From: Qian Cai <cai@lca.pw>
To: David Laight <David.Laight@ACULAB.COM>,
"vyasevich@gmail.com" <vyasevich@gmail.com>,
"nhorman@tuxdriver.com" <nhorman@tuxdriver.com>,
"marcelo.leitner@gmail.com" <marcelo.leitner@gmail.com>
Cc: "linux-sctp@vger.kernel.org" <linux-sctp@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] net/sctp: fix GCC8+ -Wpacked-not-aligned warnings
Date: Mon, 29 Jul 2019 11:16:42 -0400 [thread overview]
Message-ID: <1564413402.11067.26.camel@lca.pw> (raw)
In-Reply-To: <158b26b6f3b24164aceacd2428095315@AcuMS.aculab.com>
On Mon, 2019-07-29 at 10:39 +0000, David Laight wrote:
> From: Qian Cai
> > Sent: 26 July 2019 21:58
> >
> > There are a lot of those warnings with GCC8+ 64bit,
> >
>
> ...
> > Fix them by aligning the structures and fields to 8 bytes instead.
>
> ...
> > struct sctp_setpeerprim {
> > sctp_assoc_t sspp_assoc_id;
> > - struct sockaddr_storage sspp_addr;
> > -} __attribute__((packed, aligned(4)));
> > + struct sockaddr_storage sspp_addr __attribute__((aligned(8)));
> > +} __attribute__((packed, aligned(8)));
>
> What happens to this one if you change both to aligned(4) ?
> Much the same way as:
> struct {
> int a;
> long b __attribute__((aligned(4));
> };
> is only 12 bytes on (most) 64bit systems.
No, that won't work. It because that,
#define sockaddr_storage __kernel_sockaddr_storage
struct __kernel_sockaddr_storage {
...
} __attribute__ ((aligned(_K_SS_ALIGNSIZE)))
#define _K_SS_ALIGNSIZE (__alignof__ (struct sockaddr *))
A pointer is 8-byte on 64-bit systems. If changed "struct
__kernel_sockaddr_storage" to use,
__attribute__ ((aligned((4)))
it then silence the warnings.
prev parent reply other threads:[~2019-07-29 15:16 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-26 20:57 [PATCH] net/sctp: fix GCC8+ -Wpacked-not-aligned warnings Qian Cai
2019-07-26 21:30 ` Marcelo Ricardo Leitner
2019-07-28 17:05 ` Qian Cai
2019-07-28 19:41 ` Marcelo Ricardo Leitner
2019-07-29 10:39 ` David Laight
2019-07-29 15:16 ` Qian Cai [this message]
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