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?
Thanks,
-Sri.
>
> --
> H.J.
>
