[lwip-devel] [bug #26273] etharp.c : fix alignment issue in etharp_raw

[Bill Auerbach]

Follow-up Comment #9, bug #26273 (project lwip):

> then either sipaddr or dipaddr is not four-byte aligned (MAC addresses are
6-byte long). The question appears, how the statement
> 
>hdr->dipaddr = hdr->sipaddr;
>
>(struct to struct copy) is translated by a compiler.

Because there is no cast! The compiler has all the information it needs to
generate correct code.  It knows the base of the struct is aligned and that a
sub-structure isn’t (because of packing).

A cast tells the compiler "I know what I’m doing".  Therefore, the code
with the cast had better ensure alignment, because the compiler will not.

Bill


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