I've rewritten these macros so that they don't keep rewriting the same
value into the crLine variable. They now write it just once, before
ever testing the condition.
The point isn't the extra efficiency (which is surely negligible);
it's to make it safe to abort a coroutine and free its entire state at
unexpected moments. If you use one of these macros with a condition
that has side effects, say crWaitUntil(func()), and one of the side
effects can be to free the entire object that holds the coroutine
state, then the write to crLine after testing the condition would
previously have caused a stale-pointer dereference. But now that only
happened once, _before_ the condition was first evaluated; so as long
as func() returns false in the event that it frees the coroutine
state, it's safe - crWaitUntil will see the false condition and return
without touching the state object, and then it'll never be called
again because the whole object will have gone away.
ssh.c has been an unmanageably huge monolith of a source file for too
long, and it's finally time I started breaking it up into smaller
pieces. The first step is to move some declarations - basic types like
packets and packet queues, standard constants, enums, and the
coroutine system - into headers where other files can see them.
Simon Tatham