From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 101751 invoked by alias); 2 Mar 2018 18:32:50 -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 101741 invoked by uid 89); 2 Mar 2018 18:32:50 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-25.1 required=5.0 tests=AWL,BAYES_00,GIT_PATCH_0,GIT_PATCH_1,GIT_PATCH_2,GIT_PATCH_3,SPF_SOFTFAIL autolearn=ham version=3.3.2 spammy=wish X-HELO: mail.baldwin.cx Received: from bigwig.baldwin.cx (HELO mail.baldwin.cx) (96.47.65.170) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Fri, 02 Mar 2018 18:32:44 +0000 Received: from ralph.baldwin.cx (ralph.baldwin.cx [66.234.199.215]) by mail.baldwin.cx (Postfix) with ESMTPSA id D969B10A7DB; Fri, 2 Mar 2018 13:32:41 -0500 (EST) From: John Baldwin To: gdb-patches@sourceware.org Cc: "Maciej W. Rozycki" Subject: Re: [PATCH] Workaround a FreeBSD ptrace() bug with clearing thread events. Date: Fri, 02 Mar 2018 18:32:00 -0000 Message-ID: <1908872.BAzsX71dkG@ralph.baldwin.cx> User-Agent: KMail/4.14.10 (FreeBSD/11.1-STABLE; KDE/4.14.30; amd64; ; ) In-Reply-To: References: <20180224000935.43344-1-jhb@FreeBSD.org> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-IsSubscribed: yes X-SW-Source: 2018-03/txt/msg00066.txt.bz2 On Friday, March 02, 2018 12:13:20 AM Maciej W. Rozycki wrote: > On Fri, 23 Feb 2018, John Baldwin wrote: > > > diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c > > index d44950618c..9c87bfed33 100644 > > --- a/gdb/fbsd-nat.c > > +++ b/gdb/fbsd-nat.c > > @@ -1163,6 +1163,39 @@ fbsd_resume (struct target_ops *ops, > > } > > ptid = inferior_ptid; > > } > > + > > +#if __FreeBSD_version < 1200052 > > + /* > > + * When multiple threads within a process wish to report STOPPED > > + * events from wait(), the kernel picks one thread event as the > > + * thread event to report. The chosen thread event is retrieved via > > + * PT_LWPINFO by passing the process ID as the request pid. If > > + * multiple events are pending, then the subsequent wait() after > > + * resuming a process will report another STOPPED event after > > + * resuming the process to handle the next thread event and so on. > > + * > > + * A single thread event is cleared as a side effect of resuming the > > + * process with PT_CONTINUE, PT_STEP, etc. In older kernels, > > + * however, the request pid was used to select which thread's event > > + * was cleared rather than always clearing the event that was just > > + * reported. To avoid clearing the event of the wrong LWP, always > > + * pass the process ID instead of an LWP ID to PT_CONTINUE or > > + * PT_SYSCALL. > > Hmm, doesn't it have to be a run-time check then? Otherwise you're > basing your decision on the host system GDB has been built for and not one > it will be run on, which I suppose does not necessarily have to be of the > same version. Or am I missing anything here? FreeBSD generally does not support forwards-compatability for binaries (newer binary on older kernel), only backwards-compatability (older binary on newer kernel). In this case, using the workaround is also fine on a fixed kernel, so it doesn't hurt if GDB is compiled on an older system (thus using the workaround) and then run under a newer kernel. -- John Baldwin