report/slides/slides.tex

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\documentclass[11pt,xcolor={usenames,dvipsnames}]{beamer}
\usetheme{Warsaw}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}

\usepackage{../shared/my_listings}
%\usepackage{../shared/my_hyperref}
\usepackage{../shared/specific}
\usepackage{../shared/common}
\usepackage{../shared/todo}

\setbeamertemplate{navigation symbols}{}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\author[Théophile Bastian]{Théophile \textsc{Bastian} \\
    \small{Under supervision of Francesco Zappa Nardelli}}
\title{Internship defense, MPRI, M2}
\subtitle{Speeding up stack unwinding by compiling DWARF debugging data}
\date{March\ --\ August 2018}
%\subject{}
%\logo{}
\institute{Team PARKAS, INRIA, Paris}

\begin{document}

\begin{frame}
    \addtocounter{framenumber}{-1}
	\titlepage{}

    \begin{center}
        Slides: \url{https://tobast.fr/m2/slides.pdf} \\
        Report: \url{https://tobast.fr/m2/report.pdf}
    \end{center}
\end{frame}

\begin{frame}
    \addtocounter{framenumber}{-1}
    \tableofcontents
\end{frame}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Stack unwinding data}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Introduction}

\begin{frame}[fragile]{We often use stack unwinding!}
    \begin{lstlisting}[language=, numbers=none, escapechar=|]
Program received signal SIGSEGV, Segmentation fault.
0x0000555555554625 in fct_b (m=0x5c) at segfault.c:5
5           printf("%l\n", *m);
|\pause|
(gdb) backtrace
#0  0x0000555555554625 in fct_b (m=0x5c) at segfault.c:5
#1  0x0000555555554663 in fct_a (n=42) at segfault.c:10
#2  0x0000555555554674 in main () at segfault.c:14
|\pause|
(gdb) frame 1
#1  0x0000555555554663 in fct_a (n=42) at segfault.c:10
10          fct_b((int*)(some_fct_a_var + 8));
|\pause|
(gdb) print some_fct_a_var
$1 = 84
    \end{lstlisting}

    \pause{}
    \begin{center}
        \textbf{\Large How does it work?!}
    \end{center}
    \vspace{1em}
\end{frame}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Stack frames and unwinding}

\begin{frame}{Call stack and registers}
    \begin{columns}[c]
        \begin{column}{0.65\textwidth}
            \begin{itemize}
                \item Programs use a \alert{call stack}
                \item Organized in \alert{stack frames}
                    \begin{itemize}
                        \item Local variables
                        \item Function parameters
                        \item Keep track of nesting, registers and ``return
                            point''
                    \end{itemize}
            \end{itemize}

            Common registers:
            \begin{itemize}
                \item \reg{rip}: program counter (PC)

                \item \reg{rsp}: stack pointer

                \item \reg{rbp}: base pointer
                    \begin{itemize}
                        \item Saves \reg{rsp}
                        \item Easy access
                        \item Wastes a register
                        \item Not often used (x86\_64)
                    \end{itemize}
            \end{itemize}
        \end{column}
        \begin{column}{0.35\textwidth}
            \includegraphics[width=0.95\linewidth]{../shared/imgs/call_stack}
        \end{column}
    \end{columns}
\end{frame}

\begin{frame}{Isn't it as trivial as \texttt{pop()}?}
    \begin{itemize}
        \item This is only a \alert{blob of binary data} without mandatory
            structure
        \item We ignore \alert{which registers were saved}
        \item We ignore \alert{whether \reg{rbp} was used}
        \item We ignore \alert{where the return address is stored}
        \item We ignore \alert{where the previous frame begins}
    \end{itemize}

    \medskip

    But\ldots{} if we know how to \alert{unwind one}, we can \alert{recurse}!
\end{frame}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{DWARF tables}

\begin{frame}[fragile]{DWARF unwinding data}

    \begin{lstlisting}[numbers=none, language=]
00009b30 48 009b34 FDE cie=0000 pc=0084950..0084b37
 LOC    CFA      rbx   rbp   r12   r13   r14   r15   ra
0084950 rsp+8    u     u     u     u     u     u     c-8
0084952 rsp+16   u     u     u     u     u     c-16  c-8
0084954 rsp+24   u     u     u     u     c-24  c-16  c-8
0084956 rsp+32   u     u     u     c-32  c-24  c-16  c-8
0084958 rsp+40   u     u     c-40  c-32  c-24  c-16  c-8
0084959 rsp+48   u     c-48  c-40  c-32  c-24  c-16  c-8
008495a rsp+56   c-56  c-48  c-40  c-32  c-24  c-16  c-8
0084962 rsp+64   c-56  c-48  c-40  c-32  c-24  c-16  c-8
0084a19 rsp+56   c-56  c-48  c-40  c-32  c-24  c-16  c-8
0084a1d rsp+48   c-56  c-48  c-40  c-32  c-24  c-16  c-8
0084a1e rsp+40   c-56  c-48  c-40  c-32  c-24  c-16  c-8
0084a20 rsp+32   c-56  c-48  c-40  c-32  c-24  c-16  c-8
0084a22 rsp+24   c-56  c-48  c-40  c-32  c-24  c-16  c-8
0084a24 rsp+16   c-56  c-48  c-40  c-32  c-24  c-16  c-8
0084a26 rsp+8    c-56  c-48  c-40  c-32  c-24  c-16  c-8
0084a30 rsp+64   c-56  c-48  c-40  c-32  c-24  c-16  c-8
    \end{lstlisting}

    \pause{}

    \vspace{-4cm}
    \hfill\includegraphics[height=3cm, angle=45, origin=c]{img/dwarf_logo}
    \hspace{-1cm}

\end{frame}

\end{document}