linux-kernel - Re: [PATCH] arch/tile: new multi-core architecture for Linux

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Message-Id: <201005272253.07498.arnd@arndb.de>
Date:	Thu, 27 May 2010 22:53:06 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Jamie Lokier <jamie@...reable.org>
Cc:	Chris Metcalf <cmetcalf@...era.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH] arch/tile: new multi-core architecture for Linux

On Thursday 27 May 2010 22:34:12 Jamie Lokier wrote:
> > > > compat_sys_sendfile will not be needed with the asm-generic/unistd.h definitions,
> > > > but I think you will still need a compat_sys_sendfile64, to which the same
> > > > applies as to compat_sys_sched_rr_get_interval.
> > > >   
> > > 
> > > I think it's the other way around: compat_sys_sendfile64() is just
> > > sys_sendfile64(), but compat_sys_sendfile() needs to exist since it has
> > > to write a 32-bit pointer back to userspace.
> > 
> > Ah. I guess you're right about compat_sys_sendfile64 not being needed.
> > Funny enough, parisc, powerpc, s390 and sparc all define it anyway, so
> > it didn't occur to me that they don't actually need to.
> 
> They do need it.
> 
> For example, on Sparc, compat_sys_sendfile64 takes a 32-bit
> compat_size_t argument, and calls sys_sendfile64 with a 64-bit size_t
> argument.

But size_t is unsigned and the upper halves of the argument registers
are always zero-filled in the sparc64 compat syscall entry, so I guess the
conversion is still not necessary there.

PowerPC probably still needs it but doesn't need to do the nasty set_fs()
stuff. s390x needs a proper assembly wrapper and parisc uses the same
method as sparc64 IIRC.

mips and x86 already just call the native sendfile64 syscall.

> I'll be very surprised if 32-bit tile is using 64-bit size_t already :-)

 ** Surprise! **

Chris mentioned that the tile compat support is not actually for the
native 32 bit ABI but for a third ILP32 ABI of the 64 bit Tile-GX
processors. I assume all registers in this mode are 64 bit, and so are the
syscall arguments.

	Arnd
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