Re: [PATCH 3/3] tdesc: handle arbitrary strings in tdesc_register_in_reggroup_p

[Simon Marchi <simon dot marchi at polymtl dot ca>]

On 2017-06-09 13:45, Stafford Horne wrote:
> > Is the memory allocated by reggroup_new ever freed?
>
> It is not, and its a bit tricky.  I looked through gdb, it seems the
> reggroup objects are never freed, anywhere.  The list itself and list
> elements (reggroup_el) are all allocated on obstack, but not reggroup.
>
> It could get a bit messy to try to do something about it like refcounts 
> or
> tracking reggroups per target description.
>
> Any suggestions?
>
> -Stafford

What's tricky is that some reggroup objects are owned by tdep files and 
are more or less permanent, whereas the groups provided by the tdesc are 
more transient and owned by a gdbarch instance.  A quick fix I think 
would be to have another version of reggroup_new (or the same function 
with additional parameters) that allocates the object on the gdbarch's 
obstack instead of XNEW'ing it.  The name would be obstack_strdup'ed 
instead of xstrdup'ed.  This should ensure that when the gdbarch is 
freed, the reggroups it owns are freed as well.

I don't think reference counting is useful here, because there is always 
a single entity to which the lifetime of the object is tied, so it 
should be clear when to free it.

From what I can see, gdbarch's are never really freed right now, so it 
doesn't really matter right now, but I think we should do it right 
anyway, in case it ever changes.

Simon