+ cc -O2 -o drm_sg_probe drm_sg_probe.c
+ ./drm_sg_probe
open(/dev/dri/card0) -> fd=-1 errno=2 (No such file or directory)
open(/dev/dri/renderD128) -> fd=-1 errno=2 (No such file or directory)
open(/dev/drm/0) -> fd=-1 errno=2 (No such file or directory)
open(/dev/dri0) -> fd=-1 errno=2 (No such file or directory)
[*] kldstat modules and /boot/kernel contents carry the authoritative answer: which drm drivers exist at all.
RC=0
+ echo 'RC=0'
+ kldstat
Id Refs Address                Size Name
 1    5 0xffffffff80200000  1ad8538 kernel
 2    1 0xffffffff81cd9000    7c288 ehci.ko
 3    1 0xffffffff81d56000    8c778 xhci.ko