Merging upstream version 1.72.1+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

4 files changed, 870 insertions, 186 deletions

diff --git a/vendor/addr2line/src/builtin_split_dwarf_loader.rs b/vendor/addr2line/src/builtin_split_dwarf_loader.rs
new file mode 100644
index 000000000..471193124
--- /dev/null
+++ b/vendor/addr2line/src/builtin_split_dwarf_loader.rs
@@ -0,0 +1,164 @@
+use alloc::borrow::Cow;
+use alloc::sync::Arc;
+use std::fs::File;
+use std::path::PathBuf;
+
+use object::Object;
+
+use crate::{LookupContinuation, LookupResult};
+
+#[cfg(unix)]
+fn convert_path<R: gimli::Reader<Endian = gimli::RunTimeEndian>>(
+    r: &R,
+) -> Result<PathBuf, gimli::Error> {
+    use std::ffi::OsStr;
+    use std::os::unix::ffi::OsStrExt;
+    let bytes = r.to_slice()?;
+    let s = OsStr::from_bytes(&bytes);
+    Ok(PathBuf::from(s))
+}
+
+#[cfg(not(unix))]
+fn convert_path<R: gimli::Reader<Endian = gimli::RunTimeEndian>>(
+    r: &R,
+) -> Result<PathBuf, gimli::Error> {
+    let bytes = r.to_slice()?;
+    let s = std::str::from_utf8(&bytes).map_err(|_| gimli::Error::BadUtf8)?;
+    Ok(PathBuf::from(s))
+}
+
+fn load_section<'data: 'file, 'file, O, R, F>(
+    id: gimli::SectionId,
+    file: &'file O,
+    endian: R::Endian,
+    loader: &mut F,
+) -> Result<R, gimli::Error>
+where
+    O: object::Object<'data, 'file>,
+    R: gimli::Reader<Endian = gimli::RunTimeEndian>,
+    F: FnMut(Cow<'data, [u8]>, R::Endian) -> R,
+{
+    use object::ObjectSection;
+
+    let data = id
+        .dwo_name()
+        .and_then(|dwo_name| {
+            file.section_by_name(dwo_name)
+                .and_then(|section| section.uncompressed_data().ok())
+        })
+        .unwrap_or(Cow::Borrowed(&[]));
+    Ok(loader(data, endian))
+}
+
+/// A simple builtin split DWARF loader.
+pub struct SplitDwarfLoader<R, F>
+where
+    R: gimli::Reader<Endian = gimli::RunTimeEndian>,
+    F: FnMut(Cow<'_, [u8]>, R::Endian) -> R,
+{
+    loader: F,
+    dwarf_package: Option<gimli::DwarfPackage<R>>,
+}
+
+impl<R, F> SplitDwarfLoader<R, F>
+where
+    R: gimli::Reader<Endian = gimli::RunTimeEndian>,
+    F: FnMut(Cow<'_, [u8]>, R::Endian) -> R,
+{
+    fn load_dwarf_package(loader: &mut F, path: Option<PathBuf>) -> Option<gimli::DwarfPackage<R>> {
+        let mut path = path.map(Ok).unwrap_or_else(std::env::current_exe).ok()?;
+        let dwp_extension = path
+            .extension()
+            .map(|previous_extension| {
+                let mut previous_extension = previous_extension.to_os_string();
+                previous_extension.push(".dwp");
+                previous_extension
+            })
+            .unwrap_or_else(|| "dwp".into());
+        path.set_extension(dwp_extension);
+        let file = File::open(&path).ok()?;
+        let map = unsafe { memmap2::Mmap::map(&file).ok()? };
+        let dwp = object::File::parse(&*map).ok()?;
+
+        let endian = if dwp.is_little_endian() {
+            gimli::RunTimeEndian::Little
+        } else {
+            gimli::RunTimeEndian::Big
+        };
+
+        let empty = loader(Cow::Borrowed(&[]), endian);
+        gimli::DwarfPackage::load(
+            |section_id| load_section(section_id, &dwp, endian, loader),
+            empty,
+        )
+        .ok()
+    }
+
+    /// Create a new split DWARF loader.
+    pub fn new(mut loader: F, path: Option<PathBuf>) -> SplitDwarfLoader<R, F> {
+        let dwarf_package = SplitDwarfLoader::load_dwarf_package(&mut loader, path);
+        SplitDwarfLoader {
+            loader,
+            dwarf_package,
+        }
+    }
+
+    /// Run the provided `LookupResult` to completion, loading any necessary
+    /// split DWARF along the way.
+    pub fn run<L>(&mut self, mut l: LookupResult<L>) -> L::Output
+    where
+        L: LookupContinuation<Buf = R>,
+    {
+        loop {
+            let (load, continuation) = match l {
+                LookupResult::Output(output) => break output,
+                LookupResult::Load { load, continuation } => (load, continuation),
+            };
+
+            let mut r: Option<Arc<gimli::Dwarf<_>>> = None;
+            if let Some(dwp) = self.dwarf_package.as_ref() {
+                if let Ok(Some(cu)) = dwp.find_cu(load.dwo_id, &load.parent) {
+                    r = Some(Arc::new(cu));
+                }
+            }
+
+            if r.is_none() {
+                let mut path = PathBuf::new();
+                if let Some(p) = load.comp_dir.as_ref() {
+                    if let Ok(p) = convert_path(p) {
+                        path.push(p);
+                    }
+                }
+
+                if let Some(p) = load.path.as_ref() {
+                    if let Ok(p) = convert_path(p) {
+                        path.push(p);
+                    }
+                }
+
+                if let Ok(file) = File::open(&path) {
+                    if let Ok(map) = unsafe { memmap2::Mmap::map(&file) } {
+                        if let Ok(file) = object::File::parse(&*map) {
+                            let endian = if file.is_little_endian() {
+                                gimli::RunTimeEndian::Little
+                            } else {
+                                gimli::RunTimeEndian::Big
+                            };
+
+                            r = gimli::Dwarf::load(|id| {
+                                load_section(id, &file, endian, &mut self.loader)
+                            })
+                            .ok()
+                            .map(|mut dwo_dwarf| {
+                                dwo_dwarf.make_dwo(&load.parent);
+                                Arc::new(dwo_dwarf)
+                            });
+                        }
+                    }
+                }
+            }
+
+            l = continuation.resume(r);
+        }
+    }
+}
diff --git a/vendor/addr2line/src/function.rs b/vendor/addr2line/src/function.rs
index 44dc73f24..09c19e01e 100644
--- a/vendor/addr2line/src/function.rs
+++ b/vendor/addr2line/src/function.rs
@@ -5,7 +5,7 @@ use core::iter;
 
 use crate::lazy::LazyCell;
 use crate::maybe_small;
-use crate::{Error, RangeAttributes, ResDwarf};
+use crate::{Context, DebugFile, Error, RangeAttributes};
 
 pub(crate) struct Functions<R: gimli::Reader> {
     /// List of all `DW_TAG_subprogram` details in the unit.
@@ -49,13 +49,16 @@ pub(crate) struct InlinedFunctionAddress {
 pub(crate) struct InlinedFunction<R: gimli::Reader> {
     pub(crate) dw_die_offset: gimli::UnitOffset<R::Offset>,
     pub(crate) name: Option<R>,
-    pub(crate) call_file: u64,
+    pub(crate) call_file: Option<u64>,
     pub(crate) call_line: u32,
     pub(crate) call_column: u32,
 }
 
