Mainline Ubuntu Linux kernel builds failing for >= 5.1.17 and >= 5.2 on AMD64 and i386

[semreh]

As subject says, the compiled Ubuntu kernels for >= 5.1.17 and >= 5.2 on AMD64 and i386 are failing to build.

Build logs at (for example):

https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.2.1/BUILD.LOG.amd64
https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.2.1/BUILD.LOG.i386

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1837036

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[semreh (launchpad-via-forwarder)]

The bug is in the Ubuntu controlled mainline kernel build system, and a link to the logs generated by that system has been provided.

[semreh (launchpad-via-forwarder)]

According to this comment ( https://www.phoronix.com/forums/forum/software/general-linux-open-source/1113503-linux-5-2-1-released-for-riding-the-latest-stable-kernel?p=1113668#post1113668 )at Phoronix, the underlying cause is:

"Ubuntu is using -fcf-protection by default now and that isn't compatible with -mindirect-branch that the kernel uses for retpolines. "

Bug 1830961 appears to be an earllier report, so this is a duplicate of that bug, as is bug 1836373