Re: TLS on powerpc(32/64)

[Michael Snyder <Michael dot Snyder at palmsource dot com>]

On Fri, 2006-09-22 at 06:53 -0700, Prosun Niyogi wrote:
> How can I tell whether GDB is loading libthread_db?
> "info threads" works... I would think libthread_db
> must be loaded for that to work.

If it's a native linux (or solaris) gdb, yes.

You could also try running gdb under gdb -- with verbose 
mode turned on in the "outer" or master gdb.  Then the outer
gdb would notify you whenever the inner gdb loaded a shared
library, and you could look for libthread_db.

> Also, in gdb(linux-thread_db.c) -
>  
>  __/* glibc doesn't provide the needed interface.  */
>  if (!td_thr_tls_get_addr_p)
>    throw_error (TLS_NO_LIBRARY_SUPPORT_ERROR,
>                 _("No TLS library support"));
>  __/* Caller should have verified that lm != 0.  */
>  gdb_assert (lm != 0);
>  __/* Get info about the thread.  */
>  thread_info = find_thread_pid (ptid);
>  thread_db_map_id2thr (thread_info, 1);
>  __/* Finally, get the address of the variable.  */
>  err = td_thr_tls_get_addr_p
> (&thread_info->private->th, (void *) lm,
>                               offset, &address);
> So the glibc interface is found... does that not mean
> that libthread_db is loaded and found by GDB?

libthread_db is a separate shared library, and might be
missing or something.  But that would be unusual, I suppose.

> Apologies for the ignorance, just looking for how I
> can check to see why td_thr_tls_get_addr_p() doesnt
> return an appropriate value.

Version problem?  There were versions of glibc and libthread_db
that predated TLS.


> So judging from the tone of your comment, I should
> expect to be able to print the value of a __thread
> variable on ppc64, and there arent any known issues
> preventing me from doing so? I have tried on SLES, FC,
> and now cvs-head, and all three have failed.

Can you do a "ptype" or "whatis" on the type?

 
> Can you suggest where I should look next? I took a
> quick look at libthread_db in glibc, and it looks like
> none of the fuctions have changed in libc. 
>  
> Thanks,
>  
> Prosun Niyogi
> 
> --- Daniel Jacobowitz <drow@false.org> wrote:
> 
> > On Thu, Sep 21, 2006 at 04:20:47PM -0700, Prosun
> > Niyogi wrote:
> > > Hi, 
> > > I've been struggling the last few days on getting
> > gdb
> > > to work correctly on a powerpc64 machine. Built as
> > > ppc-64-linux, debugging ppc64 binaries linked
> > against
> > > libpthread. It seems to me that gdb's TLS access
> > does
> > > not work correctly on these platforms. Attempting
> > to
> > > print a variable of type __thread doesnt work. 
> > 
> > It looks to me like GDB has failed to load
> > libthread_db for some
> > reason.  I don't know why not; you'll have to look
> > into it.
> > 
> > -- 
> > Daniel Jacobowitz
> > CodeSourcery
> > 
> 
> 
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