Re: ARMv5 and atomic operations

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Am Sonntag, den 22.04.2012, 22:34 -0400 schrieb Chris Tyler:
> On Sun, 2012-04-22 at 18:16 -0700, Brendan Conoboy wrote:
> > As we get closer to having 100% package coverage in F17-ARM we're 
> > running into harder build failures due to the limitations of the chips 
> > we're building for.  The problem I've noticed on many of the recent 
> > failures is due to the lack of atomic operations (These didn't arrive 
> > until ARMv6).  

> 6. There is the kernel's "user space atomic helper" (kuser_cmpxchg64) at
> 0xffff0f60, see Documentation/arm/kernel_user_helpers.txt. The kernel
> puts an instruction sequence here tuned for the current arch that can be
> called by userland to provide an atomic compare/exchange -- if it can be
> done natively, the instruction sequence does that, otherwise it does a
> syscall (with IRQ protection etc). Would this solve the problems you've
> identified?

I'm running the Ubuntun 2.6.38 Tegra2 kernel (because of their fbdev
support) on top of Fedora 17 armv5el on an Toshiba AC100 Laptop. The
rsyslog package crashed everytime because of the missing kernel support
of cmpxchg64. So when relying on the kernel helpers make sure that the
resp. kernel support exists.

with kind regards
thomas

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