Re: [PATCH RFC v4 1/6] arm64: support single-step and breakpointhandler hooks

[Sandeepa Prabhu]

Hi Will,

Sorry for responding to this after long-time, I missed this review
during Linaro connect travels.

On 25 October 2013 20:52, Will Deacon <will.deacon@xxxxxxx> wrote:
> Hi Sandeepa,
>
> This is getting there, thanks for persevering with it. I still have a few
> minor comments though.
>
> On Thu, Oct 17, 2013 at 12:17:46PM +0100, Sandeepa Prabhu wrote:
>> AArch64 Single Steping and Breakpoint debug exceptions will be
>> used by multiple debug framworks like kprobes & kgdb.
>>
>> This patch implements the hooks for those frameworks to register
>> their own handlers for handling breakpoint and single step events.
>>
>> Reworked the debug exception handler in entry.S: do_dbg to route
>> software breakpoint (BRK64) exception to do_debug_exception()
>>
>> Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu@xxxxxxxxxx>
>> Signed-off-by: Deepak Saxena <dsaxena@xxxxxxxxxx>
>> ---
>>  arch/arm64/include/asm/debug-monitors.h | 21 ++++++++
>>  arch/arm64/kernel/debug-monitors.c      | 86 ++++++++++++++++++++++++++++++++-
>>  arch/arm64/kernel/entry.S               |  2 +
>>  3 files changed, 108 insertions(+), 1 deletion(-)
>
> [...]
>
>> @@ -215,7 +257,10 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
>>                */
>>               user_rewind_single_step(current);
>>       } else {
>> -             /* TODO: route to KGDB */
>> +             /* call registered single step handlers */
>
> Don't bother with this comment (it's crystal clear from the code).
OK, I will remove this unnecessary print.
>
>> +             if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
>> +                     return 0;
>> +
>>               pr_warning("Unexpected kernel single-step exception at EL1\n");
>>               /*
>>                * Re-enable stepping since we know that we will be
>> @@ -227,11 +272,50 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
>>       return 0;
>>  }
>>
>> +
>> +static LIST_HEAD(break_hook);
>> +DEFINE_RWLOCK(break_hook_lock);
>
> This guy can be a plain old spinlock. That way, the readers have less
> overhead but things still work because we only call a single hook function.
well, kprobes need to support recursive breakpoints (i.e. breakpoint
handler executing BRK once again)
so I converted this lock to rw_lock.  I should put this info in commit
description to be more clearer.
Let me know if you find any issue with re-cursing in breakpoint exception?

Thanks,
Sandeepa
>
> Will
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