From f3518400882022ddcbe1148abf2165917a7b4640 Mon Sep 17 00:00:00 2001 From: Junjie Mao Date: Thu, 24 Oct 2024 12:25:15 +0200 Subject: [PATCH] rust: introduce alternative implementation of offset_of! offset_of! was stabilized in Rust 1.77.0. Use an alternative implemenation that was found on the Rust forums, and whose author agreed to license as MIT for use in QEMU. The alternative allows only one level of field access, but apart from this can be used just by replacing core::mem::offset_of! with qemu_api::offset_of!. The actual implementation of offset_of! is done in a declarative macro, but for simplicity and to avoid introducing an extra level of indentation, the trigger is a procedural macro #[derive(offsets)]. The procedural macro is perhaps a bit overengineered, but it helps introducing some idioms that will be useful in the future as well. Signed-off-by: Junjie Mao Co-developed-by: Paolo Bonzini Signed-off-by: Paolo Bonzini --- rust/Cargo.lock | 1 + rust/hw/char/pl011/src/device.rs | 2 +- rust/qemu-api-macros/Cargo.toml | 2 +- rust/qemu-api-macros/src/lib.rs | 75 +++++++- rust/qemu-api/Cargo.toml | 6 +- rust/qemu-api/build.rs | 9 + rust/qemu-api/meson.build | 12 +- rust/qemu-api/src/device_class.rs | 8 +- rust/qemu-api/src/lib.rs | 4 + rust/qemu-api/src/offset_of.rs | 161 ++++++++++++++++++ rust/qemu-api/src/vmstate.rs | 10 +- rust/qemu-api/tests/tests.rs | 1 + subprojects/packagefiles/syn-2-rs/meson.build | 1 + 13 files changed, 274 insertions(+), 18 deletions(-) create mode 100644 rust/qemu-api/src/offset_of.rs diff --git a/rust/Cargo.lock b/rust/Cargo.lock index 9f43b33e8b89..c0c6069247a8 100644 --- a/rust/Cargo.lock +++ b/rust/Cargo.lock @@ -93,6 +93,7 @@ name = "qemu_api" version = "0.1.0" dependencies = [ "qemu_api_macros", + "version_check", ] [[package]] diff --git a/rust/hw/char/pl011/src/device.rs b/rust/hw/char/pl011/src/device.rs index 2d225d544dec..bca727e37f0d 100644 --- a/rust/hw/char/pl011/src/device.rs +++ b/rust/hw/char/pl011/src/device.rs @@ -55,7 +55,7 @@ impl DeviceId { } #[repr(C)] -#[derive(Debug, qemu_api_macros::Object)] +#[derive(Debug, qemu_api_macros::Object, qemu_api_macros::offsets)] /// PL011 Device Model in QEMU pub struct PL011State { pub parent_obj: SysBusDevice, diff --git a/rust/qemu-api-macros/Cargo.toml b/rust/qemu-api-macros/Cargo.toml index f8d6d03609fc..a8f7377106b5 100644 --- a/rust/qemu-api-macros/Cargo.toml +++ b/rust/qemu-api-macros/Cargo.toml @@ -19,4 +19,4 @@ proc-macro = true [dependencies] proc-macro2 = "1" quote = "1" -syn = "2" +syn = { version = "2", features = ["extra-traits"] } diff --git a/rust/qemu-api-macros/src/lib.rs b/rust/qemu-api-macros/src/lib.rs index a4bc5d01ee86..cf99ac04b8fa 100644 --- a/rust/qemu-api-macros/src/lib.rs +++ b/rust/qemu-api-macros/src/lib.rs @@ -3,8 +3,34 @@ // SPDX-License-Identifier: GPL-2.0-or-later use proc_macro::TokenStream; -use quote::quote; -use syn::{parse_macro_input, DeriveInput}; +use proc_macro2::Span; +use quote::{quote, quote_spanned}; +use syn::{ + parse_macro_input, parse_quote, punctuated::Punctuated, token::Comma, Data, DeriveInput, Field, + Fields, Ident, Type, Visibility, +}; + +struct CompileError(String, Span); + +impl From for proc_macro2::TokenStream { + fn from(err: CompileError) -> Self { + let CompileError(msg, span) = err; + quote_spanned! { span => compile_error!