Makefiles

It is often useful to be able to build a project for the native desktop machine and also cross compile it for running on an embedded ARM device. For our internal Bluewater Systems projects we use a Makefile setup similar to the following:

ifeq "$(ARCH)" "arm"
    CROSS=arm-none-linux-gnueabi-
else
    ARCH=i686
    CROSS=
endif

CC=$(CROSS)gcc
LD=$(CROSS)ld

ODIR = obj/$(ARCH)
ODIRDEP = $(ODIR)/.dir

PROG=hello_world
HEADERS=hello_world.h
SOURCES=hello_world.c

OBJECTS=$(patsubst %.c, $(ODIR)/%.o, $(SOURCES))

default: $(ODIR)/$(PROG)

$(ODIRDEP):
    @echo "  MKDIR $(ODIR)"
    @[ -d $(ODIR) ] || mkdir -p $(ODIR)
    @[ -f $(ODIRDEP) ] || touch $(ODIRDEP)

$(ODIR)/$(PROG): $(OBJECTS)
    @echo "  LD $@"
    @$(CC) -o $@ $^ $(LFLAGS)

$(ODIR)/%.o: %.c $(ODIRDEP) $(HEADERS)
    @[ -d $(ODIR) ] || mkdir -p $(ODIR)
    @echo "  CC $<"
    @$(CC) -c -o $@ $< $(CFLAGS)

clean:
    rm -Rf $(ODIR)

The important variables are:

• PROG: Name of the executable to build
• SOURCES: List of C source files
• HEADERS: List of header files

Running "make" with no arguments will build a native (i686) version of the application. The object files and the binary executable will be generated in the obj/i686/ directory under your projects working directory.

To build the ARM version of the binary, type:

make ARCH=arm

This will generate the ARM version of the object files and binary in the directory obj/arm/ under the project working directory.