 impl<R: gimli::Reader> Functions<R> {
-    pub(crate) fn parse(unit: &gimli::Unit<R>, dwarf: &ResDwarf<R>) -> Result<Functions<R>, Error> {
+    pub(crate) fn parse(
+        unit: &gimli::Unit<R>,
+        sections: &gimli::Dwarf<R>,
+    ) -> Result<Functions<R>, Error> {
         let mut functions = Vec::new();
         let mut addresses = Vec::new();
         let mut entries = unit.entries_raw(None)?;
@@ -73,8 +76,7 @@ impl<R: gimli::Reader> Functions<R> {
                                             ranges.low_pc = Some(val)
                                         }
                                         gimli::AttributeValue::DebugAddrIndex(index) => {
-                                            ranges.low_pc =
-                                                Some(dwarf.sections.address(unit, index)?);
+                                            ranges.low_pc = Some(sections.address(unit, index)?);
                                         }
                                         _ => {}
                                     },
@@ -83,8 +85,7 @@ impl<R: gimli::Reader> Functions<R> {
                                             ranges.high_pc = Some(val)
                                         }
                                         gimli::AttributeValue::DebugAddrIndex(index) => {
-                                            ranges.high_pc =
-                                                Some(dwarf.sections.address(unit, index)?);
+                                            ranges.high_pc = Some(sections.address(unit, index)?);
                                         }
                                         gimli::AttributeValue::Udata(val) => {
                                             ranges.size = Some(val)
@@ -92,9 +93,8 @@ impl<R: gimli::Reader> Functions<R> {
                                         _ => {}
                                     },
                                     gimli::DW_AT_ranges => {
-                                        ranges.ranges_offset = dwarf
-                                            .sections
-                                            .attr_ranges_offset(unit, attr.value())?;
+                                        ranges.ranges_offset =
+                                            sections.attr_ranges_offset(unit, attr.value())?;
                                     }
                                     _ => {}
                                 };
@@ -104,7 +104,7 @@ impl<R: gimli::Reader> Functions<R> {
                     }
 
                     let function_index = functions.len();
-                    if ranges.for_each_range(&dwarf.sections, unit, |range| {
+                    if ranges.for_each_range(sections, unit, |range| {
                         addresses.push(FunctionAddress {
                             range,
                             function: function_index,
@@ -150,13 +150,15 @@ impl<R: gimli::Reader> Functions<R> {
 
     pub(crate) fn parse_inlined_functions(
         &self,
+        file: DebugFile,
         unit: &gimli::Unit<R>,
-        dwarf: &ResDwarf<R>,
+        ctx: &Context<R>,
+        sections: &gimli::Dwarf<R>,
     ) -> Result<(), Error> {
         for function in &*self.functions {
             function
                 .1
-                .borrow_with(|| Function::parse(function.0, unit, dwarf))
+                .borrow_with(|| Function::parse(function.0, file, unit, ctx, sections))
                 .as_ref()
                 .map_err(Error::clone)?;
         }
@@ -167,8 +169,10 @@ impl<R: gimli::Reader> Functions<R> {
 impl<R: gimli::Reader> Function<R> {
     pub(crate) fn parse(
         dw_die_offset: gimli::UnitOffset<R::Offset>,
+        file: DebugFile,
         unit: &gimli::Unit<R>,
-        dwarf: &ResDwarf<R>,
+        ctx: &Context<R>,
+        sections: &gimli::Dwarf<R>,
     ) -> Result<Self, Error> {
         let mut entries = unit.entries_raw(Some(dw_die_offset))?;
         let depth = entries.next_depth();
@@ -181,18 +185,18 @@ impl<R: gimli::Reader> Function<R> {
                 Ok(ref attr) => {
                     match attr.name() {
                         gimli::DW_AT_linkage_name | gimli::DW_AT_MIPS_linkage_name => {
-                            if let Ok(val) = dwarf.sections.attr_string(unit, attr.value()) {
+                            if let Ok(val) = sections.attr_string(unit, attr.value()) {
                                 name = Some(val);
                             }
                         }
                         gimli::DW_AT_name => {
                             if name.is_none() {
-                                name = dwarf.sections.attr_string(unit, attr.value()).ok();
+                                name = sections.attr_string(unit, attr.value()).ok();
                             }
                         }
                         gimli::DW_AT_abstract_origin | gimli::DW_AT_specification => {
                             if name.is_none() {
-                                name = name_attr(attr.value(), unit, dwarf, 16)?;
+                                name = name_attr(attr.value(), file, unit, ctx, sections, 16)?;
                             }
                         }
                         _ => {}
@@ -207,8 +211,10 @@ impl<R: gimli::Reader> Function<R> {
         Function::parse_children(
             &mut entries,
             depth,
+            file,
             unit,
-            dwarf,
+            ctx,
+            sections,
             &mut inlined_functions,
             &mut inlined_addresses,
             0,
@@ -247,10 +253,12 @@ impl<R: gimli::Reader> Function<R> {
     }
 
     fn parse_children(
-        entries: &mut gimli::EntriesRaw<R>,
+        entries: &mut gimli::EntriesRaw<'_, '_, R>,
         depth: isize,
+        file: DebugFile,
         unit: &gimli::Unit<R>,
-        dwarf: &ResDwarf<R>,
+        ctx: &Context<R>,
+        sections: &gimli::Dwarf<R>,
         inlined_functions: &mut Vec<InlinedFunction<R>>,
         inlined_addresses: &mut Vec<InlinedFunctionAddress>,
         inlined_depth: usize,
@@ -272,8 +280,10 @@ impl<R: gimli::Reader> Function<R> {
                             entries,
                             abbrev,
                             next_depth,
+                            file,
                             unit,
-                            dwarf,
+                            ctx,
+                            sections,
                             inlined_functions,
                             inlined_addresses,
                             inlined_depth,
@@ -288,7 +298,7 @@ impl<R: gimli::Reader> Function<R> {
     }
 
     fn skip(
-        entries: &mut gimli::EntriesRaw<R>,
+        entries: &mut gimli::EntriesRaw<'_, '_, R>,
         abbrev: &gimli::Abbreviation,
         depth: isize,
     ) -> Result<(), Error> {
@@ -344,18 +354,20 @@ impl<R: gimli::Reader> Function<R> {
 impl<R: gimli::Reader> InlinedFunction<R> {
     fn parse(
         dw_die_offset: gimli::UnitOffset<R::Offset>,
-        entries: &mut gimli::EntriesRaw<R>,
+        entries: &mut gimli::EntriesRaw<'_, '_, R>,
         abbrev: &gimli::Abbreviation,
         depth: isize,
+        file: DebugFile,
         unit: &gimli::Unit<R>,
-        dwarf: &ResDwarf<R>,
+        ctx: &Context<R>,
+        sections: &gimli::Dwarf<R>,
         inlined_functions: &mut Vec<InlinedFunction<R>>,
         inlined_addresses: &mut Vec<InlinedFunctionAddress>,
         inlined_depth: usize,
     ) -> Result<(), Error> {
         let mut ranges = RangeAttributes::default();
         let mut name = None;
-        let mut call_file = 0;
+        let mut call_file = None;
         let mut call_line = 0;
         let mut call_column = 0;
         for spec in abbrev.attributes() {
@@ -364,40 +376,50 @@ impl<R: gimli::Reader> InlinedFunction<R> {
                     gimli::DW_AT_low_pc => match attr.value() {
                         gimli::AttributeValue::Addr(val) => ranges.low_pc = Some(val),
                         gimli::AttributeValue::DebugAddrIndex(index) => {
-                            ranges.low_pc = Some(dwarf.sections.address(unit, index)?);
+                            ranges.low_pc = Some(sections.address(unit, index)?);
                         }
                         _ => {}
                     },
                     gimli::DW_AT_high_pc => match attr.value() {
                         gimli::AttributeValue::Addr(val) => ranges.high_pc = Some(val),
                         gimli::AttributeValue::DebugAddrIndex(index) => {
-                            ranges.high_pc = Some(dwarf.sections.address(unit, index)?);
+                            ranges.high_pc = Some(sections.address(unit, index)?);
                         }
                         gimli::AttributeValue::Udata(val) => ranges.size = Some(val),
                         _ => {}
                     },
                     gimli::DW_AT_ranges => {
-                        ranges.ranges_offset =
-                            dwarf.sections.attr_ranges_offset(unit, attr.value())?;
+                        ranges.ranges_offset = sections.attr_ranges_offset(unit, attr.value())?;
                     }
                     gimli::DW_AT_linkage_name | gimli::DW_AT_MIPS_linkage_name => {
-                        if let Ok(val) = dwarf.sections.attr_string(unit, attr.value()) {
+                        if let Ok(val) = sections.attr_string(unit, attr.value()) {
                             name = Some(val);
                         }
                     }
                     gimli::DW_AT_name => {
                         if name.is_none() {
-                            name = dwarf.sections.attr_string(unit, attr.value()).ok();
+                            name = sections.attr_string(unit, attr.value()).ok();
                         }
                     }
                     gimli::DW_AT_abstract_origin | gimli::DW_AT_specification => {
                         if name.is_none() {
-                            name = name_attr(attr.value(), unit, dwarf, 16)?;
+                            name = name_attr(attr.value(), file, unit, ctx, sections, 16)?;
                         }
                     }
                     gimli::DW_AT_call_file => {
+                        // There is a spec issue [1] with how DW_AT_call_file is specified in DWARF 5.
+                        // Before, a file index of 0 would indicate no source file, however in
+                        // DWARF 5 this could be a valid index into the file table.
+                        //
+                        // Implementations such as LLVM generates a file index of 0 when DWARF 5 is
+                        // used.
+                        //
+                        // Thus, if we see a version of 5 or later, treat a file index of 0 as such.
+                        // [1]: http://wiki.dwarfstd.org/index.php?title=DWARF5_Line_Table_File_Numbers
                         if let gimli::AttributeValue::FileIndex(fi) = attr.value() {
-                            call_file = fi;
+                            if fi > 0 || unit.header.version() >= 5 {
+                                call_file = Some(fi);
+                            }
                         }
                     }
                     gimli::DW_AT_call_line => {
@@ -421,7 +443,7 @@ impl<R: gimli::Reader> InlinedFunction<R> {
             call_column,
         });
 
