RTAI for Stretch/Buster and rabbit holes

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02 Jan 2020 01:18 #153757 by JohnnyCNC
I spend the day trying to get a version of either Debian Stretch or Buster with RTAI and 2.8 working. I have a preempt version of Stretch with 2.8. I have looked at many different posts and followed several different sets of instructions all of which lead to one impasse or another. That lead me to the question of what do I need to do to get from Stretch preempt to RTAI? Can I get pre-built kernel or do I have to build it myself? About 8 months ago I did get through the process of building a preempt kernel but this one has just beat me.

Thanks
John

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02 Jan 2020 03:22 #153765 by phillc54
I have installed the packages from github.com/andypugh/RTAI/releases and they work fine.

The only issue for me is that it restricts boards with Intel graphics to 1024x768 resolution. The developers are working to rectify this.

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02 Jan 2020 03:30 #153766 by JohnnyCNC
I'll try that one again tomorrow.

John

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03 Jan 2020 03:57 #153858 by JohnnyCNC
Tried again and made it to "REBOOT". Then it would no longer boot. It gives an error: "kernel not compile with retpoline; no mitigation available"

I does mention BusyBox v1.22.1 on the screen and I end up at what looks like a prompt (initramfs). At this point it does not accept input from the keyboard.

$ sudo make
$ sudo make install
$ sudo make modules_install
On debian this will automatically update grub and set the system to boot from the new kernel.
REBOOT (and check with uname -r that the new kernel is running: 4.14.132-rtai-amd64
If it boots to the busybox boot to the old kernel then run these commands JT

cd /usr/src/linux
sudo make modules_install
sudo make install

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07 Jan 2020 23:01 #154278 by andypugh
Have you already found the deb packages here?

www.linuxcnc.org/temp/

Those should work with Buster.

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08 Jan 2020 02:33 #154285 by JohnnyCNC
I did find them and installed the image and headers but it still shows as PREEMPT.
When booting in complains that the kernel is not compiled with "Retpoline" no mitigation available.
I guess that is OK but possibly risky.
$ cat /sys/devices/system/cpu/vulnerabilities/spectre_v2
Vulnerable, IBPB: disabled, STIBP: disabled

Am I just not understanding how to tell if this is RTAI or PREEMPT?

Linux X3CNC 4.14.148-rtai-amd64 #2 SMP PREEMPT Sat Nov 9 16:29:10 GMT 2019 x86_64 GNU/Linux

I also tried these and it boots with the same warning..

linux-headers-4.14.132-rtai-amd64_4.14.132-rtai-amd64-1_amd64.deb
linux-image-4.14.132-rtai-amd64_4.14.132-rtai-amd64-1_amd64.deb

Thanks
John

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08 Jan 2020 10:40 - 08 Jan 2020 10:40 #154296 by andypugh

I did find them and installed the image and headers but it still shows as PREEMPT.


PREEMPT is a common feature of all Linux kernels. PREEMPT-RT is the realtime variant.
en.wikipedia.org/wiki/Kernel_preemption


When booting in complains that the kernel is not compiled with "Retpoline" no mitigation available.n


Yes. I haven't looked in to whether RTAI is compatible with spectre mitigation. I have been ignoring that warning.

Describes the vulnerability. You might want to consider whether this is a problem to you on your CNC controller.
Last edit: 08 Jan 2020 10:40 by andypugh.

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