Re: About the porting of libunwind

[Wu Zhou <woodzltc at cn dot ibm dot com>]

Quoting Richard Henderson <rth@redhat.com>:

> On Sun, Jul 23, 2006 at 11:39:50AM -0400, Wu Zhou wrote:
> > We are looking into how to port libunwind to ppc64.  We had done some
> > investigation work.  It seems much like what is available on x86 and
> > x86-64. So we want to see if any of you can give us some pointers on
> > how to do that on a new platform like ppc64. If you can share us with
> > how you do that (it is ok to be very general ) on x86 and x86-64, that
> > will be highly appreciated.
>
> I've been working on doing just this thing, porting to ppc32/64.

Richard,

Very happy to know that you are working on this.  Whatever I can help  
in this effort, please tell me.  Surely we can help test your code on  
various platforms, including but not limited to ppc32/ppc64 platforms.  
:-)

> Unfortunately, libunwind is very poorly arranged for such cases,
> where two ports can share the bulk of the code.  So I've been
> rearranging it.  What I have is currently in an intermediate
> state that does not compile, but as soon as I have something, I
> will check it in to the frysk repository.

Would you please talk something about your re-arrangement work?  What  
changes are you planning to add into the current code base?  Do you  
think that I can be of some help in your re-arranging work?

> > There are also some nasty details too. For example, the user context
> > and dwarf CFI are both complex data structure.  Both of them have some
> > important information about the registers. The context contain the
> > value of each registers at some point. And the CFI tells how to save
> > and restore registers when one function call another. How to get these
> > register values? How are these registers ordered?  The numbering
> > sequence?  How to map the register in context structure to these in
> > CFI information? All these should be in the questions to be answered.
> > How do you do all these for x86 and x86_64?
>
> What is needed here is familiarity with the dwarf3 spec, and the
> ELF spec for ppc64.  There is existing code in gcc to perform the
> same operations, but only within the local process.  But it is
> still helpful for understanding.

Thanks for these information. I ever had some experiences in DWARF and  
ELF.  and I am also looking at these documents right now to refresh  
them. But I am not that familar with gcc code (ever submitted one  
patch for generating better debuginfo support for Fortran main entry,  
don't got much feedback though. :-( ).  Can you give me some pointer  
on which files are involved in performing these operations?  The  
source file names are ok.  Thanks a lot!

Regards
- Wu Zhou