RISC-V: Initialize pcpu slightly earlier

[mhorne]

Summary

For some reason, the code emitted for _vprintf will try to load the pcpu
pointer, even though it does nothing with it. In certain cases, printf can be
called before pcpu is initialized, causing a hang in early boot.

Move pcpu initialization up to before any printfs occur.

Test Plan

Noticed this hang when "options TSLOG" was added to my kernel config; test
that the system boots with this option enabled.

[mhorne]

sys/riscv/riscv/machdep.c

124 ↗

(On Diff #55498)

No reason this needs to be a global, as it is not referenced outside of this file.

[markj]

For some reason, the code emitted for _vprintf will try to load the pcpu pointer, even though it does nothing with it.

This is probably the curthread reference from the TSENTER() macro?

[mhorne]

In D19726#422553, @markj wrote:

For some reason, the code emitted for _vprintf will try to load the pcpu pointer, even though it does nothing with it.

This is probably the curthread reference from the TSENTER() macro?

Yep. That would definitely explain it.

[markj]

Approved. I suggest giving other reviewers a day or so to chime in though.