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LD      .tmp_vmlinux1
sound/built-in.o: In function `gpio_switch_probe':
last.c:(.text+0x31084): undefined reference to `switch_dev_register'
last.c:(.text+0x311d4): undefined reference to `switch_dev_unregister'
last.c:(.text+0x311f0): undefined reference to `switch_dev_unregister'
sound/built-in.o: In function `earphone_switch_work':
last.c:(.text+0x31b84): undefined reference to `switch_set_state'
sound/built-in.o: In function `gpio_switch_remove':
last.c:(.devexit.text+0x78): undefined reference to `switch_dev_unregister'
Makefile:873: recipe for target '.tmp_vmlinux1' failed
make: *** [.tmp_vmlinux1] Error 1