1// SPDX-License-Identifier: Apache-2.0 OR MIT
2
3/*
4Atomic operations implementation on x86/x86_64.
5
6This module provides atomic operations not supported by LLVM or optimizes
7cases where LLVM code generation is not optimal.
8
9Note: On Miri and ThreadSanitizer which do not support inline assembly, we don't use
10this module and use CAS loop instead.
11
12Refs:
13- x86 and amd64 instruction reference https://www.felixcloutier.com/x86
14
15Generated asm:
16- x86_64 https://godbolt.org/z/ETa1MGTP3
17*/
18
19#[cfg(not(portable_atomic_no_asm))]
20use core::arch::asm;
21use core::sync::atomic::Ordering;
22
23use super::core_atomic::{
24 AtomicI8, AtomicI16, AtomicI32, AtomicI64, AtomicIsize, AtomicU8, AtomicU16, AtomicU32,
25 AtomicU64, AtomicUsize,
26};
27
28#[cfg(target_pointer_width = "32")]
29macro_rules! ptr_modifier {
30 () => {
31 ":e"
32 };
33}
34#[cfg(target_pointer_width = "64")]
35macro_rules! ptr_modifier {
36 () => {
37 ""
38 };
39}
40
41macro_rules! atomic_int {
42 ($atomic_type:ident, $ptr_size:tt) => {
43 impl $atomic_type {
44 #[inline]
45 pub(crate) fn not(&self, _order: Ordering) {
46 let dst = self.as_ptr();
47 // SAFETY: any data races are prevented by atomic intrinsics and the raw
48 // pointer passed in is valid because we got it from a reference.
49 //
50 // https://www.felixcloutier.com/x86/not
51 unsafe {
52 // atomic RMW is always SeqCst.
53 asm!(
54 concat!("lock not ", $ptr_size, " ptr [{dst", ptr_modifier!(), "}]"),
55 dst = in(reg) dst,
56 options(nostack, preserves_flags),
57 );
58 }
59 }
60 #[inline]
61 pub(crate) fn neg(&self, _order: Ordering) {
62 let dst = self.as_ptr();
63 // SAFETY: any data races are prevented by atomic intrinsics and the raw
64 // pointer passed in is valid because we got it from a reference.
65 //
66 // https://www.felixcloutier.com/x86/neg
67 unsafe {
68 // atomic RMW is always SeqCst.
69 asm!(
70 concat!("lock neg ", $ptr_size, " ptr [{dst", ptr_modifier!(), "}]"),
71 dst = in(reg) dst,
72 // Do not use `preserves_flags` because NEG modifies the CF, OF, SF, ZF, AF, and PF flag.
73 options(nostack),
74 );
75 }
76 }
77 }
78 };
79}
80
81atomic_int!(AtomicI8, "byte");
82atomic_int!(AtomicU8, "byte");
83atomic_int!(AtomicI16, "word");
84atomic_int!(AtomicU16, "word");
85atomic_int!(AtomicI32, "dword");
86atomic_int!(AtomicU32, "dword");
87#[cfg(target_arch = "x86_64")]
88atomic_int!(AtomicI64, "qword");
89#[cfg(target_arch = "x86_64")]
90atomic_int!(AtomicU64, "qword");
91#[cfg(target_pointer_width = "32")]
92atomic_int!(AtomicIsize, "dword");
93#[cfg(target_pointer_width = "32")]
94atomic_int!(AtomicUsize, "dword");
95#[cfg(target_pointer_width = "64")]
96atomic_int!(AtomicIsize, "qword");
97#[cfg(target_pointer_width = "64")]
98atomic_int!(AtomicUsize, "qword");
99
100#[cfg(target_arch = "x86")]
101impl AtomicI64 {
102 #[inline]
103 pub(crate) fn not(&self, order: Ordering) {
104 self.fetch_not(order);
105 }
106 #[inline]
107 pub(crate) fn neg(&self, order: Ordering) {
108 self.fetch_neg(order);
109 }
110}
111#[cfg(target_arch = "x86")]
112impl AtomicU64 {
113 #[inline]
114 pub(crate) fn not(&self, order: Ordering) {
115 self.fetch_not(order);
116 }
117 #[inline]
118 pub(crate) fn neg(&self, order: Ordering) {
119 self.fetch_neg(order);
120 }
121}
122
123macro_rules! atomic_bit_opts {
124 ($atomic_type:ident, $int_type:ident, $val_modifier:tt, $ptr_size:tt) => {
125 // LLVM 14 and older don't support generating `lock bt{s,r,c}`.
126 // LLVM 15 only supports generating `lock bt{s,r,c}` for immediate bit offsets.
127 // LLVM 16+ can generate `lock bt{s,r,c}` for both immediate and register bit offsets.
128 // https://godbolt.org/z/TGhr5z4ds
129 // So, use fetch_* based implementations on LLVM 16+, otherwise use asm based implementations.
