[scudo] Introduce Chunk::getHeaderSize

[cryptoad]

Summary

Instead of using AlignedChunkHeaderSize, introduce a constexpr function
getHeaderSize in the Chunk namespace. Switch RoundUpTo to a constexpr
as well (so we can use it in constexpr declarations). Mark a few variables
in the areas touched as const.

Overall this has no functional change, and is mostly to make things a bit more
consistent.

lib/scudo/scudo_allocator.h

 COMPILER_CHECK(sizeof(UnpackedHeader) == sizeof(PackedHeader));
 
 // Minimum alignment of 8 bytes for 32-bit, 16 for 64-bit
 const uptr MinAlignmentLog = FIRST_32_SECOND_64(3, 4);
 const uptr MaxAlignmentLog = 24;  // 16 MB
 const uptr MinAlignment = 1 << MinAlignmentLog;
 const uptr MaxAlignment = 1 << MaxAlignmentLog;
 
-const uptr ChunkHeaderSize = sizeof(PackedHeader);
-const uptr AlignedChunkHeaderSize =
-    (ChunkHeaderSize + MinAlignment - 1) & ~(MinAlignment - 1);
+// constexpr version of __sanitizer::RoundUp without the extraneous CHECK.
+// This way we can use it in constexpr variables and functions declarations.
+constexpr uptr RoundUpTo(uptr Size, uptr Boundary) {
+  return (Size + Boundary - 1) & ~(Boundary - 1);
+}
+
+namespace Chunk {
+  constexpr uptr getHeaderSize() {
+    return RoundUpTo(sizeof(PackedHeader), MinAlignment);
+  }
+}
 
 #if SANITIZER_CAN_USE_ALLOCATOR64
 const uptr AllocatorSpace = ~0ULL;
 struct AP64 {
   static const uptr kSpaceBeg = AllocatorSpace;
   static const uptr kSpaceSize = AllocatorSize;
   static const uptr kMetadataSize = 0;
   typedef __scudo::SizeClassMap SizeClassMap;
struct AP32 {
   typedef NoOpMapUnmapCallback MapUnmapCallback;
   static const uptr kFlags =
       SizeClassAllocator32FlagMasks::kRandomShuffleChunks |
       SizeClassAllocator32FlagMasks::kUseSeparateSizeClassForBatch;
 };
 typedef SizeClassAllocator32<AP32> PrimaryAllocator;
 #endif  // SANITIZER_CAN_USE_ALLOCATOR64
 
-// __sanitizer::RoundUp has a CHECK that is extraneous for us. Use our own.
-INLINE uptr RoundUpTo(uptr Size, uptr Boundary) {
-  return (Size + Boundary - 1) & ~(Boundary - 1);
-}
-
 #include "scudo_allocator_secondary.h"
 #include "scudo_allocator_combined.h"
 
 typedef SizeClassAllocatorLocalCache<PrimaryAllocator> AllocatorCache;
 typedef ScudoLargeMmapAllocator SecondaryAllocator;
 typedef ScudoCombinedAllocator<PrimaryAllocator, AllocatorCache,
     SecondaryAllocator> ScudoBackendAllocator;
 

lib/scudo/scudo_allocator.cpp

 static ScudoBackendAllocator &getBackendAllocator();
 
 namespace Chunk {
   // We can't use the offset member of the chunk itself, as we would double
   // fetch it without any warranty that it wouldn't have been tampered. To
   // prevent this, we work with a local copy of the header.
   static INLINE void *getBackendPtr(const void *Ptr, UnpackedHeader *Header) {
     return reinterpret_cast<void *>(reinterpret_cast<uptr>(Ptr) -
-                                    AlignedChunkHeaderSize -
-                                    (Header->Offset << MinAlignmentLog));
+        getHeaderSize() - (Header->Offset << MinAlignmentLog));
   }
 
   static INLINE AtomicPackedHeader *getAtomicHeader(void *Ptr) {
     return reinterpret_cast<AtomicPackedHeader *>(reinterpret_cast<uptr>(Ptr) -
-                                                  AlignedChunkHeaderSize);
+        getHeaderSize());
   }
   static INLINE
   const AtomicPackedHeader *getConstAtomicHeader(const void *Ptr) {
     return reinterpret_cast<const AtomicPackedHeader *>(
-        reinterpret_cast<uptr>(Ptr) - AlignedChunkHeaderSize);
+        reinterpret_cast<uptr>(Ptr) - getHeaderSize());
   }
 
   static INLINE bool isAligned(const void *Ptr) {
     return IsAligned(reinterpret_cast<uptr>(Ptr), MinAlignment);
   }
 
