Date: Tue, 1 Feb 2011 09:18:44 +0100 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: Marcel Moolenaar <xcllnt@mac.com> Cc: ia64@freebsd.org, marcel@FreeBSD.org, FreeBSD Tinderbox <tinderbox@freebsd.org>, current@freebsd.org Subject: Re: [head tinderbox] failure on ia64/ia64 Message-ID: <20110201081844.GA1897@garage.freebsd.pl> In-Reply-To: <F3F2991E-A783-451C-95B5-3E5BC2E5772B@mac.com> References: <201101312256.p0VMuI6F075840@freebsd-current.sentex.ca> <20110131235153.GC1746@garage.freebsd.pl> <F3F2991E-A783-451C-95B5-3E5BC2E5772B@mac.com>
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--oyUTqETQ0mS9luUI Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Jan 31, 2011 at 04:56:06PM -0800, Marcel Moolenaar wrote: >=20 > On Jan 31, 2011, at 3:51 PM, Pawel Jakub Dawidek wrote: >=20 > > On Mon, Jan 31, 2011 at 10:56:18PM +0000, FreeBSD Tinderbox wrote: > > [...] > >> cc -O2 -pipe -I/src/sbin/hastctl/../hastd -DINET -DINET6 -DYY_NO_UNPU= T -DYY_NO_INPUT -DHAVE_CRYPTO -std=3Dgnu99 -Wsystem-headers -Werror -Wall -= Wno-format-y2k -W -Wno-unused-parameter -Wstrict-prototypes -Wmissing-proto= types -Wpointer-arith -Wreturn-type -Wcast-qual -Wwrite-strings -Wswitch -W= shadow -Wunused-parameter -Wcast-align -Wchar-subscripts -Winline -Wnested-= externs -Wredundant-decls -Wold-style-definition -Wno-pointer-sign -c /src/= sbin/hastctl/../hastd/proto_common.c > >> cc1: warnings being treated as errors > >> /src/sbin/hastctl/../hastd/proto_common.c: In function 'proto_common_d= escriptor_send': > >> /src/sbin/hastctl/../hastd/proto_common.c:116: warning: cast increases= required alignment of target type > >> /src/sbin/hastctl/../hastd/proto_common.c: In function 'proto_common_d= escriptor_recv': > >> /src/sbin/hastctl/../hastd/proto_common.c:146: warning: cast increases= required alignment of target type > >> /src/sbin/hastctl/../hastd/proto_common.c:149: warning: cast increases= required alignment of target type > >> *** Error code 1 > >=20 > > Marcel, do you have an idea how one can use CMSG_NXTHDR() on ia64 with > > high WARNS? With WARNS=3D6 I get those errors and I've no idea how to f= ix > > it properly. If there is a fix, CMSG_NXTHDR() should probably be fixed, > > but maybe I'm wrong? >=20 > this warning indicates that you're casting from a pointer to type P > (P having alignment constraints Ap) to a pointer to type Q (Q having > alignment constraints Aq), and Aq > Ap. The compiler tells you that > you may end up with misaligned accesses. >=20 > If you know that the pointer satisfies Aq, you can cast through (void *) > to silence the compiler. If you cannot guarantee that, you have a bigger > problem. Solutions include "packing" type Q to reduce Aq or to copy the > data to a local variable. >=20 > Take the statement at line 116 for example: > *((int *)CMSG_DATA(cmsg)) =3D fd; >=20 > We're effectively casting from a (char *) to a (int *) and then doing > a 32-bit access (write). The easy fix (casting through (void *) is not > possible, because you cannot guarantee that the address is properly > aligned. cmsg points to memory set aside by the following local > variable: > unsigned char ctrl[CMSG_SPACE(sizeof(fd))]; >=20 > There's no guarantee that the compiler will align the character array > at a 32-bit boundary (though in practice it seems to be). I have seen > this kind of construct fail on ARM and PowerPC for example. >=20 > In any case: The safest approach here is to use le32enc or be32enc > rather than casting through (void *). Obviously these function encode > using a fixed byte order when the original code is using the native > byte order of the CPU. Having native encoding functions help. >=20 > You could use bcopy as well, but the compiler is typically too smart > for its own good and it will try to optimize the call away. This > leaves you with the same misaligned access that you tried to avooid > by using bcopy(). You need to trick the compiler so that it won't > optimize the bcopy away, like: > bcopy((void *)&fd, CMSG_DATA(cmsg), sizeof(fd)); Interesting. I did use bcopy() to silence the warning, but the need to cast to (void *) is surprising. Still, I'm more concerned with CMSG_NXTHDR() macro, which from what I see might not be fixed by casting arguments. --=20 Pawel Jakub Dawidek http://www.wheelsystems.com pjd@FreeBSD.org http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am! --oyUTqETQ0mS9luUI Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.14 (FreeBSD) iEYEARECAAYFAk1HweQACgkQForvXbEpPzQe3wCeJ8nssh1lMJ59WFbgVgdor5Nq LEwAmwXQN+km5rNmCtNwQSOJduXxuyl2 =TMUG -----END PGP SIGNATURE----- --oyUTqETQ0mS9luUI--
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