Thread Local Storage
Daniel Eischen
eischen at vigrid.com
Mon Mar 29 13:56:34 PST 2004
On Mon, 29 Mar 2004, Doug Rabson wrote:
> On Monday 29 March 2004 22:26, Daniel Eischen wrote:
> > On Mon, 29 Mar 2004, Doug Rabson wrote:
> > >
> > > 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.
>
> But the code it generates is at least twice the size for dynamic TLS. It
> seems that the GNU people have done a better job defining the TLS abi
> for i386.
About the only thing that uses TLS that I know is nvidia's
openGL. If you design an API correctly, there's no need
for TLS. I would hope that it's usage would be limited.
> You don't need a syscall at thread switch if you do something like:
>
> _thread_switch(...)
> {
> if (tcb doesn't have LDT entry) {
> if (!free LDT entries)
> steal LDT entry from non-running thread;
> allocate LDT entry and point it at TLS goop for tcb.
> }
> load_gs(tcb's LDT sel);
That's a system call on amd64.
> ...
> }
>
> I just have this feeling that the GNU ABI is going to get far better
> testing and support in the future since thats what linux uses.
--
Dan Eischen
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