How do shared libraries work in a mixed 64bit/32bit system?

Question

Good morning,

on a 64bit RedHat box we have to compile and run a 32bit application. Meanwhile I managed to compile the gcc version needed (4.0.3) and all required runtime libraries in 32bit and have set the LD_LIBRARY_PATH to point to the 32bit versions, but now during the remaining build process, a small java program needs to be executed which is installed in /usr/bin as a 64bit program, which now finds the 32bit version of libgcc_s.so first.

In general, if I set the LD_LIBRARY_PATH to the 32bit versions, I break the 64bit programs and vice versa.

How it this supposed to work at all? I am certain I am not the first person with this problem at hand. How is it solved usually?

Regards, Stefan

Answer 1

Add both the 32-bit and 64-bit directories to the LD_LIBRARY_PATH.

If you do this, then the ld.so for 32-bit or 64-bit will use the correct libraries.

e.g. A 32-bit test app "test32" and 64-bit test app "test", with a locally-installed copy of a (newer version of) gcc and binutils in a user homedir, to avoid clobbering the system-wide install of gcc:

=> export LD_LIBRARY_PATH=/home/user1/pub/gcc+binutils/lib:/home/user1/pub/gcc+binutils/lib64

=> ldd ./test32
    libstdc++.so.6 => /home/user1/pub/gcc+binutils/lib/libstdc++.so.6 (0x00111000)
    libgcc_s.so.1 => /home/user1/pub/gcc+binutils/lib/libgcc_s.so.1 (0x00221000)

=> ldd ./test
    libstdc++.so.6 => /home/user1/pub/gcc+binutils/lib64/libstdc++.so.6 (0x00007ffff7cfc000)
    libgcc_s.so.1 => /home/user1/pub/gcc+binutils/lib64/libgcc_s.so.1 (0x00007ffff7ad2000)

(Less interesting library paths removed)

This shows that the loaders know to ignore the libraries of the wrong architecture, at least on this Scientific Linux 6.3 (RHEL-derived) system. I would expect other distros to work similarly, but haven't tested this.

This may have only started being the case more recently than your (unspecified) distro version, however.

Answer 2

On Solaris one can use LD_LIBRARY32_PATH and LD_LIBRARY64_PATH, but that isn't supported on Linux.

In general, you should just never need to set LD_LIBRARY_PATH at all in the first place:

• either install needed libraries into /usr/lib32 or /usr/lib64 as appropriate, or
• build your 32-bit application with -Wl,-rpath=/path/to/32-bit/libs

Answer 3

As a workaround, wrap the Java call in a small shell script which unsets LD_LIBRARY_PATH and then calls the executable. Alternatively, this might also work:

LD_LIBRARY_PATH= java...

Note the space between "=" and the name of the executable.