| //! The virtual memory representation of the MIR interpreter. |
| |
| use std::borrow::Cow; |
| use std::convert::{TryFrom, TryInto}; |
| use std::iter; |
| use std::ops::{Deref, Range}; |
| use std::ptr; |
| |
| use rustc_ast::Mutability; |
| use rustc_data_structures::sorted_map::SortedMap; |
| use rustc_span::DUMMY_SP; |
| use rustc_target::abi::{Align, HasDataLayout, Size}; |
| |
| use super::{ |
| read_target_uint, write_target_uint, AllocId, InterpError, InterpResult, Pointer, Provenance, |
| ResourceExhaustionInfo, Scalar, ScalarMaybeUninit, UndefinedBehaviorInfo, UninitBytesAccess, |
| UnsupportedOpInfo, |
| }; |
| use crate::ty; |
| |
| /// This type represents an Allocation in the Miri/CTFE core engine. |
| /// |
| /// Its public API is rather low-level, working directly with allocation offsets and a custom error |
| /// type to account for the lack of an AllocId on this level. The Miri/CTFE core engine `memory` |
| /// module provides higher-level access. |
| #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Hash, TyEncodable, TyDecodable)] |
| #[derive(HashStable)] |
| pub struct Allocation<Tag = AllocId, Extra = ()> { |
| /// The actual bytes of the allocation. |
| /// Note that the bytes of a pointer represent the offset of the pointer. |
| bytes: Box<[u8]>, |
| /// Maps from byte addresses to extra data for each pointer. |
| /// Only the first byte of a pointer is inserted into the map; i.e., |
| /// every entry in this map applies to `pointer_size` consecutive bytes starting |
| /// at the given offset. |
| relocations: Relocations<Tag>, |
| /// Denotes which part of this allocation is initialized. |
| init_mask: InitMask, |
| /// The alignment of the allocation to detect unaligned reads. |
| /// (`Align` guarantees that this is a power of two.) |
| pub align: Align, |
| /// `true` if the allocation is mutable. |
| /// Also used by codegen to determine if a static should be put into mutable memory, |
| /// which happens for `static mut` and `static` with interior mutability. |
| pub mutability: Mutability, |
| /// Extra state for the machine. |
| pub extra: Extra, |
| } |
| |
| /// We have our own error type that does not know about the `AllocId`; that information |
| /// is added when converting to `InterpError`. |
| #[derive(Debug)] |
| pub enum AllocError { |
| /// Encountered a pointer where we needed raw bytes. |
| ReadPointerAsBytes, |
| /// Partially overwriting a pointer. |
| PartialPointerOverwrite(Size), |
| /// Using uninitialized data where it is not allowed. |
| InvalidUninitBytes(Option<UninitBytesAccess>), |
| } |
| pub type AllocResult<T = ()> = Result<T, AllocError>; |
| |
| impl AllocError { |
| pub fn to_interp_error<'tcx>(self, alloc_id: AllocId) -> InterpError<'tcx> { |
| use AllocError::*; |
| match self { |
| ReadPointerAsBytes => InterpError::Unsupported(UnsupportedOpInfo::ReadPointerAsBytes), |
| PartialPointerOverwrite(offset) => InterpError::Unsupported( |
| UnsupportedOpInfo::PartialPointerOverwrite(Pointer::new(alloc_id, offset)), |
| ), |
| InvalidUninitBytes(info) => InterpError::UndefinedBehavior( |
| UndefinedBehaviorInfo::InvalidUninitBytes(info.map(|b| (alloc_id, b))), |
| ), |
| } |
| } |
| } |
| |
| /// The information that makes up a memory access: offset and size. |
| #[derive(Copy, Clone, Debug)] |
| pub struct AllocRange { |
| pub start: Size, |
| pub size: Size, |
| } |
| |
| /// Free-starting constructor for less syntactic overhead. |
| #[inline(always)] |
| pub fn alloc_range(start: Size, size: Size) -> AllocRange { |
| AllocRange { start, size } |
| } |
| |
| impl AllocRange { |
| #[inline(always)] |
| pub fn end(self) -> Size { |
| self.start + self.size // This does overflow checking. |
| } |
| |
| /// Returns the `subrange` within this range; panics if it is not a subrange. |
| #[inline] |
| pub fn subrange(self, subrange: AllocRange) -> AllocRange { |
| let sub_start = self.start + subrange.start; |
| let range = alloc_range(sub_start, subrange.size); |
| assert!(range.end() <= self.end(), "access outside the bounds for given AllocRange"); |
| range |
| } |
| } |
| |
| // The constructors are all without extra; the extra gets added by a machine hook later. |
| impl<Tag> Allocation<Tag> { |
| /// Creates an allocation initialized by the given bytes |
| pub fn from_bytes<'a>( |
| slice: impl Into<Cow<'a, [u8]>>, |
| align: Align, |
| mutability: Mutability, |
| ) -> Self { |
| let bytes = Box::<[u8]>::from(slice.into()); |
| let size = Size::from_bytes(bytes.len()); |
| Self { |
| bytes, |
| relocations: Relocations::new(), |
| init_mask: InitMask::new(size, true), |
| align, |
| mutability, |
| extra: (), |
| } |
| } |
| |
| pub fn from_bytes_byte_aligned_immutable<'a>(slice: impl Into<Cow<'a, [u8]>>) -> Self { |
| Allocation::from_bytes(slice, Align::ONE, Mutability::Not) |
| } |
| |
| /// Try to create an Allocation of `size` bytes, failing if there is not enough memory |
