[RFC PATCH v3 6/6] powerpc: Enable build-time feature fixup processing by default
From: Sathvika Vasireddy <hidden>
Date: 2026-02-09 08:49:42
Also in:
linux-kbuild, lkml
Subsystem:
kernel build + files below scripts/ (unless maintained elsewhere), linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Nathan Chancellor, Nicolas Schier, Madhavan Srinivasan, Linus Torvalds
Enable HAVE_OBJTOOL_FTR_FIXUP by default on PowerPC architecture. - Remove runtime branch translation logic from patch_alt_instruction() - Add --emit-relocs linker flags for post-link fixup processing - Update ftr_alt section attributes to include executable flag - Strip the --emit-relocs relocation sections (.rel*) from the final vmlinux after processing Co-developed-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Sathvika Vasireddy <redacted> --- 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.vmlinux | 5 +++++ 6 files changed, 20 insertions(+), 15 deletions(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index b8d36a261009..aedb11912672 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig@@ -23,6 +23,9 @@ config 64BIT bool default y if PPC64 +config HAVE_OBJTOOL_FTR_FIXUP + def_bool y + config LIVEPATCH_64 def_bool PPC64 depends on LIVEPATCH
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index a58b1029592c..8e1dab5f3c9a 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile@@ -105,6 +105,11 @@ LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) := -pie --no-dynamic-linker LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) += -z notext LDFLAGS_vmlinux := $(LDFLAGS_vmlinux-y) +# --emit-relocs required for post-link fixup of alternate feature +# text section relocations. +LDFLAGS_vmlinux += --emit-relocs +KBUILD_LDFLAGS_MODULE += --emit-relocs + ifdef CONFIG_PPC64 ifndef CONFIG_PPC_KERNEL_PCREL # -mcmodel=medium breaks modules because it uses 32bit offsets from
diff --git a/arch/powerpc/include/asm/feature-fixups.h b/arch/powerpc/include/asm/feature-fixups.h
index 756a6c694018..d6ae92a292ec 100644
--- a/arch/powerpc/include/asm/feature-fixups.h
+++ b/arch/powerpc/include/asm/feature-fixups.h@@ -32,7 +32,7 @@ #define FTR_SECTION_ELSE_NESTED(label) \ label##2: \ - .pushsection __ftr_alt_##label,"a"; \ + .pushsection __ftr_alt_##label, "ax"; \ .align 2; \ label##3:
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 15850296c0a9..70a4de464b34 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S@@ -99,8 +99,8 @@ SECTIONS .text : AT(ADDR(.text) - LOAD_OFFSET) { ALIGN_FUNCTION(); #endif - /* careful! __ftr_alt_* sections need to be close to .text */ - *(.text.hot .text.hot.* TEXT_MAIN .text.fixup .text.unlikely .text.unlikely.* .fixup __ftr_alt_* .ref.text); + *(.text.hot .text.hot.* TEXT_MAIN .text.fixup .text.unlikely + .text.unlikely.* .fixup .ref.text); *(.tramp.ftrace.text); NOINSTR_TEXT SCHED_TEXT
@@ -267,6 +267,10 @@ SECTIONS _einittext = .; } :text + .__ftr_alternates.text : AT(ADDR(.__ftr_alternates.text) - LOAD_OFFSET) { + *(__ftr_alt*); + } + /* .exit.text is discarded at runtime, not link time, * to deal with references from __bug_table */
diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c
index 587c8cf1230f..269e992b1631 100644
--- a/arch/powerpc/lib/feature-fixups.c
+++ b/arch/powerpc/lib/feature-fixups.c@@ -53,22 +53,10 @@ static u32 *calc_addr(struct fixup_entry *fcur, long offset) static int patch_alt_instruction(u32 *src, u32 *dest, u32 *alt_start, u32 *alt_end) { - int err; ppc_inst_t instr; instr = ppc_inst_read(src); - if (instr_is_relative_branch(ppc_inst_read(src))) { - u32 *target = (u32 *)branch_target(src); - - /* Branch within the section doesn't need translating */ - if (target < alt_start || target > alt_end) { - err = translate_branch(&instr, dest, src); - if (err) - return 1; - } - } - raw_patch_instruction(dest, instr); return 0;
diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index e3dd7fc62f20..3d2a203b8908 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux@@ -88,6 +88,11 @@ remove-section-$(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS) += '.rel*' '!.rel*.dyn' # https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=c12d9fa2afe7abcbe407a00e15719e1a1350c2a7 remove-section-$(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS) += '.rel.*' +# --emit-relocs produces .rela.* sections needed by objtool --ftr-fixup; +# strip them from vmlinux after fixup processing is complete. +remove-section-$(CONFIG_HAVE_OBJTOOL_FTR_FIXUP) += '.rel*' '!.rel*.dyn' +remove-section-$(CONFIG_HAVE_OBJTOOL_FTR_FIXUP) += '.rel.*' + remove-symbols := -w --strip-unneeded-symbol='__mod_device_table__*' # To avoid warnings: "empty loadable segment detected at ..." from GNU objcopy,
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2.43.0