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[LLDB][NativePDB] Add non-overlapping fields in root struct #166243

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Merged
merged 6 commits into from
Nov 5, 2025
Merged

[LLDB][NativePDB] Add non-overlapping fields in root struct #166243

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22628e5
[LLDB][NativePDB] Add non-overlapping fields in root struct
Nerixyz Nov 3, 2025
fc1478f
fix: class layout test
Nerixyz Nov 4, 2025
5643c37
fix: move `parent` assignment to else branch
Nerixyz Nov 4, 2025
2e0b691
fix: test name
Nerixyz Nov 4, 2025
8207a5f
fix: handle unions as well
Nerixyz Nov 4, 2025
8135db8
fix: parentheses and assert
Nerixyz Nov 5, 2025
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23 changes: 21 additions & 2 deletions lldb/source/Plugins/SymbolFile/NativePDB/UdtRecordCompleter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -442,6 +442,10 @@ void UdtRecordCompleter::Record::ConstructRecord() {

// The end offset to a vector of field/struct that ends at the offset.
std::map<uint64_t, std::vector<Member *>> end_offset_map;
auto is_last_end_offset = [&](auto it) {
return it != end_offset_map.end() && ++it == end_offset_map.end();
};

for (auto &pair : fields_map) {
uint64_t offset = pair.first;
auto &fields = pair.second;
Expand All @@ -462,8 +466,23 @@ void UdtRecordCompleter::Record::ConstructRecord() {
}
if (iter->second.empty())
continue;
parent = iter->second.back();
iter->second.pop_back();

// If the new fields come after the already added ones
// without overlap, go back to the root.
if (iter->first <= offset && is_last_end_offset(iter)) {
if (record.kind == Member::Struct) {
parent = &record;
} else {
assert(record.kind == Member::Union &&
"Current record must be a union");
assert(!record.fields.empty());
// For unions, append the field to the last struct
parent = record.fields.back().get();
}
} else {
parent = iter->second.back();
iter->second.pop_back();
}
}
// If it's a field, then the field is inside a union, so we can safely
// increase its size by converting it to a struct to hold multiple fields.
Expand Down
8 changes: 4 additions & 4 deletions lldb/test/Shell/SymbolFile/NativePDB/class_layout.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -34,9 +34,6 @@
// CHECK-NEXT: s4 = {
// CHECK-NEXT: x = ([0] = 67, [1] = 68, [2] = 99)
// CHECK-NEXT: }
// CHECK-NEXT: s1 = {
// CHECK-NEXT: x = ([0] = 69, [1] = 70, [2] = 71)
// CHECK-NEXT: }
// CHECK-NEXT: }
// CHECK-NEXT: }
// CHECK-NEXT: }
Expand All @@ -47,6 +44,9 @@
// CHECK-NEXT: c2 = 'D'
// CHECK-NEXT: }
// CHECK-NEXT: }
// CHECK-NEXT: s1 = {
// CHECK-NEXT: x = ([0] = 69, [1] = 70, [2] = 71)
// CHECK-NEXT: }
// CHECK-NEXT: }
// CHECK-NEXT: (lldb) type lookup C
// CHECK-NEXT: struct C {
Expand All @@ -63,7 +63,6 @@
// CHECK-NEXT: struct {
// CHECK-NEXT: char c4;
// CHECK-NEXT: S3 s4;
// CHECK-NEXT: S3 s1;
// CHECK-NEXT: };
// CHECK-NEXT: };
// CHECK-NEXT: };
Expand All @@ -72,6 +71,7 @@
// CHECK-NEXT: char c2;
// CHECK-NEXT: };
// CHECK-NEXT: };
// CHECK-NEXT: S3 s1;
// CHECK-NEXT: }


