Compile error when building ardupilot

Hi

I am trying to compile arducopter myself using make px4-v2,but encountered this error:

Pruning ROMFS files.
ROMFS: romfs.img
OBJ: romfs.o
CC: romfs.o.c
CC: romfs.o.c
LINK: /home/jasontofly/ArduPilot/ardupilot/modules/PX4Firmware/Build/px4fmu-v2_APM.build/firmware.elf
/home/jasontofly/ArduPilot/ardupilot/modules/PX4Firmware/Build/px4fmu-v2_APM.build//home/jasontofly/ArduPilot/ardupilot/modules/PX4Firmware/Build/px4fmu-v2_APM.build/builtin_commands.c.o:(.rodata.g_builtins+0xc): undefined reference to sercon_main' /home/jasontofly/ArduPilot/ardupilot/modules/PX4Firmware/Build/px4fmu-v2_APM.build//home/jasontofly/ArduPilot/ardupilot/modules/PX4Firmware/Build/px4fmu-v2_APM.build/builtin_commands.c.o:(.rodata.g_builtins+0x1c): undefined reference toserdis_main’
make[2]: *** [/home/jasontofly/ArduPilot/ardupilot/modules/PX4Firmware/Build/px4fmu-v2_APM.build/firmware.elf] Error 1
make[2]: Leaving directory /home/jasontofly/ArduPilot/ardupilot/modules/PX4Firmware/Build/px4fmu-v2_APM.build' make[1]: *** [/home/jasontofly/ArduPilot/ardupilot/modules/PX4Firmware/Build/px4fmu-v2_APM.build/firmware.px4] Error 2 make[1]: Leaving directory/home/jasontofly/ArduPilot/ardupilot’
make: *** [px4-v2] Error 2

i think this is the last step to build the image ,anyone can help me fix this issue?thanks.