Re: [PATCH 2/5] kbuild: detect objtool changes correctly without .SECONDEXPANSION

Masahiro Yamada
2021-08-31T01:44:51Z

On Sat, Aug 28, 2021 at 6:51 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> This reverts commit 8852c5524029 ("kbuild: Fix objtool dependency for
> 'OBJECT_FILES_NON_STANDARD_<obj> := n'"), and fixes the dependency in
> a cleaner, more precise way.
>
> Using .SECONDEXPANSION is expensive since Makefile.build is parsed
> twice every time, and the escaping dollars makes the code unreadable.
>
> Adding include/config/* as dependency is not maintainable either because
> objtool_args is dependent on more CONFIG options.
>
> A better fix is to include the objtool command in *.cmd files so any
> command change is naturally detected by if_change.
>
> Also, include the md5sum of objtool into *.cmd files so any change in
> the objtool executable will result in rebuilding all objects that depend
> on objtool.

After more consideration, I decided not to do this.
(I retract 2/5, 4/5, 5/5 from this series).

I came up with a cleaner patch set.

I will send it later.

> This allows us to drop $(objtool_deps) entirely.
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
>
> Makefile | 3 ++-
> scripts/Makefile.build | 26 +++++++++-----------------
> scripts/link-vmlinux.sh | 3 ++-
> 3 files changed, 13 insertions(+), 19 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 829bd339ffdc..3ef3685b7e4a 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1858,7 +1858,8 @@ descend: $(build-dirs)
> $(build-dirs): prepare
> $(Q)$(MAKE) $(build)=$@ \
> single-build=$(if $(filter-out $@/, $(filter $@/%, $(KBUILD_SINGLE_TARGETS))),1) \
> - need-builtin=1 need-modorder=1
> + need-builtin=1 need-modorder=1 \
> + $(if $(CONFIG_STACK_VALIDATION),objtool-md5sum=$(firstword $(shell md5sum tools/objtool/objtool)))
>
> clean-dirs := $(addprefix _clean_, $(clean-dirs))
> PHONY += $(clean-dirs) clean
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 3efc984d4c69..8aa6eaa4bf21 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -155,7 +155,7 @@ $(obj)/%.ll: $(src)/%.c FORCE
> # (See cmd_cc_o_c + relevant part of rule_cc_o_c)
>
> quiet_cmd_cc_o_c = CC $(quiet_modtag) $@
> - cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
> + cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $< $(cmd_objtool)
>
> ifdef CONFIG_MODVERSIONS
> # When module versioning is enabled the following steps are executed:
> @@ -226,26 +226,21 @@ endif # CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
> ifdef CONFIG_STACK_VALIDATION
> ifndef CONFIG_LTO_CLANG
>
> -__objtool_obj := $(objtree)/tools/objtool/objtool
> +objtool := $(objtree)/tools/objtool/objtool
>
> # '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
> +#
> +# Record the md5sum of the objtool executable so any change in it results in
> +# rebuilding objects.
> cmd_objtool = $(if $(patsubst y%,, \
> $(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
> - $(__objtool_obj) $(objtool_args) $@)
> -objtool_obj = $(if $(patsubst y%,, \
> - $(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
> - $(__objtool_obj))
> + ; : $(objtool-md5sum) ; $(objtool) $(objtool_args) $@)
>
> endif # CONFIG_LTO_CLANG
> endif # CONFIG_STACK_VALIDATION
>
> -# Rebuild all objects when objtool changes, or is enabled/disabled.
> -objtool_dep = $(objtool_obj) \
> - $(wildcard include/config/ORC_UNWINDER \
> - include/config/STACK_VALIDATION)
> -
> ifdef CONFIG_TRIM_UNUSED_KSYMS
> cmd_gen_ksymdeps = \
> $(CONFIG_SHELL) $(srctree)/scripts/gen_ksymdeps.sh $@ >> $(dot-target).cmd
> @@ -259,7 +254,6 @@ define rule_cc_o_c
> $(call cmd,gen_ksymdeps)
> $(call cmd,checksrc)
> $(call cmd,checkdoc)
> - $(call cmd,objtool)
> $(call cmd,modversions_c)
> $(call cmd,record_mcount)
> endef
> @@ -267,13 +261,11 @@ endef
> define rule_as_o_S
> $(call cmd_and_fixdep,as_o_S)
> $(call cmd,gen_ksymdeps)
> - $(call cmd,objtool)
> $(call cmd,modversions_S)
> endef
>
> # Built-in and composite module parts
> -.SECONDEXPANSION:
> -$(obj)/%.o: $(src)/%.c $(recordmcount_source) $$(objtool_dep) FORCE
> +$(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
> $(call if_changed_rule,cc_o_c)
> $(call cmd,force_checksrc)
>
> @@ -356,7 +348,7 @@ $(obj)/%.s: $(src)/%.S FORCE
> $(call if_changed_dep,cpp_s_S)
>
> quiet_cmd_as_o_S = AS $(quiet_modtag) $@
> - cmd_as_o_S = $(CC) $(a_flags) -c -o $@ $<
> + cmd_as_o_S = $(CC) $(a_flags) -c -o $@ $< $(cmd_objtool)
>
> ifdef CONFIG_ASM_MODVERSIONS
>
> @@ -375,7 +367,7 @@ cmd_modversions_S = \
> fi
> endif
>
> -$(obj)/%.o: $(src)/%.S $$(objtool_dep) FORCE
> +$(obj)/%.o: $(src)/%.S FORCE
> $(call if_changed_rule,as_o_S)
>
> targets += $(filter-out $(subdir-builtin), $(real-obj-y))
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index d74cee5c4326..58b3a94c934b 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -335,7 +335,8 @@ else
> fi;
>
> # final build of init/
> -${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init need-builtin=1
> +${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init need-builtin=1 \
> + ${CONFIG_STACK_VALIDATION:+objtool-md5sum=$(md5sum tools/objtool/objtool | cut -d ' ' -f1)}
>
> #link vmlinux.o
> modpost_link vmlinux.o
> --
> 2.30.2
>

--
Best Regards
Masahiro Yamada