xilinx SDK编译问题，无法编译出.elf文件，请问依赖变量为什么为空的？

Question

helloworld.elf: $(OBJS) ../src/lscript.ld $(USER_OBJS)
@echo 'Building target: $@'
@echo 'Invoking: ARM v7 gcc linker'
arm-none-eabi-gcc -mcpu=cortex-a9 -mfpu=vfpv3 -mfloat-abi=hard -Wl,-build-id=none -specs=Xilinx.spec -Wl,-T -Wl,../src/lscript.ld -L../../helloworld_bsp/ps7_cortexa9_0/lib -o "helloworld.elf" $(OBJS) $(USER_OBJS) $(LIBS)
@echo 'Finished building target: $@'
@echo ' '

其中依赖的变量“OBJS”“USER_OBJS”为空的，导致没有编译出*.elf文件

USER_OBJS :=

LIBS := -Wl,--start-group,-lxil,-lgcc,-lc,--end-group

LD_SRCS :=
OBJ_SRCS :=
S_SRCS :=
C_SRCS :=
S_UPPER_SRCS :=
O_SRCS :=
EXECUTABLES :=
OBJS :=
S_UPPER_DEPS :=
C_DEPS :=
ELFSIZE :=

Every subdirectory with source files must be described here

SUBDIRS := \
src \

Answer 1

OBJS := helloworld.elf
这样试试看