linux-kernel - Re: [PATCH v2 05/13] kbuild: detect objtool update without using .SECONDEXPANSION

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Date:   Tue, 31 Aug 2021 10:33:14 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kernel@...r.kernel.org, Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v2 05/13] kbuild: detect objtool update without using .SECONDEXPANSION

On Tue, Aug 31, 2021 at 12:40 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> Redo commit 8852c5524029 ("kbuild: Fix objtool dependency for
> 'OBJECT_FILES_NON_STANDARD_<obj> := n'") to add the objtool
> dependency in a cleaner way.
>
> Using .SECONDEXPANSION ends up with unreadable code due to escaped
> dollars. Also, it is not efficient because the second half of
> Makefile.build is parsed twice every time.
>
> Append the objtool dependency to the *.cmd files at the build time.
>
> This is what fixdep and gen_ksymdeps.sh already do. So, following the
> same pattern seems a natural solution.
>
> This allows us to drop $$(objtool_deps) entirely.

s/objtool_deps/objtool_dep/

>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

You and Josh should be cc'ing each other explicitly on these kind of changes.

> ---
>
>  scripts/Makefile.build | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 720a86642f48..21b55f37a23f 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -246,14 +246,11 @@ objtool-enabled = $(if $(filter-out y%, \
>         $(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n),y)
>
>  cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool_args) $@)
> -objtool_obj = $(if $(objtool-enabled), $(objtool))
> +cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)
>
>  endif # CONFIG_LTO_CLANG
>  endif # CONFIG_STACK_VALIDATION
>
> -# Rebuild all objects when objtool changes
> -objtool_dep = $(objtool_obj)
> -
>  ifdef CONFIG_TRIM_UNUSED_KSYMS
>  cmd_gen_ksymdeps = \
>         $(CONFIG_SHELL) $(srctree)/scripts/gen_ksymdeps.sh $@ >> $(dot-target).cmd
> @@ -267,6 +264,7 @@ define rule_cc_o_c
>         $(call cmd,gen_ksymdeps)
>         $(call cmd,checksrc)
>         $(call cmd,checkdoc)
> +       $(call cmd,gen_objtooldep)
>         $(call cmd,modversions_c)
>         $(call cmd,record_mcount)
>  endef
> @@ -274,12 +272,12 @@ endef
>  define rule_as_o_S
>         $(call cmd_and_fixdep,as_o_S)
>         $(call cmd,gen_ksymdeps)
> +       $(call cmd,gen_objtooldep)
>         $(call cmd,modversions_S)
>  endef
>
>  # Built-in and composite module parts
> -.SECONDEXPANSION:
> -$(obj)/%.o: $(src)/%.c $(recordmcount_source) $$(objtool_dep) FORCE
> +$(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
>         $(call if_changed_rule,cc_o_c)
>         $(call cmd,force_checksrc)
>
> @@ -380,7 +378,7 @@ cmd_modversions_S =                                                         \
>         fi
>  endif
>
> -$(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))
> --
> 2.30.2
>


-- 
Thanks,
~Nick Desaulniers