Messages in this thread | | | Date | Wed, 30 Mar 2011 14:50:29 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH] unicore32 fix: remove arch-specific futex support |
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On Wed, 30 Mar 2011, Arnd Bergmann wrote:
> 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.
Either that or you take a trap. None of them is pretty.
If the only purpose is futex support, then we can add an extra flag to the futex ops and handle it there via asm-generic/futex.h. That would avoid an extra syscall in the contended case.
Thanks,
tglx
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