fatal error: stack overflow

runtime stack:
runtime.throw({0x4ddb79?, 0x122b6b8?})
	GOROOT/src/runtime/panic.go:1077 +0x5c fp=0x7f5f657fa000 sp=0x7f5f657f9fd0 pc=0x1238e5c
runtime.newstack()
	GOROOT/src/runtime/stack.go:1107 +0x5ac fp=0x7f5f657fa1b0 sp=0x7f5f657fa000 pc=0x125518c
runtime.morestack()
	src/runtime/asm_amd64.s:593 +0x8f fp=0x7f5f657fa1b8 sp=0x7f5f657fa1b0 pc=0x126fbaf