Merge tag 'for-upstream' of https://gitlab.com/bonzini/qemu into stagingHEADstagingmaster

* cleanups for distributed DTB files
* scripts/meson-buildoptions: Sort coroutine_backend choices lexicographically
* rust/qemu-api: Add initial logging support
: rust: pl011: Implement logging
* target/i386: fix Win98
* meson: cleanup win32 library detection
* rust: safe(r) instance_init
* rust: prepare for multiple bindgen invocations
* rust: fix new warning
* target/i386: Warn about why CPUID_EXT_PDCM is not available
* target/i386: small TDX fixes and clarifications
* target/i386: support for TDX quote generation

# -----BEGIN PGP SIGNATURE-----
#
# iQFIBAABCgAyFiEE8TM4V0tmI4mGbHaCv/vSX3jHroMFAmhVRWsUHHBib256aW5p
# QHJlZGhhdC5jb20ACgkQv/vSX3jHroOyDQf/YqX2jTZbC4jXdHZT6YiDlYPX9MPx
# emFX0S+30X5zNuGYUQufKHEJWshMtklB1seUTQathOPaNeCFK13lY4m1CRbhbrMs
# 3iG4ZQf5V+YTuB+JuE8KfclJeAPXDTnIc2uJbtXErIsPBeEGYZelFLnO5HLiMsY3
# iX9S2hSkjvjlikFv/m9ebg9SMP3+/ZunQMZxsDwgb7U3uqtuZagCJTWz0xTHHHxV
# Ko5OPA0kIydm0NnlHs2DsF1mivmYSSIfBnxg4KXgmJxd3gNGd9SemBQOwYU68x0T
# R3GzI6NLgdP/3mKOsxpM6hFiXBp84eT6zghpdqK5zQFidgz935EXP5WjvQ==
# =ttQr
# -----END PGP SIGNATURE-----
# gpg: Signature made Fri 20 Jun 2025 07:26:35 EDT
# gpg:                using RSA key F13338574B662389866C7682BFFBD25F78C7AE83
# gpg:                issuer "pbonzini@redhat.com"
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>" [full]
# gpg:                 aka "Paolo Bonzini <pbonzini@redhat.com>" [full]
# Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4  E2F7 7E15 100C CD36 69B1
#      Subkey fingerprint: F133 3857 4B66 2389 866C  7682 BFFB D25F 78C7 AE83

* tag 'for-upstream' of https://gitlab.com/bonzini/qemu: (24 commits)
  i386/tdx: handle TDG.VP.VMCALL<GetQuote>
  i386/tdx: handle TDG.VP.VMCALL<GetTdVmCallInfo>
  update Linux headers to v6.16-rc3
  i386/tdx: Clarify the error message of mrconfigid/mrowner/mrownerconfig
  i386/tdx: Fix the typo of the comment of struct TdxGuest
  i386/cpu: Rename enable_cpuid_0x1f to force_cpuid_0x1f
  i386/tdx: Error and exit when named cpu model is requested
  i386/cpu: Warn about why CPUID_EXT_PDCM is not available
  i386/cpu: Move adjustment of CPUID_EXT_PDCM before feature_dependencies[] check
  rust: hpet: fix new warning
  rust: pl011: Add missing logging to match C version
  rust: pl011: Implement logging
  rust/qemu-api: Add initial logging support based on C API
  rust: move rust.bindgen to qemu-api crate
  rust: prepare variable definitions for multiple bindgen invocations
  rust: qom: change instance_init to take a ParentInit<>
  rust: qom: make ParentInit lifetime-invariant
  rust: qom: introduce ParentInit
  rust: hpet: fully initialize object during instance_init
  rust: qemu_api: introduce MaybeUninit field projection
  ...

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

7 files changed, 380 insertions, 29 deletions

diff --git a/rust/qemu-api/src/lib.rs b/rust/qemu-api/src/lib.rs
index 93902fc..86dcd8e 100644
--- a/rust/qemu-api/src/lib.rs
+++ b/rust/qemu-api/src/lib.rs
@@ -21,12 +21,14 @@ pub mod chardev;
 pub mod errno;
 pub mod error;
 pub mod irq;
+pub mod log;
 pub mod memory;
 pub mod module;
 pub mod qdev;
 pub mod qom;
 pub mod sysbus;
 pub mod timer;
+pub mod uninit;
 pub mod vmstate;
 pub mod zeroable;
 
