Comment 35 for bug 1757517

(In reply to comment #30)
> Perhaps I should round it up to the next page size after doing the increment.
> In #25 Paul suggested I do the roundup for the increment before adding.
>
> Or perhaps the safest is to do the roundup of the TLS size and after the add.

You need to have a reason for doing the rounding, otherwise you are wasting space. What use and what alignment is required by that use should guide your decision.

The size is going to be aligned up to __static_tls_align_m1 in the next statement which is the larger of the stack alignment or the maximum alignment for any given TLS slot (slot minimum alignment is generally 16 bytes).

If you are going to use the extra space for stack then you're fine, the alignment in the next line has ensured that you get the right size given the alignment restrictions.