linux-kernel - [PATCH 22/29] Kbuild: Prepare !CLANG whole module objtool

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Message-ID: <20220218171409.872776952@infradead.org>
Date:   Fri, 18 Feb 2022 17:49:24 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        jpoimboe@...hat.com, andrew.cooper3@...rix.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com
Subject: [PATCH 22/29] Kbuild: Prepare !CLANG whole module objtool

Massage the Kbuild stuff to allow running objtool on whole modules.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 Makefile               |    2 ++
 scripts/Makefile.build |   25 ++++++++++++++++---------
 scripts/Makefile.lib   |    2 +-
 3 files changed, 19 insertions(+), 10 deletions(-)

--- a/Makefile
+++ b/Makefile
@@ -907,6 +907,8 @@ ifdef CONFIG_LTO
 KBUILD_CFLAGS	+= -fno-lto $(CC_FLAGS_LTO)
 KBUILD_AFLAGS	+= -fno-lto
 export CC_FLAGS_LTO
+BUILD_LTO	:= y
+export BUILD_LTO
 endif
 
 ifdef CONFIG_CFI_CLANG
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -88,7 +88,7 @@ endif
 
 targets-for-modules := $(patsubst %.o, %.mod, $(filter %.o, $(obj-m)))
 
-ifdef CONFIG_LTO_CLANG
+ifdef BUILD_LTO
 targets-for-modules += $(patsubst %.o, %.lto.o, $(filter %.o, $(obj-m)))
 endif
 
@@ -230,6 +230,7 @@ objtool := $(objtree)/tools/objtool/objt
 objtool_args =								\
 	$(if $(CONFIG_UNWINDER_ORC),orc generate,check)			\
 	$(if $(part-of-module), --module)				\
+	$(if $(BUILD_LTO), --lto)					\
 	$(if $(CONFIG_FRAME_POINTER),, --no-fp)				\
 	$(if $(CONFIG_GCOV_KERNEL)$(CONFIG_LTO_CLANG), --no-unreachable)\
 	$(if $(CONFIG_RETPOLINE), --retpoline)				\
@@ -242,11 +243,16 @@ cmd_gen_objtooldep = $(if $(objtool-enab
 
 endif # CONFIG_STACK_VALIDATION
 
-ifdef CONFIG_LTO_CLANG
+ifdef BUILD_LTO
 
 # Skip objtool for LLVM bitcode
 $(obj)/%.o: objtool-enabled :=
 
+# objtool was skipped for LLVM bitcode, run it now that we have compiled
+# modules into native code
+$(obj)/%.lto.o: objtool-enabled = y
+$(obj)/%.lto.o: part-of-module := y
+
 else
 
 # 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory
@@ -292,21 +298,22 @@ ifdef CONFIG_LTO_CLANG
 # Module .o files may contain LLVM bitcode, compile them into native code
 # before ELF processing
 quiet_cmd_cc_lto_link_modules = LTO [M] $@
-cmd_cc_lto_link_modules =						\
+      cmd_cc_lto_link_modules =						\
 	$(LD) $(ld_flags) -r -o $@					\
 		$(shell [ -s $(@:.lto.o=.o.symversions) ] &&		\
 			echo -T $(@:.lto.o=.o.symversions))		\
 		--whole-archive $(filter-out FORCE,$^)			\
 		$(cmd_objtool)
-
-# objtool was skipped for LLVM bitcode, run it now that we have compiled
-# modules into native code
-$(obj)/%.lto.o: objtool-enabled = y
-$(obj)/%.lto.o: part-of-module := y
+else
+quiet_cmd_cc_lto_link_modules = LD [M] $@
+      cmd_cc_lto_link_modules =						\
+	$(LD) $(ld_flags) -r -o $@					\
+		$(filter-out FORCE,$^)					\
+		$(cmd_objtool)
+endif
 
 $(obj)/%.lto.o: $(obj)/%.o FORCE
 	$(call if_changed,cc_lto_link_modules)
-endif
 
 cmd_mod = { \
 	echo $(if $($*-objs)$($*-y)$($*-m), $(addprefix $(obj)/, $($*-objs) $($*-y) $($*-m)), $(@:.mod=.o)); \
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -230,7 +230,7 @@ dtc_cpp_flags  = -Wp,-MMD,$(depfile).pre
 		 $(addprefix -I,$(DTC_INCLUDE))                          \
 		 -undef -D__DTS__
 
-ifeq ($(CONFIG_LTO_CLANG),y)
+ifdef BUILD_LTO
 # With CONFIG_LTO_CLANG, .o files in modules might be LLVM bitcode, so we
 # need to run LTO to compile them into native code (.lto.o) before further
 # processing.