diff --git a/rust/qemu-api/src/log.rs b/rust/qemu-api/src/log.rs
new file mode 100644
index 0000000..d6c3d6c
--- /dev/null
+++ b/rust/qemu-api/src/log.rs
@@ -0,0 +1,73 @@
+// Copyright 2025 Bernhard Beschow <shentey@gmail.com>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+//! Bindings for QEMU's logging infrastructure
+
+#[repr(u32)]
+/// Represents specific error categories within QEMU's logging system.
+///
+/// The `Log` enum provides a Rust abstraction for logging errors, corresponding
+/// to a subset of the error categories defined in the C implementation.
+pub enum Log {
+    /// Log invalid access caused by the guest.
+    /// Corresponds to `LOG_GUEST_ERROR` in the C implementation.
+    GuestError = crate::bindings::LOG_GUEST_ERROR,
+
+    /// Log guest access of unimplemented functionality.
+    /// Corresponds to `LOG_UNIMP` in the C implementation.
+    Unimp = crate::bindings::LOG_UNIMP,
+}
+
+/// A macro to log messages conditionally based on a provided mask.
+///
+/// The `log_mask_ln` macro checks whether the given mask matches the current
+/// log level and, if so, formats and logs the message. It is the Rust
+/// counterpart of the `qemu_log_mask()` macro in the C implementation.
+///
+/// # Parameters
+///
+/// - `$mask`: A log level mask. This should be a variant of the `Log` enum.
+/// - `$fmt`: A format string following the syntax and rules of the `format!`
+///   macro. It specifies the structure of the log message.
+/// - `$args`: Optional arguments to be interpolated into the format string.
+///
+/// # Example
+///
+/// ```
+/// use qemu_api::{log::Log, log_mask_ln};
+///
+/// let error_address = 0xbad;
+/// log_mask_ln!(Log::GuestError, "Address 0x{error_address:x} out of range");
+/// ```
+///
+/// It is also possible to use printf-style formatting, as well as having a
+/// trailing `,`:
+///
+/// ```
+/// use qemu_api::{log::Log, log_mask_ln};
+///
+/// let error_address = 0xbad;
+/// log_mask_ln!(
+///     Log::GuestError,
+///     "Address 0x{:x} out of range",
+///     error_address,
+/// );
+/// ```
+#[macro_export]
+macro_rules! log_mask_ln {
+    ($mask:expr, $fmt:tt $($args:tt)*) => {{
+        // Type assertion to enforce type `Log` for $mask
+        let _: Log = $mask;
+
+        if unsafe {
+            (::qemu_api::bindings::qemu_loglevel & ($mask as std::os::raw::c_int)) != 0
+        } {
+            let formatted_string = format!("{}\n", format_args!($fmt $($args)*));
+            let c_string = std::ffi::CString::new(formatted_string).unwrap();
+
+            unsafe {
+                ::qemu_api::bindings::qemu_log(c_string.as_ptr());
+            }
+        }
+    }};
+}
diff --git a/rust/qemu-api/src/memory.rs b/rust/qemu-api/src/memory.rs
index 9ef2694..e40fad6 100644
--- a/rust/qemu-api/src/memory.rs
+++ b/rust/qemu-api/src/memory.rs
@@ -16,6 +16,7 @@ use crate::{
     callbacks::FnCall,
     cell::Opaque,
     prelude::*,
+    uninit::MaybeUninitField,
     zeroable::Zeroable,
 };
 
@@ -147,7 +148,7 @@ impl MemoryRegion {
     #[inline(always)]
     unsafe fn do_init_io(
         slot: *mut bindings::MemoryRegion,
-        owner: *mut Object,
+        owner: *mut bindings::Object,
         ops: &'static bindings::MemoryRegionOps,
         name: &'static str,
         size: u64,
@@ -156,7 +157,7 @@ impl MemoryRegion {
             let cstr = CString::new(name).unwrap();
             memory_region_init_io(
                 slot,
-                owner.cast::<bindings::Object>(),
+                owner,
                 ops,
                 owner.cast::<c_void>(),
                 cstr.as_ptr(),
@@ -166,16 +167,15 @@ impl MemoryRegion {
     }
 
