wasmtime_cranelift/debug/transform/

unit.rs

use super::address_transform::AddressTransform;
use super::attr::{clone_die_attributes, EntryAttributesContext};
use super::debug_transform_logging::{
    dbi_log, log_begin_input_die, log_end_output_die, log_end_output_die_skipped,
    log_get_cu_summary,
};
use super::expression::compile_expression;
use super::line_program::clone_line_program;
use super::range_info_builder::RangeInfoBuilder;
use super::refs::{PendingDebugInfoRefs, PendingUnitRefs, UnitRefsMap};
use super::synthetic::ModuleSyntheticUnit;
use super::utils::{append_vmctx_info, resolve_die_ref};
use super::DebugInputContext;
use crate::debug::{Compilation, Reader};
use anyhow::{Context, Error};
use cranelift_codegen::ir::Endianness;
use cranelift_codegen::isa::TargetIsa;
use gimli::write;
use gimli::{AttributeValue, DebuggingInformationEntry, Dwarf, Unit};
use std::collections::HashSet;
use wasmtime_environ::StaticModuleIndex;
use wasmtime_versioned_export_macros::versioned_stringify_ident;

#[derive(Debug)]
pub struct InheritedAttr<T> {
    stack: Vec<(usize, T)>,
}

impl<T> InheritedAttr<T> {
    fn new() -> Self {
        InheritedAttr { stack: Vec::new() }
    }

    fn update(&mut self, depth: usize) {
        while !self.stack.is_empty() && self.stack.last().unwrap().0 >= depth {
            self.stack.pop();
        }
    }

    pub fn push(&mut self, depth: usize, value: T) {
        self.stack.push((depth, value));
    }

    pub fn top(&self) -> Option<&T> {
        self.stack.last().map(|entry| &entry.1)
    }

    pub fn top_with_depth_mut(&mut self, depth: usize) -> Option<&mut T> {
        self.stack
            .last_mut()
            .filter(|entry| entry.0 == depth)
            .map(|entry| &mut entry.1)
    }

    fn is_empty(&self) -> bool {
        self.stack.is_empty()
    }
}

fn get_base_type_name(
    type_entry: &DebuggingInformationEntry<Reader<'_>>,
    unit: &Unit<Reader<'_>>,
    dwarf: &Dwarf<Reader<'_>>,
) -> Result<String, Error> {
    // FIXME remove recursion.
    if let Some(die_ref) = type_entry.attr_value(gimli::DW_AT_type)? {
        if let Some(ref die) = resolve_die_ref(unit, &die_ref)? {
            if let Some(value) = die.attr_value(gimli::DW_AT_name)? {
                return Ok(String::from(dwarf.attr_string(unit, value)?.to_string()?));
            }
            match die.tag() {
                gimli::DW_TAG_const_type => {
                    return Ok(format!("const {}", get_base_type_name(die, unit, dwarf)?));
                }
                gimli::DW_TAG_pointer_type => {
                    return Ok(format!("{}*", get_base_type_name(die, unit, dwarf)?));
                }
                gimli::DW_TAG_reference_type => {
                    return Ok(format!("{}&", get_base_type_name(die, unit, dwarf)?));
                }
                gimli::DW_TAG_array_type => {
                    return Ok(format!("{}[]", get_base_type_name(die, unit, dwarf)?));
                }
                _ => (),
            }
        }
    }
    Ok(String::from("??"))
}

enum WebAssemblyPtrKind {
    Reference,
    Pointer,
}

/// Replaces WebAssembly pointer type DIE with the wrapper
/// which natively represented by offset in a Wasm memory.
///
/// `pointer_type_entry` is a DW_TAG_pointer_type entry (e.g. `T*`),
/// which refers its base type (e.g. `T`), or is a
/// DW_TAG_reference_type (e.g. `T&`).
///
/// The generated wrapper is a structure that contains only the
/// `__ptr` field. The utility operators overloads is added to
/// provide better debugging experience.
///
/// Wrappers of pointer and reference types are identical except for
/// their name -- they are formatted and accessed from a debugger
/// the same way.
///
/// Notice that "resolve_vmctx_memory_ptr" is external/builtin
/// subprogram that is not part of Wasm code.
fn replace_pointer_type(
    parent_id: write::UnitEntryId,
    kind: WebAssemblyPtrKind,
    comp_unit: &mut write::Unit,
    wasm_ptr_die_ref: write::Reference,
    pointer_type_entry: &DebuggingInformationEntry<Reader<'_>>,
    unit: &Unit<Reader<'_>, usize>,
    dwarf: &Dwarf<Reader<'_>>,
    out_strings: &mut write::StringTable,
    pending_die_refs: &mut PendingUnitRefs,
) -> Result<write::UnitEntryId, Error> {
    const WASM_PTR_LEN: u8 = 4;

    macro_rules! add_tag {
        ($parent_id:ident, $tag:expr => $die:ident as $die_id:ident { $($a:path = $v:expr),* }) => {
            let $die_id = comp_unit.add($parent_id, $tag);
            #[allow(unused_variables, reason = "sometimes not used below")]
            let $die = comp_unit.get_mut($die_id);
            $( $die.set($a, $v); )*
        };
    }

