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global.rs
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global.rs
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use super::*;
use crate::util::constants::{BYTES_IN_PAGE, BYTES_IN_WORD, LOG_BITS_IN_BYTE};
use crate::util::conversions::raw_align_up;
use crate::util::heap::layout::vm_layout::BYTES_IN_CHUNK;
use crate::util::memory;
use crate::util::metadata::metadata_val_traits::*;
#[cfg(feature = "vo_bit")]
use crate::util::metadata::vo_bit::VO_BIT_SIDE_METADATA_SPEC;
use crate::util::Address;
use num_traits::FromPrimitive;
use std::fmt;
use std::io::Result;
use std::sync::atomic::{AtomicU8, Ordering};
/// This struct stores the specification of a side metadata bit-set.
/// It is used as an input to the (inline) functions provided by the side metadata module.
///
/// Each plan or policy which uses a metadata bit-set, needs to create an instance of this struct.
///
/// For performance reasons, objects of this struct should be constants.
#[derive(Clone, Copy, PartialEq, Eq, Hash)]
pub struct SideMetadataSpec {
/// The name for this side metadata.
pub name: &'static str,
/// Is this side metadata global? Local metadata is used by certain spaces,
/// while global metadata is used by all the spaces.
pub is_global: bool,
/// The offset for this side metadata.
pub offset: SideMetadataOffset,
/// Number of bits needed per region. E.g. 0 = 1 bit, 1 = 2 bit.
pub log_num_of_bits: usize,
/// Number of bytes of the region. E.g. 3 = 8 bytes, 12 = 4096 bytes (page).
pub log_bytes_in_region: usize,
}
impl SideMetadataSpec {
/// Is this spec using contiguous side metadata? If not, it uses chunked side metadata.
pub const fn uses_contiguous_side_metadata(&self) -> bool {
self.is_global || cfg!(target_pointer_width = "64")
}
/// Is offset for this spec Address?
pub const fn is_absolute_offset(&self) -> bool {
self.uses_contiguous_side_metadata()
}
/// If offset for this spec relative? (chunked side metadata for local specs in 32 bits)
pub const fn is_rel_offset(&self) -> bool {
!self.is_absolute_offset()
}
/// Get the absolute offset for the spec.
pub const fn get_absolute_offset(&self) -> Address {
debug_assert!(self.is_absolute_offset());
unsafe { self.offset.addr }
}
/// Get the relative offset for the spec.
pub const fn get_rel_offset(&self) -> usize {
debug_assert!(self.is_rel_offset());
unsafe { self.offset.rel_offset }
}
/// Return the upperbound offset for the side metadata. The next side metadata should be laid out at this offset.
#[cfg(target_pointer_width = "64")]
pub const fn upper_bound_offset(&self) -> SideMetadataOffset {
debug_assert!(self.is_absolute_offset());
SideMetadataOffset {
addr: unsafe { self.offset.addr }
.add(crate::util::metadata::side_metadata::metadata_address_range_size(self)),
}
}
/// Return the upperbound offset for the side metadata. The next side metadata should be laid out at this offset.
#[cfg(target_pointer_width = "32")]
pub const fn upper_bound_offset(&self) -> SideMetadataOffset {
if self.is_absolute_offset() {
SideMetadataOffset {
addr: unsafe { self.offset.addr }
.add(crate::util::metadata::side_metadata::metadata_address_range_size(self)),
}
} else {
SideMetadataOffset {
rel_offset: unsafe { self.offset.rel_offset }
+ crate::util::metadata::side_metadata::metadata_bytes_per_chunk(
self.log_bytes_in_region,
self.log_num_of_bits,
),
}
}
}
/// The upper bound address for metadata address computed for this global spec. The computed metadata address
/// should never be larger than this address. Otherwise, we are accessing the metadata that is laid out
/// after this spec. This spec must be a contiguous side metadata spec (which uses address
/// as offset).
pub const fn upper_bound_address_for_contiguous(&self) -> Address {
debug_assert!(self.is_absolute_offset());
unsafe { self.upper_bound_offset().addr }
}
/// The upper bound address for metadata address computed for this global spec. The computed metadata address
/// should never be larger than this address. Otherwise, we are accessing the metadata that is laid out
/// after this spec. This spec must be a chunked side metadata spec (which uses relative offset). Only 32 bit local
/// side metadata uses chunked metadata.
