From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 101820 invoked by alias); 25 Aug 2015 12:47:57 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 101800 invoked by uid 89); 25 Aug 2015 12:47:56 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.2 required=5.0 tests=AWL,BAYES_00,KAM_LAZY_DOMAIN_SECURITY,RP_MATCHES_RCVD,SPF_HELO_PASS autolearn=ham version=3.3.2 X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-GCM-SHA384 encrypted) ESMTPS; Tue, 25 Aug 2015 12:47:50 +0000 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (Postfix) with ESMTPS id 9F76F8E3D1 for ; Tue, 25 Aug 2015 12:47:49 +0000 (UTC) Received: from blade.nx (ovpn-116-87.ams2.redhat.com [10.36.116.87]) by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id t7PClmM6018050; Tue, 25 Aug 2015 08:47:49 -0400 Received: by blade.nx (Postfix, from userid 1000) id 52E04262FF0; Tue, 25 Aug 2015 13:47:48 +0100 (BST) Date: Tue, 25 Aug 2015 12:47:00 -0000 From: Gary Benson To: Sergio Durigan Junior Cc: GDB Patches Subject: Re: [PATCH 2/2] Catching errors on probes-based dynamic linker interface Message-ID: <20150825124748.GA6948@blade.nx> References: <1440200253-28603-1-git-send-email-sergiodj@redhat.com> <1440200253-28603-3-git-send-email-sergiodj@redhat.com> <20150824084255.GA16508@blade.nx> <87r3msd5xr.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87r3msd5xr.fsf@redhat.com> X-IsSubscribed: yes X-SW-Source: 2015-08/txt/msg00723.txt.bz2 Sergio Durigan Junior wrote: > On Monday, August 24 2015, Gary Benson wrote: > > > diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c > > > index 1fb07d5..028c3d0 100644 > > > --- a/gdb/solib-svr4.c > > > +++ b/gdb/solib-svr4.c > > > @@ -1786,7 +1786,17 @@ solib_event_probe_action (struct probe_and_action *pa) > > > arg0: Lmid_t lmid (mandatory) > > > arg1: struct r_debug *debug_base (mandatory) > > > arg2: struct link_map *new (optional, for incremental updates) */ > > > - probe_argc = get_probe_argument_count (pa->probe, frame); > > > + TRY > > > + { > > > + probe_argc = get_probe_argument_count (pa->probe, frame); > > > + } > > > + CATCH (ex, RETURN_MASK_ERROR) > > > + { > > > + exception_print (gdb_stderr, ex); > > > + probe_argc = 0; > > > + } > > > + END_CATCH > > > + > > > if (probe_argc == 2) > > > action = FULL_RELOAD; > > > else if (probe_argc < 2) > > > > Maybe this would be clearer and more robust: > > > > TRY > > { > > unsigned probe_argc; > > > > probe_argc = get_probe_argument_count (pa->probe, frame); > > > > if (probe_argc == 2) > > action = FULL_RELOAD; > > else if (probe_argc < 2) > > action = PROBES_INTERFACE_FAILED; > > } > > CATCH (ex, RETURN_MASK_ERROR) > > { > > exception_print (gdb_stderr, ex); > > action = PROBES_INTERFACE_FAILED; > > } > > END_CATCH > > Maybe it's a matter of preference, but I don't like this (and I > don't see why it is more robust). I prefer to have as little code > as possible running on the TRY block, and handle everything else > outside of it. I think it also makes things a bit more confuse > because you have two places where action can be > PROBES_INTERFACE_FAILED. Well, there are two different failures: 1) get_probe_argument_count failed 2) get_probe_argument_count returned < 2 I think it's more robust because, imagine a future where someone adds a zero-argument probe to glibc. They update the "if (probe_argc)..." block to allow zero-argument probes through. If get_probe_argument_count with such a GDB then it will not be treated as a failure. FWIW I also like to keep code in TRY blocks to a minimum. Maybe you could do it your original way, but set probe_argc to -1 in the CATCH and have the below block like: if (probe_argc < 0) /* get_probe_argument_count failed */ action = PROBES_INTERFACE_FAILED else if (probe_argc == 2) action = FULL_RELOAD; else if (probe_argc < 2) /* we don't understand this probe with too few arguments */ action = PROBES_INTERFACE_FAILED; It looks kind of silly but the compiler will optimize it out. > > As an aside it would clarify this code greatly if "old_chain" > > were renamed "disable_probes_interface" or similar. It took > > me a while to figure out what the code was doing, and I wrote > > it! > > Yeah. I'll leave this to another patch. I'll do it if you like (but I'll wait til you've got this through). Cheers, Gary -- http://gbenson.net/