use core::intrinsics; use core::mem; // Kernel-provided user-mode helper functions: // https://www.kernel.org/doc/Documentation/arm/kernel_user_helpers.txt unsafe fn __kuser_cmpxchg(oldval: u32, newval: u32, ptr: *mut u32) -> bool { let f: extern "C" fn(u32, u32, *mut u32) -> u32 = mem::transmute(0xffff0fc0usize as *const ()); f(oldval, newval, ptr) == 0 } unsafe fn __kuser_memory_barrier() { let f: extern "C" fn() = mem::transmute(0xffff0fa0usize as *const ()); f(); } // Word-align a pointer fn align_ptr(ptr: *mut T) -> *mut u32 { // This gives us a mask of 0 when T == u32 since the pointer is already // supposed to be aligned, which avoids any masking in that case. let ptr_mask = 3 & (4 - mem::size_of::()); (ptr as usize & !ptr_mask) as *mut u32 } // Calculate the shift and mask of a value inside an aligned word fn get_shift_mask(ptr: *mut T) -> (u32, u32) { // Mask to get the low byte/halfword/word let mask = match mem::size_of::() { 1 => 0xff, 2 => 0xffff, 4 => 0xffffffff, _ => unreachable!(), }; // If we are on big-endian then we need to adjust the shift accordingly let endian_adjust = if cfg!(target_endian = "little") { 0 } else { 4 - mem::size_of::() as u32 }; // Shift to get the desired element in the word let ptr_mask = 3 & (4 - mem::size_of::()); let shift = ((ptr as usize & ptr_mask) as u32 ^ endian_adjust) * 8; (shift, mask) } // Extract a value from an aligned word fn extract_aligned(aligned: u32, shift: u32, mask: u32) -> u32 { (aligned >> shift) & mask } // Insert a value into an aligned word fn insert_aligned(aligned: u32, val: u32, shift: u32, mask: u32) -> u32 { (aligned & !(mask << shift)) | ((val & mask) << shift) } // Generic atomic read-modify-write operation unsafe fn atomic_rmw u32>(ptr: *mut T, f: F) -> u32 { let aligned_ptr = align_ptr(ptr); let (shift, mask) = get_shift_mask(ptr); loop { let curval_aligned = intrinsics::atomic_load_unordered(aligned_ptr); let curval = extract_aligned(curval_aligned, shift, mask); let newval = f(curval); let newval_aligned = insert_aligned(curval_aligned, newval, shift, mask); if __kuser_cmpxchg(curval_aligned, newval_aligned, aligned_ptr) { return curval; } } } // Generic atomic compare-exchange operation unsafe fn atomic_cmpxchg(ptr: *mut T, oldval: u32, newval: u32) -> u32 { let aligned_ptr = align_ptr(ptr); let (shift, mask) = get_shift_mask(ptr); loop { let curval_aligned = intrinsics::atomic_load_unordered(aligned_ptr); let curval = extract_aligned(curval_aligned, shift, mask); if curval != oldval { return curval; } let newval_aligned = insert_aligned(curval_aligned, newval, shift, mask); if __kuser_cmpxchg(curval_aligned, newval_aligned, aligned_ptr) { return oldval; } } } macro_rules! atomic_rmw { ($name:ident, $ty:ty, $op:expr) => { intrinsics! { pub unsafe extern "C" fn $name(ptr: *mut $ty, val: $ty) -> $ty { atomic_rmw(ptr, |x| $op(x as $ty, val) as u32) as $ty } } }; } macro_rules! atomic_cmpxchg { ($name:ident, $ty:ty) => { intrinsics! { pub unsafe extern "C" fn $name(ptr: *mut $ty, oldval: $ty, newval: $ty) -> $ty { atomic_cmpxchg(ptr, oldval as u32, newval as u32) as $ty } } }; } atomic_rmw!