| /// available to the compiler to do so. |
| pub fn uninit(size: Size, align: Align, panic_on_fail: bool) -> InterpResult<'static, Self> { |
| let bytes = Box::<[u8]>::try_new_zeroed_slice(size.bytes_usize()).map_err(|_| { |
| // This results in an error that can happen non-deterministically, since the memory |
| // available to the compiler can change between runs. Normally queries are always |
| // deterministic. However, we can be non-determinstic here because all uses of const |
| // evaluation (including ConstProp!) will make compilation fail (via hard error |
| // or ICE) upon encountering a `MemoryExhausted` error. |
| if panic_on_fail { |
| panic!("Allocation::uninit called with panic_on_fail had allocation failure") |
| } |
| ty::tls::with(|tcx| { |
| tcx.sess.delay_span_bug(DUMMY_SP, "exhausted memory during interpreation") |
| }); |
| InterpError::ResourceExhaustion(ResourceExhaustionInfo::MemoryExhausted) |
| })?; |
| // SAFETY: the box was zero-allocated, which is a valid initial value for Box<[u8]> |
| let bytes = unsafe { bytes.assume_init() }; |
| Ok(Allocation { |
| bytes, |
| relocations: Relocations::new(), |
| init_mask: InitMask::new(size, false), |
| align, |
| mutability: Mutability::Mut, |
| extra: (), |
| }) |
| } |
| } |
| |
| impl Allocation { |
| /// Convert Tag and add Extra fields |
| pub fn convert_tag_add_extra<Tag, Extra>( |
| self, |
| cx: &impl HasDataLayout, |
| extra: Extra, |
| mut tagger: impl FnMut(Pointer<AllocId>) -> Pointer<Tag>, |
| ) -> Allocation<Tag, Extra> { |
| // Compute new pointer tags, which also adjusts the bytes. |
| let mut bytes = self.bytes; |
| let mut new_relocations = Vec::with_capacity(self.relocations.0.len()); |
| let ptr_size = cx.data_layout().pointer_size.bytes_usize(); |
| let endian = cx.data_layout().endian; |
| for &(offset, alloc_id) in self.relocations.iter() { |
| let idx = offset.bytes_usize(); |
| let ptr_bytes = &mut bytes[idx..idx + ptr_size]; |
| let bits = read_target_uint(endian, ptr_bytes).unwrap(); |
| let (ptr_tag, ptr_offset) = |
| tagger(Pointer::new(alloc_id, Size::from_bytes(bits))).into_parts(); |
| write_target_uint(endian, ptr_bytes, ptr_offset.bytes().into()).unwrap(); |
| new_relocations.push((offset, ptr_tag)); |
| } |
| // Create allocation. |
| Allocation { |
| bytes, |
| relocations: Relocations::from_presorted(new_relocations), |
| init_mask: self.init_mask, |
| align: self.align, |
| mutability: self.mutability, |
| extra, |
| } |
| } |
| } |
| |
| /// Raw accessors. Provide access to otherwise private bytes. |
| impl<Tag, Extra> Allocation<Tag, Extra> { |
| pub fn len(&self) -> usize { |
| self.bytes.len() |
| } |
| |
| pub fn size(&self) -> Size { |
| Size::from_bytes(self.len()) |
| } |
| |
| /// Looks at a slice which may describe uninitialized bytes or describe a relocation. This differs |
| /// from `get_bytes_with_uninit_and_ptr` in that it does no relocation checks (even on the |
| /// edges) at all. |
| /// This must not be used for reads affecting the interpreter execution. |
| pub fn inspect_with_uninit_and_ptr_outside_interpreter(&self, range: Range<usize>) -> &[u8] { |
| &self.bytes[range] |
| } |
| |
| /// Returns the mask indicating which bytes are initialized. |
| pub fn init_mask(&self) -> &InitMask { |
| &self.init_mask |
| } |
| |
| /// Returns the relocation list. |
| pub fn relocations(&self) -> &Relocations<Tag> { |
| &self.relocations |
| } |
| } |
| |
| /// Byte accessors. |
| impl<Tag: Provenance, Extra> Allocation<Tag, Extra> { |
| /// The last argument controls whether we error out when there are uninitialized |
| /// or pointer bytes. You should never call this, call `get_bytes` or |
| /// `get_bytes_with_uninit_and_ptr` instead, |
| /// |
| /// This function also guarantees that the resulting pointer will remain stable |
| /// even when new allocations are pushed to the `HashMap`. `copy_repeatedly` relies |
| /// on that. |
| /// |
| /// It is the caller's responsibility to check bounds and alignment beforehand. |
| fn get_bytes_internal( |
| &self, |
| cx: &impl HasDataLayout, |
| range: AllocRange, |
| check_init_and_ptr: bool, |
| ) -> AllocResult<&[u8]> { |
| if check_init_and_ptr { |
| self.check_init(range)?; |
| self.check_relocations(cx, range)?; |
| } else { |
| // We still don't want relocations on the *edges*. |
| self.check_relocation_edges(cx, range)?; |
| } |
| |
| Ok(&self.bytes[range.start.bytes_usize()..range.end().bytes_usize()]) |
| } |
| |
| /// Checks that these bytes are initialized and not pointer bytes, and then return them |
| /// as a slice. |
| /// |
| /// It is the caller's responsibility to check bounds and alignment beforehand. |
| /// Most likely, you want to use the `PlaceTy` and `OperandTy`-based methods |
| /// on `InterpCx` instead. |
| #[inline] |
| pub fn get_bytes(&self, cx: &impl HasDataLayout, range: AllocRange) -> AllocResult<&[u8]> { |
