diff options
Diffstat (limited to 'vendor/portable-atomic/src/imp/arm_linux.rs')
| -rw-r--r-- | vendor/portable-atomic/src/imp/arm_linux.rs | 471 |
1 files changed, 471 insertions, 0 deletions
diff --git a/vendor/portable-atomic/src/imp/arm_linux.rs b/vendor/portable-atomic/src/imp/arm_linux.rs new file mode 100644 index 0000000..623a282 --- /dev/null +++ b/vendor/portable-atomic/src/imp/arm_linux.rs @@ -0,0 +1,471 @@ +// SPDX-License-Identifier: Apache-2.0 OR MIT + +// 64-bit atomic implementation using kuser_cmpxchg64 on pre-v6 ARM Linux/Android. +// +// Refs: +// - https://www.kernel.org/doc/Documentation/arm/kernel_user_helpers.txt +// - https://github.com/rust-lang/compiler-builtins/blob/0.1.88/src/arm_linux.rs +// +// Note: On Miri and ThreadSanitizer which do not support inline assembly, we don't use +// this module and use fallback implementation instead. + +// TODO: Since Rust 1.64, the Linux kernel requirement for Rust when using std is 3.2+, so it should +// be possible to omit the dynamic kernel version check if the std feature is enabled on Rust 1.64+. +// https://blog.rust-lang.org/2022/08/01/Increasing-glibc-kernel-requirements.html + +#[path = "fallback/outline_atomics.rs"] +mod fallback; + +use core::{arch::asm, cell::UnsafeCell, mem, sync::atomic::Ordering}; + +use crate::utils::{Pair, U64}; + +// https://www.kernel.org/doc/Documentation/arm/kernel_user_helpers.txt +const KUSER_HELPER_VERSION: usize = 0xFFFF0FFC; +// __kuser_helper_version >= 5 (kernel version 3.1+) +const KUSER_CMPXCHG64: usize = 0xFFFF0F60; +#[inline] +fn __kuser_helper_version() -> i32 { + use core::sync::atomic::AtomicI32; + + static CACHE: AtomicI32 = AtomicI32::new(0); + let mut v = CACHE.load(Ordering::Relaxed); + if v != 0 { + return v; + } + // SAFETY: core assumes that at least __kuser_memory_barrier (__kuser_helper_version >= 3) is + // available on this platform. __kuser_helper_version is always available on such a platform. + v = unsafe { (KUSER_HELPER_VERSION as *const i32).read() }; + CACHE.store(v, Ordering::Relaxed); + v +} +#[inline] +fn has_kuser_cmpxchg64() -> bool { + // Note: detect_false cfg is intended to make it easy for portable-atomic developers to + // test cases such as has_cmpxchg16b == false, has_lse == false, + // __kuser_helper_version < 5, etc., and is not a public API. + if cfg!(portable_atomic_test_outline_atomics_detect_false) { + return false; + } + __kuser_helper_version() >= 5 +} +#[inline] +unsafe fn __kuser_cmpxchg64(old_val: *const u64, new_val: *const u64, ptr: *mut u64) -> bool { + // SAFETY: the caller must uphold the safety contract. + unsafe { + let f: extern "C" fn(*const u64, *const u64, *mut u64) -> u32 = + mem::transmute(KUSER_CMPXCHG64 as *const ()); + f(old_val, new_val, ptr) == 0 + } +} + +// 64-bit atomic load by two 32-bit atomic loads. +#[inline] +unsafe fn byte_wise_atomic_load(src: *const u64) -> u64 { + // SAFETY: the caller must uphold the safety contract. + unsafe { + let (out_lo, out_hi); + asm!( + "ldr {out_lo}, [{src}]", + "ldr {out_hi}, [{src}, #4]", + src = in(reg) src, + out_lo = out(reg) out_lo, + out_hi = out(reg) out_hi, + options(pure, nostack, preserves_flags, readonly), + ); + U64 { pair: Pair { lo: out_lo, hi: out_hi } }.whole + } +} + +#[inline(always)] +unsafe fn atomic_update_kuser_cmpxchg64<F>(dst: *mut u64, mut f: F) -> u64 +where + F: FnMut(u64) -> u64, +{ + debug_assert!(dst as usize % 8 == 0); + debug_assert!(has_kuser_cmpxchg64()); + // SAFETY: the caller must uphold the safety contract. + unsafe { + loop { + // This is not single-copy atomic reads, but this is ok because subsequent + // CAS will check for consistency. + // + // Note that the C++20 memory model does not allow mixed-sized atomic access, + // so we must use inline assembly to implement byte_wise_atomic_load. + // (i.e., byte-wise atomic based on the standard library's atomic types + // cannot be used here). + let prev = byte_wise_atomic_load(dst); + let next = f(prev); + if __kuser_cmpxchg64(&prev, &next, dst) { + return prev; + } + } + } +} + +macro_rules! atomic_with_ifunc { + ( + unsafe fn $name:ident($($arg:tt)*) $(-> $ret_ty:ty)? { $($kuser_cmpxchg64_fn_body:tt)* } + fallback = $seqcst_fallback_fn:ident + ) => { + #[inline] + unsafe fn $name($($arg)*) $(-> $ret_ty)? { + unsafe fn kuser_cmpxchg64_fn($($arg)*) $(-> $ret_ty)? { + $($kuser_cmpxchg64_fn_body)* + } + // SAFETY: the caller must uphold the safety contract. + // we only calls __kuser_cmpxchg64 if it is available. + unsafe { + ifunc!