[Lldb-commits] [lldb] [lldb][DWARFASTParserClang] Support constant index encoding of DW_AT_object_pointer (PR #144998)
via lldb-commits
lldb-commits at lists.llvm.org
Fri Jun 20 01:58:50 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-lldb
Author: Michael Buch (Michael137)
<details>
<summary>Changes</summary>
Starting with https://github.com/llvm/llvm-project/pull/124790, Clang emits `DW_AT_object_pointer` encoded as integer constants rather than DIE references. This patch accounts for this.
---
Full diff: https://github.com/llvm/llvm-project/pull/144998.diff
3 Files Affected:
- (modified) lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp (+35-12)
- (modified) lldb/test/Shell/SymbolFile/DWARF/x86/explicit-member-function-quals.cpp (+13-8)
- (modified) lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp (+196)
``````````diff
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
index 4f79c8aa3f811..7d699434ca3c8 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
@@ -174,23 +174,46 @@ DWARFASTParserClang::GetCXXObjectParameter(const DWARFDIE &subprogram,
if (!decl_ctx_die.IsStructUnionOrClass())
return {};
- if (DWARFDIE object_parameter =
- subprogram.GetAttributeValueAsReferenceDIE(DW_AT_object_pointer))
- return object_parameter;
+ // The DW_AT_object_pointer may be either encoded as a reference to a DIE,
+ // in which case that's the object parameter we want. Or it can be a constant
+ // index of the parameter.
+ std::optional<size_t> object_pointer_index;
+ DWARFFormValue form_value;
+ if (subprogram.GetDIE()->GetAttributeValue(
+ subprogram.GetCU(), DW_AT_object_pointer, form_value,
+ /*end_attr_offset_ptr=*/nullptr, /*check_elaborating_dies=*/true)) {
+ if (auto ref = form_value.Reference())
+ return ref;
+
+ object_pointer_index = form_value.Unsigned();
+ }
+
+ // Try to find the DW_TAG_formal_parameter via object_pointer_index.
+ DWARFDIE object_pointer;
+ size_t param_index = 0;
+ for (const auto &child : subprogram.children()) {
+ if (child.Tag() != DW_TAG_formal_parameter)
+ continue;
- // If no DW_AT_object_pointer was specified, assume the implicit object
- // parameter is the first parameter to the function, is called "this" and is
- // artificial (which is what most compilers would generate).
- auto children = subprogram.children();
- auto it = llvm::find_if(children, [](const DWARFDIE &child) {
- return child.Tag() == DW_TAG_formal_parameter;
- });
+ if (param_index == object_pointer_index.value_or(0))
+ object_pointer = child;
+
+ ++param_index;
+ }
- if (it == children.end())
+ // No formal parameter found for object pointer index.
+ // Nothing to be done.
+ if (!object_pointer)
return {};
- DWARFDIE object_pointer = *it;
+ // We found the object pointer encoded via DW_AT_object_pointer.
+ // No need for the remaining heuristics.
+ if (object_pointer_index)
+ return object_pointer;
+ // If no DW_AT_object_pointer was specified, assume the implicit object
+ // parameter is the first parameter to the function, is called "this" and is
+ // artificial (which is what most compilers would generate).
if (!object_pointer.GetAttributeValueAsUnsigned(DW_AT_artificial, 0))
return {};
diff --git a/lldb/test/Shell/SymbolFile/DWARF/x86/explicit-member-function-quals.cpp b/lldb/test/Shell/SymbolFile/DWARF/x86/explicit-member-function-quals.cpp
index 33001db69f83e..f89f0f4a4f0bf 100644
--- a/lldb/test/Shell/SymbolFile/DWARF/x86/explicit-member-function-quals.cpp
+++ b/lldb/test/Shell/SymbolFile/DWARF/x86/explicit-member-function-quals.cpp
@@ -1,4 +1,9 @@
// XFAIL: *
+//
+// FIXME: Explicit object parameter is not shown in
+// type lookup output. This is because we don't attach
+// valid source locations to decls in the DWARF AST,
+// so the ParmVarDecl::isExplicitObjectParameter fails.
// Tests that we correctly deduce the CV-quals and storage
// class of explicit object member functions.
@@ -8,15 +13,15 @@
//
// CHECK: (lldb) type lookup Foo
// CHECK-NEXT: struct Foo {
-// CHECK-NEXT: void Method(Foo);
-// CHECK-NEXT: void cMethod(const Foo &) const;
-// CHECK-NEXT: void vMethod(volatile Foo &) volatile;
-// CHECK-NEXT: void cvMethod(const volatile Foo &) const volatile;
+// CHECK-NEXT: void Method(this Foo);
+// CHECK-NEXT: void cMethod(this const Foo &) const;
+// CHECK-NEXT: void vMethod(this volatile Foo &) volatile;
+// CHECK-NEXT: void cvMethod(this const volatile Foo &) const volatile;
// CHECK-NEXT: }
struct Foo {
- void Method(this Foo) {}
- void cMethod(this Foo const &) {}
- void vMethod(this Foo volatile &) {}
- void cvMethod(this Foo const volatile &) {}
+ [[gnu::always_inline]] void Method(this Foo) {}
+ [[gnu::always_inline]] void cMethod(this Foo const &) {}
+ [[gnu::always_inline]] void vMethod(this Foo volatile &) {}
+ [[gnu::always_inline]] void cvMethod(this Foo const volatile &) {}
} f;
diff --git a/lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp b/lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp
index 2d4b79fed4a55..3de73a64f2758 100644
--- a/lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp
+++ b/lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp
@@ -1266,3 +1266,199 @@ TEST_F(DWARFASTParserClangTests, TestParseSubroutine_ParameterCreation) {
EXPECT_EQ(func->getParamDecl(1)->getDeclContext(), func);
EXPECT_EQ(func->getParamDecl(1)->getName(), "namedParam");
}
+
+TEST_F(DWARFASTParserClangTests, TestParseDWARFAttributes_ObjectPointerIndex) {
+ // This tests the behaviour of ParsedDWARFTypeAttributes
+ // for DW_TAG_subprogram definitions which have a DW_AT_object_pointer
+ // that encodes a constant index (instead of a DIE reference).
