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</script> + + <input type="checkbox" id="sidebar-toggle-anchor" class="hidden"> + + <!-- Hide / unhide sidebar before it is displayed --> + <script> + var body = document.querySelector('body'); + var sidebar = null; + var sidebar_toggle = document.getElementById("sidebar-toggle-anchor"); + if (document.body.clientWidth >= 1080) { + try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { } + sidebar = sidebar || 'visible'; + } else { + sidebar = 'hidden'; + } + sidebar_toggle.checked = sidebar === 'visible'; + body.classList.remove('sidebar-visible'); + body.classList.add("sidebar-" + sidebar); + </script> + + <nav id="sidebar" class="sidebar" aria-label="Table of contents"> + <div class="sidebar-scrollbox"> + <ol class="chapter"><li class="chapter-item expanded affix "><a href="../intro.html">Introduction</a></li><li class="chapter-item expanded "><a href="../shells/index.html"><strong aria-hidden="true">1.</strong> Shells</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../shells/zsh.html"><strong aria-hidden="true">1.1.</strong> zsh</a></li><li class="chapter-item expanded "><a href="../shells/bash.html"><strong aria-hidden="true">1.2.</strong> bash</a></li><li class="chapter-item expanded "><a href="../shells/fish.html"><strong aria-hidden="true">1.3.</strong> fish</a></li></ol></li><li class="chapter-item expanded "><a href="../cli/index.html"><strong aria-hidden="true">2.</strong> CLI foo</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../cli/awk.html"><strong aria-hidden="true">2.1.</strong> awk</a></li><li class="chapter-item expanded "><a href="../cli/sed.html"><strong aria-hidden="true">2.2.</strong> sed</a></li><li class="chapter-item expanded "><a href="../cli/column.html"><strong aria-hidden="true">2.3.</strong> column</a></li><li class="chapter-item expanded "><a href="../cli/sort.html"><strong aria-hidden="true">2.4.</strong> sort</a></li><li class="chapter-item expanded "><a href="../cli/tr.html"><strong aria-hidden="true">2.5.</strong> tr</a></li></ol></li><li class="chapter-item expanded "><a href="../tools/index.html"><strong aria-hidden="true">3.</strong> Tools</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../tools/tmux.html"><strong aria-hidden="true">3.1.</strong> tmux</a></li><li class="chapter-item expanded "><a href="../tools/emacs.html"><strong aria-hidden="true">3.2.</strong> emacs</a></li><li class="chapter-item expanded "><a href="../tools/gpg.html"><strong aria-hidden="true">3.3.</strong> gpg</a></li><li class="chapter-item expanded "><a href="../tools/radare2.html"><strong aria-hidden="true">3.4.</strong> radare2</a></li><li class="chapter-item expanded "><a href="../tools/qemu.html"><strong aria-hidden="true">3.5.</strong> qemu</a></li><li class="chapter-item expanded "><a href="../tools/pacman.html"><strong aria-hidden="true">3.6.</strong> pacman</a></li><li class="chapter-item expanded "><a href="../tools/dot.html"><strong aria-hidden="true">3.7.</strong> dot</a></li><li class="chapter-item expanded "><a href="../tools/ffmpeg.html"><strong aria-hidden="true">3.8.</strong> ffmpeg</a></li><li class="chapter-item expanded "><a href="../tools/gnuplot.html"><strong aria-hidden="true">3.9.</strong> gnuplot</a></li><li class="chapter-item expanded "><a href="../tools/restic.html"><strong aria-hidden="true">3.10.</strong> restic</a></li></ol></li><li class="chapter-item expanded "><a href="../monitor/index.html"><strong aria-hidden="true">4.</strong> Resource analysis & monitor</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../monitor/lsof.html"><strong aria-hidden="true">4.1.</strong> lsof</a></li><li class="chapter-item expanded "><a href="../monitor/pidstat.html"><strong aria-hidden="true">4.2.</strong> pidstat</a></li><li class="chapter-item expanded "><a href="../monitor/pgrep.html"><strong aria-hidden="true">4.3.</strong> pgrep</a></li><li class="chapter-item expanded "><a href="../monitor/ps.html"><strong aria-hidden="true">4.4.</strong> ps</a></li><li class="chapter-item expanded "><a href="../monitor/pmap.html"><strong aria-hidden="true">4.5.</strong> pmap</a></li><li class="chapter-item expanded "><a href="../monitor/pstack.html"><strong aria-hidden="true">4.6.