From 6e545ffc4e99b16cab6494eba21dd3b6cf06ee68 Mon Sep 17 00:00:00 2001
From: Reid Kleckner <rnk@google.com>
Date: Tue, 11 Apr 2017 16:26:15 +0000
Subject: [PDB] Emit index/offset pairs for TPI and IPI streams

Summary:
This lets PDB readers lookup type record data by type index in O(log n)
time. It also enables makes `cvdump -t` work on PDBs produced by LLD.
cvdump will not dump a PDB that doesn't have an index-to-offset table.

The table is sorted by type index, and has an entry every 8KB. Looking
up a type record by index is a binary search of this table, followed by
a scan of at most 8KB.

Reviewers: ruiu, zturner, inglorion

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D31636

llvm-svn: 299958
---
 llvm/lib/DebugInfo/PDB/Native/TpiStreamBuilder.cpp | 64 ++++++++++++++++------
 1 file changed, 46 insertions(+), 18 deletions(-)

(limited to 'llvm/lib/DebugInfo/PDB/Native/TpiStreamBuilder.cpp')

diff --git a/llvm/lib/DebugInfo/PDB/Native/TpiStreamBuilder.cpp b/llvm/lib/DebugInfo/PDB/Native/TpiStreamBuilder.cpp
index 27b9dad02ac..375c35b1114 100644
--- a/llvm/lib/DebugInfo/PDB/Native/TpiStreamBuilder.cpp
+++ b/llvm/lib/DebugInfo/PDB/Native/TpiStreamBuilder.cpp
@@ -45,7 +45,17 @@ void TpiStreamBuilder::setVersionHeader(PdbRaw_TpiVer Version) {
 
 void TpiStreamBuilder::addTypeRecord(ArrayRef<uint8_t> Record,
                                      Optional<uint32_t> Hash) {
-  TypeRecordBytes += Record.size();
+  // If we just crossed an 8KB threshold, add a type index offset.
+  size_t NewSize = TypeRecordBytes + Record.size();
+  constexpr size_t EightKB = 8 * 1024;
+  if (NewSize / EightKB > TypeRecordBytes / EightKB || TypeRecords.empty()) {
+    TypeIndexOffsets.push_back(
+        {codeview::TypeIndex(codeview::TypeIndex::FirstNonSimpleIndex +
+                             TypeRecords.size()),
+         ulittle32_t(TypeRecordBytes)});
+  }
+  TypeRecordBytes = NewSize;
+
   TypeRecords.push_back(Record);
   if (Hash)
     TypeHashes.push_back(*Hash);
@@ -58,7 +68,6 @@ Error TpiStreamBuilder::finalize() {
   TpiStreamHeader *H = Allocator.Allocate<TpiStreamHeader>();
 
   uint32_t Count = TypeRecords.size();
-  uint32_t HashBufferSize = calculateHashBufferSize();
 
   H->Version = *VerHeader;
   H->HeaderSize = sizeof(TpiStreamHeader);
@@ -75,11 +84,15 @@ Error TpiStreamBuilder::finalize() {
   // the `HashStreamIndex` field of the `TpiStreamHeader`.  Therefore, the data
   // begins at offset 0 of this independent stream.
   H->HashValueBuffer.Off = 0;
-  H->HashValueBuffer.Length = HashBufferSize;
+  H->HashValueBuffer.Length = calculateHashBufferSize();
+
+  // We never write any adjustments into our PDBs, so this is usually some
+  // offset with zero length.
   H->HashAdjBuffer.Off = H->HashValueBuffer.Off + H->HashValueBuffer.Length;
   H->HashAdjBuffer.Length = 0;
+
   H->IndexOffsetBuffer.Off = H->HashAdjBuffer.Off + H->HashAdjBuffer.Length;
-  H->IndexOffsetBuffer.Length = 0;
+  H->IndexOffsetBuffer.Length = calculateIndexOffsetSize();
 
   Header = H;
   return Error::success();
@@ -90,34 +103,42 @@ uint32_t TpiStreamBuilder::calculateSerializedLength() {
 }
 
 uint32_t TpiStreamBuilder::calculateHashBufferSize() const {
-  assert(TypeHashes.size() == TypeHashes.size() &&
+  assert((TypeRecords.size() == TypeHashes.size() || TypeHashes.empty()) &&
          "either all or no type records should have hashes");
   return TypeHashes.size() * sizeof(ulittle32_t);
 }
 
+uint32_t TpiStreamBuilder::calculateIndexOffsetSize() const {
+  return TypeIndexOffsets.size() * sizeof(TypeIndexOffset);
+}
+
 Error TpiStreamBuilder::finalizeMsfLayout() {
   uint32_t Length = calculateSerializedLength();
   if (auto EC = Msf.setStreamSize(Idx, Length))
     return EC;
 
-  uint32_t HashBufferSize = calculateHashBufferSize();
+  uint32_t HashStreamSize =
+      calculateHashBufferSize() + calculateIndexOffsetSize();
 
-  if (HashBufferSize == 0)
+  if (HashStreamSize == 0)
     return Error::success();
 
-  auto ExpectedIndex = Msf.addStream(HashBufferSize);
+  auto ExpectedIndex = Msf.addStream(HashStreamSize);
   if (!ExpectedIndex)
     return ExpectedIndex.takeError();
   HashStreamIndex = *ExpectedIndex;
-  ulittle32_t *H = Allocator.Allocate<ulittle32_t>(TypeHashes.size());
-  MutableArrayRef<ulittle32_t> HashBuffer(H, TypeHashes.size());
-  for (uint32_t I = 0; I < TypeHashes.size(); ++I) {
-    HashBuffer[I] = TypeHashes[I] % MinTpiHashBuckets;
+  if (!TypeHashes.empty()) {
+    ulittle32_t *H = Allocator.Allocate<ulittle32_t>(TypeHashes.size());
+    MutableArrayRef<ulittle32_t> HashBuffer(H, TypeHashes.size());
+    for (uint32_t I = 0; I < TypeHashes.size(); ++I) {
+      HashBuffer[I] = TypeHashes[I] % MinTpiHashBuckets;
+    }
+    ArrayRef<uint8_t> Bytes(
+        reinterpret_cast<const uint8_t *>(HashBuffer.data()),
+        calculateHashBufferSize());
+    HashValueStream =
+        llvm::make_unique<BinaryByteStream>(Bytes, llvm::support::little);
   }
-  ArrayRef<uint8_t> Bytes(reinterpret_cast<const uint8_t *>(HashBuffer.data()),
-                          HashBufferSize);
-  HashValueStream =
-      llvm::make_unique<BinaryByteStream>(Bytes, llvm::support::little);
   return Error::success();
 }
 
@@ -141,8 +162,15 @@ Error TpiStreamBuilder::commit(const msf::MSFLayout &Layout,
     auto HVS = WritableMappedBlockStream::createIndexedStream(Layout, Buffer,
                                                               HashStreamIndex);
     BinaryStreamWriter HW(*HVS);
-    if (auto EC = HW.writeStreamRef(*HashValueStream))
-      return EC;
+    if (HashValueStream) {
+      if (auto EC = HW.writeStreamRef(*HashValueStream))
+        return EC;
+    }
+
+    for (auto &IndexOffset : TypeIndexOffsets) {
+      if (auto EC = HW.writeObject(IndexOffset))
+        return EC;
+    }
   }
 
   return Error::success();
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