1: This is not char copy, but memory copy.
2: The reason memcpy today doesn’t support this feature is
because it only work with DF=0 (REP MOVSB). We can easily extend
to support

DF=1.

[Cao, Minggui] sorry, I mixed the copy and move; it shall be like memmove.
Just checked the memory.c code in HV.

Is it OK as follows?
memcpy_erms --> memmove_erms (void *d, const void *s, size_t
slen, bool
df_flag) as a public API?

The caller side clearly know the copy to be from head to tail address
or from tail to head address.
How about to define another API like memcpy_tail_to_head or memcpy_rev
?

The caller side can choose normal memcpy or tail_to_head copy API.

[Cao, Minggui] normally memcpy (also in HV), it will not handle the src and
dst overlap case,
but memmove can handle that. I shall change copy_chars to move_chars (or
move_bytes) to use in shell input to delete/insert locally in my 2nd patch.
[acrn-dev] [PATCH 2/2 v2] hv: shell: improve console to modify input
easier

Then I thought no other will use it, I just did a simple one. If need to add new
API, it is better to add new: memmove / memmove_from_tail two APIs to
memory.c Is it OK?