Re: ARMv5 and atomic operations

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On Tue, 24 Apr 2012, Andrew Haley wrote:

> On 04/23/2012 09:31 PM, Nicolas Pitre wrote:
> > On Mon, 23 Apr 2012, Andrew Haley wrote:
> > 
> >> On 04/23/2012 06:36 PM, Thomas Meyer wrote:
> >>> 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.
> >>
> >> Indeed.  I had to write a workaround in IcedTea (i.e. java) on ARM for
> >> just this reason.  If you can't depend on a kernel helper being there I
> >> can't see it's of any use.
> > 
> > Kernel helpers don't disappear with time.  You therefore can probe for 
> > their availability (see the documentation) in case the kernel support 
> > could be backported, or just refuse to run if the kernel version isn't 
> > recent enough.  This is not much different from relying on a new 
> > syscall.
> 
> Indeed it is.  What would I gain from adding such a test?  All I can
> see is extra complication, untested code paths, and larger programs.

What alternative do you have, other than not using any atomic 
operations?

> The untested code path is particularly nasty.

How buggy the following code might be:

	fprintf(stderr, "Your kernel is too old, aborting\n")
	exit(1);

?


Nicolas
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