rust: add utility procedural macro crate

This commit adds a helper crate library, qemu-api-macros for derive (and
other procedural) macros to be used along qemu-api.

It needs to be a separate library because in Rust, procedural macros, or
macros that can generate arbitrary code, need to be special separate
compilation units.

Only one macro is introduced in this patch, #[derive(Object)]. It
generates a constructor to register a QOM TypeInfo on init and it must
be used on types that implement qemu_api::definitions::ObjectImpl trait.

Reviewed-by: Junjie Mao <junjie.mao@hotmail.com>
Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Link: https://lore.kernel.org/r/dd645642406a6dc2060c6f3f17db2bc77ed67b59.1727961605.git.manos.pitsidianakis@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

rust/qemu-api-macros/Cargo.lock

@@ -0,0 +1,47 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.86"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5e719e8df665df0d1c8fbfd238015744736151d4445ec0836b8e628aae103b77"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "qemu_api_macros"
+version = "0.1.0"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.36"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0fa76aaf39101c457836aec0ce2316dbdc3ab723cdda1c6bd4e6ad4208acaca7"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "syn"
+version = "2.0.72"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc4b9b9bf2add8093d3f2c0204471e951b2285580335de42f9d2534f3ae7a8af"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3354b9ac3fae1ff6755cb6db53683adb661634f67557942dea4facebec0fee4b"

rust/qemu-api-macros/Cargo.toml

@@ -0,0 +1,25 @@
+[package]
+name = "qemu_api_macros"
+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 - Utility macros"
+repository = "https://gitlab.com/qemu-project/qemu/"
+resolver = "2"
+publish = false
+keywords = []
+categories = []
+
+[lib]
+proc-macro = true
+
+[dependencies]
+proc-macro2 = "1"
+quote = "1"
+syn = "2"
+
+# Do not include in any global workspace
+[workspace]

rust/qemu-api-macros/README.md

@@ -0,0 +1 @@
+# `qemu-api-macros` - Utility macros for defining QEMU devices

rust/qemu-api-macros/meson.build

@@ -0,0 +1,25 @@
+add_languages('rust', required: true, native: true)
+
+quote_dep = dependency('quote-1-rs', native: true)
+syn_dep = dependency('syn-2-rs', native: true)
+proc_macro2_dep = dependency('proc-macro2-1-rs', native: true)
+
+_qemu_api_macros_rs = import('rust').proc_macro(
+  'qemu_api_macros',
+  files('src/lib.rs'),
+  override_options: ['rust_std=2021', 'build.rust_std=2021'],
+  rust_args: [
+    '--cfg', 'use_fallback',
+    '--cfg', 'feature="syn-error"',
+    '--cfg', 'feature="proc-macro"',
+  ],
+  dependencies: [
+    proc_macro2_dep,
+    quote_dep,
+    syn_dep,
+  ],
+)
+
+qemu_api_macros = declare_dependency(
+  link_with: _qemu_api_macros_rs,
+)

rust/qemu-api-macros/src/lib.rs

@@ -0,0 +1,43 @@
+// Copyright 2024, Linaro Limited
+// Author(s): Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+use proc_macro::TokenStream;
+use quote::{format_ident, quote};
+use syn::{parse_macro_input, DeriveInput};
+
+#[proc_macro_derive(Object)]
+pub fn derive_object(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+
+    let name = input.ident;
+    let module_static = format_ident!("__{}_LOAD_MODULE", name);
+
+    let expanded = quote! {
+        #[allow(non_upper_case_globals)]
+        #[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 #module_static: extern "C" fn() = {
+            extern "C" fn __register() {
+                unsafe {
+                    ::qemu_api::bindings::type_register_static(&<#name as ::qemu_api::definitions::ObjectImpl>::TYPE_INFO);
+                }
+            }
+
+            extern "C" fn __load() {
+                unsafe {
+                    ::qemu_api::bindings::register_module_init(
+                        Some(__register),
+                        ::qemu_api::bindings::module_init_type::MODULE_INIT_QOM
+                    );
+                }
+            }
+
+            __load
+        };
+    };
+
+    TokenStream::from(expanded)
+}