Re: [PATCH] gdb: fix target_ops reference count for some cases

[Simon Marchi <simark@simark.ca>]

> I agree with you 100%.  Unfortunately, the following targets all seem to
> depend on current_inferior being set (in their ::close method):
> 
>   bsd_kvm_target
>   core_target
>   darwin_nat_target
>   record_btrace_target
>   ctf_target
>   tfile_target
>   windows_nat_target (though this is only for debug output)
> 
> I suspect that this means these targets only really work when GDB has a
> single inferior maybe?  In most cases GDB seems to be clearing out some
> per-inferior state relating to the target... I need to investigate more,
> but I guess I wanted to raise this in case you (or anyone) had thoughts.

Ah, ok.  Yeah I see some targets calling exit_inferior_silent on the
current inferior, among other things.  I guess I misunderstand what
target_ops::close is meant to do, I thought this would have been done
earlier.  Different targets seem to use the close method for different
things.

So, in any case, my proposition falls into "no doable right now".

>>> At the moment the inferior's program_space is deleted in
>>> delete_inferior before we call inferior::~inferior, so, I think, to
>>> place the pop_all_targets call into inferior::~inferior would require
>>> additional adjustment to GDB.  As delete_inferior already exists, and
>>> includes various house keeping tasks, it doesn't seem unreasonable to
>>> place the pop_all_targets call there.
>>
>> I don't object to fixing it like this.  I'm just wondering, did you
>> consider changing target_stack::m_stack to make it hold string
>> references, something like std::vector<target_ops_ref>?  I haven't tried
>> so maybe this doesn't make sense / is too difficult.  But if it does, I
>> guess the problem would take care of itself.  When deleting an inferior
>> that still has some targets pushed, they would be automatically decref'd
>> and closed if needed.
> 
> I did think about this.  I think in the end the fix I proposed here
> was just less churn.

Agreed.

> As I mention above, right now it seems we do need th correct inferior
> selected, so we might need something like this, I'll see how my new
> patches work out.

I think your approach is ok, it fixes a real bug, so big refactorings
should not get in the way of that.

I'll take a look at the code now.

Simon