| self.get_bytes_internal(cx, range, true) |
| } |
| |
| /// It is the caller's responsibility to handle uninitialized and pointer bytes. |
| /// However, this still checks that there are no relocations on the *edges*. |
| /// |
| /// It is the caller's responsibility to check bounds and alignment beforehand. |
| #[inline] |
| pub fn get_bytes_with_uninit_and_ptr( |
| &self, |
| cx: &impl HasDataLayout, |
| range: AllocRange, |
| ) -> AllocResult<&[u8]> { |
| self.get_bytes_internal(cx, range, false) |
| } |
| |
| /// Just calling this already marks everything as defined and removes relocations, |
| /// so be sure to actually put data there! |
| /// |
| /// It is the caller's responsibility to check bounds and alignment beforehand. |
| /// Most likely, you want to use the `PlaceTy` and `OperandTy`-based methods |
| /// on `InterpCx` instead. |
| pub fn get_bytes_mut( |
| &mut self, |
| cx: &impl HasDataLayout, |
| range: AllocRange, |
| ) -> AllocResult<&mut [u8]> { |
| self.mark_init(range, true); |
| self.clear_relocations(cx, range)?; |
| |
| Ok(&mut self.bytes[range.start.bytes_usize()..range.end().bytes_usize()]) |
| } |
| |
| /// A raw pointer variant of `get_bytes_mut` that avoids invalidating existing aliases into this memory. |
| pub fn get_bytes_mut_ptr( |
| &mut self, |
| cx: &impl HasDataLayout, |
| range: AllocRange, |
| ) -> AllocResult<*mut [u8]> { |
| self.mark_init(range, true); |
| self.clear_relocations(cx, range)?; |
| |
| assert!(range.end().bytes_usize() <= self.bytes.len()); // need to do our own bounds-check |
| let begin_ptr = self.bytes.as_mut_ptr().wrapping_add(range.start.bytes_usize()); |
| let len = range.end().bytes_usize() - range.start.bytes_usize(); |
| Ok(ptr::slice_from_raw_parts_mut(begin_ptr, len)) |
| } |
| } |
| |
| /// Reading and writing. |
| impl<Tag: Provenance, Extra> Allocation<Tag, Extra> { |
| /// Validates that `ptr.offset` and `ptr.offset + size` do not point to the middle of a |
| /// relocation. If `allow_uninit_and_ptr` is `false`, also enforces that the memory in the |
| /// given range contains neither relocations nor uninitialized bytes. |
| pub fn check_bytes( |
| &self, |
| cx: &impl HasDataLayout, |
| range: AllocRange, |
| allow_uninit_and_ptr: bool, |
| ) -> AllocResult { |
| // Check bounds and relocations on the edges. |
| self.get_bytes_with_uninit_and_ptr(cx, range)?; |
| // Check uninit and ptr. |
| if !allow_uninit_and_ptr { |
| self.check_init(range)?; |
| self.check_relocations(cx, range)?; |
| } |
| Ok(()) |
| } |
| |
| /// Reads a *non-ZST* scalar. |
| /// |
| /// ZSTs can't be read because in order to obtain a `Pointer`, we need to check |
| /// for ZSTness anyway due to integer pointers being valid for ZSTs. |
| /// |
| /// It is the caller's responsibility to check bounds and alignment beforehand. |
| /// Most likely, you want to call `InterpCx::read_scalar` instead of this method. |
| pub fn read_scalar( |
| &self, |
| cx: &impl HasDataLayout, |
| range: AllocRange, |
| ) -> AllocResult<ScalarMaybeUninit<Tag>> { |
| // `get_bytes_with_uninit_and_ptr` tests relocation edges. |
| // We deliberately error when loading data that partially has provenance, or partially |
| // initialized data (that's the check below), into a scalar. The LLVM semantics of this are |
| // unclear so we are conservative. See <https://github.com/rust-lang/rust/issues/69488> for |
| // further discussion. |
| let bytes = self.get_bytes_with_uninit_and_ptr(cx, range)?; |
| // Uninit check happens *after* we established that the alignment is correct. |
| // We must not return `Ok()` for unaligned pointers! |
| if self.is_init(range).is_err() { |
| // This inflates uninitialized bytes to the entire scalar, even if only a few |
| // bytes are uninitialized. |
| return Ok(ScalarMaybeUninit::Uninit); |
| } |
| // Now we do the actual reading. |
| let bits = read_target_uint(cx.data_layout().endian, bytes).unwrap(); |
| // See if we got a pointer. |
| if range.size != cx.data_layout().pointer_size { |
| // Not a pointer. |
| // *Now*, we better make sure that the inside is free of relocations too. |
| self.check_relocations(cx, range)?; |
| } else { |
| // Maybe a pointer. |
| if let Some(&prov) = self.relocations.get(&range.start) { |
| let ptr = Pointer::new(prov, Size::from_bytes(bits)); |
| return Ok(ScalarMaybeUninit::from_pointer(ptr, cx)); |
| } |
| } |
| // We don't. Just return the bits. |
| Ok(ScalarMaybeUninit::Scalar(Scalar::from_uint(bits, range.size))) |
| } |
| |
| /// Writes a *non-ZST* scalar. |
| /// |
| /// ZSTs can't be read because in order to obtain a `Pointer`, we need to check |
| /// for ZSTness anyway due to integer pointers being valid for ZSTs. |
| /// |
| /// It is the caller's responsibility to check bounds and alignment beforehand. |
| /// Most likely, you want to call `InterpCx::write_scalar` instead of this method. |
| pub fn write_scalar( |
