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Message-ID: <20260209084820.57298-7-sv@linux.ibm.com>
Date: Mon, 9 Feb 2026 14:18:20 +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 6/6] powerpc: Enable build-time feature fixup processing by default
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@...il.com>
Signed-off-by: Nicholas Piggin <npiggin@...il.com>
Signed-off-by: Sathvika Vasireddy <sv@...ux.ibm.com>
---
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,
--
2.43.0
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