Expand Down
52 changes: 51 additions & 1 deletion lldb/unittests/SymbolFile/NativePDB/UdtRecordCompleterTests.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -99,7 +99,7 @@ Member *AddField(Member *member, StringRef name, uint64_t byte_offset,
std::make_unique<Member>(name, byte_offset * 8, byte_size * 8,
clang::QualType(), lldb::eAccessPublic, 0);
field->kind = kind;
field->base_offset = base_offset;
field->base_offset = base_offset * 8;
member->fields.push_back(std::move(field));
return member->fields.back().get();
}
Expand All @@ -111,6 +111,9 @@ TEST_F(UdtRecordCompleterRecordTests, TestAnonymousUnionInStruct) {
CollectMember("m2", 0, 4);
CollectMember("m3", 0, 1);
CollectMember("m4", 0, 8);
CollectMember("m5", 8, 8);
CollectMember("m6", 16, 4);
CollectMember("m7", 16, 8);
ConstructRecord();

// struct {
Expand All @@ -120,6 +123,11 @@ TEST_F(UdtRecordCompleterRecordTests, TestAnonymousUnionInStruct) {
// m3;
// m4;
// };
// m5;
// union {
// m6;
// m7;
// };
// };
Record record;
record.start_offset = 0;
Expand All @@ -128,6 +136,10 @@ TEST_F(UdtRecordCompleterRecordTests, TestAnonymousUnionInStruct) {
AddField(u, "m2", 0, 4, Member::Field);
AddField(u, "m3", 0, 1, Member::Field);
AddField(u, "m4", 0, 8, Member::Field);
AddField(&record.record, "m5", 8, 8, Member::Field);
Member *u2 = AddField(&record.record, "", 16, 0, Member::Union);
AddField(u2, "m6", 16, 4, Member::Field);
AddField(u2, "m7", 16, 8, Member::Field);
EXPECT_EQ(WrappedRecord(this->record), WrappedRecord(record));
}

Expand Down Expand Up @@ -243,3 +255,41 @@ TEST_F(UdtRecordCompleterRecordTests, TestNestedUnionStructInUnion) {
AddField(s2, "m4", 2, 4, Member::Field);
EXPECT_EQ(WrappedRecord(this->record), WrappedRecord(record));
}

TEST_F(UdtRecordCompleterRecordTests, TestNestedStructInUnionInStructInUnion) {
SetKind(Member::Kind::Union);
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@ZequanWu ZequanWu Nov 4, 2025

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Is this testing this change? This change only changed the behaviour when the root record is a struct.

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@Nerixyz Nerixyz Nov 4, 2025

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It's testing that we don't do this "going up one level" everywhere. In this test, m7 does not overlap m5, so it could be placed in the outer struct:

union {
  m1;
  m2;
  struct {
      m3;
      m4;
      union {
          m5;
          m6;
      };
      m7;
  };
};

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@ZequanWu ZequanWu Nov 4, 2025

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Doesn't putting m7 into the struct, where m3 and m4 defined, better than making m6 and m7 into a new struct since it's one less layer?

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@Nerixyz Nerixyz Nov 4, 2025

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Yes, I wanted to capture the current state with the test. But now that I think about it, we could do something similar for unions...

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@Nerixyz Nerixyz Nov 4, 2025

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Added this.

CollectMember("m1", 0, 4);
CollectMember("m2", 0, 2);
CollectMember("m3", 0, 2);
CollectMember("m4", 2, 4);
CollectMember("m5", 6, 2);
CollectMember("m6", 6, 2);
CollectMember("m7", 8, 2);
ConstructRecord();

// union {
// m1;
// m2;
// struct {
// m3;
// m4;
// union {
// m5;
// m6;
// };
// m7;
// };
// };
Record record;
record.start_offset = 0;
AddField(&record.record, "m1", 0, 4, Member::Field);
AddField(&record.record, "m2", 0, 2, Member::Field);
Member *s = AddField(&record.record, "", 0, 0, Member::Struct);
AddField(s, "m3", 0, 2, Member::Field);
AddField(s, "m4", 2, 4, Member::Field);
Member *u = AddField(s, "", 6, 0, Member::Union);
AddField(u, "m5", 6, 2, Member::Field);
AddField(u, "m6", 6, 2, Member::Field);
AddField(s, "m7", 8, 2, Member::Field);
EXPECT_EQ(WrappedRecord(this->record), WrappedRecord(record));
}
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