[LLDB] Omit loading local symbols in LLDB symbol table #154809

barsolo2000 · 2025-08-21T18:02:46Z

https://discourse.llvm.org/t/rfc-should-we-omit-local-symbols-in-eekciihgtfvflvnbieicunjlrtnufhuelf-files-from-the-lldb-symbol-table/87384

Improving symbolication by excluding local symbols that are typically not useful for debugging or symbol lookups. This aligns with the discussion that local symbols, especially those with STB_LOCAL binding and STT_NOTYPE type (including .L-prefixed symbols), often interfere with symbol resolution and can be safely omitted.

llvmbot · 2025-08-21T22:03:01Z

@llvm/pr-subscribers-lldb

Author: None (barsolo2000)

Changes

https://discourse.llvm.org/t/rfc-should-we-omit-local-symbols-in-eekciihgtfvflvnbieicunjlrtnufhuelf-files-from-the-lldb-symbol-table/87384

Improving symbolication by excluding local symbols that are typically not useful for debugging or symbol lookups. This aligns with the discussion that local symbols, especially those with STB_LOCAL binding and STT_NOTYPE type (including .L-prefixed symbols), often interfere with symbol resolution and can be safely omitted.

Full diff: https://github.com/llvm/llvm-project/pull/154809.diff

2 Files Affected:

(modified) lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp (+39-4)
(modified) lldb/unittests/ObjectFile/ELF/TestObjectFileELF.cpp (+75)

diff --git a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
index f69358de6a288..cfa446d185b14 100644
--- a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
+++ b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
@@ -2037,6 +2037,18 @@ static char FindArmAarch64MappingSymbol(const char *symbol_name) {
   return '\0';
 }
 
+static char FindRISCVMappingSymbol(const char *symbol_name) {
+  if (!symbol_name)
+    return '\0';
+
+  if (symbol_name[0] == '$' &&
+      (symbol_name[1] == 'd' || symbol_name[1] == 'x') &&
+      symbol_name[2] == '\0') {
+    return symbol_name[1];
+  }
+  return '\0';
+}
+
 #define STO_MIPS_ISA (3 << 6)
 #define STO_MICROMIPS (2 << 6)
 #define IS_MICROMIPS(ST_OTHER) (((ST_OTHER)&STO_MIPS_ISA) == STO_MICROMIPS)
@@ -2102,6 +2114,8 @@ ObjectFileELF::ParseSymbols(Symtab *symtab, user_id_t start_id,
     if (!symbol_name)
       symbol_name = "";
 
+    if (symbol_name[0] == '.' && symbol_name[1] == 'L')
+      continue;
     // No need to add non-section symbols that have no names
     if (symbol.getType() != STT_SECTION &&
         (symbol_name == nullptr || symbol_name[0] == '\0'))
@@ -2190,9 +2204,9 @@ ObjectFileELF::ParseSymbols(Symtab *symtab, user_id_t start_id,
 
     int64_t symbol_value_offset = 0;
     uint32_t additional_flags = 0;
-
+    llvm::Triple::ArchType arch_machine = arch.GetMachine();
     if (arch.IsValid()) {
-      if (arch.GetMachine() == llvm::Triple::arm) {
+      if (arch_machine == llvm::Triple::arm) {
         if (symbol.getBinding() == STB_LOCAL) {
           char mapping_symbol = FindArmAarch64MappingSymbol(symbol_name);
           if (symbol_type == eSymbolTypeCode) {
@@ -2217,7 +2231,7 @@ ObjectFileELF::ParseSymbols(Symtab *symtab, user_id_t start_id,
           if (mapping_symbol)
             continue;
         }
-      } else if (arch.GetMachine() == llvm::Triple::aarch64) {
+      } else if (arch_machine == llvm::Triple::aarch64) {
         if (symbol.getBinding() == STB_LOCAL) {
           char mapping_symbol = FindArmAarch64MappingSymbol(symbol_name);
           if (symbol_type == eSymbolTypeCode) {
@@ -2235,9 +2249,30 @@ ObjectFileELF::ParseSymbols(Symtab *symtab, user_id_t start_id,
           if (mapping_symbol)
             continue;
         }
+      } else if (arch_machine == llvm::Triple::riscv32 ||
+                 arch_machine == llvm::Triple::riscv64 ||
+                 arch_machine == llvm::Triple::riscv32be ||
+                 arch_machine == llvm::Triple::riscv64be) {
+        if (symbol.getBinding() == STB_LOCAL) {
+          char mapping_symbol = FindRISCVMappingSymbol(symbol_name);
+          if (symbol_type == eSymbolTypeCode) {
+            switch (mapping_symbol) {
+            case 'x':
+              // $x - marks a RISCV instruction sequence
+              address_class_map[symbol.st_value] = AddressClass::eCode;
+              break;
+            case 'd':
+              // $d - marks a RISCV data item sequence
+              address_class_map[symbol.st_value] = AddressClass::eData;
+              break;
+            }
+          }
+          if (mapping_symbol)
+            continue;
+        }
       }
 
