| // Copyright (c) 2017 Gilad Naaman |
| // |
| // Permission is hereby granted, free of charge, to any person obtaining a copy |
| // of this software and associated documentation files (the "Software"), to deal |
| // in the Software without restriction, including without limitation the rights |
| // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell |
| // copies of the Software, and to permit persons to whom the Software is |
| // furnished to do so, subject to the following conditions: |
| // |
| // The above copyright notice and this permission notice shall be included in all |
| // copies or substantial portions of the Software. |
| // |
| // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR |
| // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, |
| // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE |
| // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER |
| // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, |
| // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE |
| // SOFTWARE. |
| |
| /// Macro to create a local `base_ptr` raw pointer of the given type, avoiding UB as |
| /// much as is possible currently. |
| #[cfg(maybe_uninit)] |
| #[macro_export] |
| #[doc(hidden)] |
| macro_rules! _memoffset__let_base_ptr { |
| ($name:ident, $type:ty) => { |
| // No UB here, and the pointer does not dangle, either. |
| // But we have to make sure that `uninit` lives long enough, |
| // so it has to be in the same scope as `$name`. That's why |
| // `let_base_ptr` declares a variable (several, actually) |
| // instead of returning one. |
| let uninit = $crate::__priv::mem::MaybeUninit::<$type>::uninit(); |
| let $name: *const $type = uninit.as_ptr(); |
| }; |
| } |
| #[cfg(not(maybe_uninit))] |
| #[macro_export] |
| #[doc(hidden)] |
| macro_rules! _memoffset__let_base_ptr { |
| ($name:ident, $type:ty) => { |
| // No UB right here, but we will later dereference this pointer to |
| // offset into a field, and that is UB because the pointer is dangling. |
| let $name = $crate::__priv::mem::align_of::<$type>() as *const $type; |
| }; |
| } |
| |
| /// Macro to compute the distance between two pointers. |
| #[cfg(any(feature = "unstable_const", stable_const))] |
| #[macro_export] |
| #[doc(hidden)] |
| macro_rules! _memoffset_offset_from_unsafe { |
| ($field:expr, $base:expr) => {{ |
| let field = $field; // evaluate $field outside the `unsafe` block |
| let base = $base; // evaluate $base outside the `unsafe` block |
| // Compute offset, with unstable `offset_from` for const-compatibility. |
| // (Requires the pointers to not dangle, but we already need that for `raw_field!` anyway.) |
| unsafe { (field as *const u8).offset_from(base as *const u8) as usize } |
| }}; |
| } |
| #[cfg(not(any(feature = "unstable_const", stable_const)))] |
| #[macro_export] |
| #[doc(hidden)] |
| macro_rules! _memoffset_offset_from_unsafe { |
| ($field:expr, $base:expr) => { |
| // Compute offset. |
| ($field as usize) - ($base as usize) |
| }; |
| } |
| |
| /// Calculates the offset of the specified field from the start of the named struct. |
| /// |
| /// ## Examples |
| /// ``` |
| /// use memoffset::offset_of; |
| /// |
| /// #[repr(C, packed)] |
| /// struct Foo { |
| /// a: u32, |
| /// b: u64, |
| /// c: [u8; 5] |
| /// } |
| /// |
| /// fn main() { |
| /// assert_eq!(offset_of!(Foo, a), 0); |
| /// assert_eq!(offset_of!(Foo, b), 4); |
