[DWARFLinker][DWARFv5] add support for DW_FORM_implicit_const form.

[avl]

Summary

This patch adds handling of DW_FORM_implicit_const form.

[avl]

Thanks!

llvm/include/llvm/CodeGen/DIE.h

void AddAttribute(dwarf::Attribute Attribute, dwarf::Form Form) {
     Data.push_back(DIEAbbrevData(Attribute, Form));
   }
 
   /// Adds attribute with DW_FORM_implicit_const value
   void AddImplicitConstAttribute(dwarf::Attribute Attribute, int64_t Value) {
     Data.push_back(DIEAbbrevData(Attribute, Value));
   }
 
+  /// Adds another set of attribute information to the abbreviation.
+  void AddAttribute(const DIEAbbrevData &AbbrevData) {
+    Data.push_back(AbbrevData);
+  }
+
   /// Used to gather unique data for the abbreviation folding set.
   void Profile(FoldingSetNodeID &ID) const;
 
   /// Print the abbreviation using the specified asm printer.
   void Emit(const AsmPrinter *AP) const;
 
   void print(raw_ostream &O) const;
   void dump() const;

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

 //===- DWARFAbbreviationDeclaration.h ---------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_DEBUGINFO_DWARF_DWARFABBREVIATIONDECLARATION_H
 #define LLVM_DEBUGINFO_DWARF_DWARFABBREVIATIONDECLARATION_H
 
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/BinaryFormat/Dwarf.h"
+#include "llvm/DebugInfo/DWARF/DWARFFormValue.h"
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
 
 namespace llvm {
 
 class DataExtractor;
-class DWARFFormValue;
 class DWARFUnit;
 class raw_ostream;
 
 class DWARFAbbreviationDeclaration {
 public:
   struct AttributeSpec {
     AttributeSpec(dwarf::Attribute A, dwarf::Form F, int64_t Value)
         : Attr(A), Form(F), Value(Value) {
       assert(isImplicitConst());
     }
     AttributeSpec(dwarf::Attribute A, dwarf::Form F,
                   std::optional<uint8_t> ByteSize)
         : Attr(A), Form(F) {
       assert(!isImplicitConst());
       this->ByteSize.HasByteSize = ByteSize.has_value();
       if (this->ByteSize.HasByteSize)
         this->ByteSize.ByteSize = *ByteSize;
     }
 
+    DWARFFormValue getFormValue() const {
+      if (Form == dwarf::DW_FORM_implicit_const)
+        return DWARFFormValue::createFromSValue(Form, getImplicitConstValue());
+
+      return DWARFFormValue(Form);
+    }
+
     dwarf::Attribute Attr;
     dwarf::Form Form;
 
   private:
     /// The following field is used for ByteSize for non-implicit_const
     /// attributes and as value for implicit_const ones, indicated by
     /// Form == DW_FORM_implicit_const.
     /// The following cases are distinguished:

llvm/lib/DWARFLinker/DWARFLinker.cpp

void DWARFLinker::assignAbbrev(DIEAbbrev &Abbrev) {
   if (InSet) {
     // Assign existing abbreviation number.
     Abbrev.setNumber(InSet->getNumber());
   } else {
     // Add to abbreviation list.
     Abbreviations.push_back(
         std::make_unique<DIEAbbrev>(Abbrev.getTag(), Abbrev.hasChildren()));
     for (const auto &Attr : Abbrev.getData())
-      Abbreviations.back()->AddAttribute(Attr.getAttribute(), Attr.getForm());
+      Abbreviations.back()->AddAttribute(Attr);
     AbbreviationsSet.InsertNode(Abbreviations.back().get(), InsertToken);
     // Assign the unique abbreviation number.
     Abbrev.setNumber(Abbreviations.size());
     Abbreviations.back()->setNumber(Abbreviations.size());
   }
 }
 
 unsigned DWARFLinker::DIECloner::cloneStringAttribute(
unsigned DWARFLinker::DIECloner::cloneAttribute(
   case dwarf::DW_FORM_data8:
   case dwarf::DW_FORM_udata:
   case dwarf::DW_FORM_sdata:
   case dwarf::DW_FORM_sec_offset:
   case dwarf::DW_FORM_flag:
   case dwarf::DW_FORM_flag_present:
   case dwarf::DW_FORM_rnglistx:
   case dwarf::DW_FORM_loclistx:
+  case dwarf::DW_FORM_implicit_const:
     return cloneScalarAttribute(Die, InputDIE, File, Unit, AttrSpec, Val,
                                 AttrSize, Info);
   default:
     Linker.reportWarning("Unsupported attribute form " +
                              dwarf::FormEncodingString(AttrSpec.Form) +
                              " in cloneAttribute. Dropping.",
                          File, &InputDIE);
   }
DIE *DWARFLinker::DIECloner::cloneDIE(const DWARFDie &InputDIE,
   for (const auto &AttrSpec : Abbrev->attributes()) {
     if (shouldSkipAttribute(Update, AttrSpec, Die->getTag(), Info.InDebugMap,
                             Flags & TF_SkipPC, Flags & TF_InFunctionScope)) {
       DWARFFormValue::skipValue(AttrSpec.Form, Data, &Offset,
                                 U.getFormParams());
       continue;
     }
 
-    DWARFFormValue Val(AttrSpec.Form);
+    DWARFFormValue Val = AttrSpec.getFormValue();
     uint64_t AttrSize = Offset;
     Val.extractValue(Data, &Offset, U.getFormParams(), &U);
     AttrSize = Offset - AttrSize;
 
