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saethlinsaethlin
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Allow zero-size reads/writes on null pointers
1 parent 9ca739e commit 528dda2

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4 files changed

+29
-19
lines changed

4 files changed

+29
-19
lines changed

‎core/src/intrinsics.rs

+12-7
Original file line numberDiff line numberDiff line change
@@ -64,6 +64,7 @@
6464
#![allow(missing_docs)]
6565

6666
use crate::marker::{DiscriminantKind, Tuple};
67+
use crate::mem::SizedTypeProperties;
6768
use crate::{ptr, ub_checks};
6869

6970
pub mod mir;
@@ -3311,10 +3312,12 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
33113312
size: usize = size_of::<T>(),
33123313
align: usize = align_of::<T>(),
33133314
count: usize = count,
3314-
) =>
3315-
ub_checks::is_aligned_and_not_null(src, align)
3316-
&& ub_checks::is_aligned_and_not_null(dst, align)
3317-
&& ub_checks::is_nonoverlapping(src, dst, size, count)
3315+
) => {
3316+
let zero_size = count == 0 || size == 0;
3317+
ub_checks::is_aligned_and_not_null(src, align, zero_size)
3318+
&& ub_checks::is_aligned_and_not_null(dst, align, zero_size)
3319+
&& ub_checks::is_nonoverlapping(src, dst, size, count)
3320+
}
33183321
);
33193322

33203323
// SAFETY: the safety contract for `copy_nonoverlapping` must be
@@ -3412,9 +3415,10 @@ pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
34123415
src: *const () = src as *const (),
34133416
dst: *mut () = dst as *mut (),
34143417
align: usize = align_of::<T>(),
3418+
zero_size: bool = T::IS_ZST || count == 0,
34153419
) =>
3416-
ub_checks::is_aligned_and_not_null(src, align)
3417-
&& ub_checks::is_aligned_and_not_null(dst, align)
3420+
ub_checks::is_aligned_and_not_null(src, align, zero_size)
3421+
&& ub_checks::is_aligned_and_not_null(dst, align, zero_size)
34183422
);
34193423
copy(src, dst, count)
34203424
}
@@ -3491,7 +3495,8 @@ pub const unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
34913495
(
34923496
addr: *const () = dst as *const (),
34933497
align: usize = align_of::<T>(),
3494-
) => ub_checks::is_aligned_and_not_null(addr, align)
3498+
zero_size: bool = T::IS_ZST || count == 0,
3499+
) => ub_checks::is_aligned_and_not_null(addr, align, zero_size)
34953500
);
34963501
write_bytes(dst, val, count)
34973502
}

‎core/src/ptr/mod.rs

+13-8
Original file line numberDiff line numberDiff line change
@@ -448,7 +448,7 @@
448448

449449
use crate::cmp::Ordering;
450450
use crate::marker::FnPtr;
451-
use crate::mem::{self, MaybeUninit};
451+
use crate::mem::{self, MaybeUninit, SizedTypeProperties};
452452
use crate::{fmt, hash, intrinsics, ub_checks};
453453

454454
mod alignment;
@@ -1165,10 +1165,12 @@ pub const unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) {
11651165
size: usize = size_of::<T>(),
11661166
align: usize = align_of::<T>(),
11671167
count: usize = count,
1168-
) =>
1169-
ub_checks::is_aligned_and_not_null(x, align)
1170-
&& ub_checks::is_aligned_and_not_null(y, align)
1171-
&& ub_checks::is_nonoverlapping(x, y, size, count)
1168+
) => {
1169+
let zero_size = size == 0 || count == 0;
1170+
ub_checks::is_aligned_and_not_null(x, align, zero_size)
1171+
&& ub_checks::is_aligned_and_not_null(y, align, zero_size)
1172+
&& ub_checks::is_nonoverlapping(x, y, size, count)
1173+
}
11721174
);
11731175

11741176
// Split up the slice into small power-of-two-sized chunks that LLVM is able
@@ -1277,7 +1279,8 @@ pub const unsafe fn replace<T>(dst: *mut T, src: T) -> T {
12771279
(
12781280
addr: *const () = dst as *const (),
12791281
align: usize = align_of::<T>(),
1280-
) => ub_checks::is_aligned_and_not_null(addr, align)
1282+
is_zst: bool = T::IS_ZST,
1283+
) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
12811284
);
12821285
mem::replace(&mut *dst, src)
12831286
}
@@ -1806,7 +1809,8 @@ pub unsafe fn read_volatile<T>(src: *const T) -> T {
18061809
(
18071810
addr: *const () = src as *const (),
18081811
align: usize = align_of::<T>(),
1809-
) => ub_checks::is_aligned_and_not_null(addr, align)
1812+
is_zst: bool = T::IS_ZST,
1813+
) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
18101814
);
18111815
intrinsics::volatile_load(src)
18121816
}
@@ -1885,7 +1889,8 @@ pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
18851889
(
18861890
addr: *mut () = dst as *mut (),
18871891
align: usize = align_of::<T>(),
1888-
) => ub_checks::is_aligned_and_not_null(addr, align)
1892+
is_zst: bool = T::IS_ZST,
1893+
) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
18891894
);
18901895
intrinsics::volatile_store(dst, src);
18911896
}

‎core/src/slice/raw.rs

+2-2
Original file line numberDiff line numberDiff line change
@@ -132,7 +132,7 @@ pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T]
132132
align: usize = align_of::<T>(),
133133
len: usize = len,
134134
) =>
135-
ub_checks::is_aligned_and_not_null(data, align)
135+
ub_checks::is_aligned_and_not_null(data, align, false)
136136
&& ub_checks::is_valid_allocation_size(size, len)
137137
);
138138
&*ptr::slice_from_raw_parts(data, len)
@@ -187,7 +187,7 @@ pub const unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a m
187187
align: usize = align_of::<T>(),
188188
len: usize = len,
189189
) =>
190-
ub_checks::is_aligned_and_not_null(data, align)
190+
ub_checks::is_aligned_and_not_null(data, align, false)
191191
&& ub_checks::is_valid_allocation_size(size, len)
192192
);
193193
&mut *ptr::slice_from_raw_parts_mut(data, len)

‎core/src/ub_checks.rs

+2-2
Original file line numberDiff line numberDiff line change
@@ -116,8 +116,8 @@ pub(crate) const fn check_language_ub() -> bool {
116116
/// for `assert_unsafe_precondition!` with `check_language_ub`, in which case the
117117
/// check is anyway not executed in `const`.
118118
#[inline]
119-
pub(crate) const fn is_aligned_and_not_null(ptr: *const (), align: usize) -> bool {
120-
!ptr.is_null() && ptr.is_aligned_to(align)
119+
pub(crate) const fn is_aligned_and_not_null(ptr: *const (), align: usize, is_zst: bool) -> bool {
120+
if is_zst { ptr.is_aligned_to(align) } else { !ptr.is_null() && ptr.is_aligned_to(align) }
121121
}
122122

123123
#[inline]

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