[Bug gdb/31194] Stepping on "int3" instruction fails assertion.

["tromey at sourceware dot org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31194

--- Comment #9 from Tom Tromey <tromey at sourceware dot org> ---
(In reply to Peter0x44 from comment #7)
> > I'm not really sure how int3 is supposed to be handled
> Perhaps it would be beneficial to state what my preferences would be.

Yes, thanks.

I dug into the code a bit and, first of all, gdb already does
support this situation.  It's called a "permanent breakpoint"
in the implementation.

There's even a test for this, gdb.arch/i386-bp_permanent.exp.
However, that tests "continue", not stepping.

I think perhaps the issue is that we reach the end of handle_signal_stop
with:

(top-gdb) p random_signal
$30 = 0

and in particular maybe:

  /* If not, perhaps stepping/nexting can.  */
  if (random_signal)
    random_signal = !(ecs->event_thread->stop_signal () == GDB_SIGNAL_TRAP
                      && currently_stepping (ecs->event_thread));

here the call to currently_stepping returns true.

Maybe this should be checking the PC and setting random_signal if it
is out of range?
Or maybe the earlier code that calls gdbarch_program_breakpoint_here_p
should set some sort of local flag, so that this can check it?

I don't really know infrun all that well and so I'm not sure how this
is intended to work.  I wonder if there are other scenarios to be
concerned with.

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