RE: [PATCH] unicore32 fix: remove arch-specific futex support

["Guan Xuetao" <gxt@mprc.pku.edu.cn>]

> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd@arndb.de]
> Sent: Wednesday, March 30, 2011 8:40 PM
> To: Thomas Gleixner
> Cc: Guan Xuetao; Paul Mundt; linux-kernel@vger.kernel.org; linux-arch@vger.kernel.org
> Subject: Re: [PATCH] unicore32 fix: remove arch-specific futex support
> 
> On Wednesday 30 March 2011, Thomas Gleixner wrote:
> > The problem is that you need cmpxchg in user space as well.
> >
> > ARM does this with some syscall magic for machines which do not have
> > cmpxchg.
> 
> Ah, right. I wonder how sh does it.
> 
> I also remember that the original unicore32 ABI had support for a cmpxchg
> system call, but that was removed with the move to the generic syscall
> table.
> 
> It is of course possible to add it back using the __NR_arch_specific_syscall
> entry point.
> 
> 	Arnd

For cmpxchg, we have both system call and kuser_cmpxchg supports in old abi
which are similar to arm.
The performance of system call version is too poor,  so it could be only used for test.

Thanks & Regards

Guan Xuetao