From: Arnd Bergmann <arnd@arndb.de>
To: David Laight <David.Laight@aculab.com>
Cc: Christoph Hellwig <hch@lst.de>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
Helge Deller <deller@gmx.de>,
Michael Ellerman <mpe@ellerman.id.au>,
Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
"David S. Miller" <davem@davemloft.net>,
"x86@kernel.org" <x86@kernel.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
"linux-parisc@vger.kernel.org" <linux-parisc@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
"sparclinux@vger.kernel.org" <sparclinux@vger.kernel.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 5/5] compat: consolidate the compat_flock{,64} definition
Date: Mon, 12 Apr 2021 13:26:00 +0200 [thread overview]
Message-ID: <CAK8P3a1JZ=JerasdkntzX_ApaCF7C29ZS1E31aPQATOts0ZiLw@mail.gmail.com> (raw)
In-Reply-To: <5c3635a2b44a496b88d665e8686d9436@AcuMS.aculab.com>
On Mon, Apr 12, 2021 at 12:54 PM David Laight <David.Laight@aculab.com> wrote:
> From: David Laight > Sent: 12 April 2021 10:37
> ...
> > I'm guessing that compat_pid_t is 16 bits?
> > So the native 32bit version has an unnamed 2 byte structure pad.
> > The 'packed' removes this pad from the compat structure.
> >
> > AFAICT (apart from mips) the __ARCH_COMPAT_FLOCK_PAD is just
> > adding an explicit pad for the implicit pad the compiler
> > would generate because compat_pid_t is 16 bits.
>
> I've just looked at the header.
> compat_pid_t is 32 bits.
> So Linux must have gained 32bit pids at some earlier time.
> (Historically Unix pids were 16 bit - even on 32bit systems.)
>
> Which makes the explicit pad in 'sparc' rather 'interesting'.
I saw it was there since the sparc kernel support got merged in
linux-1.3, possibly copied from an older sunos version.
> oh - compat_loff_t is only used in a couple of other places.
> neither care in any way about the alignment.
> (Provided get_user() doesn't fault on a 8n+4 aligned address.)
Ah right, I also see that after this series it's only used in to other
places: compat_resume_swap_area, which could also lose the
__packed annotation, and in the declaration of
compat_sys_sendfile64, where it makes no difference.
Arnd
next prev parent reply other threads:[~2021-04-12 11:26 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-12 8:55 consolidate the flock uapi definitions Christoph Hellwig
2021-04-12 8:55 ` [PATCH 1/5] uapi: remove the unused HAVE_ARCH_STRUCT_FLOCK64 define Christoph Hellwig
2021-04-12 9:55 ` Arnd Bergmann
2021-04-14 6:45 ` Stephen Rothwell
2021-04-12 8:55 ` [PATCH 2/5] uapi: simplify __ARCH_FLOCK{,64}_PAD a little Christoph Hellwig
2021-04-12 8:55 ` [PATCH 3/5] uapi: merge the 32-bit mips struct flock into the generic one Christoph Hellwig
2021-04-12 8:55 ` [PATCH 4/5] uapi: always define F_GETLK64/F_SETLK64/F_SETLKW64 in fcntl.h Christoph Hellwig
2021-04-13 15:43 ` Helge Deller
2021-04-13 15:46 ` Christoph Hellwig
2021-04-13 15:58 ` Helge Deller
2021-04-12 8:55 ` [PATCH 5/5] compat: consolidate the compat_flock{,64} definition Christoph Hellwig
2021-04-12 9:37 ` David Laight
2021-04-12 10:53 ` David Laight
2021-04-12 11:26 ` Arnd Bergmann [this message]
2021-04-12 13:11 ` David Laight
2021-04-12 10:03 ` consolidate the flock uapi definitions Arnd Bergmann
2021-04-12 10:22 ` David Laight
2021-04-12 11:07 ` Arnd Bergmann
2021-04-15 12:20 ` Heiko Carstens
2022-01-11 8:35 consolidate the compat fcntl definitions Christoph Hellwig
2022-01-11 8:35 ` [PATCH 5/5] compat: consolidate the compat_flock{,64} definition Christoph Hellwig
2022-01-11 9:52 ` David Laight
2022-01-31 6:49 consolidate the compat fcntl definitions v2 Christoph Hellwig
2022-01-31 6:49 ` [PATCH 5/5] compat: consolidate the compat_flock{,64} definition Christoph Hellwig
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