1:N threading

[julian at elischer.org (Julian Elischer)]

On Fri, 4 Apr 2003, Peter Wemm wrote:

> Daniel Eischen wrote:
> > On Thu, 3 Apr 2003, Peter Wemm wrote:
> > 
> > > Daniel Eischen wrote:
> > > 
> > > > The patches are available:
> > > > 
> > > >   http://people.freebsd.org/~deischen/libpthread.diffs
> > > > 
> > > > FYI, since this is a new mailing list, the above changes
> > > > are meant to give libpthread M:N capability.
> > > > 
> > > > I don't need testers; I have enough bugs that I know about
> > > > to fix.
> > > 
> > > +	__asm__("movl %%gs, %0" : "=r" (id));
> > > +	id >>= 3;
> > > +	if (id - NLDT < 0)
> > > 
> > > There is a problem here, NLDT is kernel private and changes depending on
> > > things like whether SMP is enabled or what the maximum number of cpus
> > > is.
> > > 
> > > You're trying to find if its a local or global selector, right?
> > > What you really want is bit 2 which tells you which it is.
> > > 
> > > #define ISLDT(s)        ((s)&SEL_LDT)   /* is it local or global */
> > > #define SEL_LDT 4               /* local descriptor table */
> > 
> > OK, but if NLDT is kernel private, how do can I know
> > what LDTs I can use as local?
> 
> Whoops.  I misread NLDT as NGDT.
> 
> Gah.  We're doing some crufty stuff here.  For starters, we're running
> userland on a LDT for %cs and %ds/es/ss/etc.  We really should be using a
> GDT slot for those.  Most of the other stuff there is for the a.out
> "lcall 7,0" instruction and for BSDI's version of the lcall stuff.
> 
> The i386_[gs]et_ldt() syscalls really should have a way of reporting what
> is available for use.

What we SHOULD be doing is setting an LDT entry to point to the 
mailbox (puts some constraints on the mailbox but..) of each upcall
and setting %gs to teh appropriate entry before returning to userspace.

(different schemes would be used for the other architectures.)

> 
> Cheers,
> -Peter
> --
> Peter Wemm - peter_(_at_)_wemm_(_dot_)_org; peter_(_at_)_FreeBSD_(_dot_)_org; peter_(_at_)_yahoo-inc_(_dot_)_com
> "All of this is for nothing if we don't go to the stars" - JMS/B5
> 
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