On Mon, Aug 22, 2011 at 1:46 PM, Richard Guenther
<richard.guent...@gmail.com> wrote:
> On Mon, Aug 22, 2011 at 10:39 PM, H.J. Lu <hjl.to...@gmail.com> wrote:
>> On Mon, Aug 22, 2011 at 1:34 PM, Richard Guenther
>> <richard.guent...@gmail.com> wrote:
>>> On Mon, Aug 22, 2011 at 6:02 PM, H.J. Lu <hjl.to...@gmail.com> wrote:
>>>> On Mon, Aug 22, 2011 at 8:56 AM, Michael Matz <m...@suse.de> wrote:
>>>>> Hi,
>>>>>
>>>>> On Mon, 22 Aug 2011, H.J. Lu wrote:
>>>>>
>>>>>> >> Oh, I thought it was data initialized by the constructor ...
>>>>>> >
>>>>>> > Sriramans patch right now has a function __cpu_indicator_init which is
>>>>>> > called from (adhoc constructed) ctors and that initializes variables
>>>>>> > __cpu_model and __cpu_features ;-) There's no __cpu_indicator symbol
>>>>>> > :)
>>>>>> >
>>>>>> > I think the whole initializer function and the associated data blobs
>>>>>> > have
>>>>>> > to sit in static libgcc and be hidden. By that all shared modules
>>>>>> > will have their own copies of the model and features (and the
>>>>>> > initializer
>>>>>> > function) so there won't be issues with copy relocs, or cross shared
>>>>>> > lib
>>>>>> > calls while relocating the modules. Dynamically they will contain the
>>>>>> > same data always, but it's not many bytes, and only modules making use
>>>>>> > of
>>>>>> > this facility will pay it.
>>>>>> >
>>>>>> > The initializer function has to be callable from pre-.init contexts,
>>>>>> > e.g.
>>>>>> > ifunc dispatchers. And to make life easier there should be one ctor
>>>>>> > function calling this initializer function too, so that normal code can
>>>>>> > rely on it being already called saving one check.
>>>>>> >
>>>>>>
>>>>>> It sounds more complicated than necessary. Why not just do it
>>>>>> on demand like glibc does?
>>>>>
>>>>> Ehm, the only difference would be to not have a ctor in libgcc that looks
>>>>> like so:
>>>>>
>>>>> void __attribute__((constructor)) bla(void)
>>>>> {
>>>>> __cpu_indicator_init ();
>>>>> }
>>>>>
>>>>> I don't see any complication.?
>>>>>
>>>>
>>>> Order of constructors. A constructor may call functions
>>>> which use __cpu_indicator.
>>>
>>> As I said - make __cpu_indicator have a conservative
>>> default value (zero). It is irrelevant if constructors that
>>> run before initializing __cpu_indicator run with the
>>> default CPU capabilities.
>>>
>>
>> If IFUNC is used, this just disables IFUNC for those functions
>> called with the conservative default value since they are only
>> resolved once.
>
> Huh, well. So what happens if you use __cpu_indicator from the
> IFUNC selector function!? Honestly, if we care about these
> corner-cases why not make __cpu_indicator a hidden function
> instead.
>
> IMHO IFUNC selectors should simply do
>
> if (!__cpu_indicator)
> __cpu_indicator_init ();
>
Isn't it what I said before?
--
H.J.
