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Change how wasm DWARF is inserted into artifacts #5358

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Dec 6, 2022
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Change how wasm DWARF is inserted into artifacts #5358

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9 changes: 9 additions & 0 deletions crates/environ/src/obj.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -119,3 +119,12 @@ pub const ELF_WASMTIME_INFO: &'static str = ".wasmtime.info";
/// sometimes quite large (3MB seen for spidermonkey-compiled-to-wasm), can be
/// paged in lazily from an mmap and is never paged in if we never reference it.
pub const ELF_NAME_DATA: &'static str = ".name.wasm";

/// This is the name of the section in the final ELF image that contains the
/// concatenation of all the native DWARF information found in the original wasm
/// files.
///
/// This concatenation is not intended to be read by external tools at this time
/// and is instead indexed directly by relative indices stored in compilation
/// metadata.
pub const ELF_WASMTIME_DWARF: &str = ".wasmtime.dwarf";
57 changes: 7 additions & 50 deletions crates/jit/src/code_memory.rs
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Expand Up @@ -32,10 +32,7 @@ pub struct CodeMemory {
address_map_data: Range<usize>,
func_name_data: Range<usize>,
info_data: Range<usize>,

/// Map of dwarf sections indexed by `gimli::SectionId` which points to the
/// range within `code_memory`'s mmap as to the contents of the section.
dwarf_sections: Vec<Range<usize>>,
dwarf: Range<usize>,
}

impl Drop for CodeMemory {
Expand All @@ -60,8 +57,6 @@ impl CodeMemory {
/// The returned `CodeMemory` manages the internal `MmapVec` and the
/// `publish` method is used to actually make the memory executable.
pub fn new(mmap: MmapVec) -> Result<Self> {
use gimli::SectionId::*;

let obj = File::parse(&mmap[..])
.with_context(|| "failed to parse internal compilation artifact")?;

Expand All @@ -73,7 +68,7 @@ impl CodeMemory {
let mut address_map_data = 0..0;
let mut func_name_data = 0..0;
let mut info_data = 0..0;
let mut dwarf_sections = Vec::new();
let mut dwarf = 0..0;
for section in obj.sections() {
let data = section.data()?;
let name = section.name()?;
Expand All @@ -90,14 +85,6 @@ impl CodeMemory {
}
}

let mut gimli = |id: gimli::SectionId| {
let idx = id as usize;
if dwarf_sections.len() <= idx {
dwarf_sections.resize(idx + 1, 0..0);
}
dwarf_sections[idx] = range.clone();
};

match name {
obj::ELF_WASM_BTI => match data.len() {
1 => enable_branch_protection = Some(data[0] != 0),
Expand All @@ -118,31 +105,7 @@ impl CodeMemory {
obj::ELF_WASMTIME_TRAPS => trap_data = range,
obj::ELF_NAME_DATA => func_name_data = range,
obj::ELF_WASMTIME_INFO => info_data = range,

// Register dwarf sections into the `dwarf_sections`
// array which is indexed by `gimli::SectionId`
".debug_abbrev.wasm" => gimli(DebugAbbrev),
".debug_addr.wasm" => gimli(DebugAddr),
".debug_aranges.wasm" => gimli(DebugAranges),
".debug_frame.wasm" => gimli(DebugFrame),
".eh_frame.wasm" => gimli(EhFrame),
".eh_frame_hdr.wasm" => gimli(EhFrameHdr),
".debug_info.wasm" => gimli(DebugInfo),
".debug_line.wasm" => gimli(DebugLine),
".debug_line_str.wasm" => gimli(DebugLineStr),
".debug_loc.wasm" => gimli(DebugLoc),
".debug_loc_lists.wasm" => gimli(DebugLocLists),
".debug_macinfo.wasm" => gimli(DebugMacinfo),
".debug_macro.wasm" => gimli(DebugMacro),
".debug_pub_names.wasm" => gimli(DebugPubNames),
".debug_pub_types.wasm" => gimli(DebugPubTypes),
".debug_ranges.wasm" => gimli(DebugRanges),
".debug_rng_lists.wasm" => gimli(DebugRngLists),
".debug_str.wasm" => gimli(DebugStr),
".debug_str_offsets.wasm" => gimli(DebugStrOffsets),
".debug_types.wasm" => gimli(DebugTypes),
".debug_cu_index.wasm" => gimli(DebugCuIndex),
".debug_tu_index.wasm" => gimli(DebugTuIndex),
obj::ELF_WASMTIME_DWARF => dwarf = range,

_ => log::debug!("ignoring section {name}"),
}
Expand All @@ -158,7 +121,7 @@ impl CodeMemory {
trap_data,
address_map_data,
func_name_data,
dwarf_sections,
dwarf,
info_data,
wasm_data,
})
Expand All @@ -175,15 +138,9 @@ impl CodeMemory {
&self.mmap[self.text.clone()]
}

/// Returns the data in the corresponding dwarf section, or an empty slice
/// if the section wasn't present.
pub fn dwarf_section(&self, section: gimli::SectionId) -> &[u8] {
let range = self
.dwarf_sections
.get(section as usize)
.cloned()
.unwrap_or(0..0);
&self.mmap[range]
/// Returns the contents of the `ELF_WASMTIME_DWARF` section.
pub fn dwarf(&self) -> &[u8] {
&self.mmap[self.dwarf.clone()]
}

