[PATCH 1/2] kbuild: macrofy the condition of if_changed and friends

[PATCH 1/2] kbuild: macrofy the condition of if_changed and friends

[Masahiro Yamada]

Add a new macro that expands into $(newer-prereqs)$(cmd-check).

It makes it easier to add common code for if_changed, if_changed_dep,
and if_changed_rule.

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

 scripts/Kbuild.include | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index f247e691562d..c3c975a92318 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -130,13 +130,15 @@ make-cmd = $(call escsq,$(subst $(pound),$$(pound),$(subst $$,$$$$,$(cmd_$(1))))
 # PHONY targets skipped in both cases.
 newer-prereqs = $(filter-out $(PHONY),$?)
 
+if-changed-cond = $(newer-prereqs)$(cmd-check)
+
 # Execute command if command has changed or prerequisite(s) are updated.
-if_changed = $(if $(newer-prereqs)$(cmd-check),                              \
+if_changed = $(if $(if-changed-cond),                                        \
 	$(cmd);                                                              \
 	printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
 
 # Execute the command and also postprocess generated .d dependencies file.
-if_changed_dep = $(if $(newer-prereqs)$(cmd-check),$(cmd_and_fixdep),@:)
+if_changed_dep = $(if $(if-changed-cond),$(cmd_and_fixdep),@:)
 
 cmd_and_fixdep =                                                             \
 	$(cmd);                                                              \
@@ -146,7 +148,7 @@ cmd_and_fixdep =                                                             \
 # Usage: $(call if_changed_rule,foo)
 # Will check if $(cmd_foo) or any of the prerequisites changed,
 # and if so will execute $(rule_foo).
-if_changed_rule = $(if $(newer-prereqs)$(cmd-check),$(rule_$(1)),@:)
+if_changed_rule = $(if $(if-changed-cond),$(rule_$(1)),@:)
 
 ###
 # why - tell why a target got built
-- 
2.30.2

[PATCH 2/2] kbuild: warn if FORCE is missing for if_changed(_dep,_rule) and filechk

[Masahiro Yamada]

if_changed, if_changed_dep, and if_changed_rule must have FORCE as a
prerequisite so the command line change is detected.

Documentation/kbuild/makefiles.rst clearly explains it:

  Note: It is a typical mistake to forget the FORCE prerequisite.

However, not all people read the document, or understand what is written
in it.

People repeated this mistake over again, and I determined a compelling
force is needed.

Show a warning if FORCE is missing in the prerequisite of if_changed
and friends. Same for filechk.

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

 scripts/Kbuild.include | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index c3c975a92318..dd48e68965f8 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -57,6 +57,7 @@ kecho := $($(quiet)kecho)
 # - If the content differ the new file is used
 # - If they are equal no change, and no timestamp update
 define filechk
+	$(check-FORCE)
 	$(Q)set -e;						\
 	mkdir -p $(dir $@);					\
 	trap "rm -f $(dot-target).tmp" EXIT;			\
@@ -130,7 +131,11 @@ make-cmd = $(call escsq,$(subst $(pound),$$(pound),$(subst $$,$$$$,$(cmd_$(1))))
 # PHONY targets skipped in both cases.
 newer-prereqs = $(filter-out $(PHONY),$?)
 
-if-changed-cond = $(newer-prereqs)$(cmd-check)
+# It is a typical mistake to forget the FORCE prerequisite. Check it here so
+# no more breakage will slip in.
+check-FORCE = $(if $(filter FORCE, $^),,$(warning FORCE prerequsite is missing))
+
+if-changed-cond = $(newer-prereqs)$(cmd-check)$(check-FORCE)
 
 # Execute command if command has changed or prerequisite(s) are updated.
 if_changed = $(if $(if-changed-cond),                                        \
-- 
2.30.2

Re: [PATCH 2/2] kbuild: warn if FORCE is missing for if_changed(_dep,_rule) and filechk

[Nicolas Schier]

