[Lldb-commits] [lldb] [lldb][DWARF] Support DW_AT_bit_size on type tags (PR #165686)
Michael Buch via lldb-commits
lldb-commits at lists.llvm.org
Thu Oct 30 02:40:01 PDT 2025
https://github.com/Michael137 updated https://github.com/llvm/llvm-project/pull/165686
>From ef4795280878526b547d021405a1e99dee653bf1 Mon Sep 17 00:00:00 2001
From: Michael Buch <michaelbuch12 at gmail.com>
Date: Thu, 30 Oct 2025 09:36:53 +0000
Subject: [PATCH 1/2] [lldb][DWARF] Support DW_AT_bit_size on type tags
One (DWARF-spec compliant) exmample is: https://github.com/llvm/llvm-project/pull/164372, where we attach a `DW_AT_bit_size` to `_BitInt` types that can't be exactly described by a byte-size.
This patch adds support for `DW_AT_bit_size` to `DWARFASTParserClang`
when parsing type tags.
Note, we don't use this bit-size yet, but will do so in follow-up
patches.
---
.../SymbolFile/DWARF/DWARFASTParserClang.cpp | 8 +-
.../SymbolFile/DWARF/DWARFASTParserClang.h | 1 +
.../DWARF/DWARFASTParserClangTests.cpp | 90 +++++++++++++++++++
3 files changed, 97 insertions(+), 2 deletions(-)
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
index 82e9d867c3ac0..71dc3de4137d4 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
@@ -450,6 +450,10 @@ ParsedDWARFTypeAttributes::ParsedDWARFTypeAttributes(const DWARFDIE &die) {
byte_size = form_value.Unsigned();
break;
+ case DW_AT_bit_size:
+ data_bit_size = form_value.Unsigned();
+ break;
+
case DW_AT_alignment:
alignment = form_value.Unsigned();
break;
@@ -810,13 +814,13 @@ DWARFASTParserClang::ParseTypeModifier(const SymbolContext &sc,
// there...
[[fallthrough]];
- case DW_TAG_base_type:
+ case DW_TAG_base_type: {
resolve_state = Type::ResolveState::Full;
clang_type = m_ast.GetBuiltinTypeForDWARFEncodingAndBitSize(
attrs.name.GetStringRef(), attrs.encoding,
attrs.byte_size.value_or(0) * 8);
break;
-
+ }
case DW_TAG_pointer_type:
encoding_data_type = Type::eEncodingIsPointerUID;
break;
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.h b/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.h
index da58f4c146226..f5f707129d67d 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.h
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.h
@@ -574,6 +574,7 @@ struct ParsedDWARFTypeAttributes {
lldb_private::plugin::dwarf::DWARFFormValue type;
lldb::LanguageType class_language = lldb::eLanguageTypeUnknown;
std::optional<uint64_t> byte_size;
+ std::optional<uint64_t> data_bit_size;
std::optional<uint64_t> alignment;
size_t calling_convention = llvm::dwarf::DW_CC_normal;
uint32_t bit_stride = 0;
diff --git a/lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp b/lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp
index 0cae01de2902a..646426b5cb31f 100644
--- a/lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp
+++ b/lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp
@@ -1617,3 +1617,93 @@ TEST_F(DWARFASTParserClangTests, TestObjectPointer_IndexEncoding) {
EXPECT_EQ(param_die, ast_parser.GetObjectParameter(sub2, context_die));
}
}
+
+TEST_F(DWARFASTParserClangTests, TestTypeBitSize) {
+ // Tests that we correctly parse DW_AT_bit_size of a DW_AT_base_type.
