Re: PPC32 and state of the project

["Kevin B. Hendricks" <kevin dot hendricks at sympatico dot ca>]

Hi,

> > Can anything be done without an TLS register abi change?
> > And is there a target register that we should be using to keep in sync
> > with ppc64 or whatever?
>
> The main set of problems revolves around the thread register.  Getting
> LinuxThreads to run with a thread register is the first step.  The next
> step is designing and implementing ELF TLS (see
> http://people.redhat.com/drepper/tls.pdf).  Finally, the port of NPTL to
> PPC awaits.

Okay

> > Who do we have to bug to get that register decision made and the abi
> > changes made?
>
> Well, you'll now have to convince Franz.  As far as I'm concerned he
> makes now the PPC32 ABI decisions.

Okay.

> Well, I suggest to
>
> - start a discussion with interested parties about the thread register
>   decision;


Okay, back in early November I asked about this on dev@linuxppc.org after 
reading Ulrich's posts to the Kernel mailing list about NPTL.

Here is a short synopsis of what David Edelsohn and Andy Hernandez replied:

---snip--
 Kevin> Thread Library (NPTL) to add in support for ppc Linux?  Has anyone
 Kevin> decided on what register will be used for Thread Local Storage on 
 Kevin> PPC (32bit)?  (Is this r13 on ppc64?).  Have the necessary
 Kevin>  modifications to the ABI/compiler been made to support a dedicated
 Kevin>  thread local storage register?

 David>      There still is a question of what the final version of thread
 David> support will look like in Glibc.  TLS support has not been added to
 David> PowerPC GCC yet.  GPR 13 is reserved for the thread ID.  I do 
 David> not know whether that also can be used as the TLS base pointer.

Andy> Funny I was just talking to Richard Henderson on the plane about this
Andy> last week.

Andy> David, I was thinking on working on TLS for PPC (gcc side of things),
Andy> but Kevin is right, we need to get a register and change the ABI,
Andy> else things can get really spooky.  I was thinking we could use 
Andy> r13 (?) like PPC64 does.

Andy> I also vaguely recall that Geoff has a list of ABI changes pending.
Andy> Perhaps we should do all these at the same time.

So it looks like r13 was the choice and that Andy Hernandez, Richard 
Henderson, David Edelsohn, Franz and myself are the interested parties

> - implement the LinuxThreads side.  This won't need gcc support;

Okay

> - design ELF TLS; a prerequisite is a thread register;

Okay I will grab http://people.redhat.com/drepper/tls.pdf
and start reading up.

> - implement ELF TLS in gcc and binutils.  I do not know who will
>   volunteer to do this work.
>
> By the time all this is done there will most probably be a non-asm NPTL
> port and porting NPTL to PPC32 should be easy.  For the TLS design you
> might want to consider talking to the PPC64 guys.  I guess that perhaps
> after substituting the thread register name the two ABIs can share the
> same TLS design.


Okay I will wait to hear from Franz about how he wants to attack this while 
I start reading the tls.pdf file and studying the linuxthreads code.

Kevin