(#msg); } + } +} + +fn is_c_repr(input: &DeriveInput, msg: &str) -> Result<(), CompileError> { + let expected = parse_quote! { #[repr(C)] }; + + if input.attrs.iter().any(|attr| attr == &expected) { + Ok(()) + } else { + Err(CompileError( + format!("#[repr(C)] required for {}", msg), + input.ident.span(), + )) + } +} #[proc_macro_derive(Object)] pub fn derive_object(input: TokenStream) -> TokenStream { @@ -21,3 +47,48 @@ pub fn derive_object(input: TokenStream) -> TokenStream { TokenStream::from(expanded) } + +fn get_fields(input: &DeriveInput) -> Result<&Punctuated, CompileError> { + if let Data::Struct(s) = &input.data { + if let Fields::Named(fs) = &s.fields { + Ok(&fs.named) + } else { + Err(CompileError( + "Cannot generate offsets for unnamed fields.".to_string(), + input.ident.span(), + )) + } + } else { + Err(CompileError( + "Cannot generate offsets for union or enum.".to_string(), + input.ident.span(), + )) + } +} + +#[rustfmt::skip::macros(quote)] +fn derive_offsets_or_error(input: DeriveInput) -> Result { + is_c_repr(&input, "#[derive(offsets)]")?; + + let name = &input.ident; + let fields = get_fields(&input)?; + let field_names: Vec<&Ident> = fields.iter().map(|f| f.ident.as_ref().unwrap()).collect(); + let field_types: Vec<&Type> = fields.iter().map(|f| &f.ty).collect(); + let field_vis: Vec<&Visibility> = fields.iter().map(|f| &f.vis).collect(); + + Ok(quote! { + ::qemu_api::with_offsets! { + struct #name { + #(#field_vis #field_names: #field_types,)* + } + } + }) +} + +#[proc_macro_derive(offsets)] +pub fn derive_offsets(input: TokenStream) -> TokenStream { + let input = parse_macro_input!(input as DeriveInput); + let expanded = derive_offsets_or_error(input).unwrap_or_else(Into::into); + + TokenStream::from(expanded) +} diff --git a/rust/qemu-api/Cargo.toml b/rust/qemu-api/Cargo.toml index e092f61e8f3d..cc716d75d460 100644 --- a/rust/qemu-api/Cargo.toml +++ b/rust/qemu-api/Cargo.toml @@ -16,9 +16,13 @@ categories = [] [dependencies] qemu_api_macros = { path = "../qemu-api-macros" } +[build-dependencies] +version_check = "~0.9" + [features] default = [] allocator = [] [lints.rust] -unexpected_cfgs = { level = "warn", check-cfg = ['cfg(MESON)', 'cfg(HAVE_GLIB_WITH_ALIGNED_ALLOC)'] } +unexpected_cfgs = { level = "warn", check-cfg = ['cfg(MESON)', 'cfg(HAVE_GLIB_WITH_ALIGNED_ALLOC)', + 'cfg(has_offset_of)'] } diff --git a/rust/qemu-api/build.rs b/rust/qemu-api/build.rs index 419b154c2d26..20f8f718b90c 100644 --- a/rust/qemu-api/build.rs +++ b/rust/qemu-api/build.rs @@ -4,6 +4,8 @@ use std::path::Path; +use version_check as rustc; + fn main() { if !Path::new("src/bindings.rs").exists() { panic!( @@ -11,4 +13,11 @@ fn main() { (`ninja bindings.rs`) and copy them to src/bindings.rs, or build through meson." ); } + + // Check for available rustc features + if rustc::is_min_version("1.77.0").unwrap_or(false) { + println!