| &mut self, |
| cx: &impl HasDataLayout, |
| range: AllocRange, |
| val: ScalarMaybeUninit<Tag>, |
| ) -> AllocResult { |
| assert!(self.mutability == Mutability::Mut); |
| |
| let val = match val { |
| ScalarMaybeUninit::Scalar(scalar) => scalar, |
| ScalarMaybeUninit::Uninit => { |
| self.mark_init(range, false); |
| return Ok(()); |
| } |
| }; |
| |
| // `to_bits_or_ptr_internal` is the right method because we just want to store this data |
| // as-is into memory. |
| let (bytes, provenance) = match val.to_bits_or_ptr_internal(range.size) { |
| Err(val) => { |
| let (provenance, offset) = val.into_parts(); |
| (u128::from(offset.bytes()), Some(provenance)) |
| } |
| Ok(data) => (data, None), |
| }; |
| |
| let endian = cx.data_layout().endian; |
| let dst = self.get_bytes_mut(cx, range)?; |
| write_target_uint(endian, dst, bytes).unwrap(); |
| |
| // See if we have to also write a relocation. |
| if let Some(provenance) = provenance { |
| self.relocations.0.insert(range.start, provenance); |
| } |
| |
| Ok(()) |
| } |
| } |
| |
| /// Relocations. |
| impl<Tag: Copy, Extra> Allocation<Tag, Extra> { |
| /// Returns all relocations overlapping with the given pointer-offset pair. |
| pub fn get_relocations(&self, cx: &impl HasDataLayout, range: AllocRange) -> &[(Size, Tag)] { |
| // We have to go back `pointer_size - 1` bytes, as that one would still overlap with |
| // the beginning of this range. |
| let start = range.start.bytes().saturating_sub(cx.data_layout().pointer_size.bytes() - 1); |
| self.relocations.range(Size::from_bytes(start)..range.end()) |
| } |
| |
| /// Checks that there are no relocations overlapping with the given range. |
| #[inline(always)] |
| fn check_relocations(&self, cx: &impl HasDataLayout, range: AllocRange) -> AllocResult { |
| if self.get_relocations(cx, range).is_empty() { |
| Ok(()) |
| } else { |
| Err(AllocError::ReadPointerAsBytes) |
| } |
| } |
| |
| /// Removes all relocations inside the given range. |
| /// If there are relocations overlapping with the edges, they |
| /// are removed as well *and* the bytes they cover are marked as |
| /// uninitialized. This is a somewhat odd "spooky action at a distance", |
| /// but it allows strictly more code to run than if we would just error |
| /// immediately in that case. |
| fn clear_relocations(&mut self, cx: &impl HasDataLayout, range: AllocRange) -> AllocResult |
| where |
| Tag: Provenance, |
| { |
| // Find the start and end of the given range and its outermost relocations. |
| let (first, last) = { |
| // Find all relocations overlapping the given range. |
| let relocations = self.get_relocations(cx, range); |
| if relocations.is_empty() { |
| return Ok(()); |
| } |
| |
| ( |
| relocations.first().unwrap().0, |
| relocations.last().unwrap().0 + cx.data_layout().pointer_size, |
| ) |
| }; |
| let start = range.start; |
| let end = range.end(); |
| |
| // We need to handle clearing the relocations from parts of a pointer. See |
| // <https://github.com/rust-lang/rust/issues/87184> for details. |
| if first < start { |
| if Tag::ERR_ON_PARTIAL_PTR_OVERWRITE { |
| return Err(AllocError::PartialPointerOverwrite(first)); |
| } |
| self.init_mask.set_range(first, start, false); |
| } |
| if last > end { |
| if Tag::ERR_ON_PARTIAL_PTR_OVERWRITE { |
| return Err(AllocError::PartialPointerOverwrite( |
| last - cx.data_layout().pointer_size, |
| )); |
| } |
| self.init_mask.set_range(end, last, false); |
| } |
| |
| // Forget all the relocations. |
| self.relocations.0.remove_range(first..last); |
| |
| Ok(()) |
| } |
| |
| /// Errors if there are relocations overlapping with the edges of the |
| /// given memory range. |
| #[inline] |
| fn check_relocation_edges(&self, cx: &impl HasDataLayout, range: AllocRange) -> AllocResult { |
| self.check_relocations(cx, alloc_range(range.start, Size::ZERO))?; |
| self.check_relocations(cx, alloc_range(range.end(), Size::ZERO))?; |
| Ok(()) |
| } |
| } |
| |
| /// "Relocations" stores the provenance information of pointers stored in memory. |
| #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, TyEncodable, TyDecodable)] |
| pub struct Relocations<Tag = AllocId>(SortedMap<Size, Tag>); |
| |
| impl<Tag> Relocations<Tag> { |
| pub fn new() -> Self { |
| Relocations(SortedMap::new()) |
| } |
| |
| // The caller must guarantee that the given relocations are already sorted |
| // by address and contain no duplicates. |
| pub fn from_presorted(r: Vec<(Size, Tag)>) -> Self { |
| Relocations(SortedMap::from_presorted_elements(r)) |
| } |
| } |
| |
| impl<Tag> Deref for Relocations<Tag> { |
| type Target = SortedMap<Size, Tag>; |
| |
| fn deref(&self) -> &Self::Target { |
| &self.0 |
| } |
| } |
| |
| /// A partial, owned list of relocations to transfer into another allocation. |
| pub struct AllocationRelocations<Tag> { |
| relative_relocations: Vec<(Size, Tag)>, |
| } |
| |
