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. + +
+When you're done, you should see output like this when booting +xv6: + +
+... +fork -> 2 +exec -> 0 +open -> 3 +close -> 0 +$write -> 1 + write -> 1 ++ +
+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.) + +
Hint: modify the syscall() function in kernel/syscall.c. + +
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? + +
Optional: print the system call arguments. +
Modify the shell to support wait. - -
Modify the shell to support lists of commands, separated by ";" +There are endless ways in which the shell could be extended. Here are +some suggestions: -
Modify the shell to support sub-shells by implementing "(" and ")" - -
Modify the shell to allow users to edit the command line +