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Add space optimisation

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Théophile Bastian 2018-08-03 02:15:54 +02:00
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report/report.tex
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@ -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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