Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

1 files changed, 1618 insertions, 0 deletions

diff --git a/vendor/gimli/src/write/op.rs b/vendor/gimli/src/write/op.rs
new file mode 100644
index 0000000..287083b
--- /dev/null
+++ b/vendor/gimli/src/write/op.rs
@@ -0,0 +1,1618 @@
+use alloc::boxed::Box;
+use alloc::vec::Vec;
+
+use crate::common::{Encoding, Register};
+use crate::constants::{self, DwOp};
+use crate::leb128::write::{sleb128_size, uleb128_size};
+use crate::write::{
+    Address, DebugInfoReference, Error, Reference, Result, UnitEntryId, UnitOffsets, Writer,
+};
+
+/// The bytecode for a DWARF expression or location description.
+#[derive(Debug, Default, Clone, PartialEq, Eq, Hash)]
+pub struct Expression {
+    operations: Vec<Operation>,
+}
+
+impl Expression {
+    /// Create an empty expression.
+    #[inline]
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Create an expression from raw bytecode.
+    ///
+    /// This does not support operations that require references, such as `DW_OP_addr`.
+    #[inline]
+    pub fn raw(bytecode: Vec<u8>) -> Self {
+        Expression {
+            operations: vec![Operation::Raw(bytecode)],
+        }
+    }
+
+    /// Add an operation to the expression.
+    ///
+    /// This should only be used for operations that have no explicit operands.
+    pub fn op(&mut self, opcode: DwOp) {
+        self.operations.push(Operation::Simple(opcode));
+    }
+
+    /// Add a `DW_OP_addr` operation to the expression.
+    pub fn op_addr(&mut self, address: Address) {
+        self.operations.push(Operation::Address(address));
+    }
+
+    /// Add a `DW_OP_constu` operation to the expression.
+    ///
+    /// This may be emitted as a smaller equivalent operation.
+    pub fn op_constu(&mut self, value: u64) {
+        self.operations.push(Operation::UnsignedConstant(value));
+    }
+
+    /// Add a `DW_OP_consts` operation to the expression.
+    ///
+    /// This may be emitted as a smaller equivalent operation.
+    pub fn op_consts(&mut self, value: i64) {
+        self.operations.push(Operation::SignedConstant(value));
+    }
+
+    /// Add a `DW_OP_const_type` or `DW_OP_GNU_const_type` operation to the expression.
+    pub fn op_const_type(&mut self, base: UnitEntryId, value: Box<[u8]>) {
+        self.operations.push(Operation::ConstantType(base, value));
+    }
+
+    /// Add a `DW_OP_fbreg` operation to the expression.
+    pub fn op_fbreg(&mut self, offset: i64) {
+        self.operations.push(Operation::FrameOffset(offset));
+    }
+
+    /// Add a `DW_OP_bregx` operation to the expression.
+    ///
+    /// This may be emitted as a smaller equivalent operation.
+    pub fn op_breg(&mut self, register: Register, offset: i64) {
+        self.operations
+            .push(Operation::RegisterOffset(register, offset));
+    }
+
+    /// Add a `DW_OP_regval_type` or `DW_OP_GNU_regval_type` operation to the expression.
+    ///
+    /// This may be emitted as a smaller equivalent operation.
+    pub fn op_regval_type(&mut self, register: Register, base: UnitEntryId) {
+        self.operations
+            .push(Operation::RegisterType(register, base));
+    }
+
+    /// Add a `DW_OP_pick` operation to the expression.
+    ///
+    /// This may be emitted as a `DW_OP_dup` or `DW_OP_over` operation.
+    pub fn op_pick(&mut self, index: u8) {
+        self.operations.push(Operation::Pick(index));
+    }
+
+    /// Add a `DW_OP_deref` operation to the expression.
+    pub fn op_deref(&mut self) {
+        self.operations.push(Operation::Deref { space: false });
+    }
+
+    /// Add a `DW_OP_xderef` operation to the expression.
+    pub fn op_xderef(&mut self) {
+        self.operations.push(Operation::Deref { space: true });
+    }
+
+    /// Add a `DW_OP_deref_size` operation to the expression.
+    pub fn op_deref_size(&mut self, size: u8) {
+        self.operations
+            .push(Operation::DerefSize { size, space: false });
+    }
+
+    /// Add a `DW_OP_xderef_size` operation to the expression.
+    pub fn op_xderef_size(&mut self, size: u8) {
+        self.operations
+            .push(Operation::DerefSize { size, space: true });
+    }
+
+    /// Add a `DW_OP_deref_type` or `DW_OP_GNU_deref_type` operation to the expression.
+    pub fn op_deref_type(&mut self, size: u8, base: UnitEntryId) {
+        self.operations.push(Operation::DerefType {
+            size,
+            base,
+            space: false,
+        });
+    }
+
+    /// Add a `DW_OP_xderef_type` operation to the expression.
+    pub fn op_xderef_type(&mut self, size: u8, base: UnitEntryId) {
+        self.operations.push(Operation::DerefType {
+            size,
+            base,
+            space: true,
+        });
+    }
+
+    /// Add a `DW_OP_plus_uconst` operation to the expression.
+    pub fn op_plus_uconst(&mut self, value: u64) {
+        self.operations.push(Operation::PlusConstant(value));
+    }
+
+    /// Add a `DW_OP_skip` operation to the expression.
+    ///
+    /// Returns the index of the operation. The caller must call `set_target` with
+    /// this index to set the target of the branch.
+    pub fn op_skip(&mut self) -> usize {
+        let index = self.next_index();
+        self.operations.push(Operation::Skip(!0));
+        index
+    }
+
+    /// Add a `DW_OP_bra` operation to the expression.
+    ///
+    /// Returns the index of the operation. The caller must call `set_target` with
+    /// this index to set the target of the branch.
+    pub fn op_bra(&mut self) -> usize {
+        let index = self.next_index();
+        self.operations.push(Operation::Branch(!0));
+        index
+    }
+
+    /// Return the index that will be assigned to the next operation.
+    ///
+    /// This can be passed to `set_target`.
+    #[inline]
+    pub fn next_index(&self) -> usize {
+        self.operations.len()
+    }
+
+    /// Set the target of a `DW_OP_skip` or `DW_OP_bra` operation .
+    pub fn set_target(&mut self, operation: usize, new_target: usize) {
+        debug_assert!(new_target <= self.next_index());
+        debug_assert_ne!(operation, new_target);
+        match self.operations[operation] {
+            Operation::Skip(ref mut target) | Operation::Branch(ref mut target) => {
+                *target = new_target;
+            }
+            _ => unimplemented!(),
+        }
+    }
+
+    /// Add a `DW_OP_call4` operation to the expression.
+    pub fn op_call(&mut self, entry: UnitEntryId) {
+        self.operations.push(Operation::Call(entry));
+    }
+
+    /// Add a `DW_OP_call_ref` operation to the expression.
+    pub fn op_call_ref(&mut self, entry: Reference) {
+        self.operations.push(Operation::CallRef(entry));
+    }
+
+    /// Add a `DW_OP_convert` or `DW_OP_GNU_convert` operation to the expression.
+    ///
+    /// `base` is the DIE of the base type, or `None` for the generic type.
+    pub fn op_convert(&mut self, base: Option<UnitEntryId>) {
+        self.operations.push(Operation::Convert(base));
+    }
+
+    /// Add a `DW_OP_reinterpret` or `DW_OP_GNU_reinterpret` operation to the expression.
+    ///
+    /// `base` is the DIE of the base type, or `None` for the generic type.
