How to cross compile for ARM on Ubuntu conditionally?

I have written the following make file

all: writer.o

writer.o:
    gcc -Wall writer.c -o writer

clean:
    rm *.o

How do I add a functionality to this make file such that I am able to generate an application for the native build platform when GNU make variable CROSS_COMPILE is not specified on the make command line.However, when CROSS_COMPILe is set, I should generate a cross compiled output file using the compiler, aarch64-none-linux-gnu-gcc.

>Solution :

Set the CROSS_COMPILE variable itself to the compiler prefix. So for native builds:

CROSS_COMPILE = 

(i.e. there’s nothing, the variable is "empty").

And for cross-compilation:

CROSS_COMPILE = aarch64-none-linux-gnu-

Then set:

CC = $(CROSS_COMPILE)gcc

To complement the above, use implicit rules to build the program:

all: writer

writer: writer.o

That’s all that you need.