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diff --git a/labs/xv6.html b/labs/xv6.html index de18ac7..7699b06 100644 --- a/labs/xv6.html +++ b/labs/xv6.html @@ -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> |