+    pub fn op_reinterpret(&mut self, base: Option<UnitEntryId>) {
+        self.operations.push(Operation::Reinterpret(base));
+    }
+
+    /// Add a `DW_OP_entry_value` or `DW_OP_GNU_entry_value` operation to the expression.
+    pub fn op_entry_value(&mut self, expression: Expression) {
+        self.operations.push(Operation::EntryValue(expression));
+    }
+
+    /// Add a `DW_OP_regx` operation to the expression.
+    ///
+    /// This may be emitted as a smaller equivalent operation.
+    pub fn op_reg(&mut self, register: Register) {
+        self.operations.push(Operation::Register(register));
+    }
+
+    /// Add a `DW_OP_implicit_value` operation to the expression.
+    pub fn op_implicit_value(&mut self, data: Box<[u8]>) {
+        self.operations.push(Operation::ImplicitValue(data));
+    }
+
+    /// Add a `DW_OP_implicit_pointer` or `DW_OP_GNU_implicit_pointer` operation to the expression.
+    pub fn op_implicit_pointer(&mut self, entry: Reference, byte_offset: i64) {
+        self.operations
+            .push(Operation::ImplicitPointer { entry, byte_offset });
+    }
+
+    /// Add a `DW_OP_piece` operation to the expression.
+    pub fn op_piece(&mut self, size_in_bytes: u64) {
+        self.operations.push(Operation::Piece { size_in_bytes });
+    }
+
+    /// Add a `DW_OP_bit_piece` operation to the expression.
+    pub fn op_bit_piece(&mut self, size_in_bits: u64, bit_offset: u64) {
+        self.operations.push(Operation::BitPiece {
+            size_in_bits,
+            bit_offset,
+        });
+    }
+
+    /// Add a `DW_OP_GNU_parameter_ref` operation to the expression.
+    pub fn op_gnu_parameter_ref(&mut self, entry: UnitEntryId) {
+        self.operations.push(Operation::ParameterRef(entry));
+    }
+
+    /// Add a `DW_OP_WASM_location 0x0` operation to the expression.
+    pub fn op_wasm_local(&mut self, index: u32) {
+        self.operations.push(Operation::WasmLocal(index));
+    }
+
+    /// Add a `DW_OP_WASM_location 0x1` operation to the expression.
+    pub fn op_wasm_global(&mut self, index: u32) {
+        self.operations.push(Operation::WasmGlobal(index));
+    }
+
+    /// Add a `DW_OP_WASM_location 0x2` operation to the expression.
+    pub fn op_wasm_stack(&mut self, index: u32) {
+        self.operations.push(Operation::WasmStack(index));
+    }
+
+    pub(crate) fn size(&self, encoding: Encoding, unit_offsets: Option<&UnitOffsets>) -> usize {
+        let mut size = 0;
+        for operation in &self.operations {
+            size += operation.size(encoding, unit_offsets);
+        }
+        size
+    }
+
+    pub(crate) fn write<W: Writer>(
+        &self,
+        w: &mut W,
+        mut refs: Option<&mut Vec<DebugInfoReference>>,
+        encoding: Encoding,
+        unit_offsets: Option<&UnitOffsets>,
+    ) -> Result<()> {
+        // TODO: only calculate offsets if needed?
+        let mut offsets = Vec::with_capacity(self.operations.len());
+        let mut offset = w.len();
+        for operation in &self.operations {
+            offsets.push(offset);
+            offset += operation.size(encoding, unit_offsets);
+        }
+        offsets.push(offset);
+        for (operation, offset) in self.operations.iter().zip(offsets.iter().copied()) {
+            debug_assert_eq!(w.len(), offset);
+            operation.write(w, refs.as_deref_mut(), encoding, unit_offsets, &offsets)?;
+        }
+        Ok(())
+    }
+}
+
+/// A single DWARF operation.
+//
+// This type is intentionally not public so that we can change the
+// representation of expressions as needed.
+//
+// Variants are listed in the order they appear in Section 2.5.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+enum Operation {
+    /// Raw bytecode.
+    ///
+    /// Does not support references.
+    Raw(Vec<u8>),
+    /// An operation that has no explicit operands.
+    ///
+    /// Represents:
+    /// - `DW_OP_drop`, `DW_OP_swap`, `DW_OP_rot`
+    /// - `DW_OP_push_object_address`, `DW_OP_form_tls_address`, `DW_OP_call_frame_cfa`
+    /// - `DW_OP_abs`, `DW_OP_and`, `DW_OP_div`, `DW_OP_minus`, `DW_OP_mod`, `DW_OP_mul`,
+    ///   `DW_OP_neg`, `DW_OP_not`, `DW_OP_or`, `DW_OP_plus`, `DW_OP_shl`, `DW_OP_shr`,
+    ///   `DW_OP_shra`, `DW_OP_xor`
+    /// - `DW_OP_le`, `DW_OP_ge`, `DW_OP_eq`, `DW_OP_lt`, `DW_OP_gt`, `DW_OP_ne`
+    /// - `DW_OP_nop`
+    /// - `DW_OP_stack_value`
+    Simple(DwOp),
+    /// Relocate the address if needed, and push it on the stack.
+    ///
+    /// Represents `DW_OP_addr`.
+    Address(Address),
+    /// Push an unsigned constant value on the stack.
+    ///
+    /// Represents `DW_OP_constu`.
+    UnsignedConstant(u64),
+    /// Push a signed constant value on the stack.
+    ///
+    /// Represents `DW_OP_consts`.
+    SignedConstant(i64),
+    /* TODO: requires .debug_addr write support
+    /// Read the address at the given index in `.debug_addr, relocate the address if needed,
+    /// and push it on the stack.
+    ///
+    /// Represents `DW_OP_addrx`.
+    AddressIndex(DebugAddrIndex<Offset>),
+    /// Read the address at the given index in `.debug_addr, and push it on the stack.
+    /// Do not relocate the address.
+    ///
+    /// Represents `DW_OP_constx`.
+    ConstantIndex(DebugAddrIndex<Offset>),
+    */
+    /// Interpret the value bytes as a constant of a given type, and push it on the stack.
+    ///
+    /// Represents `DW_OP_const_type`.
+    ConstantType(UnitEntryId, Box<[u8]>),
+    /// Compute the frame base (using `DW_AT_frame_base`), add the
+    /// given offset, and then push the resulting sum on the stack.
+    ///
+    /// Represents `DW_OP_fbreg`.
+    FrameOffset(i64),
+    /// Find the contents of the given register, add the offset, and then
+    /// push the resulting sum on the stack.
+    ///
+    /// Represents `DW_OP_bregx`.
+    RegisterOffset(Register, i64),
+    /// Interpret the contents of the given register as a value of the given type,
+    /// and push it on the stack.
+    ///
+    /// Represents `DW_OP_regval_type`.
+    RegisterType(Register, UnitEntryId),
+    /// Copy the item at a stack index and push it on top of the stack.
+    ///
+    /// Represents `DW_OP_pick`, `DW_OP_dup`, and `DW_OP_over`.
+    Pick(u8),
+    /// Pop the topmost value of the stack, dereference it, and push the
+    /// resulting value.
+    ///
+    /// Represents `DW_OP_deref` and `DW_OP_xderef`.
+    Deref {
+        /// True if the dereference operation takes an address space
+        /// argument from the stack; false otherwise.
+        space: bool,
+    },
+    /// Pop the topmost value of the stack, dereference it to obtain a value
+    /// of the given size, and push the resulting value.
+    ///
+    /// Represents `DW_OP_deref_size` and `DW_OP_xderef_size`.
