To create a patch that changes an older version of a package into a
newer version, first make a copy of the older and newer versions in
adjacent subdirectories. It is common to do that by unpacking
tar archives of the two versions.
To generate the patch, use the command ‘diff -Naur old new’ where old and new identify the old and new directories. The names old and new should not contain any slashes. The -N option lets the patch create and remove files; -a lets the patch update non-text files; -u generates useful timestamps and enough context; and -r lets the patch update subdirectories. Here is an example command, using Bourne shell syntax:
diff -Naur gcc-3.0.3 gcc-3.0.4
Tell your recipients how to apply the patches. This should include
which working directory to use, and which patch options to
use; the option ‘-p1’ is recommended. Test your procedure by
pretending to be a recipient and applying your patches to a copy of
the original files.
See Avoiding Common Mistakes, for how to avoid common mistakes when generating a patch.