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

[Kevin Brodsky]

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.

Thanks,
Kevin