+    DerefSize {
+        /// True if the dereference operation takes an address space
+        /// argument from the stack; false otherwise.
+        space: bool,
+        /// The size of the data to dereference.
+        size: u8,
+    },
+    /// Pop the topmost value of the stack, dereference it to obtain a value
+    /// of the given type, and push the resulting value.
+    ///
+    /// Represents `DW_OP_deref_type` and `DW_OP_xderef_type`.
+    DerefType {
+        /// True if the dereference operation takes an address space
+        /// argument from the stack; false otherwise.
+        space: bool,
+        /// The size of the data to dereference.
+        size: u8,
+        /// The DIE of the base type, or `None` for the generic type.
+        base: UnitEntryId,
+    },
+    /// Add an unsigned constant to the topmost value on the stack.
+    ///
+    /// Represents `DW_OP_plus_uconst`.
+    PlusConstant(u64),
+    /// Unconditional branch to the target location.
+    ///
+    /// The value is the index within the expression of the operation to branch to.
+    /// This will be converted to a relative offset when writing.
+    ///
+    /// Represents `DW_OP_skip`.
+    Skip(usize),
+    /// Branch to the target location if the top of stack is nonzero.
+    ///
+    /// The value is the index within the expression of the operation to branch to.
+    /// This will be converted to a relative offset when writing.
+    ///
+    /// Represents `DW_OP_bra`.
+    Branch(usize),
+    /// Evaluate a DWARF expression as a subroutine.
+    ///
+    /// The expression comes from the `DW_AT_location` attribute of the indicated DIE.
+    ///
+    /// Represents `DW_OP_call4`.
+    Call(UnitEntryId),
+    /// Evaluate an external DWARF expression as a subroutine.
+    ///
+    /// The expression comes from the `DW_AT_location` attribute of the indicated DIE,
+    /// which may be in another compilation unit or shared object.
+    ///
+    /// Represents `DW_OP_call_ref`.
+    CallRef(Reference),
+    /// Pop the top stack entry, convert it to a different type, and push it on the stack.
+    ///
+    /// Represents `DW_OP_convert`.
+    Convert(Option<UnitEntryId>),
+    /// Pop the top stack entry, reinterpret the bits in its value as a different type,
+    /// and push it on the stack.
+    ///
+    /// Represents `DW_OP_reinterpret`.
+    Reinterpret(Option<UnitEntryId>),
+    /// Evaluate an expression at the entry to the current subprogram, and push it on the stack.
+    ///
+    /// Represents `DW_OP_entry_value`.
+    EntryValue(Expression),
+    // FIXME: EntryRegister
+    /// Indicate that this piece's location is in the given register.
+    ///
+    /// Completes the piece or expression.
+    ///
+    /// Represents `DW_OP_regx`.
+    Register(Register),
+    /// The object has no location, but has a known constant value.
+    ///
+    /// Completes the piece or expression.
+    ///
+    /// Represents `DW_OP_implicit_value`.
+    ImplicitValue(Box<[u8]>),
+    /// The object is a pointer to a value which has no actual location, such as
+    /// an implicit value or a stack value.
+    ///
+    /// Completes the piece or expression.
+    ///
+    /// Represents `DW_OP_implicit_pointer`.
+    ImplicitPointer {
+        /// The DIE of the value that this is an implicit pointer into.
+        entry: Reference,
+        /// The byte offset into the value that the implicit pointer points to.
+        byte_offset: i64,
+    },
+    /// Terminate a piece.
+    ///
+    /// Represents `DW_OP_piece`.
+    Piece {
+        /// The size of this piece in bytes.
+        size_in_bytes: u64,
+    },
+    /// Terminate a piece with a size in bits.
+    ///
+    /// Represents `DW_OP_bit_piece`.
+    BitPiece {
+        /// The size of this piece in bits.
+        size_in_bits: u64,
+        /// The bit offset of this piece.
+        bit_offset: u64,
+    },
+    /// This represents a parameter that was optimized out.
+    ///
+    /// The entry is the definition of the parameter, and is matched to
+    /// the `DW_TAG_GNU_call_site_parameter` in the caller that also
+    /// points to the same definition of the parameter.
+    ///
+    /// Represents `DW_OP_GNU_parameter_ref`.
+    ParameterRef(UnitEntryId),
+    /// The index of a local in the currently executing function.
+    ///
+    /// Represents `DW_OP_WASM_location 0x00`.
+    WasmLocal(u32),
+    /// The index of a global.
+    ///
+    /// Represents `DW_OP_WASM_location 0x01`.
+    WasmGlobal(u32),
+    /// The index of an item on the operand stack.
+    ///
+    /// Represents `DW_OP_WASM_location 0x02`.
+    WasmStack(u32),
+}
+
+impl Operation {
+    fn size(&self, encoding: Encoding, unit_offsets: Option<&UnitOffsets>) -> usize {
+        let base_size = |base| {
+            // Errors are handled during writes.
+            match unit_offsets {
+                Some(offsets) => uleb128_size(offsets.unit_offset(base)),
+                None => 0,
+            }
+        };
+        1 + match *self {
+            Operation::Raw(ref bytecode) => return bytecode.len(),
+            Operation::Simple(_) => 0,
+            Operation::Address(_) => encoding.address_size as usize,
+            Operation::UnsignedConstant(value) => {
+                if value < 32 {
+                    0
+                } else {
+                    uleb128_size(value)
+                }
+            }
+            Operation::SignedConstant(value) => sleb128_size(value),
+            Operation::ConstantType(base, ref value) => base_size(base) + 1 + value.len(),
+            Operation::FrameOffset(offset) => sleb128_size(offset),
+            Operation::RegisterOffset(register, offset) => {
+                if register.0 < 32 {
+                    sleb128_size(offset)
+                } else {
+                    uleb128_size(register.0.into()) + sleb128_size(offset)
+                }
+            }
+            Operation::RegisterType(register, base) => {
+                uleb128_size(register.0.into()) + base_size(base)
+            }
+            Operation::Pick(index) => {
+                if index > 1 {
+                    1
+                } else {
+                    0
+                }
+            }
+            Operation::Deref { .. } => 0,
+            Operation::DerefSize { .. } => 1,
+            Operation::DerefType { base, .. } => 1 + base_size(base),
+            Operation::PlusConstant(value) => uleb128_size(value),
+            Operation::Skip(_) => 2,
+            Operation::Branch(_) => 2,
+            Operation::Call(_) => 4,
+            Operation::CallRef(_) => encoding.format.word_size() as usize,
+            Operation::Convert(base) => match base {
+                Some(base) => base_size(base),
+                None => 1,
+            },
+            Operation::Reinterpret(base) => match base {
+                Some(base) => base_size(base),
+                None => 1,
+            },
+            Operation::EntryValue(ref expression) => {
+                let length = expression.size(encoding, unit_offsets);
+                uleb128_size(length as u64) + length
+            }
+            Operation::Register(register) => {
+                if register.0 < 32 {
+                    0
+                } else {
+                    uleb128_size(register.0.into())
+                }
+            }
+            Operation::ImplicitValue(ref data) => uleb128_size(data.len() as u64) + data.len(),
+            Operation::ImplicitPointer { byte_offset, .. } => {
+                encoding.format.word_size() as usize + sleb128_size(byte_offset)
+            }
+            Operation::Piece { size_in_bytes } => uleb128_size(size_in_bytes),
+            Operation::BitPiece {
+                size_in_bits,
+                bit_offset,
+            } => uleb128_size(size_in_bits) + uleb128_size(bit_offset),
+            Operation::ParameterRef(_) => 4,
+            Operation::WasmLocal(index)
+            | Operation::WasmGlobal(index)
+            | Operation::WasmStack(index) => 1 + uleb128_size(index.into()),
+        }
+    }
+
+    pub(crate) fn write<W: Writer>(
+        &self,
+        w: &mut W,
+        refs: Option<&mut Vec<DebugInfoReference>>,
+        encoding: Encoding,
+        unit_offsets: Option<&UnitOffsets>,
+        offsets: &[usize],
+    ) -> Result<()> {
+        let entry_offset = |entry| match unit_offsets {
+            Some(offsets) => {