On Friday, 2021-08-13 Masahiro Yamada wrote:
> if_changed, if_changed_dep, and if_changed_rule must have FORCE as a
> prerequisite so the command line change is detected.
> 
> Documentation/kbuild/makefiles.rst clearly explains it:
> 
>   Note: It is a typical mistake to forget the FORCE prerequisite.
> 
> However, not all people read the document, or understand what is written
> in it.
> 
> People repeated this mistake over again, and I determined a compelling
> force is needed.
> 
> Show a warning if FORCE is missing in the prerequisite of if_changed
> and friends. Same for filechk.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
> 
>  scripts/Kbuild.include | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index c3c975a92318..dd48e68965f8 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -57,6 +57,7 @@ kecho := $($(quiet)kecho)
>  # - If the content differ the new file is used
>  # - If they are equal no change, and no timestamp update
>  define filechk
> +	$(check-FORCE)
>  	$(Q)set -e;						\
>  	mkdir -p $(dir $@);					\
>  	trap "rm -f $(dot-target).tmp" EXIT;			\
> @@ -130,7 +131,11 @@ make-cmd = $(call escsq,$(subst $(pound),$$(pound),$(subst $$,$$$$,$(cmd_$(1))))
>  # PHONY targets skipped in both cases.
>  newer-prereqs = $(filter-out $(PHONY),$?)
>  
> -if-changed-cond = $(newer-prereqs)$(cmd-check)
> +# It is a typical mistake to forget the FORCE prerequisite. Check it here so

prerequsite -> prerequisite?

Successfully found the missing FORCE in arch/x86/entry/vdso/Makefile:135.

Tested-by: Nicolas Schier <n.schier@avm.de>

> +# no more breakage will slip in.
> +check-FORCE = $(if $(filter FORCE, $^),,$(warning FORCE prerequsite is missing))
> +
> +if-changed-cond = $(newer-prereqs)$(cmd-check)$(check-FORCE)
>  
>  # Execute command if command has changed or prerequisite(s) are updated.
>  if_changed = $(if $(if-changed-cond),                                        \
> -- 
> 2.30.2
> 

Re: [PATCH 2/2] kbuild: warn if FORCE is missing for if_changed(_dep,_rule) and filechk

[Masahiro Yamada]

On Tue, Aug 17, 2021 at 5:25 PM Nicolas Schier <n.schier@avm.de> wrote:
>
> On Friday, 2021-08-13 Masahiro Yamada wrote:
> > if_changed, if_changed_dep, and if_changed_rule must have FORCE as a
> > prerequisite so the command line change is detected.
> >
> > Documentation/kbuild/makefiles.rst clearly explains it:
> >
> >   Note: It is a typical mistake to forget the FORCE prerequisite.
> >
> > However, not all people read the document, or understand what is written
> > in it.
> >
> > People repeated this mistake over again, and I determined a compelling
> > force is needed.
> >
> > Show a warning if FORCE is missing in the prerequisite of if_changed
> > and friends. Same for filechk.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> > ---
> >
> >  scripts/Kbuild.include | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> > index c3c975a92318..dd48e68965f8 100644
> > --- a/scripts/Kbuild.include
> > +++ b/scripts/Kbuild.include
> > @@ -57,6 +57,7 @@ kecho := $($(quiet)kecho)
> >  # - If the content differ the new file is used
> >  # - If they are equal no change, and no timestamp update
> >  define filechk
> > +     $(check-FORCE)
> >       $(Q)set -e;                                             \
> >       mkdir -p $(dir $@);                                     \
> >       trap "rm -f $(dot-target).tmp" EXIT;                    \
> > @@ -130,7 +131,11 @@ make-cmd = $(call escsq,$(subst $(pound),$$(pound),$(subst $$,$$$$,$(cmd_$(1))))
> >  # PHONY targets skipped in both cases.
> >  newer-prereqs = $(filter-out $(PHONY),$?)
> >
> > -if-changed-cond = $(newer-prereqs)$(cmd-check)
> > +# It is a typical mistake to forget the FORCE prerequisite. Check it here so
>
> prerequsite -> prerequisite?

Thanks for catching it.

Applied with the typo fixed.



> Successfully found the missing FORCE in arch/x86/entry/vdso/Makefile:135.
>
> Tested-by: Nicolas Schier <n.schier@avm.de>
>
> > +# no more breakage will slip in.
> > +check-FORCE = $(if $(filter FORCE, $^),,$(warning FORCE prerequsite is missing))
> > +
> > +if-changed-cond = $(newer-prereqs)$(cmd-check)$(check-FORCE)
> >
> >  # Execute command if command has changed or prerequisite(s) are updated.
> >  if_changed = $(if $(if-changed-cond),                                        \
> > --
> > 2.30.2
> >
>


-- 
Best Regards
Masahiro Yamada