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[DebugInfo][NFCI] Refactor DWARFAbbreviationDeclaration::extract
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The motivation behind this refactor is to be able to use
DWARFAbbreviationDeclaration from LLDB. LLDB has its own implementation
of DWARFAbbreviationDeclaration that is very similar to LLVM's but it
has different semantics around error handling.

This patch modifies llvm::DWARFAbbreviationDeclaration::extract to
return an `llvm::Expected<ExtractState>` to differentiate between "I am
done extracting" and "An error has occured", something which the current
return type (bool) does not accurately capture.

Differential Revision: https://reviews.llvm.org/D150607
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@bulbazord
bulbazord committed May 16, 2023
1 parent c5c6ea8 commit 631ff46
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Showing 3 changed files with 84 additions and 67 deletions.
3 changes: 2 additions & 1 deletion llvm/include/llvm/DebugInfo/DWARF/DWARFAbbreviationDeclaration.h
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,7 @@ class raw_ostream;

class DWARFAbbreviationDeclaration {
public:
enum class ExtractState { Complete, MoreItems };
struct AttributeSpec {
AttributeSpec(dwarf::Attribute A, dwarf::Form F, int64_t Value)
: Attr(A), Form(F), Value(Value) {
Expand Down Expand Up @@ -172,7 +173,7 @@ class DWARFAbbreviationDeclaration {
getAttributeValueFromOffset(uint32_t AttrIndex, uint64_t Offset,
const DWARFUnit &U) const;

bool extract(DataExtractor Data, uint64_t* OffsetPtr);
llvm::Expected<ExtractState> extract(DataExtractor Data, uint64_t *OffsetPtr);
void dump(raw_ostream &OS) const;

// Return an optional byte size of all attribute data in this abbreviation
Expand Down
127 changes: 67 additions & 60 deletions llvm/lib/DebugInfo/DWARF/DWARFAbbreviationDeclaration.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -34,20 +34,20 @@ DWARFAbbreviationDeclaration::DWARFAbbreviationDeclaration() {
clear();
}

bool
DWARFAbbreviationDeclaration::extract(DataExtractor Data,
uint64_t* OffsetPtr) {
llvm::Expected<DWARFAbbreviationDeclaration::ExtractState>
DWARFAbbreviationDeclaration::extract(DataExtractor Data, uint64_t *OffsetPtr) {
clear();
const uint64_t Offset = *OffsetPtr;
Code = Data.getULEB128(OffsetPtr);
if (Code == 0) {
return false;
}
if (Code == 0)
return ExtractState::Complete;

CodeByteSize = *OffsetPtr - Offset;
Tag = static_cast<llvm::dwarf::Tag>(Data.getULEB128(OffsetPtr));
if (Tag == DW_TAG_null) {
clear();
return false;
return make_error<llvm::object::GenericBinaryError>(
"abbreviation declaration requires a non-null tag");
}
uint8_t ChildrenByte = Data.getU8(OffsetPtr);
HasChildren = (ChildrenByte == DW_CHILDREN_yes);
Expand All @@ -57,70 +57,77 @@ DWARFAbbreviationDeclaration::extract(DataExtractor Data,
FixedAttributeSize = FixedSizeInfo();

// Read all of the abbreviation attributes and forms.
while (true) {
while (Data.isValidOffset(*OffsetPtr)) {
auto A = static_cast<Attribute>(Data.getULEB128(OffsetPtr));
auto F = static_cast<Form>(Data.getULEB128(OffsetPtr));
if (A && F) {
bool IsImplicitConst = (F == DW_FORM_implicit_const);
if (IsImplicitConst) {
int64_t V = Data.getSLEB128(OffsetPtr);
AttributeSpecs.push_back(AttributeSpec(A, F, V));
continue;
}
std::optional<uint8_t> ByteSize;
// If this abbrevation still has a fixed byte size, then update the
// FixedAttributeSize as needed.
switch (F) {
case DW_FORM_addr:
if (FixedAttributeSize)
++FixedAttributeSize->NumAddrs;
break;

case DW_FORM_ref_addr:
if (FixedAttributeSize)
++FixedAttributeSize->NumRefAddrs;
break;
// We successfully reached the end of this abbreviation declaration
// since both attribute and form are zero. There may be more abbreviation
// declarations afterwards.
if (!A && !F)
return ExtractState::MoreItems;

case DW_FORM_strp:
case DW_FORM_GNU_ref_alt:
case DW_FORM_GNU_strp_alt:
case DW_FORM_line_strp:
case DW_FORM_sec_offset:
case DW_FORM_strp_sup:
if (FixedAttributeSize)
++FixedAttributeSize->NumDwarfOffsets;
break;

