[PATCH 1/3] x86: Initialize CPU info via IFUNC relocation [BZ 26203]

[H.J. Lu]

On Fri, Sep 18, 2020 at 6:59 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > On Fri, Sep 18, 2020 at 1:06 AM Florian Weimer <fweimer@redhat.com> wrote:
> >>
> >> * H. J. Lu via Libc-alpha:
> >>
> >> > X86 CPU features in ld.so are initialized by init_cpu_features, which is
> >> > invoked by DL_PLATFORM_INIT from _dl_sysdep_start.  But when ld.so is
> >> > loaded by static executable, DL_PLATFORM_INIT is never called.
> >>
> >> I don't think that's accurate.  It's called from elf/dl-support.c in the
> >> static case.  But I agree that it's too late in this case.
> >
> > I was referring to the ld.so case.  elf/dl-support.c isn't used for ld.so.
>
> I missed that.
>
> You cannot use ld.so in a static executable because it is
> uninitialized/dormant.
>
> If you need functionality after static dlopen, it has to reside in
> libc.so.6, not the dynamic loader.

Here is the problem.  static dlopen uses libc.so.6 which brings in ld.so
with _rtld_global and _rtld_global_ro via DT_NEEDED.  My patch is
trying to deal with it to initialize CPU info in _rtld_global_ro in this case.

-- 
H.J.