[lttng-dev] loading modules with modprobe

[François Belias]

Hello Kienan,

I've continued investigating my issue and discovered something new that
might shed some light. Here's the rundown:

1. To ensure my add-ons weren't causing problems, deleted all old modules
and I followed the documentation on the LTTng website (
https://lttng.org/docs/v2.13/#doc-building-from-source) and downloaded
`lttng-modules-2.13.13`.

2. Inside the downloaded folder, I successfully executed `make
KERNELDIR=/usr/src/linux-source-6.5.0` without any issues.

3. Subsequently, I ran `make KERNELDIR=/usr/src/linux-source-6.5.0
modules_install`, which also completed successfully.

4. After that, I updated the module dependencies using `sudo depmod -a`,
which went fine.

However, when I tried to load a module, such as `sudo modprobe
lttng-probe-kvm`, it reported that the module couldn't be found at
`/lib/modules/6.5.0-41-generic/`. Upon checking the logs, I confirmed that
step 3 had installed the modules in `/lib/modules/6.5.0/`.

To address this, I modified step 3 to simply `make modules_install`, which
then installed the modules correctly at `/lib/modules/6.5.0-41-generic/`
and ran again step 4. But now, when attempting to load a module, I'm
encountering the error `modprobe: ERROR: could not insert
'lttng_probe_kvm': Exec format error`.

Do you have any insights or ideas on what might be causing this issue?

Thanks again for your assistance.




















Le mar. 16 juill. 2024, à 09 h 05, Kienan Stewart <kstewart at efficios.com> a
écrit :

> Hi François,
>
> On 7/15/24 6:10 PM, François Belias via lttng-dev wrote:
> > Hello,
> >
> > I'm currently running Linux kernel version 6.5.0-41-generic and
> > attempting to install LTTng from source. Here are the steps I followed:
> >
> >   - I cloned the LTTng git repository to my computer from
> > [
> https://github.com/lttng/lttng-modules.git](https://github.com/lttng/lttng-modules.git)
> <
> https://github.com/lttng/lttng-modules.git](https://github.com/lttng/lttng-modules.git)
> >.
> > - Downloaded the kernel source tree corresponding to my kernel version
> > to enable compilation.
> > - Executed `make KERNELDIR=/path/to/my/linux/source`, which was
> > completed successfully.
> > - Ran `make KERNELDIR=/path/to/my/linux/source modules_install`, also
> > without any issues.
> > - Finally, I executed `sudo depmod -a`, which was completed successfully.
> >
> > However, when I attempt to load a module with commands like `sudo
> > modprobe lttng-ketprobes` or "sudo modprobe lttng-tracer", I encounter
> > the following errors:
> >
> > - For `lttng-ketprobes`: `modprobe: FATAL: Module lttng-ketprobes not
> > found in directory /lib/modules/6.5.0-41-generic`.
> > - For `lttng-tracer`: `modprobe: ERROR: could not insert 'lttng_tracer':
> > Exec format error`.
>
> If you rebuilt modules on the master branch as of yesterday you may need
> to clean the LTTng modules install directory, rebuild, and reinstall.
>
> This is due to kprobes, kretprobes, and uprobes modules being included
> in the tracer core module. C.f.
>
> https://github.com/lttng/lttng-modules/commit/0c2c6606eb66cb5222ab7a2a4f8329fd5dfdef70
>
> You may want to stick with running lttng-modules 2.13.x which will not
> have breaking changes merged in.
>
> The exec format error also could be due to modules that are installed
> but built against a different version of the Linux kernel.
>
> A few things to check
>
> - If your kernel has been upgraded recently, ensure the new kernel is
> the one actually running
> - If the modules haven't been rebuilt since the upgrade, they should be
> rebuilt and reinstalled
> - As I recall, you are playing around with some addon modules - do any
> of those modules define dependencies on the kprobes, kretprobes, or
> uprobes modules which now are no longer produced by builds of the master
> branch
>
> Is there further information in dmesg or journalctl regarding the module
> loading?
>
> hope this helps.
>
> thanks,
> kienan
>
> >
> > I've confirmed that the modules exist but can't load them. I'm unsure
> > how to resolve these issues. Could someone please assist me?
> >
> > Thank you.
> >
> > _______________________________________________
> > lttng-dev mailing list
> > lttng-dev at lists.lttng.org
> > https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
>
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