minor edits

book.tex

@@ -5337,16 +5337,16 @@ described in \cite{Matz:2013aa}), uses a combination of registers and
 stack locations for passing arguments. Up to six arguments may be
 passed in registers, using the registers \code{rdi}, \code{rsi},
 \code{rdx}, \code{rcx}, \code{r8}, and \code{r9}, in that order.  If
-there are more than six arguments, then the rest must be placed on the
-stack, which we call \emph{stack arguments}. The register \code{rax}
-is for the return value of the function.
+there are more than six arguments, then the rest are placed on the
+stack.  The register \code{rax} is for the return value of the
+function.
 
 We will be using a modification of this convention. For reasons that
 will be explained in subsequent paragraphs, we will not make use of
-stack arguments, and instead restrict functions to passing arguments
-exclusively in registers. To enforce this restriction, functions of
-too many arguments will be transformed to pass additional arguments in
-a vector.
+the stack for passing arguments, and instead use the heap when there
+are more than six arguments. In particular, functions of more than six
+arguments will be transformed to pass the additional arguments in a
+vector.
 
 %% Recall from Section~\ref{sec:x86} that the stack is also used for
 %% local variables and for storing the values of callee-saved registers