wgtmac opened a new issue, #51135:
URL: https://github.com/apache/arrow/issues/51135
### Describe the bug, including details regarding any error messages,
version, and platform.
### Describe the bug
Reading BYTE_ARRAY-backed Decimal32 values can trigger UBSan:
runtime error: store to misaligned address for type 'uint64_t'
The converter always writes two `uint64_t` values, even when the destination
is Decimal32 (4 bytes) or Decimal64 (8 bytes):
https://github.com/apache/arrow/blob/d5eb88e93ea7776a6eb3b1b59b5b795f4331d6d3/cpp/src/parquet/arrow/reader_internal.cc#L728-L730
This became reachable for Decimal32/64 after GH-44345 / PR #47427.
The stores should be replaced with:
std::memset(out_ptr, 0, type_length);
The existing `TestReadDecimals.Decimal32ByteArray` test reproduces it when
alignment sanitization is enabled.
### Component(s)
C++, Parquet
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