Re: [PATCH 3/3] [AArch64] Remove tag from address for watchpoint

[Pedro Alves <palves at redhat dot com>]

On 11/09/2017 09:09 PM, Yao Qi wrote:
> On 17-11-09 20:30:42, Pedro Alves wrote:
>> And then at places where we need to save or compare memory addresses,
>> like in the watchpoint location addresses case we strip out / ignore
>> non-significant bits.
>>
>> And the next question is: if you're adding a gdbarch hook such as
>> this one (either significant_addr_bit or addr_tag_remove)
>> why not use it for all the cases handled by the different patches in
>> this series, instead of using different solutions for each case?
>> I.e., for memory access, saving breakpoint and watchpoint
>> location addresses, the dcache, and any other future case we run
>> into, like e.g., maybe agent expressions.
> 
> I thought about this, using this new added gdbarch method everywhere.
> The reason I didn't do that is due to breakpoint location address
> comparison (I think I can use the new gdbarch method for the rest,
> watchpoint location and dcache).
> 
> As I wrote in patch #2,
> 
>> When program hits a breakpoint, the stopped pc reported by Linux kernle is
>> the address *without* tag, so it is better the address recorded in
>> breakpoint location is the one without tag too, so we can still match
>> breakpoint location address and stopped pc reported by Linux kernel, by
>> simple compare.  I did try the different approach, that is keep the tag in
>> the address saved in the breakpoint location, but I need to change many
>> places of "loc->address == pc", so I give up on this way.
> 
> I remember code pattern "loc->address == pc" exists many places in
> breakpoint.c.  I can give a try again.

Since target-reported addresses always have the non-significant bits
zeroed, you'd only need to use the new gdbarch hook in
breakpoint.c:adjust_breakpoint_address ?  Seems like that's already
used for watchpoints too, even.

Thanks,
Pedro Alves