debugging dynamically loadable code

debugging dynamically loadable code

[Pupeno]

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Hello, hope this is not off-topic,
I need to debug some code that is located in a dynamic library, a .so file. 
This file is loaded by a program at run-time (with dlopen I supouse). So I 
load this program into gdb (using ddd) and my problem is that I can't open 
the yet-unloaded sources and/or set a break point on them.
If I run the program to let it load the .so file it'll be too late because I 
need to debug the module initialization code.
I know I should put a breakpoint between the loading and the running of the 
module, but I can't find it. The module is loaded thru a custom script this 
application interprets, so, it's hard to dig that code.
Any ideas how can I do my debugging ?
Thank you.
-- 
Pupeno <pupeno@pupeno.com> (http://pupeno.com)

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Re: debugging dynamically loadable code

[Daniel Jacobowitz]

On Mon, Apr 03, 2006 at 06:09:33PM +0200, Pupeno wrote:
> Any ideas how can I do my debugging ?

You can do one of two things here:

 - "set stop-on-solib-events 1".  This will cause GDB to stop when
shared libraries are loaded or unloaded.  You can use "info shared" to
see if the library you want has been loaded after a stop.

 - Pending breakpoints.  You can set a breakpoint by filename:line or
function name, even if that object hasn't been loaded yet - you just
may not be able to do it using the DDD GUI.  You need GDB 6.3 or 6.4
for this to work.  I don't know if DDD lets you get at the GDB console
usefully.

-- 
Daniel Jacobowitz
CodeSourcery

Re: debugging dynamically loadable code

[Pupeno]

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On Monday, 3 de April de 2006 18:34, Daniel Jacobowitz wrote:
> On Mon, Apr 03, 2006 at 06:09:33PM +0200, Pupeno wrote:
> > Any ideas how can I do my debugging ?
>
> You can do one of two things here:
>
>  - "set stop-on-solib-events 1".  This will cause GDB to stop when
> shared libraries are loaded or unloaded.  You can use "info shared" to
> see if the library you want has been loaded after a stop.
It halted the process very soon, maybe some loading I was not aware of and I 
was not sure how to continue.

>  - Pending breakpoints.  You can set a breakpoint by filename:line or
> function name, even if that object hasn't been loaded yet - 
Oh, that worked, particurarly breakpoint on filename:line. I tried pending 
breakpoints once but it didn't work, it just didn't break, now it worked like 
a charm.

> you just 
> may not be able to do it using the DDD GUI.  You need GDB 6.3 or 6.4
> for this to work.  I don't know if DDD lets you get at the GDB console
> usefully.
Yes, I can do it, DDD let's you access gdb console, sometimes it behaves 
funny, but the data show makes it worth it.

Thank you.
-- 
Pupeno <pupeno@pupeno.com> (http://pupeno.com)

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Re: debugging dynamically loadable code

[Daniel Jacobowitz]

On Mon, Apr 03, 2006 at 11:21:35PM +0200, Pupeno wrote:
> On Monday, 3 de April de 2006 18:34, Daniel Jacobowitz wrote:
> > On Mon, Apr 03, 2006 at 06:09:33PM +0200, Pupeno wrote:
> > > Any ideas how can I do my debugging ?
> >
> > You can do one of two things here:
> >
> >  - "set stop-on-solib-events 1".  This will cause GDB to stop when
> > shared libraries are loaded or unloaded.  You can use "info shared" to
> > see if the library you want has been loaded after a stop.
> It halted the process very soon, maybe some loading I was not aware of and I 
> was not sure how to continue.

You can just say continue and try info shared again, until you see the
library you want.  Anyway, if pending breakpoints work for you, use
those instead.

-- 
Daniel Jacobowitz
CodeSourcery