#[cfg(target_pointer_width = "32")]
pub const fn upper_bound_address_for_chunked(&self, data_addr: Address) -> Address {
debug_assert!(self.is_rel_offset());
address_to_meta_chunk_addr(data_addr).add(unsafe { self.upper_bound_offset().rel_offset })
}
/// Used only for debugging.
/// This panics if the required metadata is not mapped
#[cfg(debug_assertions)]
pub(crate) fn assert_metadata_mapped(&self, data_addr: Address) {
let meta_start = address_to_meta_address(self, data_addr).align_down(BYTES_IN_PAGE);
trace!(
"ensure_metadata_is_mapped({}).meta_start({})",
data_addr,
meta_start
);
memory::panic_if_unmapped(meta_start, BYTES_IN_PAGE);
}
/// Used only for debugging.
/// * Assert if the given MetadataValue type matches the spec.
/// * Assert if the provided value is valid in the spec.
#[cfg(debug_assertions)]
fn assert_value_type<T: MetadataValue>(&self, val: Option<T>) {
let log_b = self.log_num_of_bits;
match log_b {
_ if log_b < 3 => {
assert_eq!(T::LOG2, 3);
if let Some(v) = val {
assert!(
v.to_u8().unwrap() < (1 << (1 << log_b)),
"Input value {:?} is invalid for the spec {:?}",
v,
self
);
}
}
3..=6 => assert_eq!(T::LOG2, log_b as u32),
_ => unreachable!("side metadata > {}-bits is not supported", 1 << log_b),
}
}
/// Check with the mmapper to see if side metadata is mapped for the spec for the data address.
pub(crate) fn is_mapped(&self, data_addr: Address) -> bool {
use crate::MMAPPER;
let meta_addr = address_to_meta_address(self, data_addr);
MMAPPER.is_mapped_address(meta_addr)
}
/// This method is used for iterating side metadata for a data address range. As we cannot guarantee
/// that the data address range can be mapped to whole metadata bytes, we have to deal with cases that
/// we need to mask and zero certain bits in a metadata byte. The end address and the end bit are exclusive.
/// The end bit for update_bits could be 8, so overflowing needs to be taken care of.
///
/// Returns true if we iterate through every bits in the range. Return false if we abort iteration early.
///
/// Arguments:
/// * `forwards`: If true, we iterate forwards (from start/low address to end/high address). Otherwise,
/// we iterate backwards (from end/high address to start/low address).
/// * `visit_bytes`/`visit_bits`: The closures returns whether the itertion is early terminated.
pub(super) fn iterate_meta_bits(
meta_start_addr: Address,
meta_start_bit: u8,
meta_end_addr: Address,
meta_end_bit: u8,
forwards: bool,
visit_bytes: &impl Fn(Address, Address) -> bool,
visit_bits: &impl Fn(Address, u8, u8) -> bool,
) -> bool {
trace!(
"iterate_meta_bits: {} {}, {} {}",
meta_start_addr,
meta_start_bit,
meta_end_addr,
meta_end_bit
);
// Start/end is the same, we don't need to do anything.
if meta_start_addr == meta_end_addr && meta_start_bit == meta_end_bit {
return false;
}
// zeroing bytes
if meta_start_bit == 0 && meta_end_bit == 0 {
return visit_bytes(meta_start_addr, meta_end_addr);
}
if meta_start_addr == meta_end_addr {
// Update bits in the same byte between start and end bit
visit_bits(meta_start_addr, meta_start_bit, meta_end_bit)
} else if meta_start_addr + 1usize == meta_end_addr && meta_end_bit == 0 {
// Update bits in the same byte after the start bit (between start bit and 8)
visit_bits(meta_start_addr, meta_start_bit, 8)
} else {
// Update each segments.
// Clippy wants to move this if block up as a else-if block. But I think this is logically more clear. So disable the clippy warning.
#[allow(clippy::collapsible_else_if)]
if forwards {
// update bits in the first byte
if Self::iterate_meta_bits(
meta_start_addr,
meta_start_bit,
meta_start_addr + 1usize,
0,
forwards,
visit_bytes,
visit_bits,
) {
return true;
}
// update bytes in the middle
if Self::iterate_meta_bits(
meta_start_addr + 1usize,
0,
meta_end_addr,
0,
forwards,
visit_bytes,
visit_bits,
) {
return true;
}
// update bits in the last byte
if Self::iterate_meta_bits(
meta_end_addr,
0,
meta_end_addr,
meta_end_bit,
forwards,
visit_bytes,
visit_bits,
) {
return true;
}
false
} else {
// update bits in the last byte
if Self::iterate_meta_bits(
meta_end_addr,
0,
meta_end_addr,
meta_end_bit,
forwards,
visit_bytes,
visit_bits,
) {
return true;
}
// update bytes in the middle
if Self::iterate_meta_bits(
meta_start_addr + 1usize,
0,
meta_end_addr,
0,
forwards,
visit_bytes,
visit_bits,
) {
return true;
}
// update bits in the first byte
if Self::iterate_meta_bits(
meta_start_addr,
meta_start_bit,
meta_start_addr + 1usize,
0,
forwards,
visit_bytes,
visit_bits,
) {
return true;
}
false
}
}
}
/// This method is used for bulk zeroing side metadata for a data address range.
