add spawn ref

Author: Vladimir Kotal

proc.tex

@@ -423,6 +423,8 @@
 around the problem that the child address space was usually rewritten on
 subsequent \texttt{exec}.  This problem was solved via already mentioned
 copy-on-write mechanism.  See \example{fork/vfork.c} on how it works.
+\item The problems of \texttt{vfork} are largely solved by
+\texttt{posix\_spawn}. See page \pageref{SPAWN}.
 \end{itemize}
 
 %%%%%
@@ -875,8 +877,8 @@
 \item Note that you have to use macros from the previous slide to get the
 child's return value out of the status information.
 \item \label{WAITPID} Example: \example{wait/wait.c}
-\item Creating new process with \texttt{fork} and replacing the process
-address space etc. with a new one after \texttt{exec} has been done is
+\item \label{SPAWN} Creating new process with \texttt{fork} and replacing the
+process address space etc. with a new one after \texttt{exec} has been done is
 expensive and has other problems. To make kernel create new process directly
 from executable \texttt{posix\_spawn} can be used.
 Example: \example{exec/spawn.c}