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Re: [4.7][google]Support for getting CPU type and feature information at run-time. (issue4893046)
On Mon, Aug 22, 2011 at 6:02 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Aug 22, 2011 at 8:56 AM, Michael Matz <matz@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.
Richard.
> --
> H.J.
>