's segfaulting.

> I find this lib management stuff way more confusing than writing or
> even debugging C code.  I don't even know where to look for a lucid
> description of what the various libc* libraries do, how they differ,
> how they're systematically (?!) named and why there are so many that
> are just symlinks.  So I haven't doggedly documented, listed and
> researched this in tedious detail because I don't really know where to
> start.

libc is the C library. libc++ is the C++ library. There's also libm in the 
same family, which is the maths library. Naming appears to be up to the 
developer, leading to whimsy such as libiberty - during compilation the 
leading "lib" is stripped from the name, so it may be referenced to as 
"-liberty" (cue groan). The library itself is named by its full version, 
then it's symlinked to the major version it's compatible with (eg I have 
/lib/libbz2.so.1.0.4 which has libbz2.so.1 and libbz2.so.1.0 symlinked to 
it). Applications are compiled against major and minor versions, eg:

dop at tbox:/bin$ ldd bzip2
         linux-gate.so.1 =>  (0xb7f61000)
         libbz2.so.1.0 => /lib/libbz2.so.1.0 (0xb7f38000)
         libc.so.6 => /lib/tls/i686/cmov/libc.so.6 (0xb7de9000)
         /lib/ld-linux.so.2 (0xb7f62000)
dop at tbox:/bin$

The other option is to set up a chroot with the libraries from the old 
system copied across en masse. I suspect at some point you're going to 
have to do this if you want to keep on running an older version of 

Cheers... Dop.

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