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Re: [Qemu-devel] [PATCH] slirp: Use lduw_be_p in slirp_input
From: |
Samuel Thibault |
Subject: |
Re: [Qemu-devel] [PATCH] slirp: Use lduw_be_p in slirp_input |
Date: |
Thu, 17 Jan 2019 14:22:57 +0100 |
User-agent: |
NeoMutt/20170113 (1.7.2) |
Philippe Mathieu-Daudé, le jeu. 17 janv. 2019 14:16:16 +0100, a ecrit:
> On 1/17/19 12:50 AM, Samuel Thibault wrote:
> > Hello,
> >
> > Richard Henderson, le mer. 26 déc. 2018 14:42:54 +1100, a ecrit:
> >> The pointer may be unaligned, so we must use our routines for that.
> >> At the same time, we might as well use the big-endian version
> >> instead of ntohs.
> >>
> >> This fixes sparc64 host SIGBUS during pxe boot.
> >
> > I'm not at ease with applying this, when Marc-André is trying to make
> > slirp an external library... I'd rather apply the change below, could
> > somebody review it?
> >
> > Samuel
> >
> >
> > slirp: Avoid unaligned 16bit memory access
> >
> > pkt parameter may be unaligned, so we must access it byte-wise.
> >
> > This fixes sparc64 host SIGBUS during pxe boot.
> >
> > Signed-off-by: Samuel Thibault <address@hidden>
> >
> > diff --git a/slirp/slirp.c b/slirp/slirp.c
> > index ab2fc4eb8b..0e41d5aedf 100644
> > --- a/slirp/slirp.c
> > +++ b/slirp/slirp.c
> > @@ -851,7 +851,7 @@ void slirp_input(Slirp *slirp, const uint8_t *pkt, int
> > pkt_len)
> > if (pkt_len < ETH_HLEN)
> > return;
> >
> > - proto = ntohs(*(uint16_t *)(pkt + 12));
> > + proto = (((uint16_t) pkt[12]) << 8) + pkt[13];
> > switch(proto) {
> > case ETH_P_ARP:
> > arp_input(slirp, pkt, pkt_len);
>
> What about using memcpy?
Well, it looks to me even more confusing than doing the shifts :)
> -- >8 --
> @@ -846,12 +846,13 @@ static void arp_input(Slirp *slirp, const uint8_t
> *pkt, int pkt_len)
> void slirp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
> {
> struct mbuf *m;
> - int proto;
> + uint16_t proto;
>
> if (pkt_len < ETH_HLEN)
> return;
>
> - proto = ntohs(*(uint16_t *)(pkt + 12));
> + memcpy(&proto, pkt + 12, sizeof(proto)); /* Avoid unaligned 16bit
> access */
> + proto = ntohs(proto);
> switch(proto) {
> case ETH_P_ARP:
> arp_input(slirp, pkt, pkt_len);
> ---
>