     pub fn init_io<T: IsA<Object>>(
-        &mut self,
-        owner: *mut T,
+        this: &mut MaybeUninitField<'_, T, Self>,
         ops: &'static MemoryRegionOps<T>,
         name: &'static str,
         size: u64,
     ) {
         unsafe {
             Self::do_init_io(
-                self.0.as_mut_ptr(),
-                owner.cast::<Object>(),
+                this.as_mut_ptr().cast(),
+                MaybeUninitField::parent_mut(this).cast(),
                 &ops.0,
                 name,
                 size,
diff --git a/rust/qemu-api/src/prelude.rs b/rust/qemu-api/src/prelude.rs
index 43bfcd5..8f9e23e 100644
--- a/rust/qemu-api/src/prelude.rs
+++ b/rust/qemu-api/src/prelude.rs
@@ -11,6 +11,8 @@ pub use crate::cell::BqlRefCell;
 
 pub use crate::errno;
 
+pub use crate::log_mask_ln;
+
 pub use crate::qdev::DeviceMethods;
 
 pub use crate::qom::InterfaceType;
diff --git a/rust/qemu-api/src/qdev.rs b/rust/qemu-api/src/qdev.rs
index 0610959..36f02fb 100644
--- a/rust/qemu-api/src/qdev.rs
+++ b/rust/qemu-api/src/qdev.rs
@@ -19,7 +19,7 @@ use crate::{
     error::{Error, Result},
     irq::InterruptSource,
     prelude::*,
-    qom::{ObjectClass, ObjectImpl, Owned},
+    qom::{ObjectClass, ObjectImpl, Owned, ParentInit},
     vmstate::VMStateDescription,
 };
 
@@ -247,15 +247,9 @@ unsafe impl ObjectType for DeviceState {
 }
 qom_isa!(DeviceState: Object);
 
-/// Trait for methods exposed by the [`DeviceState`] class.  The methods can be
-/// called on all objects that have the trait `IsA<DeviceState>`.
-///
-/// The trait should only be used through the blanket implementation,
-/// which guarantees safety via `IsA`.
-pub trait DeviceMethods: ObjectDeref
-where
-    Self::Target: IsA<DeviceState>,
-{
+/// Initialization methods take a [`ParentInit`] and can be called as
+/// associated functions.
+impl DeviceState {
     /// Add an input clock named `name`.  Invoke the callback with
     /// `self` as the first parameter for the events that are requested.
     ///
@@ -266,12 +260,15 @@ where
     /// which Rust code has a reference to a child object) it would be
     /// possible for this function to return a `&Clock` too.
     #[inline]
-    fn init_clock_in<F: for<'a> FnCall<(&'a Self::Target, ClockEvent)>>(
-        &self,
+    pub fn init_clock_in<T: DeviceImpl, F: for<'a> FnCall<(&'a T, ClockEvent)>>(
+        this: &mut ParentInit<T>,
         name: &str,
         _cb: &F,
         events: ClockEvent,
-    ) -> Owned<Clock> {
+    ) -> Owned<Clock>
+    where
+        T::ParentType: IsA<DeviceState>,
+    {
         fn do_init_clock_in(
             dev: &DeviceState,
             name: &str,
@@ -287,10 +284,10 @@ where
             unsafe {
                 let cstr = CString::new(name).unwrap();
                 let clk = bindings::qdev_init_clock_in(
-                    dev.as_mut_ptr(),
+                    dev.0.as_mut_ptr(),
                     cstr.as_ptr(),
                     cb,
-                    dev.as_void_ptr(),
+                    dev.0.as_void_ptr(),
                     events.0,
                 );
 
@@ -307,12 +304,12 @@ where
                 // SAFETY: the opaque is "this", which is indeed a pointer to T
                 F::call((unsafe { &*(opaque.cast::<T>()) }, event))
             }
-            Some(rust_clock_cb::<Self::Target, F>)
+            Some(rust_clock_cb::<T, F>)
         } else {
             None
         };
 
-        do_init_clock_in(self.upcast(), name, cb, events)
+        do_init_clock_in(unsafe { this.upcast_mut() }, name, cb, events)
     }
 