   // Returns the usable size for a chunk, meaning the amount of bytes from the
   // beginning of the user data to the end of the backend allocated chunk.
   static INLINE uptr getUsableSize(const void *Ptr, UnpackedHeader *Header) {
     const uptr Size = getBackendAllocator().getActuallyAllocatedSize(
         getBackendPtr(Ptr, Header), Header->ClassId);
-    if (Size == 0)
-      return 0;
-    return Size - AlignedChunkHeaderSize - (Header->Offset << MinAlignmentLog);
+    DCHECK_NE(Size, 0);
+    return Size - getHeaderSize() - (Header->Offset << MinAlignmentLog);
   }
 
   // Compute the checksum of the chunk pointer and its header.
   static INLINE u16 computeChecksum(const void *Ptr, UnpackedHeader *Header) {
     UnpackedHeader ZeroChecksumHeader = *Header;
     ZeroChecksumHeader.Checksum = 0;
     uptr HeaderHolder[sizeof(UnpackedHeader) / sizeof(uptr)];
     memcpy(&HeaderHolder, &ZeroChecksumHeader, sizeof(HeaderHolder));
void performSanityChecks() {
     // would already be aligned on the requested alignment, which would happen
     // to be the maximum alignment that would fit in that size class. As a
     // result, the maximum offset will be at most the maximum alignment for the
     // last size class minus the header size, in multiples of MinAlignment.
     UnpackedHeader Header = {};
     const uptr MaxPrimaryAlignment =
         1 << MostSignificantSetBitIndex(SizeClassMap::kMaxSize - MinAlignment);
     const uptr MaxOffset =
-        (MaxPrimaryAlignment - AlignedChunkHeaderSize) >> MinAlignmentLog;
+        (MaxPrimaryAlignment - Chunk::getHeaderSize()) >> MinAlignmentLog;
     Header.Offset = MaxOffset;
     if (Header.Offset != MaxOffset) {
       dieWithMessage("ERROR: the maximum possible offset doesn't fit in the "
                      "header\n");
     }
     // Verify that we can fit the maximum size or amount of unused bytes in the
     // header. Given that the Secondary fits the allocation to a page, the worst
     // case scenario happens in the Primary. It will depend on the second to
if (UNLIKELY(Alignment > MaxAlignment))
       return FailureHandler::OnBadRequest();
     if (UNLIKELY(Alignment < MinAlignment))
       Alignment = MinAlignment;
     if (UNLIKELY(Size >= MaxAllowedMallocSize))
       return FailureHandler::OnBadRequest();
     if (UNLIKELY(Size == 0))
       Size = 1;
 
-    uptr NeededSize = RoundUpTo(Size, MinAlignment) + AlignedChunkHeaderSize;
-    uptr AlignedSize = (Alignment > MinAlignment) ?
-        NeededSize + (Alignment - AlignedChunkHeaderSize) : NeededSize;
+    const uptr NeededSize = RoundUpTo(Size, MinAlignment) +
+        Chunk::getHeaderSize();
+    const uptr AlignedSize = (Alignment > MinAlignment) ?
+        NeededSize + (Alignment - Chunk::getHeaderSize()) : NeededSize;
     if (UNLIKELY(AlignedSize >= MaxAllowedMallocSize))
       return FailureHandler::OnBadRequest();
 
     if (CheckRssLimit && UNLIKELY(isRssLimitExceeded()))
       return FailureHandler::OnOOM();
 
     // Primary and Secondary backed allocations have a different treatment. We
     // deal with alignment requirements of Primary serviced allocations here,
if (UNLIKELY(!BackendPtr))
       return FailureHandler::OnOOM();
 
     // If requested, we will zero out the entire contents of the returned chunk.
     if ((ForceZeroContents || ZeroContents) && ClassId)
       memset(BackendPtr, 0,
              BackendAllocator.getActuallyAllocatedSize(BackendPtr, ClassId));
 
