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Fix unsoundness of AtomicCell<*64> arithmetics on 32-bit targets that support Atomic*64 #781

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merged 1 commit into from Feb 5, 2022
Merged

Fix unsoundness of AtomicCell<*64> arithmetics on 32-bit targets that support Atomic*64 #781

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100 changes: 90 additions & 10 deletions crossbeam-utils/src/atomic/atomic_cell.rs
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Expand Up @@ -465,8 +465,24 @@ macro_rules! impl_arithmetic {
/// ```
#[inline]
pub fn fetch_add(&self, val: $t) -> $t {
let a = unsafe { &*(self.value.get() as *const $atomic) };
a.fetch_add(val, Ordering::AcqRel)
if can_transmute::<$t, $atomic>() {
let a = unsafe { &*(self.value.get() as *const $atomic) };
a.fetch_add(val, Ordering::AcqRel)
} else {
#[cfg(crossbeam_loom)]
{
let _ = val;
unimplemented!("loom does not support non-atomic atomic ops");
}
#[cfg(not(crossbeam_loom))]
{
let _guard = lock(self.value.get() as usize).write();
let value = unsafe { &mut *(self.value.get()) };
let old = *value;
*value = value.wrapping_add(val);
old
}
}
}

/// Decrements the current value by `val` and returns the previous value.
Expand All @@ -485,8 +501,24 @@ macro_rules! impl_arithmetic {
/// ```
#[inline]
pub fn fetch_sub(&self, val: $t) -> $t {
let a = unsafe { &*(self.value.get() as *const $atomic) };
a.fetch_sub(val, Ordering::AcqRel)
if can_transmute::<$t, $atomic>() {
let a = unsafe { &*(self.value.get() as *const $atomic) };
a.fetch_sub(val, Ordering::AcqRel)
} else {
#[cfg(crossbeam_loom)]
{
let _ = val;
unimplemented!("loom does not support non-atomic atomic ops");
}
#[cfg(not(crossbeam_loom))]
{
let _guard = lock(self.value.get() as usize).write();
let value = unsafe { &mut *(self.value.get()) };
let old = *value;
*value = value.wrapping_sub(val);
old
}
}
}

/// Applies bitwise "and" to the current value and returns the previous value.
Expand All @@ -503,8 +535,24 @@ macro_rules! impl_arithmetic {
/// ```
#[inline]
pub fn fetch_and(&self, val: $t) -> $t {
let a = unsafe { &*(self.value.get() as *const $atomic) };
a.fetch_and(val, Ordering::AcqRel)
if can_transmute::<$t, $atomic>() {
let a = unsafe { &*(self.value.get() as *const $atomic) };
a.fetch_and(val, Ordering::AcqRel)
} else {
#[cfg(crossbeam_loom)]
{
let _ = val;
unimplemented!("loom does not support non-atomic atomic ops");
}
#[cfg(not(crossbeam_loom))]
{
let _guard = lock(self.value.get() as usize).write();
let value = unsafe { &mut *(self.value.get()) };
let old = *value;
*value &= val;
old
}
}
}

/// Applies bitwise "or" to the current value and returns the previous value.
Expand All @@ -521,8 +569,24 @@ macro_rules! impl_arithmetic {
/// ```
#[inline]
pub fn fetch_or(&self, val: $t) -> $t {
let a = unsafe { &*(self.value.get() as *const $atomic) };
a.fetch_or(val, Ordering::AcqRel)
if can_transmute::<$t, $atomic>() {
let a = unsafe { &*(self.value.get() as *const $atomic) };
a.fetch_or(val, Ordering::AcqRel)
} else {
#[cfg(crossbeam_loom)]
{
let _ = val;
unimplemented!("loom does not support non-atomic atomic ops");
}
#[cfg(not(crossbeam_loom))]
{
let _guard = lock(self.value.get() as usize).write();
let value = unsafe { &mut *(self.value.get()) };
let old = *value;
*value |= val;
old
}
}
}

/// Applies bitwise "xor" to the current value and returns the previous value.
Expand All @@ -539,8 +603,24 @@ macro_rules! impl_arithmetic {
/// ```
#[inline]
pub fn fetch_xor(&self, val: $t) -> $t {
let a = unsafe { &*(self.value.get() as *const $atomic) };
a.fetch_xor(val, Ordering::AcqRel)
if can_transmute::<$t, $atomic>() {
let a = unsafe { &*(self.value.get() as *const $atomic) };
a.fetch_xor(val, Ordering::AcqRel)
} else {
#[cfg(crossbeam_loom)]
{
let _ = val;
unimplemented!("loom does not support non-atomic atomic ops");
}
#[cfg(not(crossbeam_loom))]
{
let _guard = lock(self.value.get() as usize).write();
let value = unsafe { &mut *(self.value.get()) };
let old = *value;
*value ^= val;
old
}
}
}
}
};
Expand Down