From: Nathan_Lynch@mentor•com (Nathan Lynch)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v9 4/6] ARM: add vdso user-space code
Date: Fri, 12 Sep 2014 01:50:58 -0500 [thread overview]
Message-ID: <541297D2.5000705@mentor.com> (raw)
In-Reply-To: <20140910164755.GC1710@arm.com>
On 09/10/2014 11:47 AM, Will Deacon wrote:
> Hi Nathan,
>
> On Fri, Aug 22, 2014 at 10:52:29PM +0100, Nathan Lynch wrote:
>> Place vdso-related user-space code in arch/arm/kernel/vdso/.
>>
>> It is almost completely written in C with some assembly helpers to
>> load the data page address, sample the counter, and fall back to
>> system calls when necessary.
>
> I'm still a bit puzzled as to how we can implement a compat version of this
> for a 32-bit userspace running under a 64-bit kernel. Maybe the answer is
> that we don't care enough (programs will still work fine without it), but if
> we did want to then we're going to need to build the kernel with two
> toolchains and it gets really horrible.
>
> Do you have any ideas?
Assuming a GCC+binutils toolchain, I don't have any workable ideas for
generating ARMv7 shared object during an arm64 kernel build without
relying on a second compiler. I think theoretically you could do
something like what kuser32.S does, but that would be untenable for
something as complex as a vdso.
I recognize that this might present an awkward situation where an ARMv7
program could incur more system call overhead on arm64 than it does on
arm, but I don't see any way around it.
next prev parent reply other threads:[~2014-09-12 6:50 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-22 21:52 [PATCH v9 0/6] ARM: VDSO Nathan Lynch
2014-08-22 21:52 ` [PATCH v9 1/6] ARM: use _install_special_mapping for sigpage Nathan Lynch
2014-08-22 21:52 ` [PATCH v9 2/6] ARM: place sigpage at a random offset above stack Nathan Lynch
2014-08-22 21:52 ` [PATCH v9 3/6] ARM: miscellaneous vdso infrastructure, preparation Nathan Lynch
2014-08-22 21:52 ` [PATCH v9 4/6] ARM: add vdso user-space code Nathan Lynch
2014-09-10 16:47 ` Will Deacon
2014-09-10 16:52 ` Andy Lutomirski
2014-09-10 17:10 ` Will Deacon
2014-09-10 17:25 ` Nathan Lynch
2014-09-12 6:50 ` Nathan Lynch [this message]
2014-08-22 21:52 ` [PATCH v9 5/6] ARM: vdso initialization, mapping, and synchronization Nathan Lynch
2014-08-22 21:52 ` [PATCH v9 6/6] ARM: add CONFIG_VDSO Kconfig and Makefile bits Nathan Lynch
2014-08-27 20:49 ` [PATCH v9 0/6] ARM: VDSO Christopher Covington
2014-08-27 21:42 ` Andy Lutomirski
2014-09-03 5:41 ` Nathan Lynch
2014-09-03 13:13 ` Christopher Covington
2014-09-03 16:59 ` Andy Lutomirski
2014-09-03 20:03 ` Nathan Lynch
2014-09-03 20:12 ` Andy Lutomirski
2014-09-06 2:32 ` Nathan Lynch
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