Does gdb initialize uninitialized variables?

Does gdb initialize uninitialized variables?

[Edgar Mobile]

Greetings,

I currently try to find a bug that might be caused by uninitialized variables/memory. But it never appears when I use gdb. Does gdb change how memory is initialized in any way, be it on stack or via new/malloc?

Regards

Re: Does gdb initialize uninitialized variables?

[Ruslan Kabatsayev]

Hi,

On Mon, 21 Feb 2022 at 12:45, Edgar Mobile via Gdb <gdb@sourceware.org> wrote:
>
> Greetings,
>
> I currently try to find a bug that might be caused by uninitialized variables/memory. But it never appears when I use gdb. Does gdb change how memory is initialized in any way, be it on stack or via new/malloc?

Memory-related bugs that don't happen when using GDB but do without
GDB are often caused by GDB disabling ASLR. This is usually useful for
reproducibility of debugging sessions, but may indeed make address
space layout too predictable and fail to reproduce a bug. Try using
the GDB command "set disable-randomization off" (without quotes) to
undo this behavior and thus start your program in a normal,
randomized, environment.

Besides, if your problem is indeed with uninitialized variables, you
might find Valgrind memory checker more useful than a debugger.

>
> Regards

Regards,
Ruslan

Re: Does gdb initialize uninitialized variables?

[Edgar Mobile]

I tried it as the very first command even before run. Any more ideas? (tx already)

________________________________
From: Ruslan Kabatsayev <b7.10110111@gmail.com>
Sent: Monday, February 21, 2022 5:33 PM
To: Edgar Mobile <heideggm@hotmail.com>
Cc: gdb@sourceware.org <gdb@sourceware.org>
Subject: Re: Does gdb initialize uninitialized variables?

Hi,

On Mon, 21 Feb 2022 at 12:45, Edgar Mobile via Gdb <gdb@sourceware.org> wrote:
>
> Greetings,
>
> I currently try to find a bug that might be caused by uninitialized variables/memory. But it never appears when I use gdb. Does gdb change how memory is initialized in any way, be it on stack or via new/malloc?

Memory-related bugs that don't happen when using GDB but do without
GDB are often caused by GDB disabling ASLR. This is usually useful for
reproducibility of debugging sessions, but may indeed make address
space layout too predictable and fail to reproduce a bug. Try using
the GDB command "set disable-randomization off" (without quotes) to
undo this behavior and thus start your program in a normal,
randomized, environment.

Besides, if your problem is indeed with uninitialized variables, you
might find Valgrind memory checker more useful than a debugger.

>
> Regards

Regards,
Ruslan

Re: Does gdb initialize uninitialized variables?

[Martin Simmons]

I've sometimes seen different layout of the stack when running under gdb
because it changes the environment and converts argv[0] to an absolute
path.

You could try running the program without gdb and then attach gdb to it
from a different shell.

If the program crashes before you have time to attach gdb, then try
adding a call to sleep() in main() to delay it.

__Martin


>>>>> On Tue, 22 Feb 2022 21:30:26 +0000, Edgar Mobile via Gdb said:
> 
> I tried it as the very first command even before run. Any more ideas? (tx already)
> 
> ________________________________
> From: Ruslan Kabatsayev <b7.10110111@gmail.com>
> Sent: Monday, February 21, 2022 5:33 PM
> To: Edgar Mobile <heideggm@hotmail.com>
> Cc: gdb@sourceware.org <gdb@sourceware.org>
> Subject: Re: Does gdb initialize uninitialized variables?
> 
> Hi,
> 
> On Mon, 21 Feb 2022 at 12:45, Edgar Mobile via Gdb <gdb@sourceware.org> wrote:
> >
> > Greetings,
> >
> > I currently try to find a bug that might be caused by uninitialized variables/memory. But it never appears when I use gdb. Does gdb change how memory is initialized in any way, be it on stack or via new/malloc?
> 
> Memory-related bugs that don't happen when using GDB but do without
> GDB are often caused by GDB disabling ASLR. This is usually useful for
> reproducibility of debugging sessions, but may indeed make address
> space layout too predictable and fail to reproduce a bug. Try using
> the GDB command "set disable-randomization off" (without quotes) to
> undo this behavior and thus start your program in a normal,
> randomized, environment.
> 
> Besides, if your problem is indeed with uninitialized variables, you
> might find Valgrind memory checker more useful than a debugger.
> 
> >
> > Regards
> 
> Regards,
> Ruslan
>