GDB 7.4 adds shlib_events BPs, casuing problem in debugging vmlinux

Jan Kratochvil jan.kratochvil@redhat.com
Fri Jun 1 14:48:00 GMT 2012


On Thu, 31 May 2012 02:31:17 +0200, Joakim Tjernlund wrote:
> 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 */
> {
> ...
> }

Yes, I think this should work - to omit "_start" and "__start" if there is no
INTERP_NAME.


Thanks,
Jan



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