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Re: Extending GDB: Python: Wrong handling of 64-bit pointers


Andrew Pinski <pinskia@gmail.com> writes:

> On Thu, Oct 11, 2012 at 7:23 PM, chandan r <chandanrmail@gmail.com> wrote:
>>
>> Andrew Pinski <pinskia@gmail.com> writes:
>>
>>> On Tue, Oct 9, 2012 at 10:30 AM, chandan r <chandanrmail@gmail.com> wrote:
>>>> Hi all,
>>>>
>>>> As the following CLI interactions show, GDB's python support code seems to be
>>>> mishandling 64-bit pointers (GNU/Linux on x86-64):
>>>>
>>>> NOTE: "p" is a pointer of type "struct task_struct *"
>>>>
>>>> (gdb) python print gdb.parse_and_eval("p")
>>>> 0xffff88001f5f7600
>>>> (gdb) python print long(gdb.parse_and_eval("p"))
>>>> -131940868983296
>>>> (gdb) show version
>>>> show version
>>>> GNU gdb (GDB) 7.5
>>>> Copyright (C) 2012 Free Software Foundation, Inc.
>>>> License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
>>>> This is free software: you are free to change and redistribute it.
>>>> There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
>>>> and "show warranty" for details.
>>>> This GDB was configured as "x86_64-unknown-linux-gnu".
>>>> For bug reporting instructions, please see:
>>>> <http://www.gnu.org/software/gdb/bugs/>.
>>>>
>>>> Is it GDB or am I messing up something here?
>>>
>>> Nothing looks wrong as -131940868983296 is the same as
>>> 0xffff88001f5f7600 in signed integer.
>>> (gdb) p/x -131940868983296
>>> $1 = 0xffff88001f5f7600
>>>
>>> Thanks,
>>> Andrew Pinski
>>>
>>>>
>>>> --
>>>> Chandan
>>
>> But shouldn't pointer values be read/printed without interpretting the sign
>> bit?.
>>
>> Right now I have to do 'long(str(gdb.parse_and_eval('p')), 16)' to obtain the
>> correct value.
>
>
> What is the correct value for pointers cast to an long?  I don't see
> the issue here as you have a pointer which is 64bits and you cast
> directly to a signed long.
>
> Thanks,
> Andrew Pinski
>
>>
>> --
>> chandan

I used long() based on the instructions given in
http://dmalcolm.fedorapeople.org/presentations/PyCon-US-2011/GdbPythonPresentation/GdbPython.html#11 

Any suggestions for the correct way to convert the pointer into a Python
value?


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