Re: [RFA][3/5] New port: Cell BE SPU (the port itself)

["Ulrich Weigand" <uweigand at de dot ibm dot com>]

Daniel Jacobowitz wrote:

> On Sun, Nov 12, 2006 at 10:41:34PM +0100, Mark Kettenis wrote:
> > I think that what you really want is a Linux powerpc native configuration
> > that can debug both normal powerpc code and spu code.  That'd mean adding
> > spu-linux-nat.c to config/powerpc/linux.mh.  But I suppose that doesn't
> > really work right now.  But could we make that work?
> 
> In theory yes - but I'm not quite sure how.  You'd have more than one
> target that could take control when you said "run" and for Cell I think
> you'd have to disambiguate based on the architecture of the file.  But
> Ulrich said they had more patches that weren't ready for mainline and I
> bet some of them make this nicer :-)  Since really you would want to
> debug both at once.

Yes, exactly.   It's not just a matter of checking the executable file
architecture; a single process can have threads executing SPU code at
the same as other threads executing PowerPC code.

I have a set of patches that does appear to work so far; it is based
primarily on switching current_gdbarch on thread switch.  However,
there's still some work to be done before this is in a shape suitable
for mainline inclusion.

Therefore I'd hoped it would be possible to get the SPU-only port
accepted first, since this is in itself already quite useful.

> I guess what really is throwing us here is the use of "nat".  Isn't
> this really more like one of the custom remote-foo.c targets than a
> native target?  It just happens to be implemented using PowerPC/Linux
> kernel facilities spelled "ptrace" and some poking around in a PowerPC
> executable in order to implement "run".  The ptrace facilities don't
> seem to be used much to talk to the SPU; new files in /proc are used
> instead.  It's forking and running a PowerPC executable until it makes
> a special SPU-related syscall, and then it starts talking to the SPU.

I'll have a look at the remote-foo targets.  Is it just more or less just
a matter of renaming the file, or are there significant differences?

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com