Thomas, Andy,

Le 15/01/2020 à 07:15, Christophe Leroy a écrit :

Le 15/01/2020 à 00:06, Thomas Gleixner a écrit :

quoted

Christophe Leroy [off-list ref] writes:

quoted

  static __maybe_unused int
+#ifdef VDSO_GETS_VD_PTR_FROM_ARCH
+__cvdso_clock_gettime_common(const struct vdso_data *vd, clockid_t 
clock,
+              struct __kernel_timespec *ts)
+{
+#else
  __cvdso_clock_gettime_common(clockid_t clock, struct 
__kernel_timespec *ts)
  {
      const struct vdso_data *vd = __arch_get_vdso_data();
+#endif
      u32 msk;

If we do that, then there is no point in propagating this to the inner
functions. It's perfectly fine to have this distinction at the outermost
level.

In v2, I did it at the arch level (see 
https://patchwork.ozlabs.org/patch/1214983/). Andy was concerned about 
it being suboptimal for arches which (unlike powerpc) have PC related 
data addressing mode.

Wouldn't it be the same issue if doing it at the outermost level of 
generic VDSO ?

Any opinion on this ?

 From your point of view, what should I do:
A/ __arch_get_vdso_data() handled entirely at arch level and arches 
handing over the vdso data pointer to generic C VDSO functions all the 
time (as in my v2 series) ?
B/ Data pointer being handed over all the way up for arches wanting to 
do so, no changes at all for others (as in my v3 series) ?
C/ __arch_get_vdso_data() being called at the outermost generic level 
for arches not interested in handling data pointer from the caller (as 
suggested by Thomas) ?

Andy, with A/ you were concerned about arches being able to do PC 
related accesses. Would it be an issue for C/ as well ? If not, I guess 
C/ would be cleaner than B/ allthought not as clean as A which doesn't 
add any #ifdefery at all.

Thanks
Christophe