Make won't accept appended CFLAGS value - makefile

Question

I've searched around for this issue, but nobody but me seems to have it, which is why I'll now ask.
If have this basic makefile:
CCPP = arm-none-linux-gnueabi-g++
CFLAGS = "-WALL -DPLATFORM_TARGET -DPRINT_MESSAGE"
LIB = lib/libarm.a
LDFLAGS = -lpthread
OBJECTS = $(wildcard ./*/*.o)
PROG = /exports/appl
MODULES = lib src
all: $(PROG)
$(CCPP) $(LDFLAGS) $(OBJECTS) $(LIB) -o $(PROG)
$(PROG): $(MODULES)
#for i in $(MODULES); do (cd $$i && $(MAKE) \
CCPP=$(CCPP) LDPP=$(CCPP) CFLAGS=$(CFLAGS) LDFLAGS=$(LDFLAGS)) || exit 1 ;\
done
clean:
#for i in $(MODULES); do (cd $$i && $(MAKE) clean) || exit 1 ; done
rm $(PROG)
lib:
ar cr ../lib/$(LIB) $(OBJECTS)
This works. It takes whatever source file is within lib and src and compiles and links it nicely together. (By using local makefiles found in these folders which I can post too if need be)
Anyway, what I WANT now, is add more -D directives conditionally.
I've tried:
ifdef ALLOW_BACKTRACE
CFLAGS += -DALLOW_BACKTRACE
LDFLAGS += -rdynamic
endif
and also:
ifdef ALLOW_BACKTRACE
CFLAGS := $(CFLAGS) -DALLOW_BACKTRACE
#endif
or by putting the whole thing in quotes etc...but each time I try, it brings up the help page of make, telling me that it can't 'recognize' the new define.
Any idea what I'm doing wrong?
Any help is much appreciated.

Answer 1

Okay, this should be a more correct version of your makefile, I can not test it though because I don't have your sources:
export CCPP := arm-none-linux-gnueabi-g++
# Note that -pthread is required for both compiling and linking.
export CFLAGS := -pthread -WALL -DPLATFORM_TARGET -DPRINT_MESSAGE
export LDFLAGS := -pthread
LIB := lib/libarm.a
PROG := /exports/appl
MODULES := lib src
all: $(PROG)
$(PROG): $(MODULES)
$(CCPP) -o $# $(LDFLAGS) ./*/*.o $(LIB)
$(MODULES) : % :
$(MAKE) -C $#
touch $#
clean-module.%:
$(MAKE) -C $* clean
clean : $(MODULE:%=clean-module.%)
rm -f $(PROG)
.PHONY: all clean clean-module.%
What I changed:
LDFLAGS = -lpthread: when building multi-threaded applications you need both an extra compiler and linker flag, which is what -pthread/-pthreads gcc options is.
Contents of OBJECTS = $(wildcard ./*/*.o) are only correct when $(MODULES) built correctly. Removed it.
$(PROG) commands actually build $(PROG) target as it should.
$(MODULES) commands build the modules by invoking make in the corresponding directory. And then they update the timestamp of the directory to force rebuild of $(PROG). Since it is a recursive make it can't know whether anything have actually been updated in the module, hence it need to trigger the rebuild of anything that depends on the modules.
I still have a feeling that this won't work for you because your original makefile is missing dependencies.

Answer 2

Try doing this -->
ifeq ($(ALLOW_BACKTRACE),1)
CFLAGS += -DALLOW_BACKTRACE
endif

Answer 3

You've got to be KIDDING me!
Ahem. I seem to have found the solution to my own problem. I don't quite get it, but whatever works, right?
Anyway, here's what I did:
CFLAGS += -Wall -DPLATFORM_TARGET -DPRINT_MESSAGE
ifdef ALLOW_BACKTRACE
CFLAGS += -DALLOW_BACKTRACE
LDFLAGS += -rdynamic
endif
LDFLAGS += -lpthread
$(PROG): $(MODULES)
#for i in $(MODULES); do (cd $$i && $(MAKE) \
CCPP=$(CCPP) LDPP=$(CCPP) CFLAGS="$(CFLAGS)" LDFLAGS=$(LDFLAGS)) || exit 1 ;\
done
First thing: -rdynamic needs to be the first flag in the linker, otherwise it refuses to work. (Don't ask me why, if anyone could enlighten me, be my guest.
Second: I had to put quotes around the expanded $(CFLAGS) in my actual build step. As soon as I did that, it worked like a charm...probably because it had a problem with the spaces.
Thanks to everyone, who went to the trouble of trying to help me.