[scudo] Use MemMap for AllocationRingBuffer

[fmayer]

compiler-rt/lib/scudo/standalone/combined.h

1504

Is there any particular reason we put this into the RingBuffer? It's a bit weird that the mmap contains itself in a way. I would have put it in the Allocator instead.

compiler-rt/lib/scudo/standalone/combined.h

struct Entry {
       atomic_uptr Ptr;
       atomic_uptr AllocationSize;
       atomic_u32 AllocationTrace;
       atomic_u32 AllocationTid;
       atomic_u32 DeallocationTrace;
       atomic_u32 DeallocationTid;
     };
 
+    MemMapT MemMap;
     atomic_uptr Pos;
     u32 Size;
     // An array of Size (at least one) elements of type Entry is immediately
     // following to this struct.
   };
   // Pointer to memory mapped area starting with AllocationRingBuffer struct,
   // and immediately followed by Size elements of type Entry.
   char *RawRingBuffer = {};
return &reinterpret_cast<const typename AllocationRingBuffer::Entry *>(
         &RawRingBuffer[sizeof(AllocationRingBuffer)])[N];
   }
 
   void mapAndInitializeRingBuffer() {
     u32 AllocationRingBufferSize =
         static_cast<u32>(getFlags()->allocation_ring_buffer_size);
     if (AllocationRingBufferSize < 1)
       return;
-    RawRingBuffer = static_cast<char *>(
-        map(/*Addr=*/nullptr,
-            roundUp(ringBufferSizeInBytes(AllocationRingBufferSize),
-                    getPageSizeCached()),
-            "scudo:ring_buffer"));
+    MemMapT MemMap;
+    MemMap.map(
+        /*Addr=*/0U,
+        "scudo:ring_buffer");
+    RawRingBuffer = reinterpret_cast<char *>(MemMap.getBase());
     auto *RingBuffer = reinterpret_cast<AllocationRingBuffer *>(RawRingBuffer);
+    RingBuffer->MemMap = MemMap;
     RingBuffer->Size = AllocationRingBufferSize;
     static_assert(sizeof(AllocationRingBuffer) %
                           alignof(typename AllocationRingBuffer::Entry) ==
                       0,
                   "invalid alignment");
   }
 
   void unmapRingBuffer() {
-    unmap(RawRingBuffer, roundUp(getRingBufferSize(), getPageSizeCached()));
+    auto *RingBuffer = getRingBuffer();
+    if (RingBuffer != nullptr) {
+      MemMapT MemMap = RingBuffer->MemMap;
+      MemMap.unmap(MemMap.getBase(), MemMap.getCapacity());
+    }
     RawRingBuffer = nullptr;
   }
 
   static constexpr size_t ringBufferSizeInBytes(u32 AllocationRingBufferSize) {
     return sizeof(AllocationRingBuffer) +
            AllocationRingBufferSize *
                sizeof(typename AllocationRingBuffer::Entry);
   }