Add space optimisation

report/report.tex

@@ -544,6 +544,8 @@ options turned on or off, and it doesn't require to alter the base system by
 editing \eg{} \texttt{/usr/lib/libc-*.so}. Instead, when the \ehelf{} data is
 required, those files can simply be \lstc{dlopen}'d.
 
+\todo{Talk about switch structure, considered and ignored registers, etc.}
+
 \todo{More details here? Is it necessary or just too technical?}
 
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@@ -602,7 +604,26 @@ the original program size.
 
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 \subsection{Space optimization}
-\todo{}
+
+A lot of small space optimizations, such as filtering out empty FDEs, merging
+together the rows that are equivalent on all the registers kept, etc.\ were
+made in order to shrink the \ehelfs.
+
+\medskip
+
+The major optimization that most reduced the output size was to use a more
+flexible if/else if tree implementing a binary search on the program counter
+relevant intervals, instead of a huge switch. In the process, we also
+\emph{outline} a lot of code, that is, find out identical code blocks, move
+them outside of the if/else tree, identify them by a label, and jump to them
+using a \lstc{goto}, which de-duplicates a lot of code and contributes greatly
+to the shrinking. In the process, we noticed that the vast majority of FDE rows
+are actually taken among very few ``common'' FDE rows.
+
+This makes this optimisation really efficient, as seen later in
+Section~\ref{ssec:results_size}, but also makes it an interesting question ---
+not investigated during this internship --- to find out whether standard DWARF
+data could be efficiently compressed in this way.
 
 
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@@ -635,7 +656,7 @@ the original program size.
 \todo{}
 
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-\subsection{Measured compactness}
+\subsection{Measured compactness}\label{ssec:results_size}
 \todo{}
 
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