[scudo] Add Chunk::getSize, rework Chunk::getUsableSize

[cryptoad]

Summary

Using getActuallyAllocatedSize from the Combined resulting in mediocre
compiled code, as the ClassId != 0 predicament was not propagated there,
resulting in additional branches and dead code. Move the logic in the frontend,
which results in better compiled code. Also I think it makes it slightly easier
to distinguish between the size the user requested, and the size that was
actually allocated by the allocator.

const a couple of things as well.

This has no functional impact.

[alekseyshl]

lib/scudo/scudo_allocator.cpp

95

Two more spaces indent

[cryptoad]

Indentation updated.

lib/scudo/scudo_allocator.cpp

for (uptr i = 0; i < ArraySize; i++)
     Crc = computeSoftwareCRC32(Crc, Array[i]);
   return Crc;
 #endif  // defined(__SSE4_2__) || defined(__ARM_FEATURE_CRC32)
 }
 
 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) -
-        getHeaderSize() - (Header->Offset << MinAlignmentLog));
-  }
-
   static INLINE AtomicPackedHeader *getAtomicHeader(void *Ptr) {
     return reinterpret_cast<AtomicPackedHeader *>(reinterpret_cast<uptr>(Ptr) -
         getHeaderSize());
   }
   static INLINE
   const AtomicPackedHeader *getConstAtomicHeader(const void *Ptr) {
     return reinterpret_cast<const AtomicPackedHeader *>(
         reinterpret_cast<uptr>(Ptr) - getHeaderSize());
   }
 
   static INLINE bool isAligned(const void *Ptr) {
     return IsAligned(reinterpret_cast<uptr>(Ptr), MinAlignment);
   }
 
+  // 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) -
+        getHeaderSize() - (Header->Offset << MinAlignmentLog));
+  }
+
   // 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);
-    DCHECK_NE(Size, 0);
-    return Size - getHeaderSize() - (Header->Offset << MinAlignmentLog);
+    const uptr ClassId = Header->ClassId;
+    if (ClassId)
+      return PrimaryAllocator::ClassIdToSize(ClassId) - getHeaderSize() -
+          (Header->Offset << MinAlignmentLog);
+    return SecondaryAllocator::GetActuallyAllocatedSize(
+        getBackendPtr(Ptr, Header)) - getHeaderSize();
+  }
+
+  // Returns the size the user requested when allocating the chunk.
+  static INLINE uptr getSize(const void *Ptr, UnpackedHeader *Header) {
+    const uptr SizeOrUnusedBytes = Header->SizeOrUnusedBytes;
+    if (Header->ClassId)
+      return SizeOrUnusedBytes;
+    return SecondaryAllocator::GetActuallyAllocatedSize(
+        getBackendPtr(Ptr, Header)) - getHeaderSize() - SizeOrUnusedBytes;
   }
 
   // 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));
if (PrimaryAllocator::CanAllocate(AlignedSize, MinAlignment)) {
       ClassId = 0;
       BackendPtr = BackendAllocator.allocateSecondary(BackendSize, Alignment);
     }
     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));
+      memset(BackendPtr, 0, PrimaryAllocator::ClassIdToSize(ClassId));
 
     UnpackedHeader Header = {};
     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;
     }
-    CHECK_LE(UserPtr + Size, reinterpret_cast<uptr>(BackendPtr) + BackendSize);
+    DCHECK_LE(UserPtr + Size, reinterpret_cast<uptr>(BackendPtr) + BackendSize);
     Header.State = ChunkAllocated;
     Header.AllocType = Type;
     if (ClassId) {
       Header.ClassId = ClassId;
       Header.SizeOrUnusedBytes = Size;
     } else {
       // The secondary fits the allocations to a page, so the amount of unused
       // bytes is the difference between the end of the user allocation and the
if (BypassQuarantine) {
         getBackendAllocator().deallocateSecondary(BackendPtr);
       }
     } else {
       // If a small memory amount was allocated with a larger alignment, we want
       // to take that into account. Otherwise the Quarantine would be filled
       // with tiny chunks, taking a lot of VA memory. This is an approximation
       // of the usable size, that allows us to not call
       // GetActuallyAllocatedSize.
-      uptr EstimatedSize = Size + (Header->Offset << MinAlignmentLog);
+      const uptr EstimatedSize = Size + (Header->Offset << MinAlignmentLog);
       UnpackedHeader NewHeader = *Header;
       NewHeader.State = ChunkQuarantine;
       Chunk::compareExchangeHeader(Ptr, &NewHeader, Header);
       ScudoTSD *TSD = getTSDAndLock();
       AllocatorQuarantine.Put(getQuarantineCache(TSD),
                               QuarantineCallback(&TSD->Cache), Ptr,
                               EstimatedSize);
       TSD->unlock();
if (DeallocationTypeMismatch) {
       // The deallocation type has to match the allocation one.
       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("allocation type mismatch when deallocating address "
                          "%p\n", Ptr);
       }
     }
-    const uptr Size = Header.ClassId ? Header.SizeOrUnusedBytes :
-        Chunk::getUsableSize(Ptr, &Header) - Header.SizeOrUnusedBytes;
+    const uptr Size = Chunk::getSize(Ptr, &Header);
     if (DeleteSizeMismatch) {
       if (DeleteSize && DeleteSize != Size)
         dieWithMessage("invalid sized delete when deallocating address %p\n",
                        Ptr);
     }
     quarantineOrDeallocateChunk(Ptr, &Header, Size);
   }
 
if (NewSize <= UsableSize &&
           OldHeader.ClassId ? NewSize : UsableSize - NewSize;
       Chunk::compareExchangeHeader(OldPtr, &NewHeader, &OldHeader);
       return OldPtr;
     }
     // Otherwise, we have to allocate a new chunk and copy the contents of the
     // old one.
     void *NewPtr = allocate(NewSize, MinAlignment, FromMalloc);
     if (NewPtr) {
-      uptr OldSize = OldHeader.ClassId ? OldHeader.SizeOrUnusedBytes :
+      const uptr OldSize = OldHeader.ClassId ? OldHeader.SizeOrUnusedBytes :
           UsableSize - OldHeader.SizeOrUnusedBytes;
       memcpy(NewPtr, OldPtr, Min(NewSize, UsableSize));
       quarantineOrDeallocateChunk(OldPtr, &OldHeader, OldSize);
     }
     return NewPtr;
   }
 
   // Helper function that returns the actual usable size of a chunk.

lib/scudo/scudo_allocator_combined.h

public:
   void deallocatePrimary(AllocatorCache *Cache, void *Ptr, uptr ClassId) {
     Cache->Deallocate(&Primary, ClassId, Ptr);
   }
 
   void deallocateSecondary(void *Ptr) {
     Secondary.Deallocate(&Stats, Ptr);
   }
 
-  uptr getActuallyAllocatedSize(void *Ptr, uptr ClassId) {
-    if (ClassId)
-      return PrimaryAllocator::ClassIdToSize(ClassId);
-    return SecondaryAllocator::GetActuallyAllocatedSize(Ptr);
-  }
-
   void initCache(AllocatorCache *Cache) {
     Cache->Init(&Stats);
   }
 
   void destroyCache(AllocatorCache *Cache) {
     Cache->Destroy(&Primary, &Stats);
   }