fatal error: stack overflow

runtime stack:
runtime.throw({0x4db599?, 0x20?})
	GOROOT/src/runtime/panic.go:1077 +0x5c fp=0x7f39127fc000 sp=0x7f39127fbfd0 pc=0x122a6dc
runtime.newstack()
	GOROOT/src/runtime/stack.go:1107 +0x5ac fp=0x7f39127fc1b0 sp=0x7f39127fc000 pc=0x1246a0c
runtime.morestack()
	src/runtime/asm_amd64.s:593 +0x8f fp=0x7f39127fc1b8 sp=0x7f39127fc1b0 pc=0x126142f