[RFC PATCH v2 3/3] powerpc: Enable build-time feature fixup processing by default

[Sathvika Vasireddy]

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

Co-developed-by: Nicholas Piggin <npiggin at gmail.com>
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
Signed-off-by: Sathvika Vasireddy <sv at linux.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 ------------
 5 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 325c1171894d..450b5822786d 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 de6ee7d35cff..961ef49f8bd3 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;
-- 
2.43.0