+
+ const char *yamldata = R"(
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_EXEC
+ Machine: EM_AARCH64
+DWARF:
+ debug_str:
+ - Context
+ - func
+ - this
+ - self
+ - arg
+ 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_structure_type
+ Children: DW_CHILDREN_yes
+ Attributes:
+ - Attribute: DW_AT_name
+ Form: DW_FORM_strp
+ - Code: 0x3
+ Tag: DW_TAG_subprogram
+ Children: DW_CHILDREN_yes
+ Attributes:
+ - Attribute: DW_AT_name
+ Form: DW_FORM_strp
+ - Attribute: DW_AT_declaration
+ Form: DW_FORM_flag_present
+ - Attribute: DW_AT_object_pointer
+ Form: DW_FORM_implicit_const
+ Value: 1
+ - Attribute: DW_AT_external
+ Form: DW_FORM_flag_present
+ - Code: 0x4
+ Tag: DW_TAG_subprogram
+ Children: DW_CHILDREN_yes
+ Attributes:
+ - Attribute: DW_AT_name
+ Form: DW_FORM_strp
+ - Attribute: DW_AT_declaration
+ Form: DW_FORM_flag_present
+ - Attribute: DW_AT_object_pointer
+ Form: DW_FORM_implicit_const
+ Value: 0
+ - Attribute: DW_AT_external
+ Form: DW_FORM_flag_present
+
+ - Code: 0x5
+ Tag: DW_TAG_formal_parameter
+ Children: DW_CHILDREN_no
+ Attributes:
+ - Attribute: DW_AT_name
+ Form: DW_FORM_strp
+
+ - Code: 0x6
+ Tag: DW_TAG_formal_parameter
+ Children: DW_CHILDREN_no
+ Attributes:
+ - Attribute: DW_AT_name
+ Form: DW_FORM_strp
+ - Attribute: DW_AT_artificial
+ Form: DW_FORM_flag_present
+
+ 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_structure_type
+# DW_AT_name [DW_FORM_strp] ("Context")
+
+ - AbbrCode: 0x2
+ Values:
+ - Value: 0x0
+
+# DW_TAG_subprogram
+# DW_AT_name [DW_FORM_strp] ("func")
+# DW_AT_object_pointer [DW_FORM_implicit_const] (1)
+ - AbbrCode: 0x3
+ Values:
+ - Value: 0x8
+ - Value: 0x1
+ - Value: 0x1
+ - Value: 0x1
+
+# DW_TAG_formal_parameter
+# DW_AT_name [DW_FORM_strp] ("arg")
+ - AbbrCode: 0x5
+ Values:
+ - Value: 0x17
+
+# DW_TAG_formal_parameter
+# DW_AT_name [DW_FORM_strp] ("self")
+# DW_AT_artificial
+ - AbbrCode: 0x6
+ Values:
+ - Value: 0x12
+ - Value: 0x1
+
+ - AbbrCode: 0x0
+ - AbbrCode: 0x0
+
+# DW_TAG_subprogram
+# DW_AT_object_pointer [DW_FORM_implicit_const] (0)
+# DW_AT_name [DW_FORM_strp] ("func")
+ - AbbrCode: 0x4
+ Values:
+ - Value: 0x8
+ - Value: 0x1
+ - Value: 0x1
+ - Value: 0x1
+
+# DW_TAG_formal_parameter
+# DW_AT_name [DW_FORM_strp] ("this")
+# DW_AT_artificial
+ - AbbrCode: 0x6
+ Values:
+ - Value: 0xd
+ - Value: 0x1
+
+# DW_TAG_formal_parameter
+# DW_AT_name [DW_FORM_strp] ("arg")
+ - AbbrCode: 0x5
+ Values:
+ - Value: 0x17
+
+ - AbbrCode: 0x0
+ - AbbrCode: 0x0
+...
+)";
+
+ 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 context_die = cu_die.GetFirstChild();
+ ASSERT_TRUE(context_die.IsValid());
+ ASSERT_EQ(context_die.Tag(), DW_TAG_structure_type);
+
+ auto sub1 = context_die.GetFirstChild();
+ ASSERT_TRUE(sub1.IsValid());
+ ASSERT_EQ(sub1.Tag(), DW_TAG_subprogram);
+
+ auto sub2 = sub1.GetSibling();
+ ASSERT_TRUE(sub2.IsValid());
+ ASSERT_EQ(sub2.Tag(), DW_TAG_subprogram);
+
+ // Object parameter is at constant index 1
+ {
+ auto param_die = sub1.GetFirstChild().GetSibling();
+ ASSERT_TRUE(param_die.IsValid());
+
+ EXPECT_EQ(param_die, ast_parser.GetCXXObjectParameter(sub1, context_die));
+ }
+
+ // Object parameter is at constant index 0
+ {
+ auto param_die = sub2.GetFirstChild();
+ ASSERT_TRUE(param_die.IsValid());
+
+ EXPECT_EQ(param_die,
+ ast_parser.GetCXXObjectParameter(param_die, context_die));
+ }
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/144998
More information about the lldb-commits
mailing list