Le mardi 01 janvier 2013 à 15:03 +0000, Peter Maydell a écrit :
> On 31 December 2012 22:19, Laurent Vivier <laur...@vivier.eu> wrote:
> > Le lundi 31 décembre 2012 à 21:32 +0000, Peter Maydell a écrit :
> >> Also it seems rather involved since we swap things three times and
> >> have an entirely new abi_* function. Either I'm completely confused
> >> or it should be enough to just have
> >>
> >> if (type == SOCK_PACKET) {
> >> protocol = tswap16(protocol);
> >> }
>
> Looking more carefully at packet(7) this is actually the wrong
> guard anyway. You need to check for
> (domain == AF_PACKET) || (type == SOCK_PACKET)
I agree.
> since SOCK_PACKET is the obsolete Linux 2.0 way of doing packet sockets.
But dhclient is always using this...
> > works... sometime. In fact, work if target endianess is network endianess.
> >
> > Correct me if I'm wrong.
> >
> > target host
> > little endian / big endian
> >
> > memory 00 00 00 03
>
> Syscall arguments aren't generally passed in memory, they're
> in registers (and if they were pased in memory for some architecture
> then that arch would do a load-and-swap-from-memory in main.c).
> So the value you see in do_socket() is always "the integer passed
> as a syscall parameter, as a host-order integer".
Yes, I missed that.
> So in this case, with a simple guest program:
> #include <sys/socket.h>
> #include <netpacket/packet.h>
> #include <net/ethernet.h>
> #include <arpa/inet.h>
>
> int main(void) {
> return socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
> }
>
> you will find that do_socket() in QEMU is passed either 0x3 [if the
> guest is bigendian and the guest htons() is a no-op] or 0x0300
> [if the guest is littleendian]. Since what we want to pass to the
> host socket() call is 0x3 if the host is bigendian and 0x0300 if
> the host is little endian, this amounts to needing to do a 16 bit
> byteswap if the host and guest are different endianness, which
> is exactly what tswap16() does. I checked with i386-to-i386
> that do_socket() gets passed 0x300 and we correctly send it
> through to the host socket().
Yes, I agree. I correct the patch.
Thank you,
Laurent
--
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