[HALtheWise]

It looks like the TID is stored directly in the pthread struct pointed to by %fs itself, at a fixed offset which you can somewhat-hackily compile into your code. [0]

In the process of investigating this, I also realized that there's a ton of other unique-per-thread pointers accessible from that structure, most notably including the value of %fs itself (which is unfortunately unobservable afaict), the address of the TCB or TLS structures, the stack guard value, etc. Since the goal is just to have a quickly-readable unique-per-thread value, any of those should work.

Windows looks similar, but I haven't investigated as deeply.

[0] https://github.com/andikleen/glibc/blob/b0399147730d478ae451...

[1] https://github.com/andikleen/glibc/blob/b0399147730d478ae451...