TMDS64GPEVM: custom defconfig

Part Number: TMDS64GPEVM

Hi

For our custom board we want to provide custom defconfig for kernel based on TMDS64GPEVM defconfig. I'm using yocto to build image. In the meta-ti/recipes-kernel/linux I found script setup-defconfig.inc responsible for creating defconfig. In the first line of the script I see command. 

 cp ${WORKDIR}/defconfig ${B}/.config

So in my kernel .bbappend yocto recipe I added following function:

do_configure:prepend() {
        bbnote "Applying PUMA kernel defconfig..."
        cp ${WORKDIR}/puma_linux_kernel_defconfig ${S}/arch/${ARCH}/configs/
        ln -sfr ${WORKDIR}/puma_linux_kernel_defconfig ${WORKDIR}/defconfig
}

My defconfig is just a copy of defconfig found in TI kernel source tree: ./arch/arm64/configs/defconfig.  After add above function to recipe built image doubled in size. Why?

Building the same image with default defconfig cause image size is two times smaller.

Thanks for help

BR

Jakub