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Message-ID: <91237fd501de4ab895305c4d5666d822@AcuMS.aculab.com>
Date: Tue, 30 Jul 2019 09:01:43 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Qian Cai' <cai@....pw>,
"davem@...emloft.net" <davem@...emloft.net>
CC: "vyasevich@...il.com" <vyasevich@...il.com>,
"nhorman@...driver.com" <nhorman@...driver.com>,
"marcelo.leitner@...il.com" <marcelo.leitner@...il.com>,
"linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] net/socket: fix GCC8+ Wpacked-not-aligned warnings
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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