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[meta] Use memcpy instead of cast to prevent strict-aliasing error #723

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Dec 1, 2020
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[meta] Use memcpy instead of cast to prevent strict-aliasing error #723

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10 changes: 9 additions & 1 deletion meta/MetaKeyHasher.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -160,12 +160,20 @@ static inline std::size_t sai_get_hash(
return ne.ip_address.addr_family;
}

static_assert(sizeof(uint32_t) == 4, "uint32_t expected to be 4 bytes");
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static_assert [](start = 0, length = 13)

This assertion seems not needed. Do you anticipate some failure case?

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just a surprise for some wired platforms :D


static inline std::size_t sai_get_hash(
_In_ const sai_fdb_entry_t& fe)
{
SWSS_LOG_ENTER();

return *(const uint32_t*)(&fe.mac_address[2]);
uint32_t data;

// use low 4 bytes of mac address as hash value
// use memcpy instead of cast because of strict-aliasing rules
memcpy(&data, fe.mac_address + 2, sizeof(uint32_t));

return data;
}

static inline std::size_t sai_get_hash(
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