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use memoffset instead

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This commit is contained in:
mejrs 2022-06-12 18:28:21 +02:00
parent 2d3a5852ed
commit 2d94cb4a2d
2 changed files with 5 additions and 93 deletions
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1
Cargo.toml
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@ -17,6 +17,7 @@ edition = "2018"
cfg-if = "1.0"
libc = "0.2.62"
parking_lot = ">= 0.11, < 0.13"
memoffset = "0.6.5"
# ffi bindings to the python interpreter, split into a separate crate so they can be used independently
pyo3-ffi = { path = "pyo3-ffi", version = "=0.16.5" }

97
src/pycell.rs
View file

@ -433,8 +433,6 @@ pub struct PyCell<T: PyClassImpl> {
contents: PyCellContents<T>,
}
// This struct has mirrored definitions in `weaklist_offset` and `dict_offset`,
// who need the same struct layout to function correctly.
#[repr(C)]
pub(crate) struct PyCellContents<T: PyClassImpl> {
pub(crate) value: ManuallyDrop<UnsafeCell<T>>,
@ -627,54 +625,11 @@ impl<T: PyClass> PyCell<T> {
/// Gets the offset of the dictionary from the start of the struct in bytes.
pub(crate) fn dict_offset() -> ffi::Py_ssize_t {
use memoffset::offset_of;
use std::convert::TryInto;
use std::mem::MaybeUninit;
#[cfg(addr_of)]
let offset = unsafe {
// The much simpler way, using addr_of!
let cell = MaybeUninit::<Self>::uninit();
let base_ptr = cell.as_ptr();
let dict_ptr = std::ptr::addr_of!((*base_ptr).contents.dict);
(dict_ptr.cast::<u8>()).offset_from(base_ptr.cast::<u8>())
};
#[cfg(not(addr_of))]
let offset = unsafe {
// The annoying way using a dummy struct because there's no way to get
// a pointer without going through a reference, which is insta-UB
// if it is not initialized.
let offset = offset_of!(PyCell<T>, contents) + offset_of!(PyCellContents<T>, dict);
use std::mem::size_of;
#[repr(C)]
struct PyCellDummy<T: PyClassImpl> {
ob_base: MaybeUninit<<T::BaseType as PyClassBaseType>::LayoutAsBase>,
contents: PyCellContentsDummy<T>,
}
#[repr(C)]
struct PyCellContentsDummy<T: PyClassImpl> {
value: MaybeUninit<T>,
borrow_checker: MaybeUninit<<T::PyClassMutability as PyClassMutability>::Storage>,
thread_checker: MaybeUninit<T::ThreadChecker>,
dict: MaybeUninit<T::Dict>,
weakref: MaybeUninit<T::WeakRef>,
}
assert_eq!(size_of::<PyCell<T>>(), size_of::<PyCellDummy<T>>());
assert_eq!(
size_of::<PyCellContents<T>>(),
size_of::<PyCellContentsDummy<T>>()
);
// All of the pycelldummy's fields are maybeuninit, which require no initialization
let cell = MaybeUninit::<PyCellDummy<T>>::uninit().assume_init();
let base_ptr: *const PyCellDummy<T> = &cell;
let dict_ptr: *const MaybeUninit<T::Dict> = &(*base_ptr).contents.dict;
(dict_ptr.cast::<u8>()).offset_from(base_ptr.cast::<u8>())
};
// Py_ssize_t may not be equal to isize on all platforms
#[allow(clippy::useless_conversion)]
offset.try_into().expect("offset should fit in Py_ssize_t")
@ -682,55 +637,11 @@ impl<T: PyClass> PyCell<T> {
/// Gets the offset of the weakref list from the start of the struct in bytes.
pub(crate) fn weaklist_offset() -> ffi::Py_ssize_t {
use memoffset::offset_of;
use std::convert::TryInto;
use std::mem::MaybeUninit;
#[cfg(addr_of)]
let offset = unsafe {
// The much simpler way, using addr_of!
let cell = MaybeUninit::<Self>::uninit();
let base_ptr = cell.as_ptr();
let weaklist_ptr = std::ptr::addr_of!((*base_ptr).contents.weakref);
(weaklist_ptr.cast::<u8>()).offset_from(base_ptr.cast::<u8>())
};
#[cfg(not(addr_of))]
let offset = unsafe {
// The annoying way using a dummy struct because there's no way to get
// a pointer without going through a reference, which is insta-UB
// if it is not initialized.
let offset = offset_of!(PyCell<T>, contents) + offset_of!(PyCellContents<T>, weakref);
use std::mem::size_of;
#[repr(C)]
struct PyCellDummy<T: PyClassImpl> {
ob_base: MaybeUninit<<T::BaseType as PyClassBaseType>::LayoutAsBase>,
contents: PyCellContentsDummy<T>,
}
#[repr(C)]
struct PyCellContentsDummy<T: PyClassImpl> {
value: MaybeUninit<T>,
borrow_checker: MaybeUninit<<T::PyClassMutability as PyClassMutability>::Storage>,
thread_checker: MaybeUninit<T::ThreadChecker>,
dict: MaybeUninit<T::Dict>,
weakref: MaybeUninit<T::WeakRef>,
}
assert_eq!(size_of::<PyCell<T>>(), size_of::<PyCellDummy<T>>());
assert_eq!(
size_of::<PyCellContents<T>>(),
size_of::<PyCellContentsDummy<T>>()
);
// All of the pycelldummy's fields are maybeuninit, which require no initialization
let cell = MaybeUninit::<PyCellDummy<T>>::uninit().assume_init();
let base_ptr: *const PyCellDummy<T> = &cell;
let weaklist_ptr: *const MaybeUninit<<T as PyClassImpl>::WeakRef> =
&(*base_ptr).contents.weakref;
(weaklist_ptr.cast::<u8>()).offset_from(base_ptr.cast::<u8>())
};
// Py_ssize_t may not be equal to isize on all platforms
#[allow(clippy::useless_conversion)]
offset.try_into().expect("offset should fit in Py_ssize_t")