1// Copyright (c) 2017 Gilad Naaman
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/// Reexport for `local_inner_macros`; see
22/// <https://doc.rust-lang.org/edition-guide/rust-2018/macros/macro-changes.html#macros-using-local_inner_macros>.
23#[doc(hidden)]
24#[macro_export]
25macro_rules! _memoffset__compile_error {
26    ($($inner:tt)*) => {
27        compile_error! { $($inner)* }
28    }
29}
30
31/// Produces a range instance representing the sub-slice containing the specified member.
32///
33/// This macro provides 2 forms of differing functionalities.
34///
35/// The first form is identical to the appearance of the `offset_of!` macro.
36///
37/// ```ignore
38/// span_of!(Struct, member)
39/// ```
40///
41/// The second form of `span_of!` returns a sub-slice which starts at one field, and ends at another.
42/// The general pattern of this form is:
43///
44/// ```ignore
45/// // Exclusive
46/// span_of!(Struct, member_a .. member_b)
47/// // Inclusive
48/// span_of!(Struct, member_a ..= member_b)
49///
50/// // Open-ended ranges
51/// span_of!(Struct, .. end)
52/// span_of!(Struct, start ..)
53/// ```
54///
55/// ### Note
56/// This macro uses recursion in order to resolve the range expressions, so there is a limit to
57/// the complexity of the expression.
58/// In order to raise the limit, the compiler's recursion limit should be lifted.
59///
60/// ### Safety
61/// The inter-field form mentioned above assumes that the first field is positioned before the
62/// second.
63/// This is only guarenteed for `repr(C)` structs.
64/// Usage with `repr(Rust)` structs may yield unexpected results, like downward-going ranges,
65/// spans that include unexpected fields, empty spans, or spans that include *unexpected* padding bytes.
66///
67/// ## Examples
68/// ```
69/// use memoffset::span_of;
70///
71/// #[repr(C)]
72/// struct Florp {
73///     a: u32
74/// }
75///
76/// #[repr(C)]
77/// struct Blarg {
78///     x: [u32; 2],
79///     y: [u8; 56],
80///     z: Florp,
81///     egg: [[u8; 4]; 4]
82/// }
83///
84/// fn main() {
85///     assert_eq!(0..84,  span_of!(Blarg, ..));
86///     assert_eq!(0..8,   span_of!(Blarg, .. y));
87///     assert_eq!(0..64,  span_of!(Blarg, ..= y));
88///     assert_eq!(0..8,   span_of!(Blarg, x));
89///     assert_eq!(8..84,  span_of!(Blarg, y ..));
90///     assert_eq!(0..8,   span_of!(Blarg, x .. y));
91///     assert_eq!(0..64,  span_of!(Blarg, x ..= y));
92/// }
93/// ```
94#[macro_export(local_inner_macros)]
95macro_rules! span_of {
96    (@helper  $root:ident, [] ..=) => {
97        _memoffset__compile_error!("Expected a range, found '..='")
98    };
99    (@helper $root:ident, [] ..) => {
100        _memoffset__compile_error!("Expected a range, found '..'")
101    };
102    // No explicit begin for range.
103    (@helper $root:ident, $parent:path, [] ..) => {{
104        ($root as usize,
105         $root as usize + $crate::__priv::size_of_pointee($root))
106    }};
107    (@helper $root:ident, $parent:path, [] ..= $end:tt) => {{
108        let end = raw_field!($root, $parent, $end);
109        ($root as usize, end as usize + $crate::__priv::size_of_pointee(end))
110    }};
111    (@helper $root:ident, $parent:path, [] .. $end:tt) => {{
112        ($root as usize, raw_field!($root, $parent, $end) as usize)
113    }};
114    // Explicit begin and end for range.
115    (@helper $root:ident, $parent:path, # $begin:tt [] ..= $end:tt) => {{
116        let begin = raw_field!($root, $parent, $begin);
117        let end = raw_field!($root, $parent, $end);
118        (begin as usize, end as usize + $crate::__priv::size_of_pointee(end))
119    }};
120    (@helper $root:ident, $parent:path, # $begin:tt [] .. $end:tt) => {{
121        (raw_field!($root, $parent, $begin) as usize,
122         raw_field!($root, $parent, $end) as usize)
123    }};
124    // No explicit end for range.
125    (@helper $root:ident, $parent:path, # $begin:tt [] ..) => {{
126        (raw_field!($root, $parent, $begin) as usize,
127         $root as usize + $crate::__priv::size_of_pointee($root))
128    }};
129    (@helper $root:ident, $parent:path, # $begin:tt [] ..=) => {{
130        _memoffset__compile_error!(
131            "Found inclusive range to the end of a struct. Did you mean '..' instead of '..='?")
