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// This file contains code from external sources.
// Attributions: https://github.com/wasmerio/wasmer/blob/main/docs/ATTRIBUTIONS.md
//! Low-level abstraction for allocating and managing zero-filled pages
//! of memory.
use more_asserts::assert_le;
use std::io;
use std::ptr;
use std::slice;
/// Round `size` up to the nearest multiple of `page_size`.
fn round_up_to_page_size(size: usize, page_size: usize) -> usize {
(size + (page_size - 1)) & !(page_size - 1)
}
/// A simple struct consisting of a page-aligned pointer to page-aligned
/// and initially-zeroed memory and a length.
#[derive(Debug)]
pub struct Mmap {
// Note that this is stored as a `usize` instead of a `*const` or `*mut`
// pointer to allow this structure to be natively `Send` and `Sync` without
// `unsafe impl`. This type is sendable across threads and shareable since
// the coordination all happens at the OS layer.
ptr: usize,
total_size: usize,
accessible_size: usize,
sync_on_drop: bool,
}
/// The type of mmap to create
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum MmapType {
/// The memory is private to the process and not shared with other processes.
Private,
/// The memory is shared with other processes. This is only supported on Unix.
/// When the memory is flushed it will update the file data.
Shared,
}
impl Mmap {
/// Construct a new empty instance of `Mmap`.
pub fn new() -> Self {
// Rust's slices require non-null pointers, even when empty. `Vec`
// contains code to create a non-null dangling pointer value when
// constructed empty, so we reuse that here.
let empty = Vec::<u8>::new();
Self {
ptr: empty.as_ptr() as usize,
total_size: 0,
accessible_size: 0,
sync_on_drop: false,
}
}
/// Create a new `Mmap` pointing to at least `size` bytes of page-aligned accessible memory.
pub fn with_at_least(size: usize) -> Result<Self, String> {
let page_size = region::page::size();
let rounded_size = round_up_to_page_size(size, page_size);
Self::accessible_reserved(rounded_size, rounded_size, None, MmapType::Private)
}
/// Create a new `Mmap` pointing to `accessible_size` bytes of page-aligned accessible memory,
/// within a reserved mapping of `mapping_size` bytes. `accessible_size` and `mapping_size`
/// must be native page-size multiples.
#[cfg(not(target_os = "windows"))]
pub fn accessible_reserved(
mut accessible_size: usize,
mapping_size: usize,
mut backing_file: Option<std::path::PathBuf>,
memory_type: MmapType,
) -> Result<Self, String> {
use std::os::fd::IntoRawFd;
let page_size = region::page::size();
assert_le!(accessible_size, mapping_size);
assert_eq!(mapping_size & (page_size - 1), 0);
assert_eq!(accessible_size & (page_size - 1), 0);
// Mmap may return EINVAL if the size is zero, so just
// special-case that.
if mapping_size == 0 {
return Ok(Self::new());
}
// If there is a backing file, resize the file so that its at least
// `mapping_size` bytes.
let mut memory_fd = -1;
if let Some(backing_file_path) = &mut backing_file {
let file = std::fs::OpenOptions::new()
.read(true)
.write(true)
.open(&backing_file_path)
.map_err(|e| e.to_string())?;
let mut backing_file_accessible = backing_file_path.clone();
backing_file_accessible.set_extension("accessible");
let len = file.metadata().map_err(|e| e.to_string())?.len() as usize;
if len < mapping_size {
std::fs::write(&backing_file_accessible, format!("{}", len).as_bytes()).ok();
file.set_len(mapping_size as u64)
.map_err(|e| e.to_string())?;
}
if backing_file_accessible.exists() {
let accessible = std::fs::read_to_string(&backing_file_accessible)
.map_err(|e| e.to_string())?
.parse::<usize>()
.map_err(|e| e.to_string())?;
accessible_size = accessible_size.max(accessible);
} else {
accessible_size = accessible_size.max(len);
}
accessible_size = accessible_size.min(mapping_size);
memory_fd = file.into_raw_fd();
}
// Compute the flags
let mut flags = match memory_fd {
fd if fd < 0 => libc::MAP_ANON,
_ => libc::MAP_FILE,
};
flags |= match memory_type {
MmapType::Private => libc::MAP_PRIVATE,
MmapType::Shared => libc::MAP_SHARED,
};
Ok(if accessible_size == mapping_size {
// Allocate a single read-write region at once.