</strong> pstack</a></li></ol></li><li class="chapter-item expanded "><a href="../trace_profile/index.html"><strong aria-hidden="true">5.</strong> Trace and Profile</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../trace_profile/time.html"><strong aria-hidden="true">5.1.</strong> time</a></li><li class="chapter-item expanded "><a href="../trace_profile/strace.html"><strong aria-hidden="true">5.2.</strong> strace</a></li><li class="chapter-item expanded "><a href="../trace_profile/ltrace.html"><strong aria-hidden="true">5.3.</strong> ltrace</a></li><li class="chapter-item expanded "><a href="../trace_profile/perf.html"><strong aria-hidden="true">5.4.</strong> perf</a></li><li class="chapter-item expanded "><a href="../trace_profile/oprofile.html"><strong aria-hidden="true">5.5.</strong> OProfile</a></li><li class="chapter-item expanded "><a href="../trace_profile/callgrind.html"><strong aria-hidden="true">5.6.</strong> callgrind</a></li></ol></li><li class="chapter-item expanded "><a href="../debug/index.html"><strong aria-hidden="true">6.</strong> Debug</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../debug/gdb.html" class="active"><strong aria-hidden="true">6.1.</strong> gdb</a></li><li class="chapter-item expanded "><a href="../debug/gdbserver.html"><strong aria-hidden="true">6.2.</strong> gdbserver</a></li></ol></li><li class="chapter-item expanded "><a href="../binary/index.html"><strong aria-hidden="true">7.</strong> Binary</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../binary/od.html"><strong aria-hidden="true">7.1.</strong> od</a></li><li class="chapter-item expanded "><a href="../binary/xxd.html"><strong aria-hidden="true">7.2.</strong> xxd</a></li><li class="chapter-item expanded "><a href="../binary/readelf.html"><strong aria-hidden="true">7.3.</strong> readelf</a></li><li class="chapter-item expanded "><a href="../binary/objdump.html"><strong aria-hidden="true">7.4.</strong> objdump</a></li><li class="chapter-item expanded "><a href="../binary/nm.html"><strong aria-hidden="true">7.5.</strong> nm</a></li></ol></li><li class="chapter-item expanded "><a href="../development/index.html"><strong aria-hidden="true">8.</strong> Development</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../development/c++filt.html"><strong aria-hidden="true">8.1.</strong> c++filt</a></li><li class="chapter-item expanded "><a href="../development/c++.html"><strong aria-hidden="true">8.2.</strong> c++</a></li><li class="chapter-item expanded "><a href="../development/glibc.html"><strong aria-hidden="true">8.3.</strong> glibc</a></li><li class="chapter-item expanded "><a href="../development/gcc.html"><strong aria-hidden="true">8.4.</strong> gcc</a></li><li class="chapter-item expanded "><a href="../development/git.html"><strong aria-hidden="true">8.5.</strong> git</a></li><li class="chapter-item expanded "><a href="../development/cmake.html"><strong aria-hidden="true">8.6.</strong> cmake</a></li><li class="chapter-item expanded "><a href="../development/make.html"><strong aria-hidden="true">8.7.</strong> make</a></li><li class="chapter-item expanded "><a href="../development/ld.so.html"><strong aria-hidden="true">8.8.</strong> ld.so</a></li><li class="chapter-item expanded "><a href="../development/symbolver.html"><strong aria-hidden="true">8.9.</strong> symbol versioning</a></li><li class="chapter-item expanded "><a href="../development/python.html"><strong aria-hidden="true">8.10.</strong> python</a></li><li class="chapter-item expanded "><a href="../development/gcov.html"><strong aria-hidden="true">8.11.</strong> gcov</a></li><li class="chapter-item expanded "><a href="../development/pgo.html"><strong aria-hidden="true">8.12.</strong> pgo</a></li></ol></li><li class="chapter-item expanded "><a href="../linux/index.html"><strong aria-hidden="true">9.</strong> Linux</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../linux/systemd.html"><strong aria-hidden="true">9.1.</strong> systemd</a></li><li class="chapter-item expanded "><a href="../linux/coredump.html"><strong aria-hidden="true">9.2.</strong> coredump</a></li><li class="chapter-item expanded "><a href="../linux/ptrace_scope.html"><strong aria-hidden="true">9.3.</strong> ptrace_scope</a></li><li class="chapter-item expanded "><a href="../linux/cryptsetup.html"><strong aria-hidden="true">9.4.