On Fri, May 23, 2014 at 04:55:44PM +0100, Mark Rutland wrote:
On Fri, May 23, 2014 at 03:51:07PM +0100, Catalin Marinas wrote:
On Fri, May 23, 2014 at 01:11:38AM +0100, Kevin Hilman wrote: I haven't checked all the code paths but at least for pushing onto the stack we must keep it 16-bytes aligned (architecture requirement).
Sure -- if modifying the stack we need to push/pop pairs of registers to keep it aligned. It might be better to use xzr as the dummy value in that case to make it clear that the value doesn't really matter.
That said, ct_user_enter is only called in kernel_exit before we restore the values off the stack, and the only register I can spot that we need to preserve is x0 for the syscall return value. I can't see x1 or x2 being used any more specially than the rest of the remaining registers. Am I missing something, or would it be sufficient to do the following?
push x0, xzr bl context_tacking_user_enter pop x0, xzr
... and if that works, then why are we using the stack instead of a callee-saved register?
Will