     /// Add an output clock named `name`.
@@ -324,16 +321,30 @@ where
     /// which Rust code has a reference to a child object) it would be
     /// possible for this function to return a `&Clock` too.
     #[inline]
-    fn init_clock_out(&self, name: &str) -> Owned<Clock> {
+    pub fn init_clock_out<T: DeviceImpl>(this: &mut ParentInit<T>, name: &str) -> Owned<Clock>
+    where
+        T::ParentType: IsA<DeviceState>,
+    {
         unsafe {
             let cstr = CString::new(name).unwrap();
-            let clk = bindings::qdev_init_clock_out(self.upcast().as_mut_ptr(), cstr.as_ptr());
+            let dev: &mut DeviceState = this.upcast_mut();
+            let clk = bindings::qdev_init_clock_out(dev.0.as_mut_ptr(), cstr.as_ptr());
 
             let clk: &Clock = Clock::from_raw(clk);
             Owned::from(clk)
         }
     }
+}
 
+/// Trait for methods exposed by the [`DeviceState`] class.  The methods can be
+/// called on all objects that have the trait `IsA<DeviceState>`.
+///
+/// The trait should only be used through the blanket implementation,
+/// which guarantees safety via `IsA`.
+pub trait DeviceMethods: ObjectDeref
+where
+    Self::Target: IsA<DeviceState>,
+{
     fn prop_set_chr(&self, propname: &str, chr: &Owned<Chardev>) {
         assert!(bql_locked());
         let c_propname = CString::new(propname).unwrap();
diff --git a/rust/qemu-api/src/qom.rs b/rust/qemu-api/src/qom.rs
index 14f98fe..e20ee01 100644
--- a/rust/qemu-api/src/qom.rs
+++ b/rust/qemu-api/src/qom.rs
@@ -95,7 +95,8 @@
 use std::{
     ffi::{c_void, CStr},
     fmt,
-    mem::ManuallyDrop,
+    marker::PhantomData,
+    mem::{ManuallyDrop, MaybeUninit},
     ops::{Deref, DerefMut},
     ptr::NonNull,
 };
@@ -206,13 +207,190 @@ impl<T: fmt::Display + ObjectType> fmt::Display for ParentField<T> {
     }
 }
 
