Re: QEMU patches for native windows support through clang-cl

[Erwin Jansen]

Would a good next step be to work out some more details in a document that outlines what process we are using, what we are planning to do and include a set of suggestions as a starting point to see if we can upstream some of the changes to the larger community?

We currently don't have a proper solution for packing. We are tracking the issue here https://issuetracker.google.com/issues/380295845. All our code is public and development is happening on the emu-dev repository: https://android.googlesource.com/platform/external/qemu/+/emu-dev 

Greetings,

Erwin. 

On Thu, Nov 21, 2024 at 10:47 AM Paolo Bonzini <pbonzini@redhat.com> wrote:

> NB As a general point, we actively block use of clang with Windows
> builds (more strictly in 9.2 now), because it lacks support for the
> 'gcc_struct' annotation that we rely on to guarantee correct ABI for
> structs exposed to guests in particular.

Ah, good point. This is
https://github.com/llvm/llvm-project/issues/24757 for the general
tracking issue, and https://github.com/llvm/llvm-project/pull/71148
for a recent PR that attempts to implement this.

Using -mno-ms-bitfields globally is unsafe because there are probably
Windows API structs that implement it.

One solution is to add `QEMU_BUILD_BUG_ON(sizeof(...) == ...)` to all
structs in QEMU that use bitfields. That will prove very quickly if
there are issues or not.

Paolo

> Many people try to simply remove that #ifdef, mistakenly assuming that
> because the code compiles without warnings, it must be correct. Did
> you have solution for this, as it would be a blocker for enabling
> clang on Windows currently ?
>
> With regards,
> Daniel
> --
> |: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
> |: https://libvirt.org         -o-            https://fstop138.berrange.com :|
> |: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|
>