gdb user defined function

gdb user defined function

[Sinbad]

i am trying to write a user-defined function in gdb.
while analyzing the core is it possible to see if a
pointer variable is accessible or not inside a gdb
user-defined function. for example.
(gdb) p *ptr
cannot access memory at address 0x35336
is there any way to find this inside a gdb function.
i need something as follows
define sub
   is_accessible(ptr)
end

Re: gdb user defined function

[Tom Tromey]

>>>>> "Sinbad" == Sinbad  <sinbad.sinbad@gmail.com> writes:

Sinbad> i am trying to write a user-defined function in gdb.
Sinbad> while analyzing the core is it possible to see if a
Sinbad> pointer variable is accessible or not inside a gdb
Sinbad> user-defined function. for example.
Sinbad> (gdb) p *ptr
Sinbad> cannot access memory at address 0x35336
Sinbad> is there any way to find this inside a gdb function.
Sinbad> i need something as follows
Sinbad> define sub
Sinbad>    is_accessible(ptr)
Sinbad> end

I can't think of an easy way to do this from the gdb CLI, but you can do
it from Python by catching the exception.

You could straightforwardly write a $is_valid function that examines a
pointer for validity.

Tom

Re: gdb user defined function

[Sinbad]

hi tom,

i've never used python with gdb or python at all. but i want to learn
enough of python to achieve the following. how do one use python
with gdb, will gdb become slow, can you give me some pointers
on how to achieve the following using python.

Please don't yell ;)

thanks


On Tue, Jan 17, 2012 at 2:16 AM, Tom Tromey <tromey@redhat.com> wrote:
>>>>>> "Sinbad" == Sinbad  <sinbad.sinbad@gmail.com> writes:
>
> Sinbad> i am trying to write a user-defined function in gdb.
> Sinbad> while analyzing the core is it possible to see if a
> Sinbad> pointer variable is accessible or not inside a gdb
> Sinbad> user-defined function. for example.
> Sinbad> (gdb) p *ptr
> Sinbad> cannot access memory at address 0x35336
> Sinbad> is there any way to find this inside a gdb function.
> Sinbad> i need something as follows
> Sinbad> define sub
> Sinbad>    is_accessible(ptr)
> Sinbad> end
>
> I can't think of an easy way to do this from the gdb CLI, but you can do
> it from Python by catching the exception.
>
> You could straightforwardly write a $is_valid function that examines a
> pointer for validity.
>
> Tom

Re: gdb user defined function

[Tom Tromey]

>>>>> "Sinbad" == Sinbad  <sinbad.sinbad@gmail.com> writes:

Sinbad> i've never used python with gdb or python at all. but i want to learn
Sinbad> enough of python to achieve the following. how do one use python
Sinbad> with gdb, will gdb become slow, can you give me some pointers
Sinbad> on how to achieve the following using python.

There are plenty of docs:

    http://sourceware.org/gdb/onlinedocs/gdb/Python.html

What you want is the stuff about writing a function:

    http://sourceware.org/gdb/onlinedocs/gdb/Functions-In-Python.html#Functions-In-Python

and also the Value API.

The core of your function will probably be something along these lines:

    try:
      arg = arg.deref()
      return 1
    except:
      return 0

Untested of course.

About speed... well, evaluating Python does have a cost.  I wouldn't
worry about it in advance; especially if the alternative is using the
gdb CLI, which in general is less well-tuned than Python.  If your
situation is truly performance critical, then (1) measure the effects of
Python, and (2) if it is too slow, write a convenience function in C
instead.

Sinbad> Please don't yell ;)

Don't worry.

Tom

Re: gdb user defined function

[Tom Tromey]

Tom>       arg = arg.deref()

Oops.  The method is really named 'dereference'.

Tom