On Tue, Nov 19, 2013 at 05:02:20PM +0000, Mathieu Desnoyers wrote: > Unfortunately I don't have a ARM cross-compiler setup ready. Nathan could test > it for us though. > > It might shuffle things around enough to work around the issue, but with the > approach you propose, I would be concerned about the compiler being within > its rights to reorder the code into the following sequence: > > struct thread_info *ptra, *ptrb; > > ptra = current_thread_info(); > /* > * each current_thread_info() would have a clobber on *sp, which orders > * those two wrt each other. > */ > ptrb = current_thread_info(); > > load from ptra->preempt_count; > /* > * however, the following accesses that depend on ptra and ptrb could be > * reordered if the compiler has no way to know that ptra and ptrb are > * aliased. > */ > store to ptrb->preempt_count; > > One question that might be worth asking: with the local register variable > extension > (http://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/Local-Reg-Vars.html#Local-Reg-Vars) > (thanks to Jakub for the pointer), should the compiler consider two variables > bound to the same register as being aliased or not ? AFAIU, local reg vars > appear > to be architecture-specific, so maybe there is something fishy on ARM ?
Might help if you ask where the GCC people are on CC ;-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