-        ranges.for_each_range(&dwarf.sections, unit, |range| {
+        ranges.for_each_range(sections, unit, |range| {
             inlined_addresses.push(InlinedFunctionAddress {
                 range,
                 call_depth: inlined_depth,
@@ -432,8 +454,10 @@ impl<R: gimli::Reader> InlinedFunction<R> {
         Function::parse_children(
             entries,
             depth,
+            file,
             unit,
-            dwarf,
+            ctx,
+            sections,
             inlined_functions,
             inlined_addresses,
             inlined_depth + 1,
@@ -443,8 +467,10 @@ impl<R: gimli::Reader> InlinedFunction<R> {
 
 fn name_attr<R>(
     attr: gimli::AttributeValue<R>,
+    mut file: DebugFile,
     unit: &gimli::Unit<R>,
-    dwarf: &ResDwarf<R>,
+    ctx: &Context<R>,
+    sections: &gimli::Dwarf<R>,
     recursion_limit: usize,
 ) -> Result<Option<R>, Error>
 where
@@ -455,25 +481,18 @@ where
     }
 
     match attr {
-        gimli::AttributeValue::UnitRef(offset) => name_entry(unit, offset, dwarf, recursion_limit),
+        gimli::AttributeValue::UnitRef(offset) => {
+            name_entry(file, unit, offset, ctx, sections, recursion_limit)
+        }
         gimli::AttributeValue::DebugInfoRef(dr) => {
-            let res_unit = dwarf.find_unit(dr)?;
-            name_entry(
-                &res_unit.dw_unit,
-                gimli::UnitOffset(dr.0 - res_unit.offset.0),
-                dwarf,
-                recursion_limit,
-            )
+            let (unit, offset) = ctx.find_unit(dr, file)?;
+            name_entry(file, unit, offset, ctx, sections, recursion_limit)
         }
         gimli::AttributeValue::DebugInfoRefSup(dr) => {
-            if let Some(sup_dwarf) = dwarf.sup.as_ref() {
-                let res_unit = sup_dwarf.find_unit(dr)?;
-                name_entry(
-                    &res_unit.dw_unit,
-                    gimli::UnitOffset(dr.0 - res_unit.offset.0),
-                    sup_dwarf,
-                    recursion_limit,
-                )
+            if let Some(sup_sections) = sections.sup.as_ref() {
+                file = DebugFile::Supplementary;
+                let (unit, offset) = ctx.find_unit(dr, file)?;
+                name_entry(file, unit, offset, ctx, sup_sections, recursion_limit)
             } else {
                 Ok(None)
             }
@@ -483,9 +502,11 @@ where
 }
 
 fn name_entry<R>(
+    file: DebugFile,
     unit: &gimli::Unit<R>,
     offset: gimli::UnitOffset<R::Offset>,
-    dwarf: &ResDwarf<R>,
+    ctx: &Context<R>,
+    sections: &gimli::Dwarf<R>,
     recursion_limit: usize,
 ) -> Result<Option<R>, Error>
 where
@@ -504,12 +525,12 @@ where
         match entries.read_attribute(*spec) {
             Ok(ref attr) => match attr.name() {
                 gimli::DW_AT_linkage_name | gimli::DW_AT_MIPS_linkage_name => {
-                    if let Ok(val) = dwarf.sections.attr_string(unit, attr.value()) {
+                    if let Ok(val) = sections.attr_string(unit, attr.value()) {
                         return Ok(Some(val));
                     }
                 }
                 gimli::DW_AT_name => {
-                    if let Ok(val) = dwarf.sections.attr_string(unit, attr.value()) {
+                    if let Ok(val) = sections.attr_string(unit, attr.value()) {
                         name = Some(val);
                     }
                 }
@@ -527,7 +548,7 @@ where
     }
 
     if let Some(next) = next {
-        return name_attr(next, unit, dwarf, recursion_limit - 1);
+        return name_attr(next, file, unit, ctx, sections, recursion_limit - 1);
     }
 
     Ok(None)
diff --git a/vendor/addr2line/src/lazy.rs b/vendor/addr2line/src/lazy.rs
index a34ed176a..2df2ed6ca 100644
--- a/vendor/addr2line/src/lazy.rs
+++ b/vendor/addr2line/src/lazy.rs
@@ -10,6 +10,10 @@ impl<T> LazyCell<T> {
         }
     }
 
+    pub fn borrow(&self) -> Option<&T> {
+        unsafe { &*self.contents.get() }.as_ref()
+    }
+
     pub fn borrow_with(&self, closure: impl FnOnce() -> T) -> &T {
         // First check if we're already initialized...
         let ptr = self.contents.get();
diff --git a/vendor/addr2line/src/lib.rs b/vendor/addr2line/src/lib.rs
index 3afa37f8f..3270aad7e 100644
--- a/vendor/addr2line/src/lib.rs
+++ b/vendor/addr2line/src/lib.rs
@@ -25,19 +25,18 @@
 #![deny(missing_docs)]
 #![no_std]
 
+#[cfg(feature = "std")]
+extern crate std;
+
 #[allow(unused_imports)]
 #[macro_use]
 extern crate alloc;
 
-#[cfg(feature = "cpp_demangle")]
-extern crate cpp_demangle;
 #[cfg(feature = "fallible-iterator")]
 pub extern crate fallible_iterator;
 pub extern crate gimli;
 #[cfg(feature = "object")]
 pub extern crate object;
-#[cfg(feature = "rustc-demangle")]
-extern crate rustc_demangle;
 
 use alloc::borrow::Cow;
 use alloc::boxed::Box;
@@ -49,8 +48,10 @@ use alloc::vec::Vec;
 
 use core::cmp::{self, Ordering};
 use core::iter;
+use core::marker::PhantomData;
 use core::mem;
 use core::num::NonZeroU64;
+use core::ops::ControlFlow;
 use core::u64;
 
 use crate::function::{Function, Functions, InlinedFunction};
@@ -67,17 +68,124 @@ mod maybe_small {
     pub type IntoIter<T> = alloc::vec::IntoIter<T>;
 }
 
