Here are some more tests:

1. It doesn't get stuck when debugging a "hello-world.c" program. Thus it depends on the executable.
2. Regarding toggle-debug-on-quit and C-g, it doesn't work. No backtrace is produced and the CPU continues to be at 100%.
3. I tried running edebug on gdb, which wasn't easy. I had to manually first do eval-buffer on gdb-mi.el and gud.el. But in the end I managed and found that the CPU is spend during (run-hooks 'gdb-mode-hook) . I'll try to investigate it further in the next few days.

Regards,
Dov

On Wed, Jan 25, 2012 at 02:37, Glenn Morris <rgm@gnu.org> wrote:

>> I tried again with emacs -Q and the same thing happens. To be more
>> precise the startup time is about 40s at 100% CPU.

Is this with everything you try to debug, or just certain things?

Can you try M-x toggle-debug-on-quit, then interrupt Emacs with ctrl-g
during those 40 seconds and see if you get a backtrace?

Or try M-x edebug-defun on the `gdb' function, step through it, and see
what is taking the time.

Guesses: do you have a huge .gdb_history or ~/.gdbinit file?