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[llvm/DWARF] Recursively resolve DW_AT_signature references
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findRecursively follows DW_AT_specification and DW_AT_abstract_origin
references, but not DW_AT_signature. As far as I can tell, there is no
fundamental difference between these attributes that would make this
behavior desirable, and this just seems like a consequence of the fact
that this attribute is newer. This patch aims to change that.

The motivation is some code in lldb, which assumes that it can construct
a qualified name of a type by just walking the parent chain and looking
at the name attribute. This works for "regular" debug info, even when
some of the DIEs are just forward declarations, but it breaks in the
presence of type units, because of the need to explicitly resolve the
signature reference.

While LLDB does not use the llvm's DWARFDie class (yet?), this seems
like a very important change in the overall API, and any divergance here
would complicate eventual reunification, which is why I am making the
change in the llvm API first. Nonetheless, I think this change is
beneficial in llvm as well, as it allows us to remove the explicit
DW_AT_signature resolution in the DWARFTypePrinter.
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@labath
labath committed Jul 2, 2024
1 parent 8a25bb9 commit 30c7cef
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Showing 3 changed files with 40 additions and 57 deletions.
2 changes: 0 additions & 2 deletions llvm/include/llvm/DebugInfo/DWARF/DWARFDie.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -181,8 +181,6 @@ class DWARFDie {
DWARFDie getAttributeValueAsReferencedDie(dwarf::Attribute Attr) const;
DWARFDie getAttributeValueAsReferencedDie(const DWARFFormValue &V) const;

DWARFDie resolveTypeUnitReference() const;

/// Extract the range base attribute from this DIE as absolute section offset.
///
/// This is a utility function that checks for either the DW_AT_rnglists_base
Expand Down
43 changes: 15 additions & 28 deletions llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -103,10 +103,6 @@ static void dumpLocationExpr(raw_ostream &OS, const DWARFFormValue &FormValue,
.print(OS, DumpOpts, U);
}

static DWARFDie resolveReferencedType(DWARFDie D, DWARFFormValue F) {
return D.getAttributeValueAsReferencedDie(F).resolveTypeUnitReference();
}

static void dumpAttribute(raw_ostream &OS, const DWARFDie &Die,
const DWARFAttribute &AttrValue, unsigned Indent,
DIDumpOptions DumpOpts) {
Expand Down Expand Up @@ -198,8 +194,8 @@ static void dumpAttribute(raw_ostream &OS, const DWARFDie &Die,
DINameKind::LinkageName))
OS << Space << "\"" << Name << '\"';
} else if (Attr == DW_AT_type || Attr == DW_AT_containing_type) {
DWARFDie D = resolveReferencedType(Die, FormValue);
if (D && !D.isNULL()) {
if (DWARFDie D = Die.getAttributeValueAsReferencedDie(FormValue);
D && !D.isNULL()) {
OS << Space << "\"";
dumpTypeQualifiedName(D, OS);
OS << '"';
Expand Down Expand Up @@ -291,13 +287,12 @@ DWARFDie::findRecursively(ArrayRef<dwarf::Attribute> Attrs) const {
if (auto Value = Die.find(Attrs))
return Value;

if (auto D = Die.getAttributeValueAsReferencedDie(DW_AT_abstract_origin))
if (Seen.insert(D).second)
Worklist.push_back(D);

if (auto D = Die.getAttributeValueAsReferencedDie(DW_AT_specification))
if (Seen.insert(D).second)
Worklist.push_back(D);
for (dwarf::Attribute Attr :
{DW_AT_abstract_origin, DW_AT_specification, DW_AT_signature}) {
if (auto D = Die.getAttributeValueAsReferencedDie(Attr))
if (Seen.insert(D).second)
Worklist.push_back(D);
}
}

return std::nullopt;
Expand All @@ -312,27 +307,19 @@ DWARFDie::getAttributeValueAsReferencedDie(dwarf::Attribute Attr) const {

DWARFDie
DWARFDie::getAttributeValueAsReferencedDie(const DWARFFormValue &V) const {
DWARFDie Result;
if (auto SpecRef = V.getAsRelativeReference()) {
if (SpecRef->Unit)
Result = SpecRef->Unit->getDIEForOffset(SpecRef->Unit->getOffset() +
SpecRef->Offset);
else if (auto SpecUnit =
U->getUnitVector().getUnitForOffset(SpecRef->Offset))
Result = SpecUnit->getDIEForOffset(SpecRef->Offset);
}
return Result;
}

