Re: Lifetime of local variables

[Martin Baulig <martin@gnome.org>]

Daniel Jacobowitz <drow@mvista.com> writes:

> On Sat, Apr 13, 2002 at 01:31:05PM +0200, Martin Baulig wrote:
> > Daniel Jacobowitz <drow@mvista.com> writes:
> > > Also, I believe that this should be entirely subsumed by .debug_loc. 
> > > The first variable's value may no longer be available, but it has not
> > > actually gone out of scope, has it?  We should list it but claim that
> > > its value is unavailable.
> > 
> > It has actually gone out of scope. I want to use this to debug machine
> > generated IL code and the JIT may want to create local variables
> > on-the-fly. For variables which have actually been defined by a human
> > programmer, listing them and claiming that their value is no longer
> > available is IMHO the right thing to do - but I'd like to tell the
> > debugger to make a machine-generated variable disappear when it's no
> > longer used, otherwise you'd get a large number of automatic variables
> > (having numbers, not names, which makes it even more confusing to the
> > user) and only a very few of them are actually used.
> 
> What business does the JIT have actually creating local variables
> (rather than temporaries, which don't get names)?  I don't understand.

What's the difference between a local variable and a temporary variable ?

> > Btw. are there any plans to implement .debug_loc anytime soon, I need
> > this for something else ?
> 
> I believe it's in progress.

Well, this is probably the correct place to put this (and then use
DW_AT_artificial or something like this to make the variables
disappear outside their lifetime).

> On Sat, Apr 13, 2002 at 02:42:14PM +0200, Martin Baulig wrote:
> > Momchil Velikov <velco@fadata.bg> writes:
> > > One can use DT_AT_artificial to distinguish machine generated
> > > temporaries and the .debug_loc ranges to decide whether to display the
> > > variable.
> > 
> > What happens if you're outside any of the ranges listed in .debug_loc -
> > will the variable be listed or not or will this depend on DW_AT_artificial ?
> > 
> > IMHO variables which have been created by a human should always be
> > listed, but machine generated ones (since there can be a large number
> > of them) should only be listed withing their lifetime ranges.
> 
> We don't know yet, since DW_AT_artificial is currently only used for
> method arguments (and methods, but that patch is pending).  Once we've
> got .debug_loc we can decide, but this seems reasonable to me.
> 
> 
> -- 
> Daniel Jacobowitz                           Carnegie Mellon University
> MontaVista Software                         Debian GNU/Linux Developer
> 

-- 
Martin Baulig
martin@gnome.org