("cargo:rustc-cfg=has_offset_of"); + } + + println!("cargo:rerun-if-changed=build.rs"); } diff --git a/rust/qemu-api/meson.build b/rust/qemu-api/meson.build index c950b008d592..6f637af7b1be 100644 --- a/rust/qemu-api/meson.build +++ b/rust/qemu-api/meson.build @@ -1,3 +1,9 @@ +_qemu_api_cfg = ['--cfg', 'MESON'] +# _qemu_api_cfg += ['--cfg', 'feature="allocator"'] +if rustc.version().version_compare('>=1.77.0') + _qemu_api_cfg += ['--cfg', 'has_offset_of'] +endif + _qemu_api_rs = static_library( 'qemu_api', structured_sources( @@ -6,6 +12,7 @@ _qemu_api_rs = static_library( 'src/c_str.rs', 'src/definitions.rs', 'src/device_class.rs', + 'src/offset_of.rs', 'src/vmstate.rs', 'src/zeroable.rs', ], @@ -13,10 +20,7 @@ _qemu_api_rs = static_library( ), override_options: ['rust_std=2021', 'build.rust_std=2021'], rust_abi: 'rust', - rust_args: [ - '--cfg', 'MESON', - # '--cfg', 'feature="allocator"', - ], + rust_args: _qemu_api_cfg, ) rust.test('rust-qemu-api-tests', _qemu_api_rs, diff --git a/rust/qemu-api/src/device_class.rs b/rust/qemu-api/src/device_class.rs index cb4573ca6eff..56608c7f7fc8 100644 --- a/rust/qemu-api/src/device_class.rs +++ b/rust/qemu-api/src/device_class.rs @@ -23,23 +23,23 @@ macro_rules! device_class_init { #[macro_export] macro_rules! define_property { - ($name:expr, $state:ty, $field:expr, $prop:expr, $type:expr, default = $defval:expr$(,)*) => { + ($name:expr, $state:ty, $field:ident, $prop:expr, $type:expr, default = $defval:expr$(,)*) => { $crate::bindings::Property { // use associated function syntax for type checking name: ::std::ffi::CStr::as_ptr($name), info: $prop, - offset: ::core::mem::offset_of!($state, $field) as isize, + offset: $crate::offset_of!($state, $field) as isize, set_default: true, defval: $crate::bindings::Property__bindgen_ty_1 { u: $defval as u64 }, ..$crate::zeroable::Zeroable::ZERO } }; - ($name:expr, $state:ty, $field:expr, $prop:expr, $type:expr$(,)*) => { + ($name:expr, $state:ty, $field:ident, $prop:expr, $type:expr$(,)*) => { $crate::bindings::Property { // use associated function syntax for type checking name: ::std::ffi::CStr::as_ptr($name), info: $prop, - offset: ::core::mem::offset_of!($state, $field) as isize, + offset: $crate::offset_of!($state, $field) as isize, set_default: false, ..$crate::zeroable::Zeroable::ZERO } diff --git a/rust/qemu-api/src/lib.rs b/rust/qemu-api/src/lib.rs index e6bd953e10bb..aa8d16ec94b3 100644 --- a/rust/qemu-api/src/lib.rs +++ b/rust/qemu-api/src/lib.rs @@ -32,6 +32,7 @@ unsafe impl Sync for bindings::VMStateInfo {} pub mod c_str; pub mod definitions; pub mod device_class; +pub mod offset_of; pub mod vmstate; pub mod zeroable; @@ -169,3 +170,6 @@ unsafe impl GlobalAlloc for QemuAllocator { } } } + +#[cfg(has_offset_of)] +pub use core::mem::offset_of; diff --git a/rust/qemu-api/src/offset_of.rs b/rust/qemu-api/src/offset_of.rs new file mode 100644 index 000000000000..075e98f986ba --- /dev/null +++ b/rust/qemu-api/src/offset_of.rs @@ -0,0 +1,161 @@ +// SPDX-License-Identifier: MIT + +/// This macro provides the same functionality as `core::mem::offset_of`, +/// except that only one level of field access is supported. The declaration +/// of the struct must be wrapped with `with_offsets! { }`. +/// +/// It is needed because `offset_of!