fatal error: stack overflow

runtime stack:
runtime.throw({0x1303864?, 0x1efe3a0?})
	GOROOT/src/runtime/panic.go:1047 +0x5d fp=0x7ffd749c7298 sp=0x7ffd749c7268 pc=0x436efd
runtime.newstack()
	GOROOT/src/runtime/stack.go:1105 +0x5bd fp=0x7ffd749c7448 sp=0x7ffd749c7298 pc=0x45177d
runtime.morestack()
	src/runtime/asm_amd64.s:574 +0x8b fp=0x7ffd749c7450 sp=0x7ffd749c7448 pc=0x46b52b