warning求助，怎么把这两个warning去除 WARNING L1: UNRESOLVED EXTERNAL SYMBOL

ORG 0000H
JMP START
ORG 000BH
AJMP IST0
ORG 0030H
START:
MOV TMOD #01H
MOV TL0,#0CH
MOV TH0,#0FEH
MOV TCON,#10H
SETB ET0
SETB EA
AJMP $
IST0:
MOV TL0,#0CH
MOV TH0,#0FEH
CPL P1.0
RETI
END

warning是：

Build target 'Target 1'
assembling STARTUP.A51...
linking...
*** WARNING L1: UNRESOLVED EXTERNAL SYMBOL
    SYMBOL:  ?C_START
    MODULE:  STARTUP.obj (?C_STARTUP)
*** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL
    SYMBOL:  ?C_START
    MODULE:  STARTUP.obj (?C_STARTUP)
    ADDRESS: 000DH
Program Size: data=9.0 xdata=0 code=15
"eighteen example one" - 0 Error(s), 2 Warning(s).

没有调用那两个函数吧。。。