+                let offset = offsets.unit_offset(entry);
+                if offset == 0 {
+                    Err(Error::UnsupportedExpressionForwardReference)
+                } else {
+                    Ok(offset)
+                }
+            }
+            None => Err(Error::UnsupportedCfiExpressionReference),
+        };
+        match *self {
+            Operation::Raw(ref bytecode) => w.write(bytecode)?,
+            Operation::Simple(opcode) => w.write_u8(opcode.0)?,
+            Operation::Address(address) => {
+                w.write_u8(constants::DW_OP_addr.0)?;
+                w.write_address(address, encoding.address_size)?;
+            }
+            Operation::UnsignedConstant(value) => {
+                if value < 32 {
+                    w.write_u8(constants::DW_OP_lit0.0 + value as u8)?;
+                } else {
+                    w.write_u8(constants::DW_OP_constu.0)?;
+                    w.write_uleb128(value)?;
+                }
+            }
+            Operation::SignedConstant(value) => {
+                w.write_u8(constants::DW_OP_consts.0)?;
+                w.write_sleb128(value)?;
+            }
+            Operation::ConstantType(base, ref value) => {
+                if encoding.version >= 5 {
+                    w.write_u8(constants::DW_OP_const_type.0)?;
+                } else {
+                    w.write_u8(constants::DW_OP_GNU_const_type.0)?;
+                }
+                w.write_uleb128(entry_offset(base)?)?;
+                w.write_udata(value.len() as u64, 1)?;
+                w.write(value)?;
+            }
+            Operation::FrameOffset(offset) => {
+                w.write_u8(constants::DW_OP_fbreg.0)?;
+                w.write_sleb128(offset)?;
+            }
+            Operation::RegisterOffset(register, offset) => {
+                if register.0 < 32 {
+                    w.write_u8(constants::DW_OP_breg0.0 + register.0 as u8)?;
+                } else {
+                    w.write_u8(constants::DW_OP_bregx.0)?;
+                    w.write_uleb128(register.0.into())?;
+                }
+                w.write_sleb128(offset)?;
+            }
+            Operation::RegisterType(register, base) => {
+                if encoding.version >= 5 {
+                    w.write_u8(constants::DW_OP_regval_type.0)?;
+                } else {
+                    w.write_u8(constants::DW_OP_GNU_regval_type.0)?;
+                }
+                w.write_uleb128(register.0.into())?;
+                w.write_uleb128(entry_offset(base)?)?;
+            }
+            Operation::Pick(index) => match index {
+                0 => w.write_u8(constants::DW_OP_dup.0)?,
+                1 => w.write_u8(constants::DW_OP_over.0)?,
+                _ => {
+                    w.write_u8(constants::DW_OP_pick.0)?;
+                    w.write_u8(index)?;
+                }
+            },
+            Operation::Deref { space } => {
+                if space {
+                    w.write_u8(constants::DW_OP_xderef.0)?;
+                } else {
+                    w.write_u8(constants::DW_OP_deref.0)?;
+                }
+            }
+            Operation::DerefSize { space, size } => {
+                if space {
+                    w.write_u8(constants::DW_OP_xderef_size.0)?;
+                } else {
+                    w.write_u8(constants::DW_OP_deref_size.0)?;
+                }
+                w.write_u8(size)?;
+            }
+            Operation::DerefType { space, size, base } => {
+                if space {
+                    w.write_u8(constants::DW_OP_xderef_type.0)?;
+                } else {
+                    if encoding.version >= 5 {
+                        w.write_u8(constants::DW_OP_deref_type.0)?;
+                    } else {
+                        w.write_u8(constants::DW_OP_GNU_deref_type.0)?;
+                    }
+                }
+                w.write_u8(size)?;
+                w.write_uleb128(entry_offset(base)?)?;
+            }
+            Operation::PlusConstant(value) => {
+                w.write_u8(constants::DW_OP_plus_uconst.0)?;
+                w.write_uleb128(value)?;
+            }
+            Operation::Skip(target) => {
+                w.write_u8(constants::DW_OP_skip.0)?;
+                let offset = offsets[target] as i64 - (w.len() as i64 + 2);
+                w.write_sdata(offset, 2)?;
+            }
+            Operation::Branch(target) => {
+                w.write_u8(constants::DW_OP_bra.0)?;
+                let offset = offsets[target] as i64 - (w.len() as i64 + 2);
+                w.write_sdata(offset, 2)?;
+            }
+            Operation::Call(entry) => {
+                w.write_u8(constants::DW_OP_call4.0)?;
+                // TODO: this probably won't work in practice, because we may
+                // only know the offsets of base type DIEs at this point.
+                w.write_udata(entry_offset(entry)?, 4)?;
+            }
+            Operation::CallRef(entry) => {
+                w.write_u8(constants::DW_OP_call_ref.0)?;
+                let size = encoding.format.word_size();
+                match entry {
+                    Reference::Symbol(symbol) => w.write_reference(symbol, size)?,
+                    Reference::Entry(unit, entry) => {
+                        let refs = refs.ok_or(Error::InvalidReference)?;
+                        refs.push(DebugInfoReference {
+                            offset: w.len(),
+                            unit,
+                            entry,
+                            size,
+                        });
+                        w.write_udata(0, size)?;
+                    }
+                }
+            }
+            Operation::Convert(base) => {
+                if encoding.version >= 5 {
+                    w.write_u8(constants::DW_OP_convert.0)?;
+                } else {
+                    w.write_u8(constants::DW_OP_GNU_convert.0)?;
+                }
+                match base {
+                    Some(base) => w.write_uleb128(entry_offset(base)?)?,
+                    None => w.write_u8(0)?,
+                }
+            }
+            Operation::Reinterpret(base) => {
+                if encoding.version >= 5 {
+                    w.write_u8(constants::DW_OP_reinterpret.0)?;
+                } else {
+                    w.write_u8(constants::DW_OP_GNU_reinterpret.0)?;
+                }
+                match base {
+                    Some(base) => w.write_uleb128(entry_offset(base)?)?,
+                    None => w.write_u8(0)?,
+                }
+            }
+            Operation::EntryValue(ref expression) => {
+                if encoding.version >= 5 {
+                    w.write_u8(constants::DW_OP_entry_value.0)?;
+                } else {
+                    w.write_u8(constants::DW_OP_GNU_entry_value.0)?;
+                }
+                let length = expression.size(encoding, unit_offsets);
+                w.write_uleb128(length as u64)?;
+                expression.write(w, refs, encoding, unit_offsets)?;
+            }
+            Operation::Register(register) => {
+                if register.0 < 32 {
+                    w.write_u8(constants::DW_OP_reg0.0 + register.0 as u8)?;
+                } else {
+                    w.write_u8(constants::DW_OP_regx.0)?;
+                    w.write_uleb128(register.0.into())?;
+                }
+            }
+            Operation::ImplicitValue(ref data) => {
+                w.write_u8(constants::DW_OP_implicit_value.0)?;
+                w.write_uleb128(data.len() as u64)?;
+                w.write(data)?;
+            }
+            Operation::ImplicitPointer { entry, byte_offset } => {
+                if encoding.version >= 5 {
+                    w.write_u8(constants::DW_OP_implicit_pointer.0)?;
+                } else {
+                    w.write_u8(constants::DW_OP_GNU_implicit_pointer.0)?;
+                }
+                let size = if encoding.version == 2 {
+                    encoding.address_size
+                } else {
+                    encoding.format.word_size()
+                };
+                match entry {
+                    Reference::Symbol(symbol) => {
+                        w.write_reference(symbol, size)?;
+                    }
+                    Reference::Entry(unit, entry) => {
+                        let refs = refs.ok_or(Error::InvalidReference)?;
