Synchronizing C6X DSBT bits between uClibc/Kernel and GDB.

Wed Jun 5 19:50:15 UTC 2013

On 29 May 2013 17:37:35 Mark Salter <msalter at redhat.com> wrote:
> On Tue, 2013-05-28 at 13:09 +0200, Luis Machado wrote:
> > Hi,
> > C6X uses a DSBT scheme for shared libraries. Seeing how it is quite 
> similar to FDPIC, it seems all the targets doing DSBT have migrated to 
> using FDPIC structures and code.
> > C6X has done that in this patch by Mark Salter: 
> http://lists.uclibc.org/pipermail/uclibc/2012-June/046906.html
> > Since the layout of the loadmap structure has been changed to match 
> FDPIC's one, this structure went out of synch with GDB's own definition of 
> the loadmap.
> > We need backwards compatibility though (let me know if this is not the 
> case) and GDB conditionally defines the old loadmap based on the existence 
> of PT_GETDSBT (defined in libc/sysdeps/linux/c6x/sys/ptrace.h).
> > My proposal is to drop this definition in uClibc and use the more common 
> PTRACE_GETFDPIC instead (already used in the kernel, Mark can correct me if 
> i'm wrong).
> > This way we guarantee GDB will use the correct loadmap for C6X.
> > I still expect GDB to be confused if it uses recent uClibc code that 
> still defines PT_GETDSBT though, but it doesn't look like we can solve that 
> easily.
> > Thoughts? Let me know what you think and i can come up with a patch.
>
> This all sounds reasonable to me. PTRACE_GETDSBT is not used internally
> by uClibc and it has the same value as PTRACE_GETFDPIC. This all came
> about when kernel switched from a separate loader to using the fdpic
> loader when c6x kernel was pushed upstream. At that point, the uClibc
> bits were already in place.

Please update uClibc accordingly. I would not care about backward 
compatibility in this regard.

Thanks in advance!
Cheers,

>
> --Mark
>
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