` was only stabilized in Rust 1.77. +#[cfg(not(has_offset_of))] +#[macro_export] +macro_rules! offset_of { + ($Container:ty, $field:ident) => { + <$Container>::OFFSET_TO__.$field + }; +} + +/// A wrapper for struct declarations, that allows using `offset_of!` in +/// versions of Rust prior to 1.77 +#[macro_export] +macro_rules! with_offsets { + // This method to generate field offset constants comes from: + // + // https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=10a22a9b8393abd7b541d8fc844bc0df + // + // used under MIT license with permission of Yandros aka Daniel Henry-Mantilla + ( + $(#[$struct_meta:meta])* + $struct_vis:vis + struct $StructName:ident { + $( + $(#[$field_meta:meta])* + $field_vis:vis + $field_name:ident : $field_ty:ty + ),* + $(,)? + } + ) => ( + #[cfg(not(has_offset_of))] + const _: () = { + struct StructOffsetsHelper(std::marker::PhantomData); + const END_OF_PREV_FIELD: usize = 0; + + // populate StructOffsetsHelper with associated consts, + // one for each field + $crate::with_offsets! { + @struct $StructName + @names [ $($field_name)* ] + @tys [ $($field_ty ,)*] + } + + // now turn StructOffsetsHelper's consts into a single struct, + // applying field visibility. This provides better error messages + // than if offset_of! used StructOffsetsHelper:: directly. + pub + struct StructOffsets { + $( + $field_vis + $field_name: usize, + )* + } + impl $StructName { + pub + const OFFSET_TO__: StructOffsets = StructOffsets { + $( + $field_name: StructOffsetsHelper::<$StructName>::$field_name, + )* + }; + } + }; + ); + + ( + @struct $StructName:ident + @names [] + @tys [] + ) => (); + + ( + @struct $StructName:ident + @names [$field_name:ident $($other_names:tt)*] + @tys [$field_ty:ty , $($other_tys:tt)*] + ) => ( + #[allow(non_local_definitions)] + #[allow(clippy::modulo_one)] + impl StructOffsetsHelper<$StructName> { + #[allow(nonstandard_style)] + const $field_name: usize = { + const ALIGN: usize = std::mem::align_of::<$field_ty>(); + const TRAIL: usize = END_OF_PREV_FIELD % ALIGN; + END_OF_PREV_FIELD + (if TRAIL == 0 { 0usize } else { ALIGN - TRAIL }) + }; + } + const _: () = { + const END_OF_PREV_FIELD: usize = + StructOffsetsHelper::<$StructName>::$field_name + + std::mem::size_of::<$field_ty>() + ; + $crate::with_offsets! { + @struct $StructName + @names [$($other_names)*] + @tys [$($other_tys)*] + } + }; + ); +} + +#[cfg(test)] +mod tests { + use crate::offset_of; + + #[repr(C)] + struct Foo { + a: u16, + b: u32, + c: u64, + d: u16, + } + + #[repr(C)] + struct Bar { + pub a: u16, + pub b: u64, + c: Foo, + d: u64, + } + + crate::with_offsets! { + #[repr(C)] + struct Bar { + pub a: u16, + pub b: u64, + c: Foo, + d: u64, + } + } + + #[repr(C)] + pub struct Baz { + b: u32, + a: u8, + } + crate::with_offsets! { + #[repr(C)] + pub struct Baz { + b: u32, + a: u8, + } + } + + #[test] + fn test_offset_of() { + const OFFSET_TO_C: usize = offset_of!