I think they’re actually referring the stack usage from the function call itself (the creation of a new stack frame). I believe the point the author is making i

I think they’re actually referring the stack usage from the function call itself (the creation of a new stack frame). I believe the point the author is making is that while it’s common to check the return value of malloc to see if heap allocation was successful, it’s comparatively rare to do any analysis of stack usage to verify that none of your function calls are going to cause a stack overflow.