How to add a user program to xv6

Introduction to xv6

xv6 is a reimplementation of the Unix sixth edition in order to use as a learning tool. xv6 was developed by MIT as a teaching operating system for their “6.828” course. A vital fact about xv6 is that it contains all the core Unix concepts and has a similar structure to Unix even though it lacks some functionality that you would expect from a modern operating system. This is a lightweight operating system where the time to compile is very low and it also allows remote debugging.

The source code of xv6 can be cloned to your machine as follows.

git clone git://github.com/mit-pdos/xv6-public.git xv6

Add a user program to xv6

Once you have setup xv6 on your machine, you could have a look at how to add a new user program to xv6. A user program could be a simple and straightforward C program. However, just adding a file to the xv6 folder would not be sufficient as we need to make it available to the user at the shell prompt.

Step 1: Write a simple C program

First of all, create a C program as follows and save it inside the xv6 operating system folder. This can be named myprogram.c

include "types.h"
include "stat.h"
include "user.h" 
intmain(void)
{  
    printf(1, "My first xv6 program\n");  
    exit();
}   

Step 2: Edit the Makefile

The Makefile needs to be edited to make our program available for the xv6 source code for compilation.

gedit Makefile

This line of code would open the Makefile in the Gedit text editor. Next, the following sections of the Makefile needs to be edited to add your program myprogram.c

UPROGS=\
_cat\
_crash\
_echo\
_factor\
_forktest\
_grep\
_hello\
_init\
_kill\
_ln\
_ls\
_mkdir\
_null\
_rm\
_sh\
_share\
_stressfs\
_usertests\
_wc\
_zombie\
_myprogram\


EXTRA=\
mkfs.c ulib.c user.h cat.c echo.c forktest.c grep.c kill.c\
ln.c ls.c mkdir.c rm.c stressfs.c usertests.c wc.c zombie.c\
myprogram.c\
printf.c umalloc.c\
README dot-bochsrc *.pl toc.* runoff runoff1 runoff.list\
.gdbinit.tmpl gdbutil\

Once these changes are made, the user program is ready to be tested.

Run the following commands to compile the source code of xv6. This would compile the whole system.

make clean
make

Now you could go to QEMU through the command

make qemu

and then type the name of the program. This would print the statement “My first xv6 program” in the QEMU emulator window.