1 files changed, 46 insertions, 3 deletions

diff --git a/lib/DebugInfo/MSF/MSFBuilder.cpp b/lib/DebugInfo/MSF/MSFBuilder.cpp
index 0f4f785abf55..9cd22ab7d887 100644
--- a/lib/DebugInfo/MSF/MSFBuilder.cpp
+++ b/lib/DebugInfo/MSF/MSFBuilder.cpp
@@ -36,8 +36,7 @@ MSFBuilder::MSFBuilder(uint32_t BlockSize, uint32_t MinBlockCount, bool CanGrow,
                        BumpPtrAllocator &Allocator)
     : Allocator(Allocator), IsGrowable(CanGrow),
       FreePageMap(kDefaultFreePageMap), BlockSize(BlockSize),
-      MininumBlocks(MinBlockCount), BlockMapAddr(kDefaultBlockMapAddr),
-      FreeBlocks(MinBlockCount, true) {
+      BlockMapAddr(kDefaultBlockMapAddr), FreeBlocks(MinBlockCount, true) {
   FreeBlocks[kSuperBlockBlock] = false;
   FreeBlocks[kFreePageMap0Block] = false;
   FreeBlocks[kFreePageMap1Block] = false;
@@ -107,7 +106,23 @@ Error MSFBuilder::allocateBlocks(uint32_t NumBlocks,
       return make_error<MSFError>(msf_error_code::insufficient_buffer,
                                   "There are no free Blocks in the file");
     uint32_t AllocBlocks = NumBlocks - NumFreeBlocks;
-    FreeBlocks.resize(AllocBlocks + FreeBlocks.size(), true);
+    uint32_t OldBlockCount = FreeBlocks.size();
+    uint32_t NewBlockCount = AllocBlocks + OldBlockCount;
+    uint32_t NextFpmBlock = alignTo(OldBlockCount, BlockSize) + 1;
+    FreeBlocks.resize(NewBlockCount, true);
+    // If we crossed over an fpm page, we actually need to allocate 2 extra
+    // blocks for each FPM group crossed and mark both blocks from the group as
+    // used.  We may not actually use them since there are many more FPM blocks
+    // present than are required to represent all blocks in a given PDB, but we
+    // need to make sure they aren't allocated to a stream or something else.
+    // At the end when committing the PDB, we'll go through and mark the
+    // extraneous ones unused.
+    while (NextFpmBlock < NewBlockCount) {
+      NewBlockCount += 2;
+      FreeBlocks.resize(NewBlockCount, true);
+      FreeBlocks.reset(NextFpmBlock, NextFpmBlock + 2);
+      NextFpmBlock += BlockSize;
+    }
   }
 
   int I = 0;
@@ -229,6 +244,19 @@ uint32_t MSFBuilder::computeDirectoryByteSize() const {
   return Size;
 }
 
+static void finalizeFpmBlockStatus(uint32_t B, ArrayRef<ulittle32_t> &FpmBlocks,
+                                   BitVector &Fpm) {
+  if (FpmBlocks.empty() || FpmBlocks.front() != B) {
+    Fpm.set(B);
+    return;
+  }
+
+  // If the next block in the actual layout is this block, it should *not* be
+  // free.
+  assert(!Fpm.test(B));
+  FpmBlocks = FpmBlocks.drop_front();
+}
+
 Expected<MSFLayout> MSFBuilder::build() {
   SuperBlock *SB = Allocator.Allocate<SuperBlock>();
   MSFLayout L;
@@ -287,5 +315,20 @@ Expected<MSFLayout> MSFBuilder::build() {
     }
   }
 
+  // FPM blocks occur in pairs at every `BlockLength` interval.  While blocks of
+  // this form are reserved for FPM blocks, not all blocks of this form will
+  // actually be needed for FPM data because there are more blocks of this form
+  // than are required to represent a PDB file with a given number of blocks.
+  // So we need to find out which blocks are *actually* going to be real FPM
+  // blocks, then mark the reset of the reserved blocks as unallocated.
+  MSFStreamLayout FpmLayout = msf::getFpmStreamLayout(L, true);
+  auto FpmBlocks = makeArrayRef(FpmLayout.Blocks);
+  for (uint32_t B = kFreePageMap0Block; B < SB->NumBlocks;
+       B += msf::getFpmIntervalLength(L)) {
+    finalizeFpmBlockStatus(B, FpmBlocks, FreeBlocks);
+    finalizeFpmBlockStatus(B + 1, FpmBlocks, FreeBlocks);
+  }
+  L.FreePageMap = FreeBlocks;
+
   return L;
 }