pub(super) fn zero_meta_bits(
meta_start_addr: Address,
meta_start_bit: u8,
meta_end_addr: Address,
meta_end_bit: u8,
) {
let zero_bytes = |start: Address, end: Address| -> bool {
memory::zero(start, end - start);
false
};
let zero_bits = |addr: Address, start_bit: u8, end_bit: u8| -> bool {
// we are zeroing selected bits in one byte
let mask: u8 =
u8::MAX.checked_shl(end_bit.into()).unwrap_or(0) | !(u8::MAX << start_bit); // Get a mask that the bits we need to zero are set to zero, and the other bits are 1.
unsafe { addr.as_ref::<AtomicU8>() }.fetch_and(mask, Ordering::SeqCst);
false
};
Self::iterate_meta_bits(
meta_start_addr,
meta_start_bit,
meta_end_addr,
meta_end_bit,
true,
&zero_bytes,
&zero_bits,
);
}
/// This method is used for bulk setting side metadata for a data address range.
pub(super) fn set_meta_bits(
meta_start_addr: Address,
meta_start_bit: u8,
meta_end_addr: Address,
meta_end_bit: u8,
) {
let set_bytes = |start: Address, end: Address| -> bool {
memory::set(start, 0xff, end - start);
false
};
let set_bits = |addr: Address, start_bit: u8, end_bit: u8| -> bool {
// we are setting selected bits in one byte
let mask: u8 =
!(u8::MAX.checked_shl(end_bit.into()).unwrap_or(0)) & (u8::MAX << start_bit); // Get a mask that the bits we need to set are 1, and the other bits are 0.
unsafe { addr.as_ref::<AtomicU8>() }.fetch_or(mask, Ordering::SeqCst);
false
};
Self::iterate_meta_bits(
meta_start_addr,
meta_start_bit,
meta_end_addr,
meta_end_bit,
true,
&set_bytes,
&set_bits,
);
}
/// This method does bulk update for the given data range. It calculates the metadata bits for the given data range,
/// and invoke the given method to update the metadata bits.
pub(super) fn bulk_update_metadata(
&self,
start: Address,
size: usize,
update_meta_bits: &impl Fn(Address, u8, Address, u8),
) {
// Update bits for a contiguous side metadata spec. We can simply calculate the data end address, and
// calculate the metadata address for the data end.
let update_contiguous = |data_start: Address, data_bytes: usize| {
if data_bytes == 0 {
return;
}
let meta_start = address_to_meta_address(self, data_start);
let meta_start_shift = meta_byte_lshift(self, data_start);
let meta_end = address_to_meta_address(self, data_start + data_bytes);
let meta_end_shift = meta_byte_lshift(self, data_start + data_bytes);
update_meta_bits(meta_start, meta_start_shift, meta_end, meta_end_shift);
};
// Update bits for a discontiguous side metadata spec (chunked metadata). The side metadata for different
// chunks are stored in discontiguous memory. For example, Chunk #2 follows Chunk #1, but the side metadata
// for Chunk #2 does not immediately follow the side metadata for Chunk #1. So when we bulk update metadata for Chunk #1,
// we cannot update up to the metadata address for the Chunk #2 start. Otherwise it may modify unrelated metadata
// between the two chunks' metadata.
// Instead, we compute how many bytes/bits we need to update.
// The data for which the metadata will be updates has to be in the same chunk.
