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[lldb][DWARFASTParserClang][NFCI] Extract DW_AT_data_member_location …
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…calculation logic (#68231)

Currently this non-trivial calculation is repeated multiple times,
making it hard to reason about when the
`byte_offset`/`member_byte_offset` is being set or not.

This patch simply moves all those instances of the same calculation into
a helper function.

We return an optional to remain an NFC patch. Default initializing the
offset would make sense but requires further analysis and can be done in
a follow-up patch.
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@Michael137
Michael137 authored Oct 5, 2023
1 parent c72d3a0 commit 3a35ca0
Showing 1 changed file with 39 additions and 87 deletions.
126 changes: 39 additions & 87 deletions lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -519,6 +519,33 @@ TypeSP DWARFASTParserClang::ParseTypeFromDWARF(const SymbolContext &sc,
return UpdateSymbolContextScopeForType(sc, die, type_sp);
}

static std::optional<uint32_t>
ExtractDataMemberLocation(DWARFDIE const &die, DWARFFormValue const &form_value,
ModuleSP module_sp) {
// With DWARF 3 and later, if the value is an integer constant,
// this form value is the offset in bytes from the beginning of
// the containing entity.
if (!form_value.BlockData())
return form_value.Unsigned();

Value initialValue(0);
Value memberOffset(0);
const DWARFDataExtractor &debug_info_data = die.GetData();
uint32_t block_length = form_value.Unsigned();
uint32_t block_offset =
form_value.BlockData() - debug_info_data.GetDataStart();
if (!DWARFExpression::Evaluate(
nullptr, // ExecutionContext *
nullptr, // RegisterContext *
module_sp, DataExtractor(debug_info_data, block_offset, block_length),
die.GetCU(), eRegisterKindDWARF, &initialValue, nullptr, memberOffset,
nullptr)) {
return {};
}

return memberOffset.ResolveValue(nullptr).UInt();
}

lldb::TypeSP
DWARFASTParserClang::ParseTypeModifier(const SymbolContext &sc,
const DWARFDIE &die,
Expand Down Expand Up @@ -1406,26 +1433,9 @@ void DWARFASTParserClang::ParseInheritance(
encoding_form = form_value;
break;
case DW_AT_data_member_location:
if (form_value.BlockData()) {
Value initialValue(0);
Value memberOffset(0);
const DWARFDataExtractor &debug_info_data = die.GetData();
uint32_t block_length = form_value.Unsigned();
uint32_t block_offset =
form_value.BlockData() - debug_info_data.GetDataStart();
if (DWARFExpression::Evaluate(
nullptr, nullptr, module_sp,
DataExtractor(debug_info_data, block_offset, block_length),
die.GetCU(), eRegisterKindDWARF, &initialValue, nullptr,
memberOffset, nullptr)) {
member_byte_offset = memberOffset.ResolveValue(nullptr).UInt();
}
} else {
// With DWARF 3 and later, if the value is an integer constant,
// this form value is the offset in bytes from the beginning of
// the containing entity.
member_byte_offset = form_value.Unsigned();
}
if (auto maybe_offset =
ExtractDataMemberLocation(die, form_value, module_sp))
member_byte_offset = *maybe_offset;
break;

case DW_AT_accessibility:
Expand Down Expand Up @@ -2557,29 +2567,9 @@ VariantMember::VariantMember(DWARFDIE &die, lldb::ModuleSP module_sp) {
break;

case DW_AT_data_member_location:
if (form_value.BlockData()) {
Value initialValue(0);
Value memberOffset(0);
const DWARFDataExtractor &debug_info_data = die.GetData();
uint32_t block_length = form_value.Unsigned();
uint32_t block_offset =
form_value.BlockData() - debug_info_data.GetDataStart();
if (DWARFExpression::Evaluate(
nullptr, // ExecutionContext *
nullptr, // RegisterContext *
module_sp,
DataExtractor(debug_info_data, block_offset,
block_length),
die.GetCU(), eRegisterKindDWARF, &initialValue, nullptr,
memberOffset, nullptr)) {
byte_offset = memberOffset.ResolveValue(nullptr).UInt();
}
} else {
// With DWARF 3 and later, if the value is an integer constant,
// this form value is the offset in bytes from the beginning of
// the containing entity.
byte_offset = form_value.Unsigned();
}
if (auto maybe_offset =
ExtractDataMemberLocation(die, form_value, module_sp))
byte_offset = *maybe_offset;
break;

default:
Expand Down Expand Up @@ -2608,28 +2598,9 @@ DiscriminantValue::DiscriminantValue(const DWARFDIE &die, ModuleSP module_sp) {
type_ref = form_value;
break;
case DW_AT_data_member_location:
if (form_value.BlockData()) {
Value initialValue(0);
Value memberOffset(0);
const DWARFDataExtractor &debug_info_data = die.GetData();
uint32_t block_length = form_value.Unsigned();
uint32_t block_offset =
form_value.BlockData() - debug_info_data.GetDataStart();
if (DWARFExpression::Evaluate(
nullptr, // ExecutionContext *
nullptr, // RegisterContext *
module_sp,
DataExtractor(debug_info_data, block_offset, block_length),
die.GetCU(), eRegisterKindDWARF, &initialValue, nullptr,
memberOffset, nullptr)) {
byte_offset = memberOffset.ResolveValue(nullptr).UInt();
}
} else {
// With DWARF 3 and later, if the value is an integer constant,
// this form value is the offset in bytes from the beginning of
// the containing entity.
byte_offset = form_value.Unsigned();
}
if (auto maybe_offset =
ExtractDataMemberLocation(die, form_value, module_sp))
byte_offset = *maybe_offset;
break;
default:
break;
Expand Down Expand Up @@ -2686,28 +2657,9 @@ MemberAttributes::MemberAttributes(const DWARFDIE &die,
data_bit_offset = form_value.Unsigned();
break;
case DW_AT_data_member_location:
if (form_value.BlockData()) {
Value initialValue(0);
Value memberOffset(0);
const DWARFDataExtractor &debug_info_data = die.GetData();
uint32_t block_length = form_value.Unsigned();
uint32_t block_offset =
form_value.BlockData() - debug_info_data.GetDataStart();
if (DWARFExpression::Evaluate(
nullptr, // ExecutionContext *
nullptr, // RegisterContext *
module_sp,
DataExtractor(debug_info_data, block_offset, block_length),
die.GetCU(), eRegisterKindDWARF, &initialValue, nullptr,
memberOffset, nullptr)) {
member_byte_offset = memberOffset.ResolveValue(nullptr).UInt();
}
} else {
// With DWARF 3 and later, if the value is an integer constant,
// this form value is the offset in bytes from the beginning of
// the containing entity.
member_byte_offset = form_value.Unsigned();
}
if (auto maybe_offset =
ExtractDataMemberLocation(die, form_value, module_sp))
member_byte_offset = *maybe_offset;
break;

case DW_AT_accessibility:
Expand Down

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