DWARFDie DWARFDie::resolveTypeUnitReference() const {
if (auto Attr = find(DW_AT_signature)) {
if (std::optional<uint64_t> Sig = Attr->getAsReferenceUVal()) {
return SpecRef->Unit->getDIEForOffset(SpecRef->Unit->getOffset() +
SpecRef->Offset);
if (V.getForm() == dwarf::DW_FORM_ref_sig8) {
if (DWARFTypeUnit *TU = U->getContext().getTypeUnitForHash(
U->getVersion(), *Sig, U->isDWOUnit()))
U->getVersion(), SpecRef->Offset, U->isDWOUnit()))
return TU->getDIEForOffset(TU->getTypeOffset() + TU->getOffset());
}
if (auto *SpecUnit = U->getUnitVector().getUnitForOffset(SpecRef->Offset))
return SpecUnit->getDIEForOffset(SpecRef->Offset);
}
return *this;
return {};
}

std::optional<uint64_t> DWARFDie::getRangesBaseAttribute() const {
Expand Down
52 changes: 25 additions & 27 deletions llvm/lib/DebugInfo/DWARF/DWARFTypePrinter.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -62,17 +62,10 @@ void DWARFTypePrinter::appendArrayType(const DWARFDie &D) {
EndedWithTemplate = false;
}

static DWARFDie resolveReferencedType(DWARFDie D,
dwarf::Attribute Attr = DW_AT_type) {
return D.getAttributeValueAsReferencedDie(Attr).resolveTypeUnitReference();
}
static DWARFDie resolveReferencedType(DWARFDie D, DWARFFormValue F) {
return D.getAttributeValueAsReferencedDie(F).resolveTypeUnitReference();
}
DWARFDie DWARFTypePrinter::skipQualifiers(DWARFDie D) {
while (D && (D.getTag() == DW_TAG_const_type ||
D.getTag() == DW_TAG_volatile_type))
D = resolveReferencedType(D);
D = D.getAttributeValueAsReferencedDie(DW_AT_type);
return D;
}