#[cfg(target_pointer_width = "32")]
let update_discontiguous = |data_start: Address, data_bytes: usize| {
use crate::util::constants::BITS_IN_BYTE;
if data_bytes == 0 {
return;
}
debug_assert_eq!(
data_start.align_down(BYTES_IN_CHUNK),
(data_start + data_bytes - 1).align_down(BYTES_IN_CHUNK),
"The data to be zeroed in discontiguous specs needs to be in the same chunk"
);
let meta_start = address_to_meta_address(self, data_start);
let meta_start_shift = meta_byte_lshift(self, data_start);
// How many bits we need to zero for data_bytes
let meta_total_bits = (data_bytes >> self.log_bytes_in_region) << self.log_num_of_bits;
let meta_delta_bytes = meta_total_bits >> LOG_BITS_IN_BYTE;
let meta_delta_bits: u8 = (meta_total_bits % BITS_IN_BYTE) as u8;
// Calculate the end byte/addr and end bit
let (meta_end, meta_end_shift) = {
let mut end_addr = meta_start + meta_delta_bytes;
let mut end_bit = meta_start_shift + meta_delta_bits;
if end_bit >= BITS_IN_BYTE as u8 {
end_bit -= BITS_IN_BYTE as u8;
end_addr += 1usize;
}
(end_addr, end_bit)
};
update_meta_bits(meta_start, meta_start_shift, meta_end, meta_end_shift);
};
if cfg!(target_pointer_width = "64") || self.is_global {
update_contiguous(start, size);
}
#[cfg(target_pointer_width = "32")]
if !self.is_global {
// per chunk policy-specific metadata for 32-bits targets
let chunk_num = ((start + size).align_down(BYTES_IN_CHUNK)
- start.align_down(BYTES_IN_CHUNK))
/ BYTES_IN_CHUNK;
if chunk_num == 0 {
update_discontiguous(start, size);
} else {
let second_data_chunk = start.align_up(BYTES_IN_CHUNK);
// bzero the first sub-chunk
update_discontiguous(start, second_data_chunk - start);
let last_data_chunk = (start + size).align_down(BYTES_IN_CHUNK);
// bzero the last sub-chunk
update_discontiguous(last_data_chunk, start + size - last_data_chunk);
let mut next_data_chunk = second_data_chunk;
// bzero all chunks in the middle
while next_data_chunk != last_data_chunk {
update_discontiguous(next_data_chunk, BYTES_IN_CHUNK);
next_data_chunk += BYTES_IN_CHUNK;
}
}
}
}
/// Bulk-zero a specific metadata for a memory region. Note that this method is more sophisiticated than a simple memset, especially in the following
/// cases:
/// * the metadata for the range includes partial bytes (a few bits in the same byte).
/// * for 32 bits local side metadata, the side metadata is stored in discontiguous chunks, we will have to bulk zero for each chunk's side metadata.
///
/// # Arguments
///
/// * `start`: The starting address of a memory region. The side metadata starting from this data address will be zeroed.
/// * `size`: The size of the memory region.
pub fn bzero_metadata(&self, start: Address, size: usize) {
#[cfg(feature = "extreme_assertions")]
let _lock = sanity::SANITY_LOCK.lock().unwrap();
#[cfg(feature = "extreme_assertions")]
sanity::verify_bzero(self, start, size);
self.bulk_update_metadata(start, size, &Self::zero_meta_bits)
}
/// Bulk set a specific metadata for a memory region. Note that this method is more sophisiticated than a simple memset, especially in the following
/// cases:
/// * the metadata for the range includes partial bytes (a few bits in the same byte).
/// * for 32 bits local side metadata, the side metadata is stored in discontiguous chunks, we will have to bulk set for each chunk's side metadata.
///
/// # Arguments
///
/// * `start`: The starting address of a memory region. The side metadata starting from this data address will be set to all 1s in the bits.
/// * `size`: The size of the memory region.
pub fn bset_metadata(&self, start: Address, size: usize) {
#[cfg(feature = "extreme_assertions")]
let _lock = sanity::SANITY_LOCK.lock().unwrap();
#[cfg(feature = "extreme_assertions")]
sanity::verify_bset(self, start, size);
self.bulk_update_metadata(start, size, &Self::set_meta_bits)
}
/// Bulk copy the `other` side metadata for a memory region to this side metadata.
///
/// This function only works for contiguous metadata.
/// Curently all global metadata are contiguous.
/// It also requires the other metadata to have the same number of bits per region
/// and the same region size.
///
/// # Arguments
///
/// * `start`: The starting address of a memory region.
/// * `size`: The size of the memory region.
