Re: [PATCH 1/2] Use gdbarch obstack to allocate types in alloc_type_arch

[Patrick Palka <patrick at parcs dot ath dot cx>]

On Sat, Aug 29, 2015 at 6:29 PM, Patrick Palka <patrick@parcs.ath.cx> wrote:
> On Sat, Aug 29, 2015 at 5:35 PM, Doug Evans <xdje42@gmail.com> wrote:
>> On Sat, Aug 29, 2015 at 2:26 PM, Patrick Palka <patrick@parcs.ath.cx> wrote:
>>>...
>>> Some background for this change: The TYPE_OBJFILE_OWNED macro tells us
>>> who owns a given type, and according to the macro's documentation a
>>> type is always owned either by an objfile or by a gdbarch.  Given this
>>> binary encoding of ownership it doesn't seem to make much sense for
>>> _any_ type to be allocated by malloc.  All types should be allocated
>>> on an objfile obstack or on a gdbarch obstack.
>>
>> I can imagine types being allocated by malloc and tracked via whatever
>> object "owns" them. All that matters is that when the owner is freed
>> all its owned objects are freed too. Whether those objects are
>> malloc'd or in an obstack is just an implementation detail.
>>
>> I know that that's not how arch-owned types worked prior to your patch.
>> I'm just saying they *could* have worked that way.
>> Moving them to an obstack obviates the need for keeping a copy of
>> the pointer so it can later be freed.
>
> That makes sense.
>
>>
>>> To support allocating a type by malloc, I think the type ownership
>>> scheme should have three possible cases: that a type is owned by an
>>> objfile, or that it's owned by a gdbarch, or that it's owned by the
>>> caller.  This new last case could correspond to a type that's
>>> allocated by malloc instead of on an obstack.
>>>
>>> Does this make sense, or maybe I am misunderstanding what "owning" means here?
>>
>> I think you've got it right.
>>
>> There's still, technically, an open issue of "What happens if an arch
>> is freed and there's still a value in the history that uses that type?
>> Would we then have to preserve that type again? (bleah)"
>
> Ah, yeah..
>
>>
>> I don't have too strong an opinion on what's right here.
>> If someone wants to allow for arches being freed and thus
>> "preserved" types have to be "owned" by something else, ok,
>> but I don't see it as an urgent need. We *could* just say that
>> arches are never freed for now.
>
> Makes sense.
>
> I reverted this patch, with a revised one incoming.

Er, sorry, I reverted and revised the 2nd patch, not this one.