pagealloc 1.0.2

Low-level, cross-platform page allocation library
Documentation 
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

use crate::{Error, OsError, Protection, Result};
use core::ptr::NonNull;
use errno::errno;

pub type RawOsError = i32;

pub unsafe fn alloc(location: *mut u8, size: usize, protection: Protection) -> Result<NonNull<u8>> {
    let mut flags = libc::MAP_PRIVATE | libc::MAP_ANONYMOUS;
    if !location.is_null() {
        flags |= libc::MAP_FIXED;
    }
    let r = unsafe {
        libc::mmap(
            location as *mut libc::c_void,
            size,
            protection_libc(protection),
            flags,
            -1,
            0,
        )
    };
    if r == libc::MAP_FAILED || r.is_null() {
        return Err(error());
    }
    Ok(unsafe { NonNull::new_unchecked(r as *mut u8) })
}

pub unsafe fn dealloc(start: NonNull<u8>, size: usize) -> Result<()> {
    cvt(unsafe { libc::munmap(start.as_ptr() as *mut libc::c_void, size) })
}

cfg_if::cfg_if! {
    if #[cfg(any(
        target_os = "android",
        target_os = "linux",
    ))] {
        pub unsafe fn clear(start: NonNull<u8>, size: usize, protection: Protection) -> Result<()> {
            cvt(unsafe {
                libc::madvise(
                    start.as_ptr() as *mut libc::c_void,
                    size,
                    libc::MADV_DONTNEED,
                )
            })?;
            unsafe { protect(start, size, protection) }
        }
    } else {
        pub unsafe fn clear(start: NonNull<u8>, size: usize, protection: Protection) -> Result<()> {
            unsafe { alloc(start.as_ptr(), size, protection)? };
            Ok(())
        }
    }
}

pub unsafe fn protect(start: NonNull<u8>, size: usize, protection: Protection) -> Result<()> {
    cvt(unsafe {
        libc::mprotect(
            start.as_ptr() as *mut libc::c_void,
            size,
            protection_libc(protection),
        )
    })
}

cfg_if::cfg_if! {
    if #[cfg(any(
        target_os = "android",
        target_os = "linux",
    ))] {
        // Use MADV_DONTNEED.

        // Do not use MADV_FREE because it creates problems.
        // See also:
        // https://github.com/JuliaLang/julia/issues/51086
        // https://github.com/golang/go/commit/05e6d28849293266028c0bc9e9b0f8d0da38a2e2

        pub unsafe fn advise_free(start: NonNull<u8>, size: usize) -> Result<()> {
            cvt(unsafe { libc::madvise(start.as_ptr() as *mut libc::c_void, size, libc::MADV_DONTNEED) })
        }
    } else if #[cfg(any(
        target_os = "ios",
        target_os = "solaris",
        target_os = "dragonfly",
        target_os = "freebsd",
        target_os = "fuchsia",
        target_os = "haiku",
        target_os = "illumos",
        target_os = "l4re",
        target_os = "netbsd",
        target_os = "openbsd",
    ))] {
        // Use MADV_FREE

        pub unsafe fn advise_free(start: NonNull<u8>, size: usize) -> Result<()> {
            cvt(unsafe { libc::madvise(start.as_ptr() as *mut libc::c_void, size, libc::MADV_FREE) })
        }
    } else if #[cfg(target_os = "macos")] {
        // Use MADV_FREE_REUSABLE

        pub unsafe fn advise_free(start: NonNull<u8>, size: usize) -> Result<()> {
            cvt(unsafe { libc::madvise(start.as_ptr() as *mut libc::c_void, size, libc::MADV_FREE_REUSABLE) })
        }
    } else {
        // Use POSIX_MADV_DONTNEED

        pub unsafe fn advise_free(start: NonNull<u8>, size: usize) -> Result<()> {
            cvt(unsafe { libc::posix_madvise(start.as_ptr() as *mut libc::c_void, size, libc::POSIX_MADV_DONTNEED) })
        }
    }
}

pub fn page_size() -> usize {
    unsafe { libc::sysconf(libc::_SC_PAGESIZE) as _ }
}

#[inline(always)]
pub fn alloc_granularity() -> usize {
    page_size()
}

fn protection_libc(protection: Protection) -> libc::c_int {
    match protection {
        Protection::None => libc::PROT_NONE,
        Protection::Read => libc::PROT_READ,
        Protection::ReadWrite => libc::PROT_READ | libc::PROT_WRITE,
        Protection::Exec => libc::PROT_EXEC,
        Protection::ExecRead => libc::PROT_EXEC | libc::PROT_READ,
        Protection::ExecReadWrite => libc::PROT_EXEC | libc::PROT_READ | libc::PROT_WRITE,
    }
}

#[inline(always)]
fn cvt(r: i32) -> Result<()> {
    if r == 0 { Ok(()) } else { Err(error()) }
}

#[cold]
fn error() -> Error {
    Error::Os(OsError(errno().0))
}