Browse Source
Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>pull/291/head
Paolo Bonzini
1 year ago
15 changed files with 16 additions and 239 deletions
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// SPDX-License-Identifier: MIT
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#![doc(hidden)] |
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//! This module provides macros that emulate the functionality of
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//! `core::mem::offset_of` on older versions of Rust.
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//!
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//! Documentation is hidden because it only exposes macros, which
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//! are exported directly from `qemu_api`.
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/// This macro provides the same functionality as `core::mem::offset_of`,
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/// except that only one level of field access is supported. The declaration
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/// of the struct must be wrapped with `with_offsets! { }`.
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///
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/// It is needed because `offset_of!` was only stabilized in Rust 1.77.
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#[cfg(not(has_offset_of))] |
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#[macro_export] |
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macro_rules! offset_of { |
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($Container:ty, $field:ident) => { |
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<$Container>::OFFSET_TO__.$field |
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}; |
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} |
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/// A wrapper for struct declarations, that allows using `offset_of!` in
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/// versions of Rust prior to 1.77
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#[macro_export] |
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macro_rules! with_offsets { |
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// This method to generate field offset constants comes from:
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//
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// https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=10a22a9b8393abd7b541d8fc844bc0df
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//
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// used under MIT license with permission of Yandros aka Daniel Henry-Mantilla
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( |
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$(#[$struct_meta:meta])* |
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$struct_vis:vis |
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struct $StructName:ident { |
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$( |
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$(#[$field_meta:meta])* |
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$field_vis:vis |
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$field_name:ident : $field_ty:ty |
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),* |
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$(,)? |
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} |
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) => ( |
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#[cfg(not(has_offset_of))] |
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const _: () = { |
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struct StructOffsetsHelper<T>(std::marker::PhantomData<T>); |
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const END_OF_PREV_FIELD: usize = 0; |
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// populate StructOffsetsHelper<T> with associated consts,
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// one for each field
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$crate::with_offsets! { |
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@struct $StructName |
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@names [ $($field_name)* ] |
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@tys [ $($field_ty ,)*] |
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} |
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// now turn StructOffsetsHelper<T>'s consts into a single struct,
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// applying field visibility. This provides better error messages
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// than if offset_of! used StructOffsetsHelper::<T> directly.
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pub |
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struct StructOffsets { |
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$( |
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$field_vis |
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$field_name: usize, |
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)* |
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} |
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impl $StructName { |
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pub |
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const OFFSET_TO__: StructOffsets = StructOffsets { |
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$( |
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$field_name: StructOffsetsHelper::<$StructName>::$field_name, |
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)* |
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}; |
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} |
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}; |
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); |
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( |
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@struct $StructName:ident |
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@names [] |
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@tys [] |
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) => (); |
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( |
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@struct $StructName:ident |
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@names [$field_name:ident $($other_names:tt)*] |
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@tys [$field_ty:ty , $($other_tys:tt)*] |
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) => ( |
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#[allow(non_local_definitions)] |
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#[allow(clippy::modulo_one)] |
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impl StructOffsetsHelper<$StructName> { |
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#[allow(nonstandard_style)] |
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const $field_name: usize = { |
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const ALIGN: usize = std::mem::align_of::<$field_ty>(); |
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const TRAIL: usize = END_OF_PREV_FIELD % ALIGN; |
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END_OF_PREV_FIELD + (if TRAIL == 0 { 0usize } else { ALIGN - TRAIL }) |
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}; |
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} |
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const _: () = { |
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const END_OF_PREV_FIELD: usize = |
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StructOffsetsHelper::<$StructName>::$field_name + |
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std::mem::size_of::<$field_ty>() |
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; |
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$crate::with_offsets! { |
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@struct $StructName |
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@names [$($other_names)*] |
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@tys [$($other_tys)*] |
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} |
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}; |
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); |
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} |
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#[cfg(test)] |
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mod tests { |
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use crate::offset_of; |
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#[repr(C)] |
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struct Foo { |
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a: u16, |
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b: u32, |
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c: u64, |
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d: u16, |
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} |
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#[repr(C)] |
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struct Bar { |
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pub a: u16, |
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pub b: u64, |
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c: Foo, |
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d: u64, |
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} |
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crate::with_offsets! { |
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#[repr(C)] |
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struct Bar { |
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pub a: u16, |
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pub b: u64, |
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c: Foo, |
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d: u64, |
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} |
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} |
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#[repr(C)] |
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pub struct Baz { |
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b: u32, |
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a: u8, |
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} |
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crate::with_offsets! { |
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#[repr(C)] |
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pub struct Baz { |
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b: u32, |
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a: u8, |
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} |
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} |
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#[test] |
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fn test_offset_of() { |
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const OFFSET_TO_C: usize = offset_of!(Bar, c); |
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assert_eq!(offset_of!(Bar, a), 0); |
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assert_eq!(offset_of!(Bar, b), 8); |
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assert_eq!(OFFSET_TO_C, 16); |
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assert_eq!(offset_of!(Bar, d), 40); |
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assert_eq!(offset_of!(Baz, b), 0); |
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assert_eq!(offset_of!(Baz, a), 4); |
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} |
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} |
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