it is confusing, but .long is same as .int

I think you would want to move this fragment into a dedicated source, to avoid copying it to each arch locore.

I am not sure what guarantees are provided by e.g. machine/endian.h, but ideally it would allow to handle both big- and little-endian in single source.

this line is invariant for all configurations, it can be moved into DEFINE_TICKS

Just my personal opinion there:

• I hate multiline C preprocessor macros in asm, the native .macro is much more pleasent in .s
• I would go with kern/subr_tick.s instead of including into locore.S

I also think that the .p2align 3 directive is better to be added before ticksl.

I would perhaps add in the last sentence a reminder that even using ticksl doesn't mean that rollover can be ignored, as long as we support 32-bit platforms. This is implicit from the rest of the text, but I feel its current form could induce the reader to think that using ticksl is always safe. Perhaps it's because of the juxtaposition of Either can be used; 32-bit values (...) but rollover must be handled.

Arguably this is still going to catch ticks (non-l) wrapping on 64-bit platform too.

"either value can be used, but rollover must be handled" gives the impression that rollover must be handled with either value