From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTP id 9D8163858407 for ; Mon, 6 Sep 2021 14:24:21 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 9D8163858407 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-248-LAFgyCvOMQesGRckA30c0w-1; Mon, 06 Sep 2021 10:24:20 -0400 X-MC-Unique: LAFgyCvOMQesGRckA30c0w-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1CD0B801A92; Mon, 6 Sep 2021 14:24:19 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.195.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8336B5D9DD; Mon, 6 Sep 2021 14:24:17 +0000 (UTC) From: Florian Weimer To: "H.J. Lu" Cc: GNU C Library , GDB , libc-coord@lists.openwall.com, Daniel Walker Subject: Re: [PATCH v6 2/2] Extend struct r_debug to support multiple namespaces References: <20210830173844.458727-1-hjl.tools@gmail.com> <20210830173844.458727-3-hjl.tools@gmail.com> <874kay11s3.fsf@oldenburg.str.redhat.com> Date: Mon, 06 Sep 2021 16:24:15 +0200 In-Reply-To: (H. J. Lu's message of "Mon, 6 Sep 2021 06:19:36 -0700") Message-ID: <87o895ye7k.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 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-6.7 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_NONE, TXREP 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 List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 06 Sep 2021 14:24:22 -0000 * H. J. Lu: > On Mon, Sep 6, 2021 at 2:39 AM Florian Weimer wrote: >> >> * H. J. Lu: >> >> > +* The r_version update in the debugger interface makes the glibc binary >> > + incompatible with GDB binaries built without the following commits: >> > + >> > + c0154a4a21a gdb: Don't assume r_ldsomap when r_version > 1 on Linux >> > + 4eb629d50d4 gdbserver: Check r_version < 1 for Linux debugger interface >> >> Does this incompatibility happen even if audit modules and dlmopen are >> not used? > > Yes. Why? Can't we keep r_version at 1 in this case? >> This puts the assember output from the compiler through the >> preprocessor. That seems to be brittle. I think you would have to >> preprocess the manually written fragment separately. >> >> However, I think we are overdesigning things here. The following in >> dl-debug-symbols-gen.c should work (and the file should have a different >> name then): >> >> /* Alias _r_debug to a prefix of _r_debug_extended. */ >> asm (".set _r_debug, _r_debug_extended\n\t" >> ".type _r_debug, %object\n\t" >> ".symver _r_debug_extended, _r_debug@@" FIRST_VERSION_ld__r_debug_STRING); >> #if __WORDSIZE == 64 >> _Static_assert (sizeof (struct r_debug) == 40, "sizeof (struct r_debug)"); >> asm (".size _r_debug, 40"); >> #else >> _Static_assert (sizeof (struct r_debug) == 20, "sizeof (struct r_debug)"); >> asm (".size _r_debug, 20"); >> #endif >> >> It's not exactly pretty, but at least it's obvious what is going on. >> (Extended asm with input operands is not supported outside of functions.) > > This was the first thing I tried and it didn't work: > > [hjl@gnu-cfl-2 tmp]$ cat foo.s > .set _r_debug, _r_debug_extended > .globl _r_debug > .type _r_debug, %object > .size _r_debug, 40 > .data > .type _r_debug_extended, %object > .size _r_debug_extended, 48 > .globl _r_debug_extended > _r_debug_extended: > .zero 48 > [hjl@gnu-cfl-2 tmp]$ gcc -c foo.s > [hjl@gnu-cfl-2 tmp]$ readelf -sW foo.o | grep _r_debug > 1: 0000000000000000 48 OBJECT GLOBAL DEFAULT 2 _r_debug > 2: 0000000000000000 48 OBJECT GLOBAL DEFAULT 2 _r_debug_extended > [hjl@gnu-cfl-2 tmp]$ Huh. Does this mean this depends on the symbol definition order in the assembler file? I really hate the post-processing of compiler output. This isn't GHC. 8-> Can we write a portable assembler file instead? Nick Clifton has written down some guidelines: Tips for writing portable assembler with GNU Assembler (GAS) There's no initializer, so all we need to know is size and alignment. >> Is this necessary? It makes concurrent access to the list harder and > > When _dl_close_worker is called, it holds GL(dl_load_lock). Why does > this change make concurrent access harder? Something else might want to read the list directly, by starting with DT_DEBUG. Thanks, Florian