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Re: [RFC][PATCH] ARM: vDSO support


On 02/25/2014 08:01 PM, Joseph S. Myers wrote:
> On Tue, 25 Feb 2014, Nathan Lynch wrote:
> 
>> Future versions (beginning with 3.15 or 3.16) of Linux on 32-bit ARM
>> are expected to provide fast user-space implementations of the
>> following system calls:
>>
>> - gettimeofday
>> - clock_gettime
>> - clock_getres
>>
>> This patch adds support for the ARM vDSO to glibc.  The changes are
>> mostly copied from the aarch64 code, with necessary adjustments to
>> _libc_vdso_platform_setup and INTERNAL_VSYSCALL_NCS (which has
>> __thumb2__ and non-__thumb2__ versions).
> 
> It would be best to add this only once the changes are actually in the 
> kernel, given that it depends on a kernel/userspace ABI that involves a 
> version number.

Agreed.  I figured I would need more than one attempt to get this right,
so I posted this as an RFC while things are still in progress on the
kernel side.


>> Tested on OMAP5 (Cortex-A15) with the relevant kernel patch, the latest
>> posted version of which may be found here:
> 
> Testing with a kernel without the feature is also important.

Yes, and I will include such results in future submissions.


>> 2014-02-25  Nathan Lynch <nathan_lynch@mentor.com>
> 
> Mentor's FSF copyright assignment only applies to people with an 
> @codesourcery.com address, so it is advisable to use such an address when 
> posting patches to GNU projects.

Okay.  Future patches will come from my codesourcery.com address.


>> +int
>> +__gettimeofday (tv, tz)
>> +     struct timeval *tv;
>> +     struct timezone *tz;
> 
> New old-style function definitions should be avoided (I hope at some point 
> we can eliminate the existing ones and start using -Wold-style-definition 
> by default).

I'll fix this.

Thanks for reviewing.


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