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CoderSherlock
2018-02-23 15:11:20 -05:00
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_site/archivers/intro-xv6.html
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@@ -10,8 +10,8 @@
<meta name="description" content="I hate xv6, a stupid, useless education-oriented system. In this article, I will generally talk about how to implement system call to this operating system.">
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<link rel="canonical" href="http://localhost:4000/archivers/intro-xv6">
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@@ -24,10 +24,10 @@
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</head>
@@ -77,19 +77,17 @@
<h2 id="xv6-systemcall">Xv6 Systemcall</h2>
<p>To invoke a system call, we have to first define a user mode function to be the interface of the kernel instruction in file <em>user.h</em>.</p>
<div class="language-c highlighter-rouge"><pre class="highlight"><code><span class="kt">void</span> <span class="n">function</span> <span class="p">(</span><span class="kt">void</span><span class="p">);</span>
</code></pre>
</div>
<div class="language-c highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kt">void</span> <span class="n">function</span> <span class="p">(</span><span class="kt">void</span><span class="p">);</span>
</code></pre></div></div>
<p>This interface-like function will then pass the function name, in this case function, to <em>usys.S</em>. When using user mode function in programs, <em>usys.S</em> will generate a reference to SYS_function and push system call number of this function into %eax. After that, system can know from <em>syscall.c</em> and determining whether this system call is available. We must define same name system function and add it into <em>syscall.h</em> and <em>syscall.c</em>.</p>
<div class="language-c highlighter-rouge"><pre class="highlight"><code><span class="cp">#define SYS_function ## // ## is the system call number
<div class="language-c highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="cp">#define SYS_function ## // ## is the system call number
</span>
<span class="p">[</span><span class="n">SYS_function</span><span class="p">]</span> <span class="n">sys_function</span> <span class="c1">// real system function name
</span>
<span class="k">extern</span> <span class="kt">int</span> <span class="n">sys_function</span><span class="p">(</span><span class="kt">void</span><span class="p">);</span> <span class="c1">// real system function declaration
</span></code></pre>
</div>
<span class="p">[</span><span class="n">SYS_function</span><span class="p">]</span> <span class="n">sys_function</span> <span class="c1">// real system function name</span>
<span class="k">extern</span> <span class="kt">int</span> <span class="n">sys_function</span><span class="p">(</span><span class="kt">void</span><span class="p">);</span> <span class="c1">// real system function declaration</span>
</code></pre></div></div>
<p>After adding these sentences to syscall files, we can implement real function in specific place where you want to make the function works well.</p>