[PATCH v7 7/9] ARM: add vdso user-space code

Andy Lutomirski luto at amacapital.net
Mon Jun 30 08:59:53 PDT 2014

On 06/28/2014 08:26 AM, Russell King - ARM Linux wrote:
> On Sun, Jun 22, 2014 at 10:11:56PM -0500, 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.
>> If CONFIG_ARM_ARCH_TIMER is not enabled, the vdso cannot service
>> high-resolution clocks and falls back to syscalls.  Low-resolution
>> clocks e.g. CLOCK_REALTIME_COARSE can be serviced regardless.
> Okay, how is this used by userspace?
> It seems that on ARM, we generate a dso with these symbols:
> 000001e4 l    d  .eh_frame_hdr	00000000              .eh_frame_hdr
> 00000000 g    DO *ABS*	00000000  LINUX_3.17  LINUX_3.17
> 000003c4 g    DF .text	00000080  LINUX_3.17  __kernel_clock_getres
> 00000444 g    DF .text	0000002c  LINUX_3.17  __kernel_gettimeofday
> 00000298 g    DF .text	0000012c  LINUX_3.17  __kernel_clock_gettime

Sorry, late to the thread.

I think that, if your function signatures match, you should give them 
the same names and versions as for x86 (i.e. LINUX_2.6, 
__vdso_clock_gettime).  Userspace will thank you.

Don't do the weak clock_gettime, etc aliases, though.  That was never a 
good idea to begin with.


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