@func{schedule} doesn't exist, which is arguably a @command{gdb} bug.
You can work around this by setting the breakpoint by filename and
line number, e.g.@: @code{break thread.c:@var{ln}} where @var{ln} is
-the line number of the first declaration in @func{schedule}.
-Alternatively you can recompile with optimization turned off, by
-removing @samp{-O3} from the @code{CFLAGS} line in
-@file{Make.config}.} Be sure to keep track of each thread's address
+the line number of the first declaration in @func{schedule}.} Be sure
+to keep track of each thread's address
and state, and what procedures are on the call stack for each thread.
You will notice that when one thread calls @func{switch_threads},
another thread starts running, and the first thing the new thread does
interrupts in your solution by calling @func{intr_disable} or
@func{intr_set_level}, although you may find doing so to be useful
while debugging. Instead, use semaphores, locks and condition
-variables to solve synchronization problems. Hint: read the comments
+variables to solve synchronization problems. Read the tour section on
+synchronization (@pxref{Synchronization}) or the comments
in @file{threads/synch.h} if you're unsure what synchronization
primitives may be used in what situations.