rust: add crate to expose bindings and interfaces

Add rust/qemu-api, which exposes rust-bindgen generated FFI bindings and
provides some declaration macros for symbols visible to the rest of
QEMU.

Co-authored-by: Junjie Mao <junjie.mao@intel.com>
Co-authored-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Junjie Mao <junjie.mao@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Link: https://lore.kernel.org/r/0fb23fbe211761b263aacec03deaf85c0cc39995.1727961605.git.manos.pitsidianakis@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

MAINTAINERS

@@ -3291,6 +3291,12 @@ F: hw/core/register.c
 F: include/hw/register.h
 F: include/hw/registerfields.h
 
+Rust
+M: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
+S: Maintained
+F: rust/qemu-api
+F: rust/rustfmt.toml
+
 SLIRP
 M: Samuel Thibault <samuel.thibault@ens-lyon.org>
 S: Maintained

rust/meson.build

@@ -0,0 +1 @@
+subdir('qemu-api')

rust/qemu-api/.gitignore

@@ -0,0 +1,2 @@
+# Ignore generated bindings file overrides.
+src/bindings.rs

rust/qemu-api/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "qemu_api"
+version = "0.1.0"

rust/qemu-api/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "qemu_api"
+version = "0.1.0"
+edition = "2021"
+authors = ["Manos Pitsidianakis <manos.pitsidianakis@linaro.org>"]
+license = "GPL-2.0-or-later"
+readme = "README.md"
+homepage = "https://www.qemu.org"
+description = "Rust bindings for QEMU"
+repository = "https://gitlab.com/qemu-project/qemu/"
+resolver = "2"
+publish = false
+keywords = []
+categories = []
+
+[dependencies]
+
+[features]
+default = []
+allocator = []
+
+# Do not include in any global workspace
+[workspace]
+
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(MESON)', 'cfg(HAVE_GLIB_WITH_ALIGNED_ALLOC)'] }

rust/qemu-api/README.md

@@ -0,0 +1,17 @@
+# QEMU bindings and API wrappers
+
+This library exports helper Rust types, Rust macros and C FFI bindings for internal QEMU APIs.
+
+The C bindings can be generated with `bindgen`, using this build target:
+
+```console
+$ ninja bindings.rs
+```
+
+## Generate Rust documentation
+
+To generate docs for this crate, including private items:
+
+```sh
+cargo doc --no-deps --document-private-items
+```

rust/qemu-api/build.rs

@@ -0,0 +1,14 @@
+// Copyright 2024, Linaro Limited
+// Author(s): Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+use std::path::Path;
+
+fn main() {
+    if !Path::new("src/bindings.rs").exists() {
+        panic!(
+            "No generated C bindings found! Either build them manually with bindgen or with meson \
+             (`ninja bindings.rs`) and copy them to src/bindings.rs, or build through meson."
+        );
+    }
+}

rust/qemu-api/meson.build

@@ -0,0 +1,21 @@
+_qemu_api_rs = static_library(
+  'qemu_api',
+  structured_sources(
+    [
+      'src/lib.rs',
+      'src/definitions.rs',
+      'src/device_class.rs',
+    ],
+    {'.' : bindings_rs},
+  ),
+  override_options: ['rust_std=2021', 'build.rust_std=2021'],
+  rust_abi: 'rust',
+  rust_args: rustc_args + [
+    '--cfg', 'MESON',
+    # '--cfg', 'feature="allocator"',
+  ],
+)
+
+qemu_api = declare_dependency(
+  link_with: _qemu_api_rs,
+)

