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-rw-r--r--labs/xv6.html51
1 files changed, 46 insertions, 5 deletions
diff --git a/labs/xv6.html b/labs/xv6.html
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@@ -215,17 +215,58 @@ initial file system. You just ran one of them: <tt>ls</tt>.
to declare an argv.
</ul>
+<h2>System call tracing</h2>
-<h2>Optional: modify the shell</h2>
+<p>In this exercise you will modify the xv6 kernel to print out a line
+for each system call invocation. It is enough to print the name of the
+system call and the return value; you don't need to print the system
+call arguments.
+
+<p>
+When you're done, you should see output like this when booting
+xv6:
+
+<pre>
+...
+fork -> 2
+exec -> 0
+open -> 3
+close -> 0
+$write -> 1
+ write -> 1
+</pre>
+
+<p>
+That's init forking and execing sh, sh making sure only two file descriptors are
+open, and sh writing the $ prompt. (Note: the output of the shell and the
+system call trace are intermixed, because the shell uses the write syscall to
+print its output.)
-<p>Modify the shell to support wait.
+<p> Hint: modify the syscall() function in kernel/syscall.c.
+
+<p>Run the programs you wrote in the previous exercises and inspect
+ the system call trace. Are there many system calls? Which systems
+ calls correspond to code in the applications you wrote above?
+
+<p>Optional: print the system call arguments.
-<p>Modify the shell to support lists of commands, separated by ";"
+<h2>Optional: modify the shell</h2>
-<p>Modify the shell to support sub-shells by implementing "(" and ")"
+There are endless ways in which the shell could be extended. Here are
+some suggestions:
-<p>Modify the shell to allow users to edit the command line
+<ul>
+
+<li>Modify the shell to support wait.
+<li>Modify the shell to support lists of commands, separated by ";"
+
+<li>Modify the shell to support sub-shells by implementing "(" and ")"
+
+<li>Modify the shell to allow users to edit the command line
+
+</ul>
+
</body>
</html>