+/// This struct knows that the superclasses of the object have already been
+/// initialized.
+///
+/// The declaration of `ParentInit` is.. *"a kind of magic"*.  It uses a
+/// technique that is found in several crates, the main ones probably being
+/// `ghost-cell` (in fact it was introduced by the [`GhostCell` paper](https://plv.mpi-sws.org/rustbelt/ghostcell/))
+/// and `generativity`.
+///
+/// The `PhantomData` makes the `ParentInit` type *invariant* with respect to
+/// the lifetime argument `'init`.  This, together with the `for<'...>` in
+/// `[ParentInit::with]`, block any attempt of the compiler to be creative when
+/// operating on types of type `ParentInit` and to extend their lifetimes.  In
+/// particular, it ensures that the `ParentInit` cannot be made to outlive the
+/// `rust_instance_init()` function that creates it, and therefore that the
+/// `&'init T` reference is valid.
+///
+/// This implementation of the same concept, without the QOM baggage, can help
+/// understanding the effect:
+///
+/// ```
+/// use std::marker::PhantomData;
+///
+/// #[derive(PartialEq, Eq)]
+/// pub struct Jail<'closure, T: Copy>(&'closure T, PhantomData<fn(&'closure ()) -> &'closure ()>);
+///
+/// impl<'closure, T: Copy> Jail<'closure, T> {
+///     fn get(&self) -> T {
+///         *self.0
+///     }
+///
+///     #[inline]
+///     fn with<U>(v: T, f: impl for<'id> FnOnce(Jail<'id, T>) -> U) -> U {
+///         let parent_init = Jail(&v, PhantomData);
+///         f(parent_init)
+///     }
+/// }
+/// ```
+///
+/// It's impossible to escape the `Jail`; `token1` cannot be moved out of the
+/// closure:
+///
+/// ```ignore
+/// let x = 42;
+/// let escape = Jail::with(&x, |token1| {
+///     println!("{}", token1.get());
+///     // fails to compile...
+///     token1
+/// });
+/// // ... so you cannot do this:
+/// println!("{}", escape.get());
+/// ```
+///
+/// Likewise, in the QOM case the `ParentInit` cannot be moved out of
+/// `instance_init()`. Without this trick it would be possible to stash a
+/// `ParentInit` and use it later to access uninitialized memory.
+///
+/// Here is another example, showing how separately-created "identities" stay
+/// isolated:
+///
+/// ```ignore
+/// impl<'closure, T: Copy> Clone for Jail<'closure, T> {
+///     fn clone(&self) -> Jail<'closure, T> {
+///         Jail(self.0, PhantomData)
+///     }
+/// }
+///
+/// fn main() {
+///     Jail::with(42, |token1| {
+///         // this works and returns true: the clone has the same "identity"
+///         println!("{}", token1 == token1.clone());
+///         Jail::with(42, |token2| {
+///             // here the outer token remains accessible...
+///             println!("{}", token1.get());
+///             // ... but the two are separate: this fails to compile:
+///             println!("{}", token1 == token2);
+///         });
+///     });
+/// }
+/// ```
+pub struct ParentInit<'init, T>(
+    &'init mut MaybeUninit<T>,
+    PhantomData<fn(&'init ()) -> &'init ()>,
+);
+
+impl<'init, T> ParentInit<'init, T> {
+    #[inline]
+    pub fn with(obj: &'init mut MaybeUninit<T>, f: impl for<'id> FnOnce(ParentInit<'id, T>)) {
+        let parent_init = ParentInit(obj, PhantomData);
+        f(parent_init)
+    }
+}
+
+impl<T: ObjectType> ParentInit<'_, T> {
+    /// Return the receiver as a mutable raw pointer to Object.
+    ///
+    /// # Safety
+    ///
+    /// Fields beyond `Object` could be uninitialized and it's your
+    /// responsibility to avoid that they're used when the pointer is
+    /// dereferenced, either directly or through a cast.
+    pub fn as_object_mut_ptr(&self) -> *mut bindings::Object {
+        self.as_object_ptr().cast_mut()
+    }
+
+    /// Return the receiver as a mutable raw pointer to Object.
+    ///
+    /// # Safety
+    ///
+    /// Fields beyond `Object` could be uninitialized and it's your
+    /// responsibility to avoid that they're used when the pointer is
+    /// dereferenced, either directly or through a cast.
+    pub fn as_object_ptr(&self) -> *const bindings::Object {
+        self.0.as_ptr().cast()
+    }
+}
+
+impl<'a, T: ObjectImpl> ParentInit<'a, T> {
+    /// Convert from a derived type to one of its parent types, which
+    /// have already been initialized.
+    ///
+    /// # Safety
+    ///
+    /// Structurally this is always a safe operation; the [`IsA`] trait
+    /// provides static verification trait that `Self` dereferences to `U` or
+    /// a child of `U`, and only parent types of `T` are allowed.
+    ///
+    /// However, while the fields of the resulting reference are initialized,
+    /// calls might use uninitialized fields of the subclass.  It is your
+    /// responsibility to avoid this.
+    pub unsafe fn upcast<U: ObjectType>(&self) -> &'a U
+    where
+        T::ParentType: IsA<U>,
+    {
+        // SAFETY: soundness is declared via IsA<U>, which is an unsafe trait;
+        // the parent has been initialized before `instance_init `is called
+        unsafe { &*(self.0.as_ptr().cast::<U>()) }
+    }
+
+    /// Convert from a derived type to one of its parent types, which
+    /// have already been initialized.
+    ///
+    /// # Safety
+    ///
+    /// Structurally this is always a safe operation; the [`IsA`] trait
+    /// provides static verification trait that `Self` dereferences to `U` or
+    /// a child of `U`, and only parent types of `T` are allowed.
+    ///
+    /// However, while the fields of the resulting reference are initialized,
+    /// calls might use uninitialized fields of the subclass.  It is your
+    /// responsibility to avoid this.
+    pub unsafe fn upcast_mut<U: ObjectType>(&mut self) -> &'a mut U
+    where
+        T::ParentType: IsA<U>,
+    {
+        // SAFETY: soundness is declared via IsA<U>, which is an unsafe trait;
+        // the parent has been initialized before `instance_init `is called
+        unsafe { &mut *(self.0.as_mut_ptr().cast::<U>()) }
+    }
+}
+
+impl<T> Deref for ParentInit<'_, T> {
+    type Target = MaybeUninit<T>;
+
+    fn deref(&self) -> &Self::Target {
+        self.0
+    }
+}
+
+impl<T> DerefMut for ParentInit<'_, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.0
+    }
+}
+
 unsafe extern "C" fn rust_instance_init<T: ObjectImpl>(obj: *mut bindings::Object) {
-    let mut state = NonNull::new(obj).unwrap().cast::<T>();
+    let mut state = NonNull::new(obj).unwrap().cast::<MaybeUninit<T>>();
+
     // SAFETY: obj is an instance of T, since rust_instance_init<T>
     // is called from QOM core as the instance_init function
     // for class T
     unsafe {
-        T::INSTANCE_INIT.unwrap()(state.as_mut());
+        ParentInit::with(state.as_mut(), |parent_init| {
+            T::INSTANCE_INIT.unwrap()(parent_init);
+        });
     }
 }
 
