+disp_ln = $($(DISP)_disp_ln)
+disp_mkdir = $($(DISP)_disp_mkdir)
+disp_gen = $($(DISP)_disp_gen)
+disp_unifdef = $($(DISP)_disp_unifdef)
+
+any-prereq = $(filter-out $(PHONY),$?) $(filter-out $(PHONY) $(wildcard $^),$^)
+
+# ../foo/bar/baz.ext -> foo_bar_baz.ext
+variablify = $(subst /,_,$(subst $(top_builddir),,$(1)))
+# strip the top_builddir off everything to make the *string* idempotent for -C
+dirify = $(subst $(top_builddir),,$(patsubst -L$(top_builddir)%,-L%,$(patsubst -I$(top_builddir)%,-I%,$(1))))
+
+# True if not identical. Neither order nor whitespace nor identical flags
+# matter.
+compare_flags = \
+ $(strip $(filter-out $(call dirify,$(cmd_$(call variablify,$(1)))), \
+ $(call dirify,$(cmd_$(call variablify,$(@))))) \
+ $(filter-out $(call dirify,$(cmd_$(call variablify,$(@)))), \
+ $(call dirify,$(cmd_$(call variablify,$(1))))))
+
+# Rebuild if any prerequisite, the used CC or flags changed.
+# Previously used flags are stored in the corresponding .%.dep files
+maybe_exec = \
+ $(if $(strip $(compare_flags) $(any-prereq)), \
+ @set -e; \
+ $(disp_$(1)); \
+ $(cmd_$(1)); \
+ echo 'cmd_$(call variablify,$@) := $(call dirify,$(cmd_$(call variablify,$1)))' >> $(dir $@).$(notdir $@).dep)
+
+
+CFLAGS_gen.dep = -MT $@ -MD -MP -MF $(dir $@).$(notdir $@).dep
+
+cmd_compile.c = $(CC) -c $< -o $@ $(CFLAGS) $(ARCH_CFLAGS) \
+ $(CFLAGS-$(suffix $@)) \
+ $(filter-out $(CFLAGS-OMIT-$(notdir $<)),$(CFLAGS-$(notdir $(<D)))) \
+ $(CFLAGS-$(subst $(top_srcdir),,$(dir $<))) \
+ $(CFLAGS-$(notdir $<)) \
+ $(CFLAGS-$(notdir $@)) \
+ $(CFLAGS_gen.dep)
+cmd_compile.i = $(cmd_compile.c:-c=-E -dD $(EXTRA_CPPFLAGS))
+cmd_compile.s = $(cmd_compile.c:-c=-S)
+cmd_compile.u = $(CC) $^ $(DEPS-$(notdir $@)) -o $@ $(CFLAGS) $(CFLAGS-$(notdir $(^D))) $(CFLAGS-$(notdir $@)) $(CFLAGS_gen.dep)
+cmd_compile.S = $(filter-out -std=gnu99, $(cmd_compile.c)) -D__ASSEMBLER__ $(ASFLAGS) $(ARCH_ASFLAGS) $(ASFLAGS-$(suffix $@)) $(ASFLAGS-$(notdir $<)) $(ASFLAGS-$(notdir $@))