Add instructions coverage statistics
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@ -0,0 +1,25 @@
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(54666427,
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(1607, 67587841),
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(1154, 13869),
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{'UNDEFINED': 1698,
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'SAME_VALUE': 0,
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'OFFSET': 54666405,
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'VAL_OFFSET': 0,
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'REGISTER': 22,
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'EXPRESSION': 12367,
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'VAL_EXPRESSION': 0,
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'ARCHITECTURAL': 0},
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{'seen': 12922916, 'expr': 1502, 'offset': 12921414})
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(30038269,
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(1603, 42959683),
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(1114, 5977),
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{'UNDEFINED': 1698,
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'SAME_VALUE': 0,
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'OFFSET': 30038255,
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'VAL_OFFSET': 0,
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'REGISTER': 14,
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'EXPRESSION': 4475,
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'VAL_EXPRESSION': 0,
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'ARCHITECTURAL': 0},
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{'seen': 12922916, 'expr': 1502, 'offset': 12921414})
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@ -342,18 +342,14 @@ quite efficient, most of its optimization comes from fine-tuned code and good
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caching mechanisms. While parsing DWARF, \prog{libunwind} is forced to parse
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the relevant FDE from its start, until it finds the row it was seeking.
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\subsection{General statistics}
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\todo{}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\section{DWARF semantics}\label{sec:semantics}
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We will now define semantics covering most of the operations used for
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CFI\todo{To be defined elsewhere in the report} described in the DWARF
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standard~\cite{dwarf5std}, with the exception of DWARF expressions. These are
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We will now define semantics covering most of the operations used for FDEs
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described in the DWARF standard~\cite{dwarf5std}, such as seen in
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Listing~\ref{lst:ex1_dwraw}, with the exception of DWARF expressions. These are
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not exhaustively treated because they are quite rich and would take a lot of
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time and space to formalize, and in the meantime are only seldom used (see the
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DWARF statistics regarding this).
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@ -634,7 +630,7 @@ a reasonable space loss was to compile directly the \ehframe{} into native
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machine code on the x86\_64 platform.
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\subsection{Compilation: \ehelfs}
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\subsection{Compilation: \ehelfs}\label{ssec:ehelfs}
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The rough idea of the compilation is to produce, out of the \ehframe{} section
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of a binary, C code that resembles the code shown in the DWARF semantics from
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@ -1006,7 +1002,116 @@ lot.
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\subsection{Instructions coverage}
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\todo{}
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In order to determine which proportion of real-world ELF instructions are
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covered by our compiler and \ehelfs.
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The method chosen was to randomly select 4000 ELFs among those present on a
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basic ArchLinux system setup, in the directories \texttt{/bin}, \texttt{/lib},
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\texttt{/usr/bin}, \texttt{/usr/lib} and their subdirectories, making sure
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those files were ELF64 files, then gathering statistics on those files.
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\begin{table}[h]
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\centering
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\begin{tabular}{r r r r r r r}
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\toprule
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\thead{} & \thead{Unsupported \\ register rule}
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& \thead{Register \\ rules seen}
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& \thead{\% \\ supp.}
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& \thead{Unsupported \\ expression}
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& \thead{Expressions \\ seen}
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& \thead{\% \\ supp.}
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\\
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\midrule
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\makecell{Only supp. \\ columns} &
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1603 & 42959683 & 99.996\,\% &
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1114 & 5977 & 81.4\,\%
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\\
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All columns &
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1607 & 67587841 & 99.998\,\% &
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1154 & 13869 & 91.7\,\%
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\\
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\bottomrule
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\end{tabular}
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\caption{Instructions coverage statistics}\label{table:instr_cov}
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\end{table}
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\begin{table}[h]
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\centering
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\begin{tabular}{r r r r r r}
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\toprule
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\thead{}
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& \thead{\texttt{Undefined}}
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& \thead{\texttt{Same\_value}}
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& \thead{\texttt{Offset}}
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& \thead{\texttt{Val\_offset}}
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& \thead{\texttt{Register}}
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\\
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\midrule
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\makecell{Only supp. \\ columns}
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& 1698 (0.006\,\%)
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& 0
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& 30038255 (99.9\,\%)
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& 0
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& 14 (0\,\%)
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\\
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All columns
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& 1698 (0.003\,\%)
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& 0
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& 54666405 (99.9\,\%)
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& 0
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& 22 (0\,\%)
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\\
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\bottomrule
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\toprule
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\thead{}
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& \thead{\texttt{Expression}}
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& \thead{\texttt{Val\_expression}}
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& \thead{\texttt{Architectural}}
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& & \thead{Total}
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\\
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\midrule
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\makecell{Only supp. \\ columns}
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& 4475 (0.015\,\%)
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& 0
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& 0
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& & 30044442
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\\
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All columns
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& 12367 (0.02\,\%)
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& 0
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& 0
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& & 54680492
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\\
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\bottomrule
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\end{tabular}
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\caption{Instruction type statistics}\label{table:instr_types}
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\end{table}
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The Table~\ref{table:instr_cov} gives statistics about the proportion of
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instructions encountered that were not supported by \ehelfs. The first row is
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only concerned about the columns CFA, \reg{rip}, \reg{rsp}, \reg{rbp} and
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\reg{rbx} (the supported registers --~see Section~\ref{ssec:ehelfs}). The
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second row analyzes all the columns that were encountered, no matter whether
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supported or not.
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The Table~\ref{table:instr_types} analyzes the proportion of each command
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(\ie\ the formal way a register is set) for non-CFA columns in the sampled
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data. For a brief explanation, \texttt{Offset} means stored at offset from CFA,
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\texttt{Register} means the value from a machine register, \texttt{Expression}
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means stored at the value of an expression, and the \texttt{Val\_} prefix means
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that the value must not be dereferenced. Overall, it can be seen that
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supporting \texttt{Offset} already means supporting the vast majority of
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registers. The data gathered (not reproduced here) also suggests that
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supporting a few common expressions is enough to support most of them.
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It is also worth noting that of all the 4000 analyzed files, there are only 12
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that contained all the unsupported expressions seen, and only 24 that contained
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some unsupported instruction at all.
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%%%% End main text content %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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@ -1020,8 +1125,8 @@ lot.
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\hfill \begin{minipage}{0.7\textwidth}
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\begin{flushright}
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\itshape{} \small{}
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Unless otherwise explicitly stated, any image or source code snippet
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from the present document can be reused freely by anyone.
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Unless otherwise explicitly stated, any image, source code snippet or
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table from the present document can be reused freely by anyone.
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\end{flushright}
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\end{minipage}
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@ -33,7 +33,7 @@
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}
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@article{dinechin2000exn,
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title={C++ exception handling},
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title={C++ exception handling \qtodo{CHECK}},
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author={De Dinechin, Christophe},
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journal={IEEE Concurrency},
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volume={8},
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