rust/qemu-api/src/definitions.rs

@@ -0,0 +1,97 @@
+// Copyright 2024, Linaro Limited
+// Author(s): Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+//! Definitions required by QEMU when registering a device.
+
+use ::core::ffi::{c_void, CStr};
+
+use crate::bindings::{Object, ObjectClass, TypeInfo};
+
+/// Trait a type must implement to be registered with QEMU.
+pub trait ObjectImpl {
+    type Class;
+    const TYPE_INFO: TypeInfo;
+    const TYPE_NAME: &'static CStr;
+    const PARENT_TYPE_NAME: Option<&'static CStr>;
+    const ABSTRACT: bool;
+    const INSTANCE_INIT: Option<unsafe extern "C" fn(obj: *mut Object)>;
+    const INSTANCE_POST_INIT: Option<unsafe extern "C" fn(obj: *mut Object)>;
+    const INSTANCE_FINALIZE: Option<unsafe extern "C" fn(obj: *mut Object)>;
+}
+
+pub trait Class {
+    const CLASS_INIT: Option<unsafe extern "C" fn(klass: *mut ObjectClass, data: *mut c_void)>;
+    const CLASS_BASE_INIT: Option<
+        unsafe extern "C" fn(klass: *mut ObjectClass, data: *mut c_void),
+    >;
+}
+
+#[macro_export]
+macro_rules! module_init {
+    ($func:expr, $type:expr) => {
+        #[used]
+        #[cfg_attr(target_os = "linux", link_section = ".ctors")]
+        #[cfg_attr(target_os = "macos", link_section = "__DATA,__mod_init_func")]
+        #[cfg_attr(target_os = "windows", link_section = ".CRT$XCU")]
+        pub static LOAD_MODULE: extern "C" fn() = {
+            extern "C" fn __load() {
+                unsafe {
+                    $crate::bindings::register_module_init(Some($func), $type);
+                }
+            }
+
+            __load
+        };
+    };
+    (qom: $func:ident => $body:block) => {
+        // NOTE: To have custom identifiers for the ctor func we need to either supply
+        // them directly as a macro argument or create them with a proc macro.
+        #[used]
+        #[cfg_attr(target_os = "linux", link_section = ".ctors")]
+        #[cfg_attr(target_os = "macos", link_section = "__DATA,__mod_init_func")]
+        #[cfg_attr(target_os = "windows", link_section = ".CRT$XCU")]
+        pub static LOAD_MODULE: extern "C" fn() = {
+            extern "C" fn __load() {
+                #[no_mangle]
+                unsafe extern "C" fn $func() {
+                    $body
+                }
+
+                unsafe {
+                    $crate::bindings::register_module_init(
+                        Some($func),
+                        $crate::bindings::module_init_type::MODULE_INIT_QOM,
+                    );
+                }
+            }
+
+            __load
+        };
+    };
+}
+
+#[macro_export]
+macro_rules! type_info {
+    ($t:ty) => {
+        $crate::bindings::TypeInfo {
+            name: <$t as $crate::definitions::ObjectImpl>::TYPE_NAME.as_ptr(),
+            parent: if let Some(pname) = <$t as $crate::definitions::ObjectImpl>::PARENT_TYPE_NAME {
+                pname.as_ptr()
+            } else {
+                ::core::ptr::null_mut()
+            },
+            instance_size: ::core::mem::size_of::<$t>() as $crate::bindings::size_t,
+            instance_align: ::core::mem::align_of::<$t>() as $crate::bindings::size_t,
+            instance_init: <$t as $crate::definitions::ObjectImpl>::INSTANCE_INIT,
+            instance_post_init: <$t as $crate::definitions::ObjectImpl>::INSTANCE_POST_INIT,
+            instance_finalize: <$t as $crate::definitions::ObjectImpl>::INSTANCE_FINALIZE,
+            abstract_: <$t as $crate::definitions::ObjectImpl>::ABSTRACT,
+            class_size:  ::core::mem::size_of::<<$t as $crate::definitions::ObjectImpl>::Class>() as $crate::bindings::size_t,
+            class_init: <<$t as $crate::definitions::ObjectImpl>::Class as $crate::definitions::Class>::CLASS_INIT,
+            class_base_init: <<$t as $crate::definitions::ObjectImpl>::Class as $crate::definitions::Class>::CLASS_BASE_INIT,
+            class_data: ::core::ptr::null_mut(),
+            interfaces: ::core::ptr::null_mut(),
+        };
+    }
+}

