fatal error: stack overflow

runtime stack:
runtime.throw({0x4df92f?, 0x20?})
	GOROOT/src/runtime/panic.go:1077 +0x5c fp=0x7fb49f9ff000 sp=0x7fb49f9fefd0 pc=0x12450fc
runtime.newstack()
	GOROOT/src/runtime/stack.go:1107 +0x5ac fp=0x7fb49f9ff1b0 sp=0x7fb49f9ff000 pc=0x126142c
runtime.morestack()
	src/runtime/asm_amd64.s:593 +0x8f fp=0x7fb49f9ff1b8 sp=0x7fb49f9ff1b0 pc=0x127be4f