fatal error: stack overflow

runtime stack:
runtime.throw({0x122f7ca?, 0x7fff640a7d78?})
	GOROOT/src/runtime/panic.go:1077 +0x5c fp=0x7fff640a7d28 sp=0x7fff640a7cf8 pc=0x43ab5c
runtime.newstack()
	GOROOT/src/runtime/stack.go:1107 +0x5ac fp=0x7fff640a7ed8 sp=0x7fff640a7d28 pc=0x4554ac
runtime.morestack()
	src/runtime/asm_amd64.s:593 +0x8f fp=0x7fff640a7ee0 sp=0x7fff640a7ed8 pc=0x46f52f