vdso function descriptors (VDS64_HAS_DESCRIPTORS)?

[Benjamin Herrenschmidt]

On Sat, 2020-02-22 at 18:07 -0600, Segher Boessenkool wrote:
> > 
> > so I don't believe they are ever used by default -- in this case
> > V_FUNCTION_BEGIN doesn't add to the .opd section with .name, .TOC base,
> > etc.
> > 
> > Manually setting VDS64_HAS_DESCRIPTORS results in a vdso64.so in which
> > binutils tools like readelf properly report functions with symbol type
> > FUNC instead of NOTYPE.
> > 
> > Are there pieces of the build/etc toolchain unprepared for function
> > descriptors?  I'm just trying to figure out why the code defaults to
> > unsetting them.
> 
> Because direct calls are faster than indirect calls?  Ben might have a
> fuller explanation, cc:ing him.

I don't remember why :-) I think I didn't want to mess with the OPD
fixup in glibc back then.

Ben.