Re: Does the LD --wrap feature work for library internal references?

[Sebastian Huber <sebastian dot huber at embedded-brains dot de>]

Hello Nick,

On 03/01/2019 16:49, Nick Clifton wrote:
> Hi Sebastian,
>
> > For another it doesn't work:
> >
> > /build/rtems/5/bin/powerpc-rtems5-gcc -Wl,--wrap=_bsd_ether_output -qrtems -B/build/rtems/5/powerpc-
> > It links, I would have expected an undefined reference to __wrap__bsd_ether_output. In the executable I find this:
> >
> > nm media01.exe | grep ether_output
> > 0001b640 T _bsd_ether_output
> >
> > It is not clear to me why it works with one function and not with another.
> Is it possible that the _bsd_ether_output function has been inlined into
> all the places where it is used ?
>
> The wrap feature of the linker works by replacing symbols, but this is
> only effective if there are undefined references to the symbols being
> replaced.  If all of the references have already been resolved (or just
> don't exist, eg because of inlining) then wrapping will have no effect.

It is not unlined, but its only reference is done via a function pointer 
assignment here:

https://git.rtems.org/rtems-libbsd/tree/freebsd/sys/net/if_ethersubr.c#n950

[...]|
/*||
 * Perform common duties while attaching to interface list ||||
 */ |

|void ether_ifattach(struct ifnet *ifp, const u_int8_t *lla) { int i; 
struct ifaddr *ifa; struct sockaddr_dl *sdl; ifp->if_addrlen = 
ETHER_ADDR_LEN; ifp->if_hdrlen = ETHER_HDR_LEN; if_attach(ifp); 
ifp->if_mtu = ETHERMTU; ifp->if_output = ether_output; ifp->if_input = 
ether_input; |[...]

Does the wrap feature work for function pointer assignments?

--
Sebastian Huber, embedded brains GmbH

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