[Lldb-commits] [PATCH] D76808: Fix handling of bit-fields when there is a base class when parsing DWARF

[Shafik Yaghmour via Phabricator via lldb-commits]

shafik created this revision.
shafik added reviewers: aprantl, labath.
shafik added a reviewer: vsk.

When parsing DWARF and laying out bit-fields we currently don't take into account whether we have a base class or not. Currently if the first field is a bit-field but the bit offset is due a field we inherit from a base class we currently treat it as an unnamed bit-field and therefore add an extra field.

This fix will not check if we have a base class and assume that this offset is due to members we are inheriting from the base. We are currently seeing asserts during codegen when debugging `clang::DiagnosticOptions`.

This assumption will fail in the case where the first field in the derived class in an unnamed bit-field. Fixing the first field being an unnamed bit-field looks like it will require a larger change since we will need a way to track or discover the last field offset of the bases(s).


https://reviews.llvm.org/D76808

Files:
  lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
  lldb/test/API/lang/cpp/bitfields/TestCppBitfields.py
  lldb/test/API/lang/cpp/bitfields/main.cpp


Index: lldb/test/API/lang/cpp/bitfields/main.cpp
===================================================================
--- lldb/test/API/lang/cpp/bitfields/main.cpp
+++ lldb/test/API/lang/cpp/bitfields/main.cpp
@@ -60,6 +60,16 @@
     } 
   } clang_example;
 
+  class B {
+  public:
+    uint32_t b_a;
+  };
+
+  class D : public B {
+  public:
+    uint32_t d_a:1;
+  } derived;
+
   lba.a = 2;
 
   lbb.a = 1;
@@ -76,6 +86,8 @@
   lbd.arr[2] = '\0';
   lbd.a = 5;
 
+  derived.b_a=2;
+  derived.d_a=1;
 
   return 0; // Set break point at this line.
 }
Index: lldb/test/API/lang/cpp/bitfields/TestCppBitfields.py
===================================================================
--- lldb/test/API/lang/cpp/bitfields/TestCppBitfields.py
+++ lldb/test/API/lang/cpp/bitfields/TestCppBitfields.py
@@ -103,3 +103,10 @@
                    '(uint64_t:1) k = 1',
                 ])
 
+        self.expect(
+            "frame variable --show-types derived",
+            VARIABLES_DISPLAYED_CORRECTLY,
+            substrs=[
+                '(uint32_t) b_a = 2',
+                '(uint32_t:1) d_a = 1',
+                ])
Index: lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
===================================================================
--- lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
+++ lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
@@ -2670,7 +2670,10 @@
               // If we have a gap between the last_field_end and the current
               // field we have an unnamed bit-field
               if (this_field_info.bit_offset != last_field_end &&
-                  !(this_field_info.bit_offset < last_field_end)) {
+                  !(this_field_info.bit_offset < last_field_end) &&
+                  !(last_field_info.bit_offset == 0 &&
+                    last_field_info.bit_size == 0 &&
+                    layout_info.base_offsets.size() != 0)) {
                 unnamed_field_info = FieldInfo{};
                 unnamed_field_info->bit_size =
                     this_field_info.bit_offset - last_field_end;


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D76808.252686.patch
Type: text/x-patch
Size: 2084 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/lldb-commits/attachments/20200325/ac39cc5d/attachment.bin>