[PATCH v2 0/6] objtool: Fixup alternate feature relative addresses

[Shivang Upadhyay]

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.

[1] Original PowerPC tool approach:
    http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20170521010130.13552-1-npiggin@xxxxxxxxx/

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

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

--
Changes since v1: https://lore.kernel.org/all/20260505084628.17940-1-sv@xxxxxxxxxxxxx/
- rebase to upstream master
- 1/6: in arch_decode_instruction() added comment describing opcode 16.
- 1/6: in arch_decode_instruction() added missing logic to add AA flag to offset.

Changes since RFC-v4: https://lore.kernel.org/all/20260316062237.30948-1-sv@xxxxxxxxxxxxx/
- 4/6: In the instruction validation logic, update insn_call_dest() handling
  to allow unannotated intra-function calls when opts.ftr_fixup is enabled,
  and continue processing the instruction.
- 3/6: In the function processing logic, skip zero-length symbols before
  performing function boundary validation, as suggested by Sashiko.
- 3/6: In the function processing loop, add func_off to track the
  absolute/local offset and replace sym_for_each_insn() with an explicit
  loop.
- 1/6: In process_alt_data(), skip files that do not use opt.link.
- 1/6: In process_fixup_entries(), handle realloc() failure and return
  -1` when allocation fails.
- 1/6: In check_and_flatten_fixup_entries(), remove dead code that
  redundantly resets the fixup entry parent.
- 1/6: In is_local_symbol(), fix the local-symbol detection logic and add
  a comment explaining the new check.
- 1/6: In process_alt_relocations(), check that ftr_alt->data and
  ftr->data->d_buf are initialized before accessing them.
- 1/6: Remove redundant line deletions and perform minor cleanup.

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.

---

 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       |  11 +
 tools/objtool/arch/powerpc/special.c      | 451 ++++++++++++++++++++++
 tools/objtool/builtin-check.c             |   2 +
 tools/objtool/check.c                     |  55 ++-
 tools/objtool/elf.c                       |   3 +
 tools/objtool/include/objtool/builtin.h   |   1 +
 tools/objtool/include/objtool/special.h   |  56 +++
 tools/objtool/special.c                   |  29 ++
 16 files changed, 632 insertions(+), 28 deletions(-)

-- 
2.54.0