/// * `other`: The other metadata to copy from.
pub fn bcopy_metadata_contiguous(&self, start: Address, size: usize, other: &SideMetadataSpec) {
#[cfg(feature = "extreme_assertions")]
let _lock = sanity::SANITY_LOCK.lock().unwrap();
#[cfg(feature = "extreme_assertions")]
sanity::verify_bcopy(self, start, size, other);
debug_assert_eq!(other.log_bytes_in_region, self.log_bytes_in_region);
debug_assert_eq!(other.log_num_of_bits, self.log_num_of_bits);
let dst_meta_start_addr = address_to_meta_address(self, start);
let dst_meta_start_bit = meta_byte_lshift(self, start);
let dst_meta_end_addr = address_to_meta_address(self, start + size);
let dst_meta_end_bit = meta_byte_lshift(self, start + size);
let src_meta_start_addr = address_to_meta_address(other, start);
let src_meta_start_bit = meta_byte_lshift(other, start);
debug_assert_eq!(dst_meta_start_bit, src_meta_start_bit);
let copy_bytes = |dst_start: Address, dst_end: Address| -> bool {
unsafe {
let byte_offset = dst_start - dst_meta_start_addr;
let src_start = src_meta_start_addr + byte_offset;
let size = dst_end - dst_start;
std::ptr::copy::<u8>(src_start.to_ptr(), dst_start.to_mut_ptr(), size);
false
}
};
let copy_bits = |dst: Address, start_bit: u8, end_bit: u8| -> bool {
let byte_offset = dst - dst_meta_start_addr;
let src = src_meta_start_addr + byte_offset;
// we are setting selected bits in one byte
let mask: u8 =
!(u8::MAX.checked_shl(end_bit.into()).unwrap_or(0)) & (u8::MAX << start_bit); // Get a mask that the bits we need to set are 1, and the other bits are 0.
let old_src = unsafe { src.as_ref::<AtomicU8>() }.load(Ordering::Relaxed);
let old_dst = unsafe { dst.as_ref::<AtomicU8>() }.load(Ordering::Relaxed);
let new = (old_src & mask) | (old_dst & !mask);
unsafe { dst.as_ref::<AtomicU8>() }.store(new, Ordering::Relaxed);
false
};
Self::iterate_meta_bits(
dst_meta_start_addr,
dst_meta_start_bit,
dst_meta_end_addr,
dst_meta_end_bit,
true,
©_bytes,
©_bits,
);
}
/// This is a wrapper method for implementing side metadata access. It does nothing other than
/// calling the access function with no overhead, but in debug builds,
/// it includes multiple checks to make sure the access is sane.
/// * check whether the given value type matches the number of bits for the side metadata.
/// * check if the side metadata memory is mapped.
/// * check if the side metadata content is correct based on a sanity map (only for extreme assertions).
#[allow(unused_variables)] // data_addr/input is not used in release build
fn side_metadata_access<
const CHECK_VALUE: bool,
T: MetadataValue,
R: Copy,
F: FnOnce() -> R,
V: FnOnce(R),
>(
&self,
data_addr: Address,
input: Option<T>,
access_func: F,
verify_func: V,
) -> R {
// With extreme assertions, we maintain a sanity table for each side metadata access. For whatever we store in
// side metadata, we store in the sanity table. So we can use that table to check if its results are conssitent
// with the actual side metadata.
// To achieve this, we need to apply a lock when we access side metadata. This will hide some concurrency bugs,
// but makes it possible for us to assert our side metadata implementation is correct.
#[cfg(feature = "extreme_assertions")]
let _lock = sanity::SANITY_LOCK.lock().unwrap();
// A few checks
#[cfg(debug_assertions)]
{
if CHECK_VALUE {
self.assert_value_type::<T>(input);
}
#[cfg(feature = "extreme_assertions")]
self.assert_metadata_mapped(data_addr);
}
// Actual access to the side metadata
let ret = access_func();
// Verifying the side metadata: checks the result with the sanity table, or store some results to the sanity table
if CHECK_VALUE {
verify_func(ret);
}
ret
}
/// Non-atomic load of metadata.
///
/// # Safety
///
/// This is unsafe because:
///
/// 1. Concurrent access to this operation is undefined behaviour.
/// 2. Interleaving Non-atomic and atomic operations is undefined behaviour.
pub unsafe fn load<T: MetadataValue>(&self, data_addr: Address) -> T {
self.side_metadata_access::<true, T, _, _, _>(
data_addr,
None,
|| {
let meta_addr = address_to_meta_address(self, data_addr);
let bits_num_log = self.log_num_of_bits;
if bits_num_log < 3 {
let lshift = meta_byte_lshift(self, data_addr);
let mask = meta_byte_mask(self) << lshift;
let byte_val = meta_addr.load::<u8>();
FromPrimitive::from_u8((byte_val & mask) >> lshift).unwrap()
} else {
meta_addr.load::<T>()
}
},
|_v| {
#[cfg(feature = "extreme_assertions")]
sanity::verify_load(self, data_addr, _v);
},
)
}
/// Non-atomic store of metadata.
