[fedora-arm] ARMv5 and atomic operations

[Ramana Radhakrishnan]

On Monday, 23 April 2012, Thomas Meyer wrote:

> 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.
>
>

If you used the 64 bit gcc sync primitives and they called the helper
functions IIRC there is a check in there for the existence and graceful
abort of these handlers...




Ramana

> with kind regards
> thomas
>
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