| impl<Tag: Copy, Extra> Allocation<Tag, Extra> { |
| pub fn prepare_relocation_copy( |
| &self, |
| cx: &impl HasDataLayout, |
| src: AllocRange, |
| dest: Size, |
| count: u64, |
| ) -> AllocationRelocations<Tag> { |
| let relocations = self.get_relocations(cx, src); |
| if relocations.is_empty() { |
| return AllocationRelocations { relative_relocations: Vec::new() }; |
| } |
| |
| let size = src.size; |
| let mut new_relocations = Vec::with_capacity(relocations.len() * (count as usize)); |
| |
| for i in 0..count { |
| new_relocations.extend(relocations.iter().map(|&(offset, reloc)| { |
| // compute offset for current repetition |
| let dest_offset = dest + size * i; // `Size` operations |
| ( |
| // shift offsets from source allocation to destination allocation |
| (offset + dest_offset) - src.start, // `Size` operations |
| reloc, |
| ) |
| })); |
| } |
| |
| AllocationRelocations { relative_relocations: new_relocations } |
| } |
| |
| /// Applies a relocation copy. |
| /// The affected range, as defined in the parameters to `prepare_relocation_copy` is expected |
| /// to be clear of relocations. |
| pub fn mark_relocation_range(&mut self, relocations: AllocationRelocations<Tag>) { |
| self.relocations.0.insert_presorted(relocations.relative_relocations); |
| } |
| } |
| |
| //////////////////////////////////////////////////////////////////////////////// |
| // Uninitialized byte tracking |
| //////////////////////////////////////////////////////////////////////////////// |
| |
| type Block = u64; |
| |
| /// A bitmask where each bit refers to the byte with the same index. If the bit is `true`, the byte |
| /// is initialized. If it is `false` the byte is uninitialized. |
| #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Hash, TyEncodable, TyDecodable)] |
| #[derive(HashStable)] |
| pub struct InitMask { |
| blocks: Vec<Block>, |
| len: Size, |
| } |
| |
| impl InitMask { |
| pub const BLOCK_SIZE: u64 = 64; |
| |
| #[inline] |
| fn bit_index(bits: Size) -> (usize, usize) { |
| // BLOCK_SIZE is the number of bits that can fit in a `Block`. |
| // Each bit in a `Block` represents the initialization state of one byte of an allocation, |
| // so we use `.bytes()` here. |
| let bits = bits.bytes(); |
| let a = bits / InitMask::BLOCK_SIZE; |
| let b = bits % InitMask::BLOCK_SIZE; |
| (usize::try_from(a).unwrap(), usize::try_from(b).unwrap()) |
| } |
| |
| #[inline] |
| fn size_from_bit_index(block: impl TryInto<u64>, bit: impl TryInto<u64>) -> Size { |
| let block = block.try_into().ok().unwrap(); |
| let bit = bit.try_into().ok().unwrap(); |
| Size::from_bytes(block * InitMask::BLOCK_SIZE + bit) |
| } |
| |
| pub fn new(size: Size, state: bool) -> Self { |
| let mut m = InitMask { blocks: vec![], len: Size::ZERO }; |
| m.grow(size, state); |
| m |
| } |
| |
| pub fn set_range(&mut self, start: Size, end: Size, new_state: bool) { |
| let len = self.len; |
| if end > len { |
| self.grow(end - len, new_state); |
| } |
| self.set_range_inbounds(start, end, new_state); |
| } |
| |
| pub fn set_range_inbounds(&mut self, start: Size, end: Size, new_state: bool) { |
| let (blocka, bita) = Self::bit_index(start); |
| let (blockb, bitb) = Self::bit_index(end); |
| if blocka == blockb { |
| // First set all bits except the first `bita`, |
| // then unset the last `64 - bitb` bits. |
| let range = if bitb == 0 { |
| u64::MAX << bita |
| } else { |
| (u64::MAX << bita) & (u64::MAX >> (64 - bitb)) |
| }; |
| if new_state { |
| self.blocks[blocka] |= range; |
| } else { |
| self.blocks[blocka] &= !range; |
| } |
| return; |
| } |
| // across block boundaries |
| if new_state { |
| // Set `bita..64` to `1`. |
| self.blocks[blocka] |= u64::MAX << bita; |
| // Set `0..bitb` to `1`. |
| if bitb != 0 { |
| self.blocks[blockb] |= u64::MAX >> (64 - bitb); |
| } |
| // Fill in all the other blocks (much faster than one bit at a time). |
| for block in (blocka + 1)..blockb { |
| self.blocks[block] = u64::MAX; |
| } |
| } else { |
| // Set `bita..64` to `0`. |
| self.blocks[blocka] &= !(u64::MAX << bita); |
| // Set `0..bitb` to `0`. |
| if bitb != 0 { |
| self.blocks[blockb] &= !(u64::MAX >> (64 - bitb)); |
| } |
| // Fill in all the other blocks (much faster than one bit at a time). |
| for block in (blocka + 1)..blockb { |
| self.blocks[block] = 0; |
| } |
| } |
| } |
| |
| #[inline] |
| pub fn get(&self, i: Size) -> bool { |
| let (block, bit) = Self::bit_index(i); |
| (self.blocks[block] & (1 << bit)) != 0 |
| } |
| |
| #[inline] |
| pub fn set(&mut self, i: Size, new_state: bool) { |
| let (block, bit) = Self::bit_index(i); |
| self.set_bit(block, bit, new_state); |
| } |
| |
| #[inline] |
| fn set_bit(&mut self, block: usize, bit: usize, new_state: bool) { |
| if new_state { |
| self.blocks[block] |= 1 << bit; |
| } else { |
| self.blocks[block] &= !(1 << bit); |
| } |
| } |
| |
| pub fn grow(&mut self, amount: Size, new_state: bool) { |
| if amount.bytes() == 0 { |
