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authorMasahiro Yamada <masahiroy@kernel.org>2022-05-27 13:01:49 +0300
committerMasahiro Yamada <masahiroy@kernel.org>2022-05-29 12:39:35 +0300
commitc25e1c55822f9b3b53ccbf88b85644317a525752 (patch)
tree0a71732cc734866099013c08aafef8f7d4437619 /scripts/Makefile.build
parent0cfd90060d714e3d1e0d1b30cfd1c46b71f4e721 (diff)
downloadlinux-c25e1c55822f9b3b53ccbf88b85644317a525752.tar.xz
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 <masahiroy@kernel.org> Reviewed-by: Nicolas Schier <nicolas@fjasle.eu> Tested-by: Nathan Chancellor <nathan@kernel.org> Reviewed-by: Sami Tolvanen <samitolvanen@google.com> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM-14 (x86-64) Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Diffstat (limited to 'scripts/Makefile.build')
-rw-r--r--scripts/Makefile.build63
1 files changed, 20 insertions, 43 deletions
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)