+                        refs.push(DebugInfoReference {
+                            offset: w.len(),
+                            unit,
+                            entry,
+                            size,
+                        });
+                        w.write_udata(0, size)?;
+                    }
+                }
+                w.write_sleb128(byte_offset)?;
+            }
+            Operation::Piece { size_in_bytes } => {
+                w.write_u8(constants::DW_OP_piece.0)?;
+                w.write_uleb128(size_in_bytes)?;
+            }
+            Operation::BitPiece {
+                size_in_bits,
+                bit_offset,
+            } => {
+                w.write_u8(constants::DW_OP_bit_piece.0)?;
+                w.write_uleb128(size_in_bits)?;
+                w.write_uleb128(bit_offset)?;
+            }
+            Operation::ParameterRef(entry) => {
+                w.write_u8(constants::DW_OP_GNU_parameter_ref.0)?;
+                w.write_udata(entry_offset(entry)?, 4)?;
+            }
+            Operation::WasmLocal(index) => {
+                w.write(&[constants::DW_OP_WASM_location.0, 0])?;
+                w.write_uleb128(index.into())?;
+            }
+            Operation::WasmGlobal(index) => {
+                w.write(&[constants::DW_OP_WASM_location.0, 1])?;
+                w.write_uleb128(index.into())?;
+            }
+            Operation::WasmStack(index) => {
+                w.write(&[constants::DW_OP_WASM_location.0, 2])?;
+                w.write_uleb128(index.into())?;
+            }
+        }
+        Ok(())
+    }
+}
+
+#[cfg(feature = "read")]
+pub(crate) mod convert {
+    use super::*;
+    use crate::common::UnitSectionOffset;
+    use crate::read::{self, Reader};
+    use crate::write::{ConvertError, ConvertResult, UnitEntryId, UnitId};
+    use std::collections::HashMap;
+
+    impl Expression {
+        /// Create an expression from the input expression.
+        pub fn from<R: Reader<Offset = usize>>(
+            from_expression: read::Expression<R>,
+            encoding: Encoding,
+            dwarf: Option<&read::Dwarf<R>>,
+            unit: Option<&read::Unit<R>>,
+            entry_ids: Option<&HashMap<UnitSectionOffset, (UnitId, UnitEntryId)>>,
+            convert_address: &dyn Fn(u64) -> Option<Address>,
+        ) -> ConvertResult<Expression> {
+            let convert_unit_offset = |offset: read::UnitOffset| -> ConvertResult<_> {
+                let entry_ids = entry_ids.ok_or(ConvertError::UnsupportedOperation)?;
+                let unit = unit.ok_or(ConvertError::UnsupportedOperation)?;
+                let id = entry_ids
+                    .get(&offset.to_unit_section_offset(unit))
+                    .ok_or(ConvertError::InvalidUnitRef)?;
+                Ok(id.1)
+            };
+            let convert_debug_info_offset = |offset| -> ConvertResult<_> {
+                // TODO: support relocations
+                let entry_ids = entry_ids.ok_or(ConvertError::UnsupportedOperation)?;
+                let id = entry_ids
+                    .get(&UnitSectionOffset::DebugInfoOffset(offset))
+                    .ok_or(ConvertError::InvalidDebugInfoRef)?;
+                Ok(Reference::Entry(id.0, id.1))
+            };
+
+            // Calculate offsets for use in branch/skip operations.
+            let mut offsets = Vec::new();
+            let mut offset = 0;
+            let mut from_operations = from_expression.clone().operations(encoding);
+            while from_operations.next()?.is_some() {
+                offsets.push(offset);
+                offset = from_operations.offset_from(&from_expression);
+            }
+            offsets.push(from_expression.0.len());
+
+            let mut from_operations = from_expression.clone().operations(encoding);
+            let mut operations = Vec::new();
+            while let Some(from_operation) = from_operations.next()? {
+                let operation = match from_operation {
+                    read::Operation::Deref {
+                        base_type,
+                        size,
+                        space,
+                    } => {
+                        if base_type.0 != 0 {
+                            let base = convert_unit_offset(base_type)?;
+                            Operation::DerefType { space, size, base }
+                        } else if size != encoding.address_size {
+                            Operation::DerefSize { space, size }
+                        } else {
+                            Operation::Deref { space }
+                        }
+                    }
+                    read::Operation::Drop => Operation::Simple(constants::DW_OP_drop),
+                    read::Operation::Pick { index } => Operation::Pick(index),
+                    read::Operation::Swap => Operation::Simple(constants::DW_OP_swap),
+                    read::Operation::Rot => Operation::Simple(constants::DW_OP_rot),
+                    read::Operation::Abs => Operation::Simple(constants::DW_OP_abs),
+                    read::Operation::And => Operation::Simple(constants::DW_OP_and),
+                    read::Operation::Div => Operation::Simple(constants::DW_OP_div),
+                    read::Operation::Minus => Operation::Simple(constants::DW_OP_minus),
+                    read::Operation::Mod => Operation::Simple(constants::DW_OP_mod),
+                    read::Operation::Mul => Operation::Simple(constants::DW_OP_mul),
+                    read::Operation::Neg => Operation::Simple(constants::DW_OP_neg),
+                    read::Operation::Not => Operation::Simple(constants::DW_OP_not),
+                    read::Operation::Or => Operation::Simple(constants::DW_OP_or),
+                    read::Operation::Plus => Operation::Simple(constants::DW_OP_plus),
+                    read::Operation::PlusConstant { value } => Operation::PlusConstant(value),
+                    read::Operation::Shl => Operation::Simple(constants::DW_OP_shl),
+                    read::Operation::Shr => Operation::Simple(constants::DW_OP_shr),
+                    read::Operation::Shra => Operation::Simple(constants::DW_OP_shra),
+                    read::Operation::Xor => Operation::Simple(constants::DW_OP_xor),
+                    read::Operation::Eq => Operation::Simple(constants::DW_OP_eq),
+                    read::Operation::Ge => Operation::Simple(constants::DW_OP_ge),
+                    read::Operation::Gt => Operation::Simple(constants::DW_OP_gt),
+                    read::Operation::Le => Operation::Simple(constants::DW_OP_le),
+                    read::Operation::Lt => Operation::Simple(constants::DW_OP_lt),
+                    read::Operation::Ne => Operation::Simple(constants::DW_OP_ne),
+                    read::Operation::Bra { target } => {
+                        let offset = from_operations
+                            .offset_from(&from_expression)
+                            .wrapping_add(i64::from(target) as usize);
+                        let index = offsets
+                            .binary_search(&offset)
+                            .map_err(|_| ConvertError::InvalidBranchTarget)?;
+                        Operation::Branch(index)
+                    }
+                    read::Operation::Skip { target } => {
+                        let offset = from_operations
+                            .offset_from(&from_expression)
+                            .wrapping_add(i64::from(target) as usize);
+                        let index = offsets
+                            .binary_search(&offset)
+                            .map_err(|_| ConvertError::InvalidBranchTarget)?;
+                        Operation::Skip(index)
+                    }
+                    read::Operation::UnsignedConstant { value } => {
+                        Operation::UnsignedConstant(value)
+                    }
+                    read::Operation::SignedConstant { value } => Operation::SignedConstant(value),
+                    read::Operation::Register { register } => Operation::Register(register),
+                    read::Operation::RegisterOffset {
+                        register,
+                        offset,
+                        base_type,
+                    } => {
+                        if base_type.0 != 0 {
+                            Operation::RegisterType(register, convert_unit_offset(base_type)?)