(unsafe fn($($arg)*) $(-> $ret_ty)? { + if has_kuser_cmpxchg64() { + kuser_cmpxchg64_fn + } else { + // Use SeqCst because __kuser_cmpxchg64 is always SeqCst. + // https://github.com/torvalds/linux/blob/v6.1/arch/arm/kernel/entry-armv.S#L918-L925 + fallback::$seqcst_fallback_fn + } + }) + } + } + }; +} + +atomic_with_ifunc! { + unsafe fn atomic_load(src: *mut u64) -> u64 { + // SAFETY: the caller must uphold the safety contract. + unsafe { atomic_update_kuser_cmpxchg64(src, |old| old) } + } + fallback = atomic_load_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_store(dst: *mut u64, val: u64) { + // SAFETY: the caller must uphold the safety contract. + unsafe { atomic_update_kuser_cmpxchg64(dst, |_| val); } + } + fallback = atomic_store_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_swap(dst: *mut u64, val: u64) -> u64 { + // SAFETY: the caller must uphold the safety contract. + unsafe { atomic_update_kuser_cmpxchg64(dst, |_| val) } + } + fallback = atomic_swap_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_compare_exchange(dst: *mut u64, old: u64, new: u64) -> (u64, bool) { + // SAFETY: the caller must uphold the safety contract. + let prev = unsafe { + atomic_update_kuser_cmpxchg64(dst, |v| if v == old { new } else { v }) + }; + (prev, prev == old) + } + fallback = atomic_compare_exchange_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_add(dst: *mut u64, val: u64) -> u64 { + // SAFETY: the caller must uphold the safety contract. + unsafe { atomic_update_kuser_cmpxchg64(dst, |x| x.wrapping_add(val)) } + } + fallback = atomic_add_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_sub(dst: *mut u64, val: u64) -> u64 { + // SAFETY: the caller must uphold the safety contract. + unsafe { atomic_update_kuser_cmpxchg64(dst, |x| x.wrapping_sub(val)) } + } + fallback = atomic_sub_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_and(dst: *mut u64, val: u64) -> u64 { + // SAFETY: the caller must uphold the safety contract. + unsafe { atomic_update_kuser_cmpxchg64(dst, |x| x & val) } + } + fallback = atomic_and_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_nand(dst: *mut u64, val: u64) -> u64 { + // SAFETY: the caller must uphold the safety contract. + unsafe { atomic_update_kuser_cmpxchg64(dst, |x| !(x & val)) } + } + fallback = atomic_nand_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_or(dst: *mut u64, val: u64) -> u64 { + // SAFETY: the caller must uphold the safety contract. + unsafe { atomic_update_kuser_cmpxchg64(dst, |x| x | val) } + } + fallback = atomic_or_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_xor(dst: *mut u64, val: u64) -> u64 { + // SAFETY: the caller must uphold the safety contract. + unsafe { atomic_update_kuser_cmpxchg64(dst, |x| x ^ val) } + } + fallback = atomic_xor_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_max(dst: *mut u64, val: u64) -> u64 { + #[allow(clippy::cast_possible_wrap, clippy::cast_sign_loss)] + // SAFETY: the caller must uphold the safety contract. + unsafe { + atomic_update_kuser_cmpxchg64(dst, |x| core::cmp::max(x as i64, val as i64) as u64) + } + } + fallback = atomic_max_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_umax(dst: *mut u64, val: u64) -> u64 { + // SAFETY: the caller must uphold the safety contract. + unsafe { atomic_update_kuser_cmpxchg64(dst, |x| core::cmp::max(x, val)) } + } + fallback = atomic_umax_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_min(dst: *mut u64, val: u64) -> u64 { + #[allow(clippy::cast_possible_wrap, clippy::cast_sign_loss)] + // SAFETY: the caller must uphold the safety contract. + unsafe { + atomic_update_kuser_cmpxchg64(dst, |x| core::cmp::min(x as i64, val as i64) as u64) + } + } + fallback = atomic_min_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_umin(dst: *mut u64, val: u64) -> u64 { + // SAFETY: the caller must uphold the safety contract. + unsafe { atomic_update_kuser_cmpxchg64(dst, |x| core::cmp::min(x, val)) } + } + fallback = atomic_umin_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_not(dst: *mut u64) -> u64 { + // SAFETY: the caller must uphold the safety contract. + unsafe { atomic_update_kuser_cmpxchg64(dst, |x| !x) } + } + fallback = atomic_not_seqcst +} +atomic_with_ifunc! { + unsafe fn atomic_neg(dst: *mut u64) -> u64 { + // SAFETY: the caller must uphold the safety contract. + unsafe { atomic_update_kuser_cmpxchg64(dst, u64::wrapping_neg) } + } + fallback = atomic_neg_seqcst +} + +macro_rules! atomic64 { + ($atomic_type:ident, $int_type:ident, $atomic_max:ident, $atomic_min:ident) => { + #[repr(C, align(8))] + pub(crate) struct $atomic_type { + v: UnsafeCell<$int_type>, + } + + // Send is implicitly implemented. + // SAFETY: any data races are prevented by the kernel user helper or the lock. + unsafe impl Sync for $atomic_type {} + + impl_default_no_fetch_ops!($atomic_type, $int_type); + impl_default_bit_opts!($atomic_type, $int_type); + impl $atomic_type { + #[inline] + pub(crate) const fn new(v: $int_type) -> Self { + Self { v: UnsafeCell::new(v) } + } + + #[inline] + pub(crate) fn is_lock_free() -> bool { + has_kuser_cmpxchg64() + } + #[inline] + pub(crate) const fn is_always_lock_free() -> bool { + false + } + + #[inline] + pub(crate) fn get_mut(&mut self) -> &mut $int_type { + // SAFETY: the mutable reference guarantees unique ownership. + // (UnsafeCell::get_mut requires Rust 1.50) + unsafe { &mut *self.v.get() } + } + + #[inline] + pub(crate) fn into_inner(self) -> $int_type { + self.v.into_inner() + } + + #[inline] + #[cfg_attr(all(debug_assertions, not(portable_atomic_no_track_caller)), track_caller)] + pub(crate) fn load(&self, order: Ordering) -> $int_type { + crate::utils::assert_load_ordering(order); + // SAFETY: any data races are prevented by the kernel user helper or the lock + // and the raw pointer passed in is valid because we got it from a reference. + unsafe { atomic_load(self.v.get().cast::<u64>()) as $int_type } + } + + #[inline] + #[cfg_attr(all(debug_assertions, not(portable_atomic_no_track_caller)), track_caller)] + pub(crate) fn store(&self, val: $int_type, order: Ordering) { + crate::utils::assert_store_ordering(order); + // SAFETY: any data races are prevented by the kernel user helper or the lock + // and the raw pointer passed in is valid because we got it from a reference. + unsafe { atomic_store(self.v.get().cast::<u64>(), val as u64) } + } + + #[inline] + pub(crate) fn swap(&self, val: $int_type, _order: Ordering) -> $int_type { + // SAFETY: any data races are prevented by the kernel user helper or the lock + // and the raw pointer passed in is valid because we got it from a reference. + unsafe { atomic_swap(self.v.get().cast::<u64>(), val as u64) as $int_type } + } + + #[inline] + #[cfg_attr(all(debug_assertions, not(portable_atomic_no_track_caller)), track_caller)] + pub(crate) fn compare_exchange( + &self, + current: $int_type, + new: $int_type, + success: Ordering, + failure: Ordering, + ) -> Result<$int_type, $int_type> { + crate::utils::assert_compare_exchange_ordering(success, failure); + // SAFETY: any data races are prevented by the kernel user helper or the lock + // and the raw pointer passed in is valid because we got it from a reference. + unsafe { + let (prev, ok) = atomic_compare_exchange( + self.v.get().cast::<u64>(), + current as u64, + new as u64, + ); + if ok { + Ok(prev as $int_type) + } else { + Err(prev as $int_type) + } + } + } + + #[inline] + #[cfg_attr(all(debug_assertions, not(portable_atomic_no_track_caller)), track_caller)] + pub(crate) fn compare_exchange_weak( + &self, + current: $int_type, + new: $int_type, + success: Ordering, + failure: Ordering, + ) -> Result<$int_type, $int_type> { + self.compare_exchange(current, new, success, failure) + } + + #[inline] + pub(crate) fn fetch_add(&self, val: $int_type, _order: Ordering) -> $int_type { + // SAFETY: any data races are prevented by the kernel user helper or the lock + // and