Re: _lwp_setprivate and _lwp_makecontext

[yamt%mwd.biglobe.ne.jp@localhost (YAMAMOTO Takashi)]

hi,

> 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.
http://mail-index.netbsd.org/tech-kern/2009/09/27/msg006146.html
i have no idea if other ports have unused members like this, tho.

YAMAMOTO Takashi