Expand Down Expand Up @@ -103,7 +96,9 @@ DWARFTypePrinter::appendUnqualifiedNameBefore(DWARFDie D,
return DWARFDie();
}
DWARFDie InnerDIE;
auto Inner = [&] { return InnerDIE = resolveReferencedType(D); };
auto Inner = [&] {
return InnerDIE = D.getAttributeValueAsReferencedDie(DW_AT_type);
};
const dwarf::Tag T = D.getTag();
switch (T) {
case DW_TAG_pointer_type: {
Expand Down Expand Up @@ -134,7 +129,8 @@ DWARFTypePrinter::appendUnqualifiedNameBefore(DWARFDie D,
OS << '(';
else if (Word)
OS << ' ';
if (DWARFDie Cont = resolveReferencedType(D, DW_AT_containing_type)) {
if (DWARFDie Cont =
D.getAttributeValueAsReferencedDie(DW_AT_containing_type)) {
appendQualifiedName(Cont);
EndedWithTemplate = false;
OS << "::";
Expand Down Expand Up @@ -173,7 +169,8 @@ DWARFTypePrinter::appendUnqualifiedNameBefore(DWARFDie D,
case DW_TAG_base_type:
*/
default: {
const char *NamePtr = dwarf::toString(D.find(DW_AT_name), nullptr);
const char *NamePtr =
dwarf::toString(D.findRecursively(DW_AT_name), nullptr);
if (!NamePtr) {
appendTypeTagName(D.getTag());
return DWARFDie();
Expand Down Expand Up @@ -235,9 +232,9 @@ void DWARFTypePrinter::appendUnqualifiedNameAfter(
case DW_TAG_pointer_type: {
if (needsParens(Inner))
OS << ')';
appendUnqualifiedNameAfter(Inner, resolveReferencedType(Inner),
/*SkipFirstParamIfArtificial=*/D.getTag() ==
DW_TAG_ptr_to_member_type);
appendUnqualifiedNameAfter(
Inner, Inner.getAttributeValueAsReferencedDie(DW_AT_type),
/*SkipFirstParamIfArtificial=*/D.getTag() == DW_TAG_ptr_to_member_type);
break;
}
case DW_TAG_LLVM_ptrauth_type: {
Expand Down Expand Up @@ -341,7 +338,7 @@ bool DWARFTypePrinter::appendTemplateParameters(DWARFDie D,
appendTemplateParameters(C, FirstParameter);
}
if (C.getTag() == dwarf::DW_TAG_template_value_parameter) {
DWARFDie T = resolveReferencedType(C);
DWARFDie T = C.getAttributeValueAsReferencedDie(DW_AT_type);
Sep();
if (T.getTag() == DW_TAG_enumeration_type) {
OS << '(';
Expand Down Expand Up @@ -461,7 +458,7 @@ bool DWARFTypePrinter::appendTemplateParameters(DWARFDie D,
continue;
auto TypeAttr = C.find(DW_AT_type);
Sep();
appendQualifiedName(TypeAttr ? resolveReferencedType(C, *TypeAttr)
appendQualifiedName(TypeAttr ? C.getAttributeValueAsReferencedDie(*TypeAttr)
: DWARFDie());
}
if (IsTemplate && *FirstParameter && FirstParameter == &FirstParameterValue) {
Expand All @@ -473,15 +470,15 @@ bool DWARFTypePrinter::appendTemplateParameters(DWARFDie D,
void DWARFTypePrinter::decomposeConstVolatile(DWARFDie &N, DWARFDie &T,
DWARFDie &C, DWARFDie &V) {
(N.getTag() == DW_TAG_const_type ? C : V) = N;
T = resolveReferencedType(N);
T = N.getAttributeValueAsReferencedDie(DW_AT_type);
if (T) {
auto Tag = T.getTag();
if (Tag == DW_TAG_const_type) {
C = T;
T = resolveReferencedType(T);
T = T.getAttributeValueAsReferencedDie(DW_AT_type);
} else if (Tag == DW_TAG_volatile_type) {
V = T;
T = resolveReferencedType(T);
T = T.getAttributeValueAsReferencedDie(DW_AT_type);
}
}
}
Expand All @@ -491,10 +488,11 @@ void DWARFTypePrinter::appendConstVolatileQualifierAfter(DWARFDie N) {
DWARFDie T;
decomposeConstVolatile(N, T, C, V);
if (T && T.getTag() == DW_TAG_subroutine_type)
appendSubroutineNameAfter(T, resolveReferencedType(T), false, C.isValid(),
V.isValid());
appendSubroutineNameAfter(T, T.getAttributeValueAsReferencedDie(DW_AT_type),
false, C.isValid(), V.isValid());
else
appendUnqualifiedNameAfter(T, resolveReferencedType(T));
appendUnqualifiedNameAfter(T,
T.getAttributeValueAsReferencedDie(DW_AT_type));
}
void DWARFTypePrinter::appendConstVolatileQualifierBefore(DWARFDie N) {
DWARFDie C;
Expand All @@ -504,7 +502,7 @@ void DWARFTypePrinter::appendConstVolatileQualifierBefore(DWARFDie N) {
bool Subroutine = T && T.getTag() == DW_TAG_subroutine_type;
DWARFDie A = T;
while (A && A.getTag() == DW_TAG_array_type)
A = resolveReferencedType(A);
A = A.getAttributeValueAsReferencedDie(DW_AT_type);
bool Leading =
(!A || (A.getTag() != DW_TAG_pointer_type &&
A.getTag() != llvm::dwarf::DW_TAG_ptr_to_member_type)) &&
Expand Down Expand Up @@ -546,7 +544,7 @@ void DWARFTypePrinter::appendSubroutineNameAfter(
if (P.getTag() != DW_TAG_formal_parameter &&
P.getTag() != DW_TAG_unspecified_parameters)
return;
DWARFDie T = resolveReferencedType(P);
DWARFDie T = P.getAttributeValueAsReferencedDie(DW_AT_type);
if (SkipFirstParamIfArtificial && RealFirst && P.find(DW_AT_artificial)) {
FirstParamIfArtificial = T;
RealFirst = false;
Expand All @@ -567,7 +565,7 @@ void DWARFTypePrinter::appendSubroutineNameAfter(
if (DWARFDie P = FirstParamIfArtificial) {
if (P.getTag() == DW_TAG_pointer_type) {
auto CVStep = [&](DWARFDie CV) {
if (DWARFDie U = resolveReferencedType(CV)) {
if (DWARFDie U = CV.getAttributeValueAsReferencedDie(DW_AT_type)) {
Const |= U.getTag() == DW_TAG_const_type;
Volatile |= U.getTag() == DW_TAG_volatile_type;
return U;
Expand Down Expand Up @@ -653,7 +651,8 @@ void DWARFTypePrinter::appendSubroutineNameAfter(
if (D.find(DW_AT_rvalue_reference))
OS << " &&";

appendUnqualifiedNameAfter(Inner, resolveReferencedType(Inner));
appendUnqualifiedNameAfter(
Inner, Inner.getAttributeValueAsReferencedDie(DW_AT_type));
}
void DWARFTypePrinter::appendScopes(DWARFDie D) {
if (D.getTag() == DW_TAG_compile_unit)
Expand All @@ -666,7 +665,6 @@ void DWARFTypePrinter::appendScopes(DWARFDie D) {
return;
if (D.getTag() == DW_TAG_lexical_block)
return;
D = D.resolveTypeUnitReference();
if (DWARFDie P = D.getParent())
appendScopes(P);
appendUnqualifiedName(D);
Expand Down

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