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Allow zero-size reads/writes on null pointers

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This commit is contained in:
Ben Kimock 2024-10-07 19:34:13 -04:00
parent eb4e234674
commit 0c41c3414c
4 changed files with 29 additions and 19 deletions
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19
library/core/src/intrinsics.rs
View File

@ -64,6 +64,7 @@
#![allow(missing_docs)]
use crate::marker::{DiscriminantKind, Tuple};
use crate::mem::SizedTypeProperties;
use crate::{ptr, ub_checks};
pub mod mir;
@ -3311,10 +3312,12 @@ pub const fn ptr_metadata<P: ptr::Pointee<Metadata = M> + ?Sized, M>(_ptr: *cons
size: usize = size_of::<T>(),
align: usize = align_of::<T>(),
count: usize = count,
) =>
ub_checks::is_aligned_and_not_null(src, align)
&& ub_checks::is_aligned_and_not_null(dst, align)
&& ub_checks::is_nonoverlapping(src, dst, size, count)
) => {
let zero_size = count == 0 || size == 0;
ub_checks::is_aligned_and_not_null(src, align, zero_size)
&& ub_checks::is_aligned_and_not_null(dst, align, zero_size)
&& ub_checks::is_nonoverlapping(src, dst, size, count)
}
);
// SAFETY: the safety contract for `copy_nonoverlapping` must be
@ -3412,9 +3415,10 @@ pub const fn ptr_metadata<P: ptr::Pointee<Metadata = M> + ?Sized, M>(_ptr: *cons
src: *const () = src as *const (),
dst: *mut () = dst as *mut (),
align: usize = align_of::<T>(),
zero_size: bool = T::IS_ZST || count == 0,
) =>
ub_checks::is_aligned_and_not_null(src, align)
&& ub_checks::is_aligned_and_not_null(dst, align)
ub_checks::is_aligned_and_not_null(src, align, zero_size)
&& ub_checks::is_aligned_and_not_null(dst, align, zero_size)
);
copy(src, dst, count)
}
@ -3491,7 +3495,8 @@ pub const fn ptr_metadata<P: ptr::Pointee<Metadata = M> + ?Sized, M>(_ptr: *cons
(
addr: *const () = dst as *const (),
align: usize = align_of::<T>(),
) => ub_checks::is_aligned_and_not_null(addr, align)
zero_size: bool = T::IS_ZST || count == 0,
) => ub_checks::is_aligned_and_not_null(addr, align, zero_size)
);
write_bytes(dst, val, count)
}

21
library/core/src/ptr/mod.rs
View File

@ -448,7 +448,7 @@
use crate::cmp::Ordering;
use crate::marker::FnPtr;
use crate::mem::{self, MaybeUninit};
use crate::mem::{self, MaybeUninit, SizedTypeProperties};
use crate::{fmt, hash, intrinsics, ub_checks};
mod alignment;
@ -1165,10 +1165,12 @@ macro_rules! attempt_swap_as_chunks {
size: usize = size_of::<T>(),
align: usize = align_of::<T>(),
count: usize = count,
) =>
ub_checks::is_aligned_and_not_null(x, align)
&& ub_checks::is_aligned_and_not_null(y, align)
&& ub_checks::is_nonoverlapping(x, y, size, count)
) => {
let zero_size = size == 0 || count == 0;
ub_checks::is_aligned_and_not_null(x, align, zero_size)
&& ub_checks::is_aligned_and_not_null(y, align, zero_size)
&& ub_checks::is_nonoverlapping(x, y, size, count)
}
);
// Split up the slice into small power-of-two-sized chunks that LLVM is able
@ -1277,7 +1279,8 @@ macro_rules! attempt_swap_as_chunks {
(
addr: *const () = dst as *const (),
align: usize = align_of::<T>(),
) => ub_checks::is_aligned_and_not_null(addr, align)
is_zst: bool = T::IS_ZST,
) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
);
mem::replace(&mut *dst, src)
}
@ -1806,7 +1809,8 @@ pub unsafe fn read_volatile<T>(src: *const T) -> T {
(
addr: *const () = src as *const (),
align: usize = align_of::<T>(),
) => ub_checks::is_aligned_and_not_null(addr, align)
is_zst: bool = T::IS_ZST,
) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
);
intrinsics::volatile_load(src)
}
@ -1885,7 +1889,8 @@ pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
(
addr: *mut () = dst as *mut (),
align: usize = align_of::<T>(),
) => ub_checks::is_aligned_and_not_null(addr, align)
is_zst: bool = T::IS_ZST,
) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
);
intrinsics::volatile_store(dst, src);
}

4
library/core/src/slice/raw.rs
View File

@ -132,7 +132,7 @@
align: usize = align_of::<T>(),
len: usize = len,
) =>
ub_checks::is_aligned_and_not_null(data, align)
ub_checks::is_aligned_and_not_null(data, align, false)
&& ub_checks::is_valid_allocation_size(size, len)
);
&*ptr::slice_from_raw_parts(data, len)
@ -187,7 +187,7 @@
align: usize = align_of::<T>(),
len: usize = len,
) =>
ub_checks::is_aligned_and_not_null(data, align)
ub_checks::is_aligned_and_not_null(data, align, false)
&& ub_checks::is_valid_allocation_size(size, len)
);
&mut *ptr::slice_from_raw_parts_mut(data, len)

4
library/core/src/ub_checks.rs
View File

@ -116,8 +116,8 @@ const fn comptime() -> bool {
/// for `assert_unsafe_precondition!` with `check_language_ub`, in which case the
/// check is anyway not executed in `const`.
#[inline]
pub(crate) const fn is_aligned_and_not_null(ptr: *const (), align: usize) -> bool {
!ptr.is_null() && ptr.is_aligned_to(align)
pub(crate) const fn is_aligned_and_not_null(ptr: *const (), align: usize, is_zst: bool) -> bool {
if is_zst { ptr.is_aligned_to(align) } else { !ptr.is_null() && ptr.is_aligned_to(align) }
}
#[inline]