fatal error: stack overflow

runtime stack:
runtime.throw({0x122016a?, 0x42d498?})
	GOROOT/src/runtime/panic.go:1077 +0x5c fp=0xc000721e18 sp=0xc000721de8 pc=0x43ab5c
runtime.newstack()
	GOROOT/src/runtime/stack.go:1107 +0x5ac fp=0xc000721fc8 sp=0xc000721e18 pc=0x4554ac
runtime.morestack()
	src/runtime/asm_amd64.s:593 +0x8f fp=0xc000721fd0 sp=0xc000721fc8 pc=0x46f52f