CODEWITHSUNDEEP
linuxlinux-kerneldriverlinux-device-driverkbuild
Alan Spark
Alan Spark

Reputation: 8292

Problems building driver on Linux kernel 5.8.x

I'm working with a Linux driver that is building on v5.7.x kernels but not on the latest v5.8.x releases.

To summarise, most of the driver is pre-built and the kernel interface is built on the target. This involves a make -f Kbuild command.

Having checked all of the relevant kernel interface files for any changes that would affect us, normally the driver would just build as usual on a new kernel. However, this time we get the following error:

make[2]: *** [scripts/Makefile.modpost:111: /path/to/source/Module.symvers] Error 1
make[1]: *** [Makefile:1669: modules] Error 2
make[1]: Leaving directory '/usr/src/kernels/5.8.0-1.el8.elrepo.x86_64'
make: *** [Kbuild:26: default] Error 2

This is from CentOS 8.1, but the same error has been seen on Ubuntu 20.04.

I am no expert on this so interpreting these errors is a bit difficult. I have tried building with the KBUILD_VERBOSE flag and it doesn't really provide any useful information, other than the build succeeding until this point.

On previous kernels the Module.symvers file would be created but empty. On 5.8 this file is not created at all presumably due to this error. As a result, the .ko file is not created.

Finally, if we drop in the source files rather than the pre-built .o files the build does succeed. These .o files are built with a very old version of GCC (4.4.7) but we have also tried building with a much newer version (8.3.1), the same version as the target machine.

I would appreciate suggestions for things to check. Let me know if any other details would help.

Edit:

I ran make on Makefile.modpost manually and got the following output:

sudo make -f ./scripts/Makefile.modpost
WARNING: Symbol version dump "vmlinux.symvers" is missing.
         Modules may not have dependencies or modversions.
make -f /scripts/Makefile.modfinal
make[1]: Entering directory '/usr/src/linux-headers-5.8.0-050800-generic'
make[1]: /scripts/Makefile.modfinal: No such file or directory
make[1]: *** No rule to make target '/scripts/Makefile.modfinal'. Stop.
make[1]: Leaving directory '/usr/src/linux-headers-5.8.0-050800-generic'
make: *** [scripts/Makefile.modpost:117: __modpost] Error 2

Upvotes: 4

Views: 8730

Answers (1)

Alan Spark
Alan Spark

Reputation: 8292

I am answering my own question in case it helps anyone else with this problem. Although it has never been an issue in the past, we've always had a warning that the corresponding .o.cmd file was not present for our .o_shipped files. This appears to be important in kernel 5.8 onwards and my fix was to add a touch command to the Kbuild file (i.e. "touch .driver.o.cmd"). This does not remove the warning but it allows the driver to build as normal.

Upvotes: 8

Related Questions