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Re: _lwp_setprivate and _lwp_makecontext


> Hi all,
> I'm working on Thread Locale Storage support for NetBSD and I am facing
> an interesting issue with the libpthread integration. On i386 and AMD64,
> TLS support uses the segment register %gs or %fs to load the thread
> pointer. The location used as segment base is thread specific and stored
> in the PCB. It is not part of ucontext_t and therefore _lwp_makecontext
> can't store private in it. To work around this, I can think of three
> options:
> (1) Break ucontext_t and allow the private pointer as separate field
> Pro: Integrates nicely with the other platforms and debugger
> Contra: Lots of nasty interfaces to deal with in terms of compat.
> (2) Add private as argument for _lwp_create as well.
> Pro: logically fits well too, minimal amount of changes for libc and
> libpthread.
> (3) Defer calling _lwp_setprivate into the newly created thread.
> Pro: no kernel / libc changes needed
> Contra: might create complications with signal handlers etc
> I'm personally favoring (2), but looking for input.
> Joerg

when i looked at this, i abused _REG_ESP for i386.
i have no idea if other ports have unused members like this, tho.


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