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<ol class="chapter"><li class="chapter-item expanded affix "><a href="../intro.html">Introduction</a></li><li class="chapter-item expanded "><a href="../tools/index.html"><strong aria-hidden="true">1.</strong> Tools</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../tools/zsh.html"><strong aria-hidden="true">1.1.</strong> zsh</a></li><li class="chapter-item expanded "><a href="../tools/bash.html"><strong aria-hidden="true">1.2.</strong> bash</a></li><li class="chapter-item expanded "><a href="../tools/fish.html"><strong aria-hidden="true">1.3.</strong> fish</a></li><li class="chapter-item expanded "><a href="../tools/tmux.html"><strong aria-hidden="true">1.4.</strong> tmux</a></li><li class="chapter-item expanded "><a href="../tools/git.html"><strong aria-hidden="true">1.5.</strong> git</a></li><li class="chapter-item expanded "><a href="../tools/awk.html"><strong aria-hidden="true">1.6.</strong> awk</a></li><li class="chapter-item expanded "><a href="../tools/emacs.html"><strong aria-hidden="true">1.7.</strong> emacs</a></li><li class="chapter-item expanded "><a href="../tools/gpg.html"><strong aria-hidden="true">1.8.</strong> gpg</a></li><li class="chapter-item expanded "><a href="../tools/gdb.html" class="active"><strong aria-hidden="true">1.9.</strong> gdb</a></li><li class="chapter-item expanded "><a href="../tools/gdbserver.html"><strong aria-hidden="true">1.10.</strong> gdbserver</a></li><li class="chapter-item expanded "><a href="../tools/radare2.html"><strong aria-hidden="true">1.11.</strong> radare2</a></li><li class="chapter-item expanded "><a href="../tools/qemu.html"><strong aria-hidden="true">1.12.</strong> qemu</a></li><li class="chapter-item expanded "><a href="../tools/pacman.html"><strong aria-hidden="true">1.13.</strong> pacman</a></li><li class="chapter-item expanded "><a href="../tools/dot.html"><strong aria-hidden="true">1.14.</strong> dot</a></li></ol></li><li class="chapter-item expanded "><a href="../monitor/index.html"><strong aria-hidden="true">2.</strong> Resource analysis & monitor</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../monitor/lsof.html"><strong aria-hidden="true">2.1.</strong> lsof</a></li><li class="chapter-item expanded "><a href="../monitor/ss.html"><strong aria-hidden="true">2.2.</strong> ss</a></li><li class="chapter-item expanded "><a href="../monitor/pidstat.html"><strong aria-hidden="true">2.3.</strong> pidstat</a></li><li class="chapter-item expanded "><a href="../monitor/pgrep.html"><strong aria-hidden="true">2.4.</strong> pgrep</a></li><li class="chapter-item expanded "><a href="../monitor/pmap.html"><strong aria-hidden="true">2.5.</strong> pmap</a></li><li class="chapter-item expanded "><a href="../monitor/pstack.html"><strong aria-hidden="true">2.6.</strong> pstack</a></li></ol></li><li class="chapter-item expanded "><a href="../trace_profile/index.html"><strong aria-hidden="true">3.</strong> Trace and Profile</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../trace_profile/strace.html"><strong aria-hidden="true">3.1.</strong> strace</a></li><li class="chapter-item expanded "><a href="../trace_profile/ltrace.html"><strong aria-hidden="true">3.2.</strong> ltrace</a></li><li class="chapter-item expanded "><a href="../trace_profile/perf.html"><strong aria-hidden="true">3.3.</strong> perf</a></li><li class="chapter-item expanded "><a href="../trace_profile/oprofile.html"><strong aria-hidden="true">3.4.</strong> OProfile</a></li><li class="chapter-item expanded "><a href="../trace_profile/time.html"><strong aria-hidden="true">3.5.</strong> time</a></li></ol></li><li class="chapter-item expanded "><a href="../binary/index.html"><strong aria-hidden="true">4.</strong> Binary</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../binary/od.html"><strong aria-hidden="true">4.1.</strong> od</a></li><li class="chapter-item expanded "><a href="../binary/xxd.html"><strong aria-hidden="true">4.2.</strong> xxd</a></li><li class="chapter-item expanded "><a href="../binary/readelf.html"><strong aria-hidden="true">4.3.</strong> readelf</a></li><li class="chapter-item expanded "><a href="../binary/objdump.html"><strong aria-hidden="true">4.4.</strong> objdump</a></li><li class="chapter-item expanded "><a href="../binary/nm.html"><strong aria-hidden="true">4.5.</strong> nm</a></li></ol></li><li class="chapter-item expanded "><a href="../development/index.html"><strong aria-hidden="true">5.</strong> Development</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../development/c++filt.html"><strong aria-hidden="true">5.1.</strong> c++filt</a></li><li class="chapter-item expanded "><a href="../development/c++.html"><strong aria-hidden="true">5.2.</strong> c++</a></li><li class="chapter-item expanded "><a href="../development/glibc.html"><strong aria-hidden="true">5.3.</strong> glibc</a></li><li class="chapter-item expanded "><a href="../development/gcc.html"><strong aria-hidden="true">5.4.</strong> gcc</a></li><li class="chapter-item expanded "><a href="../development/make.html"><strong aria-hidden="true">5.5.</strong> make</a></li><li class="chapter-item expanded "><a href="../development/ld.so.html"><strong aria-hidden="true">5.6.</strong> ld.so</a></li><li class="chapter-item expanded "><a href="../development/symbolver.html"><strong aria-hidden="true">5.7.</strong> symbol versioning</a></li><li class="chapter-item expanded "><a href="../development/python.html"><strong aria-hidden="true">5.8.</strong> python</a></li></ol></li><li class="chapter-item expanded "><a href="../linux/index.html"><strong aria-hidden="true">6.</strong> Linux</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../linux/systemd.html"><strong aria-hidden="true">6.1.</strong> systemd</a></li><li class="chapter-item expanded "><a href="../linux/coredump.html"><strong aria-hidden="true">6.2.</strong> coredump</a></li><li class="chapter-item expanded "><a href="../linux/ptrace_scope.html"><strong aria-hidden="true">6.3.</strong> ptrace_scope</a></li><li class="chapter-item expanded "><a href="../linux/cryptsetup.html"><strong aria-hidden="true">6.4.</strong> cryptsetup</a></li><li class="chapter-item expanded "><a href="../linux/swap.html"><strong aria-hidden="true">6.5.</strong> swap</a></li></ol></li><li class="chapter-item expanded "><a href="../network/index.html"><strong aria-hidden="true">7.</strong> Network</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../network/tcpdump.html"><strong aria-hidden="true">7.1.</strong> tcpdump</a></li></ol></li><li class="chapter-item expanded "><a href="../web/index.html"><strong aria-hidden="true">8.</strong> Web</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../web/html.html"><strong aria-hidden="true">8.1.</strong> html</a></li></ol></li><li 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<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
</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"> 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.
</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>.
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.
</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="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.
</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="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 follow-fork-mode <child | parent>
Specify which process to follow when debuggee makes a fork(2)
syscall.
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 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.
</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 if i == 7
</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>
<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>
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