From: David Laight <David.Laight@ACULAB.COM>
To: 'Qian Cai' <cai@lca.pw>, "davem@davemloft.net" <davem@davemloft.net>
Cc: "vyasevich@gmail.com" <vyasevich@gmail.com>,
"nhorman@tuxdriver.com" <nhorman@tuxdriver.com>,
"marcelo.leitner@gmail.com" <marcelo.leitner@gmail.com>,
"linux-sctp@vger.kernel.org" <linux-sctp@vger.kernel.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] net/socket: fix GCC8+ Wpacked-not-aligned warnings
Date: Tue, 30 Jul 2019 09:01:43 +0000 [thread overview]
Message-ID: <91237fd501de4ab895305c4d5666d822@AcuMS.aculab.com> (raw)
In-Reply-To: <1564431838-23051-1-git-send-email-cai@lca.pw>
From: Qian Cai
> Sent: 29 July 2019 21:24
..
> To fix this, "struct sockaddr_storage" needs to be aligned to 4-byte as
> it is only used in those packed sctp structure which is part of UAPI,
> and "struct __kernel_sockaddr_storage" is used in some other
> places of UAPI that need not to change alignments in order to not
> breaking userspace.
>
> One option is use typedef between "sockaddr_storage" and
> "__kernel_sockaddr_storage" but it needs to change 35 or 370 lines of
> codes. The other option is to duplicate this simple 2-field structure to
> have a separate "struct sockaddr_storage" so it can use a different
> alignment than "__kernel_sockaddr_storage". Also the structure seems
> stable enough, so it will be low-maintenance to update two structures in
> the future in case of changes.
Does it all work if the 8 byte alignment is implicit, not explicit?
For instance if unnamed union and struct are used eg:
struct sockaddr_storage {
union {
void * __ptr; /* Force alignment */
struct {
__kernel_sa_family_t ss_family; /* address family */
/* Following field(s) are implementation specific */
char __data[_K_SS_MAXSIZE - sizeof(unsigned short)];
/* space to achieve desired size, */
/* _SS_MAXSIZE value minus size of ss_family */
};
};
};
I suspect unnamed unions and structs have to be allowed by the compiler.
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2019-07-30 9:01 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-29 20:23 [PATCH] net/socket: fix GCC8+ Wpacked-not-aligned warnings Qian Cai
2019-07-30 9:01 ` David Laight [this message]
2019-07-30 13:18 ` Qian Cai
2019-07-30 13:23 ` David Laight
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