Writing to projector framebuffer segfaults sometimes

[Beyley]

Describe the bug
Sometimes when a computer starts up, writing to the projector's FB will cause a segfault, sometimes restarting the VM fixes it inconsistently, and sometimes its broken every time, and only restarting the gameserver fixes it, its super inconsistent, but generally can be triggered quite quickly by just restarting a computer with a framebuffer a bunch, then trying to write to it using some app like fbv, where it immediately segfaults

To Reproduce
Steps to reproduce the behavior:

1. Multiplayer 1.18.2, forge latest
2. Make a computer, put linux on it, connect a projector
3. Boot computer, try to use an app like fbv (my custom rewrite is available here fbz.zip source code, but any version of fbv or similar will trigger the problem)
4. Sometimes the app will segfault upon trying to write any of the data, sometimes it wont, and restarting the VM will only sometimes fix it

Log files
nothing oc2 related in either log file, but here is server log

Expected behavior
Framebuffer works like, and you can write data to it at will

Screenshots
N/A, its just an app segfaulting

Versions (please complete the following information):

• Minecraft: 1.18.2
• Forge: 40.2.1
• OC2: 569288c with a few extra unrelated patches applied

Additional context
While this is a modified version of oc2, none of the patches applied effect the particular code at play

[Beyley]

Narrowed it down more, the segfault only occurrs when you mmap then write to the framebuffer, if you use standard filesystem syscalls access to write to the framebuffer, it always seems to work

[heipiao233]

Narrowed it down more, the segfault only occurrs when you mmap then write to the framebuffer, if you use standard filesystem syscalls access to write to the framebuffer, it always seems to work

Isn't "mmap"ing the most used method to use framebuffer?