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Re: RFC: MI - Detecting change of string contents with variable objects
- From: Vladimir Prus <ghost at cs dot msu dot su>
- To: Nick Roberts <nickrob at snap dot net dot nz>
- Cc: Daniel Jacobowitz <drow at false dot org>, gdb-patches at sources dot redhat dot com
- Date: Thu, 4 Jan 2007 23:56:46 +0300
- Subject: Re: RFC: MI - Detecting change of string contents with variable objects
- References: <17797.65268.689590.797944@kahikatea.snap.net.nz> <20070104194033.GB24634@nevyn.them.org> <17821.25837.573239.858406@kahikatea.snap.net.nz>
On Thursday 04 January 2007 23:34, Nick Roberts wrote:
> > > + char* print_value = value_get_print_value (value, var->format);
> >
> > Use "char *print_value", please.
>
> OK.
>
> > > gdb_assert (!value_lazy (var->value));
> > >
> > > ! if (var->print_value)
> > > ! {
> > > ! if (strcmp (var->print_value, print_value))
> > > ! {
> > > ! xfree (var->print_value);
> > > ! var->print_value = print_value;
> > > ! changed = 1;
> > > ! }
> > > ! }
> > > ! else
> > > ! var->print_value = print_value;
> >
> > Should we set changed = 1 in the "else"?
>
> No. This is only reached in the initial call to install_new_value i.e
> -var-create.
How so? For -var-create the 'initial' parameter to install_new_value should be
1, so we have:
if (!initial && changeable)
{
................
gdb_assert (!value_lazy (var->value));
if (var->print_value)
{
if (strcmp (var->print_value, print_value))
{
xfree (var->print_value);
var->print_value = print_value;
changed = 1;
}
}
else
var->print_value = print_value;
}
It seems to be this code is *never* reached during call from -var-create.
In fact, I don't seem to understand how var->print_value will be initialized
by -var-create.
> > Otherwise the patch seems fine, if it tests OK, but I'm still a little
> > nervous about it. For example, you'll call val_print on a struct
> > or array to see if it's changed. Depending on things like "set print
> > elements", that might not print out the whole string. This is
> > probably a behavior change. Is it a harmless one? If it is, then
> > should we be sharing the code with c_value_of_variable that avoids
> > printing structs, unions, and arrays, and never mark them as changed
> > unless their types change?
>
> The function val_print is already used for -var-evaluate-expression. AFAICS
> "set print elements" has no effect on variable objects, perhaps because
> val_print is only called on the leaves but I can see that using it might
> expose MI to the vagaries of CLI. Currently, however, string changes don't
> get reported at all, without the user changing configuration values.
The code in question is executed only for changeable values, and so will never
be executed for structures.
- Volodya