How can I make a target “private” in GNU make for internal use only? OR: how to best enforce target-specific variable-values?

Question

I have some ancillary targets in a makefile that I want to restrict for internal or \"private\" use (only) inside the makefile. That is, I want to be able to specify these targ

Answer 1

One solution to the problem is to migrate the CPPFLAGS to the pattern rules (e.g., bin_debug/%.o: CPPFLAGS...) instead of the regular rule (debug: CPPFLAGS...), final result:

bin_debug/%.o   : CPPFLAGS += -DDEBUG
bin_debug/%.o   : %.c
    $(CC) $(CFLAGS) $(CPPFLAGS) -c -o $@ $<
bin_release/%.o : CPPFLAGS += -DRELEASE
bin_release/%.o : %.c
    $(CC) $(CFLAGS) $(CPPFLAGS) -c -o $@ $<
OBJS = foo.o bar.o main.o # or $(SRCS:.o=.c)
DEBUG_OBJS   = $(addprefix bin_debug/,$OBJS)
RELEASE_OBJS = $(addprefix bin_release/,$OBJS)
debug   : $(DEBUG_OBJS)
release : $(RELEASE_OBJS)
debug release :
    $(CC) -o $@ $^ $(LDFLAGS) $(LDLIBS)

so make bin_debug/foo.o will get CPPFLAGS including -DDEBUG.

Now, lets say you have >>2 rules: debug, release, config01, config02, config03, ... each with their own CPPFLAGS.

One way might be to continue reduplicating all of the pattern rules, but that gets annoying if anything has to change. Furthermore it's not really possible to use in a foreach. This seems handy:

debug    : CPPFLAGS+=-DDEBUG
release  : CPPFLAGS+=-DRELEASE
config01 : CPPFLAGS+=-DSOMETHING
config02 : CPPFLAGS+=-DSOMETHINGELSE
TARGETS = debug release config01 config02
OBJS = foo.o bar.o main.o # or $(SRCS:.o=.c)
define TARGET_template
 bin_$(1)/%.o : %.c
    $$(CC) $$(CFLAGS) $$(CPPFLAGS) -c -o $@ $<
 $(1): $(addprefix bin_$(1)/,$(OBJS))
 # other TARGET-specific stuff here
endef
$(foreach tgt,$(TARGETS),$(eval $(call TARGET_template,$(tgt))))

But still doesn't fix the situation of make bin_debug/foo.o -- still doesn't get CPPFLAGS.

So, instead of making target-specific variable-value like debug: CPPFLAGS+=... you could have a variable that is specific to the target, like CPPFLAGS_debug, then add to each rule:

CPPFLAGS_debug    = -DDEBUG
CPPFLAGS_release  = -DRELEASE
CPPFLAGS_config01 = -DSOMETHING
CPPFLAGS_config02 = -DSOMETHINGELSE
TARGETS = debug release config01 config02
OBJS = foo.o bar.o main.o # or $(SRCS:.o=.c)
define TARGET_template
 bin_$(1)/%.o : CPPFLAGS+=$$(CPPFLAGS_$(1))
 bin_$(1)/%.o : %.c
    $$(CC) $$(CFLAGS) $$(CPPFLAGS) -c -o $$@ $$<
 $(1): $(addprefix bin_$(1)/,$(OBJS))
 # other TARGET-specific stuff here
endef
$(foreach tgt,$(TARGETS),$(eval $(call TARGET_template,$(tgt))))

Beware; above may need more $$(...)s, untested.

Problems? Better way?