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slides/img/keep_breathing.jpg
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@ -8,6 +8,8 @@
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\usepackage{amsmath}
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\usepackage{amsfonts}
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\usepackage{amssymb}
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\usepackage{booktabs}
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\usepackage{makecell}
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\usepackage{../shared/my_listings}
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%\usepackage{../shared/my_hyperref}
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@ -15,6 +17,9 @@
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\usepackage{../shared/common}
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\usepackage{../shared/todo}
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\renewcommand\theadalign{c}
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\renewcommand\theadfont{\scriptsize\bfseries}
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\setbeamertemplate{navigation symbols}{}
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\newcommand{\thenalert}[1]{\only<1>{#1}\only<2>{\alert{#1}}}
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@ -242,6 +247,50 @@ unwind_context_t _eh_elf(
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\end{itemize}
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\end{frame}
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\begin{frame}{Compilation choices}
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\textbf{In order to keep the compiler \alert{simple} and \alert{easily
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testable}, the whole DWARF5 instruction set is not supported.}
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\begin{itemize}
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\item Tailored for \alert{x86\_64} (while DWARF is
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architecture-agnostic)
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\item Only supports \alert{unwinding registers}: \reg{rip}, \reg{rsp},
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\reg{rbp}, \reg{rbx}
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\begin{itemize}
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\item[$\leadsto$] suitable for perf, not for gdb
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\end{itemize}
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\item Supports the \alert{wide majority} ($> 99.9\%$) of instructions
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used (see later)
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\begin{itemize}
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\item Only supports few common expressions: already $~ 90\,\%$
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of expressions used
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\end{itemize}
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\end{itemize}
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\end{frame}
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\begin{frame}[fragile]{A word on memory maps}
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\textbf{Various functions come from various ELFs}\\
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\pause{}
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\hfill{}\textbf{\ldots{}and thus various \ehelfs{}}
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\begin{lstlisting}[language=, numbers=none]
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55c81b11e000-55c81b126000 000k /usr/bin/cat
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55c81b325000-55c81b326000 007k /usr/bin/cat
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55c81b326000-55c81b327000 008k /usr/bin/cat
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55c81bcf3000-55c81bd14000 000k [heap]
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7f8a5b4ed000-7f8a5b50f000 000k /usr/lib/libc-2.28.so
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7f8a5b50f000-7f8a5b65a000 022k /usr/lib/libc-2.28.so
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7f8a5b65a000-7f8a5b6a6000 16dk /usr/lib/libc-2.28.so
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7f8a5b6ec000-7f8a5b6ee000 000k /usr/lib/ld-2.28.so
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7f8a5b6ee000-7f8a5b70d000 002k /usr/lib/ld-2.28.so
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7f8a5b70d000-7f8a5b715000 021k /usr/lib/ld-2.28.so
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7ffc8a66b000-7ffc8a68c000 000k [stack]
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7ffc8a74a000-7ffc8a74d000 000k [vvar]
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7ffc8a74d000-7ffc8a74f000 000k [vdso]
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\end{lstlisting}
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\end{frame}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\subsection{Outlining}
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@ -338,7 +387,183 @@ unwind_context_t _eh_elf(
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\end{itemize}
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\end{frame}
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\begin{frame}{libunwind implementation}
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\begin{itemize}
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\item \alert{libunwind}: \textit{de facto} standard library for
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unwinding
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\item Uses DWARF in background
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\item \alert{Used by perf} as a backend for unwinding
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\pause{}\vspace{1em} \item{} Easiest way to use \ehelfs{} in perf:
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\alert{implement an alternative libunwind}
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\item{} Result: \alert{alternative implementation} of libunwind, nearly
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plug-and-play!