</strong> cryptsetup</a></li><li class="chapter-item expanded "><a href="../linux/swap.html"><strong aria-hidden="true">9.5.</strong> swap</a></li><li class="chapter-item expanded "><a href="../linux/input.html"><strong aria-hidden="true">9.6.</strong> input</a></li><li class="chapter-item expanded "><a href="../linux/acl.html"><strong aria-hidden="true">9.7.</strong> acl</a></li><li class="chapter-item expanded "><a href="../linux/zfs.html"><strong aria-hidden="true">9.8.</strong> zfs</a></li></ol></li><li class="chapter-item expanded "><a href="../network/index.html"><strong aria-hidden="true">10.</strong> Network</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../network/ss.html"><strong aria-hidden="true">10.1.</strong> ss</a></li><li class="chapter-item expanded "><a href="../network/tcpdump.html"><strong aria-hidden="true">10.2.</strong> tcpdump</a></li><li class="chapter-item expanded "><a href="../network/tshark.html"><strong aria-hidden="true">10.3.</strong> tshark</a></li><li class="chapter-item expanded "><a href="../network/firewall-cmd.html"><strong aria-hidden="true">10.4.</strong> firewall-cmd</a></li><li class="chapter-item expanded "><a href="../network/nftables.html"><strong aria-hidden="true">10.5.</strong> nftables</a></li></ol></li><li class="chapter-item expanded "><a href="../web/index.html"><strong aria-hidden="true">11.</strong> Web</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../web/html.html"><strong aria-hidden="true">11.1.</strong> html</a></li><li class="chapter-item expanded "><a href="../web/css.html"><strong aria-hidden="true">11.2.</strong> css</a></li><li class="chapter-item expanded "><a href="../web/chartjs.html"><strong aria-hidden="true">11.3.</strong> chartjs</a></li></ol></li><li class="chapter-item expanded "><a href="../arch/index.html"><strong aria-hidden="true">12.</strong> Arch</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../arch/x86_64.html"><strong aria-hidden="true">12.1.</strong> x86_64</a></li><li class="chapter-item expanded "><a href="../arch/armv8.html"><strong aria-hidden="true">12.2.</strong> armv8</a></li><li class="chapter-item expanded "><a href="../arch/arm64.html"><strong aria-hidden="true">12.3.</strong> arm64</a></li><li class="chapter-item expanded "><a href="../arch/armv7.html"><strong aria-hidden="true">12.4.</strong> armv7</a></li><li class="chapter-item expanded "><a href="../arch/riscv.html"><strong aria-hidden="true">12.5.</strong> riscv</a></li></ol></li></ol> + </div> + <div id="sidebar-resize-handle" class="sidebar-resize-handle"> + <div class="sidebar-resize-indicator"></div> + </div> + </nav> + + <!-- Track and set sidebar scroll position --> + <script> + var sidebarScrollbox = document.querySelector('#sidebar .sidebar-scrollbox'); + sidebarScrollbox.addEventListener('click', function(e) { + if (e.target.tagName === 'A') { + sessionStorage.setItem('sidebar-scroll', sidebarScrollbox.scrollTop); + } + }, { passive: true }); + var sidebarScrollTop = sessionStorage.getItem('sidebar-scroll'); + 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(Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar"> + <i class="fa fa-search"></i> + </button> + </div> + + <h1 class="menu-title">Notes</h1> + + <div class="right-buttons"> + <a href="../print.html" title="Print this book" aria-label="Print this book"> + <i id="print-button" class="fa fa-print"></i> + </a> + <a href="https://github.com/johannst/notes" title="Git repository" aria-label="Git repository"> + <i id="git-repository-button" class="fa fa-github"></i> + </a> + + </div> + </div> + + <div id="search-wrapper" class="hidden"> + <form id="searchbar-outer" class="searchbar-outer"> + <input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header"> + </form> + <div id="searchresults-outer" class="searchresults-outer hidden"> + <div id="searchresults-header" class="searchresults-header"></div> + <ul id="searchresults"> + </ul> + </div> + </div> + + <!