on go tip runtime.atoi does not do any kind of overflow checks or error reporting.
which can lead to internal variables being set to surprising numbers without a warning.

What did you do?

compile a test program:

package main

import "runtime"

func main() {
	print("runtime.MemProfileRate=", runtime.MemProfileRate, "\n")
}

https://play.golang.org/p/WhUyslK_Em

supply some number value flags:
$ GODEBUG=memprofilerate=10000000000000000000 ./test

What did you expect to see?

runtime.MemProfileRate=10000000000000000000
or an error
or a documented default value

What did you see instead?

runtime.MemProfileRate=-8446744073709551616