From: Jakub Jelinek <jakub@redhat.com>

Any prelinked shared library is impossible to run on ppc64 without this
patch, as they immediately segfault.  Say:

	/bin/echo

works even if /lib64/ld64.so.1 is prelinked while

	/lib64/ld64.so.1 /bin/echo

segfaults.

The problem is that ELF_PLAT_INIT is passed the virtual address of the
shared library, not the difference between the virtual address of the
shared library and p_vaddr of the first PT_LOAD segment in that library
(while for the interpreter interp_load_address is the bias).

ELF_PLAT_INIT sets gpr[2] to this absolute address, but
arch/ppc64/kernel/process.c (start_thread) assumes it is a bias and adds it
to entry and toc values loaded from the entry point descriptor.

For non-prelinked shared libraries, first PT_LOAD segment's p_vaddr is
typically 0 and thus load_addr == load_bias (which is why this bug has not
been discovered that long).