[CodeView] Align type records on 4-bytes when emitting PDBs

When emitting PDBs, the TypeStreamMerger class is used to merge .debug$T records from the input .OBJ files into the output .PDB stream.
Records in .OBJs are not required to be aligned on 4-bytes, and "The Netwide Assembler 2.14" generates non-aligned records.

When compiling with -DLLVM_ENABLE_ASSERTIONS=ON, an assert was triggered in MergingTypeTableBuilder when non-ghash merging was used.
With ghash merging there was no assert.
As a result, LLD could potentially generate a non-aligned TPI stream.

We now align records on 4-bytes when record indices are remapped, in TypeStreamMerger::remapIndices().

Differential Revision: https://reviews.llvm.org/D75081

(cherry picked from commit a7325298e1f311b383b8ce5ba8e2d3698fef472a)

1 files changed, 8 insertions, 2 deletions

diff --git a/llvm/lib/DebugInfo/PDB/Native/TpiStreamBuilder.cpp b/llvm/lib/DebugInfo/PDB/Native/TpiStreamBuilder.cpp
index 4f10f8524a9..51a1f0a544e 100644
--- a/llvm/lib/DebugInfo/PDB/Native/TpiStreamBuilder.cpp
+++ b/llvm/lib/DebugInfo/PDB/Native/TpiStreamBuilder.cpp
@@ -44,6 +44,9 @@ void TpiStreamBuilder::setVersionHeader(PdbRaw_TpiVer Version) {
 void TpiStreamBuilder::addTypeRecord(ArrayRef<uint8_t> Record,
                                      Optional<uint32_t> Hash) {
   // If we just crossed an 8KB threshold, add a type index offset.
+  assert(((Record.size() & 3) == 0) &&
+         "The type record's size is not a multiple of 4 bytes which will "
+         "cause misalignment in the output TPI stream!");
   size_t NewSize = TypeRecordBytes + Record.size();
   constexpr size_t EightKB = 8 * 1024;
   if (NewSize / EightKB > TypeRecordBytes / EightKB || TypeRecords.empty()) {
@@ -153,8 +156,11 @@ Error TpiStreamBuilder::commit(const msf::MSFLayout &Layout,
     return EC;
 
   for (auto Rec : TypeRecords) {
-    assert(!Rec.empty()); // An empty record will not write anything, but it
-                          // would shift all offsets from here on.
+    assert(!Rec.empty() && "Attempting to write an empty type record shifts "
+                           "all offsets in the TPI stream!");
+    assert(((Rec.size() & 3) == 0) &&
+           "The type record's size is not a multiple of 4 bytes which will "
+           "cause misalignment in the output TPI stream!");
     if (auto EC = Writer.writeBytes(Rec))
       return EC;
   }