[PATCH] AArch64: Add single-step and breakpoint handler hooks

Sandeepa Prabhu sandeepa.prabhu at linaro.org
Tue Aug 20 10:00:46 EDT 2013

On 20 August 2013 18:42, Will Deacon <will.deacon at arm.com> wrote:
> On Tue, Aug 13, 2013 at 03:45:30PM +0100, Sandeepa Prabhu wrote:
>> On 13 August 2013 17:02, Will Deacon <will.deacon at arm.com> wrote:
>> > On Tue, Aug 06, 2013 at 07:12:06AM +0100, Sandeepa Prabhu wrote:
>> >> +     cmp     x24, #ESR_EL1_EC_WATCHPT_EL1
>> >> +     csel    x0, x25, x22, eq        //addr: x25->far_el1, x22->elr_el1
>> >> +     b.ge    do_dbg
>> >>       tbz     x24, #0, el1_inv                // EL1 only
>> >
>> > I'd rather you left the tbz as the first instruction in el1_dbg, then you
>> > can also lose the b.ge.
>> well, my understanding is that the tbz check is needed only for
>> Exception Class < 0x35 as per debug spec. If this is true, and if tbz
>> is first instruction, it fails for breakpoint (EC=0x3A) case and call
>> el1_inv to panic instead of routing to do_debug_exception. I am not
>> sure if we can optimize the code further to eliminate this one
>> branching as well.
> Well, you're actually only interested in 0x3c (BRK instruction executed in
> AArch64 state), so you should check for that explicitly. I guess it doesn't
> matter where you check bit #0 first or not, provided you have the branch
> logic correct.
Agreed, then 0x3c is the only case where bit #0 check shall be ignored.
I will rework this code accordingly, and as you have mentioned, I will
add this patch along with the complete kprobes series later that will
be using it.


> Will

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