[RFC PATCH v2 2/3] kbuild: Add objtool integration for PowerPC feature fixups

[Sathvika Vasireddy <sv@linux.ibm.com>]

Add build system support for PowerPC feature fixup processing:

- Add HAVE_OBJTOOL_FTR_FIXUP config option for architectures that support
  build-time feature fixup processing
- Integrate objtool feature fixup processing into vmlinux build

Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
---
 Makefile                 |  7 +++++++
 arch/Kconfig             |  3 +++
 scripts/Makefile.lib     |  5 +++--
 scripts/Makefile.vmlinux | 13 ++++++++++++-
 4 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index cf37b9407821..aa54e4348c8c 100644
--- a/Makefile
+++ b/Makefile
@@ -1419,6 +1419,13 @@ ifdef CONFIG_OBJTOOL
 prepare: tools/objtool
 endif
 
+# CONFIG_OBJTOOL and CONFIG_HAVE_OBJTOOL_FTR_FIXUP are unrelated, separate
+# options. It was integrated in objtool in order to borrow the elf parser,
+# but this is different from how the other objtool commands are used.
+ifdef CONFIG_HAVE_OBJTOOL_FTR_FIXUP
+prepare: tools/objtool
+endif
+
 ifdef CONFIG_BPF
 ifdef CONFIG_DEBUG_INFO_BTF
 prepare: tools/bpf/resolve_btfids
diff --git a/arch/Kconfig b/arch/Kconfig
index d1b4ffd6e085..d870aab17cba 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1334,6 +1334,9 @@ config HAVE_UACCESS_VALIDATION
 	bool
 	select OBJTOOL
 
+config HAVE_OBJTOOL_FTR_FIXUP
+	bool
+
 config HAVE_STACK_VALIDATION
 	bool
 	help
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 1d581ba5df66..c77d4ceff2cc 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -169,10 +169,10 @@ cpp_flags      = -Wp,-MMD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE)     \
 
 ld_flags       = $(KBUILD_LDFLAGS) $(ldflags-y) $(LDFLAGS_$(@F))
 
-ifdef CONFIG_OBJTOOL
-
 objtool := $(objtree)/tools/objtool/objtool
 
+ifdef CONFIG_OBJTOOL
+
 objtool-args-$(CONFIG_HAVE_JUMP_LABEL_HACK)		+= --hacks=jump_label
 objtool-args-$(CONFIG_HAVE_NOINSTR_HACK)		+= --hacks=noinstr
 objtool-args-$(CONFIG_MITIGATION_CALL_DEPTH_TRACKING)	+= --hacks=skylake
@@ -200,6 +200,7 @@ objtool-args = $(objtool-args-y)					\
 delay-objtool := $(or $(CONFIG_LTO_CLANG),$(CONFIG_X86_KERNEL_IBT))
 
 cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool-args) $@)
+
 cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)
 
 objtool-enabled := y
diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index b64862dc6f08..94cc2bba929a 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -84,7 +84,8 @@ ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
 # Final link of vmlinux with optional arch pass after final link
 cmd_link_vmlinux =							\
 	$< "$(LD)" "$(KBUILD_LDFLAGS)" "$(LDFLAGS_vmlinux)" "$@";	\
-	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
+	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)	\
+	$(cmd_objtool_vmlinux)
 
 targets += $(vmlinux-final)
 $(vmlinux-final): scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) FORCE
@@ -131,3 +132,13 @@ existing-targets := $(wildcard $(sort $(targets)))
 -include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
 
 .PHONY: $(PHONY)
+
+# objtool for vmlinux
+# ----------------------------------
+#
+#  For feature fixup, objtool does not run on individual
+#  translation units. Run this on vmlinux instead.
+
+ifdef CONFIG_HAVE_OBJTOOL_FTR_FIXUP
+cmd_objtool_vmlinux = ; $(objtool) --ftr-fixup --link $@
+endif
-- 
2.43.0