[DWARF] Get rid of DWARFDebugNames::HeaderPOD. NFC.

This structure was used to get the size of the fixed-size part of a Name
Index header for 32-bit DWARF. It is unsuitable for 64-bit DWARF because
the size of the unit length field is different.

Differential Revision: https://reviews.llvm.org/D73040

llvm/include/llvm/DebugInfo/DWARF/DWARFAcceleratorTable.h

@@ -222,8 +222,13 @@ class AppleAcceleratorTable : public DWARFAcceleratorTable {
 /// referenced by the name table and interpreted with the help of the
 /// abbreviation table.
 class DWARFDebugNames : public DWARFAcceleratorTable {
-  /// The fixed-size part of a DWARF v5 Name Index header
-  struct HeaderPOD {
+public:
+  class NameIndex;
+  class NameIterator;
+  class ValueIterator;
+
+  /// DWARF v5 Name Index header.
+  struct Header {
     uint32_t UnitLength;
     uint16_t Version;
     uint16_t Padding;
@@ -234,15 +239,6 @@ class DWARFDebugNames : public DWARFAcceleratorTable {
     uint32_t NameCount;
     uint32_t AbbrevTableSize;
     uint32_t AugmentationStringSize;
-  };
-
-public:
-  class NameIndex;
-  class NameIterator;
-  class ValueIterator;
-
-  /// DWARF v5 Name Index header.
-  struct Header : public HeaderPOD {
     SmallString<8> AugmentationString;
 
     Error extract(const DWARFDataExtractor &AS, uint64_t *Offset);

llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp

@@ -378,8 +378,20 @@ void DWARFDebugNames::Header::dump(ScopedPrinter &W) const {
 
 Error DWARFDebugNames::Header::extract(const DWARFDataExtractor &AS,
                                              uint64_t *Offset) {
+  // These fields are the same for 32-bit and 64-bit DWARF formats.
+  constexpr unsigned CommonHeaderSize = 2 + // Version
+                                        2 + // Padding
+                                        4 + // CU count
+                                        4 + // Local TU count
+                                        4 + // Foreign TU count
+                                        4 + // Bucket count
+                                        4 + // Name count
+                                        4 + // Abbreviations table size
+                                        4;  // Augmentation string size
+  static const unsigned DWARF32HeaderFixedPartSize =
+      dwarf::getUnitLengthFieldByteSize(dwarf::DWARF32) + CommonHeaderSize;
   // Check that we can read the fixed-size part.
-  if (!AS.isValidOffset(*Offset + sizeof(HeaderPOD) - 1))
+  if (!AS.isValidOffsetForDataOfSize(*Offset, DWARF32HeaderFixedPartSize))
     return createStringError(errc::illegal_byte_sequence,
                              "Section too small: cannot read header.");