132    }};
133    // Just one field.
134    (@helper $root:ident, $parent:path, # $field:tt []) => {{
135        let field = raw_field!($root, $parent, $field);
136        (field as usize, field as usize + $crate::__priv::size_of_pointee(field))
137    }};
138    // Parsing.
139    (@helper $root:ident, $parent:path, $(# $begin:tt)+ [] $tt:tt $($rest:tt)*) => {{
140        span_of!(@helper $root, $parent, $(#$begin)* #$tt [] $($rest)*)
141    }};
142    (@helper $root:ident, $parent:path, [] $tt:tt $($rest:tt)*) => {{
143        span_of!(@helper $root, $parent, #$tt [] $($rest)*)
144    }};
145
146    // Entry point.
147    ($sty:path, $($exp:tt)+) => ({
148        // Get a base pointer.
149        _memoffset__let_base_ptr!(root, $sty);
150        let base = root as usize;
151        let (begin, end) = span_of!(@helper root, $sty, [] $($exp)*);
152        begin-base..end-base
153    });
154}
155
156#[cfg(test)]
157mod tests {
158    use core::mem;
159
160    #[test]
161    fn span_simple() {
162        #[repr(C)]
163        struct Foo {
164            a: u32,
165            b: [u8; 2],
166            c: i64,
167        }
168
169        assert_eq!(span_of!(Foo, a), 0..4);
170        assert_eq!(span_of!(Foo, b), 4..6);
171        assert_eq!(span_of!(Foo, c), 8..8 + 8);
172    }
173
174    #[test]
175    #[cfg_attr(miri, ignore)] // this creates unaligned references
176    fn span_simple_packed() {
177        #[repr(C, packed)]
178        struct Foo {
179            a: u32,
180            b: [u8; 2],
181            c: i64,
182        }
183
184        assert_eq!(span_of!(Foo, a), 0..4);
185        assert_eq!(span_of!(Foo, b), 4..6);
186        assert_eq!(span_of!(Foo, c), 6..6 + 8);
187    }
188
189    #[test]
190    fn span_forms() {
191        #[repr(C)]
192        struct Florp {
193            a: u32,
194        }
195
196        #[repr(C)]
197        struct Blarg {
198            x: u64,
199            y: [u8; 56],
200            z: Florp,
201            egg: [[u8; 4]; 5],
202        }
203
204        // Love me some brute force
205        assert_eq!(0..8, span_of!(Blarg, x));
206        assert_eq!(64..68, span_of!(Blarg, z));
207        assert_eq!(68..mem::size_of::<Blarg>(), span_of!(Blarg, egg));
208
209        assert_eq!(8..64, span_of!(Blarg, y..z));
210        assert_eq!(0..64, span_of!(Blarg, x..=y));
211    }
212
213    #[test]
214    fn ig_test() {
215        #[repr(C)]
216        struct Member {
217            foo: u32,
218        }
219
220        #[repr(C)]
221        struct Test {
222            x: u64,
223            y: [u8; 56],
224            z: Member,
225            egg: [[u8; 4]; 4],
226        }
227
228        assert_eq!(span_of!(Test, ..x), 0..0);
229        assert_eq!(span_of!(Test, ..=x), 0..8);
230        assert_eq!(span_of!(Test, ..y), 0..8);
231        assert_eq!(span_of!(Test, ..=y), 0..64);
232        assert_eq!(span_of!(Test, ..z), 0..64);
233        assert_eq!(span_of!(Test, ..=z), 0..68);
234        assert_eq!(span_of!(Test, ..egg), 0..68);
235        assert_eq!(span_of!(Test, ..=egg), 0..84);
236        assert_eq!(span_of!(Test, ..), 0..mem::size_of::<Test>());
237        assert_eq!(
238            span_of!(Test, x..),
239            offset_of!(Test, x)..mem::size_of::<Test>()
240        );
241        assert_eq!(
242            span_of!(Test, y..),
243            offset_of!(Test, y)..mem::size_of::<Test>()
244        );
245
246        assert_eq!(
247            span_of!(Test, z..),
248            offset_of!(Test, z)..mem::size_of::<Test>()
249        );
250        assert_eq!(
251            span_of!(Test, egg..),
252            offset_of!(Test, egg)..mem::size_of::<Test>()
253        );
254        assert_eq!(
255            span_of!(Test, x..y),
256            offset_of!(Test, x)..offset_of!(Test, y)
257        );
258        assert_eq!(
259            span_of!(Test, x..=y),
260            offset_of!(Test, x)..offset_of!(Test, y) + mem::size_of::<[u8; 56]>()
261        );
262    }
263}
264