[scudo] Introduce Chunk::getHeaderSize

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.

Reviewers: alekseyshl

Reviewed By: alekseyshl

Subscribers: delcypher, #sanitizers, llvm-commits

Differential Revision: https://reviews.llvm.org/D43772

llvm-svn: 326206

compiler-rt/lib/scudo/scudo_allocator.cpp

@@ -69,18 +69,17 @@ namespace Chunk {
   // 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) {
@@ -92,9 +91,8 @@ namespace 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.
@@ -251,7 +249,7 @@ struct ScudoAllocator {
     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 "
@@ -368,9 +366,10 @@ struct ScudoAllocator {
     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();
 
@@ -403,7 +402,7 @@ struct ScudoAllocator {
              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
@@ -505,7 +504,7 @@ struct ScudoAllocator {
         }
       }
     }
-    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) {

compiler-rt/lib/scudo/scudo_allocator.h

@@ -59,9 +59,17 @@ 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;
@@ -97,11 +105,6 @@ struct AP32 {
 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"
 

compiler-rt/lib/scudo/scudo_allocator_secondary.h

@@ -28,7 +28,7 @@ class ScudoLargeMmapAllocator {
   }
 
   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;
@@ -80,7 +80,7 @@ class ScudoLargeMmapAllocator {
     // 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;
 
@@ -129,9 +129,9 @@ class ScudoLargeMmapAllocator {
   }
 
   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;