| return; |
| } |
| let unused_trailing_bits = |
| u64::try_from(self.blocks.len()).unwrap() * Self::BLOCK_SIZE - self.len.bytes(); |
| if amount.bytes() > unused_trailing_bits { |
| let additional_blocks = amount.bytes() / Self::BLOCK_SIZE + 1; |
| self.blocks.extend( |
| // FIXME(oli-obk): optimize this by repeating `new_state as Block`. |
| iter::repeat(0).take(usize::try_from(additional_blocks).unwrap()), |
| ); |
| } |
| let start = self.len; |
| self.len += amount; |
| self.set_range_inbounds(start, start + amount, new_state); // `Size` operation |
| } |
| |
| /// Returns the index of the first bit in `start..end` (end-exclusive) that is equal to is_init. |
| fn find_bit(&self, start: Size, end: Size, is_init: bool) -> Option<Size> { |
| /// A fast implementation of `find_bit`, |
| /// which skips over an entire block at a time if it's all 0s (resp. 1s), |
| /// and finds the first 1 (resp. 0) bit inside a block using `trailing_zeros` instead of a loop. |
| /// |
| /// Note that all examples below are written with 8 (instead of 64) bit blocks for simplicity, |
| /// and with the least significant bit (and lowest block) first: |
| /// |
| /// 00000000|00000000 |
| /// ^ ^ ^ ^ |
| /// index: 0 7 8 15 |
| /// |
| /// Also, if not stated, assume that `is_init = true`, that is, we are searching for the first 1 bit. |
| fn find_bit_fast( |
| init_mask: &InitMask, |
| start: Size, |
| end: Size, |
| is_init: bool, |
| ) -> Option<Size> { |
| /// Search one block, returning the index of the first bit equal to `is_init`. |
| fn search_block( |
| bits: Block, |
| block: usize, |
| start_bit: usize, |
| is_init: bool, |
| ) -> Option<Size> { |
| // For the following examples, assume this function was called with: |
| // bits = 0b00111011 |
| // start_bit = 3 |
| // is_init = false |
| // Note that, for the examples in this function, the most significant bit is written first, |
| // which is backwards compared to the comments in `find_bit`/`find_bit_fast`. |
| |
| // Invert bits so we're always looking for the first set bit. |
| // ! 0b00111011 |
| // bits = 0b11000100 |
| let bits = if is_init { bits } else { !bits }; |
| // Mask off unused start bits. |
| // 0b11000100 |
| // & 0b11111000 |
| // bits = 0b11000000 |
| let bits = bits & (!0 << start_bit); |
| // Find set bit, if any. |
| // bit = trailing_zeros(0b11000000) |
| // bit = 6 |
| if bits == 0 { |
| None |
| } else { |
| let bit = bits.trailing_zeros(); |
| Some(InitMask::size_from_bit_index(block, bit)) |
| } |
| } |
| |
| if start >= end { |
| return None; |
| } |
| |
| // Convert `start` and `end` to block indexes and bit indexes within each block. |
| // We must convert `end` to an inclusive bound to handle block boundaries correctly. |
| // |
| // For example: |
| // |
| // (a) 00000000|00000000 (b) 00000000| |
| // ^~~~~~~~~~~^ ^~~~~~~~~^ |
| // start end start end |
| // |
| // In both cases, the block index of `end` is 1. |
| // But we do want to search block 1 in (a), and we don't in (b). |
| // |
| // We subtract 1 from both end positions to make them inclusive: |
| // |
| // (a) 00000000|00000000 (b) 00000000| |
| // ^~~~~~~~~~^ ^~~~~~~^ |
| // start end_inclusive start end_inclusive |
| // |
| // For (a), the block index of `end_inclusive` is 1, and for (b), it's 0. |
| // This provides the desired behavior of searching blocks 0 and 1 for (a), |
| // and searching only block 0 for (b). |
| // There is no concern of overflows since we checked for `start >= end` above. |
| let (start_block, start_bit) = InitMask::bit_index(start); |
| let end_inclusive = Size::from_bytes(end.bytes() - 1); |
| let (end_block_inclusive, _) = InitMask::bit_index(end_inclusive); |
| |
| // Handle first block: need to skip `start_bit` bits. |
| // |
| // We need to handle the first block separately, |
| // because there may be bits earlier in the block that should be ignored, |
| // such as the bit marked (1) in this example: |
| // |
| // (1) |
| // -|------ |
| // (c) 01000000|00000000|00000001 |
| // ^~~~~~~~~~~~~~~~~~^ |
| // start end |
| if let Some(i) = |
| search_block(init_mask.blocks[start_block], start_block, start_bit, is_init) |
| { |
| // If the range is less than a block, we may find a matching bit after `end`. |
| // |
| // For example, we shouldn't successfully find bit (2), because it's after `end`: |
| // |
| // (2) |
| // -------| |
| // (d) 00000001|00000000|00000001 |
| // ^~~~~^ |
| // start end |
| // |
| // An alternative would be to mask off end bits in the same way as we do for start bits, |
| // but performing this check afterwards is faster and simpler to implement. |
| if i < end { |
| return Some(i); |
| } else { |
| return None; |
| } |
| } |
| |
| // Handle remaining blocks. |
| // |
| // We can skip over an entire block at once if it's all 0s (resp. 1s). |
| // The block marked (3) in this example is the first block that will be handled by this loop, |