     UnpackedHeader Header = {};
-    uptr UserPtr = reinterpret_cast<uptr>(BackendPtr) + AlignedChunkHeaderSize;
+    uptr UserPtr = reinterpret_cast<uptr>(BackendPtr) + Chunk::getHeaderSize();
     if (UNLIKELY(!IsAligned(UserPtr, Alignment))) {
       // Since the Secondary takes care of alignment, a non-aligned pointer
       // means it is from the Primary. It is also the only case where the offset
       // field of the header would be non-zero.
       DCHECK(ClassId);
       const uptr AlignedUserPtr = RoundUpTo(UserPtr, Alignment);
       Header.Offset = (AlignedUserPtr - UserPtr) >> MinAlignmentLog;
       UserPtr = AlignedUserPtr;
if (DeallocationTypeMismatch) {
       if (Header.AllocType != Type) {
         // With the exception of memalign'd Chunks, that can be still be free'd.
         if (Header.AllocType != FromMemalign || Type != FromMalloc) {
           dieWithMessage("ERROR: allocation type mismatch when deallocating "
                          "address %p\n", Ptr);
         }
       }
     }
-    uptr Size = Header.ClassId ? Header.SizeOrUnusedBytes :
+    const uptr Size = Header.ClassId ? Header.SizeOrUnusedBytes :
         Chunk::getUsableSize(Ptr, &Header) - Header.SizeOrUnusedBytes;
     if (DeleteSizeMismatch) {
       if (DeleteSize && DeleteSize != Size) {
         dieWithMessage("ERROR: invalid sized delete on chunk at address %p\n",
                        Ptr);
       }
     }
     quarantineOrDeallocateChunk(Ptr, &Header, Size);

lib/scudo/scudo_allocator_secondary.h

 
 class ScudoLargeMmapAllocator {
  public:
   void Init() {
     PageSizeCached = GetPageSizeCached();
   }
 
   void *Allocate(AllocatorStats *Stats, uptr Size, uptr Alignment) {
-    const uptr UserSize = Size - AlignedChunkHeaderSize;
+    const uptr UserSize = Size - Chunk::getHeaderSize();
     // The Scudo frontend prevents us from allocating more than
     // MaxAllowedMallocSize, so integer overflow checks would be superfluous.
     uptr MapSize = Size + AlignedReservedAddressRangeSize;
     if (Alignment > MinAlignment)
       MapSize += Alignment;
     const uptr PageSize = PageSizeCached;
     MapSize = RoundUpTo(MapSize, PageSize);
     // Account for 2 guard pages, one before and one after the chunk.
if (Alignment > MinAlignment) {
       }
       MapSize = MapEnd - MapBeg;
     }
 
     DCHECK_LE(UserEnd, MapEnd - PageSize);
     // Actually mmap the memory, preserving the guard pages on either side
     CHECK_EQ(MapBeg + PageSize,
              AddressRange.Map(MapBeg + PageSize, MapSize - 2 * PageSize));
-    const uptr Ptr = UserBeg - AlignedChunkHeaderSize;
+    const uptr Ptr = UserBeg - Chunk::getHeaderSize();
     ReservedAddressRange *StoredRange = getReservedAddressRange(Ptr);
     *StoredRange = AddressRange;
 
     // The primary adds the whole class size to the stats when allocating a
     // chunk, so we will do something similar here. But we will not account for
     // the guard pages.
     {
       SpinMutexLock l(&StatsMutex);
ReservedAddressRange *getReservedAddressRange(uptr Ptr) {
     return reinterpret_cast<ReservedAddressRange*>(
         Ptr - sizeof(ReservedAddressRange));
   }
   ReservedAddressRange *getReservedAddressRange(const void *Ptr) {
     return getReservedAddressRange(reinterpret_cast<uptr>(Ptr));
   }
 
   static constexpr uptr AlignedReservedAddressRangeSize =
-      (sizeof(ReservedAddressRange) + MinAlignment - 1) & ~(MinAlignment - 1);
+      RoundUpTo(sizeof(ReservedAddressRange), MinAlignment);
   static constexpr uptr HeadersSize =
-      AlignedReservedAddressRangeSize + AlignedChunkHeaderSize;
+      AlignedReservedAddressRangeSize + Chunk::getHeaderSize();
 
   uptr PageSizeCached;
   SpinMutex StatsMutex;
 };
 
 #endif  // SCUDO_ALLOCATOR_SECONDARY_H_