[RFC PATCH v2 8/8] arm64: Wire up and expose the new compat vDSO

[Catalin Marinas]

On Fri, Nov 04, 2016 at 10:30:08AM -0600, Kevin Brodsky wrote:
> On 04/11/2016 09:50, Catalin Marinas wrote:
> > On Thu, Oct 27, 2016 at 05:30:58PM +0100, Kevin Brodsky wrote:
> > > * The vDSO page replaces the vector page. The vDSO provides its own
> > >    sigreturn trampolines, replacing those in the vector page, but the
> > >    kuser helpers are gone. As a result enabling the compat vDSO will
> > >    break userspace programs relying on the kuser helpers.
> > I think vDSO and vectors page should not exclude each other. If you want
> > to disable the vectors page, let's make it an independent config option
> > like the KUSER_HELPERS in arch/arm64/mm/Kconfig. But I would very much
> > like to be able to have both the vDSO and the vectors page at the same
> > time.
> 
> Indeed, I've had exactly the same feedback from Google yesterday (apparently
> many Android apps with native libs still target ARMv6....). I'll add the
> option to keep the kuser helpers.
> 
> There's a small problem though: how to ensure that the kuser helpers +
> sigreturn trampolines are always included if the compat vDSO is not built? I
> can enforce CONFIG_KUSER_HELPERS if !CONFIG_VDSO32 (directly in the
> code/Makefiles), but the dependency cannot be expressed in Kconfig.

Or you could insert a separate "sigpage" as arm32 does. This could leave
independently of vDSO or vectors page.

-- 
Catalin