[U-Boot] Image size of u-boot.bin is too huge, why and how to correct?

[zq_fan]

hi, everybody. I've got a problem here.
My u-boot version is 1.3.0.My tool chain prefix is powerpc-linux-gnu- .
I wanna build uboot for freescale processor MPC8247
I found MPC8260ADS-config in Makefile, I thought MPC8260 was similar to MPC8247, so I choose this config target.
Then I make u-boot.bin, I found that after objcopy the file u-boot was about 700KB, but the file u-boot.bin was about xGB.

How should this happened? What Should I Do?

PS: objcopy uses an option --gap-fill=0xff, is this using right?