Re: Hardware watchpoint for read

[Xin Tong <xerox.time.tech@gmail.com>]

On Tue, Apr 24, 2012 at 9:18 AM, Luis Gustavo <luis_gustavo@mentor.com> wrote:
> On 04/24/2012 10:15 AM, Xin Tong wrote:
>>
>> On Tue, Apr 24, 2012 at 9:09 AM, Luis Gustavo<luis_gustavo@mentor.com>
>>  wrote:
>>>
>>> Hi,
>>>
>>>
>>> On 04/24/2012 10:02 AM, Xin Tong wrote:
>>>>
>>>>
>>>> Hello
>>>>
>>>> I am wondering that can gdb insert hardware watch point for read to
>>>> the watched memory ? can other debugger do that ? is it supported in
>>>> hardware watchpoint ?
>>>>
>>>> Thanks
>>>>
>>>> Xin
>>>>
>>>
>>> Read watchpoints are hard to implement as soft-watchpoints, so they're
>>> usually implemented as hardware watchpoints.
>>
>>
>> software write watchpoint is easier to implement ? do not software
>> watchpoint need to watch all memory accesses (read and write) to a
>> memory location in software ?
>
>
> Writes are "easier" to implemenet due to the fact that they usually change
> memory contents. Reads don't.

Either way, do not gdb need to instrument every memory accesses if a
software watch point is used ?
>
>
>>
>>>
>>> If a debugger knows how to properly set the bits in the hardware, either
>>> through ptrace or other means, it can configure a read/write/read-write
>>> watchpoint. Depends on hardware support really.
>>
>>
>> do you know whether this is supported on the x86 chips ? is thee a way
>> to try this out in gdb ?
>
>
> All those modes should be supported in x86. Try "watch", "rwatch" and
> "awatch".

how are hardware watch,  rwatch and awatch implemented in gdb. make
call to ptrace apis and ptrace apis  program some x86 registers
through a driver interfaces ?

>
>>
>>>
>>> Regards,
>>> Luis
>
>