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM --> + <script> + document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible'); + document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible'); + Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) { + link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1); + }); + </script> + + <div id="content" class="content"> + <main> + <h1 id="gdb1"><a class="header" href="#gdb1">gdb(1)</a></h1> +<h1 id="cli"><a class="header" href="#cli">CLI</a></h1> +<pre><code class="language-markdown"> gdb [opts] [prg [-c coredump | -p pid]] + gdb [opts] --args prg <prg-args> + opts: + -p <pid> attach to pid + -c <coredump> use <coredump> + -x <file> execute script <file> before prompt + -ex <cmd> execute command <cmd> before prompt + --tty <tty> set I/O tty for debugee + --batch run in batch mode, exit after processing options (eg used + for scripting) + --batch-silent link --batch, but surpress gdb stdout +</code></pre> +<h1 id="interactive-usage"><a class="header" href="#interactive-usage">Interactive usage</a></h1> +<h2 id="misc"><a class="header" href="#misc">Misc</a></h2> +<pre><code class="language-markdown"> apropos <regex> + Search commands matching regex. + + tty <tty> + Set <tty> as tty for debugee. + Make sure nobody reads from target tty, easiest is to spawn a shell + and run following in target tty: + > while true; do sleep 1024; done + + sharedlibrary [<regex>] + Load symbols of shared libs loaded by debugee. Optionally use <regex> + to filter libs for symbol loading. + + display [/FMT] <expr> + Print <expr> every time debugee stops. Eg print next instr, see + examples below. + + undisplay [<num>] + Delete display expressions either all or one referenced by <num>. + + info display + List display expressions. + + info sharedlibrary [<regex>] + List shared libraries loaded. Optionally use <regex> to filter. +</code></pre> +<h2 id="breakpoints"><a class="header" href="#breakpoints">Breakpoints</a></h2> +<pre><code class="language-markdown"> break [-qualified] <sym> thread <tnum> + Set a breakpoint only for a specific thread. + -qualified: Treat <sym> as fully qualified symbol (quiet handy to set + breakpoints on C symbols in C++ contexts) + + break <sym> if <cond> + Set conditional breakpoint (see examples below). + + delete [<num>] + Delete breakpoint either all or one referenced by <num>. + + info break + List breakpoints. + + cond <bp> <cond> + Make existing breakpoint <bp> conditional with <cond>. + + cond <bp> + Remove condition from breakpoint <bp>. + + tbreak + Set temporary breakpoint, will be deleted when hit. + Same syntax as `break`. + + rbreak <regex> + Set breakpoints matching <regex>, where matching internally is done + on: .*<regex>.* + + command [<bp_list>] + Define commands to run after breakpoint hit. If <bp_list> is not + specified attach command to last created breakpoint. Command block + terminated with 'end' token. + + <bp_list>: Space separates list, eg 'command 2 5-8' to run command + for breakpoints: 2,5,6,7,8. + + save break <file> + Save breakpoints to <file>. Can be loaded with the `source` command. +</code></pre> +<h2 id="watchpoints"><a class="header" href="#watchpoints">Watchpoints</a></h2> +<pre><code class="language-markdown"> watch [-location|-l] <expr> [thread <tnum>] + Create a watchpoint for <expr>, will break if <expr> is written to. + Watchpoints respect scope of variables, -l can be used to watch the + memory location instead. + + rwatch ... + Sets a read watchpoint, will break if <expr> is read from. + + awatch ... + Sets an access watchpoint, will break if <expr> is written to or read + from. +</code></pre> +<h2 id="catchpoints"><a class="header" href="#catchpoints">Catchpoints</a></h2> +<pre><code class="language-markdown"> catch load [<regex>] + Stop when shared libraries are loaded, optionally specify a <regex> + to stop only on matches. + catch unload [<regex>] + Stop when shared libraries are unloaded, optionally specify a <regex> + to stop only on matches. + + catch throw + Stop when an exception is thrown. + catch rethrow + Stop when an exception is rethrown. + catch catch + Stop when an exception is caught. + + catch fork + Stop at calls to fork (also stops at clones, as some systems + implement fork via clone). + + catch syscall [<syscall> <syscall> ..] + Stop at syscall. If no argument is given, stop at all syscalls. + Optionally give a list of syscalls to stop at. +</code></pre> +<h2 id="inspection"><a class="header" href="#inspection">Inspection</a></h2> +<pre><code class="language-markdown"> info functions [<regex>] + List