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[BOLT][DWARF] Add support for cross-cu references for debug-names (ll…
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…vm#86015)

The DW_AT_abstract_origin can be a cross-cu reference as a by-product of
LTO. On IR level for absolute references an address is stored, vs a DIE
for relative references. Added a map to keep track of cross-cu
referenced DIEs to use when we add an Entry.
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@ayermolo
ayermolo authored Mar 22, 2024
1 parent 105feb9 commit f3cfe01
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Showing 4 changed files with 796 additions and 42 deletions.
11 changes: 11 additions & 0 deletions bolt/include/bolt/Core/DebugNames.h
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Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,16 @@ class DWARF5AcceleratorTable {
std::unique_ptr<DebugBufferVector> releaseBuffer() {
return std::move(FullTableBuffer);
}
/// Adds a DIE that is referenced across CUs.
void addCrossCUDie(const DIE *Die) {
CrossCUDies.insert({Die->getOffset(), Die});
}
/// Returns true if the DIE can generate an entry for a cross cu reference.
/// This only checks TAGs of a DIE because when this is invoked DIE might not
/// be fully constructed.
bool canGenerateEntryWithCrossCUReference(
const DWARFUnit &Unit, const DIE &Die,
const DWARFAbbreviationDeclaration::AttributeSpec &AttrSpec);

private:
BinaryContext &BC;
Expand Down Expand Up @@ -128,6 +138,7 @@ class DWARF5AcceleratorTable {
llvm::DenseMap<uint64_t, uint32_t> CUOffsetsToPatch;
// Contains a map of Entry ID to Entry relative offset.
llvm::DenseMap<uint64_t, uint32_t> EntryRelativeOffsets;
llvm::DenseMap<uint64_t, const DIE *> CrossCUDies;
/// Adds Unit to either CUList, LocalTUList or ForeignTUList.
/// Input Unit being processed, and DWO ID if Unit is being processed comes
/// from a DWO section.
Expand Down
6 changes: 5 additions & 1 deletion bolt/lib/Core/DIEBuilder.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -545,6 +545,10 @@ void DIEBuilder::cloneDieReferenceAttribute(
NewRefDie = DieInfo.Die;

if (AttrSpec.Form == dwarf::DW_FORM_ref_addr) {
// Adding referenced DIE to DebugNames to be used when entries are created
// that contain cross cu references.
if (DebugNamesTable.canGenerateEntryWithCrossCUReference(U, Die, AttrSpec))
DebugNamesTable.addCrossCUDie(DieInfo.Die);
// no matter forward reference or backward reference, we are supposed
// to calculate them in `finish` due to the possible modification of
// the DIE.
Expand All @@ -554,7 +558,7 @@ void DIEBuilder::cloneDieReferenceAttribute(
std::make_pair(CurDieInfo, AddrReferenceInfo(&DieInfo, AttrSpec)));

Die.addValue(getState().DIEAlloc, AttrSpec.Attr, dwarf::DW_FORM_ref_addr,
DIEInteger(0xDEADBEEF));
DIEInteger(DieInfo.Die->getOffset()));
return;
}

Expand Down
109 changes: 68 additions & 41 deletions bolt/lib/Core/DebugNames.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -146,6 +146,55 @@ static bool shouldIncludeVariable(const DWARFUnit &Unit, const DIE &Die) {
return false;
}

bool static canProcess(const DWARFUnit &Unit, const DIE &Die,
std::string &NameToUse, const bool TagsOnly) {
switch (Die.getTag()) {
case dwarf::DW_TAG_base_type:
case dwarf::DW_TAG_class_type:
case dwarf::DW_TAG_enumeration_type:
case dwarf::DW_TAG_imported_declaration:
case dwarf::DW_TAG_pointer_type:
case dwarf::DW_TAG_structure_type:
case dwarf::DW_TAG_typedef:
case dwarf::DW_TAG_unspecified_type:
if (TagsOnly || Die.findAttribute(dwarf::Attribute::DW_AT_name))
return true;
return false;
case dwarf::DW_TAG_namespace:
// According to DWARF5 spec namespaces without DW_AT_name needs to have
// "(anonymous namespace)"
if (!Die.findAttribute(dwarf::Attribute::DW_AT_name))
NameToUse = "(anonymous namespace)";
return true;
case dwarf::DW_TAG_inlined_subroutine:
case dwarf::DW_TAG_label:
case dwarf::DW_TAG_subprogram:
if (TagsOnly || Die.findAttribute(dwarf::Attribute::DW_AT_low_pc) ||
Die.findAttribute(dwarf::Attribute::DW_AT_high_pc) ||
Die.findAttribute(dwarf::Attribute::DW_AT_ranges) ||
Die.findAttribute(dwarf::Attribute::DW_AT_entry_pc))
return true;
return false;
case dwarf::DW_TAG_variable:
return TagsOnly || shouldIncludeVariable(Unit, Die);
default:
break;
}
return false;
}

