[Bug]: BTF errors against kernel 6.10.5

potuz commented 1 month ago

Is there an existing issue for this?

[X] I have searched the existing issues

Detail

Apologies to open an issue for support, but I have been trying to compile this module against 6.10.5 for a few days now and I can't modprobe it. The same procedure works fine against 6.5.1. I tried getting support in the Arch Linux forums without much success.

$ uname -a
Linux forkchoice 6.10.5 #3 SMP PREEMPT_DYNAMIC Wed Aug 14 21:39:10 -03 2024 x86_64 GNU/Linux
$ make clean
...
$ make
...
Building v4l2-loopback driver...
make -C /lib/modules/`uname -r`/build M=/home/heluani/Documents/code/video-drivers/v4l2loopback KCPPFLAGS="-DSNAPSHOT_VERSION='"0.13.2-1-g9318243"'" modules
make -C utils V4L2LOOPBACK_SNAPSHOT_VERSION=0.13.2-1-g9318243
make[1]: Entering directory '/home/potuz/Documents/code/video-drivers/v4l2loopback/utils'
cc  -I.. -DSNAPSHOT_VERSION='"0.13.2-1-g9318243"'  -c -o v4l2loopback-ctl.o v4l2loopback-ctl.c
make[1]: Entering directory '/home/potuz/Documents/code/kernel/linux-6.10.5'
cc   v4l2loopback-ctl.o   -o v4l2loopback-ctl
make[1]: Leaving directory '/home/potuz/Documents/code/video-drivers/v4l2loopback/utils'
warning: the compiler differs from the one used to build the kernel
  The kernel was built by: gcc (GCC) 14.2.1 20240805
  You are using:           gcc (GCC) 14.2.1 20240910
  CC [M]  /home/potuz/Documents/code/video-drivers/v4l2loopback/v4l2loopback.o
  MODPOST /home/potuz/Documents/code/video-drivers/v4l2loopback/Module.symvers
  CC [M]  /home/potuz/Documents/code/video-drivers/v4l2loopback/v4l2loopback.mod.o
  LD [M]  /home/potuz/Documents/code/video-drivers/v4l2loopback/v4l2loopback.ko
  BTF [M] /home/potuz/Documents/code/video-drivers/v4l2loopback/v4l2loopback.ko
make[1]: Leaving directory '/home/potuz/Documents/code/kernel/linux-6.10.5'
$ sudo make install
...
make -C /lib/modules/`uname -r`/build M=/home/potuz/Documents/code/video-drivers/v4l2loopback modules_install
make[1]: Entering directory '/home/potuz/Documents/code/kernel/linux-6.10.5'
  INSTALL /lib/modules/6.10.5/updates/v4l2loopback.ko
  SIGN    /lib/modules/6.10.5/updates/v4l2loopback.ko
  ZSTD    /lib/modules/6.10.5/updates/v4l2loopback.ko.zst
  DEPMOD  /lib/modules/6.10.5
make[1]: Leaving directory '/home/potuz/Documents/code/kernel/linux-6.10.5'

SUCCESS (if you got 'SSL errors' above, you can safely ignore them)
$ sudo depmod -a
$ sudo modprobe v4l2loopback exclusive_caps=1
modprobe: ERROR: could not insert 'v4l2loopback': Invalid argument
$ sudo dmesg | tail
Sep14 07:37] [Sat Sep 14 07:37:35 2024] BPF:    32_NOTE_MASK type_id=13 bits_offset=8352
[  +0.000007] [Sat Sep 14 07:37:35 2024] BPF:
[  +0.000001] [Sat Sep 14 07:37:35 2024] BPF: Invalid name
[  +0.000001] [Sat Sep 14 07:37:35 2024] BPF:
[  +0.000002] [Sat Sep 14 07:37:35 2024] failed to validate module [v4l2loopback] BTF: -22

This is all the context I get on the dmesg error.

$ grep BTF .config
CONFIG_DEBUG_INFO_BTF=y
CONFIG_PAHOLE_HAS_SPLIT_BTF=y
CONFIG_DEBUG_INFO_BTF_MODULES=y
# CONFIG_MODULE_ALLOW_BTF_MISMATCH is not set
CONFIG_PROBE_EVENTS_BTF_ARGS=y

I don't think I am forced to allow for BTFs mismatches right? I am happy to provide any requested information.

v4l2loopback version

v0.13.2-1-g9318243

kernel version

Linux forkchoice 6.10.5 #3 SMP PREEMPT_DYNAMIC Wed Aug 14 21:39:10 -03 2024 x86_64 GNU/Linux

OS Version

Arch Linux, kernel manually compiled

Which CPU are you using?

amd64/x86_64 ("64bit Intel")

umlaeute commented 1 month ago

i think the BTF error is a red herring. probably getting a bit more context from dmesg could help debugging the issue
i do not see any installation of the newly compiled module (make install), so I guess you are actually trying to load an old/... version of the module that lingers in /usr/lib/$(uname -r). try using modprobe ./v4l2loopback.ko (or insmod ./v4l2loopback.ko) to force loading the just-bulit module (or run make install before). you might also need to run depmod -a)

potuz commented 1 month ago

Apologies I just simply forgot to copy/paste the sudo make install step, depmod is unnecessary in my system, but the same error exists either way, and the same error happens with modprobing directly the just built file. I'll update the issue description with the install + depmod phases.

By the way, dmesg (or journalctl -k) does not print absolutely anything more than the context provided, even with BTF debug symbols enabled in the kernel.

potuz commented 1 month ago

I think this can be safely closed, I am finding BTFs errors on other modules now, this must be something on my local configuration, apologies for the noise.

umlaeute / v4l2loopback