Re: Xen Compilation Error on Ubuntu 20.04

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 29/04/2020 18:17, Ayush Dosaj wrote:
> Hi Xen development team,
> 
> I am Ayush. I compiled Xen Hypervisor from source on Ubuntu 20.04
> machine running on an intel-i9 CPU.
> I am getting compilation error due to the following two flags.
> Error: error: ‘-mindirect-branch’ and ‘-fcf-protection’ are not compatible.
> 
> Complete Error logs can be found at https://paste.ubuntu.com/p/xvvyPnhW5c/
> 
> And when I compiled Xen commenting the two flags in Rules.mk file, it
> compiles and installs properly but on boot-up i see a blank black screen
> and i am stuck there.

That is a GCC bug (these options are actually fine in combination).  It
got fixed earlier today in master, and backported for GCC 9.4

You can work around it by appending -fcf-protection=none to CFLAGS

I wouldn't try editing the logic around -mindirect-branch, as that is
related to retpoline safety for Spectre v2, and probably relies on the
build matching the code.

~Andrew