On Mon, Aug 22, 2011 at 11:58 AM, H.J. Lu <hjl.to...@gmail.com> wrote:
> On Mon, Aug 22, 2011 at 11:50 AM, Sriraman Tallam <tmsri...@google.com> wrote:
>> On Mon, Aug 22, 2011 at 9:02 AM, 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.
>>
>> I have a suggestion that is a hybrid of the proposed solutions here:
>>
>> 1) Make a constructor in every module that calls
>> "__cpu_indicator_init" and make it to be the first constructor to run.
>> Will this solve the ordering problem?
>> 2) Change __cpu_indicator_init to run only once by using a variable to
>> check if it has been run before.
>>
>> So, each module's constructor will call __cpu_indicator_init but the
>> CPUID insns are only done once. I also avoid the extra overhead of
>> having to check if "__cpu_indicator_init" is called from within the
>> binary. Will this work?
>>
>
> Please make it simple like
>
> if __cpu_indicator is not initialized then
> call __cpu_indicator_init
> fi
>
> use __cpu_indicator
>
Will do, thanks.
-Sri.
>
> --
> H.J.
>
