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Re: [RFA] Fix breakpoint condition that use member variables.
- From: Vladimir Prus <vladimir at codesourcery dot com>
- To: Eli Zaretskii <eliz at gnu dot org>
- Cc: gdb-patches at sources dot redhat dot com
- Date: Sat, 22 Mar 2008 15:36:06 +0300
- Subject: Re: [RFA] Fix breakpoint condition that use member variables.
- References: <firstname.lastname@example.org> <email@example.com>
On Saturday 22 March 2008 15:06:35 Eli Zaretskii wrote:
> > From: Vladimir Prus <firstname.lastname@example.org>
> > Date: Sat, 22 Mar 2008 12:40:15 +0300
> > Suppose that foo.cpp:10 is a location inside member function of a
> > class, and that said class has member variable i_, and that we've
> > just started a program and are in main. Then:
> > break foo.cpp:10 if i_ == 10
> > will not work, claiming that i_ does not exist. The problem is that
> > lookup_symbol_aux uses value_of_this, which uses value_of_local and
> > that totally ignores the block that is passed to parse_exp_1 by
> > the breakpoint code and uses the block of the selected frame. Of
> > course, that either does not have "this", or has wrong "this".
> > This patch fixes the problem by looking in the right block
> > directly, and also by looking for the field in the type of "this",
> > without trying to get the value.
> What will happen after your patch if there's also a variable i_ in
> the selected frame?
The i_ in the breakpoint condition will be associated with the member
variable, not with the variable with selected frame. FWIW, it's exactly
as happens with local variables -- say, with gdb 6.6, if I have ordinary
local variable i in selected frame, and set breakpoint at
whatever.cpp:10, and there's local variable i there, then breakpoint
condition using 'i' will evaluate i at the breakpoint location, not
from the currently selected frame.
When lookup_symbol_aux is asked to find a symbol in a block, it will
carefully look in that block, not using selected frame in any way.
It's only the lookup for "this" that relied on selected frame.
I have modified my testcase to include a local variable called i_,
to make sure this does not confuse anything.