diff options
Diffstat (limited to 'library/stdarch/crates/core_arch/src/x86_64/cmpxchg16b.rs')
| -rw-r--r-- | library/stdarch/crates/core_arch/src/x86_64/cmpxchg16b.rs | 24 |
1 files changed, 13 insertions, 11 deletions
diff --git a/library/stdarch/crates/core_arch/src/x86_64/cmpxchg16b.rs b/library/stdarch/crates/core_arch/src/x86_64/cmpxchg16b.rs index a262932af..a4fc0e732 100644 --- a/library/stdarch/crates/core_arch/src/x86_64/cmpxchg16b.rs +++ b/library/stdarch/crates/core_arch/src/x86_64/cmpxchg16b.rs @@ -16,10 +16,13 @@ use stdarch_test::assert_instr; /// /// # Memory Orderings /// -/// This atomic operations has the same semantics of memory orderings as +/// This atomic operation has the same semantics of memory orderings as /// `AtomicUsize::compare_exchange` does, only operating on 16 bytes of memory /// instead of just a pointer. /// +/// The failure ordering must be [`Ordering::SeqCst`], [`Ordering::Acquire`] or +/// [`Ordering::Relaxed`]. +/// /// For more information on memory orderings here see the `compare_exchange` /// documentation for other `Atomic*` types in the standard library. /// @@ -33,15 +36,11 @@ use stdarch_test::assert_instr; /// runtime to work correctly. If the CPU running the binary does not actually /// support `cmpxchg16b` and the program enters an execution path that /// eventually would reach this function the behavior is undefined. -/// -/// The failure ordering must be [`Ordering::SeqCst`], [`Ordering::Acquire`] or -/// [`Ordering::Relaxed`], or this function call is undefined. See the `Atomic*` -/// documentation's `compare_exchange` function for more information. When -/// `compare_exchange` panics, this is undefined behavior. Currently this -/// function aborts the process with an undefined instruction. #[inline] +#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces #[cfg_attr(test, assert_instr(cmpxchg16b, success = Ordering::SeqCst, failure = Ordering::SeqCst))] #[target_feature(enable = "cmpxchg16b")] +#[stable(feature = "cmpxchg16b_intrinsic", since = "1.67.0")] pub unsafe fn cmpxchg16b( dst: *mut u128, old: u128, @@ -53,6 +52,8 @@ pub unsafe fn cmpxchg16b( debug_assert!(dst as usize % 16 == 0); + // Copied from `atomic_compare_exchange` in `core`. + // https://github.com/rust-lang/rust/blob/f8a2e49/library/core/src/sync/atomic.rs#L3046-L3079 let (val, _ok) = match (success, failure) { (Relaxed, Relaxed) => intrinsics::atomic_cxchg_relaxed_relaxed(dst, old, new), (Relaxed, Acquire) => intrinsics::atomic_cxchg_relaxed_acquire(dst, old, new), @@ -69,11 +70,12 @@ pub unsafe fn cmpxchg16b( (SeqCst, Relaxed) => intrinsics::atomic_cxchg_seqcst_relaxed(dst, old, new), (SeqCst, Acquire) => intrinsics::atomic_cxchg_seqcst_acquire(dst, old, new), (SeqCst, SeqCst) => intrinsics::atomic_cxchg_seqcst_seqcst(dst, old, new), + (_, AcqRel) => panic!("there is no such thing as an acquire-release failure ordering"), + (_, Release) => panic!("there is no such thing as a release failure ordering"), - // The above block is all copied from libcore, and this statement is - // also copied from libcore except that it's a panic in libcore and we - // have a little bit more of a lightweight panic here. - _ => crate::core_arch::x86::ud2(), + // `atomic::Ordering` is non_exhaustive. It warns when `core_arch` is built as a part of `core`. + #[allow(unreachable_patterns)] + (_, _) => unreachable!(), }; val } |