Joe McDonnell created IMPALA-9781:
-------------------------------------
Summary: Fix GCC 7 runtime issue: Unaligned loads and stores for
int128_t types
Key: IMPALA-9781
URL: https://issues.apache.org/jira/browse/IMPALA-9781
Project: IMPALA
Issue Type: Improvement
Components: Backend
Affects Versions: Impala 4.0
Reporter: Joe McDonnell
When running with a release binary built with GCC 7, Impala crashes with
multiple distinct unaligned memory errors. They are all related to manipulating
128-bit values. Presumably GCC 7 added an optimization to use an instruction
that requires alignment for setting 128-bit values. The locations impacted are:
SlotRef::GetDecimalValInterpreted():
{code:java}
case 16:
return DecimalVal(*reinterpret_cast<int128_t*>(t->GetSlot(slot_offset_)));
{code}
DecimalUtil::DecodeFromFixedLenByteArray():
{code:java}
template<typename T>
static inline void DecodeFromFixedLenByteArray(
const uint8_t* buffer, int fixed_len_size, T* v) {
...
*v = 0; <--- unaligned store
{code}
DictDecoder::GetValue():
{code:java}
virtual void GetValue(int index, void* buffer) {
T* val_ptr = reinterpret_cast<T*>(buffer);
...
*val_ptr = dict_[index]; <--- unaligned store
}
{code}
These can be converted to use memcpy / memset to avoid the unaligned
stores/loads.
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