While I disagree entirely with this kind of approach, even that
doesn't justify what you're doing here.
memcpy() and memset() are on a much more fundamental ground than
"kernel provided functions". They had better be available no matter
where you build this thing.
And doing what you're doing is foolish on so many levels. One more
duplication of code, one more place for unnecessary bugs to live, one
more place that might need optimizations and thus require duplication
of even more work people have done over the years.
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