[PATCH v7 0/9] ARM: VDSO
Nathan_Lynch at mentor.com
Mon Jun 30 08:42:13 PDT 2014
On 06/30/2014 09:40 AM, Will Deacon wrote:
> Hi Nathan,
> On Mon, Jun 23, 2014 at 04:11:49AM +0100, Nathan Lynch wrote:
>> Provide fast userspace implementations of gettimeofday and
>> clock_gettime on systems that implement the generic timers extension
>> defined in ARMv7. This follows the example of arm64 in conception but
>> significantly differs in some aspects of the implementation (C vs
>> assembly, mainly).
> This series is starting to gain traction now, so it's probably time to start
> thinking about implementing this for CONFIG_COMPAT on arm64. We currently
> map a fake vectors page there, but this would be much more flexible,
> particularly as its written in C (and so we would magically get any new
> functions added to the 32-bit version).
> So, there are a couple of questions that spring to mind:
> - How difficult is it to share the vdso code with arm64 to build a compat
> vdso? (getting the Makefile to work will be hard, as we'll need an arm
Not sure. x86 might be the best example to work from here, although it
has the advantage of everything living under arch/x86. 64-bit powerpc
kernels provide a 32-bit VDSO for compat tasks but I think it doesn't
really share code with the 64-bit VDSO.
> - If we use your code to build an arm64 vdso, how much slower is it than
> the handcrafted asm we currently have?
Someone with access to 64-bit hardware (i.e. not me) would have to find
this out, but I would not be surprised if the C code could be tightened
up -- I have not spent much time on optimizing it.
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