+                        } else {
+                            Operation::RegisterOffset(register, offset)
+                        }
+                    }
+                    read::Operation::FrameOffset { offset } => Operation::FrameOffset(offset),
+                    read::Operation::Nop => Operation::Simple(constants::DW_OP_nop),
+                    read::Operation::PushObjectAddress => {
+                        Operation::Simple(constants::DW_OP_push_object_address)
+                    }
+                    read::Operation::Call { offset } => match offset {
+                        read::DieReference::UnitRef(offset) => {
+                            Operation::Call(convert_unit_offset(offset)?)
+                        }
+                        read::DieReference::DebugInfoRef(offset) => {
+                            Operation::CallRef(convert_debug_info_offset(offset)?)
+                        }
+                    },
+                    read::Operation::TLS => Operation::Simple(constants::DW_OP_form_tls_address),
+                    read::Operation::CallFrameCFA => {
+                        Operation::Simple(constants::DW_OP_call_frame_cfa)
+                    }
+                    read::Operation::Piece {
+                        size_in_bits,
+                        bit_offset: None,
+                    } => Operation::Piece {
+                        size_in_bytes: size_in_bits / 8,
+                    },
+                    read::Operation::Piece {
+                        size_in_bits,
+                        bit_offset: Some(bit_offset),
+                    } => Operation::BitPiece {
+                        size_in_bits,
+                        bit_offset,
+                    },
+                    read::Operation::ImplicitValue { data } => {
+                        Operation::ImplicitValue(data.to_slice()?.into_owned().into())
+                    }
+                    read::Operation::StackValue => Operation::Simple(constants::DW_OP_stack_value),
+                    read::Operation::ImplicitPointer { value, byte_offset } => {
+                        let entry = convert_debug_info_offset(value)?;
+                        Operation::ImplicitPointer { entry, byte_offset }
+                    }
+                    read::Operation::EntryValue { expression } => {
+                        let expression = Expression::from(
+                            read::Expression(expression),
+                            encoding,
+                            dwarf,
+                            unit,
+                            entry_ids,
+                            convert_address,
+                        )?;
+                        Operation::EntryValue(expression)
+                    }
+                    read::Operation::ParameterRef { offset } => {
+                        let entry = convert_unit_offset(offset)?;
+                        Operation::ParameterRef(entry)
+                    }
+                    read::Operation::Address { address } => {
+                        let address =
+                            convert_address(address).ok_or(ConvertError::InvalidAddress)?;
+                        Operation::Address(address)
+                    }
+                    read::Operation::AddressIndex { index } => {
+                        let dwarf = dwarf.ok_or(ConvertError::UnsupportedOperation)?;
+                        let unit = unit.ok_or(ConvertError::UnsupportedOperation)?;
+                        let val = dwarf.address(unit, index)?;
+                        let address = convert_address(val).ok_or(ConvertError::InvalidAddress)?;
+                        Operation::Address(address)
+                    }
+                    read::Operation::ConstantIndex { index } => {
+                        let dwarf = dwarf.ok_or(ConvertError::UnsupportedOperation)?;
+                        let unit = unit.ok_or(ConvertError::UnsupportedOperation)?;
+                        let val = dwarf.address(unit, index)?;
+                        Operation::UnsignedConstant(val)
+                    }
+                    read::Operation::TypedLiteral { base_type, value } => {
+                        let entry = convert_unit_offset(base_type)?;
+                        Operation::ConstantType(entry, value.to_slice()?.into_owned().into())
+                    }
+                    read::Operation::Convert { base_type } => {
+                        if base_type.0 == 0 {
+                            Operation::Convert(None)
+                        } else {
+                            let entry = convert_unit_offset(base_type)?;
+                            Operation::Convert(Some(entry))
+                        }
+                    }
+                    read::Operation::Reinterpret { base_type } => {
+                        if base_type.0 == 0 {
+                            Operation::Reinterpret(None)
+                        } else {
+                            let entry = convert_unit_offset(base_type)?;
+                            Operation::Reinterpret(Some(entry))
+                        }
+                    }
+                    read::Operation::WasmLocal { index } => Operation::WasmLocal(index),
+                    read::Operation::WasmGlobal { index } => Operation::WasmGlobal(index),
+                    read::Operation::WasmStack { index } => Operation::WasmStack(index),
+                };
+                operations.push(operation);
+            }
+            Ok(Expression { operations })
+        }
+    }
+}
+
+#[cfg(test)]
+#[cfg(feature = "read")]
+mod tests {
+    use super::*;
+    use crate::common::{
+        DebugAbbrevOffset, DebugAddrBase, DebugInfoOffset, DebugLocListsBase, DebugRngListsBase,
+        DebugStrOffsetsBase, Format, SectionId,
+    };
+    use crate::read;
+    use crate::write::{
+        DebugLineStrOffsets, DebugStrOffsets, EndianVec, LineProgram, Sections, Unit, UnitTable,
+    };
+    use crate::LittleEndian;
+    use std::collections::HashMap;
+    use std::sync::Arc;
+
+    #[test]
+    fn test_operation() {
+        for &version in &[3, 4, 5] {
+            for &address_size in &[4, 8] {
+                for &format in &[Format::Dwarf32, Format::Dwarf64] {
+                    let encoding = Encoding {
+                        format,
+                        version,
+                        address_size,
+                    };
+
+                    let mut units = UnitTable::default();
+                    let unit_id = units.add(Unit::new(encoding, LineProgram::none()));
+                    let unit = units.get_mut(unit_id);
+                    let entry_id = unit.add(unit.root(), constants::DW_TAG_base_type);
+                    let reference = Reference::Entry(unit_id, entry_id);
+
+                    let mut sections = Sections::new(EndianVec::new(LittleEndian));
+                    let debug_line_str_offsets = DebugLineStrOffsets::none();
+                    let debug_str_offsets = DebugStrOffsets::none();
+                    let debug_info_offsets = units
+                        .write(&mut sections, &debug_line_str_offsets, &debug_str_offsets)
+                        .unwrap();
+                    let unit_offsets = debug_info_offsets.unit_offsets(unit_id);
+                    let debug_info_offset = unit_offsets.debug_info_offset(entry_id);
+                    let entry_offset =
+                        read::UnitOffset(unit_offsets.unit_offset(entry_id) as usize);
+
+                    let mut reg_expression = Expression::new();
+                    reg_expression.op_reg(Register(23));
+
+                    let operations: &[(&dyn Fn(&mut Expression), Operation, read::Operation<_>)] =
+                        &[
+                            (
+                                &|x| x.op_deref(),
+                                Operation::Deref { space: false },
+                                read::Operation::Deref {
+                                    base_type: read::UnitOffset(0),
+                                    size: address_size,
+                                    space: false,
+                                },
+                            ),
+                            (
+                                &|x| x.op_xderef(),
+                                Operation::Deref { space: true },
+                                read::Operation::Deref {
+                                    base_type: read::UnitOffset(0),
+                                    size: address_size,
+                                    space: true,
+                                },
+                            ),
+                            (
+                                &|x| x.op_deref_size(2),
+                                Operation::DerefSize {
+                                    space: false,
+                                    size: 2,
+                                },
+                                read::Operation::Deref {
+                                    base_type: read::UnitOffset(0),
+                                    size: 2,
+                                    space: false,
+                                },
+                            ),
+                            (
+                                &|x| x.op_xderef_size(2),
+                                Operation::DerefSize {
+                                    space: true,
+                                    size: 2,
+                                },
+                                read::Operation::Deref {
+                                    base_type: read::UnitOffset(0),
+                                    size: 2,
+                                    space: true,
+                                },
+                            ),
+                            (
+                                &|x| x.op_deref_type(2, entry_id),
+                                Operation::DerefType {
+                                    space: false,
+                                    size: 2,
+                                    base: entry_id,
+                                },
+                                read::Operation::Deref {
+                                    base_type: entry_offset,
+                                    size: 2,
+                                    space: false,
+                                },
+                            ),
+                            (
+                                &|x| x.op_xderef_type(2, entry_id),
+                                Operation::DerefType {
