linux-kernel - [RFC PATCH v3 0/6] objtool: Fixup alternate feature relative addresses

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Message-ID: <20260209084820.57298-1-sv@linux.ibm.com>
Date: Mon,  9 Feb 2026 14:18:14 +0530
From: Sathvika Vasireddy <sv@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Cc: nathan@...nel.org, masahiroy@...nel.org, kees@...nel.org,
        naveen@...nel.org, jpoimboe@...nel.org, peterz@...radead.org,
        npiggin@...il.com, maddy@...ux.ibm.com, segher@...nel.crashing.org,
        christophe.leroy@...roup.eu, mingo@...nel.org, mpe@...erman.id.au,
        sv@...ux.ibm.com, nsc@...nel.org
Subject: [RFC PATCH v3 0/6] objtool: Fixup alternate feature relative addresses

This patch series implements build-time fixup of alternate feature
relative addresses for powerpc.

Previously, Nicholas Piggin proposed a build-time solution using a
custom PowerPC tool [1], which provided the foundation for this approach.
The current implementation leverages objtool's existing ELF parsing
infrastructure to do the same.

This patchset applies atop powerpc/merge branch.

Links and History:
[1] Original PowerPC tool approach:
    http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20170521010130.13552-1-npiggin@gmail.com/
[2] Initial RFC v1:
    https://lore.kernel.org/linuxppc-dev/20240422092206.147078-1-sv@linux.ibm.com/T/#t
[3] PowerPC instruction decoder borrowed from:
    https://lore.kernel.org/linuxppc-dev/bfa8364da047d8610a09458a1cd924a0566aedbb.1736955567.git.christophe.leroy@csgroup.eu/#Z31tools:objtool:arch:powerpc:decode.c

Testing:
Build and Boot tested on ppc64le, ppc64be, and ppc32be configs.

Changes in V3:
- Split code into individual patches
- Put objtool call into cmd_link_vmlinux
- Move HAVE_OBJTOOL_FEATURE_FIXUP from arch/Kconfig to 
  arch/powerpc/Kconfig 

Changes in V2:
- Added implementation support for ppc64 LE, BE, ppc32 BE.

Sathvika Vasireddy (6):
  objtool/powerpc: Add build-time fixup of alternate feature branch
    targets
  objtool: Set ELF_F_LAYOUT flag to preserve vmlinux segment layout
  objtool: Fix "can't find starting instruction" warnings on vmlinux
  objtool/powerpc: Skip jump destination analysis and unnanotated
    intra-function call warnings for --ftr-fixup
  kbuild: Add objtool integration for PowerPC feature fixups
  powerpc: Enable build-time feature fixup processing by default

 Makefile                                  |   7 +
 arch/powerpc/Kconfig                      |   3 +
 arch/powerpc/Makefile                     |   5 +
 arch/powerpc/include/asm/feature-fixups.h |   2 +-
 arch/powerpc/kernel/vmlinux.lds.S         |   8 +-
 arch/powerpc/lib/feature-fixups.c         |  12 -
 scripts/Makefile.lib                      |   4 +-
 scripts/Makefile.vmlinux                  |   8 +-
 tools/objtool/arch/powerpc/decode.c       |  15 +-
 tools/objtool/arch/powerpc/special.c      | 437 ++++++++++++++++++++++
 tools/objtool/builtin-check.c             |   2 +
 tools/objtool/check.c                     |  42 ++-
 tools/objtool/elf.c                       |   4 +
 tools/objtool/include/objtool/builtin.h   |   1 +
 tools/objtool/include/objtool/special.h   |  56 +++
 tools/objtool/special.c                   |  29 ++
 16 files changed, 611 insertions(+), 24 deletions(-)

-- 
2.43.0