| /// } |
| /// ``` |
| /// |
| /// ## Notes |
| /// Rust's ABI is unstable, and [type layout can be changed with each |
| /// compilation](https://doc.rust-lang.org/reference/type-layout.html). |
| /// |
| /// Using `offset_of!` with a `repr(Rust)` struct will return the correct offset of the |
| /// specified `field` for a particular compilation, but the exact value may change |
| /// based on the compiler version, concrete struct type, time of day, or rustc's mood. |
| /// |
| /// As a result, the value should not be retained and used between different compilations. |
| #[macro_export(local_inner_macros)] |
| macro_rules! offset_of { |
| ($parent:path, $field:tt) => {{ |
| // Get a base pointer (non-dangling if rustc supports `MaybeUninit`). |
| _memoffset__let_base_ptr!(base_ptr, $parent); |
| // Get field pointer. |
| let field_ptr = raw_field!(base_ptr, $parent, $field); |
| // Compute offset. |
| _memoffset_offset_from_unsafe!(field_ptr, base_ptr) |
| }}; |
| } |
| |
| /// Calculates the offset of the specified field from the start of the tuple. |
| /// |
| /// ## Examples |
| /// ``` |
| /// use memoffset::offset_of_tuple; |
| /// |
| /// fn main() { |
| /// assert!(offset_of_tuple!((u8, u32), 1) >= 0, "Tuples do not have a defined layout"); |
| /// } |
| /// ``` |
| #[cfg(tuple_ty)] |
| #[macro_export(local_inner_macros)] |
| macro_rules! offset_of_tuple { |
| ($parent:ty, $field:tt) => {{ |
| // Get a base pointer (non-dangling if rustc supports `MaybeUninit`). |
| _memoffset__let_base_ptr!(base_ptr, $parent); |
| // Get field pointer. |
| let field_ptr = raw_field_tuple!(base_ptr, $parent, $field); |
| // Compute offset. |
| _memoffset_offset_from_unsafe!(field_ptr, base_ptr) |
| }}; |
| } |
| |
| /// Calculates the offset of the specified union member from the start of the union. |
| /// |
| /// ## Examples |
| /// ``` |
| /// use memoffset::offset_of_union; |
| /// |
| /// #[repr(C, packed)] |
| /// union Foo { |
| /// foo32: i32, |
| /// foo64: i64, |
| /// } |
| /// |
| /// fn main() { |
| /// assert!(offset_of_union!(Foo, foo64) == 0); |
| /// } |
| /// ``` |
| /// |
| /// ## Note |
| /// Due to macro_rules limitations, this macro will accept structs with a single field as well as unions. |
| /// This is not a stable guarantee, and future versions of this crate might fail |
| /// on any use of this macro with a struct, without a semver bump. |
| #[macro_export(local_inner_macros)] |
| macro_rules! offset_of_union { |
| ($parent:path, $field:tt) => {{ |
| // Get a base pointer (non-dangling if rustc supports `MaybeUninit`). |
| _memoffset__let_base_ptr!(base_ptr, $parent); |
| // Get field pointer. |
| let field_ptr = raw_field_union!(base_ptr, $parent, $field); |
| // Compute offset. |
| _memoffset_offset_from_unsafe!(field_ptr, base_ptr) |
| }}; |
| } |
| |
| #[cfg(test)] |
| mod tests { |
| #[test] |
| fn offset_simple() { |
| #[repr(C)] |
| struct Foo { |
| a: u32, |
| b: [u8; 2], |
| c: i64, |
| } |
| |
| assert_eq!(offset_of!(Foo, a), 0); |
| assert_eq!(offset_of!(Foo, b), 4); |
| assert_eq!(offset_of!(Foo, c), 8); |
| } |
| |
| #[test] |
| #[cfg_attr(miri, ignore)] // this creates unaligned references |
| fn offset_simple_packed() { |
| #[repr(C, packed)] |
| struct Foo { |
| a: u32, |
| b: [u8; 2], |
| c: i64, |
| } |
| |
| assert_eq!(offset_of!(Foo, a), 0); |
| assert_eq!(offset_of!(Foo, b), 4); |