+#[cfg(all(feature = "std", feature = "object", feature = "memmap2"))]
+/// A simple builtin split DWARF loader.
+pub mod builtin_split_dwarf_loader;
 mod function;
 mod lazy;
 
 type Error = gimli::Error;
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum DebugFile {
+    Primary,
+    Supplementary,
+    Dwo,
+}
+
+/// Operations that consult debug information may require additional files
+/// to be loaded if split DWARF is being used. This enum returns the result
+/// of the operation in the `Break` variant, or information about the split
+/// DWARF that is required and a continuation to invoke once it is available
+/// in the `Continue` variant.
+///
+/// This enum is intended to be used in a loop like so:
+/// ```no_run
+///   # use addr2line::*;
+///   # use std::sync::Arc;
+///   # let ctx: Context<gimli::EndianRcSlice<gimli::RunTimeEndian>> = todo!();
+///   # let do_split_dwarf_load = |load: SplitDwarfLoad<gimli::EndianRcSlice<gimli::RunTimeEndian>>| -> Option<Arc<gimli::Dwarf<gimli::EndianRcSlice<gimli::RunTimeEndian>>>> { None };
+///   const ADDRESS: u64 = 0xdeadbeef;
+///   let mut r = ctx.find_frames(ADDRESS);
+///   let result = loop {
+///     match r {
+///       LookupResult::Output(result) => break result,
+///       LookupResult::Load { load, continuation } => {
+///         let dwo = do_split_dwarf_load(load);
+///         r = continuation.resume(dwo);
+///       }
+///     }
+///   };
+/// ```
+pub enum LookupResult<L: LookupContinuation> {
+    /// The lookup requires split DWARF data to be loaded.
+    Load {
+        /// The information needed to find the split DWARF data.
+        load: SplitDwarfLoad<<L as LookupContinuation>::Buf>,
+        /// The continuation to resume with the loaded split DWARF data.
+        continuation: L,
+    },
+    /// The lookup has completed and produced an output.
+    Output(<L as LookupContinuation>::Output),
+}
+
+/// This trait represents a partially complete operation that can be resumed
+/// once a load of needed split DWARF data is completed or abandoned by the
+/// API consumer.
+pub trait LookupContinuation: Sized {
+    /// The final output of this operation.
+    type Output;
+    /// The type of reader used.
+    type Buf: gimli::Reader;
+
+    /// Resumes the operation with the provided data.
+    ///
+    /// After the caller loads the split DWARF data required, call this
+    /// method to resume the operation. The return value of this method
+    /// indicates if the computation has completed or if further data is
+    /// required.
+    ///
+    /// If the additional data cannot be located, or the caller does not
+    /// support split DWARF, `resume(None)` can be used to continue the
+    /// operation with the data that is available.
+    fn resume(self, input: Option<Arc<gimli::Dwarf<Self::Buf>>>) -> LookupResult<Self>;
+}
+
+impl<L: LookupContinuation> LookupResult<L> {
+    /// Callers that do not handle split DWARF can call `skip_all_loads`
+    /// to fast-forward to the end result. This result is produced with
+    /// the data that is available and may be less accurate than the
+    /// the results that would be produced if the caller did properly
+    /// support split DWARF.
+    pub fn skip_all_loads(mut self) -> L::Output {
+        loop {
+            self = match self {
+                LookupResult::Output(t) => return t,
+                LookupResult::Load { continuation, .. } => continuation.resume(None),
+            };
+        }
+    }
+
+    fn map<T, F: FnOnce(L::Output) -> T>(self, f: F) -> LookupResult<MappedLookup<T, L, F>> {
+        match self {
+            LookupResult::Output(t) => LookupResult::Output(f(t)),
+            LookupResult::Load { load, continuation } => LookupResult::Load {
+                load,
+                continuation: MappedLookup {
+                    original: continuation,
+                    mutator: f,
+                },
+            },
+        }
+    }
+
+    fn unwrap(self) -> L::Output {
+        match self {
+            LookupResult::Output(t) => t,
+            LookupResult::Load { .. } => unreachable!("Internal API misuse"),
+        }
+    }
+}
+
 /// The state necessary to perform address to line translation.
 ///
 /// Constructing a `Context` is somewhat costly, so users should aim to reuse `Context`s
 /// when performing lookups for many addresses in the same executable.
 pub struct Context<R: gimli::Reader> {
-    dwarf: ResDwarf<R>,
+    sections: Arc<gimli::Dwarf<R>>,
+    unit_ranges: Box<[UnitRange]>,
+    units: Box<[ResUnit<R>]>,
+    sup_units: Box<[SupUnit<R>]>,
 }
 
 /// The type of `Context` that supports the `new` method.
@@ -109,7 +217,7 @@ impl Context<gimli::EndianRcSlice<gimli::RunTimeEndian>> {
     /// This means it is not thread safe, has no lifetime constraints (since it copies
     /// the input data), and works for any endianity.
     ///
-    /// Performance sensitive applications may want to use `Context::from_dwarf_with_sup`
+    /// Performance sensitive applications may want to use `Context::from_dwarf`
     /// with a more specialised `gimli::Reader` implementation.
     pub fn new_with_sup<'data: 'file, 'file, O: object::Object<'data, 'file>>(
         file: &'file O,
@@ -176,7 +284,7 @@ impl<R: gimli::Reader> Context<R> {
             debug_types: default_section.clone().into(),
             locations: gimli::LocationLists::new(
                 default_section.clone().into(),
-                default_section.clone().into(),
+                default_section.into(),
             ),
             ranges: gimli::RangeLists::new(debug_ranges, debug_rnglists),
             file_type: gimli::DwarfFileType::Main,
@@ -187,18 +295,20 @@ impl<R: gimli::Reader> Context<R> {
 
     /// Construct a new `Context` from an existing [`gimli::Dwarf`] object.
     #[inline]
-    pub fn from_dwarf(sections: gimli::Dwarf<R>) -> Result<Self, Error> {
-        let mut dwarf = ResDwarf::parse(Arc::new(sections))?;
-        dwarf.sup = match dwarf.sections.sup.clone() {
-            Some(sup_sections) => Some(Box::new(ResDwarf::parse(sup_sections)?)),
-            None => None,
+    pub fn from_dwarf(sections: gimli::Dwarf<R>) -> Result<Context<R>, Error> {
+        let sections = Arc::new(sections);
+        let (unit_ranges, units) = Context::parse_units(&sections)?;
+        let sup_units = if let Some(sup) = sections.sup.as_ref() {
+            Context::parse_sup(sup)?
+        } else {
+            Vec::new()
         };
-        Ok(Context { dwarf })
-    }
-
-    /// The dwarf sections associated with this `Context`.
-    pub fn dwarf(&self) -> &gimli::Dwarf<R> {
-        &self.dwarf.sections
+        Ok(Context {
+            sections,
+            unit_ranges: unit_ranges.into_boxed_slice(),
+            units: units.into_boxed_slice(),
+            sup_units: sup_units.into_boxed_slice(),
+        })
     }
 
     /// Finds the CUs for the function address given.
@@ -229,7 +339,6 @@ impl<R: gimli::Reader> Context<R> {
         // First up find the position in the array which could have our function
         // address.
         let pos = match self
-            .dwarf
             .unit_ranges
             .binary_search_by_key(&probe_high, |i| i.range.begin)
         {
@@ -244,7 +353,7 @@ impl<R: gimli::Reader> Context<R> {
 
         // Once we have our index we iterate backwards from that position
         // looking for a matching CU.
-        self.dwarf.unit_ranges[..pos]
+        self.unit_ranges[..pos]
             .iter()
             .rev()
             .take_while(move |i| {
@@ -265,25 +374,51 @@ impl<R: gimli::Reader> Context<R> {
                 if probe_low >= i.range.end || probe_high <= i.range.begin {
                     return None;
                 }
-                Some((&self.dwarf.units[i.unit_id], &i.range))
+                Some((&self.units[i.unit_id], &i.range))
             })
     }
 
