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Change reinterpret_cast use to memcpy #2295

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Merged
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Feb 13, 2020
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Change reinterpret_cast use to memcpy #2295

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2 changes: 1 addition & 1 deletion src/coreclr/src/vm/diagnosticsprotocol.h
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Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,7 @@ bool TryParse(uint8_t *&bufferCursor, uint32_t &bufferLen, T &result)

if (bufferLen < sizeof(T))
return false;
result = *(reinterpret_cast<T *>(bufferCursor));
memcpy(&result, bufferCursor, sizeof(T));
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Might consider something like:

template <typename T>
static inline T unaligned_reinterpret_cast(const void* ptr)
{
   T tmp; 
   memcpy(&tmp, ptr, sizeof(T));
   return tmp;
}

Then just use it like:

result = unaligned_reinterpret_cast<T>(bufferCursor);

At least, for fundamental types such as int and float, this generates pretty good code that does not involve copies.

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I'm not sure I see how refactoring that code removes the need for a copy. memcpy happens either way. Are you suggesting replacing the entirety of TryParse with the above code?

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@lpereira lpereira Jan 28, 2020 •
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Oh, I mean, it still calls memcpy() (which might not even copy, just load it in a register), but there's no additional copy because it's returning tmp instead of a reference or pointer.

This just wraps memcpy() in a function in such a way that it's clear from the call site that it's a reinterpret_cast that works with unaligned pointers. It's otherwise identical to the direct memcpy() call in your patch.

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Testing with this single line change, it just worked in my case.

bufferCursor += sizeof(T);
bufferLen -= sizeof(T);
return true;
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