From mboxrd@z Thu Jan  1 00:00:00 1970
From: kevin.brodsky@arm.com (Kevin Brodsky)
Date: Fri, 4 Nov 2016 10:30:08 -0600
Subject: [RFC PATCH v2 8/8] arm64: Wire up and expose the new compat vDSO
In-Reply-To: <20161104155039.5lxubpyt2dsuqxef@localhost>
References: <20161027163058.12156-1-kevin.brodsky@arm.com>
 <20161027163058.12156-9-kevin.brodsky@arm.com>
 <20161104155039.5lxubpyt2dsuqxef@localhost>
Message-ID: <3fb402fd-a080-f327-6d86-c2d341c5e7d9@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

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