the raw pointer passed in is valid because we got it from a reference. + unsafe { atomic_add(self.v.get().cast::<u64>(), val as u64) as $int_type } + } + + #[inline] + pub(crate) fn fetch_sub(&self, val: $int_type, _order: Ordering) -> $int_type { + // SAFETY: any data races are prevented by the kernel user helper or the lock + // and the raw pointer passed in is valid because we got it from a reference. + unsafe { atomic_sub(self.v.get().cast::<u64>(), val as u64) as $int_type } + } + + #[inline] + pub(crate) fn fetch_and(&self, val: $int_type, _order: Ordering) -> $int_type { + // SAFETY: any data races are prevented by the kernel user helper or the lock + // and the raw pointer passed in is valid because we got it from a reference. + unsafe { atomic_and(self.v.get().cast::<u64>(), val as u64) as $int_type } + } + + #[inline] + pub(crate) fn fetch_nand(&self, val: $int_type, _order: Ordering) -> $int_type { + // SAFETY: any data races are prevented by the kernel user helper or the lock + // and the raw pointer passed in is valid because we got it from a reference. + unsafe { atomic_nand(self.v.get().cast::<u64>(), val as u64) as $int_type } + } + + #[inline] + pub(crate) fn fetch_or(&self, val: $int_type, _order: Ordering) -> $int_type { + // SAFETY: any data races are prevented by the kernel user helper or the lock + // and the raw pointer passed in is valid because we got it from a reference. + unsafe { atomic_or(self.v.get().cast::<u64>(), val as u64) as $int_type } + } + + #[inline] + pub(crate) fn fetch_xor(&self, val: $int_type, _order: Ordering) -> $int_type { + // SAFETY: any data races are prevented by the kernel user helper or the lock + // and the raw pointer passed in is valid because we got it from a reference. + unsafe { atomic_xor(self.v.get().cast::<u64>(), val as u64) as $int_type } + } + + #[inline] + pub(crate) fn fetch_max(&self, val: $int_type, _order: Ordering) -> $int_type { + // SAFETY: any data races are prevented by the kernel user helper or the lock + // and the raw pointer passed in is valid because we got it from a reference. + unsafe { $atomic_max(self.v.get().cast::<u64>(), val as u64) as $int_type } + } + + #[inline] + pub(crate) fn fetch_min(&self, val: $int_type, _order: Ordering) -> $int_type { + // SAFETY: any data races are prevented by the kernel user helper or the lock + // and the raw pointer passed in is valid because we got it from a reference. + unsafe { $atomic_min(self.v.get().cast::<u64>(), val as u64) as $int_type } + } + + #[inline] + pub(crate) fn fetch_not(&self, _order: Ordering) -> $int_type { + // SAFETY: any data races are prevented by the kernel user helper or the lock + // and the raw pointer passed in is valid because we got it from a reference. + unsafe { atomic_not(self.v.get().cast::<u64>()) as $int_type } + } + #[inline] + pub(crate) fn not(&self, order: Ordering) { + self.fetch_not(order); + } + + #[inline] + pub(crate) fn fetch_neg(&self, _order: Ordering) -> $int_type { + // SAFETY: any data races are prevented by the kernel user helper or the lock + // and the raw pointer passed in is valid because we got it from a reference. + unsafe { atomic_neg(self.v.get().cast::<u64>()) as $int_type } + } + #[inline] + pub(crate) fn neg(&self, order: Ordering) { + self.fetch_neg(order); + } + + #[inline] + pub(crate) const fn as_ptr(&self) -> *mut $int_type { + self.v.get() + } + } + }; +} + +atomic64!(AtomicI64, i64, atomic_max, atomic_min); +atomic64!(AtomicU64, u64, atomic_umax, atomic_umin); + +#[allow( + clippy::alloc_instead_of_core, + clippy::std_instead_of_alloc, + clippy::std_instead_of_core, + clippy::undocumented_unsafe_blocks, + clippy::wildcard_imports +)] +#[cfg(test)] +mod tests { + use super::*; + + #[test] + fn kuser_helper_version() { + let version = __kuser_helper_version(); + assert!(version >= 5, "{:?}", version); + assert_eq!(version, unsafe { (KUSER_HELPER_VERSION as *const i32).read() }); + } + + test_atomic_int!(i64); + test_atomic_int!(u64); + + // load/store/swap implementation is not affected by signedness, so it is + // enough to test only unsigned types. + stress_test!(u64); +} |