+
+ const char *yamldata = R"(
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_EXEC
+ Machine: EM_AARCH64
+DWARF:
+ debug_str:
+ - _BitInt(2)
+ debug_abbrev:
+ - ID: 0
+ Table:
+ - Code: 0x1
+ Tag: DW_TAG_compile_unit
+ Children: DW_CHILDREN_yes
+ Attributes:
+ - Attribute: DW_AT_language
+ Form: DW_FORM_data2
+ - Code: 0x2
+ Tag: DW_TAG_base_type
+ Children: DW_CHILDREN_no
+ Attributes:
+ - Attribute: DW_AT_name
+ Form: DW_FORM_strp
+ - Attribute: DW_AT_encoding
+ Form: DW_FORM_data1
+ - Attribute: DW_AT_byte_size
+ Form: DW_FORM_data1
+ - Attribute: DW_AT_bit_size
+ Form: DW_FORM_data1
+
+ debug_info:
+ - Version: 5
+ UnitType: DW_UT_compile
+ AddrSize: 8
+ Entries:
+
+# DW_TAG_compile_unit
+# DW_AT_language [DW_FORM_data2] (DW_LANG_C_plus_plus)
+
+ - AbbrCode: 0x1
+ Values:
+ - Value: 0x04
+
+# DW_TAG_base_type
+# DW_AT_name [DW_FORM_strp] ('_BitInt(2)')
+
+ - AbbrCode: 0x2
+ Values:
+ - Value: 0x0
+ - Value: 0x3e
+ - Value: 0x01
+ - Value: 0x02
+...
+)";
+
+ YAMLModuleTester t(yamldata);
+
+ DWARFUnit *unit = t.GetDwarfUnit();
+ ASSERT_NE(unit, nullptr);
+ const DWARFDebugInfoEntry *cu_entry = unit->DIE().GetDIE();
+ ASSERT_EQ(cu_entry->Tag(), DW_TAG_compile_unit);
+ ASSERT_EQ(unit->GetDWARFLanguageType(), DW_LANG_C_plus_plus);
+ DWARFDIE cu_die(unit, cu_entry);
+
+ auto holder = std::make_unique<clang_utils::TypeSystemClangHolder>("ast");
+ auto &ast_ctx = *holder->GetAST();
+ DWARFASTParserClangStub ast_parser(ast_ctx);
+
+ auto type_die = cu_die.GetFirstChild();
+ ASSERT_TRUE(type_die.IsValid());
+ ASSERT_EQ(type_die.Tag(), DW_TAG_base_type);
+
+ ParsedDWARFTypeAttributes attrs(type_die);
+ EXPECT_EQ(attrs.byte_size.value_or(0), 1U);
+ EXPECT_EQ(attrs.data_bit_size.value_or(0), 2U);
+
+ SymbolContext sc;
+ auto type_sp =
+ ast_parser.ParseTypeFromDWARF(sc, type_die, /*type_is_new_ptr=*/nullptr);
+ ASSERT_NE(type_sp, nullptr);
+
+ EXPECT_EQ(llvm::expectedToOptional(type_sp->GetByteSize(nullptr)).value_or(0),
+ 1U);
+}
>From fb45b0e7a81d429322f32ff7eb7b49b6269b5b32 Mon Sep 17 00:00:00 2001
From: Michael Buch <michaelbuch12 at gmail.com>
Date: Thu, 30 Oct 2025 09:39:50 +0000
Subject: [PATCH 2/2] fixup! remove redundant change
---
lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
index 71dc3de4137d4..2565446a26059 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
@@ -814,13 +814,13 @@ DWARFASTParserClang::ParseTypeModifier(const SymbolContext &sc,
// there...
[[fallthrough]];
- case DW_TAG_base_type: {
+ case DW_TAG_base_type:
resolve_state = Type::ResolveState::Full;
clang_type = m_ast.GetBuiltinTypeForDWARFEncodingAndBitSize(
attrs.name.GetStringRef(), attrs.encoding,
attrs.byte_size.value_or(0) * 8);
break;
- }
+
case DW_TAG_pointer_type:
encoding_data_type = Type::eEncodingIsPointerUID;
break;
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