Specify ordering of privileged and non-standard extensions

Closes #319

src/naming.tex

@@ -93,6 +93,36 @@ \section{Additional Standard Extension Names}
 from other multi-letter extensions by an underscore, e.g.,
 ``RV32IMACZicsr\_Zifencei''.
 
+\section{Supervisor-level Instruction-Set Extensions}
+
+Standard supervisor-level instruction-set extensions are defined in Volume II,
+but are named using ``S'' as a prefix, followed by an alphabetical name and an
+optional version number.  Supervisor-level extensions must be separated from
+other multi-letter extensions by an underscore.
+
+Standard supervisor-level extensions should be listed after standard
+unprivileged extensions.  If multiple supervisor-level extensions are listed,
+they should be ordered alphabetically.
+
+\section{Hypervisor-level Instruction-Set Extensions}
+
+Standard hypervisor-level instruction-set extensions are named like
+supervisor-level extensions, but beginning with the letter ``H'' instead of
+the letter ``S''.
+
+Standard hypervisor-level extensions should be listed after standard
+lesser-privileged extensions.  If multiple hypervisor-level extensions are
+listed, they should be ordered alphabetically.
+
+\section{Machine-level Instruction-Set Extensions}
+
+Standard machine-level instruction-set extensions are prefixed with the three
+letters ``Zxm''.
+
+Standard machine-level extensions should be listed after standard
+lesser-privileged extensions.  If multiple machine-level extensions are listed,
+they should be ordered alphabetically.
+
 \section{Non-Standard Extension Names}
 
 Non-standard extensions are named using a single ``X'' followed by an
@@ -104,15 +134,8 @@ \section{Non-Standard Extension Names}
 by an underscore.  For example, an ISA with non-standard extensions
 Argle and Bargle may be named ``RV64IZifencei\_Xargle\_Xbargle''.
 
-\section{Supervisor-level Instruction-Set Extensions}
-
-Standard supervisor instruction-set extensions are defined in Volume II, but
-are named using ``S'' as a prefix, followed by an
-alphabetical name and an optional version number.
-Non-standard extensions to the supervisor-level ISA are defined using
-the ``SX'' prefix.
-Supervisor extensions must be separated from other multi-letter extensions
-by an underscore.
+If multiple non-standard extensions are listed, they should be ordered
+alphabetically.
 
 \section{Subset Naming Convention}
 Table~\ref{isanametable} summarizes the standardized extension names.
@@ -134,7 +157,8 @@ \section{Subset Naming Convention}
 Control and Status Register Access & Zicsr \\
 Instruction-Fetch Fence & Zifencei \\
 \hline
-General & G = IMAFDZicsr\_Zifencei \\
+\multirow{2}{*}{General} & G = IMAFDZicsr\_Zifencei \\
+                         & (equivalently, IMADZifencei) \\
 \hline
 \multicolumn{2}{|c|}{Standard Unprivileged Extensions}\\
 \hline
@@ -151,19 +175,24 @@ \section{Subset Naming Convention}
 Total Store Ordering & Ztso \\
 \hline
 \hline
-\multicolumn{2}{|c|}{Non-Standard Unprivileged Extensions}\\
+\multicolumn{2}{|c|}{Standard Supervisor-Level Extensions}\\
+\hline
+Supervisor-level extension ``def'' & Sdef \\
+\hline
+\hline
+\multicolumn{2}{|c|}{Standard Hypervisor-Level Extensions}\\
 \hline
-Non-standard extension ``abc'' & Xabc \\
+Hypervisor-level extension ``ghi'' & Hghi \\
 \hline
 \hline
-\multicolumn{2}{|c|}{Standard Supervisor-Level ISA}\\
+\multicolumn{2}{|c|}{Standard Machine-Level Extensions}\\
 \hline
-Supervisor extension ``def'' & Sdef \\
+Machine-level extension ``jkl'' & Zxmjkl \\
 \hline
 \hline
-\multicolumn{2}{|c|}{Non-Standard Supervisor-Level Extensions}\\
+\multicolumn{2}{|c|}{Non-Standard Extensions}\\
 \hline
-Supervisor extension ``ghi'' & SXghi \\
+Non-standard extension ``mno'' & Xmno \\
 \hline
 \end{tabular}
 \caption{Standard ISA extension names.  The table also defines the