| assert_eq!(offset_of!(Foo, c), 6); |
| } |
| |
| #[test] |
| fn tuple_struct() { |
| #[repr(C)] |
| struct Tup(i32, i32); |
| |
| assert_eq!(offset_of!(Tup, 0), 0); |
| assert_eq!(offset_of!(Tup, 1), 4); |
| } |
| |
| #[test] |
| fn offset_union() { |
| // Since we're specifying repr(C), all fields are supposed to be at offset 0 |
| #[repr(C)] |
| union Foo { |
| a: u32, |
| b: [u8; 2], |
| c: i64, |
| } |
| |
| assert_eq!(offset_of_union!(Foo, a), 0); |
| assert_eq!(offset_of_union!(Foo, b), 0); |
| assert_eq!(offset_of_union!(Foo, c), 0); |
| } |
| |
| #[test] |
| fn path() { |
| mod sub { |
| #[repr(C)] |
| pub struct Foo { |
| pub x: u32, |
| } |
| } |
| |
| assert_eq!(offset_of!(sub::Foo, x), 0); |
| } |
| |
| #[test] |
| fn inside_generic_method() { |
| struct Pair<T, U>(T, U); |
| |
| fn foo<T, U>(_: Pair<T, U>) -> usize { |
| offset_of!(Pair<T, U>, 1) |
| } |
| |
| assert_eq!(foo(Pair(0, 0)), 4); |
| } |
| |
| #[cfg(tuple_ty)] |
| #[test] |
| fn test_tuple_offset() { |
| let f = (0i32, 0.0f32, 0u8); |
| let f_ptr = &f as *const _; |
| let f1_ptr = &f.1 as *const _; |
| |
| assert_eq!( |
| f1_ptr as usize - f_ptr as usize, |
| offset_of_tuple!((i32, f32, u8), 1) |
| ); |
| } |
| |
| #[test] |
| fn test_raw_field() { |
| #[repr(C)] |
| struct Foo { |
| a: u32, |
| b: [u8; 2], |
| c: i64, |
| } |
| |
| let f: Foo = Foo { |
| a: 0, |
| b: [0, 0], |
| c: 0, |
| }; |
| let f_ptr = &f as *const _; |
| assert_eq!(f_ptr as usize + 0, raw_field!(f_ptr, Foo, a) as usize); |
| assert_eq!(f_ptr as usize + 4, raw_field!(f_ptr, Foo, b) as usize); |
| assert_eq!(f_ptr as usize + 8, raw_field!(f_ptr, Foo, c) as usize); |
| } |
| |
| #[cfg(tuple_ty)] |
| #[test] |
| fn test_raw_field_tuple() { |
| let t = (0u32, 0u8, false); |
| let t_ptr = &t as *const _; |
| let t_addr = t_ptr as usize; |
| |
| assert_eq!( |
| &t.0 as *const _ as usize - t_addr, |
| raw_field_tuple!(t_ptr, (u32, u8, bool), 0) as usize - t_addr |
| ); |
| assert_eq!( |
| &t.1 as *const _ as usize - t_addr, |
| raw_field_tuple!(t_ptr, (u32, u8, bool), 1) as usize - t_addr |
| ); |
| assert_eq!( |
| &t.2 as *const _ as usize - t_addr, |
| raw_field_tuple!(t_ptr, (u32, u8, bool), 2) as usize - t_addr |
| ); |
| } |
| |
| #[test] |
| fn test_raw_field_union() { |
| #[repr(C)] |
| union Foo { |
| a: u32, |
| b: [u8; 2], |
| c: i64, |
| } |
| |
| let f = Foo { a: 0 }; |
| let f_ptr = &f as *const _; |
| assert_eq!(f_ptr as usize + 0, raw_field_union!(f_ptr, Foo, a) as usize); |
| assert_eq!(f_ptr as usize + 0, raw_field_union!(f_ptr, Foo, b) as usize); |
| assert_eq!(f_ptr as usize + 0, raw_field_union!(f_ptr, Foo, c) as usize); |
| } |
| |
| #[cfg(any(feature = "unstable_const", stable_const))] |
| #[test] |
| fn const_offset() { |
| #[repr(C)] |
| struct Foo { |
| a: u32, |
| b: [u8; 2], |
| c: i64, |
| } |
| |
| assert_eq!([0; offset_of!(Foo, b)].len(), 4); |
| } |
| |
| #[cfg(feature = "unstable_const")] |
| #[test] |
| fn const_offset_interior_mutable() { |
| #[repr(C)] |
| struct Foo { |
| a: u32, |
| b: core::cell::Cell<u32>, |
| } |
| |
| assert_eq!([0; offset_of!(Foo, b)].len(), 4); |
| } |
| |
| #[cfg(any(feature = "unstable_const", stable_const))] |
| #[test] |
| fn const_fn_offset() { |
| const fn test_fn() -> usize { |
| #[repr(C)] |
| struct Foo { |
| a: u32, |
| b: [u8; 2], |
| c: i64, |
| } |
| |
| offset_of!(Foo, b) |
| } |
| |
| assert_eq!([0; test_fn()].len(), 4); |
| } |
| } |