[Lldb-commits] [lldb] c2be035 - [LLDB] Omit loading local symbols in LLDB symbol table (#154809)
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Wed Aug 27 17:58:12 PDT 2025
Author: barsolo2000
Date: 2025-08-27T19:58:08-05:00
New Revision: c2be0351a725c95e3841a8d59ee432f5b205763f
URL: https://github.com/llvm/llvm-project/commit/c2be0351a725c95e3841a8d59ee432f5b205763f
DIFF: https://github.com/llvm/llvm-project/commit/c2be0351a725c95e3841a8d59ee432f5b205763f.diff
LOG: [LLDB] Omit loading local symbols in LLDB symbol table (#154809)
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.
---------
Co-authored-by: Bar Soloveychik <barsolo at fb.com>
Added:
Modified:
lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
lldb/unittests/ObjectFile/ELF/TestObjectFileELF.cpp
Removed:
################################################################################
diff --git a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
index f69358de6a288..931baf5927a04 100644
--- a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
+++ b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
@@ -2037,6 +2037,19 @@ static char FindArmAarch64MappingSymbol(const char *symbol_name) {
return '\0';
}
+static char FindRISCVMappingSymbol(const char *symbol_name) {
+ if (!symbol_name)
+ return '\0';
+
+ if (strcmp(symbol_name, "$d") == 0) {
+ return 'd';
+ }
+ if (strcmp(symbol_name, "$x") == 0) {
+ return 'x';
+ }
+ 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 +2115,12 @@ ObjectFileELF::ParseSymbols(Symtab *symtab, user_id_t start_id,
if (!symbol_name)
symbol_name = "";
+ // Skip local symbols starting with ".L" because these are compiler
+ // generated local labels used for internal purposes (e.g. debugging,
+ // optimization) and are not relevant for symbol resolution or external
+ // linkage.
+ if (llvm::StringRef(symbol_name).starts_with(".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'))
@@ -2190,7 +2209,6 @@ ObjectFileELF::ParseSymbols(Symtab *symtab, user_id_t start_id,
int64_t symbol_value_offset = 0;
uint32_t additional_flags = 0;
-
if (arch.IsValid()) {
if (arch.GetMachine() == llvm::Triple::arm) {
if (symbol.getBinding() == STB_LOCAL) {
@@ -2235,6 +2253,27 @@ ObjectFileELF::ParseSymbols(Symtab *symtab, user_id_t start_id,
if (mapping_symbol)
continue;
}
+ } else if (arch.GetTriple().isRISCV()) {
+ if (symbol.getBinding() == STB_LOCAL) {
+ char mapping_symbol = FindRISCVMappingSymbol(symbol_name);
+ if (symbol_type == eSymbolTypeCode) {
+ // Only handle $d and $x mapping symbols.
+ // Other mapping symbols are ignored as they don't affect address
+ // classification.
+ 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) {
diff --git a/lldb/unittests/ObjectFile/ELF/TestObjectFileELF.cpp b/lldb/unittests/ObjectFile/ELF/TestObjectFileELF.cpp
index 80abc5b80f84d..411387832f733 100644
--- a/lldb/unittests/ObjectFile/ELF/TestObjectFileELF.cpp
+++ b/lldb/unittests/ObjectFile/ELF/TestObjectFileELF.cpp
@@ -308,3 +308,84 @@ 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
+ - Name: .riscv.attributes
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC ]
+ Address: 0x0000000000610000
+ AddressAlign: 0x0000000000000004
+ Content: "00"
+ Symbols:
+ - Name: $d
+ Type: STT_NOTYPE
+ Section: .riscv.attributes
+ Value: 0x0000000000400180
+ Size: 0x10
+ Binding: STB_LOCAL
+ - Name: $x
+ Type: STT_NOTYPE
+ Section: .text
+ Value: 0xC0A1B010
+ Size: 0x10
+ Binding: STB_LOCAL
+ - Name: .Lfoo
+ Type: STT_OBJECT
+ Section: .data
+ Value: 0x0000000000601000
+ Size: 0x4
+ Binding: STB_LOCAL
+ - Name: global_func
+ Type: STT_FUNC
+ Section: .text
+ Value: 0x00000000004001A0
+ Size: 0x10
+ Binding: STB_GLOBAL
+ - Name: global_obj
+ Type: STT_OBJECT
+ Section: .data
+ Value: 0x0000000000601004
+ Size: 0x4
+ Binding: STB_GLOBAL
+...
+ )");
+ ASSERT_THAT_EXPECTED(ExpectedFile, llvm::Succeeded());
+ auto module_sp = std::make_shared<Module>(ExpectedFile->moduleSpec());
+ auto *symtab = module_sp->GetSymtab();
+ ASSERT_NE(nullptr, symtab);
+ EXPECT_EQ(nullptr, module_sp->FindFirstSymbolWithNameAndType(
+ ConstString("$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);
+}
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