Avoid unaligned writes through 'pos' pointer #6
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In `Graph::serialize_mmap`, `pos` is set to a non-4-byte aligned pointer and is then dereferenced as various other types. This is Undefined Behavior with respect to the C++ standard, due to both writing through unaligned pointers and breaking strict aliasing rules. This change replaces such writes with `memcpy` that has an exception in the standard to bypass both aliasing and alignment restrictions. This is not the only alignment/aliasing issue in this function; it looks like operations involving `end_of_lastrank` and `mapping_start` also break these rules. But these are left as-is for now.
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In
Graph::serialize_mmap,posis set to a non-4-byte aligned pointer and is then dereferenced as various other types. This is Undefined Behavior with respect to the C++ standard, due to both writing through unaligned pointers and breaking strict aliasing rules.This change replaces such writes with
memcpythat has an exception in the standard to bypass both aliasing and alignment restrictions.This is not the only alignment/aliasing issue in this function; it looks like operations involving
end_of_lastrankandmapping_startalso break these rules. But these are left as-is for now.