1// SPDX-License-Identifier: Apache-2.0 OR MIT
2
3/*
4Helper for outline-atomics.
5
6On architectures where DW atomics are not supported on older CPUs, we use
7fallback implementation when DW atomic instructions are not supported and
8outline-atomics is enabled.
9
10This module provides helpers to implement them.
11*/
12
13use core::sync::atomic::Ordering;
14
15#[cfg(any(target_arch = "x86_64", target_arch = "powerpc64", target_arch = "riscv64"))]
16pub(crate) type Udw = u128;
17#[cfg(any(target_arch = "x86_64", target_arch = "powerpc64", target_arch = "riscv64"))]
18pub(crate) type AtomicUdw = super::super::super::fallback::AtomicU128;
19#[cfg(any(target_arch = "x86_64", target_arch = "powerpc64", target_arch = "riscv64"))]
20pub(crate) type AtomicIdw = super::super::super::fallback::AtomicI128;
21
22#[cfg(any(target_arch = "arm", target_arch = "riscv32"))]
23pub(crate) type Udw = u64;
24#[cfg(any(target_arch = "arm", target_arch = "riscv32"))]
25pub(crate) type AtomicUdw = super::super::super::fallback::AtomicU64;
26#[cfg(any(target_arch = "arm", target_arch = "riscv32"))]
27pub(crate) type AtomicIdw = super::super::super::fallback::AtomicI64;
28
29// Asserts that the function is called in the correct context.
30macro_rules! debug_assert_outline_atomics {
31 () => {
32 #[cfg(target_arch = "x86_64")]
33 {
34 debug_assert!(!super::detect::detect().has_cmpxchg16b());
35 }
36 #[cfg(target_arch = "powerpc64")]
37 {
38 debug_assert!(!super::detect::detect().has_quadword_atomics());
39 }
40 #[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
41 {
42 debug_assert!(!super::detect::detect().has_zacas());
43 }
44 #[cfg(target_arch = "arm")]
45 {
46 debug_assert!(!super::has_kuser_cmpxchg64());
47 }
48 };
49}
50
51#[cold]
52pub(crate) unsafe fn atomic_load(src: *mut Udw, order: Ordering) -> Udw {
53 debug_assert_outline_atomics!();
54 #[allow(clippy::cast_ptr_alignment)]
55 // SAFETY: the caller must uphold the safety contract.
56 unsafe {
57 (*(src as *const AtomicUdw)).load(order)
58 }
59}
60fn_alias! {
61 #[cold]
62 pub(crate) unsafe fn(src: *mut Udw) -> Udw;
63 // fallback's atomic load has at least acquire semantics.
64 #[cfg(not(any(target_arch = "arm", target_arch = "x86_64")))]
65 atomic_load_non_seqcst = atomic_load(Ordering::Acquire);
66 atomic_load_seqcst = atomic_load(Ordering::SeqCst);
67}
68
69#[cfg(not(any(target_arch = "riscv32", target_arch = "riscv64")))]
70#[cold]
71pub(crate) unsafe fn atomic_store(dst: *mut Udw, val: Udw, order: Ordering) {
72 debug_assert_outline_atomics!();
73 #[allow(clippy::cast_ptr_alignment)]
74 // SAFETY: the caller must uphold the safety contract.
75 unsafe {
76 (*(dst as *const AtomicUdw)).store(val, order);
77 }
78}
79#[cfg(not(any(target_arch = "riscv32", target_arch = "riscv64")))]
80fn_alias! {
81 #[cold]
82 pub(crate) unsafe fn(dst: *mut Udw, val: Udw);
83 // fallback's atomic store has at least release semantics.
84 #[cfg(not(target_arch = "arm"))]
85 atomic_store_non_seqcst = atomic_store(Ordering::Release);
86 atomic_store_seqcst = atomic_store(Ordering::SeqCst);
87}
88
89#[cold]
90pub(crate) unsafe fn atomic_compare_exchange(
91 dst: *mut Udw,
92 old: Udw,
93 new: Udw,
94 success: Ordering,
95 failure: Ordering,
96) -> (Udw, bool) {
97 debug_assert_outline_atomics!();
98 #[allow(clippy::cast_ptr_alignment)]
99 // SAFETY: the caller must uphold the safety contract.
100 unsafe {
101 match (*(dst as *const AtomicUdw)).compare_exchange(current:old, new, success, failure) {
102 Ok(v: u128) => (v, true),
103 Err(v: u128) => (v, false),
104 }
105 }
106}
107fn_alias! {
108 #[cold]
109 pub(crate) unsafe fn(dst: *mut Udw, old: Udw, new: Udw) -> (Udw, bool);
110 // fallback's atomic CAS has at least AcqRel semantics.
