lavu/timer: use time for AV_READ_TIME on RISC-V

So far, AV_READ_TIME would return the cycle counter. This posed two
problems:
1) On recent systems, it would just raise an illegal instruction
   exception. Indeed RDCYCLE is blocked in user space to ward off some
   side channel attacks. In particular, this would cause the random
   number generator to crash.
2) It does not match the x86 behaviour and the apparent original intent
   of AV_READ_TIME in the functional code base (outside test cases).

So this replaces the cycle counter with the time counter. The unit is
a platform-dependent constant fraction of time, and the value should be
stable across harts (RISC-V lingo for physical CPU thread).

0 files changed, 0 insertions, 0 deletions