    // Build DW_TAG_structure_type for the wrapper:
    //  .. DW_AT_name = "WebAssemblyPtrWrapper<T>",
    //  .. DW_AT_byte_size = 4,
    let name = match kind {
        WebAssemblyPtrKind::Pointer => format!(
            "WebAssemblyPtrWrapper<{}>",
            get_base_type_name(pointer_type_entry, unit, dwarf)?
        ),
        WebAssemblyPtrKind::Reference => format!(
            "WebAssemblyRefWrapper<{}>",
            get_base_type_name(pointer_type_entry, unit, dwarf)?
        ),
    };
    add_tag!(parent_id, gimli::DW_TAG_structure_type => wrapper_die as wrapper_die_id {
        gimli::DW_AT_name = write::AttributeValue::StringRef(out_strings.add(name.as_str())),
        gimli::DW_AT_byte_size = write::AttributeValue::Data1(WASM_PTR_LEN)
    });

    // Build DW_TAG_pointer_type for `WebAssemblyPtrWrapper<T>*`:
    //  .. DW_AT_type = <wrapper_die>
    add_tag!(parent_id, gimli::DW_TAG_pointer_type => wrapper_ptr_type as wrapper_ptr_type_id {
        gimli::DW_AT_type = write::AttributeValue::UnitRef(wrapper_die_id)
    });

    let base_type_id = pointer_type_entry.attr_value(gimli::DW_AT_type)?;
    // Build DW_TAG_reference_type for `T&`:
    //  .. DW_AT_type = <base_type>
    add_tag!(parent_id, gimli::DW_TAG_reference_type => ref_type as ref_type_id {});
    if let Some(AttributeValue::UnitRef(ref offset)) = base_type_id {
        pending_die_refs.insert(ref_type_id, gimli::DW_AT_type, *offset);
    }

    // Build DW_TAG_pointer_type for `T*`:
    //  .. DW_AT_type = <base_type>
    add_tag!(parent_id, gimli::DW_TAG_pointer_type => ptr_type as ptr_type_id {});
    if let Some(AttributeValue::UnitRef(ref offset)) = base_type_id {
        pending_die_refs.insert(ptr_type_id, gimli::DW_AT_type, *offset);
    }

    // Build wrapper_die's DW_TAG_template_type_parameter:
    //  .. DW_AT_name = "T"
    //  .. DW_AT_type = <base_type>
    add_tag!(wrapper_die_id, gimli::DW_TAG_template_type_parameter => t_param_die as t_param_die_id {
        gimli::DW_AT_name = write::AttributeValue::StringRef(out_strings.add("T"))
    });
    if let Some(AttributeValue::UnitRef(ref offset)) = base_type_id {
        pending_die_refs.insert(t_param_die_id, gimli::DW_AT_type, *offset);
    }

    // Build wrapper_die's DW_TAG_member for `__ptr`:
    //  .. DW_AT_name = "__ptr"
    //  .. DW_AT_type = <wp_die>
    //  .. DW_AT_location = 0
    add_tag!(wrapper_die_id, gimli::DW_TAG_member => m_die as m_die_id {
        gimli::DW_AT_name = write::AttributeValue::StringRef(out_strings.add("__ptr")),
        gimli::DW_AT_type = write::AttributeValue::DebugInfoRef(wasm_ptr_die_ref),
        gimli::DW_AT_data_member_location = write::AttributeValue::Data1(0)
    });

