Subject: [RFC PATCH v4 0/6] objtool: Fixup alternate feature relative addresses

From: Sathvika Vasireddy <[email-masked]>
Date: Mon, 16 Mar 2026 11:52:31 +0530

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/[email-masked]/
[2] Initial RFC v1:
    https://lore.kernel.org/linuxppc-dev/[email-masked]/T/#t
[3] PowerPC instruction decoder borrowed from:
    https://lore.kernel.org/linuxppc-dev/bfa8364d[email-masked]/#Z31tools:objtool:arch:powerpc:decode.c

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

Changes in V4:
- consolidate emit-relocs remove-section logic for
  CONFIG_ARCH_VMLINUX_NEEDS_RELOCS and CONFIG_HAVE_OBJTOOL_FTR_FIXUP
  configs as suggested by Nathan Chancellor.

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

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                  |  11 +-
 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, 612 insertions(+), 26 deletions(-)

-- 
2.43.0