1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173

//! This module implements some wrappers around Mmap/MmapMut to also support a cheap "empty" variant.
// Unfortunately Memmap itself doesn't support a cheap zero-length variant

use std::ops::{Deref, DerefMut};
use std::io;

use memmap2::{Mmap, MmapMut};

use crate::AssemblyOffset;

/// A structure holding a buffer of executable memory. It also derefs to a `&[u8]`.
/// This structure does not allocate when its size is 0.
#[derive(Debug)]
pub struct ExecutableBuffer {
    // length of the buffer that has actually been written to
    length: usize,
    // backing buffer
    buffer: Option<Mmap>
}

/// ExecutableBuffer equivalent that holds a buffer of mutable memory instead of executable memory. It also derefs to a `&mut [u8]`.
/// This structure does not allocate when its size is 0.
#[derive(Debug)]
pub struct MutableBuffer {
    // length of the buffer that has actually been written to
    length: usize,
    // backing buffer
    buffer: Option<MmapMut>
}

impl ExecutableBuffer {
    /// Obtain a pointer into the executable memory from an offset into it.
    /// When an offset returned from `DynasmLabelApi::offset` is used, the resulting pointer
    /// will point to the start of the first instruction after the offset call,
    /// which can then be jumped or called to divert control flow into the executable
    /// buffer. Note that if this buffer is accessed through an Executor, these pointers
    /// will only be valid as long as its lock is held. When no locks are held,
    /// the assembler is free to relocate the executable buffer when it requires
    /// more memory than available.
    ///
    /// The memory this pointer points to is owned by this `ExecutableBuffer`.
    /// The programmer is responsible for ensuring that pointers generated from this API do not
    /// outlive the `ExecutableBuffer`.
    pub fn ptr(&self, offset: AssemblyOffset) -> *const u8 {
        &self[offset.0] as *const u8
    }

    /// Create a new executable buffer, backed by a buffer of size `size`.
    /// It will start with an initialized length of 0.
    pub fn new(size: usize) -> io::Result<ExecutableBuffer> {
        let buffer = if size == 0 {
            None
        } else {
            Some(MmapMut::map_anon(size)?.make_exec()?)
        };

        Ok(ExecutableBuffer {
            length: 0,
            buffer
        })
    }

    /// Query the backing size of this executable buffer
    pub fn size(&self) -> usize {
        self.buffer.as_ref().map(|b| b.len()).unwrap_or(0) as usize
    }

    /// Change this executable buffer into a mutable buffer.
    pub fn make_mut(self) -> io::Result<MutableBuffer> {
        let buffer = if let Some(map) = self.buffer {
            Some(map.make_mut()?)
        } else {
            None
        };

        Ok(MutableBuffer {
            length: self.length,
            buffer
        })
    }
}

impl MutableBuffer {
    /// Create a new mutable buffer, backed by a buffer of size `size`.
    /// It will start with an initialized length of 0.
    pub fn new(size: usize) -> io::Result<MutableBuffer> {
        let buffer = if size == 0 {
            None
        } else {
            Some(MmapMut::map_anon(size)?)
        };

        Ok(MutableBuffer {
            length: 0,
            buffer
        })
    }

    /// Query the backing size of this mutable buffer
    pub fn size(&self) -> usize {
        self.buffer.as_ref().map(|b| b.len()).unwrap_or(0) as usize
    }

    /// Set the length of the usable part of this mutable buffer. The length
    /// should not be set larger than the allocated size, otherwise methods can panic.
    pub fn set_len(&mut self, length: usize) {
        self.length = length
    }

    /// Change this mutable buffer into an executable buffer.
    pub fn make_exec(self) -> io::Result<ExecutableBuffer> {
        let buffer = if let Some(map) = self.buffer {
            Some(map.make_exec()?)
        } else {
            None
        };

        Ok(ExecutableBuffer {
            length: self.length,
            buffer
        })
    }
}

impl Default for ExecutableBuffer {
    fn default() -> ExecutableBuffer {
        ExecutableBuffer {
            length: 0,
            buffer: None
        }
    }
}

impl Default for MutableBuffer {
    fn default() -> MutableBuffer {
        MutableBuffer {
            length: 0,
            buffer: None
        }
    }
}

impl Deref for ExecutableBuffer {
    type Target = [u8];
    fn deref(&self) -> &[u8] {
        if let Some(map) = &self.buffer {
            &map[..self.length]
        } else {
            &[]
        }
    }
}

impl Deref for MutableBuffer {
    type Target = [u8];
    fn deref(&self) -> &[u8] {
        if let Some(map) = &self.buffer {
            &map[..self.length]
        } else {
            &[]
        }
    }
}

impl DerefMut for MutableBuffer {
    fn deref_mut(&mut self) -> &mut [u8] {
        if let Some(map) = &mut self.buffer {
            &mut map[..self.length]
        } else {
            &mut []
        }
    }
}