Hi,
On Sun, Feb 26, 2023 at 03:10:07PM +0100, Arne Schwabe wrote:
> > struct ifaddr {
> > struct sockaddr *ifa_addr; /* address of interface */
> > struct sockaddr *ifa_dstaddr; /* other end of p-to-p link */
> > struct sockaddr *ifa_netmask; /* used to determine subnet */
> >
> > ... so the first memcpy() isn't actually copying the MAC address around,
> > just a bunch of pointers, and then we dereference the first of them
> > for the second memcpy(), using the dereferencing macro for a
> > "sockaddr_dl" structure.
>
> The problem is that LLVM ASAN does not like access to an unaligned
> struct. Even if it just accessing a member to deference it. So you are
> right that it is just copying a bunch of pointers, to not triggers the
> warning, we have to do this nonsense. The compiler will even optimise
> this then away again on platforms that have no problem with unaligned
> accesses.
With ifr being a structure now, it is aligned just fine - I'm not objecting
to that part, just to the intermediate "sdl" thing, and the double
memcpy(), and 10 lines of comments.
> > FreeBSD also has
> >
> > #define IF_LLADDR(ifp) \
> > LLADDR((struct sockaddr_dl *)((ifp)->if_addr->ifa_addr))
> >
> > which sounds like "feed in an *ifr, out comes a pointer for the
> > memcpy() to rgi->addr".
>
> Yes but you will still get warning about casting a smaller struct to a
> larger struct and that being a bad idea.
This is not casting a struct, just casting a pointer. Does it still
warn?
gert
--
"If was one thing all people took for granted, was conviction that if you
feed honest figures into a computer, honest figures come out. Never doubted
it myself till I met a computer with a sense of humor."
Robert A. Heinlein, The Moon is a Harsh Mistress
Gert Doering - Munich, Germany g...@greenie.muc.de
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