     /// Find the DWARF unit corresponding to the given virtual memory address.
-    pub fn find_dwarf_unit(&self, probe: u64) -> Option<&gimli::Unit<R>> {
-        for unit in self.find_units(probe) {
-            match unit.find_function_or_location(probe, &self.dwarf) {
-                Ok((Some(_), _)) | Ok((_, Some(_))) => return Some(&unit.dw_unit),
-                _ => {}
-            }
+    pub fn find_dwarf_and_unit(
+        &self,
+        probe: u64,
+    ) -> LookupResult<
+        impl LookupContinuation<Output = Option<(&gimli::Dwarf<R>, &gimli::Unit<R>)>, Buf = R>,
+    > {
+        let mut units_iter = self.find_units(probe);
+        if let Some(unit) = units_iter.next() {
+            return LoopingLookup::new_lookup(
+                unit.find_function_or_location(probe, self),
+                move |r| {
+                    ControlFlow::Break(match r {
+                        Ok((Some(_), _)) | Ok((_, Some(_))) => {
+                            let (_file, sections, unit) = unit
+                                .dwarf_and_unit_dwo(self)
+                                // We've already been through both error cases here to get to this point.
+                                .unwrap()
+                                .unwrap();
+                            Some((sections, unit))
+                        }
+                        _ => match units_iter.next() {
+                            Some(next_unit) => {
+                                return ControlFlow::Continue(
+                                    next_unit.find_function_or_location(probe, self),
+                                );
+                            }
+                            None => None,
+                        },
+                    })
+                },
+            );
         }
-        None
+
+        LoopingLookup::new_complete(None)
     }
 
     /// Find the source file and line corresponding to the given virtual memory address.
     pub fn find_location(&self, probe: u64) -> Result<Option<Location<'_>>, Error> {
         for unit in self.find_units(probe) {
-            if let Some(location) = unit.find_location(probe, &self.dwarf.sections)? {
+            if let Some(location) = unit.find_location(probe, &self.sections)? {
                 return Ok(Some(location));
             }
         }
@@ -309,33 +444,95 @@ impl<R: gimli::Reader> Context<R> {
     /// If the probe address is for an inline function then the first frame corresponds
     /// to the innermost inline function.  Subsequent frames contain the caller and call
     /// location, until an non-inline caller is reached.
-    pub fn find_frames(&self, probe: u64) -> Result<FrameIter<R>, Error> {
-        for unit in self.find_units(probe) {
-            match unit.find_function_or_location(probe, &self.dwarf)? {
-                (Some(function), location) => {
-                    let inlined_functions = function.find_inlined_functions(probe);
-                    return Ok(FrameIter(FrameIterState::Frames(FrameIterFrames {
-                        unit,
-                        sections: &self.dwarf.sections,
-                        function,
-                        inlined_functions,
-                        next: location,
-                    })));
-                }
-                (None, Some(location)) => {
-                    return Ok(FrameIter(FrameIterState::Location(Some(location))));
-                }
-                _ => {}
-            }
+    pub fn find_frames(
+        &self,
+        probe: u64,
+    ) -> LookupResult<impl LookupContinuation<Output = Result<FrameIter<'_, R>, Error>, Buf = R>>
+    {
+        let mut units_iter = self.find_units(probe);
+        if let Some(unit) = units_iter.next() {
+            LoopingLookup::new_lookup(unit.find_function_or_location(probe, self), move |r| {
+                ControlFlow::Break(match r {
+                    Err(e) => Err(e),
+                    Ok((Some(function), location)) => {
+                        let inlined_functions = function.find_inlined_functions(probe);
+                        Ok(FrameIter(FrameIterState::Frames(FrameIterFrames {
+                            unit,
+                            sections: &self.sections,
+                            function,
+                            inlined_functions,
+                            next: location,
+                        })))
+                    }
+                    Ok((None, Some(location))) => {
+                        Ok(FrameIter(FrameIterState::Location(Some(location))))
+                    }
+                    Ok((None, None)) => match units_iter.next() {
+                        Some(next_unit) => {
+                            return ControlFlow::Continue(
+                                next_unit.find_function_or_location(probe, self),
+                            );
+                        }
+                        None => Ok(FrameIter(FrameIterState::Empty)),
+                    },
+                })
+            })
+        } else {
+            LoopingLookup::new_complete(Ok(FrameIter(FrameIterState::Empty)))
         }
-        Ok(FrameIter(FrameIterState::Empty))
+    }
+
+    /// Preload units for `probe`.
+    ///
+    /// The iterator returns pairs of `SplitDwarfLoad`s containing the
+    /// information needed to locate and load split DWARF for `probe` and
+    /// a matching callback to invoke once that data is available.
+    ///
+    /// If this method is called, and all of the returned closures are invoked,
+    /// addr2line guarantees that any future API call for the address `probe`
+    /// will not require the loading of any split DWARF.
+    ///
+    /// ```no_run
+    ///   # use addr2line::*;
+    ///   # use std::sync::Arc;
+    ///   # let ctx: Context<gimli::EndianRcSlice<gimli::RunTimeEndian>> = todo!();
+    ///   # let do_split_dwarf_load = |load: SplitDwarfLoad<gimli::EndianRcSlice<gimli::RunTimeEndian>>| -> Option<Arc<gimli::Dwarf<gimli::EndianRcSlice<gimli::RunTimeEndian>>>> { None };
+    ///   const ADDRESS: u64 = 0xdeadbeef;
+    ///   ctx.preload_units(ADDRESS).for_each(|(load, callback)| {
+    ///     let dwo = do_split_dwarf_load(load);
+    ///     callback(dwo);
+    ///   });
+    ///
+    ///   let frames_iter = match ctx.find_frames(ADDRESS) {
+    ///     LookupResult::Output(result) => result,
+    ///     LookupResult::Load { .. } => unreachable!("addr2line promised we wouldn't get here"),
+    ///   };
+    ///
+    ///   // ...
+    /// ```
+    pub fn preload_units(
+        &'_ self,
+        probe: u64,
+    ) -> impl Iterator<
+        Item = (
+            SplitDwarfLoad<R>,
+            impl FnOnce(Option<Arc<gimli::Dwarf<R>>>) -> Result<(), gimli::Error> + '_,
+        ),
+    > {
+        self.find_units(probe)
+            .filter_map(move |unit| match unit.dwarf_and_unit_dwo(self) {
+                LookupResult::Output(_) => None,
+                LookupResult::Load { load, continuation } => Some((load, |result| {
+                    continuation.resume(result).unwrap().map(|_| ())
+                })),
+            })
     }
 
     /// Initialize all line data structures. This is used for benchmarks.
     #[doc(hidden)]
     pub fn parse_lines(&self) -> Result<(), Error> {
-        for unit in &self.dwarf.units {
-            unit.parse_lines(&self.dwarf.sections)?;
+        for unit in self.units.iter() {
+            unit.parse_lines(&self.sections)?;
         }
         Ok(())
     }
@@ -343,8 +540,8 @@ impl<R: gimli::Reader> Context<R> {
     /// Initialize all function data structures. This is used for benchmarks.
     #[doc(hidden)]
     pub fn parse_functions(&self) -> Result<(), Error> {
-        for unit in &self.dwarf.units {
-            unit.parse_functions(&self.dwarf)?;
+        for unit in self.units.iter() {
+            unit.parse_functions(self).skip_all_loads()?;
         }
         Ok(())
     }
@@ -352,8 +549,8 @@ impl<R: gimli::Reader> Context<R> {
     /// Initialize all inlined function data structures. This is used for benchmarks.
     #[doc(hidden)]
     pub fn parse_inlined_functions(&self) -> Result<(), Error> {
-        for unit in &self.dwarf.units {
-            unit.parse_inlined_functions(&self.dwarf)?;
+        for unit in self.units.iter() {
+            unit.parse_inlined_functions(self).skip_all_loads()?;
         }
         Ok(())
     }
@@ -365,15 +562,22 @@ struct UnitRange {
     range: gimli::Range,
 }
 