-      if (arch.GetMachine() == llvm::Triple::arm) {
+      if (arch_machine == llvm::Triple::arm) {
         if (symbol_type == eSymbolTypeCode) {
           if (symbol.st_value & 1) {
             // Subtracting 1 from the address effectively unsets the low order
diff --git a/lldb/unittests/ObjectFile/ELF/TestObjectFileELF.cpp b/lldb/unittests/ObjectFile/ELF/TestObjectFileELF.cpp
index 80abc5b80f84d..9af0aeb9bab50 100644
--- a/lldb/unittests/ObjectFile/ELF/TestObjectFileELF.cpp
+++ b/lldb/unittests/ObjectFile/ELF/TestObjectFileELF.cpp
@@ -308,3 +308,78 @@ TEST_F(ObjectFileELFTest, GetSymtab_NoSymEntryPointArmAddressClass) {
   auto entry_point_addr = module_sp->GetObjectFile()->GetEntryPointAddress();
   ASSERT_EQ(entry_point_addr.GetAddressClass(), AddressClass::eCode);
 }
+
+TEST_F(ObjectFileELFTest, SkipsLocalMappingAndDotLSymbols) {
+  auto ExpectedFile = TestFile::fromYaml(R"(
+--- !ELF
+  FileHeader:
+    Class:           ELFCLASS64
+    Data:            ELFDATA2LSB
+    Type:            ET_EXEC
+    Machine:         EM_RISCV
+    Flags:           [ EF_RISCV_RVC, EF_RISCV_FLOAT_ABI_SINGLE ]
+    Entry:           0xC0A1B010
+  Sections:
+    - Name:            .text
+      Type:            SHT_PROGBITS
+      Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+      Address:         0x0000000000400180
+      AddressAlign:    0x0000000000000010
+      Content:         554889E5
+    - Name:            .data
+      Type:            SHT_PROGBITS
+      Flags:           [ SHF_WRITE, SHF_ALLOC ]
+      Address:         0x0000000000601000
+      AddressAlign:    0x0000000000000004
+      Content:         2F000000
+  Symbols:
+    - Name:            $d
+      Type:            STT_FUNC
+      Section:         .text
+      Value:           0x0000000000400180
+      Size:            0x10
+      Binding:         STB_LOCAL
+    - Name:            $x
+      Type:            STT_FUNC
+      Section:         .text
+      Value:           0xC0A1B010
+      Size:            0x10
+      Binding:         STB_LOCAL
+    - Name:            .Lfoo
+      Type:            STT_OBJECT
+      Section:         .data
+      Value:           0x0000000000601000
+      Size:            0x4
+      Binding:         STB_LOCAL
+    - Name:            global_func
+      Type:            STT_FUNC
+      Section:         .text
+      Value:           0x00000000004001A0
+      Size:            0x10
+      Binding:         STB_GLOBAL
+    - Name:            global_obj
+      Type:            STT_OBJECT
+      Section:         .data
+      Value:           0x0000000000601004
+      Size:            0x4
+      Binding:         STB_GLOBAL
+...
+  )");
+  ASSERT_THAT_EXPECTED(ExpectedFile, llvm::Succeeded());
+  auto module_sp = std::make_shared<Module>(ExpectedFile->moduleSpec());
+  auto *symtab = module_sp->GetSymtab();
+  ASSERT_NE(nullptr, symtab);
+  EXPECT_EQ(nullptr, module_sp->FindFirstSymbolWithNameAndType(
+                         ConstString("$d"), eSymbolTypeAny));
+  EXPECT_EQ(nullptr, module_sp->FindFirstSymbolWithNameAndType(
+                         ConstString("$x"), eSymbolTypeAny));
+  EXPECT_EQ(nullptr, module_sp->FindFirstSymbolWithNameAndType(
+                         ConstString(".Lfoo"), eSymbolTypeAny));
+  // assert that other symbols are present
+  const Symbol *global_func = module_sp->FindFirstSymbolWithNameAndType(
+      ConstString("global_func"), eSymbolTypeAny);
+  ASSERT_NE(nullptr, global_func);
+  const Symbol *global_obj = module_sp->FindFirstSymbolWithNameAndType(
+      ConstString("global_obj"), eSymbolTypeAny);
+  ASSERT_NE(nullptr, global_obj);
+}

lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp

satyajanga · 2025-08-21T22:25:40Z

lldb/unittests/ObjectFile/ELF/TestObjectFileELF.cpp

+      Content:         2F000000
+  Symbols:
+    - Name:            $d
+      Type:            STT_FUNC


$d and $x are not STT_FUNC type. They are unknown type, i.e. Type is empty.

github-actions · 2025-08-21T22:40:36Z

✅ With the latest revision this PR passed the C/C++ code formatter.

lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp

dmpots · 2025-08-26T16:54:16Z

lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp

I'm not sure the FindRISCVMappingSymbol is making the code cleaner here since we have to switch on the result anyway.

I think it would look cleaner to just check the symbol directly.

if (strcmp(symbol_name, "$d") == 0) { address_class_map[symbol.st_value] = AddressClass::eCode; continue; } if (strcmp(symbol_name, "$x") == 0) { address_class_map[symbol.st_value] = AddressClass::eData; continue; }

We discussed offline and decided to keep it the way I did before to follow same style as existing code.

lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp

dmpots

LGTM

satyajanga · 2025-08-28T00:58:05Z

Looks good to me as well !

Bar Soloveychik and others added 8 commits August 20, 2025 14:54

added helper function

f378e6a

fixed format

b88812a

format

9262c0f

format

d06d408

Merge branch 'main' into omitSymbols

6d5c05a

added test

e6bf2f1

Merge branch 'main' into omitSymbols

58e803e

format

0627882

barsolo2000 marked this pull request as ready for review August 21, 2025 22:02

barsolo2000 requested a review from JDevlieghere as a code owner August 21, 2025 22:02

llvmbot added the lldb label Aug 21, 2025

test_fix

d75bbbd

satyajanga reviewed Aug 21, 2025

View reviewed changes

fixed comments

315266d

barsolo2000 force-pushed the omitSymbols branch from 02e2f36 to 315266d Compare August 21, 2025 23:26

Jlalond changed the title ~~Omit loading local symbols in LLDB symbol table~~ [LLDB] Omit loading local symbols in LLDB symbol table Aug 22, 2025

Jlalond requested changes Aug 22, 2025

View reviewed changes

dmpots requested changes Aug 26, 2025

View reviewed changes

dmpots requested review from MaskRay and labath August 26, 2025 17:05

fixed comments

b97b006

barsolo2000 force-pushed the omitSymbols branch from 8b01f93 to b97b006 Compare August 26, 2025 18:44

dmpots approved these changes Aug 26, 2025

View reviewed changes

clayborg approved these changes Aug 27, 2025

View reviewed changes

Merge branch 'main' into omitSymbols

bd6f552

satyajanga merged commit c2be035 into llvm:main Aug 28, 2025
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[LLDB] Omit loading local symbols in LLDB symbol table #154809

[LLDB] Omit loading local symbols in LLDB symbol table #154809

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