(__sync_fetch_and_add_1, u8, |a: u8, b: u8| a.wrapping_add(b)); atomic_rmw!(__sync_fetch_and_add_2, u16, |a: u16, b: u16| a .wrapping_add(b)); atomic_rmw!(__sync_fetch_and_add_4, u32, |a: u32, b: u32| a .wrapping_add(b)); atomic_rmw!(__sync_fetch_and_sub_1, u8, |a: u8, b: u8| a.wrapping_sub(b)); atomic_rmw!(__sync_fetch_and_sub_2, u16, |a: u16, b: u16| a .wrapping_sub(b)); atomic_rmw!(__sync_fetch_and_sub_4, u32, |a: u32, b: u32| a .wrapping_sub(b)); atomic_rmw!(__sync_fetch_and_and_1, u8, |a: u8, b: u8| a & b); atomic_rmw!(__sync_fetch_and_and_2, u16, |a: u16, b: u16| a & b); atomic_rmw!(__sync_fetch_and_and_4, u32, |a: u32, b: u32| a & b); atomic_rmw!(__sync_fetch_and_or_1, u8, |a: u8, b: u8| a | b); atomic_rmw!(__sync_fetch_and_or_2, u16, |a: u16, b: u16| a | b); atomic_rmw!(__sync_fetch_and_or_4, u32, |a: u32, b: u32| a | b); atomic_rmw!(__sync_fetch_and_xor_1, u8, |a: u8, b: u8| a ^ b); atomic_rmw!(__sync_fetch_and_xor_2, u16, |a: u16, b: u16| a ^ b); atomic_rmw!(__sync_fetch_and_xor_4, u32, |a: u32, b: u32| a ^ b); atomic_rmw!(__sync_fetch_and_nand_1, u8, |a: u8, b: u8| !(a & b)); atomic_rmw!(__sync_fetch_and_nand_2, u16, |a: u16, b: u16| !(a & b)); atomic_rmw!(__sync_fetch_and_nand_4, u32, |a: u32, b: u32| !(a & b)); atomic_rmw!(__sync_fetch_and_max_1, i8, |a: i8, b: i8| if a > b { a } else { b }); atomic_rmw!(__sync_fetch_and_max_2, i16, |a: i16, b: i16| if a > b { a } else { b }); atomic_rmw!(__sync_fetch_and_max_4, i32, |a: i32, b: i32| if a > b { a } else { b }); atomic_rmw!(__sync_fetch_and_umax_1, u8, |a: u8, b: u8| if a > b { a } else { b }); atomic_rmw!(__sync_fetch_and_umax_2, u16, |a: u16, b: u16| if a > b { a } else { b }); atomic_rmw!(__sync_fetch_and_umax_4, u32, |a: u32, b: u32| if a > b { a } else { b }); atomic_rmw!(__sync_fetch_and_min_1, i8, |a: i8, b: i8| if a < b { a } else { b }); atomic_rmw!(__sync_fetch_and_min_2, i16, |a: i16, b: i16| if a < b { a } else { b }); atomic_rmw!(__sync_fetch_and_min_4, i32, |a: i32, b: i32| if a < b { a } else { b }); atomic_rmw!(__sync_fetch_and_umin_1, u8, |a: u8, b: u8| if a < b { a } else { b }); atomic_rmw!(__sync_fetch_and_umin_2, u16, |a: u16, b: u16| if a < b { a } else { b }); atomic_rmw!(__sync_fetch_and_umin_4, u32, |a: u32, b: u32| if a < b { a } else { b }); atomic_rmw!(__sync_lock_test_and_set_1, u8, |_: u8, b: u8| b); atomic_rmw!(__sync_lock_test_and_set_2, u16, |_: u16, b: u16| b); atomic_rmw!(__sync_lock_test_and_set_4, u32, |_: u32, b: u32| b); atomic_cmpxchg!(__sync_val_compare_and_swap_1, u8); atomic_cmpxchg!(__sync_val_compare_and_swap_2, u16); atomic_cmpxchg!(__sync_val_compare_and_swap_4, u32); intrinsics! { pub unsafe extern "C" fn __sync_synchronize() { __kuser_memory_barrier(); } }