fatal error: stack overflow

runtime stack:
runtime.throw({0x159744c?, 0x200000001?})
	GOROOT/src/runtime/panic.go:1229 +0x48 fp=0x34712b72de98 sp=0x34712b72de68 pc=0x48c928
runtime.newstack()
	GOROOT/src/runtime/stack.go:1178 +0x5fd fp=0x34712b72dfc8 sp=0x34712b72de98 pc=0x4702dd
runtime.morestack()
	src/runtime/asm_amd64.s:681 +0x7d fp=0x34712b72dfd0 sp=0x34712b72dfc8 pc=0x49389d