In order to support kpatch on s390x architecture, we'd like to have the -mpic-data-is-text-relative feature backported to RHEL7.

Quick background of how kpatch works: kpatch patches code on a per-function basis and relies on ftrace for function redirection from old to new funcs.  The patched binary code containing the new functions is placed in a kernel module, and kpatch manually applies relocations to the new code at module load time.

On s390x, things become interesting when we stick patched code for vmlinux in a kernel module. One obstacle we've run into is when the compiled code uses R_390_PC32DBL relocations, which utilize 32-bit relative displacements.  However, kernel modules are placed at the tail end of the kernel address space, rendering these relocations non-functional, since the displacement to vmlinux symbols on the other end of the address space is larger than what can fit in a 32-bit field.

To work around this issue, we worked upstream with Martin Schwidefsky and Andreas Krebbel to add 9852c8ae7856 ("S/390: New option -mpic-data-is-text-relative").  That option ensures that data references are not relative, but rather via GOT.  The change seems pretty small and hopefully easy to backport to RHEL7's gcc.