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https://github.com/cirosantilli/linux-kernel-module-cheat.git
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549 lines
35 KiB
HTML
549 lines
35 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="gdb-step-debug-userland-processes" class="article">
|
||
<div id="header">
|
||
<h1>Linux Kernel Module Cheat</h1>
|
||
</div>
|
||
<div id="content">
|
||
<div class="sect2">
|
||
<h3 id="gdb-step-debug-userland-processes"><a class="anchor" href="#gdb-step-debug-userland-processes"></a><a class="link" href="#gdb-step-debug-userland-processes">3.6. GDB step debug userland processes</a></h3>
|
||
<div class="paragraph">
|
||
<p>QEMU’s <code>-gdb</code> GDB breakpoints are set on virtual addresses, so you can in theory debug userland processes as well.</p>
|
||
</div>
|
||
<div class="ulist">
|
||
<ul>
|
||
<li>
|
||
<p><a href="https://stackoverflow.com/questions/26271901/is-it-possible-to-use-gdb-and-qemu-to-debug-linux-user-space-programs-and-kernel" class="bare">https://stackoverflow.com/questions/26271901/is-it-possible-to-use-gdb-and-qemu-to-debug-linux-user-space-programs-and-kernel</a></p>
|
||
</li>
|
||
<li>
|
||
<p><a href="https://stackoverflow.com/questions/16273614/debug-init-on-qemu-using-gdb" class="bare">https://stackoverflow.com/questions/16273614/debug-init-on-qemu-using-gdb</a></p>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>You will generally want to use <a href="gdbserver.html">gdbserver</a> for this as it is more reliable, but this method can overcome the following limitations of <code>gdbserver</code>:</p>
|
||
</div>
|
||
<div class="ulist">
|
||
<ul>
|
||
<li>
|
||
<p>the emulator does not support host to guest networking. This seems to be the case for gem5 as explained at: <a href="gem5-host-to-guest-networking.html">Section 15.3.1.3, “gem5 host to guest networking”</a></p>
|
||
</li>
|
||
<li>
|
||
<p>cannot see the start of the <code>init</code> process easily</p>
|
||
</li>
|
||
<li>
|
||
<p><code>gdbserver</code> alters the working of the kernel, and makes your run less representative</p>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>Known limitations of direct userland debugging:</p>
|
||
</div>
|
||
<div class="ulist">
|
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<ul>
|
||
<li>
|
||
<p>the kernel might switch context to another process or to the kernel itself e.g. on a system call, and then TODO confirm the PIC would go to weird places and source code would be missing.</p>
|
||
<div class="paragraph">
|
||
<p>Solutions to this are being researched at: <a href="lx-ps.html">Section 3.10.1, “lx-ps”</a>.</p>
|
||
</div>
|
||
</li>
|
||
<li>
|
||
<p>TODO step into shared libraries. If I attempt to load them explicitly:</p>
|
||
<div class="literalblock">
|
||
<div class="content">
|
||
<pre>(gdb) sharedlibrary ../../staging/lib/libc.so.0
|
||
No loaded shared libraries match the pattern `../../staging/lib/libc.so.0'.</pre>
|
||
</div>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>since GDB does not know that libc is loaded.</p>
|
||
</div>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
<div class="ulist">
|
||
<ul>
|
||
<li>
|
||
<p><a href="gdb-step-debug-userland-custom-init.html">GDB step debug userland custom init</a></p>
|
||
</li>
|
||
<li>
|
||
<p><a href="gdb-step-debug-userland-busybox-init.html">GDB step debug userland BusyBox init</a></p>
|
||
</li>
|
||
<li>
|
||
<p><a href="gdb-step-debug-userland-non-init.html">GDB step debug userland non-init</a></p>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
</div>
|
||
<div class="paragraph nav-footer">
|
||
<p>← Previous: <a href="linux-kernel-early-boot-messages.html">Linux kernel early boot messages</a> | ↑ Up: <a href="gdb.html">GDB step debug</a> | ⌂ Home: <a href="README.html">Linux Kernel Module Cheat</a> | Next: <a href="gdb-step-debug-userland-custom-init.html">GDB step debug userland custom init</a> →</p>
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