[PATCH v2 0/8] LoongArch: Add livepatch build (KLP) support

[George Guo <dongtai.guo@linux.dev>]

This series adds LoongArch support for the klp-build livepatch tooling,
enabling automated livepatch module generation using objtool on
LoongArch.

It is based on Josh Poimboeuf's klp-build series [1] (see base-commit
below) and extends it with the LoongArch-specific objtool and build
pieces, plus a few LoongArch toolchain/relocation fixes required to make
livepatch modules load and run correctly.

Overview (the feature is wired up last so the series stays bisectable:
objtool's KLP arch hooks are all in place before ARCH_HAS_KLP is turned
on):

 - Patches 1 and 6 add the objtool hooks LoongArch needs:
   arch_adjusted_addend() and arch_jump_opcode_bytes() (the latter makes
   klp checksums for jump/call instructions position-independent,
   mirroring x86/arm64).
 - Patch 2 marks the special sections so objtool can split them into
   per-entry symbols: SHF_MERGE entry sizes for the read-only
   .altinstructions/__ex_table, and ANNOTATE_DATA_SPECIAL for the
   writable __bug_table/__jump_table.
 - Patches 3-4 fix kernel panics seen when loading livepatch modules,
   caused by LoongArch code-generation/relocation assumptions:
     * disable -mdirect-extern-access for klp builds (the module loader
       relies on GOT entries for external symbol references),
     * build with -fPIC so same-compilation-unit symbol references stay
       GOT-indirect and can be relocated into the livepatch module
       (-fPIE is not enough: it emits direct, non-GOT references).
 - Patch 5 fixes EFI linking when building with -fdata-sections.
 - Patch 7 adds KLP_SYSCALL_DEFINEx() support for LoongArch.
 - Patch 8 wires up LoongArch klp-build (selects HAVE_KLP_BUILD and
   enables objtool's KLP support).

Testing:
 - objtool builds cleanly for LoongArch.
 - Livepatch modules were generated and loaded on a LoongArch machine;
   the panics addressed by patches 3-4 no longer reproduce.

Changes since v1 [2]:
 - Mark the writable special sections (__bug_table, __jump_table) with
   ANNOTATE_DATA_SPECIAL instead of SHF_MERGE+entsize, which is invalid
   for writable sections and rejected by Clang; SHF_MERGE is kept only
   for the read-only .altinstructions/__ex_table.  Also dropped a
   redundant asm-offsets.h include in head.S.  (WangYuli)
 - Rewrote the -fPIC commit message: the root cause is GOT indirection,
   not "absolute addressing".  With CONFIG_RELOCATABLE=y the kernel is
   already built -fPIE, yet -fPIE still emits direct, non-GOT references
   for same-compilation-unit symbols, so -fPIC is required.  (Xi Ruoyao)
 - Set the LoongArch CFLAGS in build_kernel(), where the variables are
   actually used; in v1 they were in clean_kernel() and had no effect.
   (WangYuli)
 - Gated the klp-build changes on CONFIG_RELOCATABLE=y and
   CONFIG_AS_HAS_EXPLICIT_RELOCS=y, and only override KBUILD_CFLAGS_KERNEL
   when needed, so other arches/configs are unaffected.
 - Reordered the series so the enabling patch ("Add livepatch build (KLP)
   support") comes last, keeping every commit buildable/bisectable.
   Patch numbers therefore differ from v1.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/log/?h=klp-build-arm64
[2] https://lore.kernel.org/all/20260604065317.219777-1-dongtai.guo@linux.dev/

George Guo (8):
  objtool/LoongArch: Add arch_adjusted_addend() for KLP support
  LoongArch: Mark special sections for KLP support
  livepatch/klp-build: disable direct-extern-access for LoongArch to fix
    kernel panic
  livepatch/klp-build: build LoongArch with -fPIC to keep GOT-indirect
    symbol references
  LoongArch: Fix EFI linking with -fdata-sections
  objtool/klp: Add LoongArch jump opcode bytes support
  klp-build: Add LoongArch syscall patching macro
  LoongArch: Add livepatch build (KLP) support

 arch/loongarch/Kconfig                       |  1 +
 arch/loongarch/include/asm/alternative-asm.h |  5 ++-
 arch/loongarch/include/asm/alternative.h     |  6 ++-
 arch/loongarch/include/asm/asm-extable.h     | 10 ++++-
 arch/loongarch/include/asm/bug.h             |  1 +
 arch/loongarch/include/asm/jump_label.h      |  2 +
 arch/loongarch/kernel/asm-offsets.c          | 20 +++++++++
 arch/loongarch/kernel/vmlinux.lds.S          |  2 +-
 include/linux/livepatch_helpers.h            | 22 ++++++++++
 scripts/livepatch/klp-build                  | 36 ++++++++++++++-
 tools/objtool/Makefile                       |  3 +-
 tools/objtool/arch/loongarch/decode.c        | 46 ++++++++++++++++++++
 12 files changed, 145 insertions(+), 9 deletions(-)


base-commit: 85afaba140a4b9f20fe8c8a64b24fc85f022d981
-- 
2.25.1