Compiling the s390-ccw bios with clang (was: Re: s390-ccw: warning: writing 1 byte into a region of size 0)

[Thomas Huth]

On 23/04/2021 08.52, Christian Borntraeger wrote:
[...]
> We can of course discuss if we compile the BIOS for z10 instead of z900. TCG
> in the mean time can handle up to z13 and z10 is now also 13 years old.

I'd really like to see us supporting Clang in the s390-ccw bios, too, since 
it provides additional useful compiler warnings ... but switching the -mz900 
to -mz10 here also means that we could not boot VMs anymore that use a CPU 
that is older than the z10...

Is anybody still using such old CPUs? Should we maybe deprecate all CPUs 
that are older than the z10 in QEMU? Alternatively, we could try to detect 
Clang in the Makefile, and only use -mz10 in that case and continue to use 
-mz900 in the other case...?

 Thomas