From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org
X-Spam-Level: 
X-Spam-Status: No, score=-3.3 required=5.0 tests=MAILING_LIST_MULTI,
	RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,
	T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4
Received: (qmail 5713 invoked from network); 10 Feb 2022 21:32:34 -0000
Received: from mother.openwall.net (195.42.179.200)
  by inbox.vuxu.org with ESMTPUTF8; 10 Feb 2022 21:32:34 -0000
Received: (qmail 12080 invoked by uid 550); 10 Feb 2022 21:32:32 -0000
Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm
Precedence: bulk
List-Post: <mailto:musl@lists.openwall.com>
List-Help: <mailto:musl-help@lists.openwall.com>
List-Unsubscribe: <mailto:musl-unsubscribe@lists.openwall.com>
List-Subscribe: <mailto:musl-subscribe@lists.openwall.com>
List-ID: <musl.lists.openwall.com>
Reply-To: musl@lists.openwall.com
Received: (qmail 12056 invoked from network); 10 Feb 2022 21:32:31 -0000
Date: Thu, 10 Feb 2022 16:32:19 -0500
From: Rich Felker <dalias@libc.org>
To: Yehuda Yitchak <yehuda80@gmail.com>
Cc: Florian Weimer <fweimer@redhat.com>, musl@lists.openwall.com
Message-ID: <20220210213219.GF7074@brightrain.aerifal.cx>
References: <CAN2=dsxXRyn60ueWTZa9drikbyxJ+Zs+X103hU3MuP-iPpspmw@mail.gmail.com>
 <20220209183326.GB7074@brightrain.aerifal.cx>
 <87h797zs6a.fsf@oldenburg.str.redhat.com>
 <20220209223155.GD7074@brightrain.aerifal.cx>
 <87a6ezx8wc.fsf@oldenburg.str.redhat.com>
 <CAN2=dsz8tob_c+nJBJnzC_dvF8J1nre5cbmL+nYERRbs9taxRg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAN2=dsz8tob_c+nJBJnzC_dvF8J1nre5cbmL+nYERRbs9taxRg@mail.gmail.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Subject: Re: [musl] Accessing Thread-Local-Storage in GDB

On Thu, Feb 10, 2022 at 08:05:15PM +0200, Yehuda Yitchak wrote:
> I forgot to mention I work on arm64
> I guess there isn't much I can do at the moment, right ?

If you're debugging live processes not core files, the dlsym approach
may work for you.


> On Thu, Feb 10, 2022, 13:23 Florian Weimer <fweimer@redhat.com> wrote:
> 
> > * Rich Felker:
> >
> > > Indeed, I was just offering a quick workaround that might help, not
> > > suggesting gdb should do that. __tls_get_addr can be used for
> > > non-dynamic symbols with information already available to the
> > > debugger. For core files you could probably simulate execution and
> > > abort if anything is reached that would need to change process state
> > > (lazy allocation) although that doesn't happen with musl anyway. But I
> > > wonder if the core file even records the x86 segment information
> > > needed to preserve thread pointer and simulate the %fs/%gs based
> > > loads on x86[_64]..?
> >
> > The register is available as $fs_base on x86-64:
> >
> > (gdb) print (void *)$fs_base
> > $1 = (void *) 0x7f2d12981740
> > (gdb) print *(void **)$fs_base
> > $2 = (void *) 0x7f2d12981740
> >
> > It probably does not work on i386 (even as $gs_base).  I do not think it
> > depends on FSGSBASE support in the kernel, but maybe I'm mistaken.  I
> > think I looked at this three years ago and couldn't make it work.
> >
> > Thanks,
> > Florian
> >
> >