    // Build wrapper_die's DW_TAG_subprogram for `ptr()`:
    //  .. DW_AT_linkage_name = "wasmtime_resolve_vmctx_memory_ptr"
    //  .. DW_AT_name = "ptr"
    //  .. DW_AT_type = <ptr_type>
    //  .. DW_TAG_formal_parameter
    //  ..  .. DW_AT_type = <wrapper_ptr_type>
    //  ..  .. DW_AT_artificial = 1
    add_tag!(wrapper_die_id, gimli::DW_TAG_subprogram => deref_op_die as deref_op_die_id {
        gimli::DW_AT_linkage_name = write::AttributeValue::StringRef(out_strings.add(versioned_stringify_ident!(wasmtime_resolve_vmctx_memory_ptr))),
        gimli::DW_AT_name = write::AttributeValue::StringRef(out_strings.add("ptr")),
        gimli::DW_AT_type = write::AttributeValue::UnitRef(ptr_type_id)
    });
    add_tag!(deref_op_die_id, gimli::DW_TAG_formal_parameter => deref_op_this_param as deref_op_this_param_id {
        gimli::DW_AT_type = write::AttributeValue::UnitRef(wrapper_ptr_type_id),
        gimli::DW_AT_artificial = write::AttributeValue::Flag(true)
    });

    // Build wrapper_die's DW_TAG_subprogram for `operator*`:
    //  .. DW_AT_linkage_name = "wasmtime_resolve_vmctx_memory_ptr"
    //  .. DW_AT_name = "operator*"
    //  .. DW_AT_type = <ref_type>
    //  .. DW_TAG_formal_parameter
    //  ..  .. DW_AT_type = <wrapper_ptr_type>
    //  ..  .. DW_AT_artificial = 1
    add_tag!(wrapper_die_id, gimli::DW_TAG_subprogram => deref_op_die as deref_op_die_id {
        gimli::DW_AT_linkage_name = write::AttributeValue::StringRef(out_strings.add(versioned_stringify_ident!(wasmtime_resolve_vmctx_memory_ptr))),
        gimli::DW_AT_name = write::AttributeValue::StringRef(out_strings.add("operator*")),
        gimli::DW_AT_type = write::AttributeValue::UnitRef(ref_type_id)
    });
    add_tag!(deref_op_die_id, gimli::DW_TAG_formal_parameter => deref_op_this_param as deref_op_this_param_id {
        gimli::DW_AT_type = write::AttributeValue::UnitRef(wrapper_ptr_type_id),
        gimli::DW_AT_artificial = write::AttributeValue::Flag(true)
    });

    // Build wrapper_die's DW_TAG_subprogram for `operator->`:
    //  .. DW_AT_linkage_name = "wasmtime_resolve_vmctx_memory_ptr"
    //  .. DW_AT_name = "operator->"
    //  .. DW_AT_type = <ptr_type>
    //  .. DW_TAG_formal_parameter
    //  ..  .. DW_AT_type = <wrapper_ptr_type>
    //  ..  .. DW_AT_artificial = 1
    add_tag!(wrapper_die_id, gimli::DW_TAG_subprogram => deref_op_die as deref_op_die_id {
        gimli::DW_AT_linkage_name = write::AttributeValue::StringRef(out_strings.add(versioned_stringify_ident!(wasmtime_resolve_vmctx_memory_ptr))),
        gimli::DW_AT_name = write::AttributeValue::StringRef(out_strings.add("operator->")),
        gimli::DW_AT_type = write::AttributeValue::UnitRef(ptr_type_id)
    });
    add_tag!(deref_op_die_id, gimli::DW_TAG_formal_parameter => deref_op_this_param as deref_op_this_param_id {
        gimli::DW_AT_type = write::AttributeValue::UnitRef(wrapper_ptr_type_id),
        gimli::DW_AT_artificial = write::AttributeValue::Flag(true)
    });

    Ok(wrapper_die_id)
}

fn is_dead_code(entry: &DebuggingInformationEntry<Reader<'_>>) -> bool {
    const TOMBSTONE: u64 = u32::MAX as u64;

    match entry.attr_value(gimli::DW_AT_low_pc) {
        Ok(Some(AttributeValue::Addr(addr))) => addr == TOMBSTONE,
        _ => false,
    }
}

pub(crate) fn clone_unit(
    compilation: &mut Compilation<'_>,
    module: StaticModuleIndex,
    skeleton_unit: &Unit<Reader<'_>>,
    split_unit: Option<&Unit<Reader<'_>>>,
    split_dwarf: Option<&Dwarf<Reader<'_>>>,
    context: &DebugInputContext,
    addr_tr: &AddressTransform,
    out_encoding: gimli::Encoding,
    out_module_synthetic_unit: &ModuleSyntheticUnit,
    out_units: &mut write::UnitTable,
    out_strings: &mut write::StringTable,
    translated: &mut HashSet<usize>,
    isa: &dyn TargetIsa,
) -> Result<Option<(write::UnitId, UnitRefsMap, PendingDebugInfoRefs)>, Error> {
    let mut die_ref_map = UnitRefsMap::new();
    let mut pending_die_refs = PendingUnitRefs::new();
    let mut pending_di_refs = PendingDebugInfoRefs::new();
    let mut stack = Vec::new();

    let skeleton_dwarf = &compilation.translations[module].debuginfo.dwarf;

