[lldb/DWARF] Follow DW_AT_signature when computing type contexts

[labath]

This is necessary to correctly resolve the context within types, as the name of the type is only present in the type unit.

(The DWARFYAML enthusiasm didn't last long, as it does not support type units. It can still be used for testing a lot of other things though.)

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Pavel Labath (labath)

Changes

This is necessary to correctly resolve the context within types, as the name of the type is only present in the type unit.

(The DWARFYAML enthusiasm didn't last long, as it does not support type units. It can still be used for testing a lot of other things though.)

---

Full diff: https://github.com/llvm/llvm-project/pull/93675.diff

3 Files Affected:

• (modified) lldb/source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp (+12)
• (modified) lldb/test/Shell/SymbolFile/DWARF/x86/Inputs/debug-types-basic.cpp (+9)
• (modified) lldb/test/Shell/SymbolFile/DWARF/x86/debug-types-basic.test (+8-1)

diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp
index 03e289bbf3300..7cf92adc6ef57 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp
@@ -16,6 +16,7 @@
 #include "lldb/Symbol/Type.h"
 
 #include "llvm/ADT/iterator.h"
+#include "llvm/BinaryFormat/Dwarf.h"
 
 using namespace lldb_private;
 using namespace lldb_private::dwarf;
@@ -390,6 +391,11 @@ static void GetDeclContextImpl(DWARFDIE die,
       die = spec;
       continue;
     }
+    // To find the name of a type in a type unit, we must follow the signature.
+    if (DWARFDIE spec = die.GetReferencedDIE(DW_AT_signature)) {
+      die = spec;
+      continue;
+    }
 
     // Add this DIE's contribution at the end of the chain.
     auto push_ctx = [&](CompilerContextKind kind, llvm::StringRef name) {
@@ -444,6 +450,12 @@ static void GetTypeLookupContextImpl(DWARFDIE die,
                                      std::vector<CompilerContext> &context) {
   // Stop if we hit a cycle.
   while (die && seen.insert(die.GetID()).second) {
+    // To find the name of a type in a type unit, we must follow the signature.
+    if (DWARFDIE spec = die.GetReferencedDIE(DW_AT_signature)) {
+      die = spec;
+      continue;
+    }
+
     // If there is no name, then there is no need to look anything up for this
     // DIE.
     const char *name = die.GetName();
diff --git a/lldb/test/Shell/SymbolFile/DWARF/x86/Inputs/debug-types-basic.cpp b/lldb/test/Shell/SymbolFile/DWARF/x86/Inputs/debug-types-basic.cpp
index defa8ba5c69e7..24fa05505fd38 100644
--- a/lldb/test/Shell/SymbolFile/DWARF/x86/Inputs/debug-types-basic.cpp
+++ b/lldb/test/Shell/SymbolFile/DWARF/x86/Inputs/debug-types-basic.cpp
@@ -10,6 +10,15 @@ struct A {
   EC ec;
 };
 
+struct Outer {
+  int i;
+  struct Inner {
+    long l;
+  };
+};
+
 extern constexpr A a{42, 47l, 4.2f, 4.7, e1, EC::e3};
 extern constexpr E e(e2);
 extern constexpr EC ec(EC::e2);
+extern constexpr Outer outer{47};
+extern constexpr Outer::Inner outer_inner{42l};
diff --git a/lldb/test/Shell/SymbolFile/DWARF/x86/debug-types-basic.test b/lldb/test/Shell/SymbolFile/DWARF/x86/debug-types-basic.test
index dc8005f73930e..47a6ecf39033d 100644
--- a/lldb/test/Shell/SymbolFile/DWARF/x86/debug-types-basic.test
+++ b/lldb/test/Shell/SymbolFile/DWARF/x86/debug-types-basic.test
@@ -51,6 +51,12 @@ type lookup EC
 # CHECK-NEXT:   e3
 # CHECK-NEXT: }
 
+type lookup Outer::Inner
+# CHECK-LABEL: type lookup Outer::Inner
+# CHECK:      struct Inner {
+# CHECK-NEXT:   long l;
+# CHECK-NEXT: }
+
 expression (E) 1
 # CHECK-LABEL: expression (E) 1
 # CHECK: (E) $0 = e2
@@ -59,8 +65,9 @@ expression (EC) 1
 # CHECK-LABEL: expression (EC) 1
 # CHECK: (EC) $1 = e2
 
-target variable a e ec
+target variable a e ec outer_inner
 # CHECK-LABEL: target variable a e ec
 # CHECK: (const A) a = (i = 42, l = 47, f = 4.{{[12].*}}, d = 4.{{[67].*}}, e = e1, ec = e3)
 # CHECK: (const E) e = e2
 # CHECK: (const EC) ec = e2
+# CHECK: (const Outer::Inner) outer_inner = (l = 42)