functions matching <regex>. List all functions if no <regex> + provided. + + info variables [<regex>] + List variables matching <regex>. List all variables if no <regex> + provided. + + info register [<reg> <reg> ..] + Dump content of all registers or only the specified <reg>ister. +</code></pre> +<h2 id="signal-handling"><a class="header" href="#signal-handling">Signal handling</a></h2> +<pre><code class="language-markdown"> info handle [<signal>] + Print how to handle <signal>. If no <signal> specified print for all + signals. + + handle <signal> <action> + Configure how gdb handles <signal> sent to debugee. + <action>: + stop/nostop Catch signal in gdb and break. + print/noprint Print message when gdb catches signal. + pass/nopass Pass signal down to debugee. + + catch signal <signal> + Create a catchpoint for <signal>. +</code></pre> +<h2 id="multi-threading"><a class="header" href="#multi-threading">Multi-threading</a></h2> +<pre><code class="language-markdown">info thread + List all threads. + +thread apply <id> [<id>] <command> + Run command on all threads listed by <id> (space separated list). + When 'all' is specified as <id> the <command> is run on all threads. + +thread name <name> + The <name> for the current thread. +</code></pre> +<h2 id="multi-process"><a class="header" href="#multi-process">Multi-process</a></h2> +<pre><code class="language-markdown"> set follow-fork-mode <child | parent> + Specify which process to follow when debuggee makes a fork(2) + syscall. + + set detach-on-fork <on | off> + Turn on/off detaching from new child processes (on by default). + Turning this off allows to debug multiple processes (inferiors) with + one gdb session. + + info inferiors + List all processes gdb debugs. + + inferior <id> + Switch to inferior with <id>. +</code></pre> +<h2 id="scheduling"><a class="header" href="#scheduling">Scheduling</a></h2> +<pre><code class="language-markdown"> set schedule-multiple <on | off> + on: Resume all threads of all processes (inferiors) when continuing + or stepping. + off: (default) Resume only threads of current process (inferior). +</code></pre> +<h2 id="shell-commands"><a class="header" href="#shell-commands">Shell commands</a></h2> +<pre><code class="language-markdown"> shell <shell_cmd> + Run the shell_cmd and print the output, can also contain a pipeline. + + pipe <gdb_cmd> | <shell_cmd> + Evaluate the gdb_cmd and run the shell_cmd which receives the output + of the gdb_cmd via stdin. +</code></pre> +<h2 id="source-file-locations"><a class="header" href="#source-file-locations">Source file locations</a></h2> +<pre><code class="language-markdown"> dir <path> + Add <path> to the beginning of the searh path for source files. + + show dir + Show current search path. + + set substitute-path <from> <to> + Add substitution rule checked during source file lookup. + + show substitute-path + Show current substitution rules. +</code></pre> +<h2 id="configuration"><a class="header" href="#configuration">Configuration</a></h2> +<pre><code class="language-markdown"> set disassembly-flavor <intel | att> + Set the disassembly style "flavor". + + set pagination <on | off> + Turn on/off gdb's pagination. + + set breakpoint pending <on | off | auto> + on: always set pending breakpoints. + off: error when trying to set pending breakpoints. + auto: interatively query user to set breakpoint. + + set print pretty <on | off> + Turn on/off pertty printing of structures. + + set style enabled <on | off> + Turn on/off styling (eg colored output). + + set logging <on | off> + Enable output logging to file (default gdb.txt). + + set logging file <fname> + Change output log file to <fname> + + set logging redirect <on | off> + on: only log to file. + off: log to file and tty. + + set logging overwrite <on | off> + on: Truncate log file on each run. + off: Append to logfile (default). + + set history filename <fname> + Change file where to save and restore command history to and from. + + set history <on | off> + Enable or disable saving of command history. +</code></pre> +<blockquote> +<p>Logging options should be configured before logging is turned on.