-struct ResDwarf<R: gimli::Reader> {
-    unit_ranges: Vec<UnitRange>,
-    units: Vec<ResUnit<R>>,
-    sections: Arc<gimli::Dwarf<R>>,
-    sup: Option<Box<ResDwarf<R>>>,
+struct ResUnit<R: gimli::Reader> {
+    offset: gimli::DebugInfoOffset<R::Offset>,
+    dw_unit: gimli::Unit<R>,
+    lang: Option<gimli::DwLang>,
+    lines: LazyCell<Result<Lines, Error>>,
+    funcs: LazyCell<Result<Functions<R>, Error>>,
+    dwo: LazyCell<Result<Option<Box<(Arc<gimli::Dwarf<R>>, gimli::Unit<R>)>>, Error>>,
+}
+
+struct SupUnit<R: gimli::Reader> {
+    offset: gimli::DebugInfoOffset<R::Offset>,
+    dw_unit: gimli::Unit<R>,
 }
 
-impl<R: gimli::Reader> ResDwarf<R> {
-    fn parse(sections: Arc<gimli::Dwarf<R>>) -> Result<Self, Error> {
+impl<R: gimli::Reader> Context<R> {
+    fn parse_units(sections: &gimli::Dwarf<R>) -> Result<(Vec<UnitRange>, Vec<ResUnit<R>>), Error> {
         // Find all the references to compilation units in .debug_aranges.
         // Note that we always also iterate through all of .debug_info to
         // find compilation units, because .debug_aranges may be missing some.
@@ -484,7 +688,7 @@ impl<R: gimli::Reader> ResDwarf<R> {
                         }
                     }
                 } else {
-                    have_unit_range |= ranges.for_each_range(&sections, &dw_unit, |range| {
+                    have_unit_range |= ranges.for_each_range(sections, &dw_unit, |range| {
                         unit_ranges.push(UnitRange {
                             range,
                             unit_id,
@@ -500,7 +704,7 @@ impl<R: gimli::Reader> ResDwarf<R> {
                 // Try to get some ranges from the line program sequences.
                 if let Some(ref ilnp) = dw_unit.line_program {
                     if let Ok(lines) = lines
-                        .borrow_with(|| Lines::parse(&dw_unit, ilnp.clone(), &*sections))
+                        .borrow_with(|| Lines::parse(&dw_unit, ilnp.clone(), sections))
                         .as_ref()
                     {
                         for sequence in lines.sequences.iter() {
@@ -523,6 +727,7 @@ impl<R: gimli::Reader> ResDwarf<R> {
                 lang,
                 lines,
                 funcs: LazyCell::new(),
+                dwo: LazyCell::new(),
             });
         }
 
@@ -537,23 +742,60 @@ impl<R: gimli::Reader> ResDwarf<R> {
             i.max_end = max;
         }
 
-        Ok(ResDwarf {
-            units: res_units,
-            unit_ranges,
-            sections,
-            sup: None,
-        })
+        Ok((unit_ranges, res_units))
     }
 
-    fn find_unit(&self, offset: gimli::DebugInfoOffset<R::Offset>) -> Result<&ResUnit<R>, Error> {
-        match self
-            .units
-            .binary_search_by_key(&offset.0, |unit| unit.offset.0)
-        {
-            // There is never a DIE at the unit offset or before the first unit.
-            Ok(_) | Err(0) => Err(gimli::Error::NoEntryAtGivenOffset),
-            Err(i) => Ok(&self.units[i - 1]),
+    fn parse_sup(sections: &gimli::Dwarf<R>) -> Result<Vec<SupUnit<R>>, Error> {
+        let mut sup_units = Vec::new();
+        let mut units = sections.units();
+        while let Some(header) = units.next()? {
+            let offset = match header.offset().as_debug_info_offset() {
+                Some(offset) => offset,
+                None => continue,
+            };
+            let dw_unit = match sections.unit(header) {
+                Ok(dw_unit) => dw_unit,
+                Err(_) => continue,
+            };
+            sup_units.push(SupUnit { dw_unit, offset });
         }
+        Ok(sup_units)
+    }
+
+    // Find the unit containing the given offset, and convert the offset into a unit offset.
+    fn find_unit(
+        &self,
+        offset: gimli::DebugInfoOffset<R::Offset>,
+        file: DebugFile,
+    ) -> Result<(&gimli::Unit<R>, gimli::UnitOffset<R::Offset>), Error> {
+        let unit = match file {
+            DebugFile::Primary => {
+                match self
+                    .units
+                    .binary_search_by_key(&offset.0, |unit| unit.offset.0)
+                {
+                    // There is never a DIE at the unit offset or before the first unit.
+                    Ok(_) | Err(0) => return Err(gimli::Error::NoEntryAtGivenOffset),
+                    Err(i) => &self.units[i - 1].dw_unit,
+                }
+            }
+            DebugFile::Supplementary => {
+                match self
+                    .sup_units
+                    .binary_search_by_key(&offset.0, |unit| unit.offset.0)
+                {
+                    // There is never a DIE at the unit offset or before the first unit.
+                    Ok(_) | Err(0) => return Err(gimli::Error::NoEntryAtGivenOffset),
+                    Err(i) => &self.sup_units[i - 1].dw_unit,
+                }
+            }
+            DebugFile::Dwo => return Err(gimli::Error::NoEntryAtGivenOffset),
+        };
+
+        let unit_offset = offset
+            .to_unit_offset(&unit.header)
+            .ok_or(gimli::Error::NoEntryAtGivenOffset)?;
+        Ok((unit, unit_offset))
     }
 }
 
