Add synthesis
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7 changed files with 150 additions and 46 deletions
7
Makefile
7
Makefile
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@ -1,5 +1,10 @@
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all:
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all: build
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build:
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latexmk -xelatex -pdf slides.tex
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clean:
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rm -f *aux *bbl *bcf *blg *_latexmk *fls *log *out *.run.xml
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upload: build
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scp slides.pdf www.tobast:~/files/sweden18.pdf
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157
slides.tex
157
slides.tex
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@ -42,7 +42,7 @@
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\newcommand{\cmark}{\color{OliveGreen}\ding{52}}
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\newcommand{\xmark}{\color{BrickRed}\ding{56}}
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\AtBeginSection[]{
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\AtBeginSection{
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\begin{frame}
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\vfill
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\centering
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@ -86,10 +86,8 @@
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\vspace{-2em}
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\begin{center}
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\todo{}
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\begin{align*}
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\text{Slides: } &\text{\url{https://tobast.fr/m2/slides.pdf}} \\
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\text{Report: } &\text{\url{https://tobast.fr/m2/report.pdf}}
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\text{Slides: } &\text{\url{https://tobast.fr/files/sweden18.pdf}} \\
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\end{align*}
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\end{center}
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\end{frame}
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@ -292,25 +290,28 @@ $1 = 84
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\end{center}
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\end{frame}
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\begin{frame}{A debugging hell: Linux kernel}
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\newcommand{\LinusMailOne}{
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``Sorry, but last time was too f\dots painful. The whole (and
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only) point of unwinders is to make debugging easy
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when a bug occurs. But \alert{the dwarf unwinder had bugs}
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itself, or \alert{our dwarf information had bugs}, and in either
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case it actually turned several trivial bugs into a \alert{total
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undebuggable hell}.''
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\vspace{1em}
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\only<1>{\hfill ---~Linus Torvalds, Kernel mailing list, 2012}
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\pause{}
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}
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\newcommand{\LinusMailTwo}{
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``If you can \alert{mathematically prove that the unwinder is
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correct} — even in the presence of bogus and actively
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incorrect unwinding information — and never ever
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follows a bad pointer, \alert{I’ll reconsider}.''
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}
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\newcommand{\LinusSource}{
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\hfill ---~Linus Torvalds, Kernel mailing list, 2012
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}
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\begin{frame}{A debugging hell: Linux kernel}
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\LinusMailOne{}
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\vspace{1em}
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\hfill ---~Linus Torvalds, Kernel mailing list, 2012
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\LinusSource{}
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\pause{}\vspace{1em}
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\begin{center}
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@ -552,7 +553,90 @@ $1 = 84
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\begin{itemize}
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\item[$\leadsto$] only \cfa{} tracking matters (for unwinding)
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\end{itemize}
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\item We had a working strategy for a \alert{linear execution}
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\item We still have to handle
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\begin{itemize}
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\item \alert{\cfa{} expression}
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\item \alert{control flow graph}
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\end{itemize}
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\end{itemize}
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\end{frame}
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\begin{frame}{\cfa{} expression}
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Two possibilities:
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\begin{itemize}
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\item Either \reg{rbp} is used as base pointer \pause{}
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\item Or we must track \cfa{} wrt. \reg{rsp}
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\begin{itemize}
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\item And update it after each instruction if needed
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\end{itemize}
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\end{itemize}
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\end{frame}
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\begin{frame}{Control flow graph}
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\begin{columns}[c]
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\column{0.4\textwidth}
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\lstinputlisting[language=C]{src/cfg/cfg.c}
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\pause{}
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\column{0.30\textwidth}
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\begin{figure}
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\centering
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\includegraphics[width=\textwidth]{src/cfg/cfg.png}
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\end{figure}
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\end{columns}
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\pause{}
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\begin{itemize}
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\item \alert{Upon split} (eg. \texttt{X})\alert{:} nothing special,
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propagate end state of X to children nodes A and B
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\item \alert{Upon join} (eg.\texttt{while\_end})\alert{:} check
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consistency of both input states
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\begin{itemize}
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\item If tricky, \texttt{gcc} will have used \reg{rbp}, even
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with \texttt{-fomit-frame-pointer}.
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\end{itemize}
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\end{itemize}
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\end{frame}
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\renewcommand{\tblrowval}[4]{#1 & #2 & #3 & #4 \\}
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\begin{frame}{Trust the compiler to avoid tricky unwinding}
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\begin{columns}[c]
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\column{0.55\textwidth}
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\lstinputlisting[language=C,firstline=3,lastline=7]
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{src/use_rbp/use_rbp.c}
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\pause{}
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\begin{itemize}
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\item At each loop cycle, \alert{\texttt{y} is larger} and
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\alert{allocated on the stack}
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\item Thus, \reg{rsp} is \alert{farther from \cfa} at each cycle: no
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constant rule $\cfa = \reg{rsp} + k$.
