system calls on FreeBSD

From: Alexander <bsdunix5_at_gmail.com>
Date: Mon, 30 Oct 2023 22:33:35 UTC
Greetings !

I am a newbie FreeBSD user, and I want to write one or two system calls on
FreeBSD.

I have a question, please :

Why FreeBSD system calls take as an argument struct thread *t, en lieu de
struct proc *p ?

Thank you !
Alexander