optimization and debugging options in Makefile

**lehe** · 08-27-2009

Hi,
I wonder where to put the optimization and debugging options in Makefile: linking stage or compiling stage? I am reading a Makefile:

Code:

ifeq ($(STATIC),yes)
  LDFLAGS=-static -lm -ljpeg -lpng -lz
else
  LDFLAGS=-lm -ljpeg -lpng
endif

ifeq ($(DEBUG),yes)
  OPTIMIZE_FLAG = -ggdb3 -DDEBUG
else
  OPTIMIZE_FLAG = -ggdb3 -O3
endif

ifeq ($(PROFILE),yes)
  PROFILE_FLAG = -pg
endif

CXXFLAGS = -Wall $(OPTIMIZE_FLAG) $(PROFILE_FLAG) $(CXXGLPK)

test: test.o rgb_image.o 
	$(CXX) $(CXXFLAGS) -o $@ $^ $(LDFLAGS)

Makefile.depend: *.h *.cc Makefile
	$(CC) -M *.cc > Makefile.depend

clean:
	\rm -f absurdity *.o Makefile.depend TAGS

-include Makefile.depend

What surprises me is CXXFLAGS is used in linking. I know it is also used in the implicit rule for compiling to generate .o files but is it necessary to use it again for linking? Specifically, where should I put optimization and debugging: linking stage or compiling stage?

Thanks and regards!

**tabstop** · 08-27-2009

Given that optimization happens only at compilation and not at linking, and that debugging information happens only at compilation and not at linking, I'm not sure why you're even asking the question.

**lehe** · 08-27-2009

Thanks! I am learning to use someone's Makefile
So it is not use to include CXXFLAG in linking as in his Makefile

Code:

test: test.o rgb_image.o 
	$(CXX) $(CXXFLAGS) -o $@ $^ $(LDFLAGS)

?

**brewbuck** · 08-27-2009

Originally Posted by lehe

Thanks! I am learning to use someone's Makefile
So it is not use to include CXXFLAG in linking as in his Makefile

Code:

test: test.o rgb_image.o 
	$(CXX) $(CXXFLAGS) -o $@ $^ $(LDFLAGS)

?

The $(CXXFLAGS) are almost redundant here. However, the linker does need access to $(PROFILE_FLAG) and so that should be added to the $(LDFLAGS).

Code:

ifeq ($(STATIC),yes)
  LDFLAGS=-static -lm -ljpeg -lpng -lz $(PROFILE_FLAG)
else
  LDFLAGS=-lm -ljpeg -lpng $(PROFILE_FLAG)
endif

Then you should be able to remove $(CXXFLAGS) from the link line.

**lehe** · 08-27-2009

Thank you!
Is it possible to point me to some references of which option is done in which stage?
Thanks!

**dwks** · 08-27-2009

Well, you could try the manual. It has some categories of options, but it's pretty detailed. I guess the best way to understand it is to know what debugging information is. Debugging information is just extra information that the compiler adds to the program so that you can tell which line of C code an assembly instruction corresponded to, for example.

The linker doesn't care about debugging information; all it does is take the already-existing object files and link them together. Its primary job is to figure out what external symbols refer to; it has to resolve all references in one object file to somewhere else, so that a coherent executable is formed in the end.

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