///
/// # Safety
///
/// This is unsafe because:
///
/// 1. Concurrent access to this operation is undefined behaviour.
/// 2. Interleaving Non-atomic and atomic operations is undefined behaviour.
pub unsafe fn store<T: MetadataValue>(&self, data_addr: Address, metadata: T) {
self.side_metadata_access::<true, T, _, _, _>(
data_addr,
Some(metadata),
|| {
let meta_addr = address_to_meta_address(self, data_addr);
let bits_num_log = self.log_num_of_bits;
if bits_num_log < 3 {
let lshift = meta_byte_lshift(self, data_addr);
let mask = meta_byte_mask(self) << lshift;
let old_val = meta_addr.load::<u8>();
let new_val = (old_val & !mask) | (metadata.to_u8().unwrap() << lshift);
meta_addr.store::<u8>(new_val);
} else {
meta_addr.store::<T>(metadata);
}
},
|_| {
#[cfg(feature = "extreme_assertions")]
sanity::verify_store(self, data_addr, metadata);
},
)
}
/// Loads a value from the side metadata for the given address.
/// This method has similar semantics to `store` in Rust atomics.
pub fn load_atomic<T: MetadataValue>(&self, data_addr: Address, order: Ordering) -> T {
self.side_metadata_access::<true, T, _, _, _>(
data_addr,
None,
|| {
let meta_addr = address_to_meta_address(self, data_addr);
let bits_num_log = self.log_num_of_bits;
if bits_num_log < 3 {
let lshift = meta_byte_lshift(self, data_addr);
let mask = meta_byte_mask(self) << lshift;
let byte_val = unsafe { meta_addr.atomic_load::<AtomicU8>(order) };
FromPrimitive::from_u8((byte_val & mask) >> lshift).unwrap()
} else {
unsafe { T::load_atomic(meta_addr, order) }
}
},
|_v| {
#[cfg(feature = "extreme_assertions")]
sanity::verify_load(self, data_addr, _v);
},
)
}
/// Store the given value to the side metadata for the given address.
/// This method has similar semantics to `store` in Rust atomics.
pub fn store_atomic<T: MetadataValue>(&self, data_addr: Address, metadata: T, order: Ordering) {
self.side_metadata_access::<true, T, _, _, _>(
data_addr,
Some(metadata),
|| {
let meta_addr = address_to_meta_address(self, data_addr);
let bits_num_log = self.log_num_of_bits;
if bits_num_log < 3 {
let lshift = meta_byte_lshift(self, data_addr);
let mask = meta_byte_mask(self) << lshift;
let metadata_u8 = metadata.to_u8().unwrap();
let _ = unsafe {
<u8 as MetadataValue>::fetch_update(meta_addr, order, order, |v: u8| {
Some((v & !mask) | (metadata_u8 << lshift))
})
};
} else {
unsafe {
T::store_atomic(meta_addr, metadata, order);
}
}
},
|_| {
#[cfg(feature = "extreme_assertions")]
sanity::verify_store(self, data_addr, metadata);
},
)
}
/// Non-atomically store zero to the side metadata for the given address.
/// This method mainly facilitates clearing multiple metadata specs for the same address in a loop.
///
/// # Safety
///
/// This is unsafe because:
///
/// 1. Concurrent access to this operation is undefined behaviour.
/// 2. Interleaving Non-atomic and atomic operations is undefined behaviour.
pub unsafe fn set_zero(&self, data_addr: Address) {
use num_traits::Zero;
match self.log_num_of_bits {
0..=3 => self.store(data_addr, u8::zero()),
4 => self.store(data_addr, u16::zero()),
5 => self.store(data_addr, u32::zero()),
6 => self.store(data_addr, u64::zero()),
_ => unreachable!(),
}
}
/// Atomiccally store zero to the side metadata for the given address.
/// This method mainly facilitates clearing multiple metadata specs for the same address in a loop.
pub fn set_zero_atomic(&self, data_addr: Address, order: Ordering) {
use num_traits::Zero;
match self.log_num_of_bits {
0..=3 => self.store_atomic(data_addr, u8::zero(), order),
4 => self.store_atomic(data_addr, u16::zero(), order),
5 => self.store_atomic(data_addr, u32::zero(), order),
6 => self.store_atomic(data_addr, u64::zero(), order),
_ => unreachable!(),
}
}
/// Atomically store one to the side metadata for the data address with the _possible_ side effect of corrupting
/// and setting the entire byte in the side metadata to 0xff. This can only be used for side metadata smaller
/// than a byte.
