Detecting when gdb is attached

Detecting when gdb is attached

[Gruenhagen, Andreas]

Dear gdb community,
I'm developing an application which cannot be started from within the gdb. Therefore, I have the start the application and attach the gdb afterwards. In some cases it would be nice to have the application wait in a spin loop until the debugger is attached. Is there any way of accomplishing such a thing?  
I certainly can program the spin loop myself, attach the debugger, and then manually change a variable from within the debugger to end the loop. But, obviously, this is not an elegant solution (lots of manual work, code has to be changed and it has to be recompiled,and eventually, I might forget to delete the spin loop after debugging).

I thought of having some sort of action which is executed when the gdb is attached and detached, this could be for example used to switch a static flag in the debugee.
Is something like this possible ?

Best regards
Andreas

Re: Detecting when gdb is attached

[Doug Evans]

On Thu, Nov 4, 2010 at 6:40 AM, Gruenhagen, Andreas
<andreas.gruenhagen@sap.com> wrote:
> Dear gdb community,
> I'm developing an application which cannot be started from within the gdb. Therefore, I have the start the application and attach the gdb afterwards. In some cases it would be nice to have the application wait in a spin loop until the debugger is attached. Is there any way of accomplishing such a thing?
> I certainly can program the spin loop myself, attach the debugger, and then manually change a variable from within the debugger to end the loop. But, obviously, this is not an elegant solution (lots of manual work, code has to be changed and it has to be recompiled,and eventually, I might forget to delete the spin loop after debugging).
>
> I thought of having some sort of action which is executed when the gdb is attached and detached, this could be for example used to switch a static flag in the debugee.
> Is something like this possible ?

Hi.  I'm not sure I understand the issue.
I can't tell if adding code to the app to detect when gdb has attached
is ok or not.
[e.g. "it would be nice to have the application wait in a spin loop
until the debugger is attached. Is there any way of accomplishing such
a thing?" versus "I might forget to delete the spin loop"]

Guessing, what if you passed a flag to the app to enable the spin
loop?  Then you can keep the spin loop and only specify the flag when
you want to attach with gdb.

Re: Detecting when gdb is attached

[paawan oza]

Hi,

In my knowledge, the moment you attach gdb, your process is in stopped state and 
done by kernel using SIGSTOP.
that time you process is already at some instruction.

I am not sure about youre requirement, but just after attach you can use signal 
command to signals the process and write your own signal handler to notify you 
app (for example 'signal SIGCONT').

but again you need to modify code.

if you are looking for no insn execution until gdb attached proabably try with 
sigsuspend,  sigprocmask sort of stuff.. but that changes code too.

I am not sure that helps.

Regards,
Oza.



----- Original Message ----
From: "Gruenhagen, Andreas" <andreas.gruenhagen@sap.com>
To: "gdb@sourceware.org" <gdb@sourceware.org>
Sent: Thu, November 4, 2010 7:10:21 PM
Subject: Detecting when gdb is attached

Dear gdb community,
I'm developing an application which cannot be started from within the gdb. 
Therefore, I have the start the application and attach the gdb afterwards. In 
some cases it would be nice to have the application wait in a spin loop until 
the debugger is attached. Is there any way of accomplishing such a thing?  

I certainly can program the spin loop myself, attach the debugger, and then 
manually change a variable from within the debugger to end the loop. But, 
obviously, this is not an elegant solution (lots of manual work, code has to be 
changed and it has to be recompiled,and eventually, I might forget to delete the 
spin loop after debugging).

I thought of having some sort of action which is executed when the gdb is 
attached and detached, this could be for example used to switch a static flag in 
the debugee.
Is something like this possible ?

Best regards
Andreas



      

Re: Detecting when gdb is attached

[Steffen Dettmer]

On Thu, Nov 4, 2010 at 2:40 PM, Gruenhagen, Andreas
<andreas.gruenhagen@sap.com> wrote:
> I'm developing an application which cannot be started from
> within the gdb. Therefore, I have the start the application and
> attach the gdb afterwards. In some cases it would be nice to
> have the application wait in a spin loop until the debugger is
> attached. Is there any way of accomplishing such a thing?

how should the application know whether to enter the wait loop
until gdb is attached or run as usual?

> I thought of having some sort of action which is executed when
> the gdb is attached and detached, this could be for example
> used to switch a static flag in the debugee.  Is something like
> this possible ?

via ~/.gdbinit for example you could simply try:

print some_sort_of_action()

to invoke the function some_sort_of_action in the application
maybe?

oki,

Steffen