From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 31086 invoked by alias); 2 Sep 2013 13:50:47 -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 31073 invoked by uid 89); 2 Sep 2013 13:50:46 -0000 Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Mon, 02 Sep 2013 13:50:46 +0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-5.8 required=5.0 tests=AWL,BAYES_00,KHOP_THREADED,RP_MATCHES_RCVD autolearn=ham version=3.3.2 X-HELO: mx1.redhat.com Received: from int-mx01.intmail.prod.int.phx2.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id r82DofQw001279 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Mon, 2 Sep 2013 09:50:41 -0400 Received: from [127.0.0.1] (ovpn01.gateway.prod.ext.ams2.redhat.com [10.39.146.11]) by int-mx01.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id r82Dodq9020842; Mon, 2 Sep 2013 09:50:40 -0400 Message-ID: <522497AF.8080800@redhat.com> Date: Mon, 02 Sep 2013 13:50:00 -0000 From: Pedro Alves User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 MIME-Version: 1.0 To: Pierre Muller CC: gdb-patches@sourceware.org Subject: Re: [RFA] gdbserver/win32-low.c: Check Read/WriteProcessMemory return value (followup to [RFA] windows-nat.c: Handle ERROR_PARTIAL_COPY in windows_xfer_memory function) References: <5223bb46.c6c0420a.5a41.008dSMTPIN_ADDED_BROKEN@mx.google.com> <52248978.90500@redhat.com> <000301cea7dd$17bc4af0$4734e0d0$@muller@ics-cnrs.unistra.fr> <52249053.6050103@redhat.com> <522494dc.297a420a.6ab0.6047SMTPIN_ADDED_BROKEN@mx.google.com> In-Reply-To: <522494dc.297a420a.6ab0.6047SMTPIN_ADDED_BROKEN@mx.google.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-SW-Source: 2013-09/txt/msg00024.txt.bz2 On 09/02/2013 02:38 PM, Pierre Muller wrote: >>>>> This is not compatible with returning information that only part of > the >>>>> request length >>>>> was read/written. >>>> >>>> Well, we could just change that interface to make it possible... >>>> >>>> The thing I don't like with doing this only on the native >>>> side, is that we're trying to get to a point where we >>>> can share the target backends between GDB and gdbserver: >>> >>> Well, when you look at the code inside child_xfer_memory, >>> you can notice that the return value of ReadProcessMemory or >>> WriteProcessMemory >>> is discarded, which means that it does behave more or less like the >>> new windows-nat.c code (at least in case of ERROR_PARTIAL_COPY) >>> for other errors, it might also return garbage... >>> anyhow, the calling code compares the returned value to the requested >> length >>> (LEN value) >> >> That's brittle... >> >>> so that the risk of generating a successful read_memory despite a > failure >>> of ReadProcessMemory function is small... (the uninitialized variable > done >>> would need to return the value LEN..) >>> It could of course still happen theoretically... >> >> This is really no argument for not fixing gdbserver... In fact, >> it's an argument _for_ fixing it. > > What about this patch, > it still does not allow to really return the number of bytes read or > written, > but at least it checks correctly if the API calls succeeded. No, as long as the read_memory/write_memory interfaces do not support partial transfers, we should only return true if the all of LEN was transferred. Otherwise, things like: static int gdb_read_memory (CORE_ADDR memaddr, unsigned char *myaddr, int len) { ... { res = read_inferior_memory (memaddr, myaddr, len); done_accessing_memory (); return res == 0 ? len : -1; } } will behave incorrectly in the ERROR_PARTIAL_COPY scenario... -- Pedro Alves