/// This means it does not only set the side metadata for the data address, and it may also have a side effect of
/// corrupting and setting the side metadata for the adjacent data addresses. This method is only intended to be
/// used as an optimization to skip masking and setting bits in some scenarios where setting adjancent bits to 1 is benign.
///
/// # Safety
/// This method _may_ corrupt and set adjacent bits in the side metadata as a side effect. The user must
/// make sure that this behavior is correct and must not rely on the side effect of this method to set bits.
pub unsafe fn set_raw_byte_atomic(&self, data_addr: Address, order: Ordering) {
debug_assert!(self.log_num_of_bits < 3);
cfg_if::cfg_if! {
if #[cfg(feature = "extreme_assertions")] {
// For extreme assertions, we only set 1 to the given address.
self.store_atomic::<u8>(data_addr, 1, order)
} else {
self.side_metadata_access::<false, u8, _, _, _>(
data_addr,
Some(1u8),
|| {
let meta_addr = address_to_meta_address(self, data_addr);
u8::store_atomic(meta_addr, 0xffu8, order);
},
|_| {}
)
}
}
}
/// Load the raw byte in the side metadata byte that is mapped to the data address.
///
/// # Safety
/// This is unsafe because:
///
/// 1. Concurrent access to this operation is undefined behaviour.
/// 2. Interleaving Non-atomic and atomic operations is undefined behaviour.
pub unsafe fn load_raw_byte(&self, data_addr: Address) -> u8 {
debug_assert!(self.log_num_of_bits < 3);
self.side_metadata_access::<false, u8, _, _, _>(
data_addr,
None,
|| {
let meta_addr = address_to_meta_address(self, data_addr);
meta_addr.load::<u8>()
},
|_| {},
)
}
/// Load the raw word that includes the side metadata byte mapped to the data address.
///
/// # Safety
/// This is unsafe because:
///
/// 1. Concurrent access to this operation is undefined behaviour.
/// 2. Interleaving Non-atomic and atomic operations is undefined behaviour.
pub unsafe fn load_raw_word(&self, data_addr: Address) -> usize {
use crate::util::constants::*;
debug_assert!(self.log_num_of_bits < (LOG_BITS_IN_BYTE + LOG_BYTES_IN_ADDRESS) as usize);
self.side_metadata_access::<false, usize, _, _, _>(
data_addr,
None,
|| {
let meta_addr = address_to_meta_address(self, data_addr);
let aligned_meta_addr = meta_addr.align_down(BYTES_IN_ADDRESS);
aligned_meta_addr.load::<usize>()
},
|_| {},
)
}
/// Stores the new value into the side metadata for the gien address if the current value is the same as the old value.
/// This method has similar semantics to `compare_exchange` in Rust atomics.
/// The return value is a result indicating whether the new value was written and containing the previous value.
/// On success this value is guaranteed to be equal to current.
pub fn compare_exchange_atomic<T: MetadataValue>(
&self,
data_addr: Address,
old_metadata: T,
new_metadata: T,
success_order: Ordering,
failure_order: Ordering,
) -> std::result::Result<T, T> {
self.side_metadata_access::<true, T, _, _, _>(
data_addr,
Some(new_metadata),
|| {
let meta_addr = address_to_meta_address(self, data_addr);
let bits_num_log = self.log_num_of_bits;
if bits_num_log < 3 {
let lshift = meta_byte_lshift(self, data_addr);
let mask = meta_byte_mask(self) << lshift;
let real_old_byte = unsafe { meta_addr.atomic_load::<AtomicU8>(success_order) };
let expected_old_byte =
(real_old_byte & !mask) | ((old_metadata.to_u8().unwrap()) << lshift);
let expected_new_byte =
(expected_old_byte & !mask) | ((new_metadata.to_u8().unwrap()) << lshift);
unsafe {
meta_addr.compare_exchange::<AtomicU8>(
expected_old_byte,
expected_new_byte,
success_order,
failure_order,
)
}
.map(|x| FromPrimitive::from_u8((x & mask) >> lshift).unwrap())
.map_err(|x| FromPrimitive::from_u8((x & mask) >> lshift).unwrap())
} else {
unsafe {
T::compare_exchange(
meta_addr,
old_metadata,
new_metadata,
success_order,
failure_order,
)
}
}
},
|_res| {
#[cfg(feature = "extreme_assertions")]
if _res.is_ok() {
sanity::verify_store(self, data_addr, new_metadata);
}
},
)
}
/// This is used to implement fetch_add/sub for bits.
