On-Target source Level Debugging Using NFS

Many a times we would like to have to have a luxury of source level debugging but do not have fancy tools like a JTAG/ICE. But thanks to NFS, we do have a solution. Using NFS one can mount the entire source directory ( or any other directory for that matter) on to the target and run a debuggger on the target.

Besides aiding source level debugging NFS can help save crucial development time by circumventing the need to flash the board for every little change. If only a small portion of the code changes, selectively compile that particular program and replace the existing program on the board with the newly built program. Copy-And-Paste instead of Flash-And-Burn!!!

1. Build the Kernel Image for the target with NFS support.

2. Install NFS server package on the host. On debian machines it is as simple as

sudo apt-get install nfs-kernel-server

3. A file called /etc/exports is created. Open this file for editing.

add the following line :-

/home/kernelexploit 192.168.1.1(rw,all_squash,anonuid=kernelexploit,anongid=1000,insecure,no_subtree_check)

where /home/kernelexploit is the path on the host. This will be mounted on the target. [192.168.1.1] is the IP address of the target in my system. Replace it with your board specific parameters.

4. On the target type the following command

mkdir -p /home/kernelexploit-target [ This is where the remote directory would be mapped]

mount -t nfs -o async,noatime,exec,rw,nfsvers=2,nolock 192.168.1.11:/home/kernelexploit /home/kernelexploit-target

Where, 192.168.1.11 is the IP address of the host machine and /home/kernelexploit is the path on the host. The trailing /home/kernelexploit-target is a directory we created on the target where the remote directory is mounted.