On Tue, Feb 28, 2017 at 11:22:27AM +0000, Abel Vesa wrote:

On Tue, Feb 28, 2017 at 11:58:49AM +0100, Nicolai Stange wrote:

quoted

Hi Abel,

On Tue, Feb 28 2017, Abel Vesa wrote:

quoted

On Mon, Feb 27, 2017 at 04:52:06PM +0100, Nicolai Stange wrote:

quoted

On Fri, Feb 24 2017, Abel Vesa wrote:
Wouldn't it be better (and more consistent with other archs) to have

  pt_regs->ARM_lr = original lr
  pt_refs->ARM_pc = current lr

instead?

The stack would look like this then

@ ...           | ARM_ip | ARM_sp | ARM_lr      | ARM_pc      | ...          |
@ 0  4          48       52       56            60            64    68       72
@ R0 | R1 | ... | LR     | SP + 4 | original LR | original PC | PSR | OLD_R0 | original LR |

I.e. the pt_regs would capture almost the full context of the
instrumented function (except for ip).

So basicly what you are saying is:
- instead of current LR save original LR (previous one saved in instrumented function epilog)
- instead of current PC save original PC (previous one saved in instrumented function epilog)

I still don't see the point of saving the actual value of PC since nobody will ever
restore it. In case of livepatch it will get overwritten anyway. As for LR, I agree,
it could be the original one in pt_regs.

I'll look into this sometime today or tomorrow and get back with updates.

Which is exactly what I proposed, with code, on one of the previous
iterations of this patch...

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