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\item A complex DWARF expression is possible, but
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\alert{the compiler won't}.
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\end{itemize}
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\pause{}
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\column{0.45\textwidth}
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\lstbash{\$ gcc -O0 -g -c src.c -fomit-frame-pointer}
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\vspace{1em}
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\begin{center}
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\tt
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\begin{tabular}{l l l l}
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\tblrowval{LOC} {CFA} {rbp} {ra}
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\tblrowval{000} {rsp+8} {u} {c-8}
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\tblrowval{001} {rsp+16} {c-16} {c-8}
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\tblrowval{004} {\alert{rbp}+16} {c-16} {c-8}
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\tblrowval{010} {\alert{rbp}+16} {c-16} {c-8}
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\tblrowval{0ce} {rsp+8} {c-16} {c-8}
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\end{tabular}
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\end{center}
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\end{columns}
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\end{frame}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\end{frame}
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\begin{frame}[t]{A word on formalization}
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\begin{itemize}
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\item First task: \alert{writing semantics} for DWARF, written as
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mapping to C code.
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\item DWARF5 specification: \alert{plain English}, no proper semantics
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\item Compiled code is in substance equivalent to semantics
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\item What remains to prove is mostly \alert{simple or classic
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optimisations}
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\end{itemize}
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\pause{}
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\vspace{-3cm}
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\begin{center}
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\includegraphics[width=0.8\linewidth, angle=10]{img/dw_spec.png}
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\end{center}
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\end{frame}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\subsection{Benchmarking}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\begin{frame}{perf instrumentation}
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\textbf{\alert{perf} is the state-of-the-art polling profiler for Linux.}
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\textbf{\alert{perf} is a state-of-the-art polling profiler for Linux.}
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\begin{itemize}
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\item{} used to get readings of the time spent in each function
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\item{} works by regularly stopping the program, unwinding its stack,
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\end{frame}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\section*{}
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\section*{Conclusion}
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\setcounter{section}{0}
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\begin{frame}{What next?}
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\begin{itemize}
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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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\begin{frame}{}
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\LinusMailOne{}
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\item{} Measure \alert{C++ exceptions overhead} precisely in common
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software
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\only<1>{\LinusSource{}}
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\only<2->\vspace{1em}
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\pause{}
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\item{} Implement \alert{\ehelfs{}} support for \alert{C++ runtime}
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exception handling, and other systems where unwinding is a
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performance bottleneck
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\LinusMailTwo{}
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\medskip
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\LinusSource{}
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\item \alert{Outlining} was effective for
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compactness\ldots{} Try outlining DWARF bytecode\@?
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\pause{}
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\vspace{1em}
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\begin{center}
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\bf
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Give us a few months to make Linus reconsider \texttt{;)}
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\end{center}
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\end{itemize}
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\end{frame}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\begin{center}
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\large
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\begin{align*}
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\textbf{Slides: } &\text{\url{https://tobast.fr/m2/slides.pdf}} \\
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\textbf{Report: } &\text{\url{https://tobast.fr/m2/report.pdf}}
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\textbf{Slides: } &\text{\url{https://tobast.fr/files/sweden18.pdf}} \\
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\end{align*}
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\end{center}
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8
src/cfg/cfg.c
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8
src/cfg/cfg.c
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while(/* ... */) {
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X;
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if(/* ... */) {
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A;
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} else {
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B;
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}
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}
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8
src/cfg/cfg.dot
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8
src/cfg/cfg.dot
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digraph {
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while_beg -> X;
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X -> A;
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X -> B;
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A -> while_end;
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B -> while_end;
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while_end -> while_beg;
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}
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BIN
src/cfg/cfg.png
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BIN
src/cfg/cfg.png
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Binary file not shown.
After Width: | Height: | Size: 20 KiB |
8
src/use_rbp/use_rbp.c
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8
src/use_rbp/use_rbp.c
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#include <stdlib.h>
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int main() {
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int z = rand();
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for(int x=1; x < z; ++x) {
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int y[x]; // Variable size
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/* do something */
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}
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}
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8
src/use_rbp/use_rbp.fde
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8
src/use_rbp/use_rbp.fde
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\begin{tabular}{l l l l}
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\tblrowval{LOC} {CFA} {rbp} {ra}
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\tblrowval{000} {rsp+8} {u} {c-8}
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\tblrowval{001} {rsp+16} {c-16} {c-8}
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\tblrowval{004} {rbp+16} {c-16} {c-8}
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\tblrowval{010} {rbp+16} {c-16} {c-8}
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\tblrowval{0ce} {rsp+8} {c-16} {c-8}
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\end{tabular}
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