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Re: PowerPC64 TLS ABI
On Fri, Jan 17, 2003 at 05:37:14PM -0800, Richard Henderson wrote:
> On Sat, Jan 18, 2003 at 11:02:53AM +1030, Alan Modra wrote:
> > I suppose there's really no
> > reason we couldn't use an offset tp with variant I, and what's more,
> > the offset would be the same as for dtv. ie. r13 - 0x8000 would point
> > at TCB. I like it!
>
> Hmm. This isn't a bad idea at all. Perhaps I should
> adopt it for Alpha as well. It's not too late...
>
> At the moment Jakub has arranged for LinuxThreads to
> have its _pthread_descr at the negative offsets from
> the TP. We can either continue with that (and have to
> use an additional addis to access it), or we can use
> the second word of the TCB to point to it.
Well, you could have _pthread_descr at the negative offsets from the TP
and have more than 32K of quickly accessable TLS data too:
if the ABI says that says that r13[-0x7000] is the DTV pointer,
then you have 60K-sizeof(tcbhead_t) big "fast" TLS area and
those 4K should be enough for the thread implementation to
have some of its most important data stored there (well, for linuxthreads
or NPTL the whole thread structure would easily fit).
Jakub