On Sat, Aug 6, 2011 at 10:17 PM, subin gangadharan <subingangadharan@gmail.com> wrote:
Hi, This is a text excerpt from the article [1]. Below paragraph I didn't understand quite well.Mainly in bold letters.Could anybody please explain how this will lead to an infinite loop.
It seems self-explanatory. Most atomic ops are written to retry upon a failed store, and on PowerPC an atomic store to an unaligned address always fails, thus the processor will infinitely try to store the value, without having the chance to fix the unaligned access (as would have happened if an exception was thrown).
Unfortunately, the PowerPC does not throw an exception when atomically storing to an unaligned address. Instead, the store simply always fails. This is bad because most atomic functions are written to retry upon a failed store, under the assumption they were preempted. These two circumstances combine to where your program will go into an infinite loop if you attempt to atomically store to an unaligned address. Oops.
thanks, Daniel.