402 lines
8.2 KiB
TeX
402 lines
8.2 KiB
TeX
% Created 2019-06-03 Mon 10:40
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% Intended LaTeX compiler: pdflatex
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\documentclass[presentation]{beamer}
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\usepackage[utf8]{inputenc}
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\usepackage[T1]{fontenc}
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\usepackage{graphicx}
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\usepackage{grffile}
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\usepackage{longtable}
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\usepackage{wrapfig}
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\usepackage{rotating}
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\usepackage[normalem]{ulem}
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\usepackage{amsmath}
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\usepackage{textcomp}
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\usepackage{amssymb}
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\usepackage{capt-of}
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\usepackage{hyperref}
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\usepackage{color}
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\usepackage{listings}
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\usetheme{default}
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\author{Sergio Durigan Junior \\ sergiodj@\{sergiodj.net,redhat.com,debian.org\}}
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\date{}
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\title{GDB Intro}
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\hypersetup{
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pdfauthor={Sergio Durigan Junior \\ sergiodj@\{sergiodj.net,redhat.com,debian.org\}},
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pdftitle={GDB Intro},
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pdfkeywords={},
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pdfsubject={},
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pdfcreator={Emacs 26.1 (Org mode 9.1.9)},
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pdflang={English}}
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\begin{document}
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\maketitle
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\begin{frame}[label={sec:orgeac0a69}]{License}
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\begin{itemize}
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\item License: \alert{Creative Commons Attribution 4.0 International License (CC-BY-4.0)}
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\item \url{https://creativecommons.org/licenses/by/4.0/}
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\end{itemize}
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\end{frame}
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\begin{frame}[fragile,label={sec:org071d481}]{Introduction}
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\begin{itemize}
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\item \texttt{GDB}: \texttt{GNU} project's Debugger \pause (it is \alert{not} a
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\emph{database}\ldots{}). Supports several programming languages.
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\item Started around 1986 by Richard Stallman (after \alert{GNU Emacs}, but
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likely before \alert{GCC}).
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\end{itemize}
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\end{frame}
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\begin{frame}[fragile,label={sec:org2d0fe11}]{Compiling your program for GDB}
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\begin{itemize}
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\item Your program needs to contain \alert{debug information} (also called
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\texttt{DWARF}) for GDB to consume.
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\end{itemize}
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\pause
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\begin{itemize}
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\item The GCC flag to include debug information is \texttt{-g}. We also use
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\texttt{-g3}, which includes information about macros (\texttt{\#define}).
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\end{itemize}
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\pause
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\begin{itemize}
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\item It's common to \alert{disable optimizations} when building the binary, by
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using the flag \texttt{-O0} (it's \emph{dash-oh-zero}).
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\pause
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\begin{itemize}
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\item \texttt{\# gcc -O0 -g program.c -o program}, \emph{or}
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\item \texttt{\# CFLAGS='-O0 -g' ./configure \&\& make}
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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,label={sec:org8bba82f}]{Running your program using GDB}
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\begin{itemize}
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\item In GDB's parlance, the program being debugged is called the
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\alert{inferior}.
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\end{itemize}
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\pause
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\begin{itemize}
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\item Some ways to start the debugger:
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\pause
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\begin{itemize}
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\item \texttt{\# gdb ./program}
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\end{itemize}
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\pause
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\begin{itemize}
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\item \texttt{\# gdb -{}-args ./program arg1 arg2}
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\end{itemize}
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\pause
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\begin{itemize}
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\item \texttt{\# gdb} \\
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\texttt{(gdb) file ./program} \\
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\texttt{(gdb) run arg1 arg2}
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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,label={sec:org5c690dd}]{\{Break,Catch,Watch\}points}
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\begin{itemize}
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\item A \alert{breakpoint} is related to \emph{source code} (location, function). A
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\alert{watchpoint} is related to \emph{data} (read/write of a variable). A
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\alert{catchpoint} is related to an \emph{event} (enter/exit a syscall, fork,
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receive a signal).
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\end{itemize}
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\pause
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\begin{itemize}
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\item Breakpoints (\emph{code})
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\begin{itemize}
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\item \texttt{break}
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\item \texttt{tbreak} (temporary)
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\end{itemize}
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\end{itemize}
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\pause
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\begin{itemize}
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\item Watchpoints (\emph{data})
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\begin{itemize}
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\item \texttt{watch} (write), \texttt{rwatch} (read), \texttt{awatch} (access)
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\item Conditional watchpoints are supported.
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\end{itemize}
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\end{itemize}
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\pause
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\begin{itemize}
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\item Catchpoints (\emph{events})
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\begin{itemize}
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\item \texttt{catch fork}
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\item \texttt{catch syscall}
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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,label={sec:orgfc53d4a}]{Resuming the execution}
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\begin{itemize}
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\item After GDB has stopped the inferior (because a \texttt{*point} has been hit,
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for example), you will probably want to resume its execution.