rust/qemu-api/src/device_class.rs

@@ -0,0 +1,128 @@
+// Copyright 2024, Linaro Limited
+// Author(s): Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+use std::sync::OnceLock;
+
+use crate::bindings::Property;
+
+#[macro_export]
+macro_rules! device_class_init {
+    ($func:ident, props => $props:ident, realize_fn => $realize_fn:expr, legacy_reset_fn => $legacy_reset_fn:expr, vmsd => $vmsd:ident$(,)*) => {
+        #[no_mangle]
+        pub unsafe extern "C" fn $func(
+            klass: *mut $crate::bindings::ObjectClass,
+            _: *mut ::core::ffi::c_void,
+        ) {
+            let mut dc =
+                ::core::ptr::NonNull::new(klass.cast::<$crate::bindings::DeviceClass>()).unwrap();
+            dc.as_mut().realize = $realize_fn;
+            dc.as_mut().vmsd = &$vmsd;
+            $crate::bindings::device_class_set_legacy_reset(dc.as_mut(), $legacy_reset_fn);
+            $crate::bindings::device_class_set_props(dc.as_mut(), $props.as_mut_ptr());
+        }
+    };
+}
+
+#[macro_export]
+macro_rules! define_property {
+    ($name:expr, $state:ty, $field:expr, $prop:expr, $type:expr, default = $defval:expr$(,)*) => {
+        $crate::bindings::Property {
+            name: {
+                #[used]
+                static _TEMP: &::core::ffi::CStr = $name;
+                _TEMP.as_ptr()
+            },
+            info: $prop,
+            offset: ::core::mem::offset_of!($state, $field)
+                .try_into()
+                .expect("Could not fit offset value to type"),
+            bitnr: 0,
+            bitmask: 0,
+            set_default: true,
+            defval: $crate::bindings::Property__bindgen_ty_1 { u: $defval.into() },
+            arrayoffset: 0,
+            arrayinfo: ::core::ptr::null(),
+            arrayfieldsize: 0,
+            link_type: ::core::ptr::null(),
+        }
+    };
+    ($name:expr, $state:ty, $field:expr, $prop:expr, $type:expr$(,)*) => {
+        $crate::bindings::Property {
+            name: {
+                #[used]
+                static _TEMP: &::core::ffi::CStr = $name;
+                _TEMP.as_ptr()
+            },
+            info: $prop,
+            offset: ::core::mem::offset_of!($state, $field)
+                .try_into()
+                .expect("Could not fit offset value to type"),
+            bitnr: 0,
+            bitmask: 0,
+            set_default: false,
+            defval: $crate::bindings::Property__bindgen_ty_1 { i: 0 },
+            arrayoffset: 0,
+            arrayinfo: ::core::ptr::null(),
+            arrayfieldsize: 0,
+            link_type: ::core::ptr::null(),
+        }
+    };
+}
+
+#[repr(C)]
+pub struct Properties<const N: usize>(pub OnceLock<[Property; N]>, pub fn() -> [Property; N]);
+
+impl<const N: usize> Properties<N> {
+    pub fn as_mut_ptr(&mut self) -> *mut Property {
+        _ = self.0.get_or_init(self.1);
+        self.0.get_mut().unwrap().as_mut_ptr()
+    }
+}
+
+#[macro_export]
+macro_rules! declare_properties {
+    ($ident:ident, $($prop:expr),*$(,)*) => {
+
+        const fn _calc_prop_len() -> usize {
+            let mut len = 1;
+            $({
+                _ = stringify!($prop);
+                len += 1;
+            })*
+            len
+        }
+        const PROP_LEN: usize = _calc_prop_len();
+
+        fn _make_properties() -> [$crate::bindings::Property; PROP_LEN] {
+            [
+                $($prop),*,
+                    unsafe { ::core::mem::MaybeUninit::<$crate::bindings::Property>::zeroed().assume_init() },
+            ]
+        }
+
+        #[no_mangle]
+        pub static mut $ident: $crate::device_class::Properties<PROP_LEN> = $crate::device_class::Properties(::std::sync::OnceLock::new(), _make_properties);
+    };
+}
+
+#[macro_export]
+macro_rules! vm_state_description {
+    ($(#[$outer:meta])*
+     $name:ident,
+     $(name: $vname:expr,)*
+     $(unmigratable: $um_val:expr,)*
+    ) => {
+        #[used]
+        $(#[$outer])*
+        pub static $name: $crate::bindings::VMStateDescription = $crate::bindings::VMStateDescription {
+            $(name: {
+                #[used]
+                static VMSTATE_NAME: &::core::ffi::CStr = $vname;
+                $vname.as_ptr()
+            },)*
+            unmigratable: true,
+            ..unsafe { ::core::mem::MaybeUninit::<$crate::bindings::VMStateDescription>::zeroed().assume_init() }
+        };
+    }
+}

