From: Nathan_Lynch@mentor•com (Nathan Lynch)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC] arm: vdso: Convert sigpage to vdso implementation
Date: Tue, 28 Jan 2014 15:05:59 -0600 [thread overview]
Message-ID: <52E81BB7.7070201@mentor.com> (raw)
In-Reply-To: <1390926308-15581-1-git-send-email-steve.capper@linaro.org>
Hi Steve,
On 01/28/2014 10:25 AM, Steve Capper wrote:
> ARM has a special sigpage that is used for signal return trampolines.
> Its implementation is very similar to a VDSO conceptually in that it
> occupies a special mapping in user address space.
>
> One could actually host the trampoline code in a VDSO instead with the
> added advantage that one could also host specialised routines there.
> One such routine could be gettimeofday where on ARM we have architected
> (and some vendor supplied) timers that can be queried entirely in
> userspace, obviating the need for an expensive syscall.
>
> This patch converts the sigpage implementation to a VDSO. It is mostly
> a direct port from Will Deacon's arm64 implementation with the ARM
> signal trampoline plumbed in.
>
> Signed-off-by: Steve Capper <steve.capper@linaro•org>
> ---
> As can be inferred from this RFC, I am interested ultimately in
> implementing a syscall-less gettimeofday for ARM. Whilst researching
> possible vectors page or VDSO implementations, I came across the
> sigpage mechanism which is very similar to a VDSO.
>
> The very simple function, __kernel_vdso_doubler, resolved in a test
> program automatically on my Arndale board (running Fedora 20) without
> any additional prodding.
>
> IPC stress tests from LTP were executed to test the signal trampoline.
>
> I would appreciate any comments on this approach of converting the
> sigpage to a VDSO. If this looks sane to people, I will work on the
> gettimeofday logic in a later patch.
As it happens, I've been working on a vDSO implementation of
gettimeofday/clock_gettime which does not mess with the signal page.
I'll reply with the patch separately in a moment.
next prev parent reply other threads:[~2014-01-28 21:05 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-28 16:25 [RFC] arm: vdso: Convert sigpage to vdso implementation Steve Capper
2014-01-28 17:10 ` Russell King - ARM Linux
2014-01-29 14:22 ` Steve Capper
2014-01-30 18:51 ` Will Deacon
2014-01-28 21:05 ` Nathan Lynch [this message]
2014-01-29 14:39 ` Steve Capper
2014-01-28 21:06 ` [RFC/PATCH] ARM: vDSO gettimeofday using generic timer architecture Nathan Lynch
2014-01-28 21:22 ` Russell King - ARM Linux
2014-01-28 21:48 ` Nathan Lynch
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