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\end{itemize}
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\pause
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\begin{itemize}
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\item You may just want to continue the program:
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\begin{itemize}
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\item \texttt{continue}
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\end{itemize}
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\end{itemize}
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\pause
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\begin{itemize}
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\item Or maybe go to the next statement/instruction:
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\begin{itemize}
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\item \texttt{next} (\emph{statement}), or \texttt{nexti} (\emph{instruction})
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\end{itemize}
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\end{itemize}
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\pause
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\begin{itemize}
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\item Or step into a function:
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\begin{itemize}
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\item \texttt{step} (\emph{statement}), or \texttt{stepi} (\emph{instruction})
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\end{itemize}
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\end{itemize}
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\pause
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\begin{itemize}
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\item Or finish executing the current function, but stop at the end:
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\begin{itemize}
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\item \texttt{finish}
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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,label={sec:org9dcb344}]{Examining data}
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\begin{itemize}
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\item The inferior has stopped\ldots{} Now what?
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\end{itemize}
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\pause
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\begin{itemize}
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\item You may want to print the value of some variable:
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\begin{itemize}
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\item \texttt{print VAR}
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\end{itemize}
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\end{itemize}
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\pause
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\begin{itemize}
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\item Or examine a memory location:
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\begin{itemize}
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\item \texttt{x ADDRESS}
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\end{itemize}
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\end{itemize}
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\pause
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\begin{itemize}
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\item The type of a variable? Easy:
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\begin{itemize}
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\item \texttt{whatis VARIABLE}
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\end{itemize}
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\end{itemize}
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\pause
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\begin{itemize}
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\item Hint: you may want to enable pretty-printing:
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\begin{itemize}
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\item \texttt{set print pretty on}
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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,label={sec:orga54b38a}]{Examining the code}
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\begin{itemize}
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\item Yes, we have \texttt{ncurses}! The \textbf{T}ext
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\textbf{U}user \textbf{I}nterface!
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\begin{itemize}
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\item \texttt{C-x a} (that's \texttt{CTRL x a}).
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\end{itemize}
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\end{itemize}
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\pause
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\begin{itemize}
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\item If you want to list the current region, or if you don't want/can't
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to use TUI:
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\begin{itemize}
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\item \texttt{list}
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\end{itemize}
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\end{itemize}
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\pause
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\begin{itemize}
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\item You can also disassemble code:
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\begin{itemize}
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\item \texttt{disassemble}
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\end{itemize}
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\end{itemize}
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\pause
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\begin{itemize}
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\item If GDB can't find the source code, you can specify its location
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using the \texttt{dir} command.
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\end{itemize}
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\end{frame}
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\begin{frame}[fragile,label={sec:orgab39cfc}]{Examining the call stack}
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\begin{itemize}
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\item If you want to see the call stack (A.K.A. stack trace) that lead to
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the current function:
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\begin{itemize}
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\item \texttt{bt}
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\end{itemize}
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\end{itemize}
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\pause
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\begin{itemize}
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\item And you can move through it:
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\begin{itemize}
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\item \texttt{up} and \texttt{down}
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\item You can also go to a specific frame: \texttt{frame NUMBER}
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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,label={sec:org66fa673}]{Corefiles}
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\begin{itemize}
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\item \alert{Corefiles} are frozen images of the inferior. You can inspect
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everything that was happening when the process was running (but you
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can't resurrect it).
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\end{itemize}
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\pause
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\begin{itemize}
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\item You can generate them \emph{outside} GDB, when a program crashes. Make
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sure you:
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\begin{itemize}
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\item \texttt{ulimit -c unlimited}
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\item Check if \texttt{systemd} is handling them
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(\texttt{/proc/sys/kernel/core\_pattern}).
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\end{itemize}
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\end{itemize}
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\pause
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\begin{itemize}
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\item You can also generate them \emph{inside} GDB, at any moment:
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\begin{itemize}
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\item \texttt{generate-core-file}
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\end{itemize}
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\end{itemize}
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\pause
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\begin{itemize}
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\item You can open a corefile using GDB:
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\begin{itemize}
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\item \texttt{\# gdb program -c corefile.PID}
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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,label={sec:orgb366da5}]{Other interesting information}
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\begin{itemize}
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\item \texttt{info breakpoints}
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\item \texttt{info locals}
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\item \texttt{info registers}
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\item Many others!
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\end{itemize}
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\end{frame}
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\begin{frame}[fragile,label={sec:org6c7407d}]{Who you gonna call?}
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\begin{itemize}
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\item Our online documentation (\texttt{info}) is very good!
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\item Every command has a \texttt{help}.
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\item You can also use \texttt{apropos} when searching for a term.
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\item \texttt{TAB}-completion is also useful.
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\end{itemize}
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\end{frame}
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\begin{frame}[label={sec:org9103f37}]{Other advanced features}
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\begin{itemize}
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\item Python support.
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\item Reverse debugging.
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\item Support for \emph{SystemTap SDT probes}.
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\end{itemize}
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\end{frame}
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\begin{frame}[label={sec:org462e66a}]{Thank you}
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\begin{itemize}
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\item Thanks to Red Hat for the support.
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\item Thanks to Paul Nijjar and Bob Jonkman for the invitation.
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\item Thanks to you for watching!
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\end{itemize}
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\end{frame}
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\end{document}
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