From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <fweimer@redhat.com>
Received: from us-smtp-delivery-124.mimecast.com
 (us-smtp-delivery-124.mimecast.com [170.10.133.124])
 by sourceware.org (Postfix) with ESMTPS id 69F983858D20
 for <gdb@sourceware.org>; Fri,  4 Feb 2022 17:04:22 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 69F983858D20
Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com
 [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS
 (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id
 us-mta-2-Op_FAKAJNh6JqdERSAVpKA-1; Fri, 04 Feb 2022 12:04:20 -0500
X-MC-Unique: Op_FAKAJNh6JqdERSAVpKA-1
Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com
 [10.5.11.12])
 (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 306CD8144E1;
 Fri,  4 Feb 2022 17:04:19 +0000 (UTC)
Received: from oldenburg.str.redhat.com (unknown [10.39.193.205])
 by smtp.corp.redhat.com (Postfix) with ESMTPS id 571987EBE6;
 Fri,  4 Feb 2022 17:04:18 +0000 (UTC)
From: Florian Weimer <fweimer@redhat.com>
To: Jacob Kroon <jacob.kroon@gmail.com>
Cc: Jacob Kroon via Gdb <gdb@sourceware.org>
Subject: Re: Debugging ld.so in gdb
References: <29e0ef71-4706-9b0f-2a68-e12c54120d8e@gmail.com>
 <8735kypwcd.fsf@oldenburg.str.redhat.com>
 <c2a11d90-6d66-000d-f91e-fa1952382580@gmail.com>
 <87y22qognw.fsf@oldenburg.str.redhat.com>
 <dd662ef3-e7b3-b566-4342-607c820f2528@gmail.com>
 <87h79eobq1.fsf@oldenburg.str.redhat.com>
 <f73d7ef6-7d2b-47c4-db0f-968608abcdd9@gmail.com>
Date: Fri, 04 Feb 2022 18:04:16 +0100
In-Reply-To: <f73d7ef6-7d2b-47c4-db0f-968608abcdd9@gmail.com> (Jacob Kroon's
 message of "Fri, 4 Feb 2022 17:53:27 +0100")
Message-ID: <87czk2o967.fsf@oldenburg.str.redhat.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux)
MIME-Version: 1.0
X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12
X-Mimecast-Spam-Score: 0
X-Mimecast-Originator: redhat.com
Content-Type: text/plain
X-Spam-Status: No, score=-6.2 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH,
 DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW,
 SPF_HELO_NONE, SPF_NONE, TXREP,
 T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on
 server2.sourceware.org
X-BeenThere: gdb@sourceware.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gdb mailing list <gdb.sourceware.org>
List-Unsubscribe: <https://sourceware.org/mailman/options/gdb>,
 <mailto:gdb-request@sourceware.org?subject=unsubscribe>
List-Archive: <https://sourceware.org/pipermail/gdb/>
List-Post: <mailto:gdb@sourceware.org>
List-Help: <mailto:gdb-request@sourceware.org?subject=help>
List-Subscribe: <https://sourceware.org/mailman/listinfo/gdb>,
 <mailto:gdb-request@sourceware.org?subject=subscribe>
X-List-Received-Date: Fri, 04 Feb 2022 17:04:23 -0000

* Jacob Kroon:

> I couldn't see that address anywhere in the output of "show files".
>
> But I did "full" recording, and found a place where just stepping a
> single instruction broke gdb interpreting the backtrace, if that is of
> any help. This is what I do:
>
> 1. goto instruction 225037
> 2. print backtrace (looks sane)
> 3. do "disas"
> 4. step one instruction with "stepi"
> 5. print backtrace (looks garbled)
> 6. do "disas"

Interesting.  Can you figure out where *rpo points right before things
go wrong?  If the debuginfo doesn't work, this should do it:

  print (void *)$rax - 8

Maybe also look at map->l_name at this point, and further up the stack,
in dl_sort_maps, at maps and nmaps.  It looks like we run off the end of
the array and write garbage to other areas of the process. 8-(

This must be caused by something unusual in the object dependencies.

Thanks,
Florian