From c25e1c55822f9b3b53ccbf88b85644317a525752 Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Fri, 27 May 2022 19:01:49 +0900 Subject: kbuild: do not create *.prelink.o for Clang LTO or IBT When CONFIG_LTO_CLANG=y, additional intermediate *.prelink.o is created for each module. Also, objtool is postponed until LLVM IR is converted to ELF. CONFIG_X86_KERNEL_IBT works in a similar way to postpone objtool until objects are merged together. This commit stops generating *.prelink.o, so the build flow will look similar with/without LTO. The following figures show how the LTO build currently works, and how this commit is changing it. Current build flow ================== [1] single-object module $(LD) $(CC) +objtool $(LD) foo.c --------------------> foo.o -----> foo.prelink.o -----> foo.ko (LLVM IR) (ELF) | (ELF) | foo.mod.o --/ (LLVM IR) [2] multi-object module $(LD) $(CC) $(AR) +objtool $(LD) foo1.c -----> foo1.o -----> foo.o -----> foo.prelink.o -----> foo.ko | (archive) (ELF) | (ELF) foo2.c -----> foo2.o --/ | (LLVM IR) foo.mod.o --/ (LLVM IR) One confusion is that foo.o in multi-object module is an archive despite of its suffix. New build flow ============== [1] single-object module Since there is only one object, there is no need to keep the LLVM IR. Use $(CC)+$(LD) to generate an ELF object in one build rule. When LTO is disabled, $(LD) is unneeded because $(CC) produces an ELF object. $(CC)+$(LD)+objtool $(LD) foo.c ----------------------------> foo.o ---------> foo.ko (ELF) | (ELF) | foo.mod.o --/ (LLVM IR) [2] multi-object module Previously, $(AR) was used to combine LLVM IR files into an archive, but there was no technical reason to do so. Use $(LD) to merge them into a single ELF object. $(LD) $(CC) +objtool $(LD) foo1.c ---------> foo1.o ---------> foo.o ---------> foo.ko | (ELF) | (ELF) foo2.c ---------> foo2.o ----/ | (LLVM IR) foo.mod.o --/ (LLVM IR) Signed-off-by: Masahiro Yamada Reviewed-by: Nicolas Schier Tested-by: Nathan Chancellor Reviewed-by: Sami Tolvanen Tested-by: Sedat Dilek # LLVM-14 (x86-64) Acked-by: Josh Poimboeuf --- scripts/Makefile.build | 63 ++++++++++++++++---------------------------------- 1 file changed, 20 insertions(+), 43 deletions(-) (limited to 'scripts/Makefile.build') diff --git a/scripts/Makefile.build b/scripts/Makefile.build index f80196eef03a..cc7061258e42 100644 --- a/scripts/Makefile.build +++ b/scripts/Makefile.build @@ -88,10 +88,6 @@ endif targets-for-modules := $(foreach x, o mod $(if $(CONFIG_TRIM_UNUSED_KSYMS), usyms), \ $(patsubst %.o, %.$x, $(filter %.o, $(obj-m)))) -ifneq ($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT),) -targets-for-modules += $(patsubst %.o, %.prelink.o, $(filter %.o, $(obj-m))) -endif - ifdef need-modorder targets-for-modules += $(obj)/modules.order endif @@ -152,8 +148,18 @@ $(obj)/%.ll: $(src)/%.c FORCE # The C file is compiled and updated dependency information is generated. # (See cmd_cc_o_c + relevant part of rule_cc_o_c) +is-single-obj-m = $(and $(part-of-module),$(filter $@, $(obj-m)),y) + +# When a module consists of a single object, there is no reason to keep LLVM IR. +# Make $(LD) covert LLVM IR to ELF here. +ifdef CONFIG_LTO_CLANG +cmd_ld_single_m = $(if $(is-single-obj-m), ; $(LD) $(ld_flags) -r -o $(tmp-target) $@; mv $(tmp-target) $@) +endif + quiet_cmd_cc_o_c = CC $(quiet_modtag) $@ - cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $< $(cmd_objtool) + cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $< \ + $(cmd_ld_single_m) \ + $(cmd_objtool) ifdef CONFIG_MODVERSIONS # When module versioning is enabled the following steps are executed: @@ -219,7 +225,7 @@ objtool_args = \ $(if $(CONFIG_STACK_VALIDATION), --stackval) \ $(if $(CONFIG_HAVE_STATIC_CALL_INLINE), --static-call) \ --uaccess \ - $(if $($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT)), --link) \ + $(if $(delay-objtool), --link) \ $(if $(part-of-module), --module) \ $(if $(CONFIG_GCOV_KERNEL), --no-unreachable) @@ -228,21 +234,15 @@ cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(o endif # CONFIG_OBJTOOL -ifneq ($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT),) - -# Skip objtool for LLVM bitcode -$(obj)/%.o: objtool-enabled := - -else - # 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory # 'OBJECT_FILES_NON_STANDARD_foo.o := 'y': skip objtool checking for a file # 'OBJECT_FILES_NON_STANDARD_foo.o := 'n': override directory skip for a file -$(obj)/%.o: objtool-enabled = $(if $(filter-out y%, \ - $(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n),y) +is-standard-object = $(if $(filter-out y%, $(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n),y) -endif +delay-objtool := $(or $(CONFIG_LTO_CLANG),$(CONFIG_X86_KERNEL_IBT)) + +$(obj)/%.o: objtool-enabled = $(if $(is-standard-object),$(if $(delay-objtool),$(is-single-obj-m),y)) ifdef CONFIG_TRIM_UNUSED_KSYMS cmd_gen_ksymdeps = \ @@ -271,24 +271,6 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE $(call if_changed_rule,cc_o_c) $(call cmd,force_checksrc) -ifneq ($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT),) -# Module .o files may contain LLVM bitcode, compile them into native code -# before ELF processing -quiet_cmd_cc_prelink_modules = LD [M] $@ - cmd_cc_prelink_modules = \ - $(LD) $(ld_flags) -r -o $@ \ - --whole-archive $(filter-out FORCE,$^) \ - $(cmd_objtool) - -# objtool was skipped for LLVM bitcode, run it now that we have compiled -# modules into native code -$(obj)/%.prelink.o: objtool-enabled = y -$(obj)/%.prelink.o: part-of-module := y - -$(obj)/%.prelink.o: $(obj)/%.o FORCE - $(call if_changed,cc_prelink_modules) -endif - cmd_mod = echo $(addprefix $(obj)/, $(call real-search, $*.o, .o, -objs -y -m)) | \ $(AWK) -v RS='( |\n)' '!x[$$0]++' > $@ @@ -298,7 +280,7 @@ $(obj)/%.mod: FORCE # List module undefined symbols cmd_undefined_syms = $(NM) $< | sed -n 's/^ *U //p' > $@ -$(obj)/%.usyms: $(obj)/%$(mod-prelink-ext).o FORCE +$(obj)/%.usyms: $(obj)/%.o FORCE $(call if_changed,undefined_syms) quiet_cmd_cc_lst_c = MKLST $@ @@ -420,16 +402,11 @@ $(obj)/modules.order: $(obj-m) FORCE $(obj)/lib.a: $(lib-y) FORCE $(call if_changed,ar) -ifneq ($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT),) -quiet_cmd_link_multi-m = AR [M] $@ -cmd_link_multi-m = \ - rm -f $@; \ - $(AR) cDPrsT $@ @$(patsubst %.o,%.mod,$@) -else quiet_cmd_link_multi-m = LD [M] $@ - cmd_link_multi-m = $(LD) $(ld_flags) -r -o $@ @$(patsubst %.o,%.mod,$@) -endif + cmd_link_multi-m = $(LD) $(ld_flags) -r -o $@ @$(patsubst %.o,%.mod,$@) $(cmd_objtool) +$(multi-obj-m): objtool-enabled := $(delay-objtool) +$(multi-obj-m): part-of-module := y $(multi-obj-m): %.o: %.mod FORCE $(call if_changed,link_multi-m) $(call multi_depend, $(multi-obj-m), .o, -objs -y -m) -- cgit