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merged 2 commits into from
Oct 31, 2025
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[LLDB][NativePDB] Estimate symbol sizes #165727

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5a71656
[LLDB][NativePDB] Estimate symbol sizes
Nerixyz Oct 29, 2025
c23bf1f
Update lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp
Nerixyz Oct 30, 2025
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67 changes: 51 additions & 16 deletions lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1130,16 +1130,47 @@ void SymbolFileNativePDB::AddSymbols(Symtab &symtab) {
if (!section_list)
return;

for (auto pid : m_index->publics().getPublicsTable()) {
PublicSym32 last_sym;
size_t last_sym_idx = 0;
lldb::SectionSP section_sp;

// To estimate the size of a symbol, we use the difference to the next symbol.
// If there's no next symbol or the section/segment changed, the symbol will
// take the remaining space. The estimate can be too high in case there's
// padding between symbols. This similar to the algorithm used by the DIA
// SDK.
auto finish_last_symbol = [&](const PublicSym32 *next) {
if (!section_sp)
return;
Symbol *last = symtab.SymbolAtIndex(last_sym_idx);
if (!last)
return;

if (next && last_sym.Segment == next->Segment) {
assert(last_sym.Offset <= next->Offset);
last->SetByteSize(next->Offset - last_sym.Offset);
} else {
// the last symbol was the last in its section
assert(section_sp->GetByteSize() >= last_sym.Offset);
assert(!next || next->Segment > last_sym.Segment);
last->SetByteSize(section_sp->GetByteSize() - last_sym.Offset);
}
};

// the address map is sorted by the address of a symbol
for (auto pid : m_index->publics().getAddressMap()) {
PdbGlobalSymId global{pid, true};
CVSymbol sym = m_index->ReadSymbolRecord(global);
auto kind = sym.kind();
if (kind != S_PUB32)
continue;
PublicSym32 pub =
llvm::cantFail(SymbolDeserializer::deserializeAs<PublicSym32>(sym));
finish_last_symbol(&pub);

if (!section_sp || last_sym.Segment != pub.Segment)
section_sp = section_list->FindSectionByID(pub.Segment);

auto section_sp = section_list->FindSectionByID(pub.Segment);
if (!section_sp)
continue;

Expand All @@ -1148,20 +1179,24 @@ void SymbolFileNativePDB::AddSymbols(Symtab &symtab) {
(pub.Flags & PublicSymFlags::Code) != PublicSymFlags::None)
type = eSymbolTypeCode;

symtab.AddSymbol(Symbol(/*symID=*/pid,
/*name=*/pub.Name,
/*type=*/type,
/*external=*/true,
/*is_debug=*/true,
/*is_trampoline=*/false,
/*is_artificial=*/false,
/*section_sp=*/section_sp,
/*value=*/pub.Offset,
/*size=*/0,
/*size_is_valid=*/false,
/*contains_linker_annotations=*/false,
/*flags=*/0));
}
last_sym_idx =
symtab.AddSymbol(Symbol(/*symID=*/pid,
/*name=*/pub.Name,
/*type=*/type,
/*external=*/true,
/*is_debug=*/true,
/*is_trampoline=*/false,
/*is_artificial=*/false,
/*section_sp=*/section_sp,
/*value=*/pub.Offset,
/*size=*/0,
/*size_is_valid=*/false,
/*contains_linker_annotations=*/false,
/*flags=*/0));
last_sym = pub;
}

finish_last_symbol(nullptr);
}

size_t SymbolFileNativePDB::ParseFunctions(CompileUnit &comp_unit) {
Expand Down
7 changes: 3 additions & 4 deletions lldb/test/API/functionalities/multiple-slides/TestMultipleSlides.py
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Expand Up @@ -12,10 +12,6 @@
class MultipleSlidesTestCase(TestBase):
NO_DEBUG_INFO_TESTCASE = True

# The intermediate object main.o is compiled without debug info, but
# a.out is linked with `-gdwarf` on Windows. This creates a PDB.
# However, in the native PDB plugin, the symbols don't have a size.
@expectedFailureWindows
def test_mulitple_slides(self):
"""Test that a binary can be slid multiple times correctly."""
self.build()
Expand All @@ -33,10 +29,13 @@ def test_mulitple_slides(self):
first_sym.GetEndAddress().GetOffset()
- first_sym.GetStartAddress().GetOffset()
)
int_size = target.FindFirstType("int").GetByteSize()
self.assertGreaterEqual(first_size, 2048 * int_size)
second_size = (
second_sym.GetEndAddress().GetOffset()
- second_sym.GetStartAddress().GetOffset()
)
self.assertGreaterEqual(second_size, 2048 * int_size)

# View the first element of `first` and `second` while
# they have no load address set.
Expand Down
30 changes: 15 additions & 15 deletions lldb/test/Shell/SymbolFile/NativePDB/symtab.cpp
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Expand Up @@ -42,18 +42,18 @@ int main(int argc, char **argv) {
return ns::a_function() + b.b_func();
}

// CHECK-DAG: Code {{.*}} main
// CHECK-DAG: Code {{.*}} ?b_func@?$B@F@ns@@QEBAHXZ
// CHECK-DAG: Code {{.*}} ?something@A@@QEAAXXZ
// CHECK-DAG: Code {{.*}} ??_GDyn@ns@@UEAAPEAXI@Z
// CHECK-DAG: Code {{.*}} ??2@YAPEAX_K@Z
// CHECK-DAG: Code {{.*}} ??3@YAXPEAX_K@Z
// CHECK-DAG: Code {{.*}} ?static_fn@C@?$B@H@ns@@SAHXZ
// CHECK-DAG: Code {{.*}} ?a_function@ns@@YAHXZ
// CHECK-DAG: Code {{.*}} ?static_fn@C@?$B@_N@ns@@SAHXZ
// CHECK-DAG: Code {{.*}} ??1Dyn@ns@@UEAA@XZ
// CHECK-DAG: Code {{.*}} ??0Dyn@ns@@QEAA@XZ
// CHECK-DAG: Data {{.*}} ?global_int@@3HA
// CHECK-DAG: Data {{.*}} ??_7Dyn@ns@@6B@
// CHECK-DAG: Data {{.*}} ?global_a@@3UA@@A
// CHECK-DAG: Data {{.*}} ?global_c@@3UC@?$B@_J@ns@@A
// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 main
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@Michael137 Michael137 Oct 30, 2025

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What would the output without this patch be?

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@Nerixyz Nerixyz Oct 30, 2025

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Without this, it would be Code <address> 0x00...000 0x00000000 <name>. The 0x00...000 is the size here. The regex only tests that it's non-zero.

// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?b_func@?$B@F@ns@@QEBAHXZ
// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?something@A@@QEAAXXZ
// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ??_GDyn@ns@@UEAAPEAXI@Z
// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ??2@YAPEAX_K@Z
// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ??3@YAXPEAX_K@Z
// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?static_fn@C@?$B@H@ns@@SAHXZ
// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?a_function@ns@@YAHXZ
// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?static_fn@C@?$B@_N@ns@@SAHXZ
// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ??1Dyn@ns@@UEAA@XZ
// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ??0Dyn@ns@@QEAA@XZ
// CHECK-DAG: Data 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?global_int@@3HA
// CHECK-DAG: Data 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ??_7Dyn@ns@@6B@
// CHECK-DAG: Data 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?global_a@@3UA@@A
// CHECK-DAG: Data 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?global_c@@3UC@?$B@_J@ns@@A
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