    // Iterate over all of this compilation unit's entries.
    let dwarf = split_dwarf.unwrap_or(skeleton_dwarf);
    let unit = split_unit.unwrap_or(skeleton_unit);
    let mut entries = unit.entries();
    dbi_log!("Cloning CU {:?}", log_get_cu_summary(unit));

    let (mut out_unit, out_unit_id, file_map, file_index_base) = if let Some((depth_delta, entry)) =
        entries.next_dfs()?
    {
        assert_eq!(depth_delta, 0);
        let (out_line_program, debug_line_offset, file_map, file_index_base) = clone_line_program(
            skeleton_dwarf,
            skeleton_unit,
            unit.name,
            addr_tr,
            out_encoding,
            out_strings,
        )?;

        if entry.tag() == gimli::DW_TAG_compile_unit {
            log_begin_input_die(dwarf, unit, entry, 0);
            let out_unit_id = out_units.add(write::Unit::new(out_encoding, out_line_program));
            let out_unit = out_units.get_mut(out_unit_id);

            let out_root_id = out_unit.root();
            die_ref_map.insert(entry.offset(), out_root_id);

            clone_die_attributes(
                dwarf,
                &unit,
                entry,
                addr_tr,
                None,
                out_unit,
                out_root_id,
                None,
                None,
                out_strings,
                &mut pending_die_refs,
                &mut pending_di_refs,
                EntryAttributesContext::Root(Some(debug_line_offset)),
                isa,
            )?;
            if split_unit.is_some() {
                if let Some((_, skeleton_entry)) = skeleton_unit.entries().next_dfs()? {
                    clone_die_attributes(
                        skeleton_dwarf,
                        skeleton_unit,
                        skeleton_entry,
                        addr_tr,
                        None,
                        out_unit,
                        out_root_id,
                        None,
                        None,
                        out_strings,
                        &mut pending_die_refs,
                        &mut pending_di_refs,
                        EntryAttributesContext::Root(Some(debug_line_offset)),
                        isa,
                    )?;
                }
            }

            log_end_output_die(entry, unit, out_root_id, out_unit, out_strings, 0);
            stack.push(out_root_id);
            (out_unit, out_unit_id, file_map, file_index_base)
        } else {
            // Can happen when the DWARF is split and we dont have the package/dwo files.
            // This is a better user experience than errorring.
            dbi_log!("... skipped: split DW_TAG_compile_unit entry missing");
            return Ok(None); // empty:
        }
    } else {
        dbi_log!("... skipped: empty CU (no DW_TAG_compile_unit entry)");
        return Ok(None); // empty
    };
    let mut current_depth = 0;
    let mut skip_at_depth = None;
    let mut current_frame_base = InheritedAttr::new();
    let mut current_value_range = InheritedAttr::new();
    let mut current_scope_ranges = InheritedAttr::new();
    let mut current_subprogram = InheritedAttr::new();
    while let Some((depth_delta, entry)) = entries.next_dfs()? {
        current_depth += depth_delta;
        log_begin_input_die(dwarf, unit, entry, current_depth);

        // If `skip_at_depth` is `Some` then we previously decided to skip over
        // a node and all it's children. Let A be the last node processed, B be
        // the first node skipped, C be previous node, and D the current node.
        // Then `cached` is the difference from A to B, `depth` is the difference
        // from B to C, and `depth_delta` is the differenc from C to D.
        let depth_delta = if let Some((depth, cached)) = skip_at_depth {
            // `new_depth` = B to D
            let new_depth = depth + depth_delta;
            // if D is below B continue to skip
            if new_depth > 0 {
                skip_at_depth = Some((new_depth, cached));
                log_end_output_die_skipped(entry, unit, "unreachable", current_depth);
                continue;
            }
            // otherwise process D with `depth_delta` being the difference from A to D
            skip_at_depth = None;
            new_depth + cached
        } else {
            depth_delta
        };

        if !context
            .reachable
            .contains(&entry.offset().to_unit_section_offset(&unit))
            || is_dead_code(&entry)
        {
            // entry is not reachable: discarding all its info.
            // Here B = C so `depth` is 0. A is the previous node so `cached` =
            // `depth_delta`.
            skip_at_depth = Some((0, depth_delta));
            log_end_output_die_skipped(entry, unit, "unreachable", current_depth);
            continue;
        }