| // and it will be skipped for that reason: |
| // |
| // (3) |
| // -------- |
| // (e) 01000000|00000000|00000001 |
| // ^~~~~~~~~~~~~~~~~~^ |
| // start end |
| if start_block < end_block_inclusive { |
| // This loop is written in a specific way for performance. |
| // Notably: `..end_block_inclusive + 1` is used for an inclusive range instead of `..=end_block_inclusive`, |
| // and `.zip(start_block + 1..)` is used to track the index instead of `.enumerate().skip().take()`, |
| // because both alternatives result in significantly worse codegen. |
| // `end_block_inclusive + 1` is guaranteed not to wrap, because `end_block_inclusive <= end / BLOCK_SIZE`, |
| // and `BLOCK_SIZE` (the number of bits per block) will always be at least 8 (1 byte). |
| for (&bits, block) in init_mask.blocks[start_block + 1..end_block_inclusive + 1] |
| .iter() |
| .zip(start_block + 1..) |
| { |
| if let Some(i) = search_block(bits, block, 0, is_init) { |
| // If this is the last block, we may find a matching bit after `end`. |
| // |
| // For example, we shouldn't successfully find bit (4), because it's after `end`: |
| // |
| // (4) |
| // -------| |
| // (f) 00000001|00000000|00000001 |
| // ^~~~~~~~~~~~~~~~~~^ |
| // start end |
| // |
| // As above with example (d), we could handle the end block separately and mask off end bits, |
| // but unconditionally searching an entire block at once and performing this check afterwards |
| // is faster and much simpler to implement. |
| if i < end { |
| return Some(i); |
| } else { |
| return None; |
| } |
| } |
| } |
| } |
| |
| None |
| } |
| |
| #[cfg_attr(not(debug_assertions), allow(dead_code))] |
| fn find_bit_slow( |
| init_mask: &InitMask, |
| start: Size, |
| end: Size, |
| is_init: bool, |
| ) -> Option<Size> { |
| (start..end).find(|&i| init_mask.get(i) == is_init) |
| } |
| |
| let result = find_bit_fast(self, start, end, is_init); |
| |
| debug_assert_eq!( |
| result, |
| find_bit_slow(self, start, end, is_init), |
| "optimized implementation of find_bit is wrong for start={:?} end={:?} is_init={} init_mask={:#?}", |
| start, |
| end, |
| is_init, |
| self |
| ); |
| |
| result |
| } |
| } |
| |
| /// A contiguous chunk of initialized or uninitialized memory. |
| pub enum InitChunk { |
| Init(Range<Size>), |
| Uninit(Range<Size>), |
| } |
| |
| impl InitChunk { |
| #[inline] |
| pub fn is_init(&self) -> bool { |
| match self { |
| Self::Init(_) => true, |
| Self::Uninit(_) => false, |
| } |
| } |
| |
| #[inline] |
| pub fn range(&self) -> Range<Size> { |
| match self { |
| Self::Init(r) => r.clone(), |
| Self::Uninit(r) => r.clone(), |
| } |
| } |
| } |
| |
| impl InitMask { |
| /// Checks whether the range `start..end` (end-exclusive) is entirely initialized. |
| /// |
| /// Returns `Ok(())` if it's initialized. Otherwise returns a range of byte |
| /// indexes for the first contiguous span of the uninitialized access. |
| #[inline] |
| pub fn is_range_initialized(&self, start: Size, end: Size) -> Result<(), Range<Size>> { |
| if end > self.len { |
| return Err(self.len..end); |
| } |
| |
| let uninit_start = self.find_bit(start, end, false); |
| |
| match uninit_start { |
| Some(uninit_start) => { |
| let uninit_end = self.find_bit(uninit_start, end, true).unwrap_or(end); |
| Err(uninit_start..uninit_end) |
| } |
| None => Ok(()), |
| } |
| } |
| |
| /// Returns an iterator, yielding a range of byte indexes for each contiguous region |
| /// of initialized or uninitialized bytes inside the range `start..end` (end-exclusive). |
| /// |
| /// The iterator guarantees the following: |
| /// - Chunks are nonempty. |
| /// - Chunks are adjacent (each range's start is equal to the previous range's end). |
| /// - Chunks span exactly `start..end` (the first starts at `start`, the last ends at `end`). |
| /// - Chunks alternate between [`InitChunk::Init`] and [`InitChunk::Uninit`]. |
| #[inline] |
| pub fn range_as_init_chunks(&self, start: Size, end: Size) -> InitChunkIter<'_> { |
| assert!(end <= self.len); |
| |
| let is_init = if start < end { |
| self.get(start) |
| } else { |
| // `start..end` is empty: there are no chunks, so use some arbitrary value |
| false |
| }; |
| |
| InitChunkIter { init_mask: self, is_init, start, end } |
| } |
| } |
| |
| /// Yields [`InitChunk`]s. See [`InitMask::range_as_init_chunks`]. |
| pub struct InitChunkIter<'a> { |
| init_mask: &'a InitMask, |
| /// Whether the next chunk we will return is initialized. |
| /// If there are no more chunks, contains some arbitrary value. |
| is_init: bool, |
| /// The current byte index into `init_mask`. |
| start: Size, |
| /// The end byte index into `init_mask`. |
| end: Size, |
| } |
| |
| impl<'a> Iterator for InitChunkIter<'a> { |
| type Item = InitChunk; |
| |
| #[inline] |
| fn next(&mut self) -> Option<Self::Item> { |
| if self.start >= self.end { |
| return None; |
| } |
| |
