Is it possible to set CFLAGS to a linux kernel module Makefile?

问题

Eg: a common device module's Makefile

obj-m:=jc.o

default:
    $(MAKE) -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) modules
clean:
    $(MAKE) -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) modules clean

I consider if I can set CFLAGS to the file. When I change default section to

$(MAKE) -O2 -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) modules

But it didn't work.

Any help? Thanks a lot.

回答1:

-O2 would be an option to make (or $(MAKE), as you're using it) in what you tried. Obviously, the compiler (probably gcc) needs this flag, not make.

Kbuild understands a make variable named CFLAGS_modulename.o to add specific C flags when compiling this unit. In your case, your module object will be jc.o, so you can specify:

CFLAGS_jc.o := -O2

and it should work. Add V=1 to your $(MAKE) lines to get a verbose output and you should see -O2 when jc.c is being compiled.

You can find more about compiling modules in the official documentation.

回答2:

You can also use

ccflags-y := -O2

This will be applied to all of the source files compiled for your module with the Makefile. This is indirectly documented in the link provided by eepp in Section 4.2

来源：https://stackoverflow.com/questions/18478859/is-it-possible-to-set-cflags-to-a-linux-kernel-module-makefile