rust/qemu-api/src/lib.rs

@@ -0,0 +1,166 @@
+// Copyright 2024, Linaro Limited
+// Author(s): Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#![cfg_attr(not(MESON), doc = include_str!("../README.md"))]
+
+#[allow(
+    dead_code,
+    improper_ctypes_definitions,
+    improper_ctypes,
+    non_camel_case_types,
+    non_snake_case,
+    non_upper_case_globals,
+    unsafe_op_in_unsafe_fn,
+    clippy::missing_const_for_fn,
+    clippy::too_many_arguments,
+    clippy::approx_constant,
+    clippy::use_self,
+    clippy::useless_transmute,
+    clippy::missing_safety_doc,
+)]
+#[rustfmt::skip]
+pub mod bindings;
+
+unsafe impl Send for bindings::Property {}
+unsafe impl Sync for bindings::Property {}
+unsafe impl Sync for bindings::TypeInfo {}
+unsafe impl Sync for bindings::VMStateDescription {}
+
+pub mod definitions;
+pub mod device_class;
+
+#[cfg(test)]
+mod tests;
+
+use std::alloc::{GlobalAlloc, Layout};
+
+#[cfg(HAVE_GLIB_WITH_ALIGNED_ALLOC)]
+extern "C" {
+    fn g_aligned_alloc0(
+        n_blocks: bindings::gsize,
+        n_block_bytes: bindings::gsize,
+        alignment: bindings::gsize,
+    ) -> bindings::gpointer;
+    fn g_aligned_free(mem: bindings::gpointer);
+}
+
+#[cfg(not(HAVE_GLIB_WITH_ALIGNED_ALLOC))]
+extern "C" {
+    fn qemu_memalign(alignment: usize, size: usize) -> *mut ::core::ffi::c_void;
+    fn qemu_vfree(ptr: *mut ::core::ffi::c_void);
+}
+
+extern "C" {
+    fn g_malloc0(n_bytes: bindings::gsize) -> bindings::gpointer;
+    fn g_free(mem: bindings::gpointer);
+}
+
+/// An allocator that uses the same allocator as QEMU in C.
+///
+/// It is enabled by default with the `allocator` feature.
+///
+/// To set it up manually as a global allocator in your crate:
+///
+/// ```ignore
+/// use qemu_api::QemuAllocator;
+///
+/// #[global_allocator]
+/// static GLOBAL: QemuAllocator = QemuAllocator::new();
+/// ```
+#[derive(Clone, Copy, Debug)]
+#[repr(C)]
+pub struct QemuAllocator {
+    _unused: [u8; 0],
+}
+
+#[cfg_attr(all(feature = "allocator", not(test)), global_allocator)]
+pub static GLOBAL: QemuAllocator = QemuAllocator::new();
+
+impl QemuAllocator {
+    // From the glibc documentation, on GNU systems, malloc guarantees 16-byte
+    // alignment on 64-bit systems and 8-byte alignment on 32-bit systems. See
+    // https://www.gnu.org/software/libc/manual/html_node/Malloc-Examples.html.
+    // This alignment guarantee also applies to Windows and Android. On Darwin
+    // and OpenBSD, the alignment is 16 bytes on both 64-bit and 32-bit systems.
+    #[cfg(all(
+        target_pointer_width = "32",
+        not(any(target_os = "macos", target_os = "openbsd"))
+    ))]
+    pub const DEFAULT_ALIGNMENT_BYTES: Option<usize> = Some(8);
+    #[cfg(all(
+        target_pointer_width = "64",
+        not(any(target_os = "macos", target_os = "openbsd"))
+    ))]
+    pub const DEFAULT_ALIGNMENT_BYTES: Option<usize> = Some(16);
+    #[cfg(all(
+        any(target_pointer_width = "32", target_pointer_width = "64"),
+        any(target_os = "macos", target_os = "openbsd")
+    ))]
+    pub const DEFAULT_ALIGNMENT_BYTES: Option<usize> = Some(16);
+    #[cfg(not(any(target_pointer_width = "32", target_pointer_width = "64")))]
+    pub const DEFAULT_ALIGNMENT_BYTES: Option<usize> = None;
+
+    pub const fn new() -> Self {
+        Self { _unused: [] }
+    }
+}
+
+impl Default for QemuAllocator {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+// Sanity check.
+const _: [(); 8] = [(); ::core::mem::size_of::<*mut ::core::ffi::c_void>()];
+
+unsafe impl GlobalAlloc for QemuAllocator {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        if matches!(Self::DEFAULT_ALIGNMENT_BYTES, Some(default) if default.checked_rem(layout.align()) == Some(0))
+        {
+            // SAFETY: g_malloc0() is safe to call.
+            unsafe { g_malloc0(layout.size().try_into().unwrap()).cast::<u8>() }
+        } else {
+            #[cfg(HAVE_GLIB_WITH_ALIGNED_ALLOC)]
+            {
+                // SAFETY: g_aligned_alloc0() is safe to call.
+                unsafe {
+                    g_aligned_alloc0(
+                        layout.size().try_into().unwrap(),
+                        1,
+                        layout.align().try_into().unwrap(),
+                    )
+                    .cast::<u8>()
+                }
+            }
+            #[cfg(not(HAVE_GLIB_WITH_ALIGNED_ALLOC))]
+            {
+                // SAFETY: qemu_memalign() is safe to call.
+                unsafe { qemu_memalign(layout.align(), layout.size()).cast::<u8>() }
+            }
+        }
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        if matches!(Self::DEFAULT_ALIGNMENT_BYTES, Some(default) if default.checked_rem(layout.align()) == Some(0))
+        {
+            // SAFETY: `ptr` must have been allocated by Self::alloc thus a valid
+            // glib-allocated pointer, so `g_free`ing is safe.
+            unsafe { g_free(ptr.cast::<_>()) }
+        } else {
+            #[cfg(HAVE_GLIB_WITH_ALIGNED_ALLOC)]
+            {
+                // SAFETY: `ptr` must have been allocated by Self::alloc thus a valid aligned
+                // glib-allocated pointer, so `g_aligned_free`ing is safe.
+                unsafe { g_aligned_free(ptr.cast::<_>()) }
+            }
+            #[cfg(not(HAVE_GLIB_WITH_ALIGNED_ALLOC))]
+            {
+                // SAFETY: `ptr` must have been allocated by Self::alloc thus a valid aligned
+                // glib-allocated pointer, so `qemu_vfree`ing is safe.
+                unsafe { qemu_vfree(ptr.cast::<_>()) }
+            }
+        }
+    }
+}