/// Returns the data in the `ELF_NAME_DATA` section.
Expand Down
67 changes: 49 additions & 18 deletions crates/jit/src/instantiate.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -95,6 +95,10 @@ struct Metadata {
/// Note that even if this flag is `true` sections may be missing if they
/// weren't found in the original wasm module itself.
has_wasm_debuginfo: bool,

/// Dwarf sections and the offsets at which they're stored in the
/// ELF_WASMTIME_DWARF
dwarf: Vec<(u8, Range<u64>)>,
}

/// Helper structure to create an ELF file as a compilation artifact.
Expand All @@ -118,6 +122,12 @@ pub struct ObjectBuilder<'a> {
///
/// This is optional and lazily created on demand.
names: Option<SectionId>,

/// The section identifier for dwarf information copied from the original
/// wasm files.
///
/// This is optional and lazily created on demand.
dwarf: Option<SectionId>,
}

impl<'a> ObjectBuilder<'a> {
Expand All @@ -133,6 +143,7 @@ impl<'a> ObjectBuilder<'a> {
tunables,
data,
names: None,
dwarf: None,
}
}

Expand Down Expand Up @@ -263,18 +274,21 @@ impl<'a> ObjectBuilder<'a> {
// requested. Note that this is distinct from the native debuginfo
// possibly generated by the native compiler, hence these sections
// getting wasm-specific names.
let mut dwarf = Vec::new();
if self.tunables.parse_wasm_debuginfo {
self.push_debug(&debuginfo.dwarf.debug_abbrev);
self.push_debug(&debuginfo.dwarf.debug_addr);
self.push_debug(&debuginfo.dwarf.debug_aranges);
self.push_debug(&debuginfo.dwarf.debug_info);
self.push_debug(&debuginfo.dwarf.debug_line);
self.push_debug(&debuginfo.dwarf.debug_line_str);
self.push_debug(&debuginfo.dwarf.debug_str);
self.push_debug(&debuginfo.dwarf.debug_str_offsets);
self.push_debug(&debuginfo.debug_ranges);
self.push_debug(&debuginfo.debug_rnglists);
self.push_debug(&mut dwarf, &debuginfo.dwarf.debug_abbrev);
self.push_debug(&mut dwarf, &debuginfo.dwarf.debug_addr);
self.push_debug(&mut dwarf, &debuginfo.dwarf.debug_aranges);
self.push_debug(&mut dwarf, &debuginfo.dwarf.debug_info);
self.push_debug(&mut dwarf, &debuginfo.dwarf.debug_line);
self.push_debug(&mut dwarf, &debuginfo.dwarf.debug_line_str);
self.push_debug(&mut dwarf, &debuginfo.dwarf.debug_str);
self.push_debug(&mut dwarf, &debuginfo.dwarf.debug_str_offsets);
self.push_debug(&mut dwarf, &debuginfo.debug_ranges);
self.push_debug(&mut dwarf, &debuginfo.debug_rnglists);
}
// Sort this for binary-search-lookup later in `symbolize_context`.
dwarf.sort_by_key(|(id, _)| *id);

Ok(CompiledModuleInfo {
module,
Expand All @@ -286,24 +300,28 @@ impl<'a> ObjectBuilder<'a> {
has_unparsed_debuginfo,
code_section_offset: debuginfo.wasm_file.code_section_offset,
has_wasm_debuginfo: self.tunables.parse_wasm_debuginfo,
dwarf,
},
})
}

fn push_debug<'b, T>(&mut self, section: &T)
fn push_debug<'b, T>(&mut self, dwarf: &mut Vec<(u8, Range<u64>)>, section: &T)
where
T: gimli::Section<gimli::EndianSlice<'b, gimli::LittleEndian>>,
{
let data = section.reader().slice();
if data.is_empty() {
return;
}
let section_id = self.obj.add_section(
self.obj.segment_name(StandardSegment::Debug).to_vec(),
format!("{}.wasm", T::id().name()).into_bytes(),
SectionKind::Debug,
);
self.obj.append_section_data(section_id, data, 1);
let section_id = *self.dwarf.get_or_insert_with(|| {
self.obj.add_section(
self.obj.segment_name(StandardSegment::Debug).to_vec(),
obj::ELF_WASMTIME_DWARF.as_bytes().to_vec(),
SectionKind::Debug,
)
});
let offset = self.obj.append_section_data(section_id, data, 1);
dwarf.push((T::id() as u8, offset..offset + data.len() as u64));
}

/// Creates the `ELF_WASMTIME_INFO` section from the given serializable data
Expand Down Expand Up @@ -614,7 +632,20 @@ impl CompiledModule {
return Ok(None);
}
let dwarf = gimli::Dwarf::load(|id| -> Result<_> {
let data = self.code_memory().dwarf_section(id);
// Lookup the `id` in the `dwarf` array prepared for this module
// during module serialization where it's sorted by the `id` key. If
// found this is a range within the general module's concatenated
// dwarf section which is extracted here, otherwise it's just an
// empty list to represent that it's not present.
let data = self
.meta
.dwarf
.binary_search_by_key(&(id as u8), |(id, _)| *id)
.map(|i| {
let (_, range) = &self.meta.dwarf[i];
&self.code_memory().dwarf()[range.start as usize..range.end as usize]
})
.unwrap_or(&[]);
Ok(EndianSlice::new(data, gimli::LittleEndian))
})?;
let cx = addr2line::Context::from_dwarf(dwarf)
Expand Down