reg: GDB's generate-core-file option

[Michael Snyder]

Aarthy wrote:
> Hi there,
> 
> I am currently working on a product which has many processes running
> in a multi threaded fashion.

Is it threads?  Or forks?
If it's threads, gdb should be able to save all the threads
into a single corefile.  Can you attach gdb to the "main" thread?

> I run my product on a device which has
> 200 MB of hard disk space to write the core file. It doesn't have any
> swap memory as such. My requirement is that I need to collect the
> snapshot of each process at a particular time.  So I used
> generate-core-file option after attaching each process to GDB.

You didn't say how much ram your device has.

Are you running a bunch of gdbs at the same time?
Or are you running them one after another?

generate-core-file uses a lot of ram -- if you are running
many gdbs at the same time, you might be running out of memory.

> The
> problem is that for one process i get the following error.
> 
> warning: Failed to write corefile contents (No space left on device).
> ../../gdb/utils.c:1058: internal-error: virtual memory exhausted:
> can't allocate 92123136 bytes.

This is an out-of-memory error.  It comes from function "nomem()"
in utils.c, and results from the failure of an xmalloc() call.

There is only one xmalloc() call in gcore.c, it looks like this:


   memhunk = xmalloc (size);


This is trying to make a copy of one of the program's memory section.

So your program (or this thread or fork) has a memory section
that is 92,123,136 bytes long, and xmalloc can't acquire that
many bytes of free memory (at least in a single hunk).

> A problem internal to GDB has been detected,
> further debugging may prove unreliable.
> 
> I would like to know what could be the reason. I have about 15
> processes running. everything except this process i was able to
> generate the forced core file.
> This is my ulimit -a output,
> 
> Linux(debug)# ulimit -a
> core file size        (blocks, -c) 73242
> data seg size         (kbytes, -d) 62500
> file size             (blocks, -f) unlimited
> max locked memory     (kbytes, -l) unlimited
> max memory size       (kbytes, -m) unlimited
> open files                    (-n) 1024
> pipe size          (512 bytes, -p) 8
> stack size            (kbytes, -s) unlimited
> cpu time             (seconds, -t) unlimited
> max user processes            (-u) 26624
> virtual memory        (kbytes, -v) 125000
> 
> If i change the virtual memory size to unlimited i was able to
> generate the core. Kindly let me know how exactly the
> generate-core-file works.
> 
> Regards,
> Aarthy.