Thread Local Storage

[Daniel Eischen]

On Mon, 29 Mar 2004, Doug Rabson wrote:

> On Monday 29 March 2004 20:36, Daniel Eischen wrote:
> > On Mon, 29 Mar 2004, Doug Rabson wrote:
> > > I've been spending a bit of time recently familiarising myself with
> > > this TLS stuff and trying out a few things. I've been playing with
> > > rtld and I have a prototype patch which implements enough TLS
> > > support to let a non-threaded program which uses static TLS work.
> > > With a tiny bit more work I can have limited support for dynamic
> > > TLS as well (not for dlopen'ed modules yet though). Is there a p4
> > > tree for this stuff yet? I'd like to check in what I have sometime.
> > >
> > > I've also been looking at libpthread and I can see some potential
> > > problems with it. Currently libpthread on i386 uses %gs to point at
> > > a struct kcb which seems to be a per-kse structure. This structure
> > > contains a pointer to a per-thread struct tcb and this pointer is
> > > managed by the userland context switch code. Other arches are
> > > similar, e.g. ia64 uses $tp to point at struct kcb.
> > >
> > > The problem with TLS is that the i386 ABI needs %gs to point at the
> > > TLS
> >
> > There are 2 different methods allowed for the i386 ABI.
> > We want to use the other method in which there is an
> > additional indirection.  The current i386 libpthread
> > stuff adheres to this method.
> 
> Surely the GNU TLS ABI is preferable? It generates much smaller code and 
> needs many fewer relocations.

No, we don't want an LDT for every thread and don't want
to force a syscall for a thread switch.

-- 
Dan Eischen