make: Nothing to be done for `all’. when i tried to compile

this is the code of my make file

obj-m +=hello-1.o
all:
<tab>make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
<tab>make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

AND I HAVE FEW QUESTIONS

1. we save C language file with extension *.c so for Makefile which extension should we use?
2. When i throw command in terminal “make” it gives me error that make: Nothing to be done for `all’.

Answer

Probably the file all already exists. As it doesn’t depend on anything, and isn’t a dependency of .PHONY, its existence is sufficient to consider it made.

I would suggest adding

.PHONY: all clean

to the end of Makefile.

You are allowed to call the file anything you like, as long as that is Makefile 😉 Actually, there’s a couple of non-standard names that may be used as fallbacks, or you can provide a name with the -f flag to make, but I wouldn’t recommend either of those if you’re in a position to avoid them.

Other comments (for which you didn’t ask, but you’re getting anyway):

1. Avoid invoking make literally in a command; always use $(MAKE). This helps when you use -n, for instance.
2. Don’t prevent your makefile’s users from building for a kernel other than that which is running now. Create a variable for it (e.g. KVER := $(shell uname -r) or KSRC := /lib/modules/$(shell uname -r)/build so it can be overridden on the command line.