Bug 1555397
| Summary: | backport s390 -mpic-data-is-text-relative feature | ||
|---|---|---|---|
| Product: | Red Hat Enterprise Linux 7 | Reporter: | Joe Lawrence <joe.lawrence> |
| Component: | gcc | Assignee: | Marek Polacek <mpolacek> |
| Status: | CLOSED ERRATA | QA Contact: | Michael Petlan <mpetlan> |
| Severity: | unspecified | Docs Contact: | Vladimír Slávik <vslavik> |
| Priority: | unspecified | ||
| Version: | 7.6 | CC: | bgollahe, jakub, jpoimboe, mcermak, mnewsome, ohudlick, vslavik |
| Target Milestone: | rc | Keywords: | FutureFeature |
| Target Release: | --- | ||
| Hardware: | Unspecified | ||
| OS: | Unspecified | ||
| Whiteboard: | |||
| Fixed In Version: | gcc-4.8.5-31.el7 | Doc Type: | No Doc Update |
| Doc Text: |
undefined
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Story Points: | --- |
| Clone Of: | Environment: | ||
| Last Closed: | 2018-10-30 07:27:17 UTC | Type: | Bug |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
| Bug Depends On: | |||
| Bug Blocks: | 1505884 | ||
Related tests passed with gcc-4.8.5-36.el7.s390x. VERIFIED. Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHBA-2018:3016 |
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.