From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 55140 invoked by alias); 25 Aug 2015 18:17:02 -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 55123 invoked by uid 89); 25 Aug 2015 18:17:01 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 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 18:17:00 +0000 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) by mx1.redhat.com (Postfix) with ESMTPS id 558EFA588C for ; Tue, 25 Aug 2015 18:16:59 +0000 (UTC) Received: from localhost (unused-10-15-17-51.yyz.redhat.com [10.15.17.51]) by int-mx10.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id t7PIGwAM011501 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Tue, 25 Aug 2015 14:16:59 -0400 From: Sergio Durigan Junior To: Gary Benson Cc: GDB Patches Subject: Re: [PATCH 2/2] Catching errors on probes-based dynamic linker interface 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> <20150825124748.GA6948@blade.nx> X-URL: http://blog.sergiodj.net Date: Tue, 25 Aug 2015 18:17:00 -0000 In-Reply-To: <20150825124748.GA6948@blade.nx> (Gary Benson's message of "Tue, 25 Aug 2015 13:47:48 +0100") Message-ID: <87wpwjgrmt.fsf@redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-IsSubscribed: yes X-SW-Source: 2015-08/txt/msg00732.txt.bz2 Thanks for the review, Gary. On Tuesday, August 25 2015, Gary Benson wrote: > Sergio Durigan Junior wrote: >> On Monday, August 24 2015, Gary Benson wrote: >> > 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 Yes, and both are covered by the proposed patch. It is not really important to distinguish between these failures today: what really matters is that GDB recognizes both as failures and acts accordingly. > 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. I think we should cross this bridge when we come to it. Plus, the version you proposed does not take that scenario into account as well: if probe_argc is zero, action will be PROBES_INTERFACE_FAILED; therefore, this code would have to be rewritten anyway (in the scenario you're proposing). > 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. This has crossed my mind when I was writing this part, but probe_argc is unsigned int and therefore is never < 0. Moreover, as I said above, we are not really interested in differentiating between the errors here; what we really want to know is if there was an error. >> > 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). Sure, no problem. Cheers, -- Sergio GPG key ID: 237A 54B1 0287 28BF 00EF 31F4 D0EB 7628 65FC 5E36 Please send encrypted e-mail if possible http://sergiodj.net/