2/2: llvm-dwarfdump: Fix DWARF-5 DW_FORM_implicit_const (used by GCC)

[jankratochvil]

Summary

Preceding D98194 is required for the patch application.

[dblaikie]

Could probably strip all the other attributes in the test if you like, but OK either way.

llvm/include/llvm/DebugInfo/DWARF/DWARFAbbreviationDeclaration.h

size_t getNumAttributes() const {
     return AttributeSpecs.size();
   }
 
   dwarf::Attribute getAttrByIndex(uint32_t idx) const {
     assert(idx < AttributeSpecs.size());
     return AttributeSpecs[idx].Attr;
   }
 
+  bool getAttrIsImplicitConstByIndex(uint32_t idx) const {
+    assert(idx < AttributeSpecs.size());
+    return AttributeSpecs[idx].isImplicitConst();
+  }
+
+  int64_t getAttrImplicitConstValueByIndex(uint32_t idx) const {
+    assert(idx < AttributeSpecs.size());
+    return AttributeSpecs[idx].getImplicitConstValue();
+  }
+
   /// Get the index of the specified attribute.
   ///
   /// Searches the this abbreviation declaration for the index of the specified
   /// attribute.
   ///
   /// \param attr DWARF attribute to search for.
   /// \returns Optional index of the attribute if found, None otherwise.
   Optional<uint32_t> findAttributeIndex(dwarf::Attribute attr) const;

llvm/lib/DebugInfo/DWARF/DWARFDie.cpp

if (abbrCode) {
         WithColor(OS, HighlightColor::Tag).get().indent(Indent)
             << formatv("{0}", getTag());
         if (DumpOpts.Verbose)
           OS << format(" [%u] %c", abbrCode,
                        AbbrevDecl->hasChildren() ? '*' : ' ');
         OS << '\n';
 
         // Dump all data in the DIE for the attributes.
-        for (const DWARFAttribute &AttrValue : attributes()) {
-          if (AttrValue.Value.getForm() == DW_FORM_implicit_const) {
-            // We are dumping .debug_info section ,
-            // implicit_const attribute values are not really stored here,
-            // but in .debug_abbrev section. So we just skip such attrs.
-            continue;
-          }
+        for (const DWARFAttribute &AttrValue : attributes())
           dumpAttribute(OS, *this, AttrValue, Indent, DumpOpts);
-        }
 
         DWARFDie child = getFirstChild();
         if (DumpOpts.ShowChildren && DumpOpts.ChildRecurseDepth > 0 && child) {
           DumpOpts.ChildRecurseDepth--;
           DIDumpOptions ChildDumpOpts = DumpOpts;
           ChildDumpOpts.ShowParents = false;
           while (child) {
             child.dump(OS, Indent + 2, ChildDumpOpts);
void DWARFDie::attribute_iterator::updateForIndex(
   Index = I;
   // AbbrDecl must be valid before calling this function.
   auto NumAttrs = AbbrDecl.getNumAttributes();
   if (Index < NumAttrs) {
     AttrValue.Attr = AbbrDecl.getAttrByIndex(Index);
     // Add the previous byte size of any previous attribute value.
     AttrValue.Offset += AttrValue.ByteSize;
     uint64_t ParseOffset = AttrValue.Offset;
+    if (AbbrDecl.getAttrIsImplicitConstByIndex(Index))
+      AttrValue.Value = DWARFFormValue::createFromSValue(
+          AbbrDecl.getFormByIndex(Index),
+          AbbrDecl.getAttrImplicitConstValueByIndex(Index));
+    else {
       auto U = Die.getDwarfUnit();
       assert(U && "Die must have valid DWARF unit");
       AttrValue.Value = DWARFFormValue::createFromUnit(
           AbbrDecl.getFormByIndex(Index), U, &ParseOffset);
+    }
     AttrValue.ByteSize = ParseOffset - AttrValue.Offset;
   } else {
     assert(Index == NumAttrs && "Indexes should be [0, NumAttrs) only");
     AttrValue = {};
   }
 }
 
 DWARFDie::attribute_iterator &DWARFDie::attribute_iterator::operator++() {

llvm/lib/DebugInfo/DWARF/DWARFFormValue.cpp

do {
     case DW_FORM_addrx2:
     case DW_FORM_addrx4:
     case DW_FORM_sec_offset:
     case DW_FORM_strp:
     case DW_FORM_strp_sup:
     case DW_FORM_line_strp:
     case DW_FORM_GNU_ref_alt:
     case DW_FORM_GNU_strp_alt:
+    case DW_FORM_implicit_const:
       if (Optional<uint8_t> FixedSize =
               dwarf::getFixedFormByteSize(Form, Params)) {
         *OffsetPtr += *FixedSize;
         return true;
       }
       return false;
 
     // signed or unsigned LEB 128 values.
case DW_FORM_strp_sup: {
       break;
     }
     case DW_FORM_flag_present:
       Value.uval = 1;
       break;
     case DW_FORM_ref_sig8:
       Value.uval = Data.getU64(OffsetPtr, &Err);
       break;
+    case DW_FORM_implicit_const:
+      // Value has been already set by DWARFFormValue::createFromSValue.
+      break;
     default:
       // DWARFFormValue::skipValue() will have caught this and caused all
       // DWARF DIEs to fail to be parsed, so this code is not be reachable.
       llvm_unreachable("unsupported form");
     }
   } while (Indirect && !Err);
 
   if (IsBlock)
if (UValue > 0) {
           ++DataPtr;
         }
       } else
         OS << "NULL";
     }
     break;
 
   case DW_FORM_sdata:
+  case DW_FORM_implicit_const:
     OS << Value.sval;
     break;
   case DW_FORM_udata:
     OS << Value.uval;
     break;
   case DW_FORM_strp:
     if (DumpOpts.Verbose)
       OS << format(" .debug_str[0x%0*" PRIx64 "] = ", OffsetDumpWidth, UValue);

llvm/test/DebugInfo/implicit-const-test2.s

+# REQUIRES: x86-registered-target
+
+# RUN: llvm-mc --filetype=obj --triple=x86_64-pc-linux %s -o %t.o -g
+
+# RUN: llvm-dwarfdump -v %t.o | FileCheck %s
+
+# CHECK:      [1] DW_TAG_compile_unit DW_CHILDREN_no
+# CHECK-NEXT: DW_AT_language  DW_FORM_implicit_const  29
+
+# CHECK:      0x0000000c: DW_TAG_compile_unit [1]  
+# CHECK-NEXT: DW_AT_language [DW_FORM_implicit_const] (DW_LANG_C11)
+
+  .section  .debug_info,"",@progbits
+.Ldebug_info0:
+  .long .Ldebug_info0_end - .Ldebug_info0_start # Length of Compilation Unit Info
+.Ldebug_info0_start:
+  .value  0x5 # DWARF version number
+  .byte 0x1 # DW_UT_compile
+  .byte 0x8 # Pointer Size (in bytes)
+  .long .Ldebug_abbrev0 # Offset Into Abbrev. Section
+  .uleb128 0x1  # (DIE DW_TAG_compile_unit)
+      # DW_AT_language
+.Ldebug_info0_end:
+  .section  .debug_abbrev,"",@progbits
+.Ldebug_abbrev0:
+  .uleb128 0x1  # (abbrev code)
+  .uleb128 0x11 # (TAG: DW_TAG_compile_unit)
+  .byte 0x0 # DW_children_no
+  .uleb128 0x13 # (DW_AT_language)
+  .uleb128 0x21   # (DW_FORM_implicit_const)
+  .sleb128 0x1d
+  .byte 0
+  .byte 0
+  .byte 0