I mentioned this link in a thread last year, but I often see posts about modifying a Puppy with a later (or older) kernel and/or glibc, so I felt that it could be useful to point to it again.
Michael Kerrisk runs the site man7.org. He is responsible for maintaining The Linux man-pages project, which documents the Linux kernel and C library interfaces. He is also an author, he has written the book The Linux Programming Interface, which he uses in his own programming classes, and which is also used in university courses.
All changes in the Linux kernel and glibc after he wrote his book in 2010, (Linux kernel (2.6.35) and glibc (2.12)), are continuously documented here:
http://man7.org/tlpi/api_changes/index.html
There are other sites, like https://kernelnewbies.org/ which document kernel changes, but those sites often have too much info to get a quick overview .
Kernel and glibc changes, follow continuously updated info
Kernel and glibc changes, follow continuously updated info
True freedom is a live Puppy on a multisession CD/DVD.