        let new_stack_len = stack.len().wrapping_add(depth_delta as usize);
        current_frame_base.update(new_stack_len);
        current_scope_ranges.update(new_stack_len);
        current_value_range.update(new_stack_len);
        current_subprogram.update(new_stack_len);
        let range_builder = if entry.tag() == gimli::DW_TAG_subprogram {
            let range_builder =
                RangeInfoBuilder::from_subprogram_die(dwarf, &unit, entry, addr_tr)?;
            if let RangeInfoBuilder::Function(func) = range_builder {
                let frame_info = compilation.function_frame_info(module, func);
                current_value_range.push(new_stack_len, frame_info);
                let (symbol, _) = compilation.function(module, func);
                translated.insert(symbol);
                current_scope_ranges.push(new_stack_len, range_builder.get_ranges(addr_tr));
                Some(range_builder)
            } else {
                // FIXME current_scope_ranges.push()
                None
            }
        } else {
            let high_pc = entry.attr_value(gimli::DW_AT_high_pc)?;
            let ranges = entry.attr_value(gimli::DW_AT_ranges)?;
            if high_pc.is_some() || ranges.is_some() {
                let range_builder = RangeInfoBuilder::from(dwarf, &unit, entry)?;
                current_scope_ranges.push(new_stack_len, range_builder.get_ranges(addr_tr));
                Some(range_builder)
            } else {
                None
            }
        };

        if depth_delta <= 0 {
            for _ in depth_delta..1 {
                stack.pop();
            }
        } else {
            assert_eq!(depth_delta, 1);
        }

        if let Some(AttributeValue::Exprloc(expr)) = entry.attr_value(gimli::DW_AT_frame_base)? {
            if let Some(expr) = compile_expression(&expr, unit.encoding(), None)? {
                current_frame_base.push(new_stack_len, expr);
            }
        }

        let parent = stack.last().unwrap();

        if entry.tag() == gimli::DW_TAG_pointer_type || entry.tag() == gimli::DW_TAG_reference_type
        {
            // Wrap pointer types.
            let pointer_kind = match entry.tag() {
                gimli::DW_TAG_pointer_type => WebAssemblyPtrKind::Pointer,
                gimli::DW_TAG_reference_type => WebAssemblyPtrKind::Reference,
                _ => panic!(),
            };
            let die_id = replace_pointer_type(
                *parent,
                pointer_kind,
                out_unit,
                out_module_synthetic_unit.wasm_ptr_die_ref(),
                entry,
                unit,
                dwarf,
                out_strings,
                &mut pending_die_refs,
            )?;
            stack.push(die_id);
            assert_eq!(stack.len(), new_stack_len);
            die_ref_map.insert(entry.offset(), die_id);
            log_end_output_die(entry, unit, die_id, out_unit, out_strings, current_depth);
            continue;
        }

        let out_die_id = out_unit.add(*parent, entry.tag());

        stack.push(out_die_id);
        assert_eq!(stack.len(), new_stack_len);
        die_ref_map.insert(entry.offset(), out_die_id);

        clone_die_attributes(
            dwarf,
            &unit,
            entry,
            addr_tr,
            current_value_range.top(),
            &mut out_unit,
            out_die_id,
            range_builder,
            current_scope_ranges.top(),
            out_strings,
            &mut pending_die_refs,
            &mut pending_di_refs,
            EntryAttributesContext::Children {
                depth: current_depth as usize,
                subprograms: &mut current_subprogram,
                file_map: &file_map,
                file_index_base,
                frame_base: current_frame_base.top(),
            },
            isa,
        )?;

        // Data in WebAssembly memory always uses little-endian byte order.
        // If the native architecture is big-endian, we need to mark all
        // base types used to refer to WebAssembly memory as little-endian
        // using the DW_AT_endianity attribute, so that the debugger will
        // be able to correctly access them.
        if entry.tag() == gimli::DW_TAG_base_type && isa.endianness() == Endianness::Big {
            let current_scope = out_unit.get_mut(out_die_id);
            current_scope.set(
                gimli::DW_AT_endianity,
                write::AttributeValue::Endianity(gimli::DW_END_little),
            );
        }

        if entry.tag() == gimli::DW_TAG_subprogram && !current_scope_ranges.is_empty() {
            append_vmctx_info(
                out_unit,
                out_die_id,
                out_module_synthetic_unit.vmctx_ptr_die_ref(),
                addr_tr,
                current_value_range.top(),
                current_scope_ranges.top().context("range")?,
                out_strings,
                isa,
            )?;
        }

        log_end_output_die(
            entry,
            unit,
            out_die_id,
            out_unit,
            out_strings,
            current_depth,
        );
    }
    die_ref_map.patch(pending_die_refs, out_unit);
    Ok(Some((out_unit_id, die_ref_map, pending_di_refs)))
}