Re: breakpoints in constructors

[Daniel Berlin <dberlin at dberlin dot org>]

On Wednesday, April 30, 2003, at 12:36  AM, Michael Elizabeth Chastain 
wrote:

> Can I de-lurk for a minute?
>
> gcc 2.95.3 had a single object code function for each constructor,
> with a hidden flag to indicate its "in-charge-ness".  I always thought
> that was much nicer for debugging.
>
> But gcc 3.X's multi-object-code implementation is mandated by the
> multi-vendor ABI, which will make it harder.

No it isn't.
It's not required multi-object-code, it's only required that it does 
the right thing when called with a certain name  (not the same at all, 
since one can  just make up the symbols for the constructors that start 
at the right points in the "one object code constructor" function, 
without even having to make stub functions with gotos in them. Just 
multiple symbol names and one object code).

One can also have "one object code implementation" with labels and use 
gotos and stub functions if you like.
Or one can have three copies of the object code.

It's not like even with three copies, that this is a laborious task.
It just means that you set multiple breakpoints.

One way is to make one "visible" breakpoint and 2 "hidden" breakpoints.
This is a bit ugly, unless you special case the breakpoint printouts so 
that it says the one "visible" breakpoint is at pc x, y, z, rather than 
just x (the code to do this is probably ugly too in this method).

Another way is to do this is make it all invisible to the user, but 
still have "hidden" breakpoints is to make breakpoints have an 
associate set of methods, where they perform this magic internally.

You could also just make a hierarchy of breakpoints and avoid the magic 
methods and hiding altogether.
You have one parent breakpoint named "Foo:Foo" that just consists of 3 
sub-breakpoints, each at the right place in the constructor.

Only non-hidden top level breakpoints (since i imagine in some 
extremely complex case, one could want to have a subbreakpoint 
consisting of subbreakpoints) are visible, and thus, Foo:Foo is visible 
in an info breakpoints printout, but it's sub-breakpoints aren't (You 
can either just make it print "exists at multiple pc's, or recursively 
print out the pc's of the sub breakpoints).

Hitting one of the subbreakpoints doesn't require any magic, since what 
we say is that we've hit the parent breakpoint, "Foo:Foo".

--Dan