[scudo] Use DefaultSizeClassMap for 32-bit

Summary:
With the recent changes to the Secondary, we use less bits for UnusedBytes,
which allows us in return to increase the bits used for Offset. That means
that we can use a Primary SizeClassMap allowing for a larger maximum size.

Reviewers: kcc, alekseyshl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D27816

llvm-svn: 289838

compiler-rt/lib/scudo/scudo_allocator.cpp

@@ -68,7 +68,7 @@ typedef FlatByteMap<NumRegions> ByteMap;
 # elif SANITIZER_WORDSIZE == 64
 typedef TwoLevelByteMap<(NumRegions >> 12), 1 << 12> ByteMap;
 # endif  // SANITIZER_WORDSIZE
-typedef SizeClassMap<3, 4, 8, 16, 64, 14> SizeClassMap;
+typedef DefaultSizeClassMap SizeClassMap;
 typedef SizeClassAllocator32<0, SANITIZER_MMAP_RANGE_SIZE, 0, SizeClassMap,
     RegionSizeLog, ByteMap> PrimaryAllocator;
 #endif  // SANITIZER_CAN_USE_ALLOCATOR64
@@ -354,11 +354,11 @@ struct Allocator {
                      "header\n");
     }
     // Verify that we can fit the maximum amount of unused bytes in the header.
-    // The worst case scenario would be when allocating 1 byte on a MaxAlignment
-    // alignment. Since the combined allocator currently rounds the size up to
-    // the alignment before passing it to the secondary, we end up with
-    // MaxAlignment - 1 extra bytes.
-    uptr MaxUnusedBytes = MaxAlignment - 1;
+    // 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 last
+    // and last class sizes, as well as the dynamic base for the Primary. The
+    // following is an over-approximation that works for our needs.
+    uptr MaxUnusedBytes = SizeClassMap::kMaxSize - 1 - AlignedChunkHeaderSize;
     Header.UnusedBytes = MaxUnusedBytes;
     if (Header.UnusedBytes != MaxUnusedBytes) {
       dieWithMessage("ERROR: the maximum possible unused bytes doesn't fit in "

compiler-rt/lib/scudo/scudo_allocator.h

@@ -44,10 +44,10 @@ enum ChunkState : u8 {
 typedef u64 PackedHeader;
 struct UnpackedHeader {
   u64 Checksum    : 16;
-  u64 UnusedBytes : 24; // Needed for reallocation purposes.
+  u64 UnusedBytes : 20; // Needed for reallocation purposes.
   u64 State       : 2;  // available, allocated, or quarantined
   u64 AllocType   : 2;  // malloc, new, new[], or memalign
-  u64 Offset      : 12; // Offset from the beginning of the backend
+  u64 Offset      : 16; // Offset from the beginning of the backend
                         // allocation to the beginning of the chunk itself,
                         // in multiples of MinAlignment. See comment about
                         // its maximum value and test in init().