let ptr = unsafe {
libc::mmap(
ptr::null_mut(),
mapping_size,
libc::PROT_READ | libc::PROT_WRITE,
flags,
memory_fd,
0,
)
};
if ptr as isize == -1_isize {
return Err(io::Error::last_os_error().to_string());
}
Self {
ptr: ptr as usize,
total_size: mapping_size,
accessible_size,
sync_on_drop: memory_fd != -1 && memory_type == MmapType::Shared,
}
} else {
// Reserve the mapping size.
let ptr = unsafe {
libc::mmap(
ptr::null_mut(),
mapping_size,
libc::PROT_NONE,
flags,
memory_fd,
0,
)
};
if ptr as isize == -1_isize {
return Err(io::Error::last_os_error().to_string());
}
let mut result = Self {
ptr: ptr as usize,
total_size: mapping_size,
accessible_size,
sync_on_drop: memory_fd != -1 && memory_type == MmapType::Shared,
};
if accessible_size != 0 {
// Commit the accessible size.
result.make_accessible(0, accessible_size)?;
}
result
})
}
/// Create a new `Mmap` pointing to `accessible_size` bytes of page-aligned accessible memory,
/// within a reserved mapping of `mapping_size` bytes. `accessible_size` and `mapping_size`
/// must be native page-size multiples.
#[cfg(target_os = "windows")]
pub fn accessible_reserved(
accessible_size: usize,
mapping_size: usize,
_backing_file: Option<std::path::PathBuf>,
_memory_type: MmapType,
) -> Result<Self, String> {
use windows_sys::Win32::System::Memory::{
VirtualAlloc, MEM_COMMIT, MEM_RESERVE, PAGE_NOACCESS, PAGE_READWRITE,
};
let page_size = region::page::size();
assert_le!(accessible_size, mapping_size);
assert_eq!(mapping_size & (page_size - 1), 0);
assert_eq!(accessible_size & (page_size - 1), 0);
// VirtualAlloc may return ERROR_INVALID_PARAMETER if the size is zero,
// so just special-case that.
if mapping_size == 0 {
return Ok(Self::new());
}
Ok(if accessible_size == mapping_size {
// Allocate a single read-write region at once.
let ptr = unsafe {
VirtualAlloc(
ptr::null_mut(),
mapping_size,
MEM_RESERVE | MEM_COMMIT,
PAGE_READWRITE,
)
};
if ptr.is_null() {
return Err(io::Error::last_os_error().to_string());
}
Self {
ptr: ptr as usize,
total_size: mapping_size,
accessible_size,
sync_on_drop: false,
}
} else {
// Reserve the mapping size.
let ptr =
unsafe { VirtualAlloc(ptr::null_mut(), mapping_size, MEM_RESERVE, PAGE_NOACCESS) };
if ptr.is_null() {
return Err(io::Error::last_os_error().to_string());
}
let mut result = Self {
ptr: ptr as usize,
total_size: mapping_size,
accessible_size,
sync_on_drop: false,
};
if accessible_size != 0 {
// Commit the accessible size.
result.make_accessible(0, accessible_size)?;
}
result
})
}
/// Make the memory starting at `start` and extending for `len` bytes accessible.
/// `start` and `len` must be native page-size multiples and describe a range within
/// `self`'s reserved memory.
#[cfg(not(target_os = "windows"))]
pub fn make_accessible(&mut self, start: usize, len: usize) -> Result<(), String> {
let page_size = region::page::size();
assert_eq!(start & (page_size - 1), 0);
assert_eq!(len & (page_size - 1), 0);
assert_le!(len, self.total_size);
assert_le!(start, self.total_size - len);
// Commit the accessible size.
let ptr = self.ptr as *const u8;
unsafe { region::protect(ptr.add(start), len, region::Protection::READ_WRITE) }
.map_err(|e| e.to_string())
}
/// Make the memory starting at `start` and extending for `len` bytes accessible.
/// `start` and `len` must be native page-size multiples and describe a range within
/// `self`'s reserved memory.
