riscv: Implement non-stub __vdso_gettc and __vdso_gettimekeep

[jrtc27]

Summary

PR: 256905
MFC after: 1 week

[jrtc27]

lib/libc/riscv/sys/__vdso_gettc.c

48

Hm, plain csr_read might be more appropriate given the result is put in a u_int, though it's a bit academic given we don't support RV32. The two are the same on RV64 but on RV32 it'll loop until it reads a consistent time and timeh to get a 64-bit value from two 32-bit CSRs and then throw away the upper half.

[jrtc27]

Use csr_read in place of csr_read64

[jrtc27]

Enable SV_TIMEKEEP

[arichardson]

Thanks! I can confirm that truss no longer shows the clock_gettime() syscalls with this version of the patch.

[mhorne]

Thanks for this one.

lib/libc/riscv/sys/__vdso_gettc.c

28

Nit: not required for new files

[imp]

lib/libc/riscv/sys/__vdso_gettc.c

28

for new files that won't be MFC'd to stable/12..... I don't think this will be, given the riscv support in 12 isn't so good (IIRC, I might be wrong), but thought I'd mention in case I am wrong.

[mhorne]

lib/libc/riscv/sys/__vdso_gettc.c

28

That's right, there's no point bringing this past stable/13, but the precision is helpful.