[Lldb-commits] [lldb] [LLDB][NativePDB] Estimate symbol sizes (PR #165727)
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lldb-commits at lists.llvm.org
Thu Oct 30 07:40:45 PDT 2025
https://github.com/Nerixyz created https://github.com/llvm/llvm-project/pull/165727
In #165604, a test was skipped on Windows, because the native PDB plugin didn't set sizes on symbols. While the test isn't compiled with debug info, it's linked with `-gdwarf`, causing a PDB to be created on Windows. This PDB will only contain the public symbols (written by the linker) and section information. The symbols themselves don't have a size, however the DIA SDK sets a size for them.
It seems like, for these data symbols, the size given from DIA is the distance to the next symbol (or the section end).
This PR implements the naive approach for the native plugin. The main difference is in function/code symbols. There, DIA searches for a corresponding `S_GPROC32` which have a "code size" that is sometimes slightly smaller than the difference to the next symbol.
>From 5a71656da61510bda407327bbf8a5b6585006c0e Mon Sep 17 00:00:00 2001
From: Nerixyz <nerixdev at outlook.de>
Date: Wed, 29 Oct 2025 21:58:44 +0100
Subject: [PATCH] [LLDB][NativePDB] Estimate symbol sizes
---
.../NativePDB/SymbolFileNativePDB.cpp | 67 ++++++++++++++-----
.../multiple-slides/TestMultipleSlides.py | 7 +-
.../Shell/SymbolFile/NativePDB/symtab.cpp | 30 ++++-----
3 files changed, 69 insertions(+), 35 deletions(-)
diff --git a/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp b/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp
index e76b7a3cf274a..be5cb1a619803 100644
--- a/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp
+++ b/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp
@@ -1130,7 +1130,35 @@ 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();
@@ -1138,8 +1166,11 @@ void SymbolFileNativePDB::AddSymbols(Symtab &symtab) {
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;
@@ -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) {
diff --git a/lldb/test/API/functionalities/multiple-slides/TestMultipleSlides.py b/lldb/test/API/functionalities/multiple-slides/TestMultipleSlides.py
index 7fd2ff4229004..5fd2b767a6237 100644
--- a/lldb/test/API/functionalities/multiple-slides/TestMultipleSlides.py
+++ b/lldb/test/API/functionalities/multiple-slides/TestMultipleSlides.py
@@ -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()
@@ -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.
diff --git a/lldb/test/Shell/SymbolFile/NativePDB/symtab.cpp b/lldb/test/Shell/SymbolFile/NativePDB/symtab.cpp
index beb5ae2f90256..75c59c560fad9 100644
--- a/lldb/test/Shell/SymbolFile/NativePDB/symtab.cpp
+++ b/lldb/test/Shell/SymbolFile/NativePDB/symtab.cpp
@@ -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@?$B at F@ns@@QEBAHXZ
-// CHECK-DAG: Code {{.*}} ?something at A@@QEAAXXZ
-// CHECK-DAG: Code {{.*}} ??_GDyn at ns@@UEAAPEAXI at Z
-// CHECK-DAG: Code {{.*}} ??2 at YAPEAX_K@Z
-// CHECK-DAG: Code {{.*}} ??3 at YAXPEAX_K@Z
-// CHECK-DAG: Code {{.*}} ?static_fn at C@?$B at H@ns@@SAHXZ
-// CHECK-DAG: Code {{.*}} ?a_function at ns@@YAHXZ
-// CHECK-DAG: Code {{.*}} ?static_fn at C@?$B at _N@ns@@SAHXZ
-// CHECK-DAG: Code {{.*}} ??1Dyn at ns@@UEAA at XZ
-// CHECK-DAG: Code {{.*}} ??0Dyn at ns@@QEAA at XZ
-// CHECK-DAG: Data {{.*}} ?global_int@@3HA
-// CHECK-DAG: Data {{.*}} ??_7Dyn at ns@@6B@
-// CHECK-DAG: Data {{.*}} ?global_a@@3UA@@A
-// CHECK-DAG: Data {{.*}} ?global_c@@3UC@?$B at _J@ns@@A
+// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 main
+// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?b_func@?$B at F@ns@@QEBAHXZ
+// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?something at A@@QEAAXXZ
+// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ??_GDyn at ns@@UEAAPEAXI at Z
+// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ??2 at YAPEAX_K@Z
+// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ??3 at YAXPEAX_K@Z
+// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?static_fn at C@?$B at H@ns@@SAHXZ
+// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?a_function at ns@@YAHXZ
+// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?static_fn at C@?$B at _N@ns@@SAHXZ
+// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ??1Dyn at ns@@UEAA at XZ
+// CHECK-DAG: Code 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ??0Dyn at ns@@QEAA at XZ
+// CHECK-DAG: Data 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?global_int@@3HA
+// CHECK-DAG: Data 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ??_7Dyn at ns@@6B@
+// CHECK-DAG: Data 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?global_a@@3UA@@A
+// CHECK-DAG: Data 0x{{[0-9a-f]+}} 0x{{0*[1-9a-f][0-9a-f]*}} 0x00000000 ?global_c@@3UC@?$B at _J@ns@@A
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