/// For fetch_and/or, we don't necessarily need this method. We could directly do fetch_and/or on the u8.
fn fetch_ops_on_bits<F: Fn(u8) -> u8>(
&self,
data_addr: Address,
meta_addr: Address,
set_order: Ordering,
fetch_order: Ordering,
update: F,
) -> u8 {
let lshift = meta_byte_lshift(self, data_addr);
let mask = meta_byte_mask(self) << lshift;
let old_raw_byte = unsafe {
<u8 as MetadataValue>::fetch_update(
meta_addr,
set_order,
fetch_order,
|raw_byte: u8| {
let old_val = (raw_byte & mask) >> lshift;
let new_val = update(old_val);
let new_raw_byte = (raw_byte & !mask) | ((new_val << lshift) & mask);
Some(new_raw_byte)
},
)
}
.unwrap();
(old_raw_byte & mask) >> lshift
}
/// Adds the value to the current value for this side metadata for the given address.
/// This method has similar semantics to `fetch_add` in Rust atomics.
/// Returns the previous value.
pub fn fetch_add_atomic<T: MetadataValue>(
&self,
data_addr: Address,
val: T,
order: Ordering,
) -> T {
self.side_metadata_access::<true, T, _, _, _>(
data_addr,
Some(val),
|| {
let meta_addr = address_to_meta_address(self, data_addr);
let bits_num_log = self.log_num_of_bits;
if bits_num_log < 3 {
FromPrimitive::from_u8(self.fetch_ops_on_bits(
data_addr,
meta_addr,
order,
order,
|x: u8| x.wrapping_add(val.to_u8().unwrap()),
))
.unwrap()
} else {
unsafe { T::fetch_add(meta_addr, val, order) }
}
},
|_old_val| {
#[cfg(feature = "extreme_assertions")]
sanity::verify_update::<T>(self, data_addr, _old_val, _old_val.wrapping_add(&val))
},
)
}
/// Subtracts the value from the current value for this side metadata for the given address.
/// This method has similar semantics to `fetch_sub` in Rust atomics.
/// Returns the previous value.
pub fn fetch_sub_atomic<T: MetadataValue>(
&self,
data_addr: Address,
val: T,
order: Ordering,
) -> T {
self.side_metadata_access::<true, T, _, _, _>(
data_addr,
Some(val),
|| {
let meta_addr = address_to_meta_address(self, data_addr);
if self.log_num_of_bits < 3 {
FromPrimitive::from_u8(self.fetch_ops_on_bits(
data_addr,
meta_addr,
order,
order,
|x: u8| x.wrapping_sub(val.to_u8().unwrap()),
))
.unwrap()
} else {
unsafe { T::fetch_sub(meta_addr, val, order) }
}
},
|_old_val| {
#[cfg(feature = "extreme_assertions")]
sanity::verify_update::<T>(self, data_addr, _old_val, _old_val.wrapping_sub(&val))
},
)
}
/// Bitwise 'and' the value with the current value for this side metadata for the given address.
/// This method has similar semantics to `fetch_and` in Rust atomics.
/// Returns the previous value.
pub fn fetch_and_atomic<T: MetadataValue>(
&self,
data_addr: Address,
val: T,
order: Ordering,
) -> T {
self.side_metadata_access::<true, T, _, _, _>(
data_addr,
Some(val),
|| {
let meta_addr = address_to_meta_address(self, data_addr);
if self.log_num_of_bits < 3 {
let lshift = meta_byte_lshift(self, data_addr);
let mask = meta_byte_mask(self) << lshift;
// We do not need to use fetch_ops_on_bits(), we can just set irrelavent bits to 1, and do fetch_and
let rhs = (val.to_u8().unwrap() << lshift) | !mask;
let old_raw_byte =
unsafe { <u8 as MetadataValue>::fetch_and(meta_addr, rhs, order) };
let old_val = (old_raw_byte & mask) >> lshift;
FromPrimitive::from_u8(old_val).unwrap()
} else {
unsafe { T::fetch_and(meta_addr, val, order) }
}
},
|_old_val| {
#[cfg(feature = "extreme_assertions")]
sanity::verify_update::<T>(self, data_addr, _old_val, _old_val.bitand(val))
},
)
}