Re: [PATCH 03/13] kbuild: detect objtool changes correctly and remove .SECONDEXPANSION

Kees Cook
2021-08-19T02:55:41Z

On Thu, Aug 19, 2021 at 09:57:34AM +0900, Masahiro Yamada wrote:
> This reverts commit 8852c5524029 ("kbuild: Fix objtool dependency for
> 'OBJECT_FILES_NON_STANDARD_<obj> := n'"), and fix the dependency in a
> cleaner 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.
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
>
> scripts/Makefile.build | 28 ++++++++++------------------
> 1 file changed, 10 insertions(+), 18 deletions(-)
>
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 31154e44c251..3e4cd1439cd4 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:
> @@ -223,6 +223,8 @@ endif # CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
>
> ifdef CONFIG_STACK_VALIDATION
>
> +objtool := $(objtree)/tools/objtool/objtool
> +
> # Objtool arguments are also needed for modfinal with LTO, so we define
> # then here to avoid duplication.
> objtool_args = \
> @@ -237,26 +239,19 @@ objtool_args = \
>
> ifndef CONFIG_LTO_CLANG
>
> -__objtool_obj := $(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
> 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) $(objtool_args) $@)

This is extremely clever -- pasting commands together. :)

Does this correctly propagate failures in the first half of the command?

For example, now we'd have:
gcc flags..... -c -o out in ; objtool...

But I think objtool will run even on gcc failure, and "make" won't see
the failure from gcc? I need to go test this.

-Kees

> +
> +# Rebuild all objects when objtool is updated
> +objtool_dep = $(objtool)
>
> 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
> @@ -270,7 +265,6 @@ 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
> @@ -278,13 +272,11 @@ 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) $$(objtool_dep) FORCE
> +$(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_dep) FORCE
> $(call if_changed_rule,cc_o_c)
> $(call cmd,force_checksrc)
>
> @@ -367,7 +359,7 @@ $(obj)/%.s: $(src)/%.S FORCE
> $(call if_changed_dep,cpp_s_S)
>
> quiet_cmd_as_o_S = AS $(quiet_modtag) $@
> - cmd_as_o_S = $(CC) $(a_flags) -c -o $@ $<
> + cmd_as_o_S = $(CC) $(a_flags) -c -o $@ $< $(cmd_objtool)
>
> ifdef CONFIG_ASM_MODVERSIONS
>
> @@ -386,7 +378,7 @@ cmd_modversions_S = \
> fi
> endif
>
> -$(obj)/%.o: $(src)/%.S $$(objtool_dep) FORCE
> +$(obj)/%.o: $(src)/%.S $(objtool_dep) FORCE
> $(call if_changed_rule,as_o_S)
>
> targets += $(filter-out $(subdir-builtin), $(real-obj-y))
> --
> 2.30.2
>

--
Kees Cook