</p> +</blockquote> +<h1 id="text-user-interface-tui"><a class="header" href="#text-user-interface-tui">Text user interface (TUI)</a></h1> +<pre><code class="language-markdown"> C-x a Toggle UI. + C-l Redraw UI (curses UI can be messed up after the debugee prints to + stdout/stderr). + C-x o Change focus. +</code></pre> +<h1 id="user-commands-macros"><a class="header" href="#user-commands-macros">User commands (macros)</a></h1> +<p>Gdb allows to create & document user commands as follows:</p> +<pre><code class="language-markdown"> define <cmd> + # cmds + end + + document <cmd> + # docu + end +</code></pre> +<p>To get all user commands or documentations one can use:</p> +<pre><code class="language-markdown"> help user-defined + help <cmd> +</code></pre> +<h1 id="hooks"><a class="header" href="#hooks">Hooks</a></h1> +<p>Gdb allows to create two types of command <code>hooks</code></p> +<ul> +<li><code>hook-</code> will be run before <code><cmd></code></li> +<li><code>hookpost-</code> will be run after <code><cmd></code></li> +</ul> +<pre><code class="language-markdown"> define hook-<cmd> + # cmds + end + + define hookpost-<cmd> + # cmds + end +</code></pre> +<h1 id="examples"><a class="header" href="#examples">Examples</a></h1> +<h2 id="automatically-print-next-instr"><a class="header" href="#automatically-print-next-instr">Automatically print next instr</a></h2> +<p>When ever the debugee stops automatically print the memory at the current +instruction pointer (<code>$rip</code> x86) and format as instruction <code>/i</code>.</p> +<pre><code class="language-markdown"> # rip - x86 + display /i $rip + + # step instruction, after the step the next instruction is automatically printed + si +</code></pre> +<h2 id="conditional-breakpoints"><a class="header" href="#conditional-breakpoints">Conditional breakpoints</a></h2> +<p>Create conditional breakpoints for a function <code>void foo(int i)</code> in the debugee.</p> +<pre><code class="language-markdown"> # Create conditional breakpoint + b foo if i == 42 + + b foo # would create bp 2 + # Make existing breakpoint conditional + cond 2 i == 7 +</code></pre> +<h2 id="set-breakpoint-on-all-threads-except-one"><a class="header" href="#set-breakpoint-on-all-threads-except-one">Set breakpoint on all threads except one</a></h2> +<p>Create conditional breakpoint using the <code>$_thread</code> <a href="https://sourceware.org/gdb/onlinedocs/gdb/Convenience-Vars.html#Convenience-Vars">convenience +variable</a>.</p> +<pre><code class="language-markdown"> # Create conditional breakpoint on all threads except thread 12. + b foo if $_thread != 12 +</code></pre> +<h2 id="catch-sigsegv-and-execute-commands"><a class="header" href="#catch-sigsegv-and-execute-commands">Catch SIGSEGV and execute commands</a></h2> +<p>This creates a <code>catchpoint</code> for the <code>SIGSEGV</code> signal and attached the <code>command</code> +to it.</p> +<pre><code class="language-markdown"> catch signal SIGSEGV + command + bt + c + end +</code></pre> +<h2 id="run-backtrace-on-thread-1-batch-mode"><a class="header" href="#run-backtrace-on-thread-1-batch-mode">Run <code>backtrace</code> on thread 1 (batch mode)</a></h2> +<pre><code class="language-markdown"> gdb --batch -ex 'thread 1' -ex 'bt' -p <pid> +</code></pre> +<h2 id="script-gdb-for-automating-debugging-sessions"><a class="header" href="#script-gdb-for-automating-debugging-sessions">Script gdb for automating debugging sessions</a></h2> +<p>To script gdb add commands into a file and pass it to gdb via <code>-x</code>. +For example create <code>run.gdb</code>:</p> +<pre><code class="language-markdown"> set pagination off + + break mmap + command + info reg rdi rsi rdx + bt + c + end + + #initial drop + c +</code></pre> +<p>This script can be used as:</p> +<pre><code class="language-markdown"> gdb --batch -x ./run.gdb -p <pid> +</code></pre> +<h2 id="hook-to-automatically-save-breakpoints-on-quit"><a class="header" href="#hook-to-automatically-save-breakpoints-on-quit">Hook to automatically save breakpoints on <code>quit</code></a></h2> +<pre><code class="language-markdown">define break-save + save breakpoint $arg0.gdb.bp +end +define break-load + source $arg0.gdb.bp +end + +define hook-quit + break-save quit +end +</code></pre> +<h2 id="watchpoint-on-struct--class-member"><a class="header" href="#watchpoint-on-struct--class-member">Watchpoint on struct / class member</a></h2> +<p>A symbolic watchpoint defined on a member variable for debugging is only valid +as long as the expression is in scope. Once out of scope the watchpoint gets +deleted.