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.
I also looked into returning a &'static [VMStateField] from vmstate_fields!, but that also fails; the fields are 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! { | | _________________^ 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 Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> --- 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 05a833a8b7d..421a236194d 100644 --- a/rust/migration/src/vmstate.rs +++ b/rust/migration/src/vmstate.rs @@ -413,19 +413,30 @@ 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.as_ptr() }} } -- 2.51.0
