Segfault on 2.9 with kernel 5.4.258-rtai-amd64

Hi,

I'm setting up a new machine with a parallel port output. I tested both the preempt-rt and rtai kernels and get 1/10th of the jitter on RTAI than on preempt-rt.

I setup a new Debian 12 installation (gnome) and installed linuxcnc as described here: gist.github.com/nathantsoi/e892965b2d97f735a51b707d4a3b1eff

Latency test and `halrun -I -f ptest.hal` both work fine.

However, when I try to launch a basic config (generated by stepconf), I get a segfault.

I've attached both the dmseg output as well as the result of the launch command: `linuxcnc -d -v /home/cnc/linuxcnc/configs/router-axis/router.ini`

I'm not sure what I'm missing here. Any direction is greatly appreciated.

Don't use gnome (or use it in X mode)

Good idea.

I switched to xfce and also from qtdragon to axis, but I am still getting the segfault (logs attached).

"/usr/bin/linuxcnc: line 977:  4507 Segmentation fault      $EMCDISPLAY -ini "$INIFILE" $EMCDISPLAYARGS $EXTRA_ARGS"

Also, I'm not sure why, but about 50% of the time, I also get a kernel panic along with the segfault:

```
Jan 18 07:55:06 router kernel: axis[4507]: segfault at 28 ip 00007fe522d03573 sp 00007ffc68980250 error 4 in libc.so.6[7fe522c92000+155000]
Jan 18 07:55:06 router kernel: Code: 41 f0 49 39 f0 0f 84 a4 05 00 00 4d 8b 49 08 48 83 c8 01 4d 8b 69 08 41 f6 c5 04 0f 85 d1 0a 00 00 4c 39 e8 0f 83 29 06 00 00 <48> 8b 46 28 66 48 0f 6e c6 66 48 0f 6e c8 66 0f 6c c1 0f 11 42 20
Jan 18 07:55:06 router kernel: hal_manualtoolc[4495]: segfault at 10 ip 00007f00bfbf7489 sp 00007ffd74306c10 error 4 in libc.so.6[7f00bfb86000+155000]
Jan 18 07:55:06 router kernel: Code: 8b 4e 08 49 39 c8 0f 82 7d 03 00 00 48 83 f9 0f 0f 86 73 03 00 00 4c 8b 06 49 83 e0 f8 49 39 c0 0f 85 db 05 00 00 4c 8b 42 18 <49> 3b 50 10 0f 85 fd 04 00 00 4c 39 7a 10 0f 85 f3 04 00 00 f6 c1
```

Would it help if I built linuxcnc from source? I could also test the 4.x RTAI kernel this way. I think I can also get the trace for the segfault if I do this, right?

Update: I also built from source and tried again, but now I'm getting a different (malloc) error. Any suggestions on how I debug this?

```
Starting TASK program: milltask
+ program_available milltask
+ type -path milltask
+ NUM=1
+ halcmd loadusr -Wn inihal milltask -ini /home/cnc/linuxcnc/configs/router-axis/router-axis.ini
++ inivar -ini /home/cnc/linuxcnc/configs/router-axis/router-axis.ini -var HALCMD -sec HAL -num 1
+ HALCOMMAND=
+ ''
+ halcmd start
+ run_applications
+ NUM=1
malloc(): unsorted double linked list corrupted
+ APPFILE=
+ ''
+ return
+ echo 'Starting DISPLAY program: axis'
Starting DISPLAY program: axis
```
 

Ok, I tried pulling each module (of 2) using them individually in each socket. This didn't help.

I ended up reverting to 2.8 with the 4.x preempt rt kernel and it's working ok, jitter spikes to 60k occasionally, but is usually around 25k.

For reference, on 2.9 with the 5.x rtai kernel I was getting ~1k jitter.

I'll try 2.8 with the 4.x rtai kernel next.

Hello, for what it's worth I've been having the same issue, although I followed a different installation procedure.
First, I installed the linuxcnc 2.9.2 iso. Then, I wanted to apt update and upgrade the system, but it gave me some errors related to raspi-firmware, but I solved it following another post . Next, I installed the packages on the downloads page (linuxcnc for RTAI, RTAI kernel and RTAI modules) and installed them with gdebi, having previously removed the linuxcnc-uspace package and the documentation.
Once everything is installed I reboot the system but during boot I see that the systemd-binfmt.service fails to load up properly.
Finally, when I launch some Stepconf generated linuxcnc instance, it crashes with the same segmentation fault as yours.
However, when I go to LinuxCNC Configuration Selector and load the Sample Configuration of axis it loads up perfectly.
I will keep looking for solutions, although I believe that the crash is related to the binfmt service not working properly.