@@ -680,16 +922,247 @@ struct LineRow {
     column: u32,
 }
 
-struct ResUnit<R: gimli::Reader> {
-    offset: gimli::DebugInfoOffset<R::Offset>,
-    dw_unit: gimli::Unit<R>,
-    lang: Option<gimli::DwLang>,
-    lines: LazyCell<Result<Lines, Error>>,
-    funcs: LazyCell<Result<Functions<R>, Error>>,
+/// This struct contains the information needed to find split DWARF data
+/// and to produce a `gimli::Dwarf<R>` for it.
+pub struct SplitDwarfLoad<R> {
+    /// The dwo id, for looking up in a DWARF package, or for
+    /// verifying an unpacked dwo found on the file system
+    pub dwo_id: gimli::DwoId,
+    /// The compilation directory `path` is relative to.
+    pub comp_dir: Option<R>,
+    /// A path on the filesystem, relative to `comp_dir` to find this dwo.
+    pub path: Option<R>,
+    /// Once the split DWARF data is loaded, the loader is expected
+    /// to call [make_dwo(parent)](gimli::read::Dwarf::make_dwo) before
+    /// returning the data.
+    pub parent: Arc<gimli::Dwarf<R>>,
+}
+
+struct SimpleLookup<T, R, F>
+where
+    F: FnOnce(Option<Arc<gimli::Dwarf<R>>>) -> T,
+    R: gimli::Reader,
+{
+    f: F,
+    phantom: PhantomData<(T, R)>,
+}
+
+impl<T, R, F> SimpleLookup<T, R, F>
+where
+    F: FnOnce(Option<Arc<gimli::Dwarf<R>>>) -> T,
+    R: gimli::Reader,
+{
+    fn new_complete(t: F::Output) -> LookupResult<SimpleLookup<T, R, F>> {
+        LookupResult::Output(t)
+    }
+
+    fn new_needs_load(load: SplitDwarfLoad<R>, f: F) -> LookupResult<SimpleLookup<T, R, F>> {
+        LookupResult::Load {
+            load,
+            continuation: SimpleLookup {
+                f,
+                phantom: PhantomData,
+            },
+        }
+    }
+}
+
+impl<T, R, F> LookupContinuation for SimpleLookup<T, R, F>
+where
+    F: FnOnce(Option<Arc<gimli::Dwarf<R>>>) -> T,
+    R: gimli::Reader,
+{
+    type Output = T;
+    type Buf = R;
+
+    fn resume(self, v: Option<Arc<gimli::Dwarf<Self::Buf>>>) -> LookupResult<Self> {
+        LookupResult::Output((self.f)(v))
+    }
+}
+
+struct MappedLookup<T, L, F>
+where
+    L: LookupContinuation,
+    F: FnOnce(L::Output) -> T,
+{
+    original: L,
+    mutator: F,
+}
+
+impl<T, L, F> LookupContinuation for MappedLookup<T, L, F>
+where
+    L: LookupContinuation,
+    F: FnOnce(L::Output) -> T,
+{
+    type Output = T;
+    type Buf = L::Buf;
+
+    fn resume(self, v: Option<Arc<gimli::Dwarf<Self::Buf>>>) -> LookupResult<Self> {
+        match self.original.resume(v) {
+            LookupResult::Output(t) => LookupResult::Output((self.mutator)(t)),
+            LookupResult::Load { load, continuation } => LookupResult::Load {
+                load,
+                continuation: MappedLookup {
+                    original: continuation,
+                    mutator: self.mutator,
+                },
+            },
+        }
+    }
+}
+
+/// Some functions (e.g. `find_frames`) require considering multiple
+/// compilation units, each of which might require their own split DWARF
+/// lookup (and thus produce a continuation).
+///
+/// We store the underlying continuation here as well as a mutator function
+/// that will either a) decide that the result of this continuation is
+/// what is needed and mutate it to the final result or b) produce another
+/// `LookupResult`. `new_lookup` will in turn eagerly drive any non-continuation
+/// `LookupResult` with successive invocations of the mutator, until a new
+/// continuation or a final result is produced. And finally, the impl of
+/// `LookupContinuation::resume` will call `new_lookup` each time the
+/// computation is resumed.
+struct LoopingLookup<T, L, F>
+where
+    L: LookupContinuation,
+    F: FnMut(L::Output) -> ControlFlow<T, LookupResult<L>>,
+{
+    continuation: L,
+    mutator: F,
+}
+
+impl<T, L, F> LoopingLookup<T, L, F>
+where
+    L: LookupContinuation,
+    F: FnMut(L::Output) -> ControlFlow<T, LookupResult<L>>,
+{
+    fn new_complete(t: T) -> LookupResult<Self> {
+        LookupResult::Output(t)
+    }
+
+    fn new_lookup(mut r: LookupResult<L>, mut mutator: F) -> LookupResult<Self> {
+        // Drive the loop eagerly so that we only ever have to represent one state
+        // (the r == ControlFlow::Continue state) in LoopingLookup.
+        loop {
+            match r {
+                LookupResult::Output(l) => match mutator(l) {
+                    ControlFlow::Break(t) => return LookupResult::Output(t),
+                    ControlFlow::Continue(r2) => {
+                        r = r2;
+                    }
+                },
+                LookupResult::Load { load, continuation } => {
+                    return LookupResult::Load {
+                        load,
+                        continuation: LoopingLookup {
+                            continuation,
+                            mutator,
+                        },
+                    };
+                }
+            }
+        }
+    }
+}
+
+impl<T, L, F> LookupContinuation for LoopingLookup<T, L, F>
+where
+    L: LookupContinuation,
+    F: FnMut(L::Output) -> ControlFlow<T, LookupResult<L>>,
+{
+    type Output = T;
+    type Buf = L::Buf;
+
+    fn resume(self, v: Option<Arc<gimli::Dwarf<Self::Buf>>>) -> LookupResult<Self> {
+        let r = self.continuation.resume(v);
+        LoopingLookup::new_lookup(r, self.mutator)
+    }
 }
 
 impl<R: gimli::Reader> ResUnit<R> {
+    fn dwarf_and_unit_dwo<'unit, 'ctx: 'unit>(
+        &'unit self,
+        ctx: &'ctx Context<R>,
+    ) -> LookupResult<
+        SimpleLookup<
+            Result<(DebugFile, &'unit gimli::Dwarf<R>, &'unit gimli::Unit<R>), Error>,
+            R,
+            impl FnOnce(
+                Option<Arc<gimli::Dwarf<R>>>,
+            )
+                -> Result<(DebugFile, &'unit gimli::Dwarf<R>, &'unit gimli::Unit<R>), Error>,
+        >,
+    > {
+        loop {
+            break SimpleLookup::new_complete(match self.dwo.borrow() {
+                Some(Ok(Some(v))) => Ok((DebugFile::Dwo, &*v.0, &v.1)),
+                Some(Ok(None)) => Ok((DebugFile::Primary, &*ctx.sections, &self.dw_unit)),
+                Some(Err(e)) => Err(*e),
+                None => {
+                    let dwo_id = match self.dw_unit.dwo_id {
+                        None => {
+                            self.dwo.borrow_with(|| Ok(None));
+                            continue;
+                        }
+                        Some(dwo_id) => dwo_id,
+                    };
+
+                    let comp_dir = self.dw_unit.comp_dir.clone();
+
+                    let dwo_name = self.dw_unit.dwo_name().and_then(|s| {
+                        if let Some(s) = s {
+                            Ok(Some(ctx.sections.attr_string(&self.dw_unit, s)?))
+                        } else {
+                            Ok(None)
+                        }
+                    });
+
+                    let path = match dwo_name {
+                        Ok(v) => v,
+                        Err(e) => {
+                            self.dwo.borrow_with(|| Err(e));
+                            continue;
+                        }
+                    };
+
+                    let process_dwo = move |dwo_dwarf: Option<Arc<gimli::Dwarf<R>>>| {
+                        let dwo_dwarf = match dwo_dwarf {
+                            None => return Ok(None),
+                            Some(dwo_dwarf) => dwo_dwarf,
+                        };
+                        let mut dwo_units = dwo_dwarf.units();
+                        let dwo_header = match dwo_units.next()? {
+                            Some(dwo_header) => dwo_header,
+                            None => return Ok(None),
+                        };
+
+                        let mut dwo_unit = dwo_dwarf.unit(dwo_header)?;
+                        dwo_unit.copy_relocated_attributes(&self.dw_unit);
+                        Ok(Some(Box::new((dwo_dwarf, dwo_unit))))
+                    };
+
+                    return SimpleLookup::new_needs_load(
+                        SplitDwarfLoad {
+                            dwo_id,
+                            comp_dir,
+                            path,
+                            parent: ctx.sections.clone(),
+                        },
+                        move |dwo_dwarf| match self.dwo.borrow_with(|| process_dwo(dwo_dwarf)) {
+                            Ok(Some(v)) => Ok((DebugFile::Dwo, &*v.0, &v.1)),
+                            Ok(None) => Ok((DebugFile::Primary, &*ctx.sections, &self.dw_unit)),
+                            Err(e) => Err(*e),
+                        },
+                    );
+                }
+            });
+        }
+    }
+
     fn parse_lines(&self, sections: &gimli::Dwarf<R>) -> Result<Option<&Lines>, Error> {
+        // NB: line information is always stored in the main debug file so this does not need
+        // to handle DWOs.
         let ilnp = match self.dw_unit.line_program {
             Some(ref ilnp) => ilnp,
             None => return Ok(None),
@@ -701,19 +1174,39 @@ impl<R: gimli::Reader> ResUnit<R> {
             .map_err(Error::clone)
     }
 
-    fn parse_functions(&self, dwarf: &ResDwarf<R>) -> Result<&Functions<R>, Error> {
+    fn parse_functions_dwarf_and_unit(
+        &self,
+        unit: &gimli::Unit<R>,
+        sections: &gimli::Dwarf<R>,
+    ) -> Result<&Functions<R>, Error> {
         self.funcs
-            .borrow_with(|| Functions::parse(&self.dw_unit, dwarf))
+            .borrow_with(|| Functions::parse(unit, sections))
             .as_ref()
             .map_err(Error::clone)
     }
 
