memoffset/
raw_field.rs

1// Copyright (c) 2020 Gilad Naaman, Ralf Jung
2//
3// Permission is hereby granted, free of charge, to any person obtaining a copy
4// of this software and associated documentation files (the "Software"), to deal
5// in the Software without restriction, including without limitation the rights
6// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
7// copies of the Software, and to permit persons to whom the Software is
8// furnished to do so, subject to the following conditions:
9//
10// The above copyright notice and this permission notice shall be included in all
11// copies or substantial portions of the Software.
12//
13// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
14// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
15// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
16// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
17// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
18// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
19// SOFTWARE.
20
21/// `addr_of!`, or just ref-then-cast when that is not available.
22#[cfg(raw_ref_macros)]
23#[macro_export]
24#[doc(hidden)]
25macro_rules! _memoffset__addr_of {
26    ($path:expr) => {{
27        $crate::__priv::ptr::addr_of!($path)
28    }};
29}
30#[cfg(not(raw_ref_macros))]
31#[macro_export]
32#[doc(hidden)]
33macro_rules! _memoffset__addr_of {
34    ($path:expr) => {{
35        // This is UB because we create an intermediate reference to uninitialized memory.
36        // Nothing we can do about that without `addr_of!` though.
37        &$path as *const _
38    }};
39}
40
41/// Deref-coercion protection macro.
42#[cfg(allow_clippy)]
43#[macro_export]
44#[doc(hidden)]
45macro_rules! _memoffset__field_check {
46    ($type:path, $field:tt) => {
47        // Make sure the field actually exists. This line ensures that a
48        // compile-time error is generated if $field is accessed through a
49        // Deref impl.
50        #[allow(clippy::unneeded_field_pattern)]
51        let $type { $field: _, .. };
52    };
53}
54#[cfg(not(allow_clippy))]
55#[macro_export]
56#[doc(hidden)]
57macro_rules! _memoffset__field_check {
58    ($type:path, $field:tt) => {
59        // Make sure the field actually exists. This line ensures that a
60        // compile-time error is generated if $field is accessed through a
61        // Deref impl.
62        let $type { $field: _, .. };
63    };
64}
65
66/// Deref-coercion protection macro.
67#[macro_export]
68#[doc(hidden)]
69macro_rules! _memoffset__field_check_tuple {
70    ($type:ty, $field:tt) => {
71        // Make sure the type argument is a tuple
72        let (_, ..): $type;
73    };
74}
75
76/// Computes a const raw pointer to the given field of the given base pointer
77/// to the given parent type.
78///
79/// The `base` pointer *must not* be dangling, but it *may* point to
80/// uninitialized memory.
81#[macro_export(local_inner_macros)]
82macro_rules! raw_field {
83    ($base:expr, $parent:path, $field:tt) => {{
84        _memoffset__field_check!($parent, $field);
85        let base = $base; // evaluate $base outside the `unsafe` block
86
87        // Get the field address.
88        // Crucially, we know that this will not trigger a deref coercion because
89        // of the field check we did above.
90        #[allow(unused_unsafe)] // for when the macro is used in an unsafe block
91        unsafe {
92            _memoffset__addr_of!((*(base as *const $parent)).$field)
93        }
94    }};
95}
96
97/// Computes a const raw pointer to the given field of the given base pointer
98/// to the given parent tuple typle.
99///
100/// The `base` pointer *must not* be dangling, but it *may* point to
101/// uninitialized memory.
102#[cfg(tuple_ty)]
103#[macro_export(local_inner_macros)]
104macro_rules! raw_field_tuple {
105    ($base:expr, $parent:ty, $field:tt) => {{
106        _memoffset__field_check_tuple!($parent, $field);
107        let base = $base; // evaluate $base outside the `unsafe` block
108
109        // Get the field address.
110        // Crucially, we know that this will not trigger a deref coercion because
111        // of the field check we did above.
112        #[allow(unused_unsafe)] // for when the macro is used in an unsafe block
113        unsafe {
114            _memoffset__addr_of!((*(base as *const $parent)).$field)
115        }
116    }};
117}
memoffset/raw_field.rs

memoffset/
raw_field.rs
