Question

in kernel Makefile

# Modules                                                                                                                                                                               
/ %/: prepare scripts FORCE
    $(cmd_crmodverdir)
    $(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1) \
    $(build)=$(build-dir)
%.ko: prepare scripts FORCE
    $(cmd_crmodverdir)
    $(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1)   \
    $(build)=$(build-dir) $(@:.ko=.o)
    $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost

causing error Makefile mixed implicit and normal rules. (to first string on provided code)

I think something wrong with / %/ syntax, how can I repair it?

so far I’m thinking about separating rules this way:

# Modules                                                                                                                                                                               
/: prepare scripts FORCE
    $(cmd_crmodverdir)
    $(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1) \
    $(build)=$(build-dir)
%/: prepare scripts FORCE
    $(cmd_crmodverdir)
    $(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1) \
    $(build)=$(build-dir)
%.ko: prepare scripts FORCE
    $(cmd_crmodverdir)
    $(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1)   \
    $(build)=$(build-dir) $(@:.ko=.o)
    $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost

But it’s confusing for me.

Answer 1

What do you think the / %/ rule is doing (apart from confuse you and make — and me)? What are you trying to achieve with the %/ bit?

You can have two (or more) targets on the left of the colon, but they both need to be percent-less.

prog1 prog2: something
    $(CC) -o $@ $@.o ${LIBRARIES}

The % metacharacter cannot be used with a rule without any % in it, but make is interpreting:

/ %/:

as similar to the prog1 prog2 example, but one of the targets has a % and the other does not, and you’re not allowed to mix these up. The / rule is the explicit rule; it appears to be instructions on how to update the root directory of your system. The %/ is the implicit rule; it might be doing something related to making directories up to date.

---

Copying some material up from the comments:

DIRECTORY_BUILD_RULES = \
    $(cmd_crmodverdir); \
    $(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1) $(build)=$(build-dir)

/:  prepare scripts FORCE; $(DIRECTORY_BUILD_RULES)

%/: prepare scripts FORCE; $(DIRECTORY_BUILD_RULES)

This notation should work (which is why I used it in the comment), but what I’d write in a makefile is:

DIRECTORY_DEPENDENCIES = prepare scripts FORCE
DIRECTORY_BUILD_RULES = \
    $(cmd_crmodverdir); \
    $(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1) $(build)=$(build-dir)

/:  $(DIRECTORY_DEPENDENCIES)
    $(DIRECTORY_BUILD_RULES)

%/: $(DIRECTORY_DEPENDENCIES)
    $(DIRECTORY_BUILD_RULES)

If this still causes trouble, review what the first (the /:) rule does. Are you sure it is needed?