130 #[cfg(not(portable_atomic_pre_llvm_16))]
131 impl_default_bit_opts!($atomic_type, $int_type);
132 #[cfg(portable_atomic_pre_llvm_16)]
133 impl $atomic_type {
134 // `<integer>::BITS` requires Rust 1.53
135 const BITS: u32 = (core::mem::size_of::<$int_type>() * 8) as u32;
136 #[inline]
137 pub(crate) fn bit_set(&self, bit: u32, _order: Ordering) -> bool {
138 let dst = self.as_ptr();
139 // SAFETY: any data races are prevented by atomic intrinsics and the raw
140 // pointer passed in is valid because we got it from a reference.
141 // the masking by the bit size of the type ensures that we do not shift
142 // out of bounds.
143 //
144 // https://www.felixcloutier.com/x86/bts
145 unsafe {
146 let r: u8;
147 // atomic RMW is always SeqCst.
148 asm!(
149 concat!("lock bts ", $ptr_size, " ptr [{dst", ptr_modifier!(), "}], {bit", $val_modifier, "}"),
150 "setb {r}",
151 dst = in(reg) dst,
152 bit = in(reg) (bit & (Self::BITS - 1)) as $int_type,
153 r = out(reg_byte) r,
154 // Do not use `preserves_flags` because BTS modifies the CF flag.
155 options(nostack),
156 );
157 crate::utils::assert_unchecked(r == 0 || r == 1); // may help remove extra test
158 r != 0
159 }
160 }
161 #[inline]
162 pub(crate) fn bit_clear(&self, bit: u32, _order: Ordering) -> bool {
163 let dst = self.as_ptr();
164 // SAFETY: any data races are prevented by atomic intrinsics and the raw
165 // pointer passed in is valid because we got it from a reference.
166 // the masking by the bit size of the type ensures that we do not shift
167 // out of bounds.
168 //
169 // https://www.felixcloutier.com/x86/btr
170 unsafe {
171 let r: u8;
172 // atomic RMW is always SeqCst.
173 asm!(
174 concat!("lock btr ", $ptr_size, " ptr [{dst", ptr_modifier!(), "}], {bit", $val_modifier, "}"),
175 "setb {r}",
176 dst = in(reg) dst,
177 bit = in(reg) (bit & (Self::BITS - 1)) as $int_type,
178 r = out(reg_byte) r,
179 // Do not use `preserves_flags` because BTR modifies the CF flag.
180 options(nostack),
181 );
182 crate::utils::assert_unchecked(r == 0 || r == 1); // may help remove extra test
183 r != 0
184 }
185 }
186 #[inline]
187 pub(crate) fn bit_toggle(&self, bit: u32, _order: Ordering) -> bool {
188 let dst = self.as_ptr();
189 // SAFETY: any data races are prevented by atomic intrinsics and the raw
190 // pointer passed in is valid because we got it from a reference.
191 // the masking by the bit size of the type ensures that we do not shift
192 // out of bounds.
193 //
194 // https://www.felixcloutier.com/x86/btc
195 unsafe {
196 let r: u8;
197 // atomic RMW is always SeqCst.
198 asm!(
199 concat!("lock btc ", $ptr_size, " ptr [{dst", ptr_modifier!(), "}], {bit", $val_modifier, "}"),
200 "setb {r}",
201 dst = in(reg) dst,
202 bit = in(reg) (bit & (Self::BITS - 1)) as $int_type,
203 r = out(reg_byte) r,
204 // Do not use `preserves_flags` because BTC modifies the CF flag.
205 options(nostack),
206 );
207 crate::utils::assert_unchecked(r == 0 || r == 1); // may help remove extra test
208 r != 0
209 }
210 }
211 }
212 };
213}
214
215impl_default_bit_opts!(AtomicI8, i8);
216impl_default_bit_opts!(AtomicU8, u8);
217atomic_bit_opts!(AtomicI16, i16, ":x", "word");
218atomic_bit_opts!(AtomicU16, u16, ":x", "word");
219atomic_bit_opts!(AtomicI32, i32, ":e", "dword");
220atomic_bit_opts!(AtomicU32, u32, ":e", "dword");
221#[cfg(target_arch = "x86_64")]
222atomic_bit_opts!(AtomicI64, i64, "", "qword");
223#[cfg(target_arch = "x86_64")]
224atomic_bit_opts!(AtomicU64, u64, "", "qword");
225#[cfg(target_arch = "x86")]
226impl_default_bit_opts!(AtomicI64, i64);
227#[cfg(target_arch = "x86")]
228impl_default_bit_opts!(AtomicU64, u64);
229#[cfg(target_pointer_width = "32")]
230atomic_bit_opts!(AtomicIsize, isize, ":e", "dword");
231#[cfg(target_pointer_width = "32")]
232atomic_bit_opts!(AtomicUsize, usize, ":e", "dword");
233#[cfg(target_pointer_width = "64")]
234atomic_bit_opts!(AtomicIsize, isize, "", "qword");
235#[cfg(target_pointer_width = "64")]
236atomic_bit_opts!(AtomicUsize, usize, "", "qword");
237