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Subject: Re: GDB 7.4 adds shlib_events BPs, casuing problem in debugging vmlinux
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To: Jan Kratochvil <jan.kratochvil@redhat.com>
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From: Joakim Tjernlund <joakim.tjernlund@transmode.se>
Date: Thu, 31 May 2012 00:31:00 -0000
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Jan Kratochvil <jan.kratochvil@redhat.com> wrote on 2012/05/30 23:35:39:
>
> On Wed, 30 May 2012 16:25:29 +0200, Joakim Tjernlund wrote:
> > Found this in solib-svr4.c which I think is the problem:
> > static const char * const bkpt_names[] =
> > {
> >   "_start",
> >   "__start",
> >   "main",
> >   NULL
> > };
> > ...
> > ...
> >  if (!current_inferior ()->attach_flag)
> >     {
> >       for (bkpt_namep = bkpt_names; *bkpt_namep != NULL; bkpt_namep++)
> >    {
> >      msymbol = lookup_minimal_symbol (*bkpt_namep, NULL, symfile_objfile);
> >      if ((msymbol != NULL) && (SYMBOL_VALUE_ADDRESS (msymbol) != 0))
> >        {
> >          sym_addr = SYMBOL_VALUE_ADDRESS (msymbol);
> >          sym_addr = gdbarch_convert_from_func_ptr_addr (target_gdbarch,
> >                           sym_addr,
> >                           &current_target);
> >          create_solib_event_breakpoint (target_gdbarch, sym_addr);
> >          return 1;
> >        }
> >    }
> >     }
> >
> > This will insert the above BP just because the symbol  _start is present. Seems like
> > there are missing safe guards to avoid the unwanted BP
>
> This breakpoint is wanted.  If GDB fails to insert the "_r_debug_state"
> breakpoint into ld.so for whatever reason then after initial DT_NEEDED loading
> of shared libraries ld.so gives away control to the main executable.
> "_start" is the possible symbol there how to catch just exit from ld.so.

BTW, if this is all about ld.so, then why not guard this with
if (interp_name) /* Check if there is a ld.so at all */
{
...
}