[PATCH v7 7/9] ARM: add vdso user-space code
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:
> DYNAMIC SYMBOL TABLE:
> 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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