-    fn parse_inlined_functions(&self, dwarf: &ResDwarf<R>) -> Result<(), Error> {
-        self.funcs
-            .borrow_with(|| Functions::parse(&self.dw_unit, dwarf))
-            .as_ref()
-            .map_err(Error::clone)?
-            .parse_inlined_functions(&self.dw_unit, dwarf)
+    fn parse_functions<'unit, 'ctx: 'unit>(
+        &'unit self,
+        ctx: &'ctx Context<R>,
+    ) -> LookupResult<impl LookupContinuation<Output = Result<&'unit Functions<R>, Error>, Buf = R>>
+    {
+        self.dwarf_and_unit_dwo(ctx).map(move |r| {
+            let (_file, sections, unit) = r?;
+            self.parse_functions_dwarf_and_unit(unit, sections)
+        })
+    }
+    fn parse_inlined_functions<'unit, 'ctx: 'unit>(
+        &'unit self,
+        ctx: &'ctx Context<R>,
+    ) -> LookupResult<impl LookupContinuation<Output = Result<(), Error>, Buf = R> + 'unit> {
+        self.dwarf_and_unit_dwo(ctx).map(move |r| {
+            let (file, sections, unit) = r?;
+            self.funcs
+                .borrow_with(|| Functions::parse(unit, sections))
+                .as_ref()
+                .map_err(Error::clone)?
+                .parse_inlined_functions(file, unit, ctx, sections)
+        })
     }
 
     fn find_location(
@@ -741,27 +1234,35 @@ impl<R: gimli::Reader> ResUnit<R> {
         LocationRangeUnitIter::new(self, sections, probe_low, probe_high)
     }
 
-    fn find_function_or_location(
-        &self,
+    fn find_function_or_location<'unit, 'ctx: 'unit>(
+        &'unit self,
         probe: u64,
-        dwarf: &ResDwarf<R>,
-    ) -> Result<(Option<&Function<R>>, Option<Location<'_>>), Error> {
-        let functions = self.parse_functions(dwarf)?;
-        let function = match functions.find_address(probe) {
-            Some(address) => {
-                let function_index = functions.addresses[address].function;
-                let (offset, ref function) = functions.functions[function_index];
-                Some(
-                    function
-                        .borrow_with(|| Function::parse(offset, &self.dw_unit, dwarf))
-                        .as_ref()
-                        .map_err(Error::clone)?,
-                )
-            }
-            None => None,
-        };
-        let location = self.find_location(probe, &dwarf.sections)?;
-        Ok((function, location))
+        ctx: &'ctx Context<R>,
+    ) -> LookupResult<
+        impl LookupContinuation<
+            Output = Result<(Option<&'unit Function<R>>, Option<Location<'unit>>), Error>,
+            Buf = R,
+        >,
+    > {
+        self.dwarf_and_unit_dwo(ctx).map(move |r| {
+            let (file, sections, unit) = r?;
+            let functions = self.parse_functions_dwarf_and_unit(unit, sections)?;
+            let function = match functions.find_address(probe) {
+                Some(address) => {
+                    let function_index = functions.addresses[address].function;
+                    let (offset, ref function) = functions.functions[function_index];
+                    Some(
+                        function
+                            .borrow_with(|| Function::parse(offset, file, unit, ctx, sections))
+                            .as_ref()
+                            .map_err(Error::clone)?,
+                    )
+                }
+                None => None,
+            };
+            let location = self.find_location(probe, sections)?;
+            Ok((function, location))
+        })
     }
 }
 
@@ -778,7 +1279,7 @@ pub struct LocationRangeIter<'ctx, R: gimli::Reader> {
 impl<'ctx, R: gimli::Reader> LocationRangeIter<'ctx, R> {
     #[inline]
     fn new(ctx: &'ctx Context<R>, probe_low: u64, probe_high: u64) -> Result<Self, Error> {
-        let sections = &ctx.dwarf.sections;
+        let sections = &ctx.sections;
         let unit_iter = ctx.find_units_range(probe_low, probe_high);
         Ok(Self {
             unit_iter: Box::new(unit_iter),
@@ -879,12 +1380,11 @@ impl<'ctx> LocationRangeUnitIter<'ctx> {
 
             let row_idx = if let Some(seq) = lines.sequences.get(seq_idx) {
                 let idx = seq.rows.binary_search_by(|row| row.address.cmp(&probe_low));
-                let idx = match idx {
+                match idx {
                     Ok(x) => x,
                     Err(0) => 0, // probe below sequence, but range could overlap
                     Err(x) => x - 1,
-                };
-                idx
+                }
             } else {
                 0
             };
@@ -906,12 +1406,7 @@ impl<'ctx> Iterator for LocationRangeUnitIter<'ctx> {
     type Item = (u64, u64, Location<'ctx>);
 
     fn next(&mut self) -> Option<(u64, u64, Location<'ctx>)> {
-        loop {
-            let seq = match self.seqs.get(self.seq_idx) {
-                Some(seq) => seq,
-                None => break,
-            };
-
+        while let Some(seq) = self.seqs.get(self.seq_idx) {
             if seq.start >= self.probe_high {
                 break;
             }
@@ -1038,11 +1533,11 @@ impl<R: gimli::Reader> RangeAttributes<R> {
 /// An iterator over function frames.
 pub struct FrameIter<'ctx, R>(FrameIterState<'ctx, R>)
 where
-    R: gimli::Reader + 'ctx;
+    R: gimli::Reader;
 
 enum FrameIterState<'ctx, R>
 where
-    R: gimli::Reader + 'ctx,
+    R: gimli::Reader,
 {
     Empty,
     Location(Option<Location<'ctx>>),
@@ -1051,7 +1546,7 @@ where
 
 struct FrameIterFrames<'ctx, R>
 where
-    R: gimli::Reader + 'ctx,
+    R: gimli::Reader,
 {
     unit: &'ctx ResUnit<R>,
     sections: &'ctx gimli::Dwarf<R>,
@@ -1111,9 +1606,9 @@ where
                 None
             },
         };
-        if func.call_file != 0 {
+        if let Some(call_file) = func.call_file {
             if let Some(lines) = frames.unit.parse_lines(frames.sections)? {
-                next.file = lines.files.get(func.call_file as usize).map(String::as_str);
+                next.file = lines.files.get(call_file as usize).map(String::as_str);
             }
         }
         frames.next = Some(next);
@@ -1163,12 +1658,12 @@ pub struct FunctionName<R: gimli::Reader> {
 
 impl<R: gimli::Reader> FunctionName<R> {
     /// The raw name of this function before demangling.
-    pub fn raw_name(&self) -> Result<Cow<str>, Error> {
+    pub fn raw_name(&self) -> Result<Cow<'_, str>, Error> {
         self.name.to_string_lossy()
     }
 
     /// The name of this function after demangling (if applicable).
-    pub fn demangle(&self) -> Result<Cow<str>, Error> {
+    pub fn demangle(&self) -> Result<Cow<'_, str>, Error> {
         self.raw_name().map(|x| demangle_auto(x, self.language))
     }
 }
@@ -1204,7 +1699,7 @@ pub fn demangle(name: &str, language: gimli::DwLang) -> Option<String> {
 /// demangle the name. Currently, these heuristics are very basic.
 ///
 /// If demangling fails or is not required, then `name` is returned unchanged.
-pub fn demangle_auto(name: Cow<str>, language: Option<gimli::DwLang>) -> Cow<str> {
+pub fn demangle_auto(name: Cow<'_, str>, language: Option<gimli::DwLang>) -> Cow<'_, str> {
     match language {
         Some(language) => demangle(name.as_ref(), language),
         None => demangle(name.as_ref(), gimli::DW_LANG_Rust)
@@ -1229,6 +1724,6 @@ mod tests {
     #[test]
     fn context_is_send() {
         fn assert_is_send<T: Send>() {}
-        assert_is_send::<crate::Context<gimli::read::EndianSlice<gimli::LittleEndian>>>();
+        assert_is_send::<crate::Context<gimli::read::EndianSlice<'_, gimli::LittleEndian>>>();
     }
 }