Date: Wed, 18 Feb 2009 08:25:59 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: andrew-freebsd@areilly.bpc-users.org Cc: mips@freebsd.org, tinderbox@freebsd.org, current@freebsd.org Subject: Re: [head tinderbox] failure on mips/mips Message-ID: <20090218.082559.-1112729020.imp@bsdimp.com> In-Reply-To: <20090218110402.GA13040@duncan.reilly.home> References: <20090217.203647.-1518647466.imp@bsdimp.com> <20090217.222152.-109416210.imp@bsdimp.com> <20090218110402.GA13040@duncan.reilly.home>
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In message: <20090218110402.GA13040@duncan.reilly.home>
Andrew Reilly <andrew-freebsd@areilly.bpc-users.org> writes:
: On Tue, Feb 17, 2009 at 10:21:52PM -0700, M. Warner Losh wrote:
: > In message: <20090217.203647.-1518647466.imp@bsdimp.com>
: > "M. Warner Losh" <imp@bsdimp.com> writes:
: > : In message: <20090218023328.227617302F@freebsd-current.sentex.ca>
: > : FreeBSD Tinderbox <tinderbox@freebsd.org> writes:
: > : : /src/usr.sbin/bsnmpd/modules/snmp_mibII/../../../../contrib/bsnmp/snmp_mibII/mibII.c:1016: warning: cast increases required alignment of target type
: > The first one is:
: >
: > case RTM_IFINFO:
: > ifm = (struct if_msghdr *)rtm;
: > mib_extract_addrs(ifm->ifm_addrs, (u_char *)(ifm + 1), addrs);
: > if ((ifp = mib_find_if_sys(ifm->ifm_index)) == NULL)
: > break;
: >
: > rtm is of type struct rt_msghdr. This has an alignment requirement of
: > 4 on mips, at least on 32-bit mips (the biggest data element is a
: > u_long). struct if_msghdr has an alignment requirement of 8, because
: > time_t is int64_t on MIPS, which is 8-bytes in size.
:
: If the memory that rtm can be pointing to can be either a struct
: rt_msghdr or a struct if_msghdr, then shouldn't it really be
: pointing to a union of those two, and then the alignment will
: sort itself out? (As far as I know, that's the only way that
: C99 will guarantee that the right thing happens anyway,
: otherwise strict aliasing analysis would allow much worse
: badness to happen, potentially.)
:
: Not looked at the code myself. Perhaps there's a reason why
: that would be unworkable.
There's a second issue. There's a number of different structures that
are type punned to rt_msghdr. I'm worried it would be an ABI change
to do that as well.
In this case, code inspection shows the code to be fine since the
dangerous element isn't touched.
Warner
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