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Re: [RFA/PATCH] breakpoint.c: fix until command
- From: Michael Snyder <msnyder at redhat dot com>
- To: Elena Zannoni <ezannoni at redhat dot com>
- Cc: Daniel Jacobowitz <drow at mvista dot com>, gdb-patches at sources dot redhat dot com
- Date: Thu, 02 Jan 2003 17:44:42 -0800
- Subject: Re: [RFA/PATCH] breakpoint.c: fix until command
- Organization: Red Hat, Inc.
- References: <firstname.lastname@example.org> <3E07A1F2.E7B77C89@redhat.com> <20021224000211.GA8155@nevyn.them.org> <3E07B0DC.CC733B10@redhat.com> <20021224010306.GA10409@nevyn.them.org> <3E14A019.4A600913@redhat.com> <email@example.com> <firstname.lastname@example.org>
Elena Zannoni wrote:
> Elena Zannoni writes:
> > > Nevertheless, that is and has always been the intent.
> > > If you're in factorial(5), and you say "until 100",
> > > you don't stop until line 100 is hit by factorial(5).
> > I am tracking down this to something that changed between (ahem...)
> > 4.18 and 5.0. The code in breakpoint.c didn't change. Right now,
> > stepping the two gdb's side to side, I can see a difference in
> > get_prev_frame, because of a different value returned by
> > FRAME_CHAIN_VALID. :-( (i have not still stepped past that to see how
> > that could influence the until foo behavior, maybe it doesn't).
> > The behavior you specify above is in 5.0 and not in 4.18, while the
> > 'until foo' works in 4.18 and is broken in 5.0.
> > More digging.
> > Elena
> OK. The reason for which 'until foo' worked at all in 4.18 is totally
> fortuitous. It is because of this patch in breakpoint.c:
> 1998-09-08 Jason Molenda (email@example.com)
> * breakpoint.c (bpstat_stop_status): Declare a bp match if the
> current fp matches the bp->fp OR if the current fp is less than
> the bp->fp if we're looking at a bp_step_resume breakpoint.
> Index: breakpoint.c
> RCS file: /cvs/cvsfiles/src/gdb/breakpoint.c,v
> retrieving revision 1.190
> retrieving revision 1.191
> diff -u -p -p -r1.190 -r1.191
> --- breakpoint.c 1998/07/17 15:29:10 1.190
> +++ breakpoint.c 1998/09/09 04:16:57 1.191
> @@ -1506,7 +1506,9 @@ bpstat_stop_status (pc, not_a_breakpoint
> else if (DECR_PC_AFTER_BREAK != 0 || must_shift_inst_regs)
> real_breakpoint = 1;
> - if (b->frame && b->frame != (get_current_frame ())->frame)
> + if (b->frame && b->frame != (get_current_frame ())->frame &&
> + (b->type == bp_step_resume &&
> + (get_current_frame ())->frame INNER_THAN b->frame))
> bs->stop = 0;
> Note that this added condition is always false for a bp_until type
> breakpoint. So, effectively we were invalidating the check of the
> current frame vs. bp->frame. And we always stopped.
> However, since we were not checking the frames, the case Michael wants
> didn't work.
> The patch above was reverted in 1999:
> 1999-08-13 Jim Kingdon <http://developer.redhat.com/>
> * breakpoint.c (bpstat_stop_status): Revert 1998-09-08 change
> to ->frame matching. The change did not match the ChangeLog
> entry, looked fishy, and caused infinite stepping when running
> "next" from main on sparc w/ RH Linux. Thanks to Jakub for the
> the effect was that the frame matching check was re-enabled, and so
> 'until foo' stopped working.
> I don't think there is a way to have both behaviors work correctly. I
> thought of checking that the pc which you want to run until is in
> the same function as the one of the selected frame, and in that case
> enforce the check (by using a non-null frame for the bp_until),
> otherwise use the null frame (which disables the check). But what would
> be the correct behavior if you say:
> "until bar" where bar is recursive, and you are in "bar" at the
> moment? This doesn't work currently. It seems intuitive that you
> would stop the next time you enter "bar". Right now you end up at the
> caller of "bar".
> I think it is a matter of deciding which behavior is more useful.
> (note that I tried to revert Jason's patch in stock 4.18 and 'until
> foo' stopped working, i.e. it wasn't something else that broke between
> 4.18 and 5.0)
You raise a good point. The commands "until <line>" and "until <func>"
are inconsistant. Moreover the docs do not seem to describe this
recursion behavior. Maybe a conversation with a wider audience is
in order (the gdb list)? I'm sure I can't be the only one who
remembers that "until" behaved this way, and we shouldn't change
the behavior precipitously.