[pdb] handle checksum and line info records that are not aligned to 4 bytes

[inglorion]

Summary

This avoids yaml2pdb aborting with stream_too_long.

[inglorion]

This is not ready for review just yet. There are some other problems with the line information (all offsets show up as 0 when read with the DIA library) that I want to look into a bit more before I'm confident that this change is doing the right thing.

[inglorion]

Superseded by D33785

lib/DebugInfo/CodeView/ModuleDebugFileChecksumFragment.cpp

void ModuleDebugFileChecksumFragment::addChecksum(StringRef FileName,
   SerializedSize += Len;
 }
 
 uint32_t ModuleDebugFileChecksumFragment::calculateSerializedLength() {
   return SerializedSize;
 }
 
 Error ModuleDebugFileChecksumFragment::commit(BinaryStreamWriter &Writer) {
+  auto StartingOffset = Writer.getOffset();
   for (const auto &FC : Checksums) {
     FileChecksumEntryHeader Header;
     Header.ChecksumKind = uint8_t(FC.Kind);
     Header.ChecksumSize = FC.Checksum.size();
     Header.FileNameOffset = FC.FileNameOffset;
     if (auto EC = Writer.writeObject(Header))
       return EC;
     if (auto EC = Writer.writeArray(makeArrayRef(FC.Checksum)))
       return EC;
-    if (auto EC = Writer.padToAlignment(4))
-      return EC;
+    auto Offset = Writer.getOffset();
+    auto Padding = 4 - ((Offset - StartingOffset) % 4);
+    if (Padding < 4) {
+      Offset += Padding;
+      Writer.setOffset(Offset);
+    }
+    StartingOffset = Offset;
   }
   return Error::success();
 }
 
 uint32_t
 ModuleDebugFileChecksumFragment::mapChecksumOffset(StringRef FileName) const {
   uint32_t Offset = Strings.getStringId(FileName);
   auto Iter = OffsetMap.find(Offset);
   assert(Iter != OffsetMap.end());
   return Iter->second;
 }

lib/DebugInfo/CodeView/ModuleDebugFragmentRecord.cpp

 uint32_t ModuleDebugFragmentRecordBuilder::calculateSerializedLength() {
   uint32_t Size = sizeof(ModuleDebugFragmentHeader) +
                   alignTo(Frag.calculateSerializedLength(), 4);
   return Size;
 }
 
 Error ModuleDebugFragmentRecordBuilder::commit(BinaryStreamWriter &Writer) {
   ModuleDebugFragmentHeader Header;
+  auto SerializedLength = calculateSerializedLength();
+  auto ExpectedOffset = Writer.getOffset() + SerializedLength;
   Header.Kind = uint32_t(Kind);
-  Header.Length =
-      calculateSerializedLength() - sizeof(ModuleDebugFragmentHeader);
+  Header.Length = SerializedLength - sizeof(ModuleDebugFragmentHeader);
 
   if (auto EC = Writer.writeObject(Header))
     return EC;
   if (auto EC = Frag.commit(Writer))
     return EC;
-  if (auto EC = Writer.padToAlignment(4))
-    return EC;
+  // Pad if necessary.
+  if (ExpectedOffset > Writer.getOffset())
+    Writer.setOffset(ExpectedOffset);
+  assert(Writer.getOffset() == ExpectedOffset);
 
   return Error::success();
 }