+                                    space: true,
+                                    size: 2,
+                                    base: entry_id,
+                                },
+                                read::Operation::Deref {
+                                    base_type: entry_offset,
+                                    size: 2,
+                                    space: true,
+                                },
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_drop),
+                                Operation::Simple(constants::DW_OP_drop),
+                                read::Operation::Drop,
+                            ),
+                            (
+                                &|x| x.op_pick(0),
+                                Operation::Pick(0),
+                                read::Operation::Pick { index: 0 },
+                            ),
+                            (
+                                &|x| x.op_pick(1),
+                                Operation::Pick(1),
+                                read::Operation::Pick { index: 1 },
+                            ),
+                            (
+                                &|x| x.op_pick(2),
+                                Operation::Pick(2),
+                                read::Operation::Pick { index: 2 },
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_swap),
+                                Operation::Simple(constants::DW_OP_swap),
+                                read::Operation::Swap,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_rot),
+                                Operation::Simple(constants::DW_OP_rot),
+                                read::Operation::Rot,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_abs),
+                                Operation::Simple(constants::DW_OP_abs),
+                                read::Operation::Abs,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_and),
+                                Operation::Simple(constants::DW_OP_and),
+                                read::Operation::And,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_div),
+                                Operation::Simple(constants::DW_OP_div),
+                                read::Operation::Div,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_minus),
+                                Operation::Simple(constants::DW_OP_minus),
+                                read::Operation::Minus,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_mod),
+                                Operation::Simple(constants::DW_OP_mod),
+                                read::Operation::Mod,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_mul),
+                                Operation::Simple(constants::DW_OP_mul),
+                                read::Operation::Mul,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_neg),
+                                Operation::Simple(constants::DW_OP_neg),
+                                read::Operation::Neg,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_not),
+                                Operation::Simple(constants::DW_OP_not),
+                                read::Operation::Not,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_or),
+                                Operation::Simple(constants::DW_OP_or),
+                                read::Operation::Or,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_plus),
+                                Operation::Simple(constants::DW_OP_plus),
+                                read::Operation::Plus,
+                            ),
+                            (
+                                &|x| x.op_plus_uconst(23),
+                                Operation::PlusConstant(23),
+                                read::Operation::PlusConstant { value: 23 },
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_shl),
+                                Operation::Simple(constants::DW_OP_shl),
+                                read::Operation::Shl,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_shr),
+                                Operation::Simple(constants::DW_OP_shr),
+                                read::Operation::Shr,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_shra),
+                                Operation::Simple(constants::DW_OP_shra),
+                                read::Operation::Shra,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_xor),
+                                Operation::Simple(constants::DW_OP_xor),
+                                read::Operation::Xor,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_eq),
+                                Operation::Simple(constants::DW_OP_eq),
+                                read::Operation::Eq,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_ge),
+                                Operation::Simple(constants::DW_OP_ge),
+                                read::Operation::Ge,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_gt),
+                                Operation::Simple(constants::DW_OP_gt),
+                                read::Operation::Gt,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_le),
+                                Operation::Simple(constants::DW_OP_le),
+                                read::Operation::Le,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_lt),
+                                Operation::Simple(constants::DW_OP_lt),
+                                read::Operation::Lt,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_ne),
+                                Operation::Simple(constants::DW_OP_ne),
+                                read::Operation::Ne,
+                            ),
+                            (
+                                &|x| x.op_constu(23),
+                                Operation::UnsignedConstant(23),
+                                read::Operation::UnsignedConstant { value: 23 },
+                            ),
+                            (
+                                &|x| x.op_consts(-23),
+                                Operation::SignedConstant(-23),
+                                read::Operation::SignedConstant { value: -23 },
+                            ),
+                            (
+                                &|x| x.op_reg(Register(23)),
+                                Operation::Register(Register(23)),
+                                read::Operation::Register {
+                                    register: Register(23),
+                                },
+                            ),
+                            (
+                                &|x| x.op_reg(Register(123)),
+                                Operation::Register(Register(123)),
+                                read::Operation::Register {
+                                    register: Register(123),
+                                },
+                            ),
+                            (
+                                &|x| x.op_breg(Register(23), 34),
+                                Operation::RegisterOffset(Register(23), 34),
+                                read::Operation::RegisterOffset {
+                                    register: Register(23),
+                                    offset: 34,
+                                    base_type: read::UnitOffset(0),
+                                },
+                            ),
+                            (
+                                &|x| x.op_breg(Register(123), 34),
+                                Operation::RegisterOffset(Register(123), 34),
+                                read::Operation::RegisterOffset {
+                                    register: Register(123),
+                                    offset: 34,
+                                    base_type: read::UnitOffset(0),
+                                },
+                            ),
+                            (
+                                &|x| x.op_regval_type(Register(23), entry_id),
+                                Operation::RegisterType(Register(23), entry_id),
+                                read::Operation::RegisterOffset {
+                                    register: Register(23),
+                                    offset: 0,
+                                    base_type: entry_offset,
+                                },
+                            ),
+                            (
+                                &|x| x.op_fbreg(34),
+                                Operation::FrameOffset(34),
+                                read::Operation::FrameOffset { offset: 34 },
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_nop),
+                                Operation::Simple(constants::DW_OP_nop),
+                                read::Operation::Nop,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_push_object_address),
+                                Operation::Simple(constants::DW_OP_push_object_address),
+                                read::Operation::PushObjectAddress,
+                            ),
+                            (
+                                &|x| x.op_call(entry_id),
+                                Operation::Call(entry_id),
+                                read::Operation::Call {
+                                    offset: read::DieReference::UnitRef(entry_offset),
+                                },
+                            ),
+                            (
+                                &|x| x.op_call_ref(reference),
+                                Operation::CallRef(reference),
+                                read::Operation::Call {
+                                    offset: read::DieReference::DebugInfoRef(debug_info_offset),
+                                },
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_form_tls_address),
+                                Operation::Simple(constants::DW_OP_form_tls_address),
+                                read::Operation::TLS,
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_call_frame_cfa),
+                                Operation::Simple(constants::DW_OP_call_frame_cfa),
+                                read::Operation::CallFrameCFA,
+                            ),
+                            (
+                                &|x| x.op_piece(23),
+                                Operation::Piece { size_in_bytes: 23 },
+                                read::Operation::Piece {
+                                    size_in_bits: 23 * 8,
