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    SubjectRe: [PATCH 16/31] nds32: VDSO support
    On Wed, Nov 8, 2017 at 6:55 AM, Greentime Hu <green.hu@gmail.com> wrote:

    > --- /dev/null
    > +++ b/arch/nds32/include/asm/vdso_datapage.h
    > @@ -0,0 +1,51 @@

    > +#ifndef __ASM_VDSO_DATAPAGE_H
    > +#define __ASM_VDSO_DATAPAGE_H
    > +
    > +#ifdef __KERNEL__
    > +
    > +#ifndef __ASSEMBLY__
    > +
    > +struct vdso_data {
    > + bool cycle_count_down; /* timer cyclye counter is decrease with time */
    > + u32 cycle_count_offset; /* offset of timer cycle counter register */
    > + u32 seq_count; /* sequence count - odd during updates */
    > + u32 xtime_coarse_sec; /* coarse time */
    > + u32 xtime_coarse_nsec;
    > +
    > + u32 wtm_clock_sec; /* wall to monotonic offset */
    > + u32 wtm_clock_nsec;
    > + u32 xtime_clock_sec; /* CLOCK_REALTIME - seconds */
    > + u32 cs_mult; /* clocksource multiplier */
    > + u32 cs_shift; /* Cycle to nanosecond divisor (power of two) */
    > +
    > + u64 cs_cycle_last; /* last cycle value */
    > + u64 cs_mask; /* clocksource mask */
    > +
    > + u64 xtime_clock_nsec; /* CLOCK_REALTIME sub-ns base */
    > + u32 tz_minuteswest; /* timezone info for gettimeofday(2) */
    > + u32 tz_dsttime;
    > +};

    I need some insight from Deepa and Palmer here: to prepare for 64-bit
    time_t in the
    future, would it make sense to define the vdso to use 64-bit seconds numbers
    consistently, and provide vdso symbols that return 64-bit times, having the
    glibc convert that to normal timespec values, or should we leave it for now?

    For the normal syscalls I think we are better off keeping things consistent
    between architectures, but the vdso is architecture specific by definition, so
    we may as well use 64-bit times there now (same for risc-v, which still
    has time to modify this before the 4.15 release and glibc merge).

    > +/*
    > + * This controls what symbols we export from the DSO.
    > + */
    > +VERSION
    > +{
    > + LINUX_2.6 {
    > + global:
    > + __kernel_rt_sigreturn;
    > + __vdso_gettimeofday;
    > + __vdso_clock_getres;
    > + __vdso_clock_gettime;
    > + local: *;
    > + };
    > +}

    I still struggle to understand how symbol versioning is supposed to work
    in a vdso (as opposed to a library you compile against), but I think this should
    use the version from the kernel that you plan to merge into, i.e. LINUX_4
    or LINUX_4_16.

    Arnd

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