word smithing

book.tex

@@ -1628,16 +1628,17 @@ $\Rightarrow$
 The \key{read} operation does not have a direct counterpart in x86-64
 assembly, so we have instead implemented this functionality in the C
 language, with the function \code{read\_int} in the file
-\code{runtime.c}. In general, we have refer to all of the
-functionality in this file as the \emph{runtime system}, or simply
-\emph{runtime} for short. When compiling your generated x86-64
-assembly code, you will need to compile \code{runtime.c} and link it
-in. For our purposes of code generation, all you need to do is
+\code{runtime.c}. In general, we refer to all of the functionality in
+this file as the \emph{runtime system}, or simply the \emph{runtime}
+for short. When compiling your generated x86-64 assembly code, you
+will need to compile \code{runtime.c} to \code{runtime.o} (an ``object
+file'', using \code{gcc} option \code{-c}) and link it into the final
+executable. For our purposes of code generation, all you need to do is
 translate an assignment of \key{read} to some variable $\itm{lhs}$
-(for left-hand side) into call to the \code{read\_int} function
-followed by a move from \code{rax} into the left-hand side. Also,
-recall that the return value of a function is typically placed in the
-\code{rax} register.  \\
+(for left-hand side) into a call to the \code{read\_int} function
+followed by a move from \code{rax} to the left-hand side.  The move
+from \code{rax} is needed because the return value from
+\code{read\_int} goes into \code{rax}, as is the case in general.  \\
 \begin{tabular}{lll}
 \begin{minipage}{0.4\textwidth}
 \begin{lstlisting}