rust: pl011: fix migration stream

The Rust vmstate macros lack the type-safety of their C equivalents (so
safe, much abstraction), and therefore they were predictably wrong.

The registers have already been changed to 32-bits in the previous patch,
but read_pos/read_count/read_trigger also have to be u32 instead of usize.
The easiest way to do so is to let the FIFO use u32 indices instead
of usize.

My plan for making VMStateField typesafe is to have a trait to retrieve
a basic VMStateField; for example something like vmstate_uint32 would
become an implementation of the VMState trait on u32.  Then you'd write
something like "vmstate_of!(Type, field).with_version_id(2)".  That is,
vmstate_of retrieves the basic VMStateField and fills in the offset,
and then more changes can be applied on top.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

rust/hw/char/pl011/src/device.rs

@@ -31,7 +31,7 @@
 const FBRD_MASK: u32 = 0x3f;
 
 /// QEMU sourced constant.
-pub const PL011_FIFO_DEPTH: usize = 16_usize;
+pub const PL011_FIFO_DEPTH: u32 = 16;
 
 #[derive(Clone, Copy, Debug)]
 enum DeviceId {
@@ -56,6 +56,32 @@ impl DeviceId {
     const PL011_ID_LUMINARY: [c_uchar; 8] = [0x11, 0x00, 0x18, 0x01, 0x0d, 0xf0, 0x05, 0xb1];
 }
 
+// FIFOs use 32-bit indices instead of usize, for compatibility with
+// the migration stream produced by the C version of this device.
+#[repr(transparent)]
+#[derive(Debug, Default)]
+pub struct Fifo([registers::Data; PL011_FIFO_DEPTH as usize]);
+
+impl Fifo {
+    const fn len(&self) -> u32 {
+        self.0.len() as u32
+    }
+}
+
+impl std::ops::IndexMut<u32> for Fifo {
+    fn index_mut(&mut self, idx: u32) -> &mut Self::Output {
+        &mut self.0[idx as usize]
+    }
+}
+
+impl std::ops::Index<u32> for Fifo {
+    type Output = registers::Data;
+
+    fn index(&self, idx: u32) -> &Self::Output {
+        &self.0[idx as usize]
+    }
+}
+
 #[repr(C)]
 #[derive(Debug, qemu_api_macros::Object, qemu_api_macros::offsets)]
 /// PL011 Device Model in QEMU
@@ -73,14 +99,14 @@ pub struct PL011State {
     pub dmacr: u32,
     pub int_enabled: u32,
     pub int_level: u32,
-    pub read_fifo: [registers::Data; PL011_FIFO_DEPTH],
+    pub read_fifo: Fifo,
     pub ilpr: u32,
     pub ibrd: u32,
     pub fbrd: u32,
     pub ifl: u32,
-    pub read_pos: usize,
-    pub read_count: usize,
-    pub read_trigger: usize,
+    pub read_pos: u32,
+    pub read_count: u32,
+    pub read_trigger: u32,
     #[doc(alias = "chr")]
     pub char_backend: CharBackend,
     /// QEMU interrupts
@@ -480,7 +506,7 @@ pub fn loopback_enabled(&self) -> bool {
     }
 
     #[inline]
-    pub fn fifo_depth(&self) -> usize {
+    pub fn fifo_depth(&self) -> u32 {
         // Note: FIFO depth is expected to be power-of-2
         if self.fifo_enabled() {
             return PL011_FIFO_DEPTH;

rust/hw/char/pl011/src/device_class.rs

@@ -6,8 +6,8 @@
 use std::os::raw::{c_int, c_void};
 
 use qemu_api::{
-    bindings::*, c_str, vmstate_clock, vmstate_fields, vmstate_int32, vmstate_subsections,
-    vmstate_uint32, vmstate_uint32_array, vmstate_unused, zeroable::Zeroable,
+    bindings::*, c_str, vmstate_clock, vmstate_fields, vmstate_subsections, vmstate_uint32,
+    vmstate_uint32_array, vmstate_unused, zeroable::Zeroable,
 };
 
 use crate::device::{PL011State, PL011_FIFO_DEPTH};
@@ -64,9 +64,9 @@ extern "C" fn pl011_post_load(opaque: *mut c_void, version_id: c_int) -> c_int {
         vmstate_uint32!(ibrd, PL011State),
         vmstate_uint32!(fbrd, PL011State),
         vmstate_uint32!(ifl, PL011State),
-        vmstate_int32!(read_pos, PL011State),
-        vmstate_int32!(read_count, PL011State),
-        vmstate_int32!(read_trigger, PL011State),
+        vmstate_uint32!(read_pos, PL011State),
+        vmstate_uint32!(read_count, PL011State),
+        vmstate_uint32!(read_trigger, PL011State),
     },
     subsections: vmstate_subsections! {
         VMSTATE_PL011_CLOCK

rust/qemu-api/src/vmstate.rs

@@ -106,28 +106,6 @@ macro_rules! vmstate_uint32 {
     }};
 }
 
-#[doc(alias = "VMSTATE_INT32_V")]
-#[macro_export]
-macro_rules! vmstate_int32_v {
-    ($field_name:ident, $struct_name:ty, $version_id:expr) => {{
-        $crate::vmstate_single!(
-            $field_name,
-            $struct_name,
-            $version_id,
-            ::core::ptr::addr_of!($crate::bindings::vmstate_info_int32),
-            ::core::mem::size_of::<i32>()
-        )
-    }};
-}
-
-#[doc(alias = "VMSTATE_INT32")]
-#[macro_export]
-macro_rules! vmstate_int32 {
-    ($field_name:ident, $struct_name:ty) => {{
-        $crate::vmstate_int32_v!($field_name, $struct_name, 0)
-    }};
-}
-
 #[doc(alias = "VMSTATE_ARRAY")]
 #[macro_export]
 macro_rules! vmstate_array {