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\end{itemize}
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\end{frame}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\section{Results}
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\begin{frame}{Time performance}
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\small
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\centering
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\begin{tabular}{l r r r r r}
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\toprule
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\thead{Unwinding method} & \thead{Frames \\ unwound}
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& \thead{Tot.\ time \\ ($\mu s$)}
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& \thead{Avg. \\ time / frame \\ ($ns$)}
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& \thead{Time \\ ratio} \\
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\midrule
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\alert{\ehelfs{}}
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& 23506 % Frames unwound
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& 14837 % Total time
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& 631 % Avg time
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& 1
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\\
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\prog{libunwind}, \alert{cached}
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& 27058 % Frames unwound
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& 441601 % Total time
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& 16320 % Avg time
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& \alert{25.9}
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\\
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\prog{libunwind}, \alert{uncached}
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& 27058 % Frames unwound
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& 671292 % Total time
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& 24809 % Avg time
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& \alert{39.3}
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\\
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\bottomrule
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\end{tabular}
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\end{frame}
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\begin{frame}{Space performance}
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\begin{center}
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\begin{tabular}{r r r r r r}
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\toprule
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\thead{Object}
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& \thead{Original \\ program size \\ (KiB)}
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& \thead{Original \\ \lstc{.eh\_frame} \\ (KiB)}
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& \thead{Generated \\ \ehelf{} \\ (KiB)}
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& \thead{\% \\ original \\ size}
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& \thead{Growth \\ factor} \\
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\midrule
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libc
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& 1\,434 & 130.1 & 313.2 & 21.88 & 2.41 \\
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libpthread
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& 58.1 & 11.6 & 25.4 & 43.71 & 2.19 \\
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ld
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& 129.6 & 9.6 & 28.6 & 22.09 & 2.97 \\
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hackbench
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& 2.9 & 0.555 & 2.8 & 93.87 & 4.99 \\
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Total
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& 1\,638 & 151.8 & 370.0 & 22.81 & \alert{2.44} \\
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\bottomrule
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\end{tabular}
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\end{center}
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\end{frame}
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\newcommand{\ofsupp}[1]{$\left[\text{#1}\right]$}
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\begin{frame}{Instructions coverage}
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\scriptsize\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{Undef}
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& \thead{Same \\ value}
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& \thead{Offset}
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& \thead{Val \\ offset}
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& \thead{Reg}
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\\
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\midrule
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\makecell{Only supp. \\ columns} \vspace{.4em}
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& 1698 (0.006\,\%)
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& 0
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& 30\,M (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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& 55\,M (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{Expr \\ \ofsupp{supported}}
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& \thead{Val \\ expr}
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& \thead{Archi.}
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& & \thead{Total}
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\\
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\midrule
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\makecell{Only supp. \\ columns} \vspace{.4em}
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& \makecell{4475 (0.015\,\%) \\ \ofsupp{81.4\,\%}}
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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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& \makecell{12367 (0.02\,\%) \\ \ofsupp{91.7\,\%}}
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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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\vspace{2em}\pause{}
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\textbf{Among \alert{4000} randomly sampled filed, only \alert{24}
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containing unsupported instructions}
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\end{frame}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\section{A glance at future work}
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\begin{frame}{What next?}
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\begin{itemize}
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\item \alert{Outlining} was super efficient for
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compactness\ldots{} Worth trying on standard DWARF\@?
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\item Implement a release-ready, packageable, easy to use version of
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perf with \ehelfs{} and submit it for inclusion
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\item{} Measure \alert{C++ exceptions overhead} precisely in common
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software
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\item{} Implement \alert{\ehelfs{}} support for \alert{C++ runtime}
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exception handling
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\item{} \ldots{}and many more possibilities to explore!
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\end{itemize}
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\end{frame}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\section*{}
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\begin{frame}
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\begin{columns}[c]
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\begin{column}{0.35\textwidth}
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\includegraphics[width=\linewidth]{img/keep_breathing}
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\end{column}
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\begin{column}{0.65\textwidth}
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\begin{center}
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\huge
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And remember\ldots{}
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\smallskip
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DWARF is slow!
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\end{center}
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\end{column}
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\end{columns}
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\begin{center}
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\Huge\bfseries
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Thank you!
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\end{center}
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\end{frame}
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\end{document}
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