Getting /usr/src to match specific git hash?

[Simon J. Gerraty]

Steve Kargl <sgk at troutmask.apl.washington.edu> wrote:
> Suppose further that one had to re-install a 32-bit
> i386-*-freebsd with the 24 Dec 2020 image available
> from freebsd.org.
> 
> uname -a for the booted kernel shows
> 
> % uname -a
> FreeBSD mobile 13.0-CURRENT FreeBSD 13.0-CURRENT #0 \
> 3cc0c0d66a0-c255241(main)-dirty: Thu Dec 24 05:43:23 UTC 2020 \
> root at releng1.nyi.freebsd.org:/usr/obj/usr/src/i386.i386/sys/GENERIC i386
> 
> How does one use git to pull the exact sources that match
> this specifc kernel?

As others have  described,  you can clone and 'git checkout 3cc0c0d66a0'
but that "-dirty" above implies the tree had changes, so you cannot
reproduce "the exact sources".

--sjg