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|
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<T>(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::<T>());
(ptr as usize & !ptr_mask) as *mut u32
}
// Calculate the shift and mask of a value inside an aligned word
fn get_shift_mask<T>(ptr: *mut T) -> (u32, u32) {
// Mask to get the low byte/halfword/word
let mask = match mem::size_of::<T>() {
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::<T>() as u32
};
// Shift to get the desired element in the word
let ptr_mask = 3 & (4 - mem::size_of::<T>());
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<T, F: Fn(u32) -> 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<T>(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();
}
}
|