(Bar, c); + + assert_eq!(offset_of!(Bar, a), 0); + assert_eq!(offset_of!(Bar, b), 8); + assert_eq!(OFFSET_TO_C, 16); + assert_eq!(offset_of!(Bar, d), 40); + + assert_eq!(offset_of!(Baz, b), 0); + assert_eq!(offset_of!(Baz, a), 4); + } +} diff --git a/rust/qemu-api/src/vmstate.rs b/rust/qemu-api/src/vmstate.rs index 9c252ce18ef6..bedcf1e8f39e 100644 --- a/rust/qemu-api/src/vmstate.rs +++ b/rust/qemu-api/src/vmstate.rs @@ -58,7 +58,7 @@ macro_rules! vmstate_single_test { .as_bytes() .as_ptr() as *const ::std::os::raw::c_char, err_hint: ::core::ptr::null(), - offset: ::core::mem::offset_of!($struct_name, $field_name), + offset: $crate::offset_of!($struct_name, $field_name), size: $size, start: 0, num: 0, @@ -135,7 +135,7 @@ macro_rules! vmstate_array { .as_bytes() .as_ptr() as *const ::std::os::raw::c_char, err_hint: ::core::ptr::null(), - offset: ::core::mem::offset_of!($struct_name, $field_name), + offset: $crate::offset_of!($struct_name, $field_name), size: $size, start: 0, num: $length as _, @@ -183,7 +183,7 @@ macro_rules! vmstate_struct_pointer_v { .as_bytes() .as_ptr() as *const ::std::os::raw::c_char, err_hint: ::core::ptr::null(), - offset: ::core::mem::offset_of!($struct_name, $field_name), + offset: $crate::offset_of!($struct_name, $field_name), size: ::core::mem::size_of::<*const $type>(), start: 0, num: 0, @@ -212,7 +212,7 @@ macro_rules! vmstate_array_of_pointer { info: unsafe { $info }, size: ::core::mem::size_of::<*const $type>(), flags: VMStateFlags(VMStateFlags::VMS_ARRAY.0 | VMStateFlags::VMS_ARRAY_OF_POINTER.0), - offset: ::core::mem::offset_of!($struct_name, $field_name), + offset: $crate::offset_of!($struct_name, $field_name), err_hint: ::core::ptr::null(), start: 0, num_offset: 0, @@ -241,7 +241,7 @@ macro_rules! vmstate_array_of_pointer_to_struct { | VMStateFlags::VMS_STRUCT.0 | VMStateFlags::VMS_ARRAY_OF_POINTER.0, ), - offset: ::core::mem::offset_of!($struct_name, $field_name), + offset: $crate::offset_of!($struct_name, $field_name), err_hint: ::core::ptr::null(), start: 0, num_offset: 0, diff --git a/rust/qemu-api/tests/tests.rs b/rust/qemu-api/tests/tests.rs index 381ac84657b3..7442f6956464 100644 --- a/rust/qemu-api/tests/tests.rs +++ b/rust/qemu-api/tests/tests.rs @@ -21,6 +21,7 @@ fn test_device_decl_macros() { ..Zeroable::ZERO }; + #[derive(qemu_api_macros::offsets)] #[repr(C)] #[derive(qemu_api_macros::Object)] pub struct DummyState { diff --git a/subprojects/packagefiles/syn-2-rs/meson.build b/subprojects/packagefiles/syn-2-rs/meson.build index a53335f3092e..9f56ce1c24d0 100644 --- a/subprojects/packagefiles/syn-2-rs/meson.build +++ b/subprojects/packagefiles/syn-2-rs/meson.build @@ -24,6 +24,7 @@ _syn_rs = static_library( '--cfg', 'feature="printing"', '--cfg', 'feature="clone-impls"', '--cfg', 'feature="proc-macro"', + '--cfg', 'feature="extra-traits"', ], dependencies: [ quote_dep,