Re: [XEN PATCH v8 00/47] xen: Build system improvements, now with out-of-tree build!

[Jan Beulich <jbeulich@xxxxxxxx>]

On 25.11.2021 14:39, Anthony PERARD wrote:
> Patch series available in this git branch:
> https://xenbits.xen.org/git-http/people/aperard/xen-unstable.git 
> br.build-system-xen-v8
> 
> v8:
>     Mostly rework of v7. With many patch already applied.
>     Some detail changes that are spread through many patches:
>     - `make cloc` recipe should now work throughout the series, update of it 
> is
>       done in 3 patches.
>     - new patch "build: fix enforce unique symbols for recent clang version"
>       to fix an issue with clang.
>     - introducing $(srctree) and $(objtree) earlier
>     - introducing $(srcdir) as shortcut for $(srctree)/$(src)
>     - introduce usage of -iquote instead of -I in some cases
>     More detail change log can be found in patches notes.
> 
>     Also this v8 present a work-in-progress of the ability to do out-of-tree
>     build without setting VPATH. This is presented as an alternative to force
>     use of out-of-tree build. As the last patch show, it allows to build the
>     xen-shim without the linkfarm and we don't need to make any other changes
>     to any thing that build xen (osstest, distribution packages, xen.git, ...,
>     and developers finger macros). The patches are only there as WIP / RFC as
>     they were some concern about the usefulness and extra changes needed.
>     We can decide whether those changes are good or if this is too much and we
>     should force out-of-tree build for the hypervisor.

I'm afraid I'm of two minds here. I don't think we want to force people to
do out-of-tree builds, but I also dislike the idea of mixing in-tree and
out-of-tree builds. Yet reading the above I understand that the shim build
would conflict with an in-tree build because certain files would be picked
(the shim build being an out-of-tree one) from the (dirtied) source tree,
rather than the shim's build tree. Perhaps the extra path prefixes that I
commented upon in an individual patch are then indeed the least bad route
to take.

There's one compromise which comes to mind, but which may also not be
liked: We could simply fail out-of-tree builds when the source tree is
dirty. Then people wanting the shim built would need to use out-of-tree
builds also for the "main" hypervisor, but people suppressing the shim
build anyway (or doing it separately, e.g. using a non-default .config)
could continue to do in-tree builds. The one puzzle piece I'm lacking so
far (perhaps simply because of having overlooked where it is) is how, for
a full-build-of-everything, one would control where the xen/ part of the
build would go _outside_ of the source (sub-)tree.

Jan