quoted

I notice that a 32 bit process running on a 64 bit kernel is expected to
know that it should fill in mips64_watch_regs --- even though it is running
against a 32 bit ABI.

Is this an oversight, or am I missing something ?

It is intentional.

Oh I see ... I have to call PTRACE_SET_WATCH_REGS first in order to figure
out whether the kernel is expecting me to use pt_watch_style_mips32 or
pt_watch_style_mips64.

Thanks.

Earl