> > The UTCB is a central information page for L4 userspace threads > > and it's pretty difficult to find another x86 register that can > > be used to point to it. > > What's wrong with %fs? But anyway, that is fine if the one word at %gs:0 > can be made available for user use. Ideally that word would be writable > (which you could manage along with read-only use by situating the segment > base on a page boundary, one page writable and one not). But the only > thing that would write it is pthreads innards, so it would be workable to > have a system call to set the %gs:0 word for a thread. Hmmm, the L4 X.2 spec only says that %gs:0 points to the UTCB area and that it should be read out.
If userspace threads can change %gs:0 without interfering with L4, fine. We could just squirrel %gs:0 away in crt0.c before glibc takes over and changes %gs. BUT, I'm not sure if * %gs:0 can be written to by userspace threads * the L4 API _implementation_ reads %gs:0 afterwards. > I don't know the L4 interfaces, but why not just make this page accessible > at a canonical address accessible from the standard user %ds segment? %ds and other registers are needed for the L4 syscalls. The problem is that especially x86 has so few registers :-( Espen or someone from the L4ka team should comment on this, please. -Farid. -- Farid Hajji -- Unix Systems and Network Admin | Phone: +49-2131-67-555 Broicherdorfstr. 83, D-41564 Kaarst, Germany | [EMAIL PROTECTED] - - - - - - - - - - - - - - - - - - - - - - - + - - - - - - - - - - - - One OS To Rule Them All And In The Darkness Bind Them... --Bill Gates. _______________________________________________ Bug-hurd mailing list [EMAIL PROTECTED] http://mail.gnu.org/mailman/listinfo/bug-hurd