#[cfg(target_os = "windows")]
pub fn make_accessible(&mut self, start: usize, len: usize) -> Result<(), String> {
use std::ffi::c_void;
use windows_sys::Win32::System::Memory::{VirtualAlloc, MEM_COMMIT, PAGE_READWRITE};
let page_size = region::page::size();
assert_eq!(start & (page_size - 1), 0);
assert_eq!(len & (page_size - 1), 0);
assert_le!(len, self.len());
assert_le!(start, self.len() - len);
// Commit the accessible size.
let ptr = self.ptr as *const u8;
if unsafe {
VirtualAlloc(
ptr.add(start) as *mut c_void,
len,
MEM_COMMIT,
PAGE_READWRITE,
)
}
.is_null()
{
return Err(io::Error::last_os_error().to_string());
}
Ok(())
}
/// Return the allocated memory as a slice of u8.
pub fn as_slice(&self) -> &[u8] {
unsafe { slice::from_raw_parts(self.ptr as *const u8, self.total_size) }
}
/// Return the allocated memory as a slice of u8.
pub fn as_slice_accessible(&self) -> &[u8] {
unsafe { slice::from_raw_parts(self.ptr as *const u8, self.accessible_size) }
}
/// Return the allocated memory as a slice of u8.
pub fn as_slice_arbitary(&self, size: usize) -> &[u8] {
let size = usize::min(size, self.total_size);
unsafe { slice::from_raw_parts(self.ptr as *const u8, size) }
}
/// Return the allocated memory as a mutable slice of u8.
pub fn as_mut_slice(&mut self) -> &mut [u8] {
unsafe { slice::from_raw_parts_mut(self.ptr as *mut u8, self.total_size) }
}
/// Return the allocated memory as a mutable slice of u8.
pub fn as_mut_slice_accessible(&mut self) -> &mut [u8] {
unsafe { slice::from_raw_parts_mut(self.ptr as *mut u8, self.accessible_size) }
}
/// Return the allocated memory as a mutable slice of u8.
pub fn as_mut_slice_arbitary(&mut self, size: usize) -> &mut [u8] {
let size = usize::min(size, self.total_size);
unsafe { slice::from_raw_parts_mut(self.ptr as *mut u8, size) }
}
/// Return the allocated memory as a pointer to u8.
pub fn as_ptr(&self) -> *const u8 {
self.ptr as *const u8
}
/// Return the allocated memory as a mutable pointer to u8.
pub fn as_mut_ptr(&mut self) -> *mut u8 {
self.ptr as *mut u8
}
/// Return the length of the allocated memory.
pub fn len(&self) -> usize {
self.total_size
}
/// Return whether any memory has been allocated.
pub fn is_empty(&self) -> bool {
self.len() == 0
}
/// Duplicate in a new memory mapping.
#[deprecated = "use `copy` instead"]
pub fn duplicate(&mut self, size_hint: Option<usize>) -> Result<Self, String> {
self.copy(size_hint)
}
/// Duplicate in a new memory mapping.
pub fn copy(&mut self, size_hint: Option<usize>) -> Result<Self, String> {
// NOTE: accessible_size != used size as the value is not
// automatically updated when the pre-provisioned space is used
let mut copy_size = self.accessible_size;
if let Some(size_hint) = size_hint {
copy_size = usize::max(copy_size, size_hint);
}
let mut new =
Self::accessible_reserved(copy_size, self.total_size, None, MmapType::Private)?;
new.as_mut_slice_arbitary(copy_size)
.copy_from_slice(self.as_slice_arbitary(copy_size));
Ok(new)
}
}
impl Drop for Mmap {
#[cfg(not(target_os = "windows"))]
fn drop(&mut self) {
if self.total_size != 0 {
if self.sync_on_drop {
let r = unsafe {
libc::msync(
self.ptr as *mut libc::c_void,
self.total_size,
libc::MS_SYNC | libc::MS_INVALIDATE,
)
};
assert_eq!(r, 0, "msync failed: {}", io::Error::last_os_error());
}
let r = unsafe { libc::munmap(self.ptr as *mut libc::c_void, self.total_size) };
assert_eq!(r, 0, "munmap failed: {}", io::Error::last_os_error());
}
}
#[cfg(target_os = "windows")]
fn drop(&mut self) {
if self.len() != 0 {
use std::ffi::c_void;
use windows_sys::Win32::System::Memory::{VirtualFree, MEM_RELEASE};
let r = unsafe { VirtualFree(self.ptr as *mut c_void, 0, MEM_RELEASE) };
assert_ne!(r, 0);
}
}
}
fn _assert() {
fn _assert_send_sync<T: Send + Sync>() {}
_assert_send_sync::<Mmap>();
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_round_up_to_page_size() {
assert_eq!(round_up_to_page_size(0, 4096), 0);
assert_eq!(round_up_to_page_size(1, 4096), 4096);
assert_eq!(round_up_to_page_size(4096, 4096), 4096);
assert_eq!(round_up_to_page_size(4097, 4096), 8192);
}
}