8000 `readMemoryAt` is broken · Issue #54 · dfinity/wasmtime-hs · GitHub
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readMemoryAt is broken #54

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kirisaki opened this issue Feb 26, 2025 · 0 comments
Open

readMemoryAt is broken #54

kirisaki opened this issue Feb 26, 2025 · 0 comments

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@kirisaki
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I tried the following test code at test/memory.hs:

  putStrLn "Read memory at 0x1003..."
  x <- readMemoryAt store memory 0x1003 4
  B.decode (LBS.fromStrict x) @?= (4 :: Int32)

But it failed without so much as returning a Left value. Then, I checked the code of readMemoryAt:

readMemoryAt store mem offset sz = do
  max_sz <- getMemorySizeBytes store mem
  unsafeIOToPrim $ do
    if offset + sz > max_sz
      then pure $ Left MemoryAccessError
      else do
        res <- unsafeWithMemory store mem $ \mem_data_ptr mem_size ->
          BI.create (fromIntegral mem_size) $ \dst_ptr ->
            copyBytes
              dst_ptr
              (advancePtr mem_data_ptr (fromIntegral offset))
              (fromIntegral mem_size)
        pure $ Right res

It seems to return the entire memory with the offset. When I set the offset to 0, it yielded a very long byte string.
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