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Re: Watchpoint on an unloaded shared library(2)
- From: Joel Brobecker <brobecker at adacore dot com>
- To: Emi SUZUKI <emi-suzuki at tjsys dot co dot jp>
- Cc: gdb at sourceware dot org
- Date: Mon, 29 Dec 2008 09:13:17 +0400
- Subject: Re: Watchpoint on an unloaded shared library(2)
- References: <20081217.154039.01371590.emi-suzuki@tjsys.co.jp>
> The cause of a crash is that print_one_breakpoint_location in breakpoint.c
> doesn't care about whether the expression for the watchpoint is valid:
>
> case bp_watchpoint:
> case bp_hardware_watchpoint:
> case bp_read_watchpoint:
> case bp_access_watchpoint:
> /* Field 4, the address, is omitted (which makes the columns
> not line up too nicely with the headers, but the effect
> is relatively readable). */
> if (opts.addressprint)
> ui_out_field_skip (uiout, "addr");
> annotate_field (5);
> print_expression (b->exp, stb->stream);
> ui_out_field_stream (uiout, "what", stb);
> break;
>
> Here, b->exp for the watchpoints set on an unloaded shared library can
> be NULL, because breakpoint_re_set_one has done it. However, what
> should we do instead?
>
> I have considered two solutions:
>
> a) Print b->exp_string and b->cond_string.
> We might make some effort to display it like as its expression is
> valid for annotations... I have no idea whether it is worthwhile
> to try.
I think that this is the best we can do (print exp_string).
I personally wouldn't worry about trying to massage the string
into something that would look like we're printing an expression.
I'm not even sure why we use "print_expression (b->exp) rather
than printing exp_string directly - perhaps someone does?
> b) Don't set b->exp to NULL in update_watchpoint (called by
> breakpoint_re_set_one), do_enable_breakpoint and so on.
> Maybe we should add some flags to `struct expression' to avoid
> passing invalid symtabs to some interacting functions.
I don't think we can do that. Otherwise, the expression could
reference some symbols that no longer exist.
> "Skip printing" is another possibility, but I'd ignore it: skipping
> means that the user can't refer to the information about what they
> were.
Right, as long as the watchpoint is defined, albeit disabled,
we need to show it in the list. Another alternative of your suggestion
is to not print the "what". But I would find this confusing, since
you would no longer know what the watchpoint entry is watching.
--
Joel