Getting /usr/src to match specific git hash?

[Don Lewis]

On 24 Jan, Yasuhiro Kimura wrote:
> From: Steve Kargl <sgk at troutmask.apl.washington.edu>
> Subject: Getting /usr/src to match specific git hash?
> Date: Sat, 23 Jan 2021 19:58:52 -0800
> 
>> Suppose one has an empty /usr/src.
>> 
>> 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?
> 
> cd /usr
> git clone https://git.freebsd.org/src.git
> cd src
> git checkout 3cc0c0d66a0

And don't take the git warning about having a detached HEAD as a
criticism.