Messages in this thread | | | Date | Fri, 23 May 2014 17:12:19 +0100 | From | Will Deacon <> | Subject | Re: [PATCH v4 2/2] arm64: enable context tracking |
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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
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