On Wed, Nov 8, 2017 at 1:37 AM, Arnd Bergmann [off-list ref] wrote:

On Wed, Nov 8, 2017 at 6:55 AM, Greentime Hu [off-list ref] wrote:

quoted

--- /dev/null
+++ b/arch/nds32/include/asm/vdso_datapage.h

@@ -0,0 +1,51 @@

quoted

+#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?

Other architectures also have a similar way of defining these as u32
(eg: x86) I think for performance reasons on 32 bit systems.
u32 still works until 2106 as the timekeeping structures are s64. I
was planning to leave it that way for x86.
If this architecture can live with u64, then it will be better to use it here.

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).

But, I don't think this vdso can return 64 bit times without syscalls
for the architecture also supporting that. The problem is that all
fallback paths depend on syscalls directly.
Also I couldn't find any arch specific handling of vdso interfaces in
glibc. I think they expect the vdso wrappers in the kernel to handle
this part.

-Deepa