how to build KERNEL/u-boot with customer CFLAG

Hi,

not familiar with building kernel/u-boot, can I change the CFLAG while making uImage?

I saw in building QT, suggested 

QMAKE_CFLAGS_RELEASE = -O3 -march=armv7-a -mtune=cortex-a8 -mfpu=neon-mfloat-abi=softfp

so, I'm thinking if I could put  -march=armv7-a -mtune=cortex-a8 into kernel CFLAG and test. 

could below make action do what I want?

make uImage ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabi- CFLAGS_KERNEL="-march=armv7-a -mtune=cortex-a8"

or I had to modify the Makefile to fill the blank of CFLAGS_KERNEL?

thanks.

Pan