</p> +<p>When debugging some memory corruption we want to keep the watchpoint even the +expression goes out of scope to find the location that overrides the variable +and introduces the corruption.</p> +<pre><code class="language-markdown">(gdb) l +1 struct S { int v; }; +2 +3 void set(struct S* s, int v) { +4 s->v = v; +5 } +6 +7 int main() { +8 struct S s; +9 set(&s, 1); +10 set(&s, 2); +11 set(&s, 3); +... + +(gdb) s +set (s=0x7fffffffe594, v=1) at test.c:4 +4 s->v = v; + +# Define a new watchpoint on the member of the struct. The expression however +# is only valid in the current functions scope. + +(gdb) watch s->v +Hardware watchpoint 2: s->v + +(gdb) c +Hardware watchpoint 2: s->v +Old value = 0 +New value = 1 +set (s=0x7fffffffe594, v=1) at test.c:5 +5 } + +# The watchpoint gets deleted as soon as we leave the function scope. + +(gdb) c +Watchpoint 2 deleted because the program has left the block in +which its expression is valid. +main () at test.c:10 +10 set(&s, 2); + +# Define the watchpoint on the location of the object to watch. + +(gdb) watch -l s->v + +# This is equivalent to the following. + +(gdb) p &s->v +$1 = (int *) 0x7fffffffe594 + +# Define a watchpoint to the address of the member variable of the s instance. +# This of course only makes sense as long as the s instance is not moved in memory. + +(gdb) watch *0x7fffffffe594 +Hardware watchpoint 3: *0x7fffffffe594 + +(gdb) c +Hardware watchpoint 3: *0x7fffffffe594 +Old value = 1 +New value = 2 +set (s=0x7fffffffe594, v=2) at test.c:5 +5 } + +(gdb) c +Hardware watchpoint 3: *0x7fffffffe594 +Old value = 2 +New value = 3 +set (s=0x7fffffffe594, v=3) at test.c:5 +5 } +</code></pre> +<h2 id="shell-commands-1"><a class="header" href="#shell-commands-1">Shell commands</a></h2> +<pre><code class="language-markdown"># Run shell commands. + +(gdb) shell zcat /proc/config.gz | grep CONFIG_KVM= +CONFIG_KVM=m + +# Pipe gdb command to shell command. + +(gdb) pipe info proc mapping | grep libc + 0x7ffff7a1a000 0x7ffff7a42000 0x28000 0x0 r--p /usr/lib/libc.so.6 + 0x7ffff7a42000 0x7ffff7b9d000 0x15b000 0x28000 r-xp /usr/lib/libc.so.6 + 0x7ffff7b9d000 0x7ffff7bf2000 0x55000 0x183000 r--p /usr/lib/libc.so.6 + 0x7ffff7bf2000 0x7ffff7bf6000 0x4000 0x1d7000 r--p /usr/lib/libc.so.6 + 0x7ffff7bf6000 0x7ffff7bf8000 0x2000 0x1db000 rw-p /usr/lib/libc.so.6 +</code></pre> +<h1 id="know-bugs"><a class="header" href="#know-bugs">Know Bugs</a></h1> +<h2 id="workaround-command--finish-bug"><a class="header" href="#workaround-command--finish-bug">Workaround <code>command + finish</code> bug</a></h2> +<p>When using <code>finish</code> inside a <code>command</code> block, commands after <code>finish</code> are not +executed. To workaround that bug one can create a wrapper function which calls +<code>finish</code>.</p> +<pre><code class="language-markdown"> define handler + bt + finish + info reg rax + end + + command + handler + end +</code></pre> + + </main> + + <nav class="nav-wrapper" aria-label="Page navigation"> + <!-- Mobile navigation buttons --> + <a rel="prev" href="../debug/index.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> + <i class="fa fa-angle-left"></i> + </a> + + <a rel="next prefetch" href="../debug/gdbserver.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> + <i class="fa fa-angle-right"></i> + </a> + + <div style="clear: both"></div> + </nav> + </div> + </div> + + <nav class="nav-wide-wrapper" aria-label="Page navigation"> + <a rel="prev" href="../debug/index.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> + <i class="fa fa-angle-left"></i> + </a> + + <a rel="next prefetch" href="../debug/gdbserver.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> + <i class="fa fa-angle-right"></i> + </a> + </nav> + + </div> + + + + + <script> + window.playground_copyable = true; + </script> + + + <script src="../elasticlunr.min.js"></script> + <script src="../mark.min.js"></script> + <script src="../searcher.js"></script> + + <script src="../clipboard.min.js"></script> + <script src="../highlight.js"></script> + <script src="../book.js"></script> + + <!-- Custom JS scripts --> + + + </div> + </body> +</html> |