111 #[cfg(not(any(target_arch = "arm", target_arch = "x86_64")))]
112 atomic_compare_exchange_non_seqcst
113 = atomic_compare_exchange(Ordering::AcqRel, Ordering::Acquire);
114 atomic_compare_exchange_seqcst
115 = atomic_compare_exchange(Ordering::SeqCst, Ordering::SeqCst);
116}
117
118macro_rules! atomic_rmw_3 {
119 (
120 $name:ident($atomic_type:ident::$method_name:ident),
121 $non_seqcst_alias:ident, $seqcst_alias:ident
122 ) => {
123 #[cold]
124 pub(crate) unsafe fn $name(dst: *mut Udw, val: Udw, order: Ordering) -> Udw {
125 debug_assert_outline_atomics!();
126 #[allow(
127 clippy::as_underscore,
128 clippy::cast_possible_wrap,
129 clippy::cast_ptr_alignment,
130 clippy::cast_sign_loss
131 )]
132 // SAFETY: the caller must uphold the safety contract.
133 unsafe {
134 (*(dst as *const $atomic_type)).$method_name(val as _, order) as Udw
135 }
136 }
137 fn_alias! {
138 #[cold]
139 pub(crate) unsafe fn(dst: *mut Udw, val: Udw) -> Udw;
140 // fallback's atomic RMW has at least AcqRel semantics.
141 #[cfg(not(any(target_arch = "arm", target_arch = "x86_64")))]
142 $non_seqcst_alias = $name(Ordering::AcqRel);
143 $seqcst_alias = $name(Ordering::SeqCst);
144 }
145 };
146}
147macro_rules! atomic_rmw_2 {
148 (
149 $name:ident($atomic_type:ident::$method_name:ident),
150 $non_seqcst_alias:ident, $seqcst_alias:ident
151 ) => {
152 #[cold]
153 pub(crate) unsafe fn $name(dst: *mut Udw, order: Ordering) -> Udw {
154 debug_assert_outline_atomics!();
155 #[allow(clippy::cast_ptr_alignment)]
156 // SAFETY: the caller must uphold the safety contract.
157 unsafe {
158 (*(dst as *const $atomic_type)).$method_name(order) as Udw
159 }
160 }
161 fn_alias! {
162 #[cold]
163 pub(crate) unsafe fn(dst: *mut Udw) -> Udw;
164 // fallback's atomic RMW has at least AcqRel semantics.
165 #[cfg(not(any(target_arch = "arm", target_arch = "x86_64")))]
166 $non_seqcst_alias = $name(Ordering::AcqRel);
167 $seqcst_alias = $name(Ordering::SeqCst);
168 }
169 };
170}
171
172atomic_rmw_3!(atomic_swap(AtomicUdw::swap), atomic_swap_non_seqcst, atomic_swap_seqcst);
173atomic_rmw_3!(atomic_add(AtomicUdw::fetch_add), atomic_add_non_seqcst, atomic_add_seqcst);
174atomic_rmw_3!(atomic_sub(AtomicUdw::fetch_sub), atomic_sub_non_seqcst, atomic_sub_seqcst);
175atomic_rmw_3!(atomic_and(AtomicUdw::fetch_and), atomic_and_non_seqcst, atomic_and_seqcst);
176atomic_rmw_3!(atomic_nand(AtomicUdw::fetch_nand), atomic_nand_non_seqcst, atomic_nand_seqcst);
177atomic_rmw_3!(atomic_or(AtomicUdw::fetch_or), atomic_or_non_seqcst, atomic_or_seqcst);
178atomic_rmw_3!(atomic_xor(AtomicUdw::fetch_xor), atomic_xor_non_seqcst, atomic_xor_seqcst);
179atomic_rmw_3!(atomic_max(AtomicIdw::fetch_max), atomic_max_non_seqcst, atomic_max_seqcst);
180atomic_rmw_3!(atomic_umax(AtomicUdw::fetch_max), atomic_umax_non_seqcst, atomic_umax_seqcst);
181atomic_rmw_3!(atomic_min(AtomicIdw::fetch_min), atomic_min_non_seqcst, atomic_min_seqcst);
182atomic_rmw_3!(atomic_umin(AtomicUdw::fetch_min), atomic_umin_non_seqcst, atomic_umin_seqcst);
183
184atomic_rmw_2!(atomic_not(AtomicUdw::fetch_not), atomic_not_non_seqcst, atomic_not_seqcst);
185atomic_rmw_2!(atomic_neg(AtomicUdw::fetch_neg), atomic_neg_non_seqcst, atomic_neg_seqcst);
186