default:
// The form has a byte size that doesn't depend on Params.
// If it's a fixed size, keep track of it.
if ((ByteSize = dwarf::getFixedFormByteSize(F, dwarf::FormParams()))) {
if (FixedAttributeSize)
FixedAttributeSize->NumBytes += *ByteSize;
break;
}
// Indicate we no longer have a fixed byte size for this
// abbreviation by clearing the FixedAttributeSize optional value
// so it doesn't have a value.
FixedAttributeSize.reset();
break;
}
// Record this attribute and its fixed size if it has one.
AttributeSpecs.push_back(AttributeSpec(A, F, ByteSize));
} else if (A == 0 && F == 0) {
// We successfully reached the end of this abbreviation declaration
// since both attribute and form are zero.
break;
} else {
if (!A || !F) {
// Attribute and form pairs must either both be non-zero, in which case
// they are added to the abbreviation declaration, or both be zero to
// terminate the abbrevation declaration. In this case only one was
// zero which is an error.
clear();
return false;
return make_error<llvm::object::GenericBinaryError>(
"malformed abbreviation declaration attribute. Either the attribute "
"or the form is zero while the other is not");
}

bool IsImplicitConst = (F == DW_FORM_implicit_const);
if (IsImplicitConst) {
int64_t V = Data.getSLEB128(OffsetPtr);
AttributeSpecs.push_back(AttributeSpec(A, F, V));
continue;
}
std::optional<uint8_t> ByteSize;
// If this abbrevation still has a fixed byte size, then update the
// FixedAttributeSize as needed.
switch (F) {
case DW_FORM_addr:
if (FixedAttributeSize)
++FixedAttributeSize->NumAddrs;
break;

case DW_FORM_ref_addr:
if (FixedAttributeSize)
++FixedAttributeSize->NumRefAddrs;
break;

case DW_FORM_strp:
case DW_FORM_GNU_ref_alt:
case DW_FORM_GNU_strp_alt:
case DW_FORM_line_strp:
case DW_FORM_sec_offset:
case DW_FORM_strp_sup:
if (FixedAttributeSize)
++FixedAttributeSize->NumDwarfOffsets;
break;

default:
// The form has a byte size that doesn't depend on Params.
// If it's a fixed size, keep track of it.
if ((ByteSize = dwarf::getFixedFormByteSize(F, dwarf::FormParams()))) {
if (FixedAttributeSize)
FixedAttributeSize->NumBytes += *ByteSize;
break;
}
// Indicate we no longer have a fixed byte size for this
// abbreviation by clearing the FixedAttributeSize optional value
// so it doesn't have a value.
FixedAttributeSize.reset();
break;
}
// Record this attribute and its fixed size if it has one.
AttributeSpecs.push_back(AttributeSpec(A, F, ByteSize));
}
return true;
return make_error<llvm::object::GenericBinaryError>(
"abbreviation declaration attribute list was not terminated with a null "
"entry");
}

void DWARFAbbreviationDeclaration::dump(raw_ostream &OS) const {
Expand Down
21 changes: 15 additions & 6 deletions llvm/lib/DebugInfo/DWARF/DWARFDebugAbbrev.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -32,14 +32,23 @@ bool DWARFAbbreviationDeclarationSet::extract(DataExtractor Data,
Offset = BeginOffset;
DWARFAbbreviationDeclaration AbbrDecl;
uint32_t PrevAbbrCode = 0;
while (AbbrDecl.extract(Data, OffsetPtr)) {
while (true) {
llvm::Expected<DWARFAbbreviationDeclaration::ExtractState> ES =
AbbrDecl.extract(Data, OffsetPtr);
if (!ES) {
// FIXME: We should propagate the error upwards.
llvm::consumeError(ES.takeError());
break;
}

if (*ES == DWARFAbbreviationDeclaration::ExtractState::Complete)
break;

if (FirstAbbrCode == 0) {
FirstAbbrCode = AbbrDecl.getCode();
} else {
if (PrevAbbrCode + 1 != AbbrDecl.getCode()) {
// Codes are not consecutive, can't do O(1) lookups.
FirstAbbrCode = UINT32_MAX;
}
} else if (PrevAbbrCode + 1 != AbbrDecl.getCode()) {
// Codes are not consecutive, can't do O(1) lookups.
FirstAbbrCode = UINT32_MAX;
}
PrevAbbrCode = AbbrDecl.getCode();
Decls.push_back(std::move(AbbrDecl));
Expand Down

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