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 (); Richard. > > -- > H.J. >