Re: TLS on powerpc(32/64)

Michael Snyder
2006-09-22T18:03:01Z

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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