rust/qemu-api/src/tests.rs

@@ -0,0 +1,49 @@
+// Copyright 2024, Linaro Limited
+// Author(s): Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+use crate::{
+    bindings::*, declare_properties, define_property, device_class_init, vm_state_description,
+};
+
+#[test]
+fn test_device_decl_macros() {
+    // Test that macros can compile.
+    vm_state_description! {
+        VMSTATE,
+        name: c"name",
+        unmigratable: true,
+    }
+
+    #[repr(C)]
+    pub struct DummyState {
+        pub char_backend: CharBackend,
+        pub migrate_clock: bool,
+    }
+
+    declare_properties! {
+        DUMMY_PROPERTIES,
+            define_property!(
+                c"chardev",
+                DummyState,
+                char_backend,
+                unsafe { &qdev_prop_chr },
+                CharBackend
+            ),
+            define_property!(
+                c"migrate-clk",
+                DummyState,
+                migrate_clock,
+                unsafe { &qdev_prop_bool },
+                bool
+            ),
+    }
+
+    device_class_init! {
+        dummy_class_init,
+        props => DUMMY_PROPERTIES,
+        realize_fn => None,
+        reset_fn => None,
+        vmsd => VMSTATE,
+    }
+}

rust/rustfmt.toml

@@ -0,0 +1,7 @@
+edition = "2021"
+format_generated_files = false
+format_code_in_doc_comments = true
+format_strings = true
+imports_granularity = "Crate"
+group_imports = "StdExternalCrate"
+wrap_comments = true