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https://github.com/cirosantilli/linux-kernel-module-cheat.git
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541 lines
34 KiB
HTML
541 lines
34 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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|
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</head>
|
||
<body id="userland-objects-vs-header-only" class="article">
|
||
<div id="header">
|
||
<h1>Linux Kernel Module Cheat</h1>
|
||
</div>
|
||
<div id="content">
|
||
<div class="sect4">
|
||
<h5 id="userland-objects-vs-header-only"><a class="anchor" href="#userland-objects-vs-header-only"></a><a class="link" href="#userland-objects-vs-header-only">38.15.1.1. Userland objects vs header-only</a></h5>
|
||
<div class="paragraph">
|
||
<p>When factoring out functionality across userland examples, there are two main options:</p>
|
||
</div>
|
||
<div class="ulist">
|
||
<ul>
|
||
<li>
|
||
<p>use header-only implementations</p>
|
||
</li>
|
||
<li>
|
||
<p>use separate C files and link to separate objects.</p>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>The downsides of the header-only implementation are:</p>
|
||
</div>
|
||
<div class="ulist">
|
||
<ul>
|
||
<li>
|
||
<p>slower compilation time, especially for C++</p>
|
||
</li>
|
||
<li>
|
||
<p>cannot call C implementations from assembly files</p>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>The advantages of header-only implementations are:</p>
|
||
</div>
|
||
<div class="ulist">
|
||
<ul>
|
||
<li>
|
||
<p>easier to use, just <code>#include</code> and you are done, no need to modify build metadata.</p>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>As a result, we are currently using the following rule:</p>
|
||
</div>
|
||
<div class="ulist">
|
||
<ul>
|
||
<li>
|
||
<p>if something is only going to be used from C and not assembly, define it in a header which is easier to use</p>
|
||
<div class="paragraph">
|
||
<p>The slower compilation should be OK as long as split functionality amongst different headers and only include the required ones.</p>
|
||
</div>
|
||
<div class="paragraph">
|
||
<p>Also we don’t have a choice in the case of C++ template, which must stay in headers.</p>
|
||
</div>
|
||
</li>
|
||
<li>
|
||
<p>if the functionality will be called from assembly, then we don’t have a choice, and must add it to a separate source file and link against it.</p>
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