This is useful when building a VMState for generic structs, because you have
to avoid nested statics. Using vmstate_fields! will fail in the likely case
where the _FIELDS static uses Self from an outer item, because that is
forbidden.
The separate macros are needed because you cannot just do
.fields(vmstate_fields_ref! {
vmstate_of!(PL011State, clock),
})
The value returned by vmstate_fields_ref! is not promoted to static, which is
unfortunate but intentional (https://github.com/rust-lang/rust/issues/60502):
error[E0716]: temporary value dropped while borrowed
--> rust/hw/char/pl011/libpl011.rlib.p/structured/device.rs:743:17
|
738 | / VMStateDescriptionBuilder::<PL011State>::new()
739 | | .name(c"pl011/clock")
740 | | .version_id(1)
741 | | .minimum_version_id(1)
742 | | .needed(&PL011State::clock_needed)
743 | | .fields(vmstate_fields_ref! {
| | _________________^
744 | || vmstate_of!(PL011State, clock),
745 | || })
| ||_________^- argument requires that borrow lasts for `'static`
| |_________|
| creates a temporary value which is freed while still in use
746 | .build();
| - temporary value is freed at the end of this statement
Thus it is necessary to use the "static", whether explicitly or hidden by
vmstate_fields.
Signed-off-by: Paolo Bonzini <[email protected]>
---
rust/migration/src/vmstate.rs | 23 +++++++++++++++++------
1 file changed, 17 insertions(+), 6 deletions(-)
diff --git a/rust/migration/src/vmstate.rs b/rust/migration/src/vmstate.rs
index 22799dffdc7..2900ef1127a 100644
--- a/rust/migration/src/vmstate.rs
+++ b/rust/migration/src/vmstate.rs
@@ -411,19 +411,30 @@ const fn phantom__<T>(_: &T) ->
::core::marker::PhantomData<T> {
}};
}
+/// Add a terminator to the fields in the arguments, and return
+/// a reference to the resulting array of values.
+#[macro_export]
+macro_rules! vmstate_fields_ref {
+ ($($field:expr),*$(,)*) => {
+ &[
+ $($field),*,
+ $crate::bindings::VMStateField {
+ flags: $crate::bindings::VMStateFlags::VMS_END,
+ ..::common::zeroable::Zeroable::ZERO
+ }
+ ]
+ }
+}
+
/// Helper macro to declare a list of
/// ([`VMStateField`](`crate::bindings::VMStateField`)) into a static and
return
/// a pointer to the array of values it created.
#[macro_export]
macro_rules! vmstate_fields {
($($field:expr),*$(,)*) => {{
- static _FIELDS: &[$crate::bindings::VMStateField] = &[
+ static _FIELDS: &[$crate::bindings::VMStateField] =
$crate::vmstate_fields_ref!(
$($field),*,
- $crate::bindings::VMStateField {
- flags: $crate::bindings::VMStateFlags::VMS_END,
- ..::common::zeroable::Zeroable::ZERO
- }
- ];
+ );
_FIELDS
}}
}
--
2.51.0
