ld.so

To develop ld.so:

    - get the glibc source rpm
    - install and build it (using ~/.rpmmacros so you don't have to be root)
    - hack up the source, and recompile
         (not sure what the right way to rebuild is-- "make" doesn't seem
         to work from anywhere in the tree. this is the best I found:
            % cd /var/tmp/doNotRemove/dhatch/rpmbuild/BUILD/glibc-2.12-2-gc4ccff1/build-x86_64-linuxnptl
            % make -r -C .. objdir=`pwd` elf/ldso_install
         that actually tries to install, ending with "permission denied"
         (do NOT do any of this as root!!!)

To run it, find the executable ld.so
(e.g. in /var/tmp/doNotRemove/dhatch/rpmbuild/BUILD/glibc-2.12-2-gc4ccff1/build-x86_64-linuxnptl/elf/ld.so); you can run it directly:

        ld.so <program> <args> ...

To get all subprocesses of a given process to use it,
you can do the following:
    mkdir jail
    sudo mount --rbind / jail
    sudo mount --bind /path/to/my/ld.so jail/lib64/ld-2.12.so
Then to use it:
    sudo /usr/sbin/chroot jail su - $USER

Optionally, wait til the jailed shell has already started
before mounting ld.so...
and you can mount and umount it on the fly while the jailed shell is running,
to switch back and forth between using the test ld.so and the normal one.


THINGS TO BE AWARE OF:
After testing this for a while,
 I found I was unable to umount jail afterwards; "device is busy".
But "/sbin/fuser jail" doesn't help--
it gets confused and shows all processes using /, instead.
Also some things go haywire, e.g. if I try to access something
through the jail that would cause an automount to happen outside the jail,
that directory gets in a bad state, and, again, it becomes impossible
to unmount the jail directory.