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Date:      Mon, 13 Nov 2006 02:28:54 +0300
From:      Ruslan Ermilov <ru@FreeBSD.org>
To:        "M. Warner Losh" <imp@bsdimp.com>, Joseph Koshy <jkoshy@FreeBSD.org>
Cc:        arm@FreeBSD.org, keramida@FreeBSD.org, current@FreeBSD.org
Subject:   Re: [head tinderbox] failure on arm/arm
Message-ID:  <20061112232854.GC45238@rambler-co.ru>
In-Reply-To: <20061112.160539.-1350496508.imp@bsdimp.com>
References:  <20061112132105.6bac38d6@kan.dnsalias.net> <20061112192810.GC1173@rambler-co.ru> <4557825E.3070009@errno.com> <20061112.160539.-1350496508.imp@bsdimp.com>

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On Sun, Nov 12, 2006 at 04:05:39PM -0700, M. Warner Losh wrote:
> Yea, that's clearly bogus of it.  It does this because it thinks that
> eh is going to be 4-byte aligned, which it isn't in this case.  I
> think that we may need to change:
>=20
> /*
>  * Structure of a 10Mb/s Ethernet header.
>  */
> struct	ether_header {
> 	u_char	ether_dhost[ETHER_ADDR_LEN];
> 	u_char	ether_shost[ETHER_ADDR_LEN];
> 	u_short	ether_type;
> };
>=20
> to be
>=20
> struct	ether_header {
> 	u_char	ether_dhost[ETHER_ADDR_LEN];
> 	u_char	ether_shost[ETHER_ADDR_LEN];
> 	u_short	ether_type;
> } __packed;
>=20
> since that would fit.
>=20
"fit" =3D=3D avoid 32-bit loads (I've similarly checked adding
__packed to "struct ar_hdr" here, and it indeed stops using
32-bit loads instructions now):

%%%
Index: ar.h
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
RCS file: /home/ncvs/src/include/ar.h,v
retrieving revision 1.1.1.1
diff -u -p -r1.1.1.1 ar.h
--- ar.h	24 May 1994 09:57:26 -0000	1.1.1.1
+++ ar.h	12 Nov 2006 23:26:38 -0000
@@ -44,6 +44,8 @@
 #ifndef _AR_H_
 #define	_AR_H_
=20
+#include <sys/cdefs.h>
+
 /* Pre-4BSD archives had these magic numbers in them. */
 #define	OARMAG1	0177555
 #define	OARMAG2	0177545
@@ -62,6 +64,6 @@ struct ar_hdr {
 	char ar_size[10];		/* size in bytes */
 #define	ARFMAG	"`\n"
 	char ar_fmag[2];		/* consistency check */
-};
+} __packed;
=20
 #endif /* !_AR_H_ */
%%%

> There's one caveat that I'd caution people about.  NetBSD had lots of
> issues with gcc4 and packed when the struct doesn't need to be packed.
>=20
We don't have a lot of packed structs yet, and we should certainly
have more of them.  :-)


Cheers,
--=20
Ruslan Ermilov
ru@FreeBSD.org
FreeBSD committer

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