bool DWARF5AcceleratorTable::canGenerateEntryWithCrossCUReference(
const DWARFUnit &Unit, const DIE &Die,
const DWARFAbbreviationDeclaration::AttributeSpec &AttrSpec) {
if (!isCreated())
return false;
std::string NameToUse = "";
if (!canProcess(Unit, Die, NameToUse, true))
return false;
return (AttrSpec.Attr == dwarf::Attribute::DW_AT_abstract_origin ||
AttrSpec.Attr == dwarf::Attribute::DW_AT_specification) &&
AttrSpec.Form == dwarf::DW_FORM_ref_addr;
}
/// Returns name offset in String Offset section.
static uint64_t getNameOffset(BinaryContext &BC, DWARFUnit &Unit,
const uint64_t Index) {
Expand Down Expand Up @@ -175,41 +224,6 @@ DWARF5AcceleratorTable::addAccelTableEntry(
if (Unit.getVersion() < 5 || !NeedToCreate)
return std::nullopt;
std::string NameToUse = "";
auto canProcess = [&](const DIE &Die) -> bool {
switch (Die.getTag()) {
case dwarf::DW_TAG_base_type:
case dwarf::DW_TAG_class_type:
case dwarf::DW_TAG_enumeration_type:
case dwarf::DW_TAG_imported_declaration:
case dwarf::DW_TAG_pointer_type:
case dwarf::DW_TAG_structure_type:
case dwarf::DW_TAG_typedef:
case dwarf::DW_TAG_unspecified_type:
if (Die.findAttribute(dwarf::Attribute::DW_AT_name))
return true;
return false;
case dwarf::DW_TAG_namespace:
// According to DWARF5 spec namespaces without DW_AT_name needs to have
// "(anonymous namespace)"
if (!Die.findAttribute(dwarf::Attribute::DW_AT_name))
NameToUse = "(anonymous namespace)";
return true;
case dwarf::DW_TAG_inlined_subroutine:
case dwarf::DW_TAG_label:
case dwarf::DW_TAG_subprogram:
if (Die.findAttribute(dwarf::Attribute::DW_AT_low_pc) ||
Die.findAttribute(dwarf::Attribute::DW_AT_high_pc) ||
Die.findAttribute(dwarf::Attribute::DW_AT_ranges) ||
Die.findAttribute(dwarf::Attribute::DW_AT_entry_pc))
return true;
return false;
case dwarf::DW_TAG_variable:
return shouldIncludeVariable(Unit, Die);
default:
break;
}
return false;
};

auto getUnitID = [&](const DWARFUnit &Unit, bool &IsTU,
uint32_t &DieTag) -> uint32_t {
Expand All @@ -223,7 +237,7 @@ DWARF5AcceleratorTable::addAccelTableEntry(
return CUList.size() - 1;
};

if (!canProcess(Die))
if (!canProcess(Unit, Die, NameToUse, false))
return std::nullopt;

// Addes a Unit to either CU, LocalTU or ForeignTU list the first time we
Expand Down Expand Up @@ -318,10 +332,24 @@ DWARF5AcceleratorTable::addAccelTableEntry(
const DIEValue Value = Die.findAttribute(Attr);
if (!Value)
return std::nullopt;
const DIEEntry &DIEENtry = Value.getDIEEntry();
DIE &EntryDie = DIEENtry.getEntry();
addEntry(EntryDie.findAttribute(dwarf::Attribute::DW_AT_linkage_name));
return addEntry(EntryDie.findAttribute(dwarf::Attribute::DW_AT_name));
const DIE *EntryDie = nullptr;
if (Value.getForm() == dwarf::DW_FORM_ref_addr) {
auto Iter = CrossCUDies.find(Value.getDIEInteger().getValue());
if (Iter == CrossCUDies.end()) {
BC.errs() << "BOLT-WARNING: [internal-dwarf-warning]: Could not find "
"referenced DIE in CrossCUDies for "
<< Twine::utohexstr(Value.getDIEInteger().getValue())
<< ".\n";
return std::nullopt;
}
EntryDie = Iter->second;
} else {
const DIEEntry &DIEENtry = Value.getDIEEntry();
EntryDie = &DIEENtry.getEntry();
}

addEntry(EntryDie->findAttribute(dwarf::Attribute::DW_AT_linkage_name));
return addEntry(EntryDie->findAttribute(dwarf::Attribute::DW_AT_name));
};

if (std::optional<BOLTDWARF5AccelTableData *> Entry =
Expand All @@ -332,7 +360,6 @@ DWARF5AcceleratorTable::addAccelTableEntry(
return *Entry;

return addEntry(Die.findAttribute(dwarf::Attribute::DW_AT_name));
;
}

/// Algorithm from llvm implementation.
Expand Down
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