When you back out a patch, the patch tools restore all files modified by that patch, unless any of the following are true:
The patch was installed with the patchadd -d option, which instructs patchadd to not save copies of files being updated or replaced.
The patch has been obsoleted by a later patch.
The patch is required by another patch.
The patch tools call the pkgadd command to restore packages that were saved from the initial patch installation.
During the patch removal process, the patchrm command keeps a log of the back out process in /tmp/backoutlog.process_id. This log file is removed if the patch backs out successfully.