Date: Tue, 10 Aug 2010 22:41:20 +0200 From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no> To: "M. Warner Losh" <imp@bsdimp.com> Cc: src-committers@FreeBSD.org, jilles@stack.nl, svn-src-all@FreeBSD.org, olli@fromme.com, olli@FreeBSD.org, svn-src-head@FreeBSD.org Subject: Re: svn commit: r211023 - head/usr.sbin/syslogd Message-ID: <8639ump5e7.fsf@ds4.des.no> In-Reply-To: <20100810.120103.69891821625677670.imp@bsdimp.com> (M. Warner Losh's message of "Tue, 10 Aug 2010 12:01:03 -0600 (MDT)") References: <201008101623.o7AGNs7I042679@haluter.fromme.com> <20100810.110642.335141733495090585.imp@bsdimp.com> <86sk2m1hsj.fsf@ds4.des.no> <20100810.120103.69891821625677670.imp@bsdimp.com>
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"M. Warner Losh" <imp@bsdimp.com> writes:
> Dag-Erling Smørgrav <des@des.no> writes:
> > "M. Warner Losh" <imp@bsdimp.com> writes:
> > > /*
> > > * Macros to cast a struct sockaddr, or parts thereof.
> > > * On architectures with strict alignment requirements, the compiler
> > > * can bogusly warn about alignment problems since its static analysis
> > > * is insufficient for it to know that with the APIs used, there
> > > * really is no alignment issue.
> > > */
> > That's a bit harsh on the compiler, don't you think? It never pays to
> > hurt the compiler's feelings :)
>
> /*
> * Macros to cast a struct sockaddr, or parts thereof. struct
> * sockaddr's alginment is loose to later be cast to a sockaddr_in or
> * sockaddr_in6. On architectures with strict alignment requirements,
> * this leads to compiler warnings because the compiler doesn't know
> * the ABI guarantees proper alignment.
> */
That sounds more like what I had in mind (my point being that the
compiler is *right* to not make any such assumptions unless we say it's
safe to do so)
> But this leads me to think that the right fix might be:
>
> /*
> * Structure used by kernel to store most
> * addresses.
> */
> struct sockaddr {
> unsigned char sa_len; /* total length */
> sa_family_t sa_family; /* address family */
> char sa_data[14]; /* actually longer; address value */
> } __aligned(4);
>
> since that's what the ABI defines....
Yes, unfortunately that's not portable. I like the way it's done in
sockaddr_storage, but we can't do that here except possibly using
anonymous unions, which aren't portable either.
> > > Why 16 and 4 here? What's so magical about them?
> > 4 = bytes in a uint32_t, 16 = bytes in an ipv6 address.
> Isn't that better served by 'sizeof(uint32_t)' and
> 'sizeof(ipv6_addr_t)'?
Probably...
DES
--
Dag-Erling Smørgrav - des@des.no
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