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 -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
