[NFC][Asan] Set AP32::kMetadataSize to 0

[vitalybuka]

Summary

Asan does not use metadata with primary allocators.
It should match AP64::kMetadataSize whic is 0.

Depends on D86917.

[morehouse]

LGTM

compiler-rt/lib/asan/asan_allocator.h

 using PrimaryAllocatorASVT = SizeClassAllocator64<AP64<AddressSpaceView>>;
 using PrimaryAllocator = PrimaryAllocatorASVT<LocalAddressSpaceView>;
 #else  // Fallback to SizeClassAllocator32.
 typedef CompactSizeClassMap SizeClassMap;
 template <typename AddressSpaceViewTy>
 struct AP32 {
   static const uptr kSpaceBeg = 0;
   static const u64 kSpaceSize = SANITIZER_MMAP_RANGE_SIZE;
-  static const uptr kMetadataSize = 16;
+  static const uptr kMetadataSize = 0;
   typedef __asan::SizeClassMap SizeClassMap;
   static const uptr kRegionSizeLog = 20;
   using AddressSpaceView = AddressSpaceViewTy;
   typedef AsanMapUnmapCallback MapUnmapCallback;
   static const uptr kFlags = 0;
 };
 template <typename AddressSpaceView>
 using PrimaryAllocatorASVT = SizeClassAllocator32<AP32<AddressSpaceView> >;

compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary32.h

public:
   }
 
   static bool CanAllocate(uptr size, uptr alignment) {
     return size <= SizeClassMap::kMaxSize &&
       alignment <= SizeClassMap::kMaxSize;
   }
 
   void *GetMetaData(const void *p) {
+    CHECK(kMetadataSize);
     CHECK(PointerIsMine(p));
     uptr mem = reinterpret_cast<uptr>(p);
     uptr beg = ComputeRegionBeg(mem);
     uptr size = ClassIdToSize(GetSizeClass(p));
     u32 offset = mem - beg;
     uptr n = offset / (u32)size;  // 32-bit division
     uptr meta = (beg + kRegionSize) - (n + 1) * kMetadataSize;
     return reinterpret_cast<void*>(meta);

compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary64.h

public:
   uptr GetActuallyAllocatedSize(void *p) {
     CHECK(PointerIsMine(p));
     return ClassIdToSize(GetSizeClass(p));
   }
 
   static uptr ClassID(uptr size) { return SizeClassMap::ClassID(size); }
 
   void *GetMetaData(const void *p) {
+    CHECK(kMetadataSize);
     uptr class_id = GetSizeClass(p);
     uptr size = ClassIdToSize(class_id);
     uptr chunk_idx = GetChunkIdx(reinterpret_cast<uptr>(p), size);
     uptr region_beg = GetRegionBeginBySizeClass(class_id);
     return reinterpret_cast<void *>(GetMetadataEnd(region_beg) -
                                     (1 + chunk_idx) * kMetadataSize);
   }