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https://github.com/cirosantilli/linux-kernel-module-cheat.git
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570 lines
36 KiB
HTML
570 lines
36 KiB
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<meta name="description" content="The perfect emulation setup to study and develop the <<linux-kernel>> v5.9.2, kernel modules, <<qemu-buildroot-setup,QEMU>>, <<gem5-buildroot-setup,gem5>> and x86_64, ARMv7 and ARMv8 <<userland-assembly,userland>> and <<baremetal-setup,baremetal>> assembly, <<c,ANSI C>>, <<cpp,C++>> and <<posix,POSIX>>. EVERYTHING is built from source. <<gdb>> and <<kgdb>> just work. Powered by <<about-the-qemu-buildroot-setup,Buildroot>> and <<about-the-baremetal-setup,crosstool-NG>>. Highly automated. Thoroughly documented. Automated <<test-this-repo,tests>>. "Tested" in an Ubuntu 20.04 host.">
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<title>Linux Kernel Module Cheat</title>
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</head>
|
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<body id="debug-the-emulator" class="article">
|
||
<div id="header">
|
||
<h1>Linux Kernel Module Cheat</h1>
|
||
</div>
|
||
<div id="content">
|
||
<div class="sect2">
|
||
<h3 id="debug-the-emulator"><a class="anchor" href="#debug-the-emulator"></a><a class="link" href="#debug-the-emulator">23.8. Debug the emulator</a></h3>
|
||
<div class="paragraph">
|
||
<p>When you start hacking QEMU or gem5, it is useful to see what is going on inside the emulator themselves.</p>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>This is of course trivial since they are just regular userland programs on the host, but we make it a bit easier with:</p>
|
||
</div>
|
||
<div class="literalblock">
|
||
<div class="content">
|
||
<pre>./run --debug-vm</pre>
|
||
</div>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>Or for a faster development loop you can pass <code>-ex</code> command as a semicolon separated list:</p>
|
||
</div>
|
||
<div class="literalblock">
|
||
<div class="content">
|
||
<pre>./run --debug-vm-ex 'break qemu_add_opts;run'</pre>
|
||
</div>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>which is equivalent to the more verbose:</p>
|
||
</div>
|
||
<div class="literalblock">
|
||
<div class="content">
|
||
<pre>./run --debug-vm-args '-ex "break qemu_add_opts" -ex "run"'</pre>
|
||
</div>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>if you ever want need anything besides -ex.</p>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>Or if things get really involved and you want a debug script:</p>
|
||
</div>
|
||
<div class="literalblock">
|
||
<div class="content">
|
||
<pre>printf 'break qemu_add_opts
|
||
run
|
||
' > data/vm.gdb
|
||
./run --debug-vm-file data/vm.gdb</pre>
|
||
</div>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>Our default emulator builds are optimized with <code>gcc -O2 -g</code>. To use <code>-O0</code> instead, build and run with:</p>
|
||
</div>
|
||
<div class="literalblock">
|
||
<div class="content">
|
||
<pre>./build-qemu --qemu-build-type debug --verbose
|
||
./run --debug-vm
|
||
./build-gem5 --gem5-build-type debug --verbose
|
||
./run --debug-vm --emulator-gem5</pre>
|
||
</div>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>The <code>--verbose</code> is optional, but shows clearly each GCC build command so that you can confirm what <code>--*-build-type</code> is doing.</p>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>The build outputs are automatically stored in a different directories for optimized and debug builds, which prevents <code>debug</code> files from overwriting <code>opt</code> ones. Therefore, <code>--gem5-build-id</code> is not required.</p>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>The price to pay for debuggability is high however: a Linux kernel boot was about 3x slower in QEMU and 14 times slower in gem5 debug compared to opt, see benchmarks at: <a href="benchmark-linux-kernel-boot.html">Section 35.2.1, “Benchmark Linux kernel boot”</a>.</p>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>Similar slowdowns can be observed at: <a href="benchmark-emulators-on-userland-executables.html">Section 35.2.2, “Benchmark emulators on userland executables”</a>.</p>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>When in <a href="qemu-text-mode.html">QEMU text mode</a>, using <code>--debug-vm</code> makes Ctrl-C not get passed to the QEMU guest anymore: it is instead captured by GDB itself, so allow breaking. So e.g. you won’t be able to easily quit from a guest program like:</p>
|
||
</div>
|
||
<div class="literalblock">
|
||
<div class="content">
|
||
<pre>sleep 10</pre>
|
||
</div>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>In graphic mode, make sure that you never click inside the QEMU graphic while debugging, otherwise you mouse gets captured forever, and the only solution I can find is to go to a TTY with <code>Ctrl-Alt-F1</code> and <code>kill</code> QEMU.</p>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>You can still send key presses to QEMU however even without the mouse capture, just either click on the title bar, or alt tab to give it focus.</p>
|
||
</div>
|
||
<div class="ulist">
|
||
<ul>
|
||
<li>
|
||
<p><a href="reverse-debug-the-emulator.html">Reverse debug the emulator</a></p>
|
||
</li>
|
||
<li>
|
||
<p><a href="debug-gem5-python-scripts.html">Debug gem5 Python scripts</a></p>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
</div>
|
||
<div class="paragraph nav-footer">
|
||
<p>← Previous: <a href="qemu-monitor-from-gdb.html">QEMU monitor from GDB</a> | ↑ Up: <a href="qemu.html">QEMU</a> | ⌂ Home: <a href="README.html">Linux Kernel Module Cheat</a> | Next: <a href="reverse-debug-the-emulator.html">Reverse debug the emulator</a> →</p>
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