@@ -479,7 +657,7 @@ pub trait ObjectImpl: ObjectType + IsA<Object> {
     ///
     /// FIXME: The argument is not really a valid reference. `&mut
     /// MaybeUninit<Self>` would be a better description.
-    const INSTANCE_INIT: Option<unsafe fn(&mut Self)> = None;
+    const INSTANCE_INIT: Option<unsafe fn(ParentInit<Self>)> = None;
 
     /// Function that is called to finish initialization of an object, once
     /// `INSTANCE_INIT` functions have been called.
diff --git a/rust/qemu-api/src/uninit.rs b/rust/qemu-api/src/uninit.rs
new file mode 100644
index 0000000..04123b4
--- /dev/null
+++ b/rust/qemu-api/src/uninit.rs
@@ -0,0 +1,85 @@
+//! Access fields of a [`MaybeUninit`]
+
+use std::{
+    mem::MaybeUninit,
+    ops::{Deref, DerefMut},
+};
+
+pub struct MaybeUninitField<'a, T, U> {
+    parent: &'a mut MaybeUninit<T>,
+    child: *mut U,
+}
+
+impl<'a, T, U> MaybeUninitField<'a, T, U> {
+    #[doc(hidden)]
+    pub fn new(parent: &'a mut MaybeUninit<T>, child: *mut U) -> Self {
+        MaybeUninitField { parent, child }
+    }
+
+    /// Return a constant pointer to the containing object of the field.
+    ///
+    /// Because the `MaybeUninitField` remembers the containing object,
+    /// it is possible to use it in foreign APIs that initialize the
+    /// child.
+    pub fn parent(f: &Self) -> *const T {
+        f.parent.as_ptr()
+    }
+
+    /// Return a mutable pointer to the containing object.
+    ///
+    /// Because the `MaybeUninitField` remembers the containing object,
+    /// it is possible to use it in foreign APIs that initialize the
+    /// child.
+    pub fn parent_mut(f: &mut Self) -> *mut T {
+        f.parent.as_mut_ptr()
+    }
+}
+
+impl<'a, T, U> Deref for MaybeUninitField<'a, T, U> {
+    type Target = MaybeUninit<U>;
+
+    fn deref(&self) -> &MaybeUninit<U> {
+        // SAFETY: self.child was obtained by dereferencing a valid mutable
+        // reference; the content of the memory may be invalid or uninitialized
+        // but MaybeUninit<_> makes no assumption on it
+        unsafe { &*(self.child.cast()) }
+    }
+}
+
+impl<'a, T, U> DerefMut for MaybeUninitField<'a, T, U> {
+    fn deref_mut(&mut self) -> &mut MaybeUninit<U> {
+        // SAFETY: self.child was obtained by dereferencing a valid mutable
+        // reference; the content of the memory may be invalid or uninitialized
+        // but MaybeUninit<_> makes no assumption on it
+        unsafe { &mut *(self.child.cast()) }
+    }
+}
+
+/// ```
+/// #[derive(Debug)]
+/// struct S {
+///     x: u32,
+///     y: u32,
+/// }
+///
+/// # use std::mem::MaybeUninit;
+/// # use qemu_api::{assert_match, uninit_field_mut};
+///
+/// let mut s: MaybeUninit<S> = MaybeUninit::zeroed();
+/// uninit_field_mut!(s, x).write(5);
+/// let s = unsafe { s.assume_init() };
+/// assert_match!(s, S { x: 5, y: 0 });
+/// ```
+#[macro_export]
+macro_rules! uninit_field_mut {
+    ($container:expr, $($field:tt)+) => {{
+        let container__: &mut ::std::mem::MaybeUninit<_> = &mut $container;
+        let container_ptr__ = container__.as_mut_ptr();
+
+        // SAFETY: the container is not used directly, only through a MaybeUninit<>,
+        // so the safety is delegated to the caller and to final invocation of
+        // assume_init()
+        let target__ = unsafe { std::ptr::addr_of_mut!((*container_ptr__).$($field)+) };
+        $crate::uninit::MaybeUninitField::new(container__, target__)
+    }};
+}