kinst: fix memcpy() tracing crash

[christos]

Summary

Tracing memcpy() would crash the kernel, because we'd also trace the
memcpy()s called from kinst. To fix this, introduce kinst_memcpy() whose
arguments are 'volatile', so that we avoid having the compiler replace
it with a regular memcpy().

[markj]

sys/cddl/dev/kinst/amd64/kinst_isa.c

485

These calls can simply be memcpy().

sys/cddl/dev/kinst/kinst.c

68

I think there's no need to have a volatile qualifier on the return type.

69

This function should have a comment explaining its existence.

sys/cddl/dev/kinst/trampoline.c

57

This can be regular memcpy().

[christos]

sys/cddl/dev/kinst/kinst.c

68

It didn't compile without it.

69

Forgot about it. Thanks.

[christos]

Use regular memcpy()s outside of probe context.

[markj]

Approved with the comments addressed

sys/cddl/dev/kinst/amd64/kinst_isa.c

245

This also can use regular memcpy().

sys/cddl/dev/kinst/kinst.c

70

[christos]

Address comments.