+                                    bit_offset: None,
+                                },
+                            ),
+                            (
+                                &|x| x.op_bit_piece(23, 34),
+                                Operation::BitPiece {
+                                    size_in_bits: 23,
+                                    bit_offset: 34,
+                                },
+                                read::Operation::Piece {
+                                    size_in_bits: 23,
+                                    bit_offset: Some(34),
+                                },
+                            ),
+                            (
+                                &|x| x.op_implicit_value(vec![23].into()),
+                                Operation::ImplicitValue(vec![23].into()),
+                                read::Operation::ImplicitValue {
+                                    data: read::EndianSlice::new(&[23], LittleEndian),
+                                },
+                            ),
+                            (
+                                &|x| x.op(constants::DW_OP_stack_value),
+                                Operation::Simple(constants::DW_OP_stack_value),
+                                read::Operation::StackValue,
+                            ),
+                            (
+                                &|x| x.op_implicit_pointer(reference, 23),
+                                Operation::ImplicitPointer {
+                                    entry: reference,
+                                    byte_offset: 23,
+                                },
+                                read::Operation::ImplicitPointer {
+                                    value: debug_info_offset,
+                                    byte_offset: 23,
+                                },
+                            ),
+                            (
+                                &|x| x.op_entry_value(reg_expression.clone()),
+                                Operation::EntryValue(reg_expression.clone()),
+                                read::Operation::EntryValue {
+                                    expression: read::EndianSlice::new(
+                                        &[constants::DW_OP_reg23.0],
+                                        LittleEndian,
+                                    ),
+                                },
+                            ),
+                            (
+                                &|x| x.op_gnu_parameter_ref(entry_id),
+                                Operation::ParameterRef(entry_id),
+                                read::Operation::ParameterRef {
+                                    offset: entry_offset,
+                                },
+                            ),
+                            (
+                                &|x| x.op_addr(Address::Constant(23)),
+                                Operation::Address(Address::Constant(23)),
+                                read::Operation::Address { address: 23 },
+                            ),
+                            (
+                                &|x| x.op_const_type(entry_id, vec![23].into()),
+                                Operation::ConstantType(entry_id, vec![23].into()),
+                                read::Operation::TypedLiteral {
+                                    base_type: entry_offset,
+                                    value: read::EndianSlice::new(&[23], LittleEndian),
+                                },
+                            ),
+                            (
+                                &|x| x.op_convert(None),
+                                Operation::Convert(None),
+                                read::Operation::Convert {
+                                    base_type: read::UnitOffset(0),
+                                },
+                            ),
+                            (
+                                &|x| x.op_convert(Some(entry_id)),
+                                Operation::Convert(Some(entry_id)),
+                                read::Operation::Convert {
+                                    base_type: entry_offset,
+                                },
+                            ),
+                            (
+                                &|x| x.op_reinterpret(None),
+                                Operation::Reinterpret(None),
+                                read::Operation::Reinterpret {
+                                    base_type: read::UnitOffset(0),
+                                },
+                            ),
+                            (
+                                &|x| x.op_reinterpret(Some(entry_id)),
+                                Operation::Reinterpret(Some(entry_id)),
+                                read::Operation::Reinterpret {
+                                    base_type: entry_offset,
+                                },
+                            ),
+                            (
+                                &|x| x.op_wasm_local(1000),
+                                Operation::WasmLocal(1000),
+                                read::Operation::WasmLocal { index: 1000 },
+                            ),
+                            (
+                                &|x| x.op_wasm_global(1000),
+                                Operation::WasmGlobal(1000),
+                                read::Operation::WasmGlobal { index: 1000 },
+                            ),
+                            (
+                                &|x| x.op_wasm_stack(1000),
+                                Operation::WasmStack(1000),
+                                read::Operation::WasmStack { index: 1000 },
+                            ),
+                        ];
+
+                    let mut expression = Expression::new();
+                    let start_index = expression.next_index();
+                    for (f, o, _) in operations {
+                        f(&mut expression);
+                        assert_eq!(expression.operations.last(), Some(o));
+                    }
+
+                    let bra_index = expression.op_bra();
+                    let skip_index = expression.op_skip();
+                    expression.op(constants::DW_OP_nop);
+                    let end_index = expression.next_index();
+                    expression.set_target(bra_index, start_index);
+                    expression.set_target(skip_index, end_index);
+
+                    let mut w = EndianVec::new(LittleEndian);
+                    let mut refs = Vec::new();
+                    expression
+                        .write(&mut w, Some(&mut refs), encoding, Some(&unit_offsets))
+                        .unwrap();
+                    for r in &refs {
+                        assert_eq!(r.unit, unit_id);
+                        assert_eq!(r.entry, entry_id);
+                        w.write_offset_at(
+                            r.offset,
+                            debug_info_offset.0,
+                            SectionId::DebugInfo,
+                            r.size,
+                        )
+                        .unwrap();
+                    }
+
+                    let read_expression =
+                        read::Expression(read::EndianSlice::new(w.slice(), LittleEndian));
+                    let mut read_operations = read_expression.operations(encoding);
+                    for (_, _, operation) in operations {
+                        assert_eq!(read_operations.next(), Ok(Some(*operation)));
+                    }
+
+                    // 4 = DW_OP_skip + i16 + DW_OP_nop
+                    assert_eq!(
+                        read_operations.next(),
+                        Ok(Some(read::Operation::Bra {
+                            target: -(w.len() as i16) + 4
+                        }))
+                    );
+                    // 1 = DW_OP_nop
+                    assert_eq!(
+                        read_operations.next(),
+                        Ok(Some(read::Operation::Skip { target: 1 }))
+                    );
+                    assert_eq!(read_operations.next(), Ok(Some(read::Operation::Nop)));
+                    assert_eq!(read_operations.next(), Ok(None));
+
+                    // Fake the unit.
+                    let unit = read::Unit {
+                        header: read::UnitHeader::new(
+                            encoding,
+                            0,
+                            read::UnitType::Compilation,
+                            DebugAbbrevOffset(0),
+                            DebugInfoOffset(0).into(),
+                            read::EndianSlice::new(&[], LittleEndian),
+                        ),
+                        abbreviations: Arc::new(read::Abbreviations::default()),
+                        name: None,
+                        comp_dir: None,
+                        low_pc: 0,
+                        str_offsets_base: DebugStrOffsetsBase(0),
+                        addr_base: DebugAddrBase(0),
+                        loclists_base: DebugLocListsBase(0),
+                        rnglists_base: DebugRngListsBase(0),
+                        line_program: None,
+                        dwo_id: None,
+                    };
+
+                    let mut entry_ids = HashMap::new();
+                    entry_ids.insert(debug_info_offset.into(), (unit_id, entry_id));
+                    let convert_expression = Expression::from(
+                        read_expression,
+                        encoding,
+                        None, /* dwarf */
+                        Some(&unit),
+                        Some(&entry_ids),
+                        &|address| Some(Address::Constant(address)),
+                    )
+                    .unwrap();
+                    let mut convert_operations = convert_expression.operations.iter();
+                    for (_, operation, _) in operations {
+                        assert_eq!(convert_operations.next(), Some(operation));
+                    }
+                    assert_eq!(
+                        convert_operations.next(),
+                        Some(&Operation::Branch(start_index))
+                    );
+                    assert_eq!(convert_operations.next(), Some(&Operation::Skip(end_index)));
+                    assert_eq!(
+                        convert_operations.next(),
+                        Some(&Operation::Simple(constants::DW_OP_nop))
+                    );
+                }
+            }
+        }
+    }
+}