Update xv6

_site/feed.xml

@@ -6,10 +6,46 @@
 </description>
     <link>https://codersherlock.github.com//</link>
     <atom:link href="https://codersherlock.github.com//feed.xml" rel="self" type="application/rss+xml"/>
-    <pubDate>Wed, 26 Jul 2017 12:52:19 -0400</pubDate>
-    <lastBuildDate>Wed, 26 Jul 2017 12:52:19 -0400</lastBuildDate>
+    <pubDate>Fri, 28 Jul 2017 15:25:24 -0400</pubDate>
+    <lastBuildDate>Fri, 28 Jul 2017 15:25:24 -0400</lastBuildDate>
     <generator>Jekyll v3.5.1</generator>
     
+      <item>
+        <title>Xv6 introduction</title>
+        <description>&lt;p&gt;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.&lt;/p&gt;
+
+&lt;hr /&gt;
+
+&lt;h2 id=&quot;xv6-systemcall&quot;&gt;Xv6 Systemcall&lt;/h2&gt;
+&lt;p&gt;To invoke a system call, we have to first define a user mode function to be the interface of the kernel instruction  in file &lt;em&gt;user.h&lt;/em&gt;.&lt;/p&gt;
+
+&lt;div class=&quot;language-c highlighter-rouge&quot;&gt;&lt;pre class=&quot;highlight&quot;&gt;&lt;code&gt;&lt;span class=&quot;kt&quot;&gt;void&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;function&lt;/span&gt; &lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;void&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;);&lt;/span&gt;
+&lt;/code&gt;&lt;/pre&gt;
+&lt;/div&gt;
+
+&lt;p&gt;This interface-like function will then pass the function name, in this case function, to &lt;em&gt;usys.S&lt;/em&gt;. When using user mode function in programs, &lt;em&gt;usys.S&lt;/em&gt; will generate a reference to SYS_function and push system call number of this function into %eax. After that, system can know from &lt;em&gt;syscall.c&lt;/em&gt; and determining whether this system call is available. We must define same name system function and add it into &lt;em&gt;syscall.h&lt;/em&gt; and &lt;em&gt;syscall.c&lt;/em&gt;.&lt;/p&gt;
+
+&lt;div class=&quot;language-c highlighter-rouge&quot;&gt;&lt;pre class=&quot;highlight&quot;&gt;&lt;code&gt;&lt;span class=&quot;cp&quot;&gt;#define SYS_function ##		// ## is the system call number
+&lt;/span&gt;
+&lt;span class=&quot;p&quot;&gt;[&lt;/span&gt;&lt;span class=&quot;n&quot;&gt;SYS_function&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;]&lt;/span&gt;  &lt;span class=&quot;n&quot;&gt;sys_function&lt;/span&gt;	&lt;span class=&quot;c1&quot;&gt;// real system function name
+&lt;/span&gt;
+&lt;span class=&quot;k&quot;&gt;extern&lt;/span&gt; &lt;span class=&quot;kt&quot;&gt;int&lt;/span&gt; &lt;span class=&quot;n&quot;&gt;sys_function&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;(&lt;/span&gt;&lt;span class=&quot;kt&quot;&gt;void&lt;/span&gt;&lt;span class=&quot;p&quot;&gt;);&lt;/span&gt;	&lt;span class=&quot;c1&quot;&gt;// real system function declaration
+&lt;/span&gt;&lt;/code&gt;&lt;/pre&gt;
+&lt;/div&gt;
+
+&lt;p&gt;After adding these sentences to syscall files, we can implement real function in specific place where you want to make the function works well.&lt;/p&gt;
+
+&lt;p&gt;Sometimes, we need to pass variables among system calls. In this case, variables’ values are not necessary and even can’t be pass directly into system_function. When invoke a system call function, all variables of this system call will be pushed into current process’ stack. In file &lt;em&gt;syscall.c&lt;/em&gt;, multiple functions are provided to get these variables from the process. I won’t waste time on explaining how to use these functions especially when elegant and detailed comments were written in source codes. However, I will explain concepts and how process organized and works in xv6 in future articles.&lt;/p&gt;
+</description>
+        <pubDate>Fri, 28 Jul 2017 14:56:55 -0400</pubDate>
+        <link>https://codersherlock.github.com//archivers/intro-xv6</link>
+        <guid isPermaLink="true">https://codersherlock.github.com//archivers/intro-xv6</guid>
+        
+        
+        <category>xv6</category>
+        
+      </item>
+    
       <item>
         <title>Short talk about Unikernels</title>
         <description>&lt;h2 id=&quot;what-is-unikernel&quot;&gt;What is Unikernel?&lt;/h2&gt;
@@ -32,8 +68,8 @@
 
 </description>
         <pubDate>Wed, 26 Jul 2017 12:42:33 -0400</pubDate>
-        <link>https://codersherlock.github.com//archivers/term-comp</link>
-        <guid isPermaLink="true">https://codersherlock.github.com//archivers/term-comp</guid>
+        <link>https://codersherlock.github.com//archivers/intro-unikernel</link>
+        <guid isPermaLink="true">https://codersherlock.github.com//archivers/intro-unikernel</guid>
         
         
         <category>unikernel</category>