     OutOffset += cloneAttribute(*Die, InputDIE, File, Unit, StringPool, Val,
                                 AttrSpec, AttrSize, AttrInfo, IsLittleEndian);
   }
 

llvm/test/tools/llvm-dwarfutil/ELF/X86/dwarf5-attributes.test

+## Test that DWARFv5 DW_FORM_implicit_const is correctly recognized
+## and copied into the result.
+
+# RUN: yaml2obj %s -o %t.o
+
+# RUN: llvm-dwarfutil %t.o %t1
+# RUN: llvm-dwarfdump -verify %t1 | FileCheck %s --check-prefix VERIFY-CHECK
+# RUN: llvm-dwarfdump -a --verbose %t1 | FileCheck %s
+#
+# RUN: llvm-dwarfutil --no-garbage-collection %t.o %t1
+# RUN: llvm-dwarfdump -verify %t1 | FileCheck %s --check-prefix VERIFY-CHECK
+# RUN: llvm-dwarfdump -a --verbose %t1 | FileCheck %s
+#
+# RUN: llvm-dwarfutil --no-garbage-collection --build-accelerator=DWARF %t.o %t1
+# RUN: llvm-dwarfdump -verify %t1 | FileCheck %s --check-prefix VERIFY-CHECK
+# RUN: llvm-dwarfdump -a --verbose %t1 | FileCheck %s
+
+#VERIFY-CHECK: No errors.
+
+#CHECK: .debug_abbrev
+#CHECK: DW_TAG_compile_unit
+#CHECK: DW_TAG_subprogram
+#CHECK: DW_TAG_base_type
+#CHECK: DW_TAG_variable
+#CHECK: DW_AT_name
+#CHECK: DW_AT_const_value       DW_FORM_implicit_const  33
+#CHECK: DW_AT_type
+#CHECK: DW_TAG_compile_unit
+#CHECK:   DW_AT_name {{.*}}"CU1"
+#CHECK:   DW_AT_low_pc
+#CHECK:   DW_AT_high_pc
+#CHECK:   DW_TAG_subprogram
+#CHECK:     DW_AT_name {{.*}}"foo1"
+#CHECK:     DW_AT_low_pc
+#CHECK:     DW_AT_high_pc
+#CHECK:  DW_TAG_variable
+#CHECK:     DW_AT_name {{.*}}"var1"
+#CHECK:     DW_AT_const_value [DW_FORM_implicit_const]      (33)
+#CHECK:     DW_AT_type {{.*}}"int"
+
+--- !ELF
+FileHeader:
+  Class:    ELFCLASS64
+  Data:     ELFDATA2LSB
+  Type:     ET_REL
+  Machine:  EM_X86_64
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Address:         0x1130
+    Size:            0x60
+DWARF:
+  debug_abbrev:
+    - Table:
+      - Tag:      DW_TAG_compile_unit
+        Children: DW_CHILDREN_yes
+        Attributes:
+          - Attribute: DW_AT_producer
+            Form:      DW_FORM_string
+          - Attribute: DW_AT_language
+            Form:      DW_FORM_data2
+          - Attribute: DW_AT_name
+            Form:      DW_FORM_string
+          - Attribute: DW_AT_low_pc
+            Form:      DW_FORM_addrx
+          - Attribute: DW_AT_high_pc
+            Form:      DW_FORM_data8
+          - Attribute: DW_AT_addr_base
+            Form:      DW_FORM_sec_offset
+      - Tag:      DW_TAG_subprogram
+        Children: DW_CHILDREN_yes
+        Attributes:
+          - Attribute: DW_AT_name
+            Form:      DW_FORM_string
+          - Attribute: DW_AT_low_pc
+            Form:      DW_FORM_addrx
+          - Attribute: DW_AT_high_pc
+            Form:      DW_FORM_data8
+          - Attribute: DW_AT_type
+            Form:      DW_FORM_ref4
+      - Tag:      DW_TAG_base_type
+        Children: DW_CHILDREN_no
+        Attributes:
+          - Attribute: DW_AT_name
+            Form:      DW_FORM_string
+      - Tag:      DW_TAG_variable
+        Children: DW_CHILDREN_no
+        Attributes:
+          - Attribute: DW_AT_name
+            Form:      DW_FORM_string
+          - Attribute: DW_AT_const_value
+            Form:      DW_FORM_implicit_const
+            Value:     33
+          - Attribute: DW_AT_type
+            Form:      DW_FORM_ref4
+  debug_info:
+    - Version: 5
+      UnitType:   DW_UT_compile
+      Entries:
+        - AbbrCode: 1
+          Values:
+            - CStr: by_hand
+            - Value:  0x04
+            - CStr: CU1
+            - Value:  0x0
+            - Value:  0x10
+            - Value:  0x8
+        - AbbrCode: 2
+          Values:
+            - CStr: foo1
+            - Value: 0x0
+            - Value: 0x10
+            - Value: 0x3c
+        - AbbrCode: 0
+        - AbbrCode: 3
+          Values:
+            - CStr: int
+        - AbbrCode: 4
+          Values:
+            - CStr: var1
+            - Value:  0x00000000
+            - Value:  0x0000003c
+        - AbbrCode: 0
+  debug_addr:
+    - Version: 5
+      AddressSize: 0x08
+      Entries:
+        - Address: 0x1130
+...