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[ping v2] [PATCH 1/2] gdbserver: catch fetch registers error


ping
 
> > -----Original Message-----
> > From: Metzger, Markus T
> > Sent: Tuesday, December 6, 2016 4:55 PM
> > To: gdb-patches@sourceware.org
> > Cc: Daniel Jacobowitz <drow@false.org>
> > Subject: [PATCH 1/2] gdbserver: catch fetch registers error
> >
> > When the PTRACE_PEEKUSER ptrace request to read registers fails, gdbserer
> > throws
> > an error that is caught in captured_main, where it causes a E01 error packet to
> > be sent and gdbserer to quit (if --once was specified) or the event loop to be
> > re-started (otherwise).
> >
> > We may get such ptrace errors when trying to fetch registers for an exited or
> > running thread.  There are checks in GDB that check those conditions and throw
> > meaningful error messages before we could run into the above ptrace error,
> > e.g. thread.c:validate_registers_access.
> >
> > I ran into a new case and, rather than adding another call to
> > validate_registers_access in GDB, I propose to catch the error already when
> > handling the 'g' packet in gdbserver and reply with an error packet - assuming
> > that gdbserver's internal state is still intact.
> >
> > To not replace a meaningful error message with E01, I'm trying to generate a
> > useful error message when the error is detected and the exception is thrown.
> >
> > It would look like this ...
> >
> > gdb) PASS: gdb.btrace/enable-running.exp: continue to breakpoint: cont to 44
> > cont&
> > Continuing.
> > (gdb) PASS: gdb.btrace/enable-running.exp: cont&
> > record btrace
> > warning: Remote failure reply: E.Selected thread is running.
> > warning: Remote failure reply: E.Selected thread is running.
> >
> > ... although in this particular case, I'm going to suppress the warning.
> >
> > To make this look a bit nicer, we could consider stripping the "E." or the
> > entire "Remote failure reply: E." when (re-)throwing the error inside GDB in
> > remote.c.
> >
> > CC:  Daniel Jacobowitz	<drow@false.org>
> >
> > 2016-12-06  Markus Metzger  <markus.t.metzger@intel.com>
> >
> > gdbserver/
> > 	* server.c (process_serial_event): Add TRY/CATCH.
> > 	* linux-low.c (fetch_register): Improve error message.
> > ---
> >  gdb/gdbserver/linux-low.c | 19 ++++++++++++++++++-
> >  gdb/gdbserver/server.c    | 18 ++++++++++++++++--
> >  2 files changed, 34 insertions(+), 3 deletions(-)
> >
> > diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
> > index e3e372c..a942b87 100644
> > --- a/gdb/gdbserver/linux-low.c
> > +++ b/gdb/gdbserver/linux-low.c
> > @@ -5692,7 +5692,24 @@ fetch_register (const struct usrregs_info *usrregs,
> >  		(PTRACE_TYPE_ARG3) (uintptr_t) regaddr, (PTRACE_TYPE_ARG4)
> > 0);
> >        regaddr += sizeof (PTRACE_XFER_TYPE);
> >        if (errno != 0)
> > -	error ("reading register %d: %s", regno, strerror (errno));
> > +	{
> > +	  /* ESRCH could mean that the thread is not traced, exited, or is not
> > +	     stopped.  */
> > +	  if (errno == ESRCH)
> > +	    {
> > +	      struct lwp_info *lwp = get_thread_lwp (current_thread);
> > +
> > +	      if (!lwp_is_stopped (lwp))
> > +		error (_("Selected thread is running."));
> > +
> > +	      if (lwp_is_marked_dead (lwp))
> > +		error (_("Selected thread has terminated."));
> > +	    }
> > +
> > +	  /* Report a generic error if we could not determine the exact
> > +	     reason.  */
> > +	  error (_("Could not read register %d: %s."), regno, strerror (errno));
> > +	}
> >      }
> >
> >    if (the_low_target.supply_ptrace_register)
> > diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
> > index ef8dd03..3064b4f 100644
> > --- a/gdb/gdbserver/server.c
> > +++ b/gdb/gdbserver/server.c
> > @@ -4132,8 +4132,22 @@ process_serial_event (void)
> >  	    write_enn (own_buf);
> >  	  else
> >  	    {
> > -	      regcache = get_thread_regcache (current_thread, 1);
> > -	      registers_to_string (regcache, own_buf);
> > +	      TRY
> > +		{
> > +		  regcache = get_thread_regcache (current_thread, 1);
> > +		  registers_to_string (regcache, own_buf);
> > +		}
> > +	      CATCH (exception, RETURN_MASK_ALL)
> > +		{
> > +		  const char *message;
> > +
> > +		  message = exception.message;
> > +		  if (message == NULL)
> > +		    message = _("Reading registers failed.");
> > +
> > +		  sprintf (own_buf, "E.%s", message);
> > +		}
> > +	      END_CATCH
> >  	    }
> >  	}
> >        break;
> > --
> > 1.8.3.1

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