| let end_of_chunk = |
| self.init_mask.find_bit(self.start, self.end, !self.is_init).unwrap_or(self.end); |
| let range = self.start..end_of_chunk; |
| |
| let ret = |
| Some(if self.is_init { InitChunk::Init(range) } else { InitChunk::Uninit(range) }); |
| |
| self.is_init = !self.is_init; |
| self.start = end_of_chunk; |
| |
| ret |
| } |
| } |
| |
| /// Uninitialized bytes. |
| impl<Tag: Copy, Extra> Allocation<Tag, Extra> { |
| /// Checks whether the given range is entirely initialized. |
| /// |
| /// Returns `Ok(())` if it's initialized. Otherwise returns the range of byte |
| /// indexes of the first contiguous uninitialized access. |
| fn is_init(&self, range: AllocRange) -> Result<(), Range<Size>> { |
| self.init_mask.is_range_initialized(range.start, range.end()) // `Size` addition |
| } |
| |
| /// Checks that a range of bytes is initialized. If not, returns the `InvalidUninitBytes` |
| /// error which will report the first range of bytes which is uninitialized. |
| fn check_init(&self, range: AllocRange) -> AllocResult { |
| self.is_init(range).or_else(|idx_range| { |
| Err(AllocError::InvalidUninitBytes(Some(UninitBytesAccess { |
| access_offset: range.start, |
| access_size: range.size, |
| uninit_offset: idx_range.start, |
| uninit_size: idx_range.end - idx_range.start, // `Size` subtraction |
| }))) |
| }) |
| } |
| |
| pub fn mark_init(&mut self, range: AllocRange, is_init: bool) { |
| if range.size.bytes() == 0 { |
| return; |
| } |
| assert!(self.mutability == Mutability::Mut); |
| self.init_mask.set_range(range.start, range.end(), is_init); |
| } |
| } |
| |
| /// Run-length encoding of the uninit mask. |
| /// Used to copy parts of a mask multiple times to another allocation. |
| pub struct InitMaskCompressed { |
| /// Whether the first range is initialized. |
| initial: bool, |
| /// The lengths of ranges that are run-length encoded. |
| /// The initialization state of the ranges alternate starting with `initial`. |
| ranges: smallvec::SmallVec<[u64; 1]>, |
| } |
| |
| impl InitMaskCompressed { |
| pub fn no_bytes_init(&self) -> bool { |
| // The `ranges` are run-length encoded and of alternating initialization state. |
| // So if `ranges.len() > 1` then the second block is an initialized range. |
| !self.initial && self.ranges.len() == 1 |
| } |
| } |
| |
| /// Transferring the initialization mask to other allocations. |
| impl<Tag, Extra> Allocation<Tag, Extra> { |
| /// Creates a run-length encoding of the initialization mask; panics if range is empty. |
| /// |
| /// This is essentially a more space-efficient version of |
| /// `InitMask::range_as_init_chunks(...).collect::<Vec<_>>()`. |
| pub fn compress_uninit_range(&self, range: AllocRange) -> InitMaskCompressed { |
| // Since we are copying `size` bytes from `src` to `dest + i * size` (`for i in 0..repeat`), |
| // a naive initialization mask copying algorithm would repeatedly have to read the initialization mask from |
| // the source and write it to the destination. Even if we optimized the memory accesses, |
| // we'd be doing all of this `repeat` times. |
| // Therefore we precompute a compressed version of the initialization mask of the source value and |
| // then write it back `repeat` times without computing any more information from the source. |
| |
| // A precomputed cache for ranges of initialized / uninitialized bits |
| // 0000010010001110 will become |
| // `[5, 1, 2, 1, 3, 3, 1]`, |
| // where each element toggles the state. |
| |
| let mut ranges = smallvec::SmallVec::<[u64; 1]>::new(); |
| |
| let mut chunks = self.init_mask.range_as_init_chunks(range.start, range.end()).peekable(); |
| |
| let initial = chunks.peek().expect("range should be nonempty").is_init(); |
| |
| // Here we rely on `range_as_init_chunks` to yield alternating init/uninit chunks. |
| for chunk in chunks { |
| let len = chunk.range().end.bytes() - chunk.range().start.bytes(); |
| ranges.push(len); |
| } |
| |
| InitMaskCompressed { ranges, initial } |
| } |
| |
| /// Applies multiple instances of the run-length encoding to the initialization mask. |
| pub fn mark_compressed_init_range( |
| &mut self, |
| defined: &InitMaskCompressed, |
| range: AllocRange, |
| repeat: u64, |
| ) { |
| // An optimization where we can just overwrite an entire range of initialization |
| // bits if they are going to be uniformly `1` or `0`. |
| if defined.ranges.len() <= 1 { |
| self.init_mask.set_range_inbounds( |
| range.start, |
| range.start + range.size * repeat, // `Size` operations |
| defined.initial, |
| ); |
| return; |
| } |
| |
| for mut j in 0..repeat { |
| j *= range.size.bytes(); |
| j += range.start.bytes(); |
| let mut cur = defined.initial; |
| for range in &defined.ranges { |
| let old_j = j; |
| j += range; |
| self.init_mask.set_range_inbounds( |
| Size::from